Stimuli-Responsive Materials for Tissue Engineering and Drug Delivery.

Smart or stimuli-responsive materials are an emerging class of materials used for tissue engineering and drug delivery. A variety of stimuli (including temperature, pH, redox-state, light, and magnet fields) are being investigated for their potential to change a material's properties, interactions, structure, and/or dimensions. The specificity of stimuli response, and ability to respond to endogenous cues inherently present in living systems provide possibilities to develop novel tissue engineering and drug delivery strategies (for example materials composed of stimuli responsive polymers that self-assemble or undergo phase transitions or morphology transformations). Herein, smart materials as controlled drug release vehicles for tissue engineering are described, highlighting their potential for the delivery of precise quantities of drugs at specific locations and times promoting the controlled repair or remodeling of tissues.

3D In Vitro Models of Early Pregnancy: How to Choose the Right Scaffolding Material?

Following fertilization, the blastocyst has to complete two distinct steps to assure further development of pregnancy. After apposition it establishes a firm connection with the luminal epithelium of the endometrium (attachment) and subsequently enters the decidualizing stroma (invasion). If this step is not achieved successfully, fertility problems arise. Development of the placenta ensures an adequate supply of nutrients and gas between the mother and the fetus. Preeclampsia is a prevalent disorder arising from defects in the process of placentation. It is associated with an increase of maternal morbidity and mortality. Numerous attempts have been made in order to elucidate the etiology of the syndrome and identify women at risk. The lack of reliable animal models has turned the attention to the development of in vitro assays, which could provide a better insight into the individual processes that will later trigger preeclampsia symptoms. In particular, 3D in vitro models more closely resemble the complexity of the extracellular environment. The choice of the scaffolding material should be done carefully as cell-matrix interactions are very often as important as cell-cell interactions for the correct attachment, proliferation and differentiation of cells. The following review is aimed to provide a general overview of the scaffolds available for the in vitro modeling of these complicated systems as well as to discuss the importance surrounding the choice of the scaffolding material and its influence on the results obtained.

Innovative Immobilization Matrices.

We present a brief survey of some of the recent work of Professor Luis E. Díaz, performed together with his students and collaborators at the University of Buenos Aires. Dr Luis E. Díaz has been involved in research on biochemical and pharmaceutical sciences solving scientific and industry problems for over 40 years until he passed away. Prof. Díaz scientific interests included various topics from NMR spectroscopy to biomedicine but fundamentally he focused in various aspects of chemistry (analytical, organic, inorganic and environmental). This is not a complete survey but a sampling of prominent projects related to sol-gel chemistry with a focus on some of his recent publications.

Nanotoxicological Effects of SiO2 Nanoparticles on Spodoptera frugiperda Sf9 Cells.

The application of silica nanoparticles (NPs) in the biomedical field experienced a great development. The driving forces for these and future developments are the possibility to design NPs with homogeneous size and structure amenable to specific grafting. Moreover, it is possible to tune the characteristics of the NPs to meet the requirements of each specific cell and desired application. Herein, we analyzed the effect of silica NPs of various sizes and surface charge on the viability of Spodoptera frugiperda cells (Sf9 cell line) with the aim of extending the knowledge of possible toxicity of the NPs in the environment and development of new tools for insect control. Moreover, these results will also contribute to develop more effective systems for gene vectors delivery and recombinant proteins expression. Bare silica NPs of 14 nm, 380 nm and 1430 nm as well as amine-modified silica NPs of 131 nm and 448 nm were obtained by the Stöber method. The NPs were characterized by DLS and zeta potential measurements. The cell viability was assessed by the MTT test. It was observed that the 14 nm NPs possess the highest toxic effect. Indeed, after 24 h, the viability of the cells exposed to the lower concentration of NPs (0.12 mg/ml) was about 40% of the value obtained for the control cells not exposed to NPs. Moreover, the exposure to other negative charged NPs also causes a lower activity when compared with the control. Alternatively, lower concentrations of positive charged NPs (i.e.: 0.12 or 0.6 mg/ml) demonstrated to stimulate the proliferation of the cells and higher concentrations (i.e.: 7.2 mg/ml) did not present significant differences with the control. In conclusion, we have demonstrated that the NPs possess an effect that is highly influenced by the size, charge and concentration. Although, silica NPs are being used in the biomedical field, these results contribute to further understanding the risk that could be associated to nanoparticles and how these can be modified in order to meet the requirements of each desired application.

Development of sol-gel hybrid materials for whole cell immobilization.

The development of a good biocompatible matrix for immobilization of cells is very crucial for improving the performance of functional biohybrids. The synthesis of solid inorganic materials from alkoxide, aqueous and polyol-modified silanes routes, as well as the incorporation of organic polymers, are further areas being developed to improve the viability of encapsulated cells. This emerging field of material science has generated considerable and increasing interest during the past decade. Recent advances in the field involving biomaterials, biohybrids, and functional nanomaterials provided novel materials, which have gained the attention of the scientific community, Governments and industrial companies. Overall, this review is intended to give an overview on the current state of the art of the patents associated to the immobilization of whole living cells in sol-gel derived hybrid materials and to describe the major challenges to be addressed in the forthcoming years.

Effect of various parameters on viability and growth of bacteria immobilized in sol-gel-derived silica matrices.

Immobilized bacteria are being extensively used for metabolite production, biocatalysts, and biosensor construction. However, long-term viability and metabolic activity of entrapped bacteria is affected by several conditions such as their physiological state, the presence of high-osmolarity environments, porous structure and shrinkage of the matrix. The aim of this work was to evaluate the effect of various parameters on bacteria immobilized in sol-gel-derived silica matrices. With this purpose, we evaluated the stress of immobilization over bacteria cultures obtained from different growing states, the effect of cell density and bacteria capability to proliferate inside matrices. Best results to attain longer preservation times were obtained when we immobilized suspensions with an optimized bacterial number of 1 x 10(7) cfu/gel in the presence of LB medium using aqueous silica precursors. Furthermore, the impact of osmotic stress with the subsequent intracellular trehalose accumulation and the addition of osmolites were investigated. Shorter preservation times were found for bacteria immobilized in the presence of osmolites while trehalose accumulation in stressed cells did not produce changes on entrapped bacteria viability. Finally, nutrient addition in silica matrices was studied indicating that the presence of a carbon source without the simultaneous addition of nitrogen was detrimental for immobilized E. coli. However, when both carbon and nitrogen sources were present, bacteria were able to survive longer periods of time.