507 research outputs found

    Non-steady scaling model for the kinetics of the photo-induced free radical polymerization of crosslinking networks

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    Recently, a semi-empirical scaling model was introduced to account for the free-radical polymerization kinetics of acrylated urethane precursors in the solid-state. By describing the radical initiation process in more detail, the kinetic model is extended herein towards general free-radical crosslinking irrespective of the initial physical state of the multifunctional precursors. Effects referred to as radical trapping and caging in the literature are clearly specified and a closed-form expression with a limited number of adjustable parameters is obtained which can be compared to experimental kinetics. In particular, the relation between polymerization rate and functional conversion can be reduced to expressions with three and four parameters in the limits of "solid-state" and "steady-state" kinetics, respectively. In the case of photoinduced free-radical polymerization and within the slow decomposition regime of the initiator, the single parameter with an explicit dependence on the incident light intensity is predicted to behave proportionally. The model is validated by comparing the relevant expressions to original calorimetric data for the free-radical photopolymerization kinetics of different acrylate urethane precursors at two temperatures, providing illustrations for solid-to-solid and liquid-to-rubber transformations. Careful monitoring of the effect of light intensity corroborates the expected scaling and additionally offers reliable estimates for the kinetic coefficients of propagation and termination

    Crack mitigation in concrete : superabsorbent polymers as key to success?

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    Cracking is a major concern in building applications. Cracks may arise from shrinkage, freeze/thawing and/or structural stresses, amongst others. Several solutions can be found but superabsorbent polymers (SAPs) seem to be interesting to counteract these problems. At an early age, the absorbed water by the SAPs may be used to mitigate autogenous and plastic shrinkage. The formed macro pores may increase the freeze/thaw resistance. The swelling upon water ingress may seal a crack from intruding fluids and may regain the overall water-tightness. The latter water may promote autogenous healing. The use of superabsorbent polymers is thus very interesting. This review paper summarizes the current research and gives a critical note towards the use of superabsorbent polymers in cementitious materials

    Injectable biomaterials as minimal invasive strategy towards soft tissue regeneration-an overview

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    Soft tissue engineering has been gaining increasing interest as an approach to overcome the limitations posed by current clinical procedures such as invasiveness of the surgery, post-operative complications and volume loss. Soft tissue damage occurs either due to congenital malformation, trauma/disease or surgical resection. Through the use of autologous cells, such as mesenchymal stem cells, combined with a biomaterial acting as a support, biological substitutes can be developed. A promising pathway in terms of delivery of these engineered constructs is the use of an injectable system, able to provide a minimally invasive approach. Advances have been made in the development of biocompatible biomaterials able to induce soft tissue regeneration. The present review provides an overview of fillers used in the clinic as well as a non-exhaustive overview of all injectable systems reported for soft tissue engineering. A particular focus is placed on the benefits and drawbacks of the biomaterials and the underlying polymerisation strategy. Furthermore, focus is placed on the mechanical properties of the systems

    Affinity study of novel gelatin cell carriers for fibronectin

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    In the present work, the gelatin/fibronectin affinity was evaluated using SPR, QCM and radiolabelling. The results indicate that type A gelatin films possess a higher affinity for Fn compared to type B gelatin. This is due to a combined hydrophobic and electrostatic interaction between gelatin type A and Fn. In a second part, the affinity of Fn for porous gelatin scaffolds was evaluated. The scaffolds were prepared by a cryogenic treatment and subsequent freeze-drying yielding type I and type II scaffolds which possess different pore geometries/sizes. The results indicate that the Fn density on the scaffolds can be fine-tuned by varying the Fn concentration, the gelatin type (A vs. 13), the pore size/geometry (type I vs. type II scaffolds)

    Effect of cryogenic treatment on the rheological properties of gelatin hydrogels

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    Gelatin has the ability to form a gel when cooled below the sol-gel temperature. In this study, the effects of various cryo-parameters, including the number of freeze-thaw cycles, cooling rate, thawing rate, and gelatin concentration, on the material properties were examined. The rheological properties of the cryogels improved with increasing cryo-cycles and decreasing cooling and thawing rates as well as were superior to those of the corresponding hydrogels formed at room temperature. In addition, the critical gelation concentration decreased after repeated cryo-treatments. Methacrylamide-modified gelatin was also treated cryogenically, followed by in situ UV irradiation to enable radical cross-linking. The cross-linking efficiency of specific gelatin concentrations improved with freeze-thawing. Cryogelation can be used to fine-tune the mechanical properties of hydrogels. This is of relevance to tissue engineering where porous gelatin hydrogels are used as biomaterials
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