Читать книгу Poly(lactic acid) - Группа авторов - Страница 119

Lately, there have been important advances in sc blends of PLA copolymers for biomedical implant applications. In a study reported by us [70], diblock copolymers of PCL‐PLLA and PCL‐PDLA were synthesized by two‐step ROP followed by blending them in a 1 : 1 ratio to achieve sc blends of the enantiomeric diblock copolymers. Using this strategy, it was possible to obtain enantiomeric diblock copolymers having enhanced mechanical properties (28 MPa strength and ~80% elongation at break), which were also processed by the conventional injection moulding technique to develop cancellous bone screws (orthopedic implants). The study reported the thermomechanical stability of the cancellous bone screw at 121°C in comparison to commercial PLA (2003D, NatureWorks LLC). The stereococomplexed diblock copolymer was found to be stable at the sterilization temperature of biomedical devices, unlike the commercial PLA sample. The biocompatibility of the synthesized sc diblock copolymer blend was also ascertained by MTT (3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazolium bromide) assay using MG‐63 cells (human bone osteosarcoma). In another study reported by our group, the triblock copolymers of PLLA‐PCL‐PLLA and PDLA‐PCL‐PDLA were synthesized by sequential ROP, where the block length of the terminal as well the mid segment was tailored. The enantiomeric triblock copolymers were blended in equal ratios to achieve the sc blends of triblock copolymers. Such blends of triblock copolymers resulted in a significant improvement in the elongation at break (~400 ‐ 700%) as well as Young’s modulus (0.3 ‐ 0.9 GPa), with a very low degree of sc crystallinity. The adhesion and growth of UMR‐106 cells (rat bone osteosarcoma) on the surface of the developed sc triblock copolymer further indicated its non‐toxic nature. [100].