Nesse trabalho, compósitos de matriz polimérica foram projetados para reproduzir duas importantes características dos vidros bioativos, que são responsáveis por capacitar a tais materiais se ligarem rapidamente ao tecido ósseo: (1) capacidade de prover íons, como os de cálcio e fosfato, ao ambiente vizinho; e (2) possuir uma estrutura de superfície ideal que favoreça uma rápida precipitação heterogênea de hidroxiapatita carbonatada (HCA). Este novo compósito foi preparado através da incorporação de partículas de vidro bioativo numa matriz polimérica. O teste in vitro de bioatividade foi realizado através da introdução das amostras em soluções-tampão, assim como em soluções simuladoras dos fluidos orgânicos. Espectroscopia no infravermelho foi usada para avaliar a cinética de precipitação da HCA. Os resultados mostraram que os compósitos desenvolvidos podem suprir íons em taxas e concentrações comparáveis ou superiores às de vidros bioativos puros. Além disso, a química de superfície dos compósitos foi alterada para reproduzir o tipo de superfície presente em vidros bioativos. Os resultados demonstraram que a bioatividade in vitro de compósitos pode ser ampliada através da modificação química das superfícies do polímero via introdução de grupos alcoxissilanos especiais.

Composites that can mimic the in vitro bioactive behavior of bioactive glasses were designed to fulfill two main features of bioactive glasses that are responsible for their high bond-to-bone rates: (1) capability of providing ions such as calcium and phosphate to the nearby environment and (2) ideal surface structure that allows fast heterogeneous precipitation of hydroxy-carbonate-apatite (HCA). The novel composites were prepared by incorporating bioactive glass particles into polymer matrices. The in vitro bioactivity test was performed by introducing samples into a buffered solution as well as into a simulated body fluid solution. FTIR was used to evaluate the kinetics of HCA (hydroxy-carbonate-apatite) precipitation. The results showed that the obtained composites can supply ions, such as silicates and phosphates in rates and concentrations comparable or superior than bulk bioactive glasses. Moreover, the surface chemistry of the composites was altered to mimic the surface of bioactive glasses. It was demonstrated that the in vitro bioactivity of the composites was enhanced by chemically modifying polymer surfaces through the introduction of special alkoxysilane groups.

Many chemical and physical methods, such as plasma, e-beam, sputtering, CVD and others, have been used to modify the structure of polymer surfaces by depositing thin inorganic films. Most of these techniques are based upon the use of high energy sources that ultimately can damage either chemically or physically polymer surfaces. Moreover, these methods are usually not versatile enough to allow the design of structurally and chemically tailored surfaces through the control of the distribution of chemical functionalities throughout the surface. In this work, inorganic species were introduced onto polymer substrates in a controlled manner by performing a sequence of chemical reactions at the surface. Sulfonation followed by silanization reactions were used to graft alkoxysilane species at the surface of poly(aryl sulfones). The heterogeneous chemical modification of poly(aryl sulfones) was monitored by FTIR-ATR (Attenuated Total Reflection - FTIR). Model compounds were used to study the chemical reactions occurring during the grafting procedure. The results showed that the developed procedure can allow a controlled introduction of inorganic species onto polymer surfaces. Furthermore, in order to prove that this procedure enables the deposition of specific chemical functionalities onto polymer surfaces that can be used to create chemically and structurally tailored surfaces, silicate films were deposited on previously silanated PAS bioactive glass composites. In vitro tests showed that the surface modified composite can enhance the rates of hydroxy-carbonate-apatite precipitation.

ABSTRACT: Silane coupling agents have been frequently used as interfacial agents in polymer composites to improve interfacial strength and resistance to fluid migration. Although the capability of these agents in improving properties and performance of composites has been reported, there are still many uncertainties regarding the processing-structure-property relationships and the mechanisms of coupling developed by silane agents. In this work, an Atomic Force Microscope (AFM) was used to measure interactions between polymers and silica substrates, where silane networks with a series of different structures were processed. The influence of the structure of silane networks on the interactions with polymers was studied and used to determine the mechanisms involved in the coupling phenomenon. The AFM results showed that phenomena such as chain penetration, entanglements, intersegment bonding, chain conformation in the vicinities of rigid surfaces were identified as being relevant for the overall processes of adhesion and adsorption of polymeric chains within a silane network. AFM adhesion curves showed that penetration of polymeric chains through a more open silane network can lead to higher levels of interactions between polymer and silane agents.

Interactions between polymers and inorganic surfaces are present in a series of phenomena involving processes such as coagulation and deffloculation of ceramic powder and adsorption of organic macromolecules on the surface of implants, among others. In this work, Atomic Force Microscopy (AFM) was modified to allow the evaluation of interactions between polymeric chains and inorganic surfaces (silica) with different structures. Polymers (sulfonated polysulfone) were grafted onto AFM cantilevers. AFM force-distance curves were obtained for this modified tip against a series of substrates produced by depositing silica films on silicon wafers. The structure of the silica layer was modified by employing heat treatments at different temperatures. The results showed that the interactions between polymer and surfaces are dependent on the structure of the surfaces. Penetration of the polymeric chains can occur through a soft gel layer (substrates treated at low temperature, 110 °C). For surfaces with dense silica layers, the results showed that not only the concentration of hydroxy groups but also their spatial distribution along the surfaces are important in defining the magnitude of interactions between polymers and surfaces. A model involving a molecular recognition process, in which interactions are maximized for inorganic surfaces with structures that can match the chemical architecture of the polymer, was then used to explain the obtained results.