Strontium ion reinforced bioceramic scaffold for load bearing bone regeneration.

Bone defects in load bearing areas require bone reconstruction with strong biomaterial having mechanical characteristics like cortical bone. Bioceramics are biomaterials that support bone formation as well as provide adequate mechanical properties. A strontium substitution of the bioceramic is expected to further increase its bioactivity by enhancing osteogenesis and protect the bone from osteoclastic resorption. The study involves development, characterization and in vivo testing of a newly developed strontium substituted hydroxyapatite based bioceramic scaffold (SrHAB) with sufficient biomechanical properties. Optimal concentration of strontium ion required for enhanced osteogenic differentiation was identified by comparing three compositions of SrHAB scaffold; namely Sr10HAB, Sr30HAB and Sr50 HAB for their Alkaline phosphatase activity in vitro. The selected Sr10HAB scaffold demonstrated in vivo bone formation with osteogenic differentiation of stromal derived mesenchymal stem cells (MSC) from human and ovine sources in ectopic and ovine models. Thus, Sr10HAB scaffold has a potential for application in load bearing bone requirements of orthopaedics and dentistry.

Currently practised sterilization methods--some inadvertent consequences.

Currently used sterilization techniques such as ethylene oxide, gamma irradiation, and steam sterilization could introduce inadvertent consequences, especially in polymeric materials. These could have far-reaching effects on the biocompatibility of the materials. Some of these consequences are reviewed and a typical example of the effect of steam sterilization on the properties and biocompatibility of polyethylene terephthalate is discussed.

Studies on the effect of degree of hydrophilicity on tissue response of polyurethane interpenetrating polymer networks.

Interpenetrating polymer networks of polyurethane and vinyl monomers such as polyacrylamide, polyvinyl pyrrolidone, poly(hydroxyethyl methacrylate) and poly(methyl methacrylate) were implanted intramuscularly in rabbits. Attempts were made to correlate the morphological aspects of the interpenetrating polymer networks to their histological response. A relatively increased hydrophilicity of hydrophobicity of the interpenetrating polymer networks as in the case of polyurethane-polyvinyl pyrrolidone and polyurethane-poly(methyl methacrylate) interpenetrating polymer networks, respectively, could elicit an inert response whilst degradation of materials promoted reactivity.

Morphological changes of poly(ethylene terephthalate) on multiple steam sterilization.

Poly(ethylene terephthalate) (PET) was steam sterilized by autoclaving for 15, 30 and 60 min. The thermal properties, T m, delta-H and percent crystallinity were determined using differential scanning calorimetry. Molecular weight distribution was determined using gel permeation liquid chromatography. Crystallinity of PET was also monitored by infrared spectrophotometry. The analyses indicate that that chain scission and cyclization reactions take place in PET, forming cyclic oligomers, that can migrate to the polymer surface and which may affect long term performance of PET.

Ageing of radiation-sterilized polypropylene: changes in semicrystallinity.

Studies on radiation sterilization of isotactic polypropylene intended for biomedical applications were carried out for uncovered and covered samples. The effect of ageing on these samples was studied by determining the changes in relative crystallinity. The semicrystalline nature of the polymer is responsible for the changes in crystallinity. The transitions between short- and long-range order and short- and long-duration stiffness in both covered and uncovered samples, reflected in changes in relative crystallinity, were highly affected by the formation of branches in the backbone of the polymer. The high degree of branching in covered samples resulted in greater long-duration stiffness in the transition between short- and long-duration stiffness. The high degree of branching in covered samples was attributed to the high diffusion of energized oxygen into the polymer matrix compared with uncovered samples. The changes in relative crystallinity were rapid in uncovered samples (70% max; 34% min) but rather slow in covered samples (87% max; 43% min).

Multiple gamma radiation sterilization of polyester fibres.

Gamma radiation with a dose of 2.5 Mrad has been found to be suitable to sterilize polyethylene terephthalate (PET) bulk materials intended for biomedical applications. The radiation stability of PET bulk materials and fibre may not however be taken as identical due to the changes in the polymer structure during the processing of bulk materials for fibre. The chemical changes occurring in PET fibres during single and multiple (prolonged) sterilization in air were investigated. It was found that single sterilization (2.5 Mrad) itself affected the PET yarn and fibre. This was exhibited by the increase of crystallinity from 30.5 to 37% in the case of yarn and from 40 to 44% in the case of fibre. The breaking load of the yarn also increased from 441 g to 451 g. These changes were attributed to the degradation of PET in the amorphous region and the recombination of degraded aliphatic segments. Sterilization at higher doses affected the crystalline region which decreased the crystallinity, breaking load and molecular weight. For samples irradiated at 2.5 Mrad, the breaking load increased, though the dispersity increased. This was attributed to cross-linking by recombination. The increase in crystallinity also enhanced the breaking load of the samples. Higher doses of sterilization led to drastic microstructural and macrostructural changes as seen from the molecular weight. It was inferred that the changes in crystallinity and microstructure that occurred during multiple sterilization might affect the biocompatibility of the material.

Characterisation of a polyester material for biomedical applications.

The characterisation of a polyester material for cardiovascular applications can be carried out to various levels of sophistication. This paper focuses on certain methods which could give information about important aspects of material characterisation such as chemical identity, molecular parameters, surface studies, extraction studies, removal of oligomers, mechanical properties and thermal properties. Significance of the results obtained from such analyses are also discussed.

Effect of steam sterilization on polyethylene terephthalate.

Subtle changes on the surface of polymeric materials on autoclaving have been ignored so far. An increase in cyclic trimer content on the surface of polyethylene terephthalate on autoclaving is reported. This increase may affect the biocompatibility of polyethylene terephthalate. Quantification of the cyclic trimer was done by high performance liquid chromatography.