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Silk fibroin-based biomaterials have recently found increasing applications in the tissue-engineering field including the generation of artificial nerve guides for peripheral nerve repair. The aim of this study was to investigate the suitability of silk fibroin as a candidate biomaterial for central nervous system (CNS) therapy. We found that substrates made up of silk fibroin fibers supported the survival and growth of the attached hippocampal neurons by using morphological observation. We also cultured the hippocampal neurons in silk fibroin extract for different times, and observed no significant difference occurring in their morphology, cell viability for these cultured hippocampal neurons as compared to those cultured in plain neuronal culture medium. Moreover, immunocytochemistry, RT-PCR, and Western blot analysis revealed that no significant difference was found in mRNA or protein levels of the growth-associated molecules, such as brain-derived neurotrophic factor, growth-associated protein-43, neurofilament, nerve growth factor, and nerve growth factor-receptor P75, between the hippocampal neurons cultured in the silk fibroin extract and in plain neuronal culture medium. Taken together, all the results demonstrate that silk fibroin has good biocompatibility with primarily cultured hippocampal neurons without any significant cytotoxic effects on their cell phenotype and functions, suggesting a potential possible use of silk fibroin for preparing the tissue-engineered nerve guides or drug delivery vehicles to treat CNS injuries or diseases.

Calcium phosphate cement (CPC) is a highly promising bone substitute and an excellent carrier for delivering growth factors. Yet, the lack of macro-porosity and osteoinductive ability, limit its use. This study is aimed at developing a novel biodegradable biomaterial for bone repair with both highly osteoconductive and osteoinductive properties. RhBMP-2 loaded PLGA microspheres were incorporated into rhBMP-2/CPC for macropores for bone ingrowth. The compressive strength, crystallinity, microscopic structure, and bioactivity of the composites were investigated. The results showed that with the incorporation of rhBMP-2 loaded PLGA microspheres, the compressive strength was decreased from (29.48+/-6.42) MPa to (8.26+/-3.58) MPa. X-ray diffraction revealed that the crystallinity pattern of HA formed by CPC had no significant change. Inside the composite, the microspheres distributed homogeneously and contacted intimately with the HA matrix, as observed by scanning electron microscopy (SEM). When the PLGA microspheres dissolved after having been emerged in PBS for 56 days, macropores were created within the CPC. The rhBMP-2/PLGA/CPC composite, showing a 4.9% initial release of rhBMP-2 in 24 h, followed by a prolonged release for 28 days, should have a greater amount of rhBMP-2 released compared to the CPC delivery system. When rabbit marrow stromal cells were cocultured with the composite, the alkaline phosphatase (ALP) and osteocalcin (OC) showed a dose response to the rhBMP-2 released from the composite, indicating that the activity of rhBMP-2 was retained. This study shows that the new composite reveals more rhBMP-2 release and osteogenic activity. This novel BMP/PLGA/CPC composite could be a promising synthetic bone graft in craniofacial and orthopedic repairs.

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