To effectively harness the great potential of stem cells, I designed a dual growth factor (GF) delivery system for the application toward stem cell differentiation into specific lineages. This system carries a core-shell (C-S) structure within microcapsule (MC)s made of poly (L-lactide-co-glycolide) (PLGA) and alginate, which were fabricated using a coaxial electro-dropping method. Both PLGA and alginate were supplied from the inner and outer nozzle, respectively. The size and shape of MCs were greatly varying depending on the variables: nozzle size, applied voltage, volumetric feeding ratio (PLGA: alginate), feeding rate, and polymer concentrations. Once proper conditions were met, single or multi PLGA cores were found settled within the MCs. From the microscopic images, wrinkled surfaces of MCs were observed, along with the PLGA cores inside the alginate domain. When two different MCs were made, switching the position of bone morphogenetic protein (BMP)-2 and dexamethasone (Dex) for either core or shell domain, their release profiles were very unique on a temporal basis, based on their location in the MCs. An initial burst of biomolecules was highly suppressed when either biomolecule was loaded in the PLGA core. It was clear that the osteogenic biomolecules encapsulated in the MC could be released together and their concentrations were disparate at each time point. Meanwhile as the hydrogel constructs including rat bone marrow stromal cells (BMSCs) and osteogenic factors-loaded MCs were cultured for up to 4 weeks, the gene expressions levels of osteopontin, type I collagen, and osteocalcin were significantly upregulated as compared to the control group. The present coaxial system was very effective in manufacturing PLGA core- alginate shell MCs and in encapsulating multiple biomolecules essential for stem cell differentiation
An optimized electro-dropping system produces homogeneous C-S MCs by using PLGA and alginate. Fluorescence imaging clearly shows the C-S domain in the MC. For release control, the use of high-molecular-weight PLGA (HMW 270 000) restrains the initial burst release of protein compared to that of low-MW PLGA (LMW 40 000). Layer-by-layer (LBL) assembly of chitosan and alginate on MCs is also useful in controlling the release profile of biomolecules. LBL (7-layer) treatment is effective in suppressing the initial burst release of protein compared to no LBL (0-layer). The difference of cumulative albumin release between HMW (7-layer LBL) and LMW (0-layer LBL) PLGA is determined to be more than 40% on day 5. When dual angiogenic growth factors (GFs), such as platelet-derived GF (PDGF) and vascular endothelial GF (VEGF), are encapsulated separately in the core and shell domains, respectively, the VEGF release rate is much greater than that of PDGF, and the difference of the cumulative release percentage between the two GFs is about 30% on day 7 with LMW core PLGA and more than 45% with HMW core PLGA. As for the angiogenic potential of MC GFs with human umbilical vein endothelial cells (HUVECs), the fluorescence signal of CD31 + suggests that the angiogenic sprout of ECs is more active in MC-mediated GF delivery than conventional GF delivery and this difference is significant, based on the number of capillary branches in the unit area. This study demonstrates that the fabrication of biocompatible C-S MCs is possible, and that the release control of biomolecules is adjustable. Furthermore, MC-mediated GFs remain in an active form and can upregulate the angiogenic activity of ECs.