Reconstruction of Anorganic Mammalian Bone by Surface-Initiated Polymerization of L-Lactide Troy Wiegand, † Jeremy Karr, ‡ Jay D. Steinkruger, § Kris Hiebner, † Bobby Simetich, | Mark Beatty, | and Jody Redepenning* ,† Department of Chemistry, UniVersity of Nebraska, Lincoln, Nebraska 68588 and College of Dentistry, UniVersity of Nebraska Medical Center, Lincoln, Nebraska 68583 ReceiVed March 28, 2008. ReVised Manuscript ReceiVed May 24, 2008 Polymerization of L-lactide within the pores of anorganic mammalian bone is described. No additional solvent or catalyst is used. The resulting composites exhibit macroscopic morphologies and mechanical properties similar to that of the original bone. We observe an average compressive strength of 194 MPa and an elastic modulus of 8.8 GPa for composites comprised of poly-L-lactide and anorganic bone derived from bovine femurs. Modeling of the reaction kinetics with synthetic sources of crystalline hydroxyapatite powder suggests that polymerization proceeds via a surface-initiated mechanism that is first order in surface area of hydroxyapatite and first order in mole fraction of L-lactide. Introduction Challenges to materials science and medicine regarding hard tissue replacement have existed for at least 3000 years. Archeological records from the early Bronze Age demon- strate that attempts were made, probably unsuccessfully, to repair trephinated human skulls with autografts. 1 By 600 A.D. the Mayan civilization used seashell nacre with some success for dental implants. 2 Shortly after Hulagu Khan led the 1258 A.D. Mongol invasion of Baghdad, Zakaria al-Qazwini, an Arab scientist and cosmographer, documented problematic tissue rejection associated with transplantation of interspecies mammalian bone tissue into humans. He also noted the superior performance of porcine bone as a viable source of bone tissue when a human source was not available. 3 In present day Iraq, the medical response to traumatized bone remains an important issue. Soldiers in ongoing armed conflicts are experiencing high rates of orthopedic trauma, such as segmental bone defects, caused by improvised explosive devices (IEDs). 4 The need for improved orthopedic biomaterials is no less relevant to the civilian population. As baby boomers approach retirement age, there is an increasing need to repair and restore their damaged bones and tissues. As individuals age, their mus- culoskeletal support structures lose resilience in response to trauma. Additionally, inherited disorders and disease can cause life-changing or life-threatening damage to the skeletal system. Significant challenges confront materials scientists and physicians interested in viable sources of materials for tissue repair and replacement. 5,6 Tissues for allografts, where the donor and recipient are the same species, are frequently in short supply. For some applications, xenogeneic tissues are a viable alternative to human sources of materials; however, immunological barriers prevent routine transplantation of tissue from one species to another. 7 The use of tissues from species genetically similar to humans is desirable to lessen the severity of rejection. Unfortunately, tissues from these species pose a threat because of the higher likelihood of pathogens or infectious disease being transmitted to the recipient. 8 The use of xenogeneic materials for restorative surgery can also present ethical and religious complexities that can be imposing. 3,9 Research into bioceramic composites is playing an increasingly important role in the repair, reconstruction, and replacement of hard tissues. The use of synthetic materials for tissue repair or replacement is generally unencumbered by the ethical and religious concerns associated with the use of xenogeneic materials. Although synthetic materials lessen the threat of certain forms of rejection, challenges to the development of biomaterials that exhibit desirable chemical, physical, and mechanical proper- ties remain daunting. The morphologies of the desired materials are often quite complex, and even if the desired structures can be constructed, the biological and biomechani- cal viability is not certain a priori. * To whom correspondence should be addressed. E-mail: jredepen@unl.edu. † University of Nebraska, Lincoln. ‡ Present address: Department of Chemistry, Newman University, Wichita, KS 67213. § Present address: Department of Chemistry, University of Wisconsin, Madison, WI 53706. | University of Nebraska Medical Center. (1) (a) Guthrie, D. A History of Medicine; J. B. Lippincott: Philadelphia, 1949; pp 7-9. (b) Westbroek, P.; Marin, F. Nature 1998, 392, 861. (2) Bobbio, A. Bull. Hist. Dent. 1972, 20, 1. (3) Albar, M. A. The Fountain 1995, 12–34. (4) Owens, B. D.; Kragh, J. F.; Macaitis, J.; Svoboda, S. J.; Wenke, J. C. J. Orthop. Trauma 2007, 21, 254. (5) Ratner, B. D. Biomaterials Science: An Introduction to Materials in Medicine; Elsevier: Boston, 2004. (6) Stock, U. A.; Vacanti, J. P. Ann. ReV. Med. 2001, 52, 443. (7) Townsend, C. M.; Beauchamp, R. D.; Evers, B. M.; Mattox, K. L. Section IV. Transplantation and Immunology. In Sabiston Textbook of Surgery, 17th ed.; Saunders: Philadelphia, 2004. (8) Bach, F. H. Annu. ReV. Med. 1998, 49, 301. (9) Albar, M. A. Saudi J. Kidney Dis. Transplant 1996, 7, 109. 5016 Chem. Mater. 2008, 20, 5016–5022 10.1021/cm800895r CCC: $40.75  2008 American Chemical Society Published on Web 07/09/2008