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Lingxiao Xie, Xiong Ding, Rachel Budry, Guangzhao Mao Department of Chemical Engineering and Materials Science, Wayne State University, Detroit, MI, USA Background: The layer-by-layer (LbL) assembly method offers a molecular level control of the amount and spatial distribution of bioactive molecules. However, successful clinical translation of LbL film technology will most certainly require a better understanding and control of not only the film assembly process, but also film disassembly kinetics in physiologic conditions. Purpose: This work focuses on the understanding and control of degradation properties of LbL films for localized gene delivery. Methods: Bioreducible poly(amido amine)s (PAAs) containing cystaminebisacrylamide (CBA), methylenebisacrylamide, and 5-amino-1-pentanol (APOL) were synthesized by Michael addition polymerization for the construction of bioreducible LbL films capable of sequential gene delivery. Results: The synthesized PAAs were screened for desirable buffering capacity, cell transfection, and cytotoxicity characteristics together with 25 kDa branched polyethylenimine (PEI) and cross-linked 800 Da PEI. By screening the various polycations we were able to identify a copolymer of CBA and APOL for the subsequent construction of the LbL films. By incorporating a highly transfecting polycation and a nondiffusing polycation we were able to improve the overall transfection of HEK293 and MC3T3 cells from the bioreducible LbL films. We also demonstrated the dual-stage release and transfection of two different DNAs from the LbL films. Conclusion: The results indicate that LbL films consisting of bioreducible PAAs and non-diffusing polyelectrolytes have excellent degradation properties for the development of LbL coating technology for localized gene delivery applications. Keywords: biodegradable polymers, cell transfection, interlayer diffusion, localized gene delivery, polyelectrolyte multilayers, sequential release

Wei Song1, Xiaowei Yu2, Sunxi Wang5, Ralph Blasier4, David C Markel3, Guangzhao Mao5, Tong Shi1, Weiping Ren1,31Department of Biomedical Engineering, Wayne State University, Detroit, MI, USA; 2Department of Orthopedic Surgery, Second Affiliated Hospital of Nanjing Medical University, Nanjing, People's Republic of China; 3Detroit Medical Center and Providence Hospital Orthopedic Residency, Detroit, 4Orthopedic Section, St Francis Hospital, Escanaba, 5Department of Chemical Engineering, Wayne State University, Detroit, MI, USABackground: Erythromycin, a hydrophobic antibiotic used to treat infectious diseases, is now gaining attention because of its anti-inflammatory effects and ability to inhibit osteoclasts formation. The aim of this study was to explore a cyclodextrin-erythromycin (CD-EM) complex for sustained treatment of orthopedic inflammation.Methods and results: Erythromycin was reacted with ß-cyclodextrin to form a nonhost-guest CD-EM complex using both kneading and stirring approaches. Physiochemical measurement data indicated that erythromycin and cyclodextrin formed a packing complex driven by intermolecular forces instead of a host-guest structure due to the limited space in the inner cavity of ß-cyclodextrin. The CD-EM complex improved the stability of erythromycin in aqueous solution and had a longer duration of bactericidal activity than free erythromycin. Cytotoxicity and cell differentiation were evaluated in both murine MC3T3 preosteoblast cells and RAW 264.7 murine macrophage cells. The CD-EM complex was noncytotoxic and showed significant inhibition of osteoclast formation but had little effect on osteoblast viability and differentiation.Conclusion: These attributes are especially important for the delivery of an adequate amount of erythromycin to the site of periprosthetic inflammation and reducing local inflammation in a sustained manner.Keywords: erythromycin, cyclodextrin, drug stability, bactericidal activity, osteoclastogenesis