Small molecule stimulation enhances bone regeneration but not titanium implant osseointegration

Abstract The osteogenic and osseointegrative potential of a small molecule was examined to assess its usefulness in regenerative procedures. Purmorphamine was used to stimulate bone growth and repair in an in vitro cell based assay and an in vivo chick embryo CAM-assay with and without the presence of an implant. Purmorphamine adhered to precipitated hydroxyapatite coating, could activate the sonic hedgehog pathway and thereby stimulated osteodifferentiation. Porous calcium phosphate beads were used to deliver this small molecule in vivo and showed that purmorphamine increased the trabecular bone-to-bone area significantly. The assay showed Purmorphamine failed to induce any significant difference in osseointegration on titanium coated PTFE implants. This suggests that, whilst a small molecule can enhance osteogenesis and might be useful in regenerative procedures, it failed to enhance the osseointegration of a Ti coated implant, suggesting that this sort of stimulation might be useful for enhancing bone regeneration where bone loss due to disease exists, but not for enhancing early stability of an implant

Silk and spider silk in tissue engineering

Silk is rediscovered the past decade as a possible biomaterial. As a strong and flexible natural material that biodegrades slowly, which is promising for tissue engineering applications. Spider silk exceeds the mechanical properties of silkworm silk. In this research silkworm mechanical and biochemical test analyzed the differences between the different silk fibres. To establish the biomedical possibilities, the cytotoxicity of the fibres was tested by culturing cells attached to the fibres for several weeks. Next to the cytotoxicity, the biocompatibility is a necessity before a material can be used as an implant material. In vivo studies were performed by implanting steam sterilized spider silk fibres subcutaneous in white Whistar rats. The acute reaction showing lots of ganulocytes by histological examination could be diminished significantly by cleaning the fiber-surface with enzymes. Also the fibrotic formation around the implant was comparable to the widely accepted polyglactin material that was brought under the skin heterolateral to the silk fibres. Mechanical tests showed that trypsin could be used in contrast to proteinase K. Cocoon silk, spider dragline and egg sac silk were used as fibres and as proteinic polymers to create porous 3D scaffolds for cartilage regeneration. Human chondrocytes were seeded on it and cultured for several weeks to establish the scaffolds are not cytotoxic and cells can migrate, attach, grow and express their ECM in the pores of the spider silk matrix. Immunohistochemistry showed that the seeded chondrocytes expressed collagen II an aggrecan up to 6 weeks, which are typical for cartilage extracellular matrix. In a lesser extent there was also collagen I, showing some cells dedifferentiated in the material. Creating scaffolds with different pore-sizes and porosity, it was described that this influenced the mechanical properties of the construct. Bigger pore-sizes have a better interconnectivity, which improves the migration of the cells after seeding, but smaller pores give the cells a better surrounding, which chondrocytes need to maintain their differentiation and to express their extracellular matrix. Adding the mechanical stimulation and growth factors these scaffolds can be used for cartilage regeneration. Silk scaffolds could be reinforced with silk yarns to use them for tendon or ligament regeneration and as the shape can be adjusted other applications as meniscus regeneration also belong to the possibilities