Segmental fixation of burst fractures with screws at the level of the fracture offers improved biomechanical stability. Theoretically, segmental fixation provides for additional fixation points that may aid in fracture reduction and kyphosis correction. This specific parameter is not evaluated in this study but will be an important outcome measure for a planned randomized controlled trial.

Syndecans are a family of four cell surface proteoglycans that bind to various components of the extracellular environment and can regulate many cellular behaviors including growth, adhesion, and movement. To determine whether syndecans can function during wound repair, we have examined expression of the syndecans during wound repair of adult mouse and neonatal or fetal human skin. Syndecan-1 and -4 were induced in the dermis within 12 h after incisional injury of murine or neonatal human skin. Syndecan-1 was induced primarily on endothelium, and syndecan-4 was present throughout the dermis at the site of injury. Following re-epithelialization, expression of the syndecans return to their baseline level. In marked contrast to these observations, wounded human fetal skin showed no increase in expression of syndecans. This lack of increase in the expression of syndecans by cells of the dermis correlates with prior observations that fetal skin heals without a polymorphonuclear cell infiltrate, appreciable fibrosis, or clinically apparent scar. Thus, induced expression of syndecans is not an absolute requirement for wound repair but does correlate with the occurrence of fibrosis in mature skin. These findings support the role of syndecans as regulators of cell behavior and suggest that syndecan-1 and -4 induction in the dermis may contribute to events that lead to inflammation and fibrosis.

The ideal biomaterial for the repair of bone defects is expected to have good mechanical properties, be fabricated easily into a desired shape, support cell attachment, allow controlled release of bioactive factors to induce bone formation, and biodegrade into nontoxic products to permit natural bone formation and remodeling. The synthetic polymer poly(propylene fumarate) (PPF) holds great promise as such a biomaterial. In previous work we developed poly(DL-lactic-co-glycolic acid) (PLGA) and PPF microspheres for the controlled delivery of bioactive molecules. This study presents an approach to incorporate these microspheres into an injectable, porous PPF scaffold. Model drug Texas red dextran (TRD) was encapsulated into biodegradable PLGA and PPF microspheres at 2 microg/mg microsphere. Five porous composite formulations were fabricated via a gas foaming technique by combining the injectable PPF paste with the PLGA or PPF microspheres at 100 or 250 mg microsphere per composite formulation, or a control aqueous TRD solution (200 microg per composite). All scaffolds had an interconnected pore network with an average porosity of 64.8 +/- 3.6%. The presence of microspheres in the composite scaffolds was confirmed by scanning electron microscopy and confocal microscopy. The composite scaffolds exhibited a sustained release of the model drug for at least 28 days and had minimal burst release during the initial phase of release, as compared to drug release from microspheres alone. The compressive moduli of the scaffolds were between 2.4 and 26.2 MPa after fabrication, and between 14.9 and 62.8 MPa after 28 days in PBS. The scaffolds containing PPF microspheres exhibited a significantly higher initial compressive modulus than those containing PLGA microspheres. Increasing the amount of microspheres in the composites was found to significantly decrease the initial compressive modulus. The novel injectable PPF-based microsphere/scaffold composites developed in this study are promising to serve as vehicles for controlled drug delivery for bone tissue engineering.

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