Barbieri Thesis - BioMedical Materials program (BMM)

Chapter 2 – The role of gels in instructive putties
ADDENDUM
2a.1. Introduction
As mentioned in §2.1., improved handling properties of bone graft substitutes (e.g.
cohesive moldability or injectability) are desired to fill morphologically complex defects
such as those encountered during mandibular alveolar ridge reconstruction [297] or
spine fusion procedures. [298] Reducing the granule size of the ceramic phase added to
polymer carriers may lead to paste–like materials that might be more easily placed
and shaped in the defect sites. Such pastes may be delivered to the site by injection
from a syringe and modelled to fit the defect. Thus, in this study we evaluated the
osteoinductive potential of pastes comprising the most promising gels (amongst those
studied in Chapter 2, i.e. CMC and PLU) and osteoinductive small granule size
calcium phosphate ceramic. By virtue of the results described in Chapter 2, we
expected that such pastes would be as osteoinductive as the loose ceramic granules.
2a.2. Materials and methods
2a.2.1. Preparation of injectable pastes
In this study we used small granules of osteoinductive biphasic calcium phosphate
ceramic (BCP, particle size 212–300 m, Xpand Biotechnology BV). CMC and PLU
gels were prepared as described in §2.2.1. and pastes were made following the
procedure described in §2.2.2. Briefly, the gel and BCP granules were mixed to obtain
a gel/BCP volume ratio as low as possible but high enough to guarantee good
flowability (i.e. the paste should flush out from the syringe with no effort and keep the
shape). Once the materials were ready, they were placed in 2cc plastic syringes
(Braun Medical Ltd) and sealed with caps. The materials were then sterilized using –
rays (average irradiation dose ~25 kGy, IsoTron Nederland BV) for further studies.
2a.2.2. Animal study (dog model)
With the permission of the local animal care committee (Animal Center, Sichuan
University, Chengdu, China; protocol #P07047), BCP granules (1 cc, size 212–300
m) and injectable pastes based on CMC and PLU gels (1 cc) were implanted in the
paraspinal muscles of eight skeletally mature mongrel dogs (male, 1–4 years old,
weight 10–15 kg) for 12 weeks to evaluate their osteoinductive property. The surgical
procedure was performed under general anaesthesia (pentobarbital sodium,
Organon; 30 mg kg –1 body weight) and sterile conditions. The back of the dogs was
shaved and the skin cleaned with iodine. A longitudinal incision was made and the
paraspinal muscle was exposed by blunt separation. Longitudinal muscle incisions
were subsequently made with a scalpel and four separate muscle pouches were
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