Barbieri Thesis - BioMedical Materials program (BMM)

Chapter 2 – The role of gels in instructive putties
with synthetic raw polymer powders (i.e. PLU and PVA) or in refrigerator at 4°C to
prevent possible mildew formation in the case of natural origin gels, i.e. CMC, ALG
and CHI (Table 2).
2.2.2. Preparation of putties
Irregularly shaped granules of osteoinductive surface micro–structured biphasic
calcium phosphate ceramic (BCP, particle size 1–2 mm, kindly supplied by Xpand
Biotechnology BV, Bilthoven, the Netherlands) were used. The chemistry of the
ceramic granules was analysed by X–ray diffraction (XRD, Rigaku MiniFlex I, Rigaku,
Tokyo, Japan), while the surface morphology and the grain size were evaluated
with scanning electron microscopy (SEM, Philips XL 30 ESEM–FEG, Philips,
Eindhoven, the Netherlands). For each putty, one cc of ceramic particles was mixed
with the respective gel to obtain a volume ratio gel/BCP as low as possible but high
enough to guarantee the moldability of the resulting putties. Once the materials were
ready, they were placed in plastic syringes (Braun Injekt TM , 2 cc, Braun Medical Ltd,
Sheffield, United Kingdom) and sealed with syringe caps. The materials were then
sterilized using –rays (average irradiation dose ~25 kGy, IsoTron Nederland BV,
Ede, the Netherlands) for further studies.
2.2.3. Dissolution of the gels and disintegration of the putties
The dissolution rate of the gels was based on the time it took for the putties to fully
disintegrate. This was evaluated by placing 1 cc of each material (n=3 per material) in
wells containing 8 mL of phosphate buffered saline (PBS, Sigma–Aldrich) at 37±1°C.
Table 1. Details on the raw polymers used to prepare the gels.
Polymer Uses
CMC
[viscosity in 1% water at 20°C: 1500–2500 mPa s –1 ]
Used in several fields, including the preparation
of putties and injectable pastes for tissue
engineering. [270, 276, 277]
PLU
Used in pharmaceutical applications as drug
[Mw=12,600, molar ratio PEO–PPO–PEO 98:68:98] deliver material. [276, 278]
PVA
[Merck, Mw=22 kDa, degree of hydrolysis ≥ 98%]
Excellent material for medical applications such
as long–term implants [276, 279] and soft contact
CHI
[degree of deacetylation: 94%]
ALG
[native, low guluronic content, but the
guluronic/mannuronic ratio (i.e. G/M) was not
released by the supplier]
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lenses. [280]
Recently approved for clinical use as wound
bandage thanks to its biocompatibility and anti–
bacterial properties. [276, 281]
Clinically used in dental (e.g. dental impression
material and denture fixative) and drug fields
(controlled release tablets and encapsulation),
but it has also been studied as attractive
material for bone tissue engineering. [276, 282, 283]