To quantitatively evaluate the correlations between the amount of initial burst release and the surface-associated protein, and between the onset time for the second burst release and the matrix polymer degradation. Methods. Human serum albumin (HSA) was microencapsulated in polylactide (PLA) and poly-dl-lactide-poly(ethylene glycol) (PELA) with PEG contents of 5, 10, 20, and 30%, respectively, using the solvent extraction procedure based on formation of double emulsion w/o/w. Microspheres with similar particle size (1.7-2.0mm), similar protein entrapment (2.1-2.8%) but different surface-associated proteins (9.3-53.6%) were used to evaluate the in vitro matrix degradation and protein release profiles. Degradation was characterized by studying the intrinsic viscosity decrease, medium pH change, and weight loss of the microspheres. Results. The matrix degradation and protein release profiles were highly dependent on the polymer composition of the microspheres. Faster decreases in the intrinsic viscosity of recovered matrix polymer, the microspheres weight, and the pH of degradation medium, and earlier onsets for the break in intrinsic viscosity reduction and the mass loss were detected for PELA microspheres with higher PEG content. The hydration and swelling of microspheres matrix contributed greatly to the degradation of matrix polymer. The HSA release showed triphasic profile and involved two mechanisms for all the microsphere samples. Smaller amount of initial burst release, larger gradual release rate, and earlier onset for the second burst release were observed for HSA from matrix polymer with higher PEG content. The extent of the initial burst release was quantitatively related with the surface-associated protein. The second burst release of HSA was observed to occur within 1 week after the onset for mass loss, which was also the break in the intrinsic viscosity reduction rate. Conclusion. Protein release profiles could be rationalized by optimizing the matrix polymer degradation and microsphere characteristics.

Poly(D,L-lactide) (PDLLA) and Hydroxyapatite (HA) are compounded, which possess biodegradation, biocompatibility and shape memory properties. In the paper, we prepared serial imposing shape memory composites with different shapes, composite ratios and sample thicknesses. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were carried out to examine surface morphology, glass transition temperature (Tg), dynamic mechanical properties, and shape memory effect of PDLLA/HA composites, respectively. Moreover, some interesting shape memory behaviors were investigated. The results show that the better disperse morphology of HA grains using the experiment methods, and PDLLA/HA composites at a definite range of compound ratio have much better shape memory effect than pure PDLLA polymer. It indicates that HA particles can improve shape memory effect and PDLLA/HA composites are potential for biomedical applications.

In this study, a newapproach for protein delivery is introduced, involving biodegradable porous poly(d,llactic-co-glycolic acid) (PLGA) microspheres blockedwith calcium alginatehydrogel. Porous microsphereswere prepared by solvent evaporation method using sodium oleate as an extractable porogen. The resultantmicrospheres show porous surface and three-dimensional network structure with interconnectingpores. Human serum albumin (HSA) used as model protein, was adsorbed into micropores of porousmicrospheres by a solution immersing method. Thus, the harsh preparation conditions, such as the aqueous/organic interface produced by awater-in-oil microemulsion and the acute shearing strength broughtby a high-speed homogenizer or a sonicater, inducing protein denaturation and aggregation could beavoided. Then, calcium alginate hydrogel was fabricated to block micropores of protein-loaded porousmicrospheres. A sustained protein release in vitro could be achieved in this way. Furthermore, it is noteworthythat the protein maintained its structural integrity after this preparation. The porous polymericmicrospheres may have great potential application for water-soluble drugs, such as protein, vaccine andgene delivery.

Poly(e-caprolactone)-poly(ethylene glycol) (PECL)copolymers were synthesized from polyethylene glycol (PEG) and ecaprolactone(e-CL) using stannous octoate as catalyst at 160℃ by bulk polymerization. The effect of the molecular weight of PEG and the copolymer ratio on the properties of the copolymers was investigated by 1H-NMR, IR, DSC and GPC. PCL and PECL microspheres containing human serum albumin were elaborated by solvent extraction method based on the formation of double w/o/w emulsion. Microspheres were characterized in terms of morphology, size, loading efficiency, and the efficiency of microspheres formation. The results show that the microspheres prepared from PECL-10 and PECL-15 copolymers achieved the highest loading efficiency (about 50%) among all copolymers. These results indicate that the properties of copolymers could be tailored by adjusting polymer composition. It is suggested that these matrix polymers may be optimized as carriers in the protein (antigen) delivery system for different purposes

Adjuvants aimed at increasing the immunogenicity of recombinant antigens remain a focus in vaccine development. Worldwide, there is currently considerable care for the development of biodegradable microspheres as controlled release ofvaccines, since the major disadvantage of several currently available vaccines is the need for repeated administration.Microspheres prepared from the biodegradable and biocompatible polymers, the polylactide (PLA) or polylactide-coglycolide(PLGA), have been shown to be effective adjuvants for a number of antigens. This review mainly focuses onpolylactide-co-poly(ethylene glycol) (PELA) microspheres adjuvant as vaccine delivery systems by summarizing our andother research groups' investigation on properties of the microspheres formulation encapsulating several kinds of antigens.The results indicate that compared with the commonly used PLA and PLGA, PELA showed several potentials in vaccinedelivery systems, which may be due to the block copolymer have its capability to provide a biomaterial having a broad rangeof amphiphilic structure. PELA microspheres can control the rate of release of entrapped antigens and therefore, offerpotential for the development of single-dose vaccines. The PELA microspheres have shown great potential as a nextgeneration adjuvant to replace or complement existing aluminum salts for vaccine potential. The review mainly aims topromote the investigation of PELA microspheres adjuvant for antigens for worldwide researcher.