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Understanding the degradation behavior of polymeric microspheres is crucial for the successful application of such devices in controlled drug delivery. The degradation mechanism of poly(lactic-co-glycolic acid) (PLGA) microspheres inside phagocytic cells is not known, but different models for degradation in aqueous solution have been proposed. We have used confocal Raman spectroscopy and imaging to study the intracellular degradation of PLGA microspheres inside individual macrophages. Our results show that ingested microspheres degrade in a heterogeneous manner, with a more rapid degradation in the center. Comparison of Raman spectra from degrading beads with those of uningested beads reveals that ester hydrolysis occurs throughout the phagocytosed microspheres, with a selective loss of glycolic acid units. Furthermore, we show that PLGA degradation is a cell-mediated process, possibly caused by the low pH of the phagosome and/or the presence of hydrolytic enzymes. In conclusion, we have demonstrated that the chemical composition of degrading polymers inside cells can be probed by Raman spectral imaging. This technique will expand the capabilities of investigating biomaterial degradation in vivo.

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The aim of this study was to evaluate two biodegradable polymeric systems as scaffolds for bone tissue engineering. Rat bone marrow cells were seeded and cultured for 1 week on two biodegradable porous polymeric systems, one composed of poly(ethylene glycol)-terephthalate/poly(butylene terephthalate) (PEGT/PBT) and the other composed of cornstarch blended with poly(epsilon-caprolactone) (SPCL). Porous hydroxyapatite granules were used as controls. The ability of cells to proliferate and form extracellular matrix on these scaffolds was assessed by a DNA quantification assay and by scanning electron microscopy examination; their osteogenic differentiation was screened by the expression of alkaline phosphatase. In addition, the in vivo osteogenic potential of the engineered constructs was evaluated through ectopic implantation in a nude mouse model. Results revealed that cells were able to proliferate, differentiate, and form extracellular matrix on all materials tested. Moreover, all constructs induced abundant formation of bone and bone marrow after 4 weeks of implantation. The extent of osteogenesis (approximately 30% of void volume) was similar in all types of implants. However, the amount of bone marrow and the degree of bone contact were higher on HA scaffolds, indicating that the polymers still need to be modulated for higher osteoconductive capacity. Nevertheless, the findings suggest that both PEGT/PBT and SPCL systems are excellent candidates to be used as scaffolds for a cell therapy approach in the treatment of bone defects.