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    Hydrogel substrate stress-relaxation regulates the spreading and proliferation of mouse myoblasts. Bauer Aline,Gu Luo,Kwee Brian,Li Weiwei Aileen,Dellacherie Maxence,Celiz Adam D,Mooney David J Acta biomaterialia Mechanical properties of the extracellular microenvironment are known to alter cellular behavior, such as spreading, proliferation or differentiation. Previous studies have primarily focused on studying the effect of matrix stiffness on cells using hydrogel substrates that exhibit purely elastic behavior. However, these studies have neglected a key property exhibited by the extracellular matrix (ECM) and various tissues; viscoelasticity and subsequent stress-relaxation. As muscle exhibits viscoelasticity, stress-relaxation could regulate myoblast behavior such as spreading and proliferation, but this has not been previously studied. In order to test the impact of stress relaxation on myoblasts, we created a set of two-dimensional RGD-modified alginate hydrogel substrates with varying initial elastic moduli and rates of relaxation. The spreading of myoblasts cultured on soft stress-relaxing substrates was found to be greater than cells on purely elastic substrates of the same initial elastic modulus. Additionally, the proliferation of myoblasts was greater on hydrogels that exhibited stress-relaxation, as compared to cells on elastic hydrogels of the same modulus. These findings highlight stress-relaxation as an important mechanical property in the design of a biomaterial system for the culture of myoblasts. STATEMENT OF SIGNIFICANCE:This article investigates the effect of matrix stress-relaxation on spreading and proliferation of myoblasts by using tunable elastic and stress-relaxing alginate hydrogels substrates with different initial elastic moduli. Many past studies investigating the effect of mechanical properties on cell fate have neglected the viscoelastic behavior of extracellular matrices and various tissues and used hydrogels exhibiting purely elastic behavior. Muscle tissue is viscoelastic and exhibits stress-relaxation. Therefore, stress-relaxation could regulate myoblast behavior if it were to be incorporated into the design of hydrogel substrates. Altogether, we showed that stress-relaxation impacts myoblasts spreading and proliferation. These findings enable a better understanding of myoblast behavior on viscoelastic substrates and could lead to the design of more suitable substrates for myoblast expansion in vitro. 10.1016/j.actbio.2017.08.041
    In-situ doping of a conductive hydrogel with low protein absorption and bacterial adhesion for electrical stimulation of chronic wounds. Lu Yuhui,Wang Yanan,Zhang Jieyu,Hu Xuefeng,Yang Zeyu,Guo Yi,Wang Yunbing Acta biomaterialia Electrical stimulation (ES) via electrodes is promising for treating chronic wounds, but this electrode-based strategy is unable to stimulate the whole wound area and the therapeutic outcome may be compromised. In this study, a conductive poly(2-hydroxyethyl methacrylate) (polyHEMA)/polypyrrole (PPY) hydrogel was developed, and 3-sulfopropyl methacrylate was covalently incorporated in the hydrogel's network to in-situ dope the PPY and maintain the hydrogel's conductivity in the weak alkaline physiological environment. The obtained hydrogel was superior to the commercial Hydrosorb® dressing for preventing bacterial adhesion and protein absorption, and this is helpful to reduce the possibilities of infection and secondary damage during dressing replacement. The in vitro scratch assay demonstrates that ES through the hydrogel enhanced fibroblast migration, and this enhancement effect remained even after the ES was ended. The in vivo assay using diabetic rats shows that when ES was conducted with this polyHEMA/PPY hydrogel, the healing rate was faster than that achieved by the electrode-based ES strategy. Therefore, this polyHEMA/PPY hydrogel shows a great potential for developing the next generation of ES treatment for chronic wounds. STATEMENT OF SIGNIFICANCE: Electrical stimulation (ES) via separated electrodes is promising for treating chronic wounds, but this electrode-based strategy is unable to stimulate the whole wound area, compromising the therapeutic outcome. Herein, a hydrogel was developed with stable electrical conductivity in the physiological environment and strong resistance to protein absorption and bacterial adhesion. The in vitro and in vivo tests proved that ES applied through the flexible and conductive hydrogel that covered the wound was superior to ES through electrodes for promoting the healing of the chronic wound. This hydrogel-based ES strategy combines the advantages of ES and hydrogel dressing and will pave the way for the next generation of ES treatment for chronic wounds. 10.1016/j.actbio.2019.03.018
    Biodegradation of ECM hydrogel promotes endogenous brain tissue restoration in a rat model of stroke. Ghuman Harmanvir,Mauney Carrinton,Donnelly Julia,Massensini Andre R,Badylak Stephen F,Modo Michel Acta biomaterialia The brain is considered to have a limited capacity to repair damaged tissue and no regenerative capacity following injury. Tissue lost after a stroke is therefore not spontaneously replaced. Extracellular matrix (ECM)-based hydrogels implanted into the stroke cavity can attract endogenous cells. These hydrogels can be formulated at different protein concentrations that govern their rheological and inductive properties. We evaluated histologically 0, 3, 4 and 8 mg/mL of porcine-derived urinary bladder matrix (UBM)-ECM hydrogel concentrations implanted in a 14-day old stroke cavity. Less concentrated hydrogels (3 and 4 mg/mL) were efficiently degraded with a 95% decrease in volume by 90 days, whereas only 32% of the more concentrated and stiffer hydrogel (8 mg/mL) was resorbed. Macrophage infiltration and density within the bioscaffold progressively increased in the less concentrated hydrogels and decreased in the 8 mg/mL hydrogels. The less concentrated hydrogels showed a robust invasion of endothelial cells with neovascularization. No neovascularization occurred with the stiffer hydrogel. Invasion of neural cells increased with time in all hydrogel concentrations. Differentiation of neural progenitors into mature neurons with axonal projections was evident, as well as a robust invasion of oligodendrocytes. However, relatively few astrocytes were present in the ECM hydrogel, although some were present in the newly forming tissue between degrading scaffold patches. Implantation of an ECM hydrogel partially induced neural tissue restoration, but a more complete understanding is required to evaluate its potential therapeutic application. STATEMENT OF SIGNIFICANCE: Extracellular matrix hydrogel promotes tissue regeneration in many peripheral soft tissues. However, the brain has generally been considered to lack the potential for tissue regeneration. We here demonstrate that tissue regeneration in the brain can be achieved using implantation of ECM hydrogel into a tissue cavity. A structure-function relationship is key to promote tissue regeneration in the brain. Specifically, weaker hydrogels that were retained in the cavity underwent an efficient biodegradation within 14 days post-implantation to promote a tissue restoration within the lesion cavity. In contrast, stiffer ECM hydrogel only underwent minor biodegradation and did not lead to a tissue restoration. Inductive hydrogels weaker than brain tissue provide the appropriate condition to promote an endogenous regenerative response that restores tissue in a cavity. This approach offers new avenues for the future treatment of chronic tissue damage caused by stroke and other acute brain injuries. 10.1016/j.actbio.2018.09.020