Orthopedic care for lower extremity fracture management includes realigning (reduction) and stabilizing (fixation) the fracture. Traditional care includes metallic rods inserted into the medullary canal of bone, external metallic pins and rods, casting the limb with plaster or polymer-based materials. These options provide a satisfactory level of clinical outcome for civilian applications. The battlefield environment introduces an elevated level of fracture management concern and challenge. There is the life-threatening, serious issue of fracture infection for the soldier as well as therapeutic ease-of-use for the treating surgeon. We are addressing elevated concerns and aim to improve orthopedic fracture management for the warfighter with bone/polymer composite fracture fixation devices that will facilitate fracture reduction and enhance biological healing and biomechanical function.  

Composites fabricated from bone and thermoplastic polymers have been shown to remodel in vivo.¹  However, the polymers must be heated above the glass transition or melting temperature (typically in the range of 100^oC) and compression-molded.  We are pursuing a reactive liquid molding approach wherein bone/poly(ester urethane) composites are mixed and compression-molded at ambient (e.g., 25^oC) temperature, thus rendering them useful for injectable applications as well.  Furthermore, by enhancing the reactivity of the surface of the bone particles, the interfacial binding, and therefore the mechanical properties, can be improved.  

We have synthesized bone/poly(ester urethane) (PEUR) composites from lysine diisocyanate (LDI), polycaprolactone (molecular weight 300) (PCL 300), and mineralized bone powder (100-500 microns) (MBP).  Polymers synthesized from LDI and polyester polyols have been reported to support cell attachment and biodegrade to non-cytotoxic degradation products.^2-4  We have synthesized composites incorporating 80 wt% MBP over a range of isocyanate index (index = 100 x NCO:OH equivalent ratio).  Samples were cast as 6 mm x 25 mm cylinders.  Mechanical properties were measured in compression mode, and dynamic mechanical properties were measured by dynamic mechanical analysis (DMA) in 3-point bending mode.  Composites with compression modulus up to 3.3 GPa and compression strengths up to 40 MPa have been prepared.  Preliminary results show that index has a large effect on mechanical properties, with a maximum in the modulus occurring at an index of 150.  The glass transition temperature, also obtained from DMA via temperature sweeps, was observed to be 62 ˚C.  FT-IR was performed to ensure that there was no residual free NCO remaining.  In vitro studies have shown that the MBP/PEUR composites support cell attachment.  These preliminary studies suggest that MBP/PEUR composites are promising biomaterials for bone tissue engineering.   

1.         Boyce TM, Winterbottom JM, Lee S, Kaes DR, Belaney RM, Shimp LA, Knaack D. Cellular Penetration And Bone Formation Depends Upon Allograft Bone Fraction In A Loadbearing Composite Implant. 2005. p 133.

2.         Guelcher SA, Patel V, Gallagher K, Connolly S, Didier JE, Doctor J, Hollinger JO. Synthesis and biocompatibility of polyurethane foam scaffolds from lysine diisocyanate and polyester polyols. Tissue Eng 2006;12(5):1247-1259.

3.         Guelcher SA, Gallagher KM, Srinivasan A, McBride SB, Didier JE, Doctor JS, Hollinger JO. Synthesis, in vitro biocompatibility and biodegradation, and mechanical properties of two-component polyurethane scaffolds: effects of water and polyol composition. Tissue Eng In Press.

4.         Guelcher SA, Didier JE, Srinivasan A, Hollinger JO. Synthesis, mechanical properties, biocompatibility, and biodegradation of cast poly(ester urethane)s from lysine-based polyisocyanates and polyester triols. Manuscript in preparation.