Evaluation Of A Bilayered, Micropatterned Hydrogel Dressing For Full-Thickness Wound Healing

Nearly 12 million wounds are treated in emergency departments throughout the United States every year. The limitations of current treatments for complex, full-thickness wounds are the driving force for the development of new wound treatment devices that result in faster healing of both dermal and epidermal tissue. Here, a bilayered, biodegradable hydrogel dressing that uses microarchitecture to guide two key steps in the proliferative phase of wound healing, re-epithelialization, and revascularization, was evaluated in vitro in a cell migration assay and in vivo in a bipedicle ischemic rat wound model. Results indicate that the Sharklet™-micropatterned apical layer of the dressing increased artificial wound coverage by up to 64%, P = 0.024 in vitro. In vivo evaluation demonstrated that the bilayered dressing construction enhanced overall healing outcomes significantly compared to untreated wounds and that these outcomes were not significantly different from a leading clinically available wound dressing. Collectively, these results demonstrate high potential for this new dressing to effectively accelerate wound healing

Clickable, hybrid hydrogels as tissue culture platforms for modeling chronic pulmonary diseases in vitro

Statement of Purpose: Many chronic pulmonary diseases, including idiopathic pulmonary fibrosis (IPF), pulmonary hypertension (PH) and chronic obstructive pulmonary disease (COPD), are complex and poorly understood. While great progress has been made to elucidate the cellular and molecular pathways underlying these diseases, treatment options remain limited. The dynamic alterations in mechanical properties and composition of the ECM that occur during pathologic tissue remodeling have been extensively studied as a major driver of cellular activation and disease progression. However, current in vitro models of pulmonary tissues rely almost exclusively on naturally derived materials, such as Matrigel, collagen or decellularized ECM (dECM), which provide biological activity but cannot be easily tuned to emulate the time-dependent changes in mechanical properties that occur during disease progression. We aim to develop a new class of clickable, dynamically tunable hybrid hydrogels that will allow for the manipulation of microenvironmental mechanical properties through a two-stage polymerization process while also maintaining the complex biological composition of the lung ECM to provide a new tool for studying cell behavior in vitro. Using PH as a model, this hydrogel system will contain dECM from healthy and pathologic lung tissue in order to study the influence of both composition and dynamic mechanical properties on the initiation and progression of PH. Here, we determined the primary amine content in Rat-Tail Collagen Type I (Col I) and three decellularized porcine lung samples. We converted free amines to thiol groups using Traut’s reagent. These thiol groups will ultimately be used to crosslink polyethylene glycol alpha methacrylate (PEGαMA) off-stoichiometry in a Michael addition reaction to form the hybrid hydrogel that can later be stiffened through a secondary, light-initiated homopolymerization of MA moieties to emulate disease progression in vitro (Fig 1A)

Engineered Antifouling Microtopographies: An Energetic Model That Predicts Cell Attachment

We have developed a model for the prediction of cell attachment to engineered microtopographies based on two previous models: the attachment point theory and the engineered roughness index (ERI) model. The new surface energetic attachment (SEA) model is based on both the properties of the cell-material interface and the size and configuration of the topography relative to the organism. We have used Monte Carlo simulation to examine the SEA model\u27s ability to predict relative attachment of the green alga Ulva linza to different locations within a unit cell. We have also compared the predicted relative attachment for Ulva linza, the diatom Navicula incerta, the marine bacterium Cobetia marina, and the barnacle cyprid Balanus amphitrite to a wide variety of microtopographies. We demonstrate good correlation between the experimental results and the model results for all tested experimental data and thus show the SEA model may be used as a powerful indicator of the efficacy for antifouling topographies. © 2013 American Chemical Society

Antifouling Performance of Cross-linked Hydrogels: Refinement of an Attachment Model

