Abstract: Surfaces and biointerfaces are recurrent when materials are used in bio-related applications. Bio-inspired concepts have been implemented in this field and gained increasing interest. In this context, stimuli-responsive surfaces have found applicability in a variety of subjects, including switchable surfaces to control protein immobilization or cell adhesion, porous membranes for controlled drug delivery applications, substrates and scaffolds for tissue engineering applications, biosensors, or membranes for bioseparation. Moreover, self-assembly strategies and hierarchical structures often found in Nature could inspire scientist and engineers to propose new solutions in the design and fabrication of surfaces with special features, such as wettability within extreme ranges, improved adhesion, optical and mechanical properties and specific bioactivity. In this work some aspects related to the use of stimuli-responsive and biomimetic surfaces in the field of biomedicine and biotechnology are highlighted and some examples are presented.
Abstract: The need for biomaterials in dental and orthopedic applications has increased as the world population ages. Synthetic calcium phosphate bioceramics and calcium phosphate cements are proved potential substitutes for bone and teeth due to their structural and crystallographic similarities with the biological apatites, and their biocompatibility but they show poor mechanical properties. Chlorapatite and hydroxyapatite whiskers with high aspect ratio can be used to improve this drawback. This work describes a method to transform chlorapatite single crystals into hydroxyapatite whiskers, suitable for the reinforcement of calcium phosphate bioceramics and calcium phosphate cements. Hydroxyapatite whiskers were obtained by treating chlorapatite single crystals in high-temperature hydrothermal conditions. The variable studied was furnace temperature with and without moisture conditions. The characterization of the chlorapatite and hydroxyapatite whiskers was carried out by SEM, XRD, EDS and FTIR. SXRD data were analyzed for the description of the chlorapatite structure.
Abstract: Formation of porous TiOx layers on Ti during electrochemical etching in H3PO4, CH3COOH electrolytes modified by HF and NH4F was described. The anodization resulted in porous TiOx formation, useful in tissue growth and bone bonding. The pore dimensions increased due to the increase of HF or NH4F content in H3PO4 electrolyte. During anodization at 10 V for 30 min, when the HF content increased from 0.5 to 10%, the pore diameter increased from 30 nm up to 8 m, respectively. Anodization in CH3COOH electrolyte resulted in non-uniform etching with flat hexagonal islands with nanopores inside surrounded by micropores.
Corrosion properties of the etched samples were investigated in Ringer’s solution at 37oC and were compared to the unetched sample. The best corrosion resistance showed the samples etched at 10 V for 30 min in 1M H3PO4 + 2% HF and 1M H3PO4 + 10% NH4F, what can be attributed to thick oxide layer. We find, that porous sample presented good biocompatibility with human osteoblasts.
Abstract: The aim of this study was to evaluate the possibility of preparing chitosan porous matrixes using supercritical fluid technology. Supercritical immersion precipitation technique was used to prepare scaffolds of a natural biocompatible polymer, chitosan, for tissue engineering purposes. The physicochemical and biological properties of chitosan make it an excellent material for the preparation of drug delivery systems and for the development of new biomedical applications in many fields from skin to bone or cartilage.
Immersion precipitation experiments were carried out at different operational conditions in order to optimize the processing method. The effect of different organic solvents on the morphology of the scaffolds was assessed. Additionally, different parameters that influence the process were tested and the effect of the processing variables such as polymer concentration, temperature and pressure in the chitosan scaffold morphology, porosity and interconnectivity was evaluated by micro computed tomography. The preparation of a highly porous and interconnected structure of a natural material, chitosan, using a clean and environmentally friendly technology constitutes a new processing technology for the preparation of scaffolds for tissue engineering using these materials.
Abstract: A number of combinations of biodegradable polymers and bioactive ceramics have been used for orthopaedic applications including in hard tissue regeneration. Ideally, composites aimed to be used in orthopaedic applications should combine adequate mechanical properties and bioactivity. Chitosan (CTS) has been widely used for biomedical applications, namely in tissue regeneration or drug delivery. In this sense, membranes of chitosan and chitosan with Bioglass® (BG) were prepared by solvent casting and characterised using Scanning Electron Microscopy. In vitro bioactivity tests were performed in the composite membranes, namely by monitoring their capability to induce the precipitation of apatite upon immersion in simulated body fluid (SBF). The results showed that the addition of BG promoted the deposition of an apatite-like layer. The deposition of apatite could influence the mechanical performance of the material. Therefore, in order to follow this biomineralization, the viscoelastic properties of these composite membranes (immersed in SBF) were evaluated. The change in the storage modulus (E’) and the loss factor (Tan δ) were measured as a function of immersion time using non-conventional dynamic mechanical analysis (DMA) tests, in which the samples were kept in wet conditions and at 37°C during the measurements. The mechanical properties of the chitosan membranes were improved by the addition of BG particles. An increase on the storage modulus was observed by the composite membranes while for the pure chitosan membranes the storage modulus was stable up to 7 days. Clear changes were detected in the composite membranes that contrasted with pure chitosan (CTS) membranes that exhibit stable viscoelastic properties up to 7 days. In addition, this work showed that sample characterization in the hydrated state can be useful to predict the mechanical performance of composites under meaningful physiological conditions.
Abstract: In this study a new P-free system applied to the production of Bioactive Glass Nanoparticles (BG-NPs) is proposed, in order to evaluate the effect of suppressing this component, in the bioactivity capability of the materials. The BG-NPs, based on both ternary (SiO2-CaO-P2O5) and binary (SiO2-CaO) systems, were prepared via a sol-gel method. The morphology and composition of the BG-NPs were studied using FTIR and SEM. New composite membranes were produced combining chitosan and the BG-NPs. The bioactive character of the prepared biodegradable membranes was accessed in vitro by analyzing the capability for apatite formation onto the surface after being immersed in simulated body fluid (SBF). EDX and SEM were used to confirm the bioactivity of the materials.
Abstract: The thermal insulation of a clothing system represents a quantitative assessment of the way cloth provides thermal barrier to the user. One of this clothing systems, the surgical gown used in the operating theatre, is considered as a non-active medical device and obeys the Medical Device Directive 93/43/EEC. New materials and gowns are being developed, fitting the level of the barrier function with the comfort issues and therefore the selection of the most suitable gown is vital. During the last 60 years, thermal manikins have been used to measure clothing insulation and to assess the thermal environment regarding comfort issues. The main goal of the present study is the comparison of the thermal insulation values during the objective evaluation using the dry thermal manikin with the results obtained using an Infra-Red camera ThermaCAM, monitoring the temperature development of different surgical gowns at a constant skin temperature of 33 °C in neutral environmental conditions.