Smooth Muscle Stiffness Sensitivity is Driven by Soluble and Insoluble ECM Chemistry

Bioinspired, Artificial, Small-Diameter Vascular Grafts with Selective and Rapid Endothelialization Based on an Amniotic Membrane-Derived Hydrogel

Clinical application of the amniotic membrane (AM) in vascular reconstruction was limited by poor processability, rapid biodegradation, and insufficient hemocompatibility. In this work, decellularized AM was digested to a thermosensitive hydrogel and densely cross-linked in the nanoscale as "enhanced" collagenous fibers. Via N-(3-dimehylaminopropyl)-N'-ethylcarbodiimide and N-hydroxysuccinimide (EDC/NHS) catalysis, REDV was further grafted to simulate anticoagulant substances on naturally derived blood vessels. This modification approach endowed AM with rapid endothelialization and rare vascular restenosis. Through adjusting the fixation condition, the pore size and mechanical stability of the fiber network were approximate to those of natural tissues and precisely designed to fit for cell adhesion. AM was synchronously fixed by alginate dialdehyde (ADA) and EDC/NHS, forming a "double-cross-linked" stable structure with significantly improved mechanical strength and resistance against enzymic degradation. The hemolytic and platelet adhesion test indicated that ADA/REDV-AM could inhibit hemolysis and coagulation. It also exhibited excellent cytocompatibility. It selectively accelerated adsorption and migration of endothelial cells (ECs) while impeding adhesion and proliferation of smooth muscle cells (SMCs). It maintained EC superiority in competitive growth and avoided thrombosis in vivo. Furthermore, its property of promoting reconstruction and repair of blood vessels was proved in an animal experiment. Overall, the present study demonstrates that ADA/REDV-AM has potential application as a small-diameter artificial vascular intima with rapid endothelialization and reduced SMC/platelet adhesion.

Burn-Induced Impairment of Ileal Muscle Contractility Is Associated with Increased Extracellular Matrix Components

INTRODUCTION

Severe burns lead to marked impairment of gastrointestinal motility, such as delayed gastric emptying and small and large intestinal ileus. However, the cellular mechanism of these pathologic changes remains largely unknown.

METHODS

Male Sprague Dawley rats approximately 3 months old and weighing 300-350 g were randomized to either a 60% total body surface area full-thickness scald burn or sham procedure and were sacrificed 24 h after the procedure. Gastric emptying, gastric antrum contractility ileal smooth muscle contractility, and colonic contractility were measured. Muscularis externa was isolated from the ileal segment to prepare smooth muscle protein extracts for Western blot analysis.

RESULTS

Compared with sham controls, the baseline rhythmic contractile activities of the antral, ileal, and colonic smooth muscle strips were impaired in the burned rats. Simultaneously, our data showed that ileal muscularis ECM proteins fibronectin and laminin were significantly up-regulated in burned rats compared with sham rats. TGF-β signaling is an important stimulating factor for ECM protein expression. Our results revealed that TGF-β signaling was activated in the ileal muscle of burned rats evidenced by the activation of Smad2/3 expression and phosphorylation. In addition, the total and phosphorylated AKT, which is an important downstream factor of ECM signaling in smooth muscle cells, was also up-regulated in burned rats' ileal muscle. Notably, these changes were not seen in the colonic or gastric tissues.

CONCLUSION

Deposition of fibrosis-related proteins after severe burn is contributors to decreased small intestinal motility.

Adhesion G protein-coupled receptors: opportunities for drug discovery

Adhesion G protein-coupled receptors (aGPCRs) - one of the five main families in the GPCR superfamily - have several atypical characteristics, including large, multi-domain N termini and a highly conserved region that can be autoproteolytically cleaved. Although GPCRs overall have well-established pharmacological tractability, currently no therapies that target any of the 33 members of the aGPCR family are either approved or in clinical trials. However, human genetics and preclinical research have strengthened the links between aGPCRs and disease in recent years. This, together with a greater understanding of their functional complexity, has led to growing interest in aGPCRs as drug targets. A framework for prioritizing aGPCR targets and supporting approaches to develop aGPCR modulators could therefore be valuable in harnessing the untapped therapeutic potential of this family. With this in mind, here we discuss the unique opportunities and challenges for drug discovery in modulating aGPCR functions, including target identification, target validation, assay development and safety considerations, using ADGRG1 as an illustrative example.

Biomechanics and Mechanobiology of Saphenous Vein Grafts

Within several weeks of use as coronary artery bypass grafts (CABG), saphenous veins (SV) exhibit significant intimal hyperplasia (IH). IH predisposes vessels to thrombosis and atherosclerosis, the two major modes of vein graft failure. The fact that SV do not develop significant IH in their native venous environment coupled with the rapidity with which they develop IH following grafting into the arterial circulation suggests that factors associated with the isolation and preparation of SV and/or differences between the venous and arterial environments contribute to disease progression. There is strong evidence suggesting that mechanical trauma associated with traditional techniques of SV preparation can significantly damage the vessel and might potentially reduce graft patency though modern surgical techniques reduces these injuries. In contrast, it seems possible that modern surgical technique, specifically endoscopic vein harvest, might introduce other mechanical trauma that could subtly injure the vein and perhaps contribute to the reduced patency observed in veins harvested using endoscopic techniques. Aspects of the arterial mechanical environment influence remodeling of SV grafted into the arterial circulation. Increased pressure likely leads to thickening of the medial wall but its role in IH is less clear. Changes in fluid flow, including increased average wall shear stress, may reduce IH while disturbed flow likely increase IH. Nonmechanical stimuli, such as exposure to arterial levels of oxygen, may also have a significant but not widely recognized role in IH. Several potentially promising approaches to alter the mechanical environment to improve graft patency are including extravascular supports or altered graft geometries are covered.

Zwitterionic PEG-PC Hydrogels Modulate the Foreign Body Response in a Modulus-Dependent Manner

Reducing the foreign body response (FBR) to implanted biomaterials will enhance their performance in tissue engineering. Poly(ethylene glycol) (PEG) hydrogels are increasingly popular for this application due to their low cost, ease of use, and the ability to tune their compliance via molecular weight and cross-linking densities. PEG hydrogels can elicit chronic inflammation in vivo, but recent evidence has suggested that extremely hydrophilic, zwitterionic materials and particles can evade the immune system. To combine the advantages of PEG-based hydrogels with the hydrophilicity of zwitterions, we synthesized hydrogels with comonomers PEG and the zwitterion phosphorylcholine (PC). Recent evidence suggests that stiff hydrogels elicit increased immune cell adhesion to hydrogels, which we attempted to reduce by increasing hydrogel hydrophilicity. Surprisingly, hydrogels with the highest amount of zwitterionic comonomer elicited the highest FBR. Lowering the hydrogel modulus (165 to 3 kPa), or PC content (20 to 0 wt %), mitigated this effect. A high density of macrophages was found at the surface of implants associated with a high FBR, and mass spectrometry analysis of the proteins adsorbed to these gels implicated extracellular matrix, immune response, and cell adhesion protein categories as drivers of macrophage recruitment. Overall, we show that modulus regulates macrophage adhesion to zwitterionic-PEG hydrogels, and demonstrate that chemical modifications to hydrogels should be studied in parallel with their physical properties to optimize implant design.

Micromechanical characterization of soft, biopolymeric hydrogels: stiffness, resilience, and failure

Detailed understanding of the local structure-property relationships in soft biopolymeric hydrogels can be instrumental for applications in regenerative tissue engineering. Resilin-like polypeptide (RLP) hydrogels have been previously demonstrated as useful biomaterials with a unique combination of low elastic moduli, excellent resilience, and cell-adhesive properties. However, comprehensive mechanical characterization of RLP hydrogels under both low-strain and high-strain conditions has not yet been conducted, despite the unique information such measurements can provide about the local structure and macromolecular behavior underpinning mechanical properties. In this study, mechanical properties (elastic modulus, resilience, and fracture initiation toughness) of equilibrium swollen resilin-based hydrogels were characterized via oscillatory shear rheology, small-strain microindentation, and large-strain puncture tests as a function of polypeptide concentration. These methods allowed characterization, for the first time, of the resilience and failure in hydrogels with low polypeptide concentrations (<20 wt%), as the employed methods obviate the handling difficulties inherent in the characterization of such soft materials via standard mechanical techniques, allowing characterization without any special sample preparation and requiring minimal volumes (as low as 50 μL). Elastic moduli measured from small-strain microindentation showed good correlation with elastic storage moduli obtained from oscillatory shear rheology at a comparable applied strain rate, and evaluation of multiple loading-unloading cycles revealed decreased resilience values at lower hydrogel concentrations. In addition, large-strain indentation-to-failure (or puncture) tests were performed to measure large-strain mechanical response and fracture toughness on length scales similar to biological cells (∼10-50 μm) at various polypeptide concentrations, indicating very high fracture initiation toughness for high-concentration hydrogels. Our results establish the utility of employing microscale mechanical methods for the characterization of the local mechanical properties of biopolymeric hydrogels of low concentrations (<20 wt%), and show how the combination of small and large-strain measurements can provide unique insight into structure-property relationships for biopolymeric elastomers. Overall, this study provides new insight into the effects on local mechanical properties of polypeptide concentration near the overlap polymer concentration c* for resilin-based hydrogels, confirming their unique elastomeric features for applications in regenerative medicine.

Construction of cell-containing, anisotropic, three-dimensional collagen fibril scaffolds using external vibration and their influence on smooth muscle cell phenotype modulation

Numerous methods have been developed for preparing guiding channels/tracks to promote the alignment of highly oriented cell types. However, these manufacture methods cannot fabricate interconnected guiding channels within three-dimensional (3D) scaffolds. Providing a suitable architectural scaffold for cell attachment could lead cells to more rapidly display a desired phenotype and perform their unique functions. Previously, we developed a simple device composed of a pneumatic membrane that can generate a tunable vibration frequency to apply physical stimulation for fabricating a 3D aligned collagen fibril matrix with the characteristic D-period structure in one step. In the present study, we aimed to evaluate the cellular responses of thoracic aortic smooth muscle cells (A7r5) incorporated during the fabrication of 3D-aligned collagen fibrils with D-periods and compared these cells with those incorporated in a 3D, randomly distributed collagen matrix and in a two-dimensional (2D) aligned substrate after up to 10 days of culture. The results consistently demonstrated that A7r5 cells cultured within the 3D and 2D anisotropic matrices were aligned. Cells cultured in the 3D aligned scaffolds exhibited a higher proliferation rate as well as higher F-actin and smoothelin expression levels compared with cells cultured in 3D randomly distributed scaffolds. Together, these results indicate that a 3D-reconstituted, anisotropic collagen matrix fabricated by our process provides synergistic effects of tension stimulation and matrix stiffness on encapsulated cells and can direct A7r5 cells to transform from a synthetic phenotype into a contractile state.