AbstractsBiology & Animal Science

A biomimetic approach to active microencapsulation of proteins based on the self-healing capacity of poly (DL)-lactic-co-glycolic acid (PLGA) microspheres containing glycosaminoglycan like biopolymers (BPs) was developed. To screen BPs, aqueous solutions of BP [high molecular weight dextran sulfate (HDS), low molecular weight dextran sulfate (LDS), chondroitin sulfate (CS), heparin (HP), hyaluronic acid (HA), chitosan (CH)] and a model protein, lysozyme (LYZ), were combined in different ratios. LDS and HP had excellent binding to LYZ over a wide range of BP-LYZ ratios, whereas HDS and CS had only specific optimal binding ratios. BP-PLGA microspheres (20???63 ??m) were prepared by a double water???oil???water emulsion method with a range of BP content, trehalose, and MgCO3 to control microclimate pH and to create percolating pores for protein. Biomimetic active self-encapsulation (ASE) of proteins [LYZ, vascular endothelial growth factor165 (VEGF) and fibroblast growth factor (FgF-20)] was accomplished by incubating blank BP-PLGA microspheres in low concentration protein solutions at ~ 24 ??C, for 48 h. Pore closure was induced at 42.5 ??C under mild agitation for 42 h. Formulation parameters of BP-PLGA microspheres and loading conditions were optimized for protein loading. HA-PLGA microspheres were found to be not ideal for obtaining high protein loading. In contrast, sulfated BP-PLGA microspheres were capable of loading LYZ (~ 2???7% w/w), VEGF (~ 4% w/w), and FgF-20 (~ 2% w/w) with high efficiency. Protein loading was found to be dependent on the loading solution concentration and BP content, with higher protein loading obtained at higher loading solution concentration. Upon analyzing in vitro release, the rate and extent of release were found to depend upon volume of release, ionic strength of release media and loading solution concentration. HDS-PLGA formulations were identified as having ideal loading and release characteristics. These optimal microspheres released ~ 73???80% of highly active LYZ over 60 days and nearly 72% of heparin-binding immunoreactive VEGF over 42 days, in the release medium. Protein-BP interactions were studied using a range of calorimetric and spectroscopic techniques. The interactions were found to be enthalpically driven and BPs were identified for their ability to stabilize proteins.