Utility of pH-sensitive superabsorbent polymers in concrete repair

The largest issue with concrete is that cracks can occur due to its relatively low tensile strength. These cracks can generate an entrance for harmful compounds which are dissolved in fluids and gases and endanger the durability of concrete. The cost for crack repair is very high. Alternatively, introducing a polymer during concrete mixing can create a self-sealing material. Fresh cement pore solution possesses a pH value of 12.8, but when a crack occurs, the pH drops to 9 - 10 or even lower, depending on the environment. At this lower pH value, the swelling degree of the hydrogel incorporated must be sufficiently high in order to fill up the crack. As a result, a cross-linked pH-sensitive copolymer of acrylic acid and acrylamide has been synthesized in the present work. The chemical structure has been characterized and sorption and desorption effects have been investigated using dynamic vapour sorption experiments. In addition, a swelling curve was established over the entire pH-range (pH 1-13). Interestingly, the hydrogel developed possessed a maximal swelling capacity of more than 400 times its own weight. Next, water permeability and flexural and compressive strength tests were performed on these samples. The significant decrease in water permeability of hydrogel containing cracked concrete relative to the cracked reference concrete is a quantitative indication of the sealing capacity of the applied hydrogel. The uptake of mixing water by the hydrogel will reduce the effective water/cement ratio of the cementitious matrix. This water will then be released later-on and will cause internal curing. In the present work, experiments have been performed using additional mixing water. Additional mixing water resulted in a higher apparent water/cement factor during internal curing and, together with macro-pore formation, in a lower strength. The results indicate that the polymer developed can be promising to introduce crack-sealing potential in concrete

Gelatin-based hydrogels promote chondrogenic differentiation of human adipose tissue-derived mesenchymal stem cells in vitro

Due to the weak regeneration potential of cartilage, there is a high clinical incidence of articular joint disease, leading to a strong demand for cartilaginous tissue surrogates. The aim of this study was to evaluate a gelatin-based hydrogel for its suitability to support chondrogenic differentiation of human mesenchymal stem cells. Gelatin-based hydrogels are biodegradable, show high biocompatibility, and offer possibilities to introduce functional groups and/or ligands. In order to prove their chondrogenesis-supporting potential, a hydrogel film was developed and compared with standard cell culture polystyrene regarding the differentiation behavior of human mesenchymal stem cells. Cellular basis for this study were human adipose tissue-derived mesenchymal stem cells, which exhibit differentiation potential along the adipogenic, osteogenic and chondrogenic lineage. The results obtained show a promotive effect of gelatin-based hydrogels on chondrogenic differentiation of mesenchymal stem cells in vitro and therefore encourage subsequent in vivo studies

Towards A More Uniform Functionality Of Lignin

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Biodegradable polyesters as sensor substrates

Microfluidic biosensors are generally designed for single use, due to their troublesome rinsing and the likeness for degradation of the active components to occur. The present project aims to meet the need to develop truly disposable biosensors by applying biodegradable polyesters as sensor substrate. When considering optical biosensors, the applied biodegradable materials should exhibit specific optical, thermal and mechanical properties in order to overcome the disadvantages related to the use of traditional polymers. In that respect, poly(mandelide) has recently been introduced as a biodegradable poly(styrene) analogue. Its high glass transition temperature and its excellent optical transmission render poly(mandelide) a very interesting material for microfluidic biosensor applications. In the present work, the synthesis and the characterisation of poly(mandelide) will be discussed. First, the effect of the solvent on the achieved yield during monomer synthesis will be dealt with. Next, the polymerised mandelide was subjected to an in depth characterisation using size exclusion chromatography, thermal analysis and optical transmission measurements. Interestingly, the results indicate that poly(mandelide) shows a high thermal stability both under inert as well as in oxidative atmosphere and confirm its high glass transition temperature. These properties therefore enable the processing of poly(mandelide) into microfluidic biosensors using hot embossing

Degradable polyesters for optical applications

The consumption of contaminated water still poses a real threat in developing countries. The assessment of water safety is currently based on cell-culture based techniques that require expensive equipment and skilled operators. The implementation of lab-on-a-chip (LoC) technologies for water analysis will therefore lead to a paradigm shift since it will enable a low-cost, straightforward, real-time and reliable analysis of samples. Within LoC set-ups, optical detection methods are considered to be the front runners based on their sensitivity and simple sample preparation. Despite these clear advantages, LoC sensors are generally designed for single use as the regeneration of the active components in the channels is troublesome. Therefore, we propose the application of degradable, bio-based polyesters as sensor substrate to limit the environmental impact that will come with the mass application of microfluidic sensors. In order to design degradable, transparent and mechanically stable materials, mandelic acid has been shown to be an interesting monomer due to its interesting thermal and optical properties.1 In the current work, O-carboxyanhydrides are applied as monomers as they are readily accessible in contrast to cyclic diesters of mandelic acid. The current contribution will highlight the copolymerisation with lactic acid based monomers to tune the glass transition. Given the optical application, light absorbance in thin sheets will be discussed. Future work will focus on the controlled processing of the obtained polymers into microfluidic chips that can be applied in an optical read-out system