Poly(ethylene glycol) dimethacrylate (PEGDMA), PEGDMA-co-glycidyl methacrylate (PEGDMA-co-GMA), and PEGDMA-co-hydroxyethyl methacrylate (PEGDMA-co-HEMA) hydrogels were polymerized using ammonium persulfate and ascorbic acid as radical initiators. Surface energies of the hydrogels and a standard, poly(dimethylsiloxane) elastomer (PDMSe), were characterized using captive bubble and sessile drop measurements, respectively (γ = 52 mN/m, γ0 = 19 mN/m). The chemical composition of the hydrogels was characterized by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. All three hydrogel compositions reduced significantly (p = 0.05) initial attachment of zoospores of the green alga Ulva linza (up to 97%), cells of the diatom Navicula incerta (up to 58%) and the bacterium Cobetia marina (up to 62%), compared to a smooth PDMSe standard. A shear stress (45 Pa), generated in a water channel, eliminated up to 95% of the initially attached cells of Navicula from the smooth hydrogel surfaces relative to smooth PDMSe surfaces. Compared to the PDMSe standard, 79% of the cells of C. marina were removed from all smooth hydrogel compositions when exposed to a 50 Pa wall shear stress. Attachment of spores of the green alga Ulva to microtopographies replicated in PEGDMA-co-HEMA was also evaluated. The Sharklet AF microtopography patterned, PEGDMA-co-HEMA surfaces reduced attachment of spores of Ulva by 97% compared to a smooth PDMSe standard. The attachment densities of spores to engineered microtopographies in PDMSe and PEGDMA-co-HEMA were shown to correlate with a modified attachment model through the inclusion of a surface energy term. Attachment densities of spores of Ulva to engineered topographies replicated in a material other than PDMSe are now correlated with the attachment model (R2 = 0.80)

Clickable decellularized extracellular matrix as a new tool for building hybrid-hydrogels to model chronic fibrotic diseases in vitro

Fibrotic disorders account for over one third of mortalities worldwide. Despite great efforts to study the cellular and molecular processes underlying fibrosis, there are currently few effective therapies. Dual-stage polymerization reactions are an innovative tool for recreating heterogeneous increases in extracellular matrix (ECM) modulus, a hallmark of fibrotic diseases in vivo. Here, we present a clickable decellularized ECM (dECM) crosslinker incorporated into a dynamically responsive poly(ethylene glycol)-α-methacrylate (PEGαMA) hybrid-hydrogel to recreate ECM remodeling in vitro. An off-stoichiometry thiol-ene Michael addition between PEGαMA (8-arm, 10 kg mol-1) and the clickable dECM resulted in hydrogels with an elastic modulus of E = 3.6 ± 0.24 kPa, approximating healthy lung tissue (1-5 kPa). Next, residual αMA groups were reacted via a photo-initiated homopolymerization to increase modulus values to fibrotic levels (E = 13.4 ± 0.82 kPa) in situ. Hydrogels with increased elastic moduli, mimicking fibrotic ECM, induced a significant increase in the expression of myofibroblast transgenes. The proportion of primary fibroblasts from dual-reporter mouse lungs expressing collagen 1a1 and alpha-smooth muscle actin increased by approximately 60% when cultured on stiff and dynamically stiffened hybrid-hydrogels compared to soft. Likewise, fibroblasts expressed significantly increased levels of the collagen 1a1 transgene on stiff regions of spatially patterned hybrid-hydrogels compared to the soft areas. Collectively, these results indicate that hybrid-hydrogels are a new tool that can be implemented to spatiotemporally induce a phenotypic transition in primary murine fibroblasts in vitro

Disulfide disruption reverses mucus dysfunction in allergic airway disease

Airway mucus is essential for lung defense, but excessive mucus in asthma obstructs airflow, leading to severe and potentially fatal outcomes. Current asthma treatments have minimal effects on mucus, and the lack of therapeutic options stems from a poor understanding of mucus function and dysfunction at a molecular level and in vivo. Biophysical properties of mucus are controlled by mucin glycoproteins that polymerize covalently via disulfide bonds. Once secreted, mucin glycopolymers can aggregate, form plugs, and block airflow. Here we show that reducing mucin disulfide bonds disrupts mucus in human asthmatics and reverses pathological effects of mucus hypersecretion in a mouse allergic asthma model. In mice, inhaled mucolytic treatment loosens mucus mesh, enhances mucociliary clearance, and abolishes airway hyperreactivity (AHR) to the bronchoprovocative agent methacholine. AHR reversal is directly related to reduced mucus plugging. These findings establish grounds for developing treatments to inhibit effects of mucus hypersecretion in asthma