Study On PHBV Blends Scaffold For Tissue Engineering

Tissue engineering scaffolds take the most basic constituent in tissue engineering. As the front discipline and the interdisciplinary studies, tissue engineering will change the traditional ideas for the transplanting of the tissues and organs and show people the new domain of being reconstructed and regenerated.The nature of the material for scaffold and its physical and chemical properties are critical to creating the desired conditions for tissue formation. A host of different materials have been used in tissue engineering. As the most widely used members in polyhydroxy-alkanoates(PHAs) which are of natural origin, polyhydroxybutyrate-co-hydroxyvalerate(PHBV) is biodegradable, biocompatible and non-toxic. Its degradation rate could be adjusted by variation of HV. Plus it has less crystalline and melting temperature and is more flexible and more readily processable than Poly(3-hydroxybutyrate) (PHB) itself.In this study, PHBV/ECOFLEX was used to prepare porous scaffolds. ECOFLEX is a new biodegradable polymer produced by BASF Corporation, which is often used to be blended with other biodegradable polymers to improve their process abilities. Its monomers are composed by terephthalic acid, fatty acid and 1,4-butylene glycol. The chemical structure, thermal properties and crystallinity of the PHBV/Ecoflex were characterized by FT-IR DSC and POM, respectively. According to the IR spectra of the PHBV and PHBV/ECOFLEX, it proved that the PHBV/ECOFLEX blends include a plenty of ester groups. The results of DSC tests indicated the excellent compatibility between the two components. The crystallinity of PHBV was destroyed and receded with the add of ECOFLEX. POM photos further proved the crystallinity of PHBV was destroyed. Therefore, the percent water absorption increased and the hydrophilicity of PHBV was improved .However, the dilatability was very low which will contribute to the dimensional stability.With the approach of tissue engineering, the preparation of porous scaffolds plays an important role in manipulating cell functions. The structure and property of the scaffold depend on the preparation methods of the scaffolds, and then have a great influence on the division and proliferation of the cells. In this paper, PHBV/ECOFLEX composites as well as the chloroform were used to prepare polymer solution and the NaCl particulates were used as porogen. Based on the conventional technique, porous polymeric structures which its shape and pore size are controllable and has high porosity were obtained by adjusting the polymer solution concentrations. The influences of the polymer solution concentration and porogen sizes on the stability and porosity of the scaffold were studied .The pore size, morphology and distribution of the scaffold were measured according to Scanning Electron Microscopy (SEM).The results show that the solution concentration has a great influence on the stability of the scaffold. The structure stability was unstable if the concentration was too high or too low. The optimum concentration should be 12% to 15%.A complicated structure was obtained using a polymer solution of 15% concentration. It was observed that the scaffolds were highly porous with evenly distributed and interconnected pore structures. Their sizes could be controlled exactly by varying the porogen size. The porosity of the scaffold ranged from 86% to 91%.Furthermore, multi-casting method was used to prepare the scaffolds with more complicated shapes which had an interconnected pore structure and high porosity of above 80%.A novel method for the preparation of three dimensional porous scaffolds was also studied in this paper. Poly(3-hydroxybutyric acid-co-3- hydroxyvaleric acid) (PHBV) composites were used to prepare three dimensional scaffolds for tissue engineering after melt-spinning, molding and fiber bonding .Surface characteristics, pore sizes and their distribution and the bonding temperature of the scaffold were investigated by optical microscope (OM), scanning electron microscopy (SEM) and differential scanning calorimeter (DSC), respectively. The in vitro degrading activities were studied by immersing the scaffold into the SBF solution for ten weeks. Cell culturing was also conducted in the 3-D scaffolds prepared by fiber-bonding. The results show that the optimum bonding temperature should be from 130-140℃.The porosity decreased with the increase of the pressure. The scaffold had a satisfied stability and a highest porosity of 59.5% when the pressure was 5MPa.The OM photos of the scaffold show the pores distributed evenly in the scaffold surface. The SEM photos show the pore sizes range from 300-500μm .And the scaffold exhibited 3D, connected network macro structures. The degradation of the fiber will cause a tiny decline of the pH value and the weight of the matrix was almost unchanged for a period of 10 weeks. And a surface erode on the surface of the fibers was observed according to the SEM photos. The results of Cell culturing proved the 3D porous scaffolds prepared by fiber boding were suitable for the cell proliferation.