The objective of our paper was to determine the effects of composite formulation on the compressive modulus and ultimate strength of a biodegradable, in situ polymerizable poly(propylene fumarate) (PPF) and bone fiber scaffold. The following parameters were investigated: the incorporation of bone fibers (either mineralized or demineralized), PPF molecular weight, N-vinyl pyrrolidinone (NVP) crosslinker amount, benzoyl peroxide (BP) initiator amount, and sodium chloride porogen amount. Eight formulations were chosen based on a resolution III two-level fractional factorial design. The compressive modulus and ultimate strength of these formulations were measured on a materials testing machine. Absolute values for compressive modulus varied from 21.3 to 271？MPa and 2.8 to 358？MPa for dry and wet samples, respectively. The ultimate strength of the crosslinked composites varied from 2.1 to 20.3？MPa for dry samples and from 0.4 to 16.6？MPa for wet samples. Main effects of each parameter on the measured property were calculated. The incorporation of mineralized bone fibers and an increase in PPF molecular weight resulted in higher compressive modulus and ultimate strength. Both mechanical properties also increased as the amount of benzoyl peroxide increased or the NVP amount decreased in the formulation. Sodium chloride had a dominating effect on the increase of mechanical properties in dry samples but showed little effects in wet samples. Demineralization of bone fibers led to a decrease in the compressive modulus and ultimate strength. Our results suggest that bone fibers are appropriate as structural enforcement components in PPF scaffolds. The desired orthopaedic PPF scaffold might be obtained by changing a variety of composite formulation parameters. 1. Introduction There has been a great need for the treatment of skeletal defects which may result from tumors, trauma, or abnormal development [1]. The current methods for restoring tissue structure and function rely mostly on autograft and allograft [2–4]. Both methods, while appropriate for management of many bone defects, do have certain limitations. These include donor site morbidity after autograft harvesting and slow incorporation of cortical allograft. The other materials commonly used such as polymers, ceramics, and metals all have their associated drawbacks, such as poor integration with the host tissue, stress shielding of adjacent bone, and osteolysis from particulate wear debris [5]. The treatment regimen could be improved with the availability of a skeletal regeneration biomaterial that could be
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