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

(Photo-)crosslinkable gelatin derivatives for biofabrication applications

Over the recent decades gelatin has proven to be very suitable as an extracellular matrix mimic for bio-fabrication and tissue engineering applications. However, gelatin is prone to dissolution at typical cell culture conditions and is therefore often chemically modified to introduce (photo-)crosslinkable functionalities. These modifications allow to tune the material properties of gelatin, making it suitable for a wide range of biofabrication techniques both as a bioink and as a biomaterial ink (component). The present review provides a non-exhaustive overview of the different reported gelatin modification strategies to yield crosslinkable materials that can be used to form hydrogels suitable for biofabrication applications. The different crosslinking chemistries are discussed and classified according to their mechanism including chain-growth and step-growth polymerization. The step-growth polymerization mechanisms are further classified based on the specific chemistry including different (photo-)click chemistries and reversible systems. The benefits and drawbacks of each chemistry are also briefly discussed. Furthermore, focus is placed on different biofabrication strategies using either inkjet, deposition or light-based additive manufacturing techniques, and the applications of the obtained 3D constructs

Creating the storyworld of Kalevala characters for travel service

The thesis is product-oriented with the main objective of creating several stories about six of the Kalevala characters. The idea is that these stories will be used for the commissioners company Kalevala kartalle. A secondary objective is then to give the commissioner a concept or idea on how to infiltrate the characters into an experience. The thesis is divided into two parts. The first part storytelling and the second part is about an idea or concept to create an experience in which the characters, from the first part, can appear. The student first reviewed and researched the theoretical part of storytelling. To get a good idea of how a story is put together. After understanding this, the student was able to compose her own stories by researching the characters. After the student had created the stories, she was able to move on to theoretical research on perception. Also how an experience can be created and processed. After the theory, the student then came up with two concepts that the commissioner could possibly work out in real life. Further, the student had then also described how the entire process went, communication with the commissioner and the timeline of the process. At the end, she then discussed the results and has made a reflection

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