The Bioartificial Pancreas: Progress and Challenges Review

DIABETES TECHNOLOGY & THERAPEUTICS 

Volume 7, Number 6, 2005 

© Mary Ann Liebert, Inc. 

The Bioartificial Pancreas: Progress and Challenges 

SEDA KIZILEL, Ph.D., 1 MARC GARFINKEL, M.D., 1 and EMMANUEL OPARA, Ph.D. 2 

ABSTRACT 

Diabetes remains a devastating disease, with tremendous cost in terms of human suffering 

and healthcare expenditures. A bioartificial pancreas has the potential as a promising approach 

to preventing or reversing complications associated with this disease. Bioartificial pancreatic constructs 

are based on encapsulation of islet cells with a semipermeable membrane so that cells 

can be protected from the host’s immune system. Encapsulation of islet cells eliminates the requirement 

of immunosuppressive drugs, and offers a possible solution to the shortage of donors 

as it may allow the use of animal islets or insulin-producing cells engineered from stem cells. 

During the past 2 decades, several major approaches for immunoprotection of islets have been 

studied. The microencapsulation approach is quite promising because of its improved diffusion 

capacity, and technical ease of transplantation. It has the potential for providing an effective 

long-term treatment or cure of Type 1 diabetes. 

INTRODUCTION 

DIABETES MELLITUS represents a major public 

health problem, as it is the most frequent 

endocrine disease in industrialized countries. 1,2 

According to the latest estimates, the number 

of people with this disease worldwide is 177 

million, and this figure will double by the year 

2025. 3 The complications of diabetes are associated 

with multiple medical problems related 

to ophthalmic, renal, neurological, cerebrovascular, 

cardiovascular, and peripheral vascular 

disease. 4–9 The economic burden of diabetes is 

related to its management, to the treatment of 

its secondary complications, and to resultant 

productivity loss. 10 While one estimate shows 

that the cost of treating diabetes in the United 

States in 1997 was $44 billion, 3 another study 

Review 

968 

has shown that it cost about $100 billion to treat 

diabetes and its complications in this country 

in 1992. 10 

Type 1 diabetes, also previously known as 

insulin-dependent diabetes mellitus, occurs 

when pancreatic islet cells are unable to produce 

insulin. Consequently, the blood glucose 

concentration becomes high while tissues are 

starving for metabolic fuel. In Type 2 diabetes, 

previously referred to as non–insulin-dependent 

diabetes, the body continues to make at 

least some insulin, but is unable to respond 

properly to the action of insulin produced by 

the pancreas. The Diabetes Control and Complications 

Trial 11 showed that an improved 

metabolic control was achieved using intensive 

insulin treatment in Type 1 diabetes patients. 

However, the aggressive management of dia- 

1 Section of Transplantation, Department of Surgery, The University of Chicago, Chicago, Illinois. 

2 Pritzker Institute of Biomedical Science and Engineering, Illinois Institute of Technology, Chicago, Illinois.

THE BIOARTIFICIAL PANCREAS 969 

betes with exogenous insulin only delayed the 

progression and development of complications 

of this disease. Also, intensive insulin treatment 

could only be applied to fewer than 10% 

of patients due an increased risk of severe 

episodes of hypoglycemia. Furthermore, it appears 

that C-peptide, a cleavage product from 

the processing of pro-insulin to insulin, prevents 

diabetes and hyperglycemia-induced 

vascular and neural dysfunction in animal and 

clinical models of diabetes and should therefore 

be used in combination with insulin to 

maintain vascular and neural functions as well 

as blood glucose levels. 12–15 

Advances in transplantation and in immunosuppression 

have made pancreas transplantation 

another treatment option for Type 1 

diabetes. The main objective for pancreas transplantation 

is to achieve normal level of glucose 

in the blood and to free the patient from exogenous 

insulin requirements based on multiple 

finger stick glucose measurements. 16 Even 

though successful pancreas transplantation 

provides normal glucose homeostasis, the 

requirement of lifelong immunosuppression 

makes it unclear whether transplantation is advantageous 

over continued insulin treatment. 17 

Also, because of the need for immunosuppression, 

most pancreas transplantations have been 

done simultaneously with a kidney transplant 

in patients who have advanced nephropathy. 18 

In contrast to pancreas transplantation, islet 

transplantation requires no major surgery. 

Also, islet transplantation offers an alternative 

to exogenous insulin treatment, as it can result 

in better glycemic control 19 and potentially 

avoids surgical complications associated with 

whole-organ pancreas transplantation. It is 

known that islet cell transplantation can prevent, 

and, in some cases, reverse existing complications 

of diabetes probably because of the 

role played by C-peptide. 20 However, major 

challenges remain to be addressed before islet 

transplantation can be used routinely and applied 

more widely to patients with diabetes. 

One major barrier is the shortage of human 

pancreas as a source of islet cells. Also, lifelong 

use of immunosuppressive drugs to overcome 

the rejection of transplanted tissue poses a significant 

risk to patients, as the use of glucocorticoids 

and cyclosporine have dose-dependent 

deleterious effects on glucose homeostasis and 

-cell function, and result in increased incidences 

of infection and cancer. 20–24 The introduction 

of the steroid-free immunosuppressive 

drug regimen has resulted in long-term graft 

survival of islets with concomitant control of 

blood glucose levels. 25 However, this immunosuppressive 

drug regimen is also not without 

risks to graft recipients. 26 

The routine application of islet transplantation 

would be tremendously enhanced by an 

unlimited supply of donor tissue, a standard 

implantation procedure, and the ability to 

maintain the transplanted tissue without the requirement 

of immunosuppressive drugs. 27 To 

achieve these goals, immunoisolation (encapsulation) 

of islet cells has been proposed to protect 

cells from attack by the host immune system. 

Using immunoisolation of the islets, 

chronic administration of immunosuppressive 

drugs can be theoretically eliminated or minimized, 

as transplanted cells are separated from 

the host immune system by a biocompatible 

and semipermeable membrane. 28,29 Moreover, 

immunoisolation of pancreatic islet cells for 

transplantation into patients with diabetes theoretically 

permits grafting of xenogenic islets, 

thus expanding the potential supply of donor 

islet tissue. 25 Hence, immunoisolation could 

open up the possibility of using islets harvested 

from animals, or insulin-producing cells engineered 

from stem cells without the requirement 

of immunosuppression of transplant recipients. 

Porcine and bovine insulin amino acid sequences 

have considerable sequence homology 

with human insulin, 30 and therefore pigs and 

cows are considered attractive as options for 

xenogeneic donors. 

One important consideration in using microencapsulated 

islets is defining the optimal 

site for transplantation. To date, most research 

has considered peritoneal cavity as the optimal 

site for implantation of encapsulated islets, as 

it is possible to transplant microcapsules into 

the peritoneal cavity using a simple procedure 

that could be suitable for routine outpatient 

use. 29,31–34 Also, this site allows for implantation 

of high numbers of islets, which can be retrieved 

by peritoneal lavage 35 if necessary. 36 

However, this site limits graft viability because 

of low blood supply, oxygen tension, and con-

970 

centration of essential minerals. 34 In addition, 

the release of insulin from the peritoneal cavity 

to the blood stream is delayed compared 

with hormones released to the portal vein. 37 

Also, peritoneal macrophages have a high toxicity 

against encapsulated islets. 38 

Several researchers have also explored the 

portal vein of the liver as an alternative site for 

transplantation of immunoisolated islets. 39 

Based on its double vascularization (hepatic 

artery and portal vein), the intraportal location 

has a high oxygen and nutrient supply, which 

could be beneficial for the performance and the 

longevity of microencapsulated cells. 39 Also, 

the liver is considered to be an immunologically 

privileged site. 40 But, even more clinically 

relevant, is the use of percutaneous transhepatic 

catheterization, which provides relatively 

simple, inexpensive, and non-surgical access to 

the liver. 41 In addition, The International Islet 

Registry reports more C-peptide-positive cases 

(more than 0.5 ng/mL) 1 year after transplantation 

into the portal vein than from any other 

site. 42 

This article reviews the recent progress and 

challenges remaining for the successful development 

of a bioartificial pancreas, and discusses 

the requirements to bring this technology 

closer to clinical application. 

HISTORICAL DEVELOPMENT 

The pancreatic origin of diabetes was discovered 

in 1889 by Mering and Minkowski, 

when surgical removal of the pancreas caused 

dogs to develop diabetes. In 1913, Murlin and 

Kramer prepared extracts of bovine pancreas 

to lower the blood glucose in a dog with diabetes. 

However, the benefit of the extract was 

explained by the presence of lactate. Finally, in 

1922, Banting and Best developed a method for 

preparing a pancreatic extract, and a few years 

later, injection of the active factor in this extract, 

insulin, became the main therapy for Type 1 diabetes. 

As of today, the treatment options for Type 

1 diabetes are exogenous insulin with external 

glucose monitoring, whole-organ pancreas 

transplantation, islet cell transplantation, the artificial 

pancreas, and the bioartificial pancreas. 

KIZILEL ET AL. 

Among these treatments, the bioartificial 

pancreas avoids the use of immunosuppressive 

drugs while providing moment-to-moment 

glucose homeostasis consistent with a wellfunctioning 

native pancreas. It is important in 

this context to distinguish between the terms 

“artificial pancreas” (sometimes called “mechanical 

artificial pancreas”) and “bioartificial 

pancreas.” 

The mechanical artificial pancreas consists of 

a glucose sensor, an insulin pump, and a computer, 

which determines the rate of insulin delivery. 

The sensor may be implanted in the 

vena cava, and may require periodic replacement. 

The development of a glucose biosensor 

has been challenged by the difficulty of creating 

a sensitive, stable, and accurate sensor, despite 

the capability of a mechanical artificial 

pancreas to regulate glucose levels. An error in 

sensing, computation, or delivery could result 

in insulin overdosing, which could be potentially 

risky with life-threatening hypoglycemia, 

43–46 an unacceptable potential side effect 

of an artificial pancreas. It is also very difficult 

to produce a mechanical artificial pancreas that 

responds quickly enough to changes in blood 

sugar (islets respond in less than 10 min). 47 

In contrast, a bioartificial pancreas is a device 

that substitutes for the endocrine portion 

of the pancreas. Devices in this category contain 

synthetic materials and functional islets 

encapsulated within a semipermeable membrane 

to protect cells from the host immune response. 

The semipermeable membrane permits 

exchange of nutrients, glucose, and insulin 

with the host, but excludes the diffusion of immunoglobulins, 

complement, and white blood 

cells. The device may be implanted into a vascularized 

site 48,49 or into the peritoneal cavity. 36 

The idea of using ultrathin polymer membrane 

microcapsules was proposed by Chang 50 

in 1964 for the immunoprotection of transplanted 

cells. Nearly 2 decades later, the concept 

of bioencapsulation was successfully 

shown to maintain glucose homeostasis in rats 

with diabetes using encapsulated allogeneic 

islets. 32 When alginate microcapsules containing 

islets were implanted in rats, normal blood 

glucose levels were achieved for 13 weeks. The 

microcapsule used in that study consisted of an 

inner alginate core surrounded by a polylysine


membrane, which was then surrounded by an 

outer polyethyleneimine coating. In later studies, 

the outer layer was replaced by the more 

biocompatible alginate coating because of an 

inflammatory reaction induced by polyethyleneimine. 

51 Since then, a variety of studies have 

been performed to understand the requirements 

for successful transplantation of encapsulated 

islet cells, but there is still a need for 

convincing evidence of success of encapsulated 

islet transplantation in either non-human primates 

or humans. 49 

IMPEDIMENTS TO THE PROGRESS OF 

CELL ENCAPSULATION TECHNOLOGY 

Fibrotic overgrowth of the implanted microcapsules 

is one of the major obstacles to progress 

in cell encapsulation technology. Invariably, 

the materials used for encapsulation are 

not completely inert, and can induce foreign 

body and inflammatory reactions. As a result of 

this fibrous tissue overgrowth, the diffusion of 

nutrients, oxygen, hormones, and waste products 

through the capsule is diminished, and encapsulated 

islets are destroyed because of hypoxia, 

starvation, and the secretion of nitric 

oxide by the stimulated macrophages. 52 This fibrotic 

reaction to implanted microcapsules had 

previously been associated with commercially 

available alginate with high mannuronic acid 

content, which activates macrophages in vivo, 

resulting in fibroblast proliferation and eventual 

overgrowth. 53 However, later studies did 

not support that notion. 33 It has also been 

shown that polylysine may cause a fibrotic response 

through the induction of cytokines. 54 

Another important component of capsular 

design is permselectivity. Most capsule designs 

are based on the presumption that the effectiveness 

of immunoisolation of a polymer capsule 

is closely related to the pore size of the capsule 

membrane. 55–57 However, pore sizes of 

polymer membranes are not homogeneous by 

nature, and consist of a broad spectrum of 

sizes. 58 Total immunoprotection of encapsulated 

cells can only be provided if the polymer 

membrane does not have any pores larger than 

the antibody complement component. 59 This 

fact has been largely ignored by researchers 

and has resulted in inconsistent findings in the 

field. 60–66 

Mechanism of immunologic attack of allografts 

and xenografts 

With regard to specific immunologic attack 

of encapsulated cell implants, there are differences 

in the immune protection requirement of 

allografts versus xenografts. An allograft is a 

graft between genetically different individuals 

within the same species, while a xenograft is a 

graft between individuals from different 

species. Allograft rejection occurs as result of 

activation of cellular immunity by interactions 

of host T cells with a graft, while humoral immunity, 

including antibodies and complement 

proteins, is responsible for the rejection of 

xenografts. 67,68 In the direct pathway of antigen 

presentation, the T cell receptor recognizes 

T cells presented by donor-type antigen-presenting 

cells along with Class I or II major histocompatibility 

complex (MHC) molecules. 

The idea of immunoisolation using a polymer 

membrane is to separate allogeneic or xenogeneic 

tissue from the immune system of the 

recipient. Therefore, microencapsulation of 

islets within effective permselective membranes 

would prevent contact with immunoglobulin, 

complement components, and 

inflammatory cells. However, there is also a potential 

immune response towards antigens 

shed by encapsulated allogeneic or xenogeneic 

cells. Such antigens could be therapeutic agent 

themselves, cell surface molecules, or cell components 

(phospholipids, DNA), including 

those released upon cell death. Shedding of 

antigens from encapsulated cells would initiate 

a molecular tissue response around the implant, 

which could affect the viability and function 

of the encapsulated cells. As a result of this 

immunological reaction, these shedded antigens 

may be internalized, processed, and presented 

in association with host Class II MHC 

molecules (macrophages and dendritic cells) to 

host CD4 helper T cells (Fig. 1). The recognition 

of antigens through this indirect pathway 

may lead to the activation of T helper cells, 

which then secrete cytokines and regulate cellmediated 

immune response and inflammation. 

69,70 Small molecules, such as reactive oxy-

972 

FIG. 1. Schematic representation of antigen recognition 

via (A) the direct pathway and (B) the indirect pathway. 

APC, antigen-presenting cells; TCR, T cell receptor. 

gen species and cytokines, may also pass 

through the polymer membrane and damage 

the transplanted tissue. 

Owing to the complexity of the immune response 

mechanism, it is important to understand 

the mechanism of immune protection, 

and considerable efforts have been made to investigate 

this issue. Chen et al. 71 developed cell 

lines that have resistance to cytokines and oxygen 

radical-induced damage. Recently, macrophage 

depletion has also been used as a tool to 

protect xenografts from immune destruction. It 

has been found that depletion of peritoneal 

macrophages with clodronate liposomes improved 

the survival of macroencapsulated 

porcine neonatal pancreatic cell clusters. 35 

Safley et al. 72 evaluated the cellular immune response 

in non-obese diabetic (NOD) mice after 

two different pathways of T cell co-stimulation 

were blocked. Alginate–poly-L-lysine-encapsulated 

porcine islet xenografts were transplanted 

intraperitoneally in NOD mice treated 

with CTLA4-immunoglobulin to block CD28/ 

B7 and with anti-CD154 monoclonal antibody 

to inhibit CD40/CD40–ligand interactions. It 

was concluded that blocking two different 

pathways of T cell co-stimulation inhibited T 

cell-dependent inflammatory responses, and 


significantly prolonged the survival of encapsulated 

islet xenografts. 

Another approach to improving the survival 

of microencapsulated islets can be to use local 

immunosuppression. Studies have shown that 

preimplantation of an immunoisolating device 

improved the survival of an encapsulated islet 

graft and reduced fibroblast outgrowth. 73 Functional 

capsules may also be designed to release 

the immunosuppressive agent in a controlled 

manner. Local immunosuppression induced using 

this approach may prevent the occurrence 

of an undesirable reaction around the implant. 

Inflammatory reaction in response to the implantation 

of cell-free capsules involves a sequence 

of events similar to a foreign body reaction, 

starting with an acute inflammatory 

response and leading to a chronic inflammatory 

response or granulation tissue development 

and fibrous capsule development. The intensity 

and duration of each of these responses 

are dependent upon several factors, such as the 

extent of injury created in the implantation, 

biomaterial chemical composition, surface free 

energy, surface charge, porosity, surface 

roughness, and implant size and shape. 74,75 The 

biocompatibility of the material is determined 

by the extent and deviation from the optimal 

wound healing conditions. 76 

Sources of donor islets 

Despite all of the advances in islet transplantation 

and in encapsulation technology, some 

challenges must be still overcome before the 

bioartificial pancreas can be broadly applied. 

The most significant of these challenges is the 

shortage of donor islets. This shortage is the 

motivation for researchers to find alternative 

sources of insulin-producing cells. Promising 

approaches for resolving this problem are differentiation 

of stem cells into cells with -celllike 

characteristics77–80 and genetic engineering 

of adult cells for secretion of recombinant insulin. 

81–86 Based on similarities between mechanisms 

that control the development of both the 

adult pancreas and the central nervous system, 

methods promoting neural differentiation of 

embryonic stem cells have been adapted by researchers 

to derive insulin-producing cells. 87–91 

Hori et al. 92 investigated the possibility of directing 

neural progenitors to develop into glu-


cose-responsive insulin-producing cells using 

inductive signals involved in normal pathways 

of islet development. Compared with other 

methods for insulin-producing cell development 

from human stem cells, 91,93 the method 

developed by this group produced insulin at 

the highest levels yet achieved from an expandable, 

human stem cell-derived tissue. 

However, the method developed in the study 

still needs to be improved, perhaps through the 

addition of glucagon-like peptide-1, transforming 

growth factor- ligands, or other factors 

to potentiate -cell maturation, growth, 

and insulin secretion. 94–96 

Gene therapy has also been suggested as a 

treatment of insulin-dependent diabetes mellitus. 

This strategy can be applied by preventing 

the autoimmune destruction of -cells, 97,98 by 

regenerating -cells, 99,100 or by engineering insulin-secreting 

surrogate -cells. 99,101–103 Sapir 

et al. 104 recently suggested the potential use of 

adult human liver as an alternate tissue for autologous 

-cell-replacement therapy. Using 

pancreatic and duodenal homeobox gene 1 

(PDX-1) and soluble factors, they managed to 

induce a comprehensive developmental shift of 

adult human liver cells into functional insulinproducing 

cells. According to the findings of 

that study, PDX-1-treated human liver cells expressed 

insulin, stored it in defined granules, 

and secreted the hormone in a glucose-regulated 

manner. When these cells were implanted 

under the renal capsule of immunodeficient 

mice with diabetes, the cells ameliorated hyperglycemia 

for prolonged periods of time. The 

technique offers both the potential of a cell-replacement 

therapy for patients with diabetes 

and allows the patient to be the donor of his or 

her own insulin-producing tissue. 

Intestinal K cells have also been engineered 

to express and secrete insulin in a glucose dependent 

manner, generating functional cells. 

105,106 With the development of robust and 

safe gene therapy, this strategy may lead to effective 

therapy in the future. 

Preservation of encapsulated cell systems 

The last challenge for a bioartificial pancreas 

to become a routine clinical application is the 

long-term cryopreservation of encapsulated 

cells. Validated technologies are required for 

long-term preservation of encapsulated cell systems 

to maintain a product inventory, and in order 

to meet end-user demands. One of the current 

strategies for overcoming the problem of 

cryopreservation of tissue is the reduction of cryoprotectant 

[dimethyl sulfoxide (DMSO)] concentration 

or complete replacement by equally 

powerful substances. Recent work in Dr. Opara’s 

laboratory has demonstrated that cryopreservation 

of islet cells cultured overnight in the presence 

of 10% polyvinylpyrrolidone yielded higher 

intact islet recovery compared with islets frozen 

in the presence of DMSO and glycerol. 107 The 

lower islet cell integrity and function were explained 

on the basis of hypothesis that low-molecular-weight 

compounds, such as DMSO and 

glycerol, permeate the cell and interact hydrophobically 

with intracellular proteins, which 

results in perturbed cytoskeletal architecture of 

the frozen cells and diminished islet cell integrity 

and function. 

The other promising technical improvement 

of the cryopreservation technology is the reduction 

of total sample volume. Miniaturization 

of the cryosubstrates from 1 mL to microliters 

reduces temperature gradients in cryosubstrates, 

which makes it possible to achieve 

higher freezing rates and more homogeneous 

freezing of the sample. 108 Islets cryopreserved 

with this strategy were highly functional even 

with the lower DMSO concentrations. 109 

Misler et al. 110 studied stimulus–secretion 

coupling in whole islets as well as single cells 

from carefully selected cryopreserved and 

thawed human islets of Langerhans. They found 

that without using any of the recent advances in 

cryopreservation technique, cryopreserved and 

thawed human islets, which were selected based 

on their smooth surface and diameter, responded 

to glucose in a calcium- and metabolicdependent 

fashion. In another study by von 

Mach et al., 111 viability of pancreatic islets after 

cryopreservation was correlated negatively with 

their size, and suppression of insulin release was 

not observed for islets 300 m. 

DIFFERENT FORMS OF BIOARTIFICIAL 

PANCREAS 

Various configurations have been studied for 

the purpose of immunoisolation of islets. These

974 

include biohybrid vascular devices, extravascular 

chambers, and encapsulation. 112,113 Encapsulation 

is the technique of islet immunoisolation 

using biopolymeric spheres of 

different sizes. Currently, results in rodents 

and dogs with diabetes indicate that spherical 

micro- and macrocapsules appear to have the 

highest therapeutic potential. 60,65,114 A microcapsule 

typically contains only a few hundred 

cells or a single islet, and to provide a therapeutic 

dosage, tens of hundreds of thousands 

of cells are required. In contrast, macrocapsules 

employ much larger depots to contain the full 

therapeutic dosage in one or a few implants. 

Macrocapsules are shaped as cylinders or 

planes, and typically one dimension is in the 

range of 2–6 mm (Fig. 2a). 115,116 One advantage 

of the implantation of macrocapsules is the ease 

of retrieval in case of complications. However, 

despite reports of reduced risks in the implantation 

of macrocapsules, it has been shown that 

macroencapsulated islets have significantly impaired 

insulin secretion because of necrosis in 

the center of aggregated islet clumps as a result 

of diffusion limitations of nutrients and 

oxygen. 116,117 

Encouraging results have been obtained by 

immobilization of the islets in a matrix before 

final macroencapsulation. 115,118 Limited diffusion 

of nutrients, as well as slow exchange of 

glucose and insulin, occurs as a result of relative 

large surface-to-volume ratio of these devices. 

To ensure sufficient nutrient and oxygen 

diffusion to the cells, islet cell density within 

the macrocapsules is kept to around 5–10% of 

the volume fraction. This approach, however, 

requires the implantation of large devices in order 

to provide adequate masses of insulin-producing 

cells, and large grafts are not practical 

and cannot be transplanted in conventional 

sites. 119 

In contrast, microencapsulation offers an optimal 

volume-to-surface ratio for fast exchange 

of hormones and nutrients without a large device. 

The technique involves enclosure of one 

or two islets within small spheres, which have 

diameters of less than 1 mm (Fig. 2b). Also, because 

of reduced volume of the islet transplants, 

and in contrast to macroencapsulated islets, microcapsules 

can theoretically be transplanted in 

delicate sites, such as the portal vein. The trans- 

(a) Macroencapsulation 

(b) Microencapsulation 

plantation of microcapsules into the peritoneal 

cavity, an outpatient-based procedure, 33,120–122 

makes it particularly attractive to patients and 

doctors. Interestingly, intraperitoneally implanted 

microencapsulated islets have shown 

promising results in large animal 122–124 models 

as well as in limited clinical trials. 33 

TECHNIQUES IN 

MICROENCAPSULATION 


FIG. 2. Immunoisolated islets within (a) membrane diffusion 

chambers (macrocapsules) and (b) microcapsules. 

Materials used for microencapsulation 

Various materials have been used as biopolymeric 

coats in islet microencapsulation. These 

have included alginate, agarose, tissue-engineered 

chondrocytes, polyacrylates, 125,126 and 

poly(ethylene glycol) (PEG). 

Alginate–polylysine-based microencapsulation 

of islets, first described by Lim and Sun, 32 

has been found not to interfere with cellular function, 

and these microcapsules have been shown 

to be stable for years in small and large animals 

as well as in human beings. 127–132 Alginate is a 

linear polysaccharide extracted from seaweed. 133 

It is composed of three types of 1 4-linked 

polyuronic acid blocks containing poly-L-guluronic 

acid segments (G blocks), poly-D-manuronic 

acid segments (M blocks), and segments 

of alternating L-guluronic and D-mannuronic 

acid residues, and it has gel-forming properties 

in the presence of most polyvalent cations. 133,134 

Impurities, such as monomers, catalysts, and initiators 

present in synthetic polymers, may contribute 

to the failure of the encapsulated islet im-


plants. 135 Other impurities, such as pyrogens and 

mitogens, can be found in polymers derived 

from natural substances, such as seaweed. 135 Up 

to 90% of the impurities can be removed by electrophoresis 

or by the Klock extraction purification 

procedure. 130,135 Conflicting reports exist on 

whether alginate with high M blocks or high G 

blocks results in increased fibrosis. 53 It has been 

shown, however, that the inflammatory response 

to alginate becomes less with purification, 

irrespective of the composition used. 36,136 

The immunoisolating permselectivity of alginate 

microcapsules can be achieved by soaking 

the initial alginate beads in 0.05–0.1% 

polylysine dissolved in normal saline for 6–20 

min. This occurs as a result of the binding of 

negatively charged carboxyl groups on the alginate 

to positively charged -amino groups on 

the amino acid polymer. The droplets are again 

rinsed with normal saline, followed by the addition 

of an outer alginate layer by soaking in 

a lower concentration of 0.06–0.25% sodium alginate 

for 4 min. It is extremely important that 

the outer coating of alginate on top of the 

polylysine membrane is complete. In the case 

of incomplete cover of the polylysine coating 

and when an impure alginate is used for the 

outer coating, microcapsules may become completely 

covered by cell overgrowths within 1 

week of transplantation because of the inflammatory 

reactions attributable to polylysine and 

the impurities in the alginate. 137 To dissolve the 

intracapsular sodium alginate by chelation of 

the cross-linking calcium, the resulting microcapsules 

are treated with 55 mM sodium citrate 

for 7 min. The hollow microcapsules containing 

a few islets are then washed with saline 

(Fig. 3). It appears that liquefaction of the inner 

alginate core of microcapsules is required 

for optimal function of the enclosed islets. 138 

One successful transplantation of encapsulated 

islets performed with this technique was reported 

by a team of investigators at Duke University. 

The encapsulated islets were made 

with an outer alginate coating and inner poly- 

L-ornithine layer for permselectivity. To liquefy 

the inner alginate core of each bead a salt treatment 

was used. After transplantation, encapsulated 

islet cells were shown to keep a baboon 

with diabetes from requiring exogenous insulin 

for more than 9 months. 122 

FIG. 3. Microencapsulation of islets with alginate– 

polylysine. 

For a capsule to be stable in vivo it has to be 

water insoluble, as capsule dissolution will 

elicit a continuing inflammatory response and 

will ultimately expose the transplanted cells to 

the host. Both alginate and polylysine are water-soluble 

polymers and are both expected to 

elicit an inflammatory or foreign body response. 

However, findings indicate that the 

polyelectrolyte complex formed during encapsulation 

is biocompatible and less soluble in 

water than the individual components. 62,139,140 

Differences in biocompatibility were also noted 

between empty and cell-containing capsules in 

NOD mice, 141,142 which could be due to the difficulty 

of producing reproducible cell-containing 

capsules. For better biocompatibility, one 

group has suggested the use of high guluronic 

acid-containing alginates, 53 while another 

group modified alginate–polylysine capsules 

with PEG. 132 An alternative approach has been 

chosen to obtain stronger and more biocompatible 

microcapsules using synthetic polyacrylates 

such as the water-insoluble synthetic 

copolymer hydroxyethyl methacrylate-methyl 

methacrylate. 143 This research group has selected 

the acrylate monomers because of their 

diversity and has shown that mammalian cells

976 

may be microencapsulated in uncharged and 

polyelectrolyte polymer, in polyelectrolyte 

complexes, and inside a cohesive precipitate 

from a destabilized emulsion, without loss of 

viability. 

Polymerization of acrylamide monomer on 

islet cells encapsulated in agarose microspheres 

has also been reported. 144 However, when 

polymerization is in direct contact with tissue, 

this can generate excessive local heating and 

cytotoxicity. 145 Poly(styrene sulfonic acid), one 

of the most potent complement-interacting 

polymers, was selected for the purpose of consuming 

cytolytic complement activity and 

mixed with agarose for the preparation of microbeads 

to protect xenogeneic islets in mice 

with diabetes from the humoral immune reaction. 

63,146 Antibodies and complement proteins 

play a major role in the rejection of xenografts. 

Binding of antibodies to the antigens on the 

xenogeneic cell surface cannot alone damage 

the islet cell. For destruction of the xenogeneic 

cells to occur, complement activation by antigen–antibody 

complexes present on the cell 

surface is required. 147 Various polymers bearing 

hydroxyl groups such as regenerated cellulose, 

cellulose acetate, and poly(ethylene-covinyl 

alcohol) activate the complement system 

through the alternative pathway, 148 whereas 

other polymers bearing sulfonic acid or sulfate 

groups strongly interact with complement proteins 

and decrease the cytolytic complement activity. 

149 

As previously noted, a fibrotic reaction after 

implantation would limit the diffusion of essential 

nutrients or metabolites, leading to reduced 

viability or impaired functional activity 

of the encapsulated cells. Several studies have 

reported the usefulness of coating membrane 

surfaces with poly(ethylene oxide) (PEO) in order 

to reduce protein adsorption and associated 

fibrotic reaction. 150 This was achieved by 

exposing the poly(acrylonitrile-vinyl chloride) 

membrane surface to amine-terminated PEO 

after acid hydrolysis of the nitrile group to a 

carboxylic acid. Membrane surfaces were also 

exposed to PEO-succinimide after base reduction 

to an amine. 151 The in vivo response 

proved that a smaller number of macrophages 

and foreign body giant cells were present on 

the PEO-grafted membrane surface without 


any change in transport properties. The other 

application to modify the membrane surface 

was achieved by synthesizing a graft copolymer 

having poly-L-lysine as the backbone and 

the monomethoxy PEG as pendant chains. Microcapsules 

with sodium alginate were formed 

using this polycationic copolymer, which demonstrated 

reduced protein adsorption, complement 

binding, and cell adhesion in vitro compared 

with materials with unmodified poly- 

L-lysine. 132 

That artificial materials used for immunoisolation 

purposes are not completely inert and 

can induce foreign body and inflammatory reactions 

have led researchers to study tissue-engineered 

capsules of rat chondrocytes. Pollok 

et al. 126 proposed the encapsulation of islets 

with a layer of chondrocytes and their matrix 

to prevent immunorecognition and destruction 

of transplanted allogeneic or xenogeneic islets. 

This investigation demonstrated the membrane’s 

ability as an immunoisolation barrier 

by utilizing the immunoprivileged properties 

of the chondrocyte matrix. This approach 

might offer a therapeutic advantage for patients 

with diabetes, using the patient’s own 

chondrocytes from a cartilage biopsy specimen 

as the encapsulation material. 

PEG is another polymer that has been utilized 

for the purpose of encapsulating islets. In 

order to obtain stable and biocompatible gels 

without any cytotoxicity generation, Pathak et 

al. 152 and Cruise et al. 153 reported rapid photopolymerization 

of water-soluble PEG-based 

macromers in direct contact with islet cells. 

PEG is biocompatible, nontoxic, non-immunogenic, 

and hydrophilic and can be chemically 

cross-linked into hydrogels for a variety of applications. 

154,155 Diffusion profiles of proteins 

through PEG diacrylate hydrogels showed that 

gels formed with the proper formulation were 

capable of being immunoprotective. The semipermeable 

properties of cross-linked PEG hydrogels 

made by interfacial photopolymerization 

of PEG diacrylate were also studied by 

Cruise et al. 156 by forming hydrogels upon 

poly(vinylidiene fluoride) microporous filters. 

This approach allowed them to study the effect 

of molecular weight and concentration of the 

PEG diacrylate on the diffusivity of biological 

molecules.


Techniques used for droplet generation 

The other major consideration in microencapsulation 

technology is how to get the cells 

into the individual polymer capsules. Techniques 

to form such a physical barrier include 

air-jet syringe pump droplet generator, interfacial 

photopolymerization, and selective withdrawal. 

One of the main devices used for microencapsulation 

of islets with alginate–polylysine is 

the air-jet syringe pump droplet generator. 157 

The device consists of an air jacket surrounding 

an alginate nozzle through which alginate 

solution is injected. 158,159 Islets are suspended 

in a solution of 1.4–3% sodium alginate, and 

spherical droplets of this suspension are 

formed by an air-jet syringe pump generator. 

As alginate droplets are forced out of the end 

of the needle by the syringe pump, the droplets 

are pulled off by the shear forces set up by the 

flowing air stream. The size of the spherical 

droplets is controlled by adjusting the flow rate 

of the air jacket. The spherical droplets are collected 

in a funnel containing HEPES acid buffer 

supplemented with 1.1% CaCl2 solution, which 

transformed alginate droplets into rigid beads 

by gelation. 110 Excess fluid is drained with the 

aid of a filtering device consisting of a nylon 

mesh and a stopcock at the exit end of the funnel, 

and the droplets are washed in normal 

saline. 

As noted earlier, an air jet-syringe pump extrusion 

method generates gel droplets containing 

entrapped islets from the suspension of the 

islets in aqueous sodium alginate solution. 

However, there are various constraints concerning 

the use of this procedure to produce 

microcapsule diameters of less than 700 m. To 

form perfectly spherical capsules, the viscosity 

of the gel-forming liquid must be greater than 

30 cp. Also, to prevent the blockage of the needle 

by the islets, the minimum internal diameter 

of the needle must be greater than 300 m. 

Finally, the volumetric airflow rate must remain 

below 2,000 mL/min in order to produce 

capsules of uniform diameter. This procedure 

was improved by employing an electrostatic 

droplet generator to form uniform, smooth, 

and perfectly spherical microcapsules having a 

diameter about 150–500 m. 160 A droplet, 

which is charged with high static voltage, is 

suspended from a needle and attracted to a collecting 

vessel with opposing polarity. Once the 

voltage threshold potential is passed, the 

droplet moves from the needle to the collecting 

vessel. Droplets with predetermined sizes 

may be repeatedly generated as the voltage 

pulse height, pulse frequency and length, and 

extrusion rate of the droplets are adjustable. As 

shown in Figure 4, droplets are formed as the 

plunger is driven by the syringe pump and expelled 

towards a collecting vessel containing a 

hardening solution, which may be aqueous calcium 

chloride in the case of an aqueous droplet 

forming liquid containing sodium alginate. 

Negative polarity was attached to the needle, 

while positive polarity was attached to the 

metal ring. As the voltage applied during 

droplet formation is a static voltage, the viability 

of the encapsulated islets is not compromised. 

Biomolecules such as proteins and cells can 

also be deposited as patterned droplets onto 

surfaces for the development of cell-based 

biosensing devices for applications such as 

high-throughput drug screening. 161 There are 

numerous techniques for microfabrication of 

patterned polymer surfaces for protein delivery. 

Lithographic techniques and microcontact 

printing have been most widely used to generate 

patterned droplets of cells. 162–168 PEG hy- 

FIG. 4. Schematic representation of an electrostatic 

droplet generator.

978 

drogel is the most commonly used material for 

cell patterning purposes. In the case of surfaceinitiated 

photopolymerization of PEG, the technique 

involves immobilization of initiator onto 

a substrate surface using a stamp such as 

poly(dimethyl siloxane), followed by polymerization 

of precursor solution. 169 One recent 

study focused on the cellular delivery based on 

micro- and nanotechnology. 170 To provide an 

immunoisolating microenvironment for islet 

cells, nanoporous biocapsules were bulk and 

surface micromachined to present uniform and 

well-controlled pore sizes. The designs of the 

membranes with defined nanopores were fabricated 

using a thermally grown silicon oxide 

sandwiched between two structural layers of 

silicon. 

Another technique used to generate droplets 

of encapsulated islet cells was proposed by 

Cruise et al. 153 using interfacial photopolymerization. 

The technique involves physical adsorption 

of the initiator eosin Y on the islet cell 

surface, which then allows polymerization to 

occur on the islet–prepolymer interface. The interfacial 

photoinitiation process employed with 

this technique results in conformal coating of 

cross-linked PEG-based hydrogel on the islet 

cell surface. 

The process of selective withdrawal is another 

novel method reported recently for the 

purpose of coating cell clusters, such as islet 

cells. 171 Briefly, the process involves the insertion 

of a tube into a container such that its tip 

is suspended at a specific height above an interface 

separating two immiscible fluids (Fig. 

5). In the case of a low fluid withdrawal rate, 

only the upper fluid (oil) is withdrawn through 

the tube. Increasing the fluid flow rate or de- 

Oil 

Water 

To pump 

FIG. 5. Diagram of the selective withdrawal apparatus. 

creasing the height of the tip above the interface 

results in a transition where the lower liquid 

(water) is incorporated in a thin spout 

along with the oil. The technique was demonstrated 

through encapsulation of a poppy seed 

in a poly(styrenesulfonic acid). The particles 

were coated with the prepolymer solution, 

which has styrene sulfonic acid sodium salt 

and triethylene glycol diacrylate, and mixed 

with the initiator eosin Y and co-initiator triethanolamine 

used for the purpose of initiating 

polymerization. 171 After the selective withdrawal 

step, the coated particles were collected 

and photopolymerized with a halogen lamp. 

The technique could also be used to encapsulate 

cells through surface initiated photopolymerization 

of PEG. The photoinitiator eosin Y 

could be immobilized on the islet cell surface 

through covalent attachment, 169 and after the 

selective withdrawal process, cells could be collected 

and illuminated for 2–3 min with an argon 

ion laser in order to cross-link the coat 

around the cells. 

CONCLUSIONS 


The successful development of a bioartificial 

pancreas involves several considerations. Two 

major obstacles in islet transplantation are the 

limited supply of islet cells and the use of immunosuppressive 

drugs to prevent transplant 

rejection. It is hoped that the use of encapsulated 

islets as a form of bioartificial pancreas 

would overcome these obstacles. Three potential 

sources of islet cell tissue, including human 

or allogeneic cells, porcine or xenogenic cells, 

and engineered cells, are currently under investigation. 

Among these sources, human islet 

cells would be the least immunogenic; however, 

there is a shortage of pancreata retrieved 

from human cadaveric donors, and these cells 

have a limited secretory capacity and life span. 

The use of porcine islet cells could be a better 

option, because these are readily available, and 

there is an unlimited supply of donors. However, 

one major concern about the use of islets 

harvested from pigs has been the possibility of 

transmittance of porcine endogenous retroviruses 

(PERVs) to humans during transplantation. 

This concept arose from studies on the


infection of humans and immunodeficient mice 

after pig cell xenotransplantation. 172,173 There 

are studies, however, showing no possibility of 

transmission of PERVs from pigs to human recipients 

of islet xenografts. 120,174,175 Indeed, one 

recent study showed that the porcine genome 

harbors a limited number of infectious PERV 

sequences, which suggests that many breeds of 

pig fail to produce PERVs capable of infecting 

human cells even in laboratory testing. 176 This 

raises the possibility of using special breeds of 

pig for an unlimited supply of islet cells for encapsulation 

and use as a bioartificial pancreas 

in clinical xenotransplantation. 

The other attractive approach to generate unlimited 

supply of islets is the use of embryonic 

stem cells, which have the ability to differentiate 

into a variety of cell lineages in vitro. Recent 

studies in small animals showing successful 

transplantation of pancreatic stem cells 

suggest that this approach could provide an 

unlimited source of allogeneic insulin-producing 

tissue in the future. 177–179 

The maintenance of cell viability is another 

important concern in the development of a successful 

bioartificial pancreas. When cells are encapsulated 

and implanted in an environment 

without a natural circulation, lack of an adequate 

supply of oxygen and nutrients results in 

cell necrosis, making implantation unsuccessful. 

To improve long-term islet survival and 

function, vascularization of transplanted islets 

has been proposed. 180–182 An ideal architecture 

for implantation would be to promote vascularization 

around encapsulated cells using a 

novel approach. Recently, a technique to form 

covalently bonded multilayers of PEG hydrogels 

has been developed. This approach may 

be used to encapsulate cells with bilayers such 

that outer layer would promote vascularization 

around the inner layer. 183,184 

There are other areas of urgent need for the 

successful development of a bioartificial pancreas 

through islet cell microencapsulation. All 

current techniques for cell microencapsulation 

are slow in producing desirable microcapsules, 

requiring days to generate enough encapsulated 

islets for one transplantation. 185 An ideal 

procedure for routine use of encapsulated islets 

would require the development of massively 

parallel concepts in microencapsulation, which 

would generate sufficient quantities of microcapsules 

for multiple transplantations in a matter 

of minutes. In the absence of a technique 

based on such a principle, there is a need for 

an adequate procedure for long-term storage of 

encapsulated cells to enhance their use for 

transplantation. It is also highly desirable to develop 

rapid in vitro techniques for determination 

of the functional viability of encapsulated 

islets prior to transplantation. 

In summary, a potential cure for Type 1 diabetes 

could be the use of bioartificial pancreatic 

constructs based on insulin-secreting cells 

(allogeneic or xenogeneic islet cells) that are immunoisolated 

with the microencapsulation 

technique. Additionally, enhanced survival of 

the graft might be supported with a novel approach 

to induce neovascularization, which 

could make this technology a clinical reality in 

the near future. This will in turn serve as an 

important progress in cell therapy for the treatment 

of diabetes as well as other diseases, such 

as cancer, hemophilia, liver failure, and Parkinson’s 

disease. 

REFERENCES 

1. Kleinman JC, Donahue RP, Harris MI, Finucane FF, 

Madans JH, Brock DB: Mortality among diabetics in 

a national sample. Am J Epidemiol 1988;128:389–401. 

2. Drury TF: Disability among adult diabetics. In: National 

Diabetes Group, eds. Diabetes in America: Diabetes 

Data Compiled. Publication 85-1468. Bethesda, 

MD: National Diabetes Data Group, 1985. 

3. World Health Organization: Definition, Diagnosis 

and Classification of Diabetes Mellitus and Its Complications. 

Report of a WHO Consultation. Geneva: 

World Health Organization, 1999. 

4. Nathan DM: Long term complications of diabetes 

mellitus. N Engl J Med 1993;328:1676–1685. 

5. Barrett-Connor E, Orchard T: Insulin-dependent diabetes 

mellitus and ischemic heart disease. Diabetes 

Care 1985;8:65–70. 

6. Barret-Conor E, Khaw KT: Diabetes mellitus and independent 

risk factor for stroke. Am J Epidemiol 

1988;128:116–123. 

7. Bild DE, Selby JV, Sinnock P, Browner WS, Braveman 

P, Showstack JA: Lower extremity amputation 

in people with diabetes: epidemiology and prevention. 

Diabetes Care 1989;12:24–29. 

8. Geiss LS, Herman WH, Teutsch SM: Diabetes and 

renal mortality in the United States. Am J Public 

Health 1985;75:1325–1326.

980 

9. Moss SE, Klein R, Klein BE: The incidence of vision 

loss in a diabetic population. Ophthalmology 1988; 

95:1340–1348. 

10. Rubin RJ, Altman WM, Mendelson DN: Health care 

expenditures for people with diabetes mellitus. J 

Clin Endocrinol Metab 1994;78:809A–809F. 

11. Diabetes Control and Complications Trial Research 

Group: The effect of intensive treatment of diabetes 

on the development and progression of long-term 

complications in insulin-dependent diabetes mellitus. 

N Engl J Med 1993;329:977–986. 

12. Ido Y, Vindignia A, Chang K, Stramm L, Chance R, 

Heath WF, DiMarchi RD, Di Cera E, Williamson JR: 

Prevention of vascular and neural dysfunction in diabetic 

rats by C-peptide. Science 1997;277:563–566. 

13. Johansson BL, Borg K, Fernqvist-Forbes E, Kernell 

A, Odergren T, Wahren J: Beneficial effects of C-peptide 

on incipient nephropathy and neuropathy in patients 

with Type 1 diabetes mellitus. Diabet Med 

2000;17:181–189. 

14. Hansen A, Johansson BL, Wahren J, Bibra HV: Cpeptide 

exerts beneficial effects on myocardial blood 

flow and function in patients with Type 1 diabetes. 

Diabetes 2002;51:3077–3082. 

15. Ekberg K, Brismar T, Johansson BL, Jonsson B, Lindström 

P, Wahren J: Amelioration of sensory nerve 

dysfunction by C-peptide in patients with Type 1 diabetes. 

Diabetes 2003;52:536–541. 

16. Sutherland DE, Gruessner RW, Gruessner AC: Pancreas 

transplantation for treatment of diabetes mellitus. 

World J Surg 2001;25:487–496. 

17. Venstrom JM, McBride MA, Rother KI, Hirshberg B, 

Orchard TJ, Harlan DM: Survival after pancreas 

transplantation in patients with diabetes and preserved 

kidney function. JAMA 2003;290:2817–2823. 

18. Sutherland DE, Stratta RJ, Gruessner AC: Pancreas 

transplant outcome by recipient category: single 

pancreas versus combined kidney-pancreas. Curr 

Opin Organ Transplant 1998;3:231–241. 

19. de Groot M, Schuurs TA, van Schilfgaarde R: Causes 

of limited survival of microencapsulated pancreatic 

islet grafts. J Surg Res 2004;121:141–150. 

20. Kendall WFJ, Opara EC: Immunoisolation techniques 

for islet cell transplantation. Expert Opin Biol 

Ther 2002;2:503–511. 

21. Alejandro R, Feldman EC, Bloom AD, Kenyon NS: 

Effects of cyclosporin on insulin and C-peptide secretion 

in healthy beagles. Diabetes 1989;38:698–703. 

22. Gunnarsson R, Klintmalm G, Lundgren G, Wilczek 

H, Ostman J, Groth CG: Deterioration in glucose metabolism 

in pancreatic transplant recipients given cyclosporine. 

Lancet 1983;2:571–572. 

23. Schlumpf R, Largiader F, Uhlschmid GK, Baumgartner 

D: Is cyclosporine toxic for transplanted pancreatic 

islets? Transplant Proc 1986;28:1169–1170. 

24. Van Schilfgaarde R, van der Burg MPM, van 

Suylichem HG, Goosen HG, Frolich M: Does cyclosporine 

influence beta cell function? Transplant 

Proc 1986;28:1175–1176. 


25. Shapiro AM, Lakey JR, Ryan EA, Korbutt GS, Toth E, 

Warnock GL, Kneteman NM, Rajotte RV: Islet transplantation 

in seven patients with Type I diabetes 

mellitus using a glucocorticoid-free immunosuppressive 

regimen. N Engl J Med 2000;343:230–238. 

26. Ryan EA, Lakey JRT, Paty BW, Imes S, Korbutt GS, 

Kneteman, NM, Bigam D, Rajotte RV, Shapiro AM: 

Successful islet transplantation: continued insulin reverse 

provides long-term glycemic control. Diabetes 

2002;51:2148–2157. 

27. Brunicardi FC, Mullen Y: Issues in clinical islet transplantation. 

Pancreas 1994;9:281–290. 

28. De Vos P, Van Schilfgaarde R: Biocompatibility issues. 

In: Chick WL, ed. Cell Encapsulation Technology 

and Therapeutics. Boston: Birkhauser, 1999: 

63–79. 

29. De Vos P, Van Straaten JF, Nieuwenhuizen AG, de 

Groot M, Ploeg RJ, De Haan BJ, Van Schlifgaarde R: 

Why do microencapsulated islet grafts fail in the 

presence of fibrotic overgrowth? Diabetes 1999;48: 

1381–1388. 

30. Ortiz C, Zhang D, Xie Y, Davisson VJ, Ben-Amotz 

D: Identification of insulin variants using Raman 

spectroscopy. Anal Biochem 2004;332:245–252. 

31. Lanza RP, Ecker DM, Kuhtreiber WM, Marsh JP, 

Ringeling J, Chick WL: Transplantation of islets using 

microencapsulation: studies in diabetic rodents 

and dogs. J Mol Med 1999;77:206–210. 

32. Lim F, Sun AM: Microencapsulated islets as bioartificial 

endocrine pancreas. Science 1980;210:908–910. 

33. Soon-Shiong P, Heintz RE, Merideth N, Yao QX, Yao 

ZW, Zheng TL, Murphy M, Moloney MK, Schmehl 

M, Harris M, Mendez R, Mendez R, Sandford PA: 

Insulin independence in a type I diabetic patient after 

encapsulated islet transplantation. Lancet 

1994;343:950–951. 

34. Zekorn TD, Horcher A, Siebers U, Federlin K, Bretzel 

RG: Synergistic effect of microencapsulation and 

immunoalteration on islet allograft survival in bioartificial 

pancreas. J Mol Med 1999;77:193–199. 

35. Omer A, Keegan M, Czismadia E, De Vos P, Van 

Rooijen N, Bonner-Weir S, Weir GC: Macrophage depletion 

improves survival of porcine neonatal pancreatic 

cell clusters contained in alginate macrocapsules 

transplanted into rats. Xenotransplantation 

2003;10:240–251. 

36. de Vos P, Hamel AF, Tatarkiewicz K: Considerations 

for successful transplantation of encapsulated pancreatic 

islets. Diabetologia 2002;45:159–173. 

37. De Vos P, Vegter D, De Haan BJ, Strubbe JH, Bruggink 

JE, Van Schilfgaarde R: Kinetics of intraperitoneally 

infused insulin in rats. Functional implications 

for the bioartificial pancreas. Diabetes 1996; 

45:1102–1107. 

38. Kessler L, Jesser C, Lombard Y, Karsten V, Belcourt 

A, Pinget M, Poindron P: Cytotoxicity of peritoneal 

murine macrophages against encapsulated pancreatic 

rat islets: in vivo and in vitro studies. J Leuk Biol 

1996;60:729–736.


39. Toso C, Oberholzer J, Ceausoglu I, Ris F, Rochat B, 

Rehor A, Bucher P, Wandrey C, Schuldt U, Belenger 

J, Bosco D, Morel P, Hunkeler D: Intra-portal injection 

of 400 microcapsules in a large animal model. 

Transplant Int 2003;16:405–410. 

40. Qian JH, Hashimoto T, Fujiwara H, Hamaoka T: 

Studies on the induction of tolerance of alloantigens. 

I. The abrogation of potentials for delayed-type-hypersensitivity 

responses to alloantigens by portal venous 

inoculations with allogeneic cells. J Immunol 

1985;134:3656–3661. 

41. Alejandro R, Mintz DH, Noel J, Latif Z, Koh N, Russell 

E, Miller J: Islet cell transplantation in Type I 

diabetes mellitus. Transplant Proc 1987;19:2359– 

2361. 

42. Brendel MD, Hering B, Schultz AO, Bretzel RG: 

International Islet Transplant Registry. Newsletter 

8. Giessen, Germany: Justus-Liebig-University of 

Giessen, 1999. 

43. Pfeiffer EF: Artificial pancreas, glucose sensors and 

the impact upon diabetology. Int J Artif Organs 

1993;16:636–644. 

44. Pfeiffer EF, Kerner W, Beischer W: Substitution of 

islet cell function by mechanical device: extracorporeal 

artificial pancreas. Adv Exp Med Biol 1979; 

119:501–508. 

45. Kruse-Jarres JD, Braun G, Naegele R, Bresch M, 

Lehmann U: Blood glucose monitoring and computer 

regulation by means of an artificial endocrine 

pancreas. Horm Metab Res Suppl 1979;8:42–45. 

46. Kerner W, Beischer W, Herfarth C, Pfeiffer EF: Application 

of an artificial endocrine pancreas in the 

management of the diabetic surgical patient. Horm 

Metab Res Suppl 1979;8:159–161. 

47. Hunkeler D: Allo transplants xeno: as bioartificial organs 

move to the clinic. Ann N Y Acad Sci 2001;944: 

1–6. 

48. Encapsulation & immunoprotective strategies of 

islet cells. Diabetes Technol Ther 2002;4:361. 

49. Prokop A: Bioartificial pancreas: materials, devices, 

function and limitations. Diabetes Technol Ther 

2001;3:431–449. 

50. Chang TMS: Semipermeable microcapsules. Science 

1964;146:524–525. 

51. Sun AM, O’Shea GM, Goosen MF: Injectable microencapsulated 

islet cells as bioartificial pancreas. 

Appl Biochem Biotechnol 1984;10:87–99. 

52. Wiegand F, Kroncke KD, Kolb-Bachofen V: Macrophage 

generated nitric-oxide as cytptoxic factor in 

destruction of alginate-encapsulated islets. Transplant 

Proc 1993;56:1206–1212. 

53. Soon-Shiong P, Otterlie M, Skjak-Braek G, Smidsrod 

O, Heintz R, Lanza RP, Espevik T: An immunologic 

basis for the fibrotic reaction to implanted microcapsules. 

Transplant Proc 1991;23:758–759. 

54. Strand BL, Ryan TL, In’t Veld P, Kulseng B, Rokstad 

AM, Skjak-Brek G, Espevik T: Poly-L-lysine induces 

fibrosis on alginate microcapsules via the induction 

of cytokines. Cell Transplant 2001;10:263–275. 

55. De Vos P, Wolters GHJ, Fritschy WM, Van Schilfgaarde 

R: Obstacles in the application of microencapsulation 

in islet transplantation. Int J Artif Organs 

1993;16:205–212. 

56. Goosen MFA: In: Lanza RR, Chick WL, eds. Immunoisolation 

of Pancreatic Islets. Austin, TX: R.G. 

Landes Co., 1994:21–44. 

57. Soon-Shiong P, Feldman E, Nelson R, Heintz R, Yao 

Q, Yao Z, Zheng T, Merideth N, Skjak-Braek G, Espevik 

T, Smidsrod O, Sandford P: Long-term reversal 

of diabetes by the injection of immunoprotected 

islets. Proc Natl Acad Sci U S A 1993;90:5843–5847. 

58. Lanza R, Langer R, Chick WL: Principles of Tissue 

Engineering, 2 nd ed. Orlando, FL: Academic Press, 

2000. 

59. Colton CK, Avgoustiniatos ES: Bioengineering in development 

of the hybrid artificial pancreas. J Biomech 

Eng 1991;113:152–170. 

60. Brissova M, Lacik I, Powers AC, Anilkumar AV, 

Wang TG: Control and measurement of permeability 

for design of microcapsule cell delivery system. 

J Biomed Mater Res 1998;39:61–70. 

61. Cole DR, Waterfall M, McIntyre M, Baird JD: Microencapsulated 

islet grafts in the BB/E rat: a possible 

role for cytokines in graft failure. Diabetologia 

1992;35:231–237. 

62. Fan MY, Lum Z, Levesque L, Tai IT, Sun AM: Reversal 

of diabetes in BB rats by transplantation of encapsulated 

rat islets. Diabetes 1990;39:519–522. 

63. Iwata H, Takagi T, Kobayashi K, Oka T, Tsuki T, Ito 

F: Strategy for developing microbeads applicable to 

islet xenotransplantation into a spontaneous diabetic 

NOD mice. J Biomed Mater Res 1994;28:1201–1207. 

64. Lanza RR, Chick WL, eds.: Immunoisolation of Pancreatic 

Islets. Austin, TX: R.G. Landes Co., 1994. 

65. Lacik I, Brissova M, Anilkumar AV, Powers AC, 

Wang TG: New capsule with tailored properties for 

the encapsulation of living cells. J Biomed Mater Res 

1998;39:52–60. 

66. Lum ZP, Tai P, Krestow I, Tai T, Sun AM: Xenografts 

of microencapsulated rat islets into diabetic mice. 

Transplant Proc 1992;53:1180–1183. 

67. Iwata H, Murakami Y, Ikada Y: Control of complement 

activities for immunoisolation. Ann N Y Acad 

Sci 1999;875:7–23. 

68. Paul LC: Mechanism of humoral xenograft rejection. 

In: Cooper DKC, Kemp E, Reemtsma K, White D, 

eds. Xenotransplantation. Berlin: Springer-Verlag, 

1991:47–67. 

69. Auchincloss HJ, Moses R, Conti D, Sundt T, Smith 

C, Sachs DH, Winn HJ: Rejection of transgenic skin 

expressing a xeno-class I antigen is CD4-dependent 

and CD8-independent. Transplant Proc 1990;22: 

1059–1060. 

70. Sayegh MH, Watschinger B, Carpenter CB: Mechanisms 

of T cell recognition of alloantigen. The role 

of peptides. Transplantation 1994;57:1295–1302. 

71. Chen G, Hohmeier HE, Gasa R, Tran VV, Newgard 

CB: Selection of insulinoma cell lines with resistance

982 

to interleukin-1beta- and gamma-interferon-induced 

cytotoxicity. Diabetes 2000;49:562–570. 

72. Safley SA, Kapp LM, Tucker-Burden C, Hering B, 

Kapp JA, Weber CJ: Inhibition of cellular immune 

responses to encapsulated porcine islet xenografts 

by simultaneous blockade of two different costimulatory 

pathways. Transplantation 2005;79:409–418. 

73. Rafael E, Wu GS, Hultenby K, Tibell A, Wernerson 

A: Improved survival of macroencapsulated islets of 

Langerhans by preimplantation of the immunoisolating 

device: a morphometric study. Cell Transplant 

2003;12:407–412. 

74. Anderson JM: Inflammatory response to implants. 

ASAIO Trans 1988;34:101–107. 

75. Anderson JM: Mechanisms of inflammation and infection 

with implanted devices. Cardiovasc Pathol 

1993;2(Suppl):33S–41S. 

76. Anderson JM: Biocompatibility of tissue engineered 

implants. In: CW Patrick Jr, AG Mikos, LV McIntire, 

eds. Frontiers in Tissue Engineering. Oxford: Elsevier 

Science, 1998:152–165. 

77. Bonner-Weir S, Sharma A: Pancreatic stem cells. J 

Pathol 2002;197:519–526. 

78. Lumelsky N, Blondel O, Laeng P, Velasco I, Ravin 

R, McKay R: Differentiation of embryonic stem cells 

to insulin-secreting structures similar to pancreatic 

islets. Science 2001;292:1389–1394. 

79. Peck AB, Cornelius JG, Schatz D, Ramiya VK: Generation 

of islets of Langerhans from adult pancreatic 

stem cells. J Hepatobil Pancreat Surg 2002;9:704–709. 

80. Ramiya VK, Maraist M, Arfors KE, Schatz DA, Peck 

AB, Cornelius JG: Reversal of insulin-dependent diabetes 

using islets generated in vitro from pancreatic 

stem cells. Nat Med 2000;6:278–282. 

81. Chen R, Meseck ML, Woo SL: Auto-regulated hepatic 

insulin gene expression in type I diabetic rats. 

Mol Ther 2001;3:584–590. 

82. Lee HC, Kim SJ, Kim KS, Shin HC, Yoon JW: Remission 

in models of Type I diabetes by gene therapy 

using a single-chain insulin analogue. Nature 

2000;408:483–488. 

83. Tang SC, Sambanis A: Development of genetically 

engineered human intestinal cells for regulated insulin 

secretion using rAAV-mediated gene transfer. 

Biochem Biophys Res Commun 2003;303:645–652. 

84. Tang SC, Sambanis A: Preproinsulin mRNA engineering 

and its application to the regulation of insulin 

secretion from human hepatomas. FEBS Lett 

2003;537:193–197. 

85. Thule PM, Liu JM: Regulated hepatic insulin gene 

therapy of STZ-diabetic rats. Gene Ther 2000; 

7:1744–1752. 

86. Thule PM, Liu J, Philips LS: Glucose regulated production 

of human insulin in rat hepatocytes. Gene 

Ther 2000;7:205–214. 

87. Lumelsky N, Blondel O, Laeng P, Velasco I, Ravin 

R, McKay R: Differentiation of embryonic stem cells 

to insulin secreting structures similar to pancreaticislets. 

Science 2001;292:1389–1394. 


88. Hori Y, Rulifson IC, Tsai BC, Heit JJ, Cahoy JD, Kim 

SK: Growth inhibitors promote differentiation of insulin-producing 

tissue from embryonic stem cells. 

Proc Natl Acad Sci U S A 2002;99:16105–16110. 

89. Blyszczuk P, Czyz J, Kania G, Wagner M, Roll U, St- 

Onge L, Wobus AM: Expression of Pax4 in embryonic 

stem cells promotes differentiation of nestinpositive 

progenitor and insulin-producing cells. Proc 

Natl Acad Sci U S A 2003;100:998–1003. 

90. Moritoh Y, Yamato E, Yasui Y, Miyazaki S, Miyazaki 

J: Analysis of insulin-producing cells during in vitro 

differentiation from feeder-free embryonic stem 

cells. Diabetes 2003;52:1163–1168. 

91. Segev H, Fishman B, Ziskind A, Shulman M, Itskovitz-Eldor 

J: Differentiation of human embryonic 

stem cells into insulin-producing clusters. Stem Cells 

2004;22:265–274. 

92. Hori Y, Gu X, Xie X, Kim SK: Differentiation of insulin-producing 

cells from human neural progenitor 

cells. PLoS Med 2005;2:e103. 

93. Assady S, Maor G, Amit M, Itskovitz-Eldor J, Skorecki 

KL, Tzukerman M: Insulin production by human 

embryonic stem cells. Diabetes 2001;50:1691– 

1697. 

94. Xu G, Stoffers DA, Habener JF, Bonner-Weir S: Exendin-4 

stimulates both beta-cell replication and 

neogenesis, resulting in increased beta-cell mass and 

improved glucose tolerance in diabetic rats. Diabetes 

1999;48:2270–2276. 

95. Gromada J, Brock B, Schmitz O, Rorsman P: 

Glucagon-like peptide-1: regulation of insulin secretion 

and therapeutic potential. Basic Clin Pharmacol 

Toxicol 2004;95:252–262. 

96. Harmon EB, Apelqvist AA, Smart NG, Gu X, Osborne 

DH, Kim SK: GDF11 modulates NGN3 islet 

progenitor cell number and promotes beta-cell differentiation 

in pancreas development. Development 

2004;131:6163–6174. 

97. Bach JF: Immunotherapy of insulin-dependent diabetes 

mellitus. Curr Opin Immunol 2001;13:601–605. 

98. Giannoukakis N, Rudert WA, Robbins PD, Trucco 

M: Targeting autoimmune diabetes with gene therapy. 

Diabetes 1999;48:2107–2121. 

99. Docherty K: Gene therapy for diabetes mellitus. Clin 

Sci (Lond) 1997;92:321–330. 

100. Soria B, Skoudy A, Martin F: From stem cells to beta 

cells: new strategies in cell therapy of diabetes mellitus. 

Diabetologia 2001;44:407–415. 

101. Selden RF, Skoskiewicz MJ, Russell PS, Goodman 

HM: Regulation of insulin-gene expression. Implications 

for gene therapy. N Engl J Med 1987; 

317:1067–1076. 

102. Newgard CB: Cellular engineering and gene therapy 

strategies for insulin replacement in diabetes. Diabetes 

1994;43:341–350. 

103. Halban PA, Kahn SE, Lernmark A, Rhodes CJ: Gene 

and cell-replacement therapy in the treatment of 

type 1 diabetes: how high must the standards be set? 

Diabetes 2001;50:2181–2191.


104. Sapir T, Shternhall K, Meivar-Levy I, Blumenfeld T, 

Cohen H, Skutelsky E, Eventov-Friedman S, Barshack 

I, Goldberg I, Pri-Chen S, Ben-Dor L, Polak- 

Charcon S, Karasik A, Shimon I, Mor E, Ferber S: 

Cell-replacement therapy for diabetes: generating 

functional insulin-producing tissue from adult 

human liver cells. Proc Natl Acad Sci U S A 

2005;102:7964–7969. 

105. Fujita Y, Cheung AT, Kieffer TJ: Harnessing the gut 

to treat diabetes. Pediatr Diabetes 2004;5:57–69. 

106. Cheung AT, Dayanandan B, Lewis JT, Korbutt GS, 

Rajotte RV, Bryer-Ash M, Boylan MO, Wolfe MM, 

Kieffer TJ: Glucose-dependent insulin release from 

genetically engineered K cells. Science 2000;290: 

1959–1962. 

107. El-Shewy HM, Kendall WFJ, Darrabie M, Collins BH, 

Opara EC: Polyvinyl pyrrolidone: a novel cryoprotectant 

in islet cell cryopreservation. Cell Transplant 

2004;13:237–243. 

108. Zimmermann H, Katsen AD, Ihmig FR, Durst CHP, 

Shirley SG, Fuhr GR: First steps of an interdisciplinary 

approach towards miniaturised cryopreservation 

for cellular nanobiotechnology. IEE Proc Nanobiotechnol 

2004;151:134–138. 

109. Zimmermann H, Zimmermann D, Reuss R, Feilen 

PJ, Manz B, Katsen A, Weber M, Ihmig FR, Ehrhart 

F, Gessner P, Behringer M, Steinbach A, Wegner LH, 

Sukhorukov VL, Vasquez JA, Schneider S, Weber 

MM, Volke F, Wolf R, Zimmermann U: Towards a 

medically approved technology for alginate-based 

microcapsules allowing long-term immunoisolated 

transplantation. J Mater Sci Mater Med 2005;16: 

491–501. 

110. Misler S, Dickey A, Barnett DW: Maintenance of 

stimulus-secretion coupling and single beta-cell 

function in cryopreserved-thawed human islets of 

Langerhans. Pflugers Arch 2005;450:395–404. 

111. von Mach MA, Schlosser J, Weiland M, Feilen PJ, 

Ringel M, Hengstler JG, Weilemann LS, Beyer J, 

Kann P, Schneider S: Size of pancreatic islets of 

Langerhans: a key parameter for viability after cryopreservation. 

Acta Diabetol 2003;40:123–129. 

112. Lanza RP, Chick WL: Transplantation of encapsulated 

cells and tissues. Surgery 1997;121:1–9. 

113. Lanza RP, Chick WL: Immunoisolation strategies for 

the transplantation of pancreatic islets. Ann N Y 

Acad Sci 1997;831:323–331. 

114. Wang TG: Progress in bioartificial pancreas. J Regen 

Med 2000;1:93–98. 

115. Jain K, Yang H, Cai BR, Haque B, Hurvitz AI, Diehl 

C, Miyata T, Smith BH, Stenzel K, Suthanthiran M: Retrievable, 

replaceable, macroencapsulated pancreatic 

islet xenografts. Long-term engraftment without immunosuppression. 

Transplantation 1995;59:319–324. 

116. Trivedi N, Keegan M, Steil GM, Hollister-Lock J, 

Hasenkamp WM, Colton CK, Bonner-Weir S, Weir 

GC: Islets in alginate macrobeads reverse diabetes 

despite minimal acute insulin secretory responses. 


117. Lacy PE, Hegre OD: Maintenance of normoglycemia 

in diabetic mice by subcutaneous xenografts of encapsulated 

islets. Science 1991;254:1782–1784. 

118. Scharp DW, Swanson CJ, Olack BJ, Latta PP, Hegre 

OD, Doherty EJ, Gentile FT, Flavin KS, Ansara MF, 

Lacy P: Protection of encapsulated human islets implanted 

without immunosuppression in patients 

with type I or type II diabetes and in nondiabetic 

control subjects. Diabetes 1994;43:1167–1170. 

119. van Suylichem PT, Strubbe JH, Houwing H, Wolters 

GH, van Schilfgaarde R: Insulin secretion by rat islet 

isografts of a defined endocrine volume after transplantation 

to three different sites. Diabetologia 

1992;35:917–923. 

120. Elliott RB, Escobar L, Garkavenko O, Croxson MC, 

Schroeder BA, McGregor M, Ferguson G, Beckman 

N, Ferguson S: No evidence of infection with porcine 

endogenous retrovirus in recipients of encapsulated 

porcine islet xenografts. Cell Transplant 2000;9: 

895–901. 

121. Sun YL, Ma X, Zhou D, Vacek I, Sun AM: Normalization 

of diabetes in spontaneously diabetic 

cynomologus monkeys by xenografts of microencapsulated 

porcine islets without immunosuppression. 

J Clin Invest 1996;98:1417–1422. 

122. Kendall WF, Collins BH, Hobbs HA, Bollinger RR, 

Opara EC: Long-term normoglycemia induced by 

microencapsulated porcine islet xenotransplantation 

in a diabetic baboon [abstract]. Acta Chir Austriaca 

2001;33(Suppl 174):56. 

123. Soon-Shiong P, Feldman E, Nelson R, Komtebedde 

J, Smidsrod O, Skjak-Braek G, Espevik T, Heintz R, 

Lee M: Successful reversal of spontaneous diabetes 

in dogs by intraperitoneal microencapsulated islets. 


124. Sun Y, Ma X, Zhou D, Vacek I, Sun AM: Normalization 

of diabetes in spontaneously diabetic cynomologous 

monkeys by xenografts of microencapsulated 

porcine islets without immunosuppression. J Clin Invest 

1996;98:1417–1422. 

125. Uludag H, De Vos P, Tresco PA: Technology of 

mammalian cell encapsulation. Adv Drug Deliv Rev 

2000;42:29–64. 

126. Pollok JM, Kolin PA, Lorenzen M, Torok E, Kaufmann 

PM, Kluth D, Bohuslavizki KH, Gundlach M, 

Rogiers X: Islets of Langerhans encapsulated with a 

tissue engineered membrane of rat chondrocytes 

maintain insulin secretion and glucose insulin feedback 

for at least 30 days in culture. Transplant Proc 

2001;33:1713–1714. 

127. Sandler S, Andersson A, Eizirik DL, Hellerstrom C, 

Espevik T, Kulseng B, Thu B, Pipeleers DG, Skjak- 

Braek G: Assessment of insulin secretion in vitro 

from microencapsulated fetal porcine islet like cell 

clusters and rat, mouse, and human pancreatic islets. 


128. Halle JP, Leblond FA, Pariseau JF, Jutras P, Brabant 

MJ, Lepage Y: Studies on small (300 microns) microcapsules: 

II—Parameters governing the produc-

984 

tion of alginate beads by high voltage electrostatic 

pulses. Cell Transplant 1994;3:365–372. 

129. Duvivier-Kali VF, Omer A, Parent RJ, O’Neil JJ, Weir 

GC: Complete protection of islets against allorejection 

and autoimmunity by a simple barium alginate 

membrane. Diabetes 2001;50:1698–1705. 

130. Klock G, Frank H, Houben R, Zekorn T, Horcher A, 

Siebers U, Wöhrle M, Federlin K, Zimmermann U: 

Production of purified alginates suitable for use in 

immunoisolated transplantation. Appl Microbiol 

Biotechnol 1994;40:638–643. 

131. Kulseng B, Thu T, Espevik T, Skjk-Brk G: Alginate 

poly-lysine microcapsules as immune barrier: permeability 

of cytokines and immunoglobins over the 

capsule membrane. Cell Transplant 1997;6:387–394. 

132. Sawhney AS, Hubbell JA: Poly(ethylene oxide)graft-poly(L-lysine) 

copolymers to enhance the biocompatibility 

of poly(L-lysine)-alginate microcapsule 

membranes. Biomaterials 1992;13:863–870. 

133. Lim F: Microencapsulation of living mammalian 

cells. Adv Biotechnol Processes 1988;7:185–197. 

134. Smidsrod O, Skjak-Braek G: Alginate as immobilization 

matrix for cells. Trends Biotechnol 1990;8: 

71–78. 

135. Prokop A, Wang TG: Purification of polymers used 

for fabrication of an immunoisolation barrier. Ann 

N Y Acad Sci 1997;831:223–231. 

136. Zekorn T, Klock G, Horcher A, Siebers U, Wohrle M, 

Kowalski M, Arnold M, Federlin K, Bretzel R, Zimmermann 

U: Lymphoid activation by different crude 

alginates and the effect of purification. Transplant 

Proc 1992;24:2952–2953. 

137. Ricker A, Stockberger S: Hyperimmune response to 

microencapsulated xenogeneic tissue in NOD mice 

[abstract]. Diabetes 1986;35:61A. 

138. Garfinkel MR, Harland RC, Opara EC: Optimization 

of the microencapsulated islet for transplantation. J 

Surg Res 1998;76:7–10. 

139. Ar’Rajab A, Bengmark S, Ahren B: Insulin secretion 

in streptozotocin-diabetic rats transplanted with immunoisolated 

islets. Transplantation 1991;51:571– 

574. 

140. Calafiore R, Calcinaro F, Basta G, Pietropoalo M, 

Falorni A, Piermattei M, Brunetti P: A method for 

the massive separation of highly purified, adult 

porcine islets of Langerhans. Metabolism 1990;39: 

175–181. 

141. Carani BS, Edwin G, eds.: Annals of the New York 

Academy of Sciences, Vol. 1037: Immunology of Diabetes 

III. New York: New York Academy of Sciences, 

2005. 

142. Mazaheri R, Atkison P, Stiller C, Dupre J, Vose J, 

O’Shea G: Transplantation of encapsulated allogeneic 

islets into diabetic BB/W rats. Effects of immunosuppression. 


143. Sefton MV, Stevenson WTK: Microencapsulation of 

live animal cells using polyacrylates. Adv Polym Sci 

1993;107:145–198. 

144. Dupuy B, Gin H, Baquey C, Ducassou D: In situ 

polymerization of a microencapsulating medium 


round living cells. J Biomed Mater Res 1988;22: 

1061–1070. 

145. Gin H, Dupuy B, Baquey C, Ducassou D, Aubertin 

J: Agarose encapsulation of islets of Langerhans: reduced 

toxicity in vitro. J Microencapsul 1987;4: 

239–242. 

146. Takagi T, Iwata H, Tashiro H, Tsuji T, Ito F: Development 

of a novel microbead applicable to xenogeneic 

islet transplantation. J Control Rel 1994;31: 

283–291. 

147. Iwata H, Murakami Y, Ikada Y: Control of complement 

activities for immunoisolation. Ann N Y Acad 

Sci 1999;875:7–23. 

148. Deppsich R, Goehl H, Ritz E, Haensch GM: Complement 

activation on artificial surfaces in biomedical 

therapies. In: Rother K, Till GO, Hänsch GM, eds. 

The Complement System, 2 nd ed. Berlin: Springer- 

Verlag, 1998, pp. 487–504. 

149. Pangburn MK: Alternative pathway: activation and 

regulation. In: Rother K, Till GO, Hänsch GM, eds. 

The Complement System, 2 nd ed. Berlin: Springer- 

Verlag, 1998:93–115. 

150. Chaikof EL: Engineering and material considerations 

in islet cell transplantation. Annu Rev Biomed 

Eng 1999;1:103–127. 

151. Shoichet MS, Winn SR, Gentile FT, Athavale S, Harris 

JM: Poly(ethylene oxide) grafted thermoplastic 

membranes for use as cellular hybrid bioartificial organs 

in the central nervous system. Biotechnol Bioengin 

1994;43:563–572. 

152. Pathak CP, Sawhney AS, Hubbell JA: Rapid photopolymerization 

of immunoprotective gels in contact 

with cells and tissue. J Am Chem Soc 1992; 

114:8311–8312. 

153. Cruise GM, Hegre OD, Scharp DS, Hubbell JA: A 

sensitivity study of the key parameters in the interfacial 

photopolymerization of poly(ethylene glycol) 

diacrylate upon porcine islets. Biotechnol Bioengin 

1998;57:655–665. 

154. Harris JM: Poly(ethylene Glycol) Chemistry: Biotechnical 

and Biomedical Applications. New York: 

Plenum Press, 1992. 

155. Sawhney AS, Pathak CP, Hubbell JA: Bioerodible 

hydrogels based on photopolymerized poly(ethylene 

glycol)-co-poly(-hydroxy acid) diacrylate 

macromers. Macromolecules 1993;26:581–587. 

156. Cruise GM, Scharp DS, Hubbell JA: Characterization 

of permeability and network structure of interfacially 

photopolymerized poly(ethylene glycol) 

diacrylate hydrogels. Biomaterials 1998;19:1287– 

1294. 

157. Wolters GH, Fritschy WM, Gerrits D, Van Schilfgaarde 

R: A versatile alginate droplet generator applicable 

for microencapsulation of pancreatic islets. 

J Appl Biomater 1992;3:281–286. 

158. Opara EC: The therapeutic potential of islet cell 

transplants in the treatment of diabetes. Expert Opin 

Invest Drugs 1998;7:1–11. 

159. Hobbs H, Kendall W, Darrabie M, Collins B, Bridges 

S, Opara EC: Substitution of polyornithine for


polylysine in alginate microcapsules [abstract]. Diabetes 

2000;49:A111. 

160. Hommel M, Sun AM, Goosen MFA, inventors; Connaught 

Laboratories Limited, assignee: Droplet generation. 

US Patent 4,956,128. September 11, 1990. 

161. Sundberg C: High-throughput and ultra-highthroughput 

screening: solution- and cell-based approaches. 

Curr Opin Biotechnol 2000;11:47–53. 

162. Kane RS, Takayama S, Ostuni E, Ingber DE, Whitesides 

GM: Patterning proteins and cells using soft 

lithography. Biomaterials 1999;20:2363–2376. 

163. Singhvi R, Kumer A, Lopez GP, Stephanopoulos GN, 

Wang DIC, Whitesides GM, Ingber DE: Engineering 

cell shape and function. Science 1994;264:696–698. 

164. Amirpour ML, Ghosh P, Lackowski WM, Crooks 

RM, Pishko MV: Mammalian cell cultures on micropatterned 

surfaces of weak-acid, polyelectrolyte 

hyperbranched thin films on gold. Anal Chem 

2001;73:1560–1566. 

165. Chen CS, Mrksich M, Huang S, Whitesides GM, Ingber 

DE: Micropatterned surfaces for control of cell 

shape, position, and function. Biotechnol Prog 

1998;14:356–363. 

166. Ito Y: Surface micropatterning to regulate cell functions. 

Biomaterials 1999;20:2333–2342. 

167. Koh W, Revzin A, Simonian A, Reeves T, Pishko M: 

Control of mammalian cell and bacteria adhesion on 

substrates micropatterned with poly(ethylene glycol) 

hydrogels. Biomed Microdev 2003;5:11–19. 

168. Matsuda T, Sugawara T: Development of surface 

photochemical modification method for micropatterning 

of cultured cells. J Biomed Mater Res 

1995;29:749–756. 

169. Kizilel S, Perez-Luna VH, Teymour F: Photopolymerization 

of poly(ethylene glycol) diacrylate on 

eosin-functionalized surfaces. Langmuir 2004;20: 

8652–8658. 

170. Desai TA, West T, Cohen M, Boiarski T, Rampersaud 

A: Nanoporous microsystems for islet cell replacement. 

Adv Drug Deliv Rev 2004;56:1661–1673. 

171. Cohen I, Li H, Hougland JL, Mrksich M, Nagel SR: 

Using selective withdrawal to coat microparticles. 

Science 2001;292:265–267. 

172. Patience C, Takeuchi Y, Weiss RA: Infection of human 

cells by an endogeneous retrovirus of pigs. Nat 

Med 1997;3:282–286. 

173. van der Laan LJW, Lockey C, Griffeth BC, Frasier FS, 

Wilson CA, Onions DE, Hering BJ, Long Z, Otto E, 

Torbett BE, Salomon DR: Infection by porcine endogeneous 

retrovirus after islet xenotransplantation in 

SCID mice. Nature 2000;407:90–94. 

174. Heneine W, Tibell A, Switzer WM, Sandstrom P, 

Rosales GV, Mathews A, Korsgren O, Chapman LE, 

Folks TM, Groth CG: No evidence of infection with 

porcine endogeneous retrovirus in recipients of 

porcine islet-cell xenografts. Lancet 1998;352:695– 

699. 

175. Paradis K, Langford G, Long Z, Heneine W, Sandstrom 

P, Switzer WM, Chapman LE, Lockey C, 

Onions D, Otto E: Search for cross species transmis- 

sion of porcine endogeneous retrovirus in patients 

treated with living pig tissue. The XEN 111 Study 

Group. Science 1999;285:1236–1241. 

176. Niebert M, Rogel-Gaillard C, Chardon P, Tonjes RR: 

Characterization of chromosomally assigned replication-component 

gamma porcine endogenous 

retroviruses derived from a large white pig and expression 

in human cells. J Virol 2002;76:2714–2720. 

177. Soria B, Roche E, Berna G, Leon-Quinto T, Reig JA, 

Martin F: Insulin secreting cells derived from embryonic 

stem cells normalize glycemia in streptozotocin 

induced diabetic mice. Diabetes 2000;49:157–162. 

178. Soria B, Andreu E, Berna G, Fuentes E, Gil A, Leon- 

Quinto T, Martin F, Montanya E, Nadal A, Reig JA, 

Ripoll C, Roche E, Sanchez-Andres JV, Segura J: Engineering 

pancreatic islets. Pflugers Arch 2000; 

440:1–18. 

179. Ramiya VK, Maraist M, Arfors KE, Schatz DA, Peck 

AB, Cornelius JG: Reversal of insulin dependent diabetes 

using islets generated in vitro from pancreatic 

stem cells. Nat Med 2000;6:278–282. 

180. Zhang N, Richter A, Suriawinata J, Harbaran S, Altomonte 

J, Cong L, Zhang H, Song K, Meseck M, 

Bromberg J, Dong H: Elevated vascular endothelial 

growth factor production in islets improves islet 

graft vascularization. Diabetes 2004;53:963–970. 

181. Sigrist S, Mechine-Neuville A, Mandes K, Calenda 

V, Braun S, Legeay G, Bellocq JP, Pinget M, Kessler 

L: Influence of VEGF on the viability of encapsulated 

pancreatic rat islets after transplantation in diabetic 

mice. Cell Transplant 2003;12:627–635. 

182. Narang AS, Cheng K, Henry J, Zhang C, Sabek O, 

Fraga D, Kotb M, Gaber AO, Mahato RI: Vascular 

endothelial growth factor gene delivery for revascularization 

in transplanted human islets. Pharm Res 

2004;21:15–25. 

183. Kizilel S: Theoretical and experimental investigation 

for interfacial photopolymerization of poly(ethylene 

glycol) diacrylate [Ph.D. thesis]. Chicago: Biomedical 

Engineering, Illinois Institute of Technology, 2004. 

184. Kizilel S, Sawardecker E, Teymour F, Perez-Luna 

VH: Sequential formation of covalently bonded hydrogel 

multilayers through surface initiated photopolymerization. 

Biomaterials 2005 Sept 10 [Epub 

ahead of print]. 

185. De Vos P, De Haan BJ, Van Schilfgaarde R: Upscaling 

the production of microencapsulated pancreatic 

islets. Biomaterials 1997;18:1085–1090. 

Address reprint requests to: 

Emmanuel C. Opara, Ph.D. 

Pritzker Institute of Biomedical Science & 

Engineering 

Illinois Institute of Technology 

10 West 32 nd Street, E1-116 

Chicago, IL 60616 

E-mail: opara@iit.edu

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