Nano-Mechanical Studies on Polyglactin Sutures Subjected to In Vitro Hydrolytic and Enzymatic Degradation.

An experimental investigation on the effects of in vitro hydrolytic and enzymatic degradation on mechanical properties of polyglactin 910 monofilament sutures was performed by conducting nanoindentation studies using an atomic force microscope (AFM). For hydrolytic degradation, the sutures were incubated in phosphate buffered saline (PBS) solution at three different pH conditions, 5, 7.4, and 10. For enzymatic degradation, esterase was employed at pH condition of 7.4. The property of the sutures changed with time at different conditions were investigated by nanoindentation, tensile test experiments, image analysis using both of scanning electron microscopy (SEM) and AFM, and also Fourier transform infrared spectroscopy (FTIR). The effects of degradation on gradation of Young's modulus values across the cross section of the sutures were studied by doing progressive nanoindentation from center to surface. FTIR studies revealed the formation of new hydroxyl bonds due to both hydrolytic and enzymatic degradations. Nanoindentation results indicated that the degradation does not cause a gradient of Young's modulus of the polyglactin 910 monofilament sutures across the cross section from center to surface at different degradation times for both hydrolytic and enzymatic degradations. However, in general, the Young's modulus of all samples was decreased over 4 weeks of degradation. The microscopic evaluation of the samples also showed both qualitative changes in surface morphology and quantitative changes in surface roughness on the surface of degraded sutures. This study provided a deep understanding of the polyglactin sutures subjected to in vitro hydrolytic and enzymatic degradation, and also opened a new avenue to study the biomaterials at nano-scale.

Mechanical and biological properties of chitin/polylactide (PLA)/hydroxyapatite (HAP) composites cast using ionic liquid solutions.

This research investigates the potential development of lobster shell waste-derived chitin reinforced with poly(lactic acid) (PLA) and nano-hydroxyapatite (nHAP) into new materials with potentially superior mechanical and thermal properties for biomedical applications. The ionic liquid 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) was used as a solvent to prepare chitin/PLA/nHAP composites. The effect of variation of the polymer concentrations on the conduct of the resulting composite was explored. The detailed physico-mechanical, thermal and surface morphology properties were evaluated with different thermal and optical characterization techniques. When the concentration of PLA in the composite was increased from 20 to 80 wt%, the tensile strength improved by ~77% while the elongation at break and the toughness of the material decreased significantly. The addition of hydroxyapatite was observed to improve strength of the composites up to 140% with an increase in elongation at break up to 465%. Cell growth study show that the composite materials support the growth and proliferation of Ocy 454 osteocyte cells. The materials were shown to have no effect on osteocyte gene expression, as well as minimal cytotoxicity and biodegradability. These results reveal that the biocomposites would be suitable candidates for use in bone regeneration that are not exposed to excessive forces.