The molecular and mechanical characteristics of in situ degradation behavior of chitosan-polygalacturonic acid/hydroxyapatite (Chi-PgA-HAP) nanocomposite films is investigated using Fourier Transform Infrared spectroscopy (FTIR), Atomic Force Microscopy (AFM), and modulus mapping techniques for up to 48 days of soaking in cell culture media. The surface molecular structure of media-soaked samples changes over the course of 48 days of soaking, as indicated by significant changes in phosphate vibrations (1200–900？ ) indicating apatite formation. Chitosan-Polygalacturonic acid polyelectrolyte complexes (PECs) govern structural integrity of Chi-PgA-HAP nanocomposites and FTIR spectra indicate that PECs remain intact until 48 days of soaking. In situ AFM experiments on media-soaked samples indicate that soaking results in a change in topography and swelling proceeds differently at the initial soaking periods of about 8 days than for longer soaking. In situ modulus mapping experiments are done on soaked samples by probing 1–3？nm of surface indicating elastic moduli of 4？GPa resulting from proteins adsorbed on Chi-PgA-HAP nanocomposites. The elastic modulus decreases by 2？GPa over a long exposure to cell culture media (48 days). Thus, as water enters the Chi-PgA-HAP sample, surface molecular interactions in Chi-PgA-HAP structure occur that result in swelling, causing small changes in nanoscale mechanical properties. 1. Introduction Recent developments in design of novel polymeric biomaterials have allowed researchers to confront many of the challenges dealing with the design of novel biomaterials. The tremendous potential of biodegradable polymers for tissue engineering and medical devices results from their biocompatibility, ease in processing, and capability of controlled degradation in response to biological environment. Candidate materials for bone tissueengineering include natural polymers (chitosan, collagen, hyaluronan, fibrin), synthetic polymers (polycaprolactone, polylactic acid, polyglycolic acid, and their copolymers) and inorganic materials (tricalcium phosphate, hydroxyapatite). Also, the natural biodegradable and biofunctional biopolymer, chitosan, has been considered as a potential candidate material for numerous biomedical applications including controlled drug release [1, 2], wound dressing [3], and more recently, for tissue engineering application [4–13]. Chitosan [ (1,4)-linked 2-amino-2-deoxy-D glucan] is a cationic polysaccharide obtained by N-acetylation of chitin. Chitosan provides improved cell attachment, since the polysaccharide
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