Bacteria microencapsulation in PLGA microdevices by supercritical emulsion extraction

Abstract

Cell microencapsulation continues to hold significant promise for biotechnology and medicine and is considered an important tool for tissue engineering. Encapsulated cells would also provide a source of sustained continuous release of therapeutic products for longer durations at the site of implantation. The present work investigates the possibility of prokaryotic cells microencapsulation by Supercritical Emulsion Extraction (SEE) technology; Lactobacillus acidophilus was selected as a model bacterium and poly-lactic-co-glycolic acid (PLGA, 75:25) was chosen as biopolymer because FDA approved in devices for biomedical applications.A double emulsion (w1-o-w2 ratio 2:18:80) was used with an internal water phase (w1) composition of L. acidophilus suspended in MRS broth plus the 0.4% of poly-vinyl alcohol (PVA), as surfactant; the best overall cell mass content was found to be not higher than 10mg/mL (that correspond to 7.5×106UFC/mL). Other emulsion phases were: o-phase containing ethyl acetate (EA) and PLGA at 10% (w/w) and w2-phase of water plus 0.6% of PVA (w/w). This emulsion treated by SEE at 90bar and 37°C for 30min allowed the formation of PLGA microcapsules with a mean size of 20μm (±10μm) loaded with the 0.6% (w/w) of microorganism with an excellent encapsulation efficiency (80%).Size and morphology of the produced microdevices were monitored by laser scattering and by SEM-EDX analyses and confirmed SEE as an innovative and efficient encapsulation technology. Particularly, the microspheres were constituted by a PLGA wall containing the cells entrapped into the polymeric matrix. Cell viability less than 5% (w/w) with respect to the loaded microorganism was also evaluated; nevertheless the biodegradable microdevice produced may be particularly interesting for several biotechnological application in which mainly the killed vectors is used as bioactive signal delivery.