Sterilization of hydrogels for biomedical applications: A review.

Despite the beneficial properties and outstanding potential of hydrogels for biomedical applications, several unmet challenges must be overcome, especially regarding to their known sensitivity to conventional sterilization methods. It is crucial for any biomaterial to withstand an efficient sterilization to obtain approval from regulatory organizations and to safely proceed to clinical trials. Sterility assurance minimizes the incidence of medical device-related infections, which still constitute a major concern in health care. In this review, we provide a detailed and comprehensive description of the published work from the past decade regarding the effects of sterilization on different types of hydrogels for biomedical applications. Advances in hydrogel production methods with simultaneous sterilization are also reported. Terminal sterilization methods can induce negative or positive effects on several material properties (e.g., aspect, size, color, chemical structure, mechanical integrity, and biocompatibility). Due to the complexity of factors involved (e.g., material properties, drug stability, sterilization conditions, and parameters), it is important to note the virtual impossibility of predicting the outcome of sterilization methods to determine a set of universal rules. Each system requires case-by-case testing to select the most suitable, effective method that allows for the main properties to remain unaltered. The impact of sterilization methods on the intrinsic properties of these systems is understudied, and further research is needed. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2472-2492, 2018.

About the Sterilization of Chitosan Hydrogel Nanoparticles.

In the last years, nanostructured biomaterials have raised a great interest as platforms for delivery of drugs, genes, imaging agents and for tissue engineering applications. In particular, hydrogel nanoparticles (HNP) associate the distinctive features of hydrogels (high water uptake capacity, biocompatibility) with the advantages of being possible to tailor its physicochemical properties at nano-scale to increase solubility, immunocompatibility and cellular uptake. In order to be safe, HNP for biomedical applications, such as injectable or ophthalmic formulations, must be sterile. Literature is very scarce with respect to sterilization effects on nanostructured systems, and even more in what concerns HNP. This work aims to evaluate the effect and effectiveness of different sterilization methods on chitosan (CS) hydrogel nanoparticles. In addition to conventional methods (steam autoclave and gamma irradiation), a recent ozone-based method of sterilization was also tested. A model chitosan-tripolyphosphate (TPP) hydrogel nanoparticles (CS-HNP), with a broad spectrum of possible applications was produced and sterilized in the absence and in the presence of protective sugars (glucose and mannitol). Properties like size, zeta potential, absorbance, morphology, chemical structure and cytotoxicity were evaluated. It was found that the CS-HNP degrade by autoclaving and that sugars have no protective effect. Concerning gamma irradiation, the formation of agglomerates was observed, compromising the suspension stability. However, the nanoparticles resistance increases considerably in the presence of the sugars. Ozone sterilization did not lead to significant physical adverse effects, however, slight toxicity signs were observed, contrarily to gamma irradiation where no detectable changes on cells were found. Ozonation in the presence of sugars avoided cytotoxicity. Nevertheless, some chemical alterations were observed in the nanoparticles.

Contact lenses as drug controlled release systems: a narrative review / As lentes de contacto como sistema de libertação controlada de fármacos: uma revisão narrativa

ABSTRACT Topically applied therapy is the most common way to treat ocular diseases, however given the anatomical and physiological constraints of the eye, frequent dosing is required with possible repercussions in terms of patient compliance. Beyond refractive error correction, contact lenses (CLs) have, in the last few decades emerged as a potential ophthalmic drug controlled release system (DCRS). Extensive research is underway to understand how to best modify CLs to increase residence time and bioavailability of drugs within therapeutic levels on the ocular surface.These devices may simultaneously correct ametropia and have a role in managing ophthalmic disorders that can hinder CL wear such as dry eye, glaucoma, ocular allergy and cornea infection and injury. In this narrative review the authors explain how the ocular surface structures determine drug diffusion in the eye and summarize the strategies to enhance drug residence time and bioavailability. They synthesize findings and clinical applications of drug soaked CLs as DCRS combined with delivery diffusion barriers, incorporation of functional monomers, ion related controlled release, molecular imprinting, nanoparticles and layering. The authors draw conclusions about the impact of these novel ophthalmic agents delivery systems in improving drug transport in the target tissue and patient compliance, in reducing systemic absorption and undesired side effects, and discuss future perspectives.

RESUMO A forma mais frequente de aplicação terapêutica em oftalmologia consiste na instilação de gotas oculares, mas dadas as limitações anatómicas e fisiológicas do olho, é necessária dosagem frequente com possível repercussão na adesão do paciente à terapêutica. Nas últimas décadas, as lentes de contacto (CLs) têm surgido como um potencial sistema de libertação controlada de fármacos na superfície ocular (DCRS) para correção do erro refrativo. Está em curso uma extensa investigação para entender a melhor forma de modificar as CLs, de modo a aumentar o tempo de residência e a biodisponibilidade do medicamento na superfície ocular dentro de níveis terapêuticos. Ao corrigirem a ametropia, estes dispositivos poderão simultaneamente desempenhar um papel na gestão de perturbações oftalmológicas, tais como a síndrome do olho seco, glaucoma, alergia ocular e infecção corneana, que podem comprometer o porte seguro e confortável das CLs. Nesta revisão narrativa, os autores explicam como as estruturas da superfície ocular determinam a difusão de fármacos no olho e sintetizam as estratégias para aumentar a permanência e biodisponibilidade dos mesmos. Em seguida, apresentam os resultados e as aplicações clínicas das CLs embebidas em fármacos, como DCRS, através da incorporação de barreiras de difusão, de monómeros funcionais, da liberação controlada por iões, da impressão molecular, de nanopartículas e pelo processo camada sobre camada. Os autores concluem avaliando o impacto destes novos sistemas de entrega de agentes farmacológicos ao melhorar o seu transporte no tecido alvo, reduzindo a sua absorção sistémica e os seus efeitos colaterais indesejáveis, e discutem perspectivas futuras.