Key Engineering Materials Vols. 334-335

Abstract: Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was used to fabricate micro- and nano-fibrous, non-woven mats by electrospinning for potential tissue engineering applications. The morphology and size of electrospun fibers were assessed systematically by varying the processing parameters. It was found that the diameter of the fibers produced generally increased with electrospinning voltage, needle diameter for the polymer jet and polymer solution concentration. Beaded fibers were readily produced at low PHBV concentrations, whereas the needle was blocked within a very short time during electrospinning when the PHBV concentration was too high. At the polymer concentration of 7.5 % w/v, it was shown that beadless PHBV fibers could be generated continuously by adjusting the electrospinning parameters to appropriate values. This study has clearly demonstrated that electrospinning can be an effective technique to produce PHBV micro- and nano-fibers. It has also been shown that composite fibers containing hydroxyapatite (HA) can be produced using the electrospinning technique.

Abstract: This paper describes a novel method for coating hydroxyapatite (HA, Ca10(PO4)6(OH)2) nano-particles onto poly(DL-lactic-co-glycolic acid) (PLGA) scaffold. Paraffin micro-spheres were used as porogens to create porous scaffolds and as vehicles to transfer HA into PLGA scaffold. HA nano-particles / 50% ethanol suspension was mixed with paraffin micro-spheres. The paraffin micro-spheres / HA suspension were pressed together to form a paraffin scaffold. After it was dried, the HA was coated on the surface of the paraffin spheres. Then, PLGA solution was cast into the inter space among the paraffin micro-spheres and then the solvent was evaporated. Afterwards, the paraffin micro-spheres were dissolved and removed. PLGA scaffolds with controlled pore size, good interconnectivity and high porosity were obtained. The HA nano-particles were transferred from the paraffin surface to the surface of the pore wall throughout the PLGA scaffold.

Abstract: Processing of polymers plays an important role in application of polymers in biomedical engineering, for instance in manufacture of scaffolds for tissue engineering applications. Rapid prototyping technologies like fused deposition modeling (FDM) has been widely used in processing polymers for biomedical applications. The present work is focused on modeling of flow behavior in the extrusion liquefier in FDM. A finite element (FE) model of extrusion liquefier was constructed on ANSYS after verification of internal geometry using X-ray imaging. Polycaprolactone (PCL) is used as the base bio polymer for analysis. Experiments were carried out to characterize the physical properties like thermal conductivity, specific heat, viscosity and shear thinning property of PCL. These values were used for behavior modeling in the extrusion liquefier. The thermal and flow behavior in the extrusion liquefier is studied by varying input conditions and analyzing the velocity, pressure drop profiles at various zones of extrusion liquefier. Experimental values of parameters and the simulated flow model showed good correlation. The current model can be extended to predict the flow behavior of PCL/ Hydroxyapatite composites in a FDM head which in turn will reflect on the quality of scaffold constructed using the Biocomposite.

Abstract: Electrohydrodynamic (EHD) dispersion of macromolecular components in a biological bearing consisting of a poorly conducting synovial fluid both in the cavity of the bones and in the bounding porous cartilage of finite thickness is investigated using Taylor’s [4] dispersion model . It is shown that artificial joints involving smart materials of nanostructure discussed here work more efficiently than the natural joints.

Abstract: A bioactive composite coating consisting of one layer of titania and one layer of apatite was formed on Ti substrate. The first layer of crystalline titania was deposited on Ti at low temperatures either through oxidation of Ti by hydrogen peroxide solution or through hydrolysis of TiF4 or TiCl4 solution. It was shown that the crystalline titania, either in the form of anatase or rutile, induced formation of the second layer of apatite in a simulated body fluid. However, the trace elements in the titania layer affected greatly apatite formation. The Cl incorporated in the titania layer did not hinder apatite formation while F did. The two-layer composite coating should enhance bonding of Ti implants to bone tissue.

Abstract: A nano-micro structured protein/octacalcium phosphate composite coating was prepared by electrochemically-induced deposition (ED) onto titanium surface. The characterizations of XRD, SEM and FT-IR indicate that the as prepared composite coating consists of protein and octacalcium phosphate with a highly and hierarchically porous structure in nano-micro scale, similaring to the natural bone structure.

Abstract: A femoral Prosthesis Stem made from composite material is investigating to apply to real body. The purpose of this study is to propose a design method of novel composite stem. Finite element models of stem and femur have been developed by using CT images. Some design parameters of the stem have been described and the effect of mechanical properties on the femur has been also described and compared with a traditional metal stem. The evaluation procedure for the stem has been proposed and been applied to a composite stem. It is revealed that the stem made of composite is more effective than the traditional stem made of metal.

Abstract: Natural bone is a typical example of an “organic matrix-mediated” biomineralization process which constituted of hydroxyapatite(HA) nanocrystals orderly grown in intimate contact with collagen fibers. Bone morphogenetic protein 2 (BMP2) is the most powerful osteogenic factor. But it is extremely difficult to be manufactured in large scale. In previous study, we have designed a novel oligopeptide (P24) derived from BMP2 knuckle epitope and it contained abundant Asp(aspartic acid) and phosphorylated Ser(serine) which may be helpful for self-assambly biomineralization and osteogenesis. Previous In vivo experiments have shown that this novel oligopeptide had excellent osteoinductive and ectopic bone formation property which was similar to that of BMP2. In this study, PLGA-(PEG-ASP)n scaffolds were modified with P24 and a new biomimetic bone tissue engineering scaffold material with enhanced bioactivity was synthesized by a biologically inspired mineralization approach. Peptide P24 was introduced into PLGA-(PEG-ASP)n scaffolds using cross-linkers. Then the P24 modified scaffolds and the simple PLGA-(PEG-ASP)n scaffolds were incubated in modified simulated body fluid (mSBF) for 10 days. Growth of HA nanocrystals on the materials was confirmed by observation SEM and measurements EDS and XRD. SEM analysis demonstrated the well growth of bonelike HA nanocrystals on P24 modified PLGA-(PEG-ASP)n scaffolds than that of the control scaffolds. The main component of mineral of the P24 modified scaffolds was hydroxyapatite containing low crystalline nanocrystals, and the Ca/P ratio was nearly 1.60, similar to that of natural bone, while that of the control scaffolds was 1.52. The introduction of peptide P24 into PLGA- (PEG- ASP)n copolymer provides abundant active sites to mediate the nucleation and self- ssembling of HA nanocrystals in mSBF. the resulted peptide P24 modified- HA/PLGA- (PEG- ASP)n composite shows some features of natural bone both in main composition and and hierarchical microstructure. This biomimetic treatment provides a simple method for surface functionalization and subsequent biomineralization on biodegradable polymer scaffolds for tissue engineering.