Investigation On Biodegradable Polymeric Microspheres Loaded Protein

Inherent protein instability problems, such as unfolding, covalent/non-covalent aggregation and non-specific adsorption, occurred during application. Polymer microspheres were used to encapsulate protein to preserve their activity. This research focused on changing the matrix and morphology of microspheres to improve the bioavailability of protein.Firstly, the matrix of microspheres was investigated in this work. Poly(l,3-bis-(p-carboxyphenoxy propane)-co-(sebacic anhydride) (P(CPP-SA)) which degradated in surface erosion, was chosen as the microspheres matrix. The P(CPP-SA) microspheres were fabricated by double emulsion method based on solvent evaporation. Human serum albumin (HSA) was used as the model protein. This paper aimed at researching the erosion and degradation of P(CPP-SA) microspheres with CPP/SA monomer ratios of 20:80, 35:65 and 50:50. Scanning electron microscopy (SEM) was carried out to examine surface, size and size distribution. P(CPP-SA) microspheres exhibited spherical structure and rough surface morphology with the mean size 10μm. Next, in vitro protein release from the microspheres was also investigated in this work. The degradation and the protein release in vitro were performed in PBS (pH 7.4). As the results shown, P(CPP-SA) degradation and HSA release in vitro were related to monomer ratio of CPP/SA. 20:80P(CPP-SA) was more hydrophilic than 35:65 P(CPP-SA) and 50:50 P(CPP-SA). Thereby, degradation rate of 20:80 P(CPP-SA) was the fastest. Moreover, the microspheres degradation and drug release rate from microspheres can be adjusted by altering the CPP/SA ratios of P(CPP-SA). The features of surface-erosion were observed in SEM. To sum up, polyanhydride copolymers are desirable biodegradable polymer for biomedical applications as protein carriers.Secondly, a new approach for protein delivery is introduced, involving biodegradable porous poly(D,L-lactic-co-glycolic acid) (PLGA) microspheres blocked with calcium alginate hydrogel. Porous microspheres were prepared by solvent evaporation method using sodium oleate as an extractable porogen. The resultant microspheres show porous surface and 3-dimension network structure with interconnecting pores. Human serum albumin (HSA) used as model protein, was adsorbed into micropores of porous microspheres by a solution immersing method. Thus, the harsh preparation conditions, such as the aqueous/organic interface produced by a water-in-oil microemulsion and the acute shearing strength brought by a high-speed homogenizer or a sonicater, inducing protein denaturation and aggregation could be avoided. Then, calcium alginate hydrogel was fabricated to block micropores of protein-loaded porous microspheres. A sustained protein release in vitro could be achieved in this way. Furthermore, it is noteworthy that the protein maintained its structural integrity after this preparation. The porous polymeric microspheres may have great potential application for water-soluble drugs, such as protein, vaccine and gene delivery.