Mechanical Properties Of Natural Tissue Research Articles

Highly resilient and fatigue-resistant poly(4-methyl-ε-caprolactone) porous scaffold fabricated via thiol-yne photo-crosslinking/salt-templating for soft tissue regeneration

Elastomeric scaffolds, individually customized to mimic the structural and mechanical properties of natural tissues have been used for tissue regeneration. In this regard, polyester elastic scaffolds with tunable mechanical properties and exceptional biological properties have been reported to provide mechanical support and structural integrity for tissue repair. Herein, poly(4-methyl-ε-caprolactone) (PMCL) was first double-terminated by alkynylation (PMCL-DY) as a liquid precursor at room temperature. Subsequently, three-dimensional porous scaffolds with custom shapes were fabricated from PMCL-DY via thiol-yne photocrosslinking using a practical salt template method. By manipulating the Mn of the precursor, the modulus of compression of the scaffold was easily adjusted. As evidenced by the complete recovery from 90% compression, the rapid recovery rate of >500 mm min−1, the extremely low energy loss coefficient of <0.1, and the superior fatigue resistance, the PMCL20-DY porous scaffold was confirmed to harbor excellent elastic properties. In addition, the high resilience of the scaffold was confirmed to endow it with a minimally invasive application potential. In vitro testing revealed that the 3D porous scaffold was biocompatible with rat bone marrow stromal cells (BMSCs), inducing BMSCs to differentiate into chondrogenic cells. In addition, the elastic porous scaffold demonstrated good regenerative efficiency in a 12-week rabbit cartilage defect model. Thus, the novel polyester scaffold with adaptable mechanical properties may have extensive applications in soft tissue regeneration.

Bioinspired stretchable helical nanofiber yarn scaffold for locomotive tissue dynamic regeneration

<h2>Summary</h2> Simulating the microstructure and mechanical properties of natural tissues to achieve rapid tissue regeneration and protect cells under strain during body movement is a giant challenge in locomotive tissue engineering. Here, we built a hierarchical helical scaffold with high stretchability, which not only structurally resembles natural tissues but also matches their non-affine deformation mechanical properties. The cells on this scaffold can maintain high viability under cyclic strains, because the non-planar motion of coil structures mitigates the local maximum strain during stretching. Moreover, the <i>in vivo</i> experiments demonstrated that the scaffold affords a stable structural and mechanical microenvironment for cell growth and tissue morphogenesis. This helical scaffold breaks the inherent mindset of fixation repairing and makes it possible for reconstruction of the defective tissue even in moderate motion. The study proposes a new thinking about construction of stretchable scaffolds with superior mechanical properties for repairing locomotive tissue injuries.

Alginate Hydrogels as Scaffolds and Delivery Systems to Repair the Damaged Spinal Cord.

Alginate (ALG) is a lineal hydrophilic polysaccharide present in brown algae cell walls, which turns into a gel state when hydrated. Gelation readily produces a series of three dimensional (3D) architectures like fibers, capillaries, and microspheres, used as biosensors and bio-actuators in a plethora of biomedical applications like drug delivery and wound healing. Hydrogels have made a great impact on regenerative medicine and tissue engineering because they are able to mimic the mechanical properties of natural tissues due to their high water content. Recent advances in neurosciences have led to promising strategies for repairing and/or regenerating the damaged nervous system. Spinal cord injury (SCI) is particularly challenging, owing to its devastating medical, human, and social consequences. Although effective therapies to repair the damaged spinal cord (SC) are still lacking, multiple pharmacological, genetic, and cell-based therapies are currently under study. In this framework, ALG hydrogels constitute a source of potential tools for the development of implants capable of promoting axonal growth and/or delivering cells or drugs at specific damaged sites, which may result in therapeutic strategies for SCI. In this mini-review, the current state of the art of ALG applications in neural tissues for repairing the damaged spinal cord is discussed.

Anisotropic Hybrid Hydrogels with Superior Mechanical Properties Reminiscent of Tendons or Ligaments

AbstractMimicking the hierarchically anisotropic structure and excellent mechanical properties of natural tissues, such as tendons and ligaments, using biomaterials is challenging. Despite recent achievements with anisotropic hydrogels, limitations remain because of difficulties in achieving both structural and mechanical characteristics simultaneously. A simple approach for fabricating hybrid hydrogels with a hierarchically anisotropic structure and superior mechanical properties that are reminiscent of tendons or ligaments is proposed. Alginate–polyacrylamide double‐network (DN) hydrogels incorporated with high aspect ratio mesoporous silica microparticles are stretched and fixed via subsequent drying and ionic crosslinking to achieve multiscale structures composed of an anisotropically aligned polymer network embedded with aligned microparticles. The mechanical properties of hydrogels can be further controlled by the degree of stretching, quantities, and functional groups of inorganic microparticles, and types of crosