Electrospinning of Hyaluronic Acid (HA) and HA/Gelatin Blends

Electrospinning of Hyaluronic Acid (HA) and HA/Gelatin Blends 115
processability to fabricating into novel nanofibrous
composites.
Hyaluronic acid, as a naturally occurring linear polysaccharide,
consists of repeating disaccharide units (b-1,4-
D-glucuronic acid and b-1,3-N-acetyl-D-glucosamine), is
the main component of the ECM of connective tissues, and
has many important biological functions. [33–35] Due to its
excellent properties of biocompatibility and biodegradability,
HA and its derivatives have been used extensively in
biomedical field, for example in wound dressings, tissue
scaffolds, arthritis treatment, drug delivery, and components
of implant materials. [35–38] However, medical studies
on HA nanofibrous membranes have hardly been reported
in spite of its importance in medical applications.
Generally, it was very difficult to carry out electrospinning
of HA aqueous solution. The molecular weight of
native HA is typically several million. The unusually high
viscosity and surface tension of HA were thought to be the
key factors that hinder the electrospinning of HA solution.
Additionally, the strong water retention ability of HA might
lead to the fuse of nanofibers electrospun on the collector
due to the insufficient evaporation of solvents in electrospinning.
The fabrication of HA into nanofibrous nonwoven
membranes from aqueous solution was successfully
carried out only after the development of blowing-assisted
electrospinning. [9]
In this paper, the electrospinning process of HA and
hyaluronic acid/gelatin (HA-GE) blends in mixed solvents
has been investigated. The main objectives are as follows:
(a) Explore the electrospinning process of pure HA
solution in water and mixed solvents, find the key factor
which hinders the electrospinning of HA aqueous solution,
and provide the solution to this spinning difficulty.
(b) Find a novel and simple way to electrospin HA
solutions with the common electrospinning setup.
(c) Investigate the effects of GE on the electrospinning
process of HA solutions. The characteristics of GE, such as
relatively lower molecular weight and amphiphilic property,
might favor the electrospinning of HA solution.
(d) Obtain HA-GE nanofibrous membranes with various
blending ratios. The HA-GE nanofibrous membranes with
different compositions and sized scale could have different
clinical applications to drug delivery, wound healings, and
tissue engineering scaffolds.
The present report shows that with the aid of N,Ndimethylformamide
(DMF), HA can be electrospun successfully
with common electrospinning setup at neutral pH,
and HA-GE aqueous solutions were first co-electrospun to
produce HA-GE composite fibrous non-woven membranes.
Experimental Part
Materials
Hyaluronic acid (sodium salt, Mw ¼ 2 000 000) was purchased
from Dali Co. (Nanning, China). Polymers of GE Type A
(Approx. 220 Bloom, Mn ¼ 80 000), extracted from porcine
skin by acidic process, were purchased from Sanhesheng
Gelatin Co. (Wenzhou, China). DMF and ethanol were
obtained from Beijing Chem. Co. (Beijing, China). All the
solvents were used without further purification.
Preparation of Spinning Solution
HA Solutions in Water System
Transparent aqueous solutions of HA were prepared by dissolving
a specific amount of HA powder in the mixed solvents
consisting of distilled water (w) and ethanol (e) (w/e ¼ 9/1,
volume ratio). Pure HA solutions with concentrations of 1.3 w/
v% (w in grams and v in milliliters) and 1.5 w/v% were
obtained.
1.5 w/v% HA Solutions in DMF/Water System
Dissolve certain amounts of HA powder in DMF under gentle
stirring for 10 min, and then add a specific amount of distilled
water into the HA solution according to the volume ratio of
DMF to water (2, 1.5, 1 and 0.5), respectively, and continue to
stir the solution for 20 min until the solution became
transparent. The spinning solution of 1.5 w/v% HA in DMF/
water system (2, 1.5, 1 and 0.5) was prepared.
HA-GE Blends Solutions
1.875 w/v% HA in DMF/water (volume ratio ¼ 1.5) solution
was prepared using the same procedure as above. 1.5, 3, 4.5, 6,
and 7.5 w/v% GE solutions with the solvent being pure water
was prepared at 40 8C under gentle stirring for 20 min. Add the
GE solution into the HA solution with specific volumes to
obtain the HA-GE solutions (HA/GE ¼ 100/20, 100/40, 100/
60, 100/80, 100/100, weight ratio), and in each solution the
concentration of HA was fixed at 1.5 w/v%.
Electrospinning
All electrospinning solutions, spinneret, and the environmental
temperatures were controlled at 40 3 8C. The electrospinning
solutions were placed into a 5 ml syringe with a capillary tip
having an inner diameter of 0.3 mm. A syringe pump was used
to feed the polymer solution and the feeding rate was fixed
at 60 ml min 1 . A high-voltage power supply was employed
to generate the electric field (0–50 kV). The applied voltage
was fixed at 22 kV. The tip-to-collector distance was fixed at
15 cm.
Hyaluronic acid has strong water retention ability. The residual
water could dissolve the electrospun fibers on the collector
if the aluminum foil was used. In this study, the ethanol bath
was used as a collector because ethanol is a poor solvent for
both HA and GE. A piece of aluminum foil, connecting to the
ground, was immersed in a vessel filled with ethanol. After
electrospinning, the vessel was put into the vacuum oven at
50 8C for 30 min to dry off ethanol and other solvents. Then the
aluminum foil can be taken out. Through this method, HA and
HA-GE films can be peeled off easily.
Macromol. Rapid Commun. 2006, 27, 114–120 www.mrc-journal.de ß 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim