In Vitro Studies of Composite Bone Filler Based on Poly(Propylene Fumarate) and Biphasic a-Tricalcium Phosphate/Hydroxyapatite Ceramic Powder *†‡Chang-Chin Wu, §**Kai-Chiang Yang, ‡Shu-Hua Yang, *Min-Huei Lin, ††Tzong-Fu Kuo, and *Feng-Huei Lin *Institute of Biomedical Engineering, College of Engineering and College of Medicine, National Taiwan University; †Department of Orthopedics, En-Chu-Kong-Hospital; ‡Department of Orthopedics, National Taiwan University Hospital and National Taiwan University College of Medicine; §Institute of Biotechnology, National Taiwan University; **Research Center for Biomedical Devices,Taipei Medical University; and ††Department and Graduate Institute of Veterinary Medicine, School of Veterinary Medicine, National Taiwan University,Taipei,Taiwan Abstract: While many different filler materials have been applied in vertebral augmentation procedures, none is perfect in all biomechanical and biological characteristics. To minimize possible shortages, we synthesized a new bio- degradable, injectable, and premixed composite made from poly(propylene fumarate) (PPF) and biphasic a-tricalcium phosphate (a-TCP)/hydroxyapatite (HAP) ceramics powder and evaluated the material properties of the com- pound in vitro. We mixed the PPF cross-linked by N-vinyl pyrrolidinone and biphasic a-TCP/HAP powder in differ- ent ratios with benzoyl peroxide as an initiator. The setting time and temperature were recorded, although they could be manipulated by modulating the concentrations of hyd- roquinone and N,N-dimethyl-p-toluidine. Degradation, cytocompatibility, mechanical properties, and radiopacity were analyzed after the composites were cured by a cylin- drical shape. We also compared the study materials with poly(methyl methacrylate) (PMMA) and PPF with pure HAP particles. Results showed that lower temperature during curing process (38–44°C), sufficient initial mechani- cal compressive fracture strength (61.1  3.7 MPa), and gradual degradation were observed in the newly developed bone filler. Radiopacity in Hounsfield units was similar to PMMA as determined by computed tomography scan. Both pH value variation and cytotoxicity were within bio- logical tolerable limits based on the biocompatibility tests. Mixtures with 70% a-TCP/HAP powder were superior to other groups.This study indicated that a composite of PPF and biphasic a-TCP/HAP powder is a promising, pre- mixed, injectable biodegradable filler and that a mixture containing 70% a-TCP/HAP exhibits the best properties. Key Words: Osteoporosis—Vertebral fracture—Verte- broplasty—Poly(methyl methacrylate)—Poly(propylene fumarate)—Hydroxyapatite. As the proportion and number of older adults increase worldwide, more osteoporotic fractures will occur. The vertebral body fracture is the most common and disabling type of osteoporotic fracture. Patients with vertebral body fractures first suffer from severe back pain, but, despite the severity of the disease, most fractures heal with conservative treatment, such as bed rest, brace protection, and analgesics. However, a small percentage of vertebral body fractures remain ununited, resulting in disabling back pain, deformities, or even neurological deficits. Traditional invasive treatments for nonunion frac- tures can sometimes result in severe perioperative morbidity or mortality (1–6). The innovative vertebroplasty/kyphoplasty procedures (or verte- bral augmentation procedures, VAP), in which bone cement, originally poly(methyl methacrylate) (PMMA), is injected into the vertebrae defect, have doi:10.1111/j.1525-1594.2011.01372.x Received April 2011; revised June 2011. Address correspondence and reprint requests to Prof. Feng- Huei Lin, Institute of Biomedical Engineering, College of Medi- cine and College of Engineering, National Taiwan University, No.1, Jen Ai Road, Sec. 1,Taipei 10051,Taiwan. E-mail: dtorth65@yahoo. com.tw Co-corresponding author: Prof.Tzong-Fu Kuo, Department and Graduate Institute of Veterinary Medicine, School of Veterinary- Medicine, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei, 10617,Taiwan. E-mail: tzongfu@ntu.edu.tw © 2011, Copyright the Authors Artificial Organs © 2011, International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc. Artificial Organs 2012, 36(4):418–428