Controlled release from poly(lactic-co-glycolic acid) microspheres embedded in an injectable, biodegradable scaffold for bone tissue engineering

For the repair of bone defects, the ideal biomaterial has good mechanical properties, can be fabricated easily into a desired shape, supports cell attachment, contains factors to induce bone formation, and is biodegradable to permit natural bone formation and remodeling. The synthetic polymer poly(propylene fumarate) (PPF) satisfies these criteria. This study presents a new approach to fabricate porous PPF scaffolds with incorporated microspheres for the release of bioactive molecules. Using a double emulsion-solvent extraction technique, the model drug Texas red dextran was encapsulated into poly(lactic-co-glycolic acid) microspheres. Porous scaffolds were fabricated by injecting PPF in a low viscosity state with 100 or 250 mg microspheres into a Teflon coated mold using a disposable syringe with needle. A foaming technique was used to create porosity. The average porosity of the scaffolds was 65.5 (± 3.5) % and 62.8 (± 7.8) % for the 100 mg and 250 mg microsphere loading respectively. Scanning electron microscopy (SEM) and confocal microscopy showed interconnectivity of the pores and presence of microspheres within the scaffold. For all formulations, the compressive modulus values of the scaffold-microsphere composites were between 2.4-15.3 MPa initially and between 14.9-62.8 MPa after 28 days of degradation in phosphate buffered saline. Scaffold and microspheres exhibited a sustained release of the model drug for at least 28 days. Compared to microspheres alone, the scaffold-microsphere composite had a lower burst release during the initial phase of release. This study shows a promising system for delivery of bioactive molecules from an injectable, biodegradable scaffold-microsphere composite.