Effect of Polymer Porosity on Aqueous Self‐Healing Encapsulation of Proteins in PLGA Microspheres

Abstract

Self-healing (SH) poly(lactic-co-glycolic acid) (PLGA) microspheres are a unique class of functional biomaterials capable of microencapsulating process-sensitive proteins by simple mixing and heating the drug-free polymer in aqueous protein solution. Drug-free SH microspheres of PLGA 50/50 with percolating pore networks of varying porosity (ε = 0.49–73) encapsulate increasing lysozyme (~1–10% w/w) with increasing ε, with typically ~20–25% pores estimated assessible to entry by the enzyme from the external solution. Release kinetics of lysozyme under physiological conditions is continuous over > 2 weeks and most strongly influenced by ε and protein loading before reaching a lag phase until 28 days at the study completion. Recovered enzyme after release is typically predominantly monomeric and active. Formulations containing acid-neutralizing MgCO3 at >4.3% exhibit >97% monomeric and active protein after the release with full mass balance recovery. Hence, control of SH polymer ε is a key parameter to development of this new class of biomaterials.

Injectable controlled release depots for large molecules

“…Common protein assays and bioassays also can have interference with components of the release media. The total polypeptide loading in PLGA can be determined definitively by amino acid analysis after acid hydrolysis [45–47]. Knowing this value irrespective of the drug's stability is always important when beginning formulation work.…”

A biomimetic approach to active self-microencapsulation of proteins in PLGA

“…This work builds upon the previous work done by our group [16, 17], by expanding our self-encapsulation paradigm for therapeutic proteins at low protein concentrations making it possible to quickly develop and evaluate controlled release formulations. Recently, 4–10 % w/w LYZ loading was reported via passive self-encapsulation using 250 mg/ml LYZ [45], but the prohibitive cost of this approach is not very feasible for encapsulation of recombinant therapeutic proteins. In contrast, ASE of pharmaceutical proteins using the approach described here could be brought about by simply mixing microsphere formulations with low concentration protein solutions (<10 mg/ml), to reduce losses of expensive recombinant proteins during formulation.…”

Critical attributes of formulation and of elaboration process of PLGA-protein microparticles

“…Poly(D,L-lactic-co-glycolic) acid (PLGA) has been widely studied to develop controlled release systems for proteins and vaccines, and water-in oil-in water (W/O/W) solvent evaporation technique has been commonly used to entrap protein into PLGA microparticles (Bodmeier et al, 1992;Mundargi et al, 2008;Reinhold and Schwendeman, 2013;Sophocleous et al, 2013). In this process, the drug is dissolved in an inner aqueous phase, which is emulsified in the organic phase containing the polymer dissolved in an organic solvent, usually dichloromethane (DCM).…”