Chitosan nanogels for biomedical applications: Choosing a suitable sterilization method

Abstract

Event Abstract Back to Event Chitosan nanogels for biomedical applications: Choosing a suitable sterilization method Raquel Galante1, 2, Irene Satiko1, Nádia A. Bou-Chacra1, Rogério Colaço2, Ana P. Serro2, 3 and Terezinha J. Pinto1 1 Faculdade de Ciências Farmacêuticas - Universidade de São Paulo, Departamento de Farmácia, Brazil 2 Instituto Superior Técnico - Universidade de Lisboa, Centro de Química Estrutural, Portugal 3 Instituto Superior de Ciências da Saúde Egas Moniz, Centro De Investigação Interdisciplinar Egas Moniz, Portugal Introduction: Nanostructured hydrogels have been subject of detailed studies aiming a wide range of biomedical and pharmaceutical applications. Sterilization is a crucial step in the development of this type of materials[1]. Although often effective, the conventional sterilization methods may change the physico-chemical properties of the gels and their biocompatibility, compromising their functionality[1],[2]. The main goal of this work is to study the effect of different sterilization methods on the intrinsic properties of chitosan nanogels. In addition to conventional methods (autoclave and gamma radiation) a recent and promising ozone-based method of sterilization, still in the development phase, was also evaluated to assess its applicability to the studied material. Method: A model chitosan-based nanostructured hydrogel (nanogel), with broad spectrum of possible applications was produced by ionic gelation, using sodium tripolyphosphate (TPP) as a crosslinking agent. The nanogel was sterilized by autoclave, gamma irradiation and by ozone gas in the absence and in the presence of protective sugars (dextrose and mannitol). Sterilization parameters, such as temperature, time of exposure and irradiation dose, were varied in order to study their effect. A complete characterization protocol was carried out, before and after each sterilization method, as follows: size, dispersion and zeta potential alterations where analyzed by Zetasizer measurements; surface topography and morphology were studied by Scanning Electronic Microscopy and physicochemical alterations were monitored by Fourier Transform Infrared Spectroscopy analysis. In order to ensure the effectiveness of the ozone method, sterility efficacy tests were carried out by purposely contaminating the samples with different loads of a microorganism known to be resistant to the technique. Results and Discussion: Exposing the nanogel, as it is, to gamma rays, let to the immediately visible formation of sediments. Although the UV-Vis spectra data did not show significant alterations, the size and zeta potential measurements displayed significant effects on Z-average size, PDI and zeta potential values, thus resulting in a degraded nanogel.Upon the sugar addition (D-glucose and mannitol) to the nanogel suspension, the results showed a substantial increase of the resistance to irradiation.The variation of average particle due to gamma rays irradiation can be observed in Figure 1, for all the studied conditions. In both cases, size, PDI, and zeta potential values variations were significantly reduced.Concerning the ozone gas method, the nanogel revealed a promising resistance to the ozonation, having shown no major sings of alteration in size, zeta potential and PDI..The variation of average particle due to ozonation can be observed in Figure 2, for all the studied conditions. Conclusions: Sterilization of soft polymeric biomaterials such as nanogels is a challenging task. The information available in the literature about the sterilization of chitosan nanogels is scarce, which reinforces the importance of this work. It was found that the nanogel resistance to irradiation increases considerably in the presence of protective sugars. The results obtained are also promising with regard to the possible applicability of the ozone sterilization since the nanogel seems to withstand the method without displaying significant adverse effects. Figure 1: Average particle size before and after sterilization by gamma irradiation Figure 2: Average particle size before and after sterilization by ozone gas. Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Fundação para a Ciência e Tecnologia (FCT), Project SurfLenses - MERA-NET; A special thanks to Dr. Pablo Vásquez from IPEN (Instituto de Pesquisas Energéticas e Nucleares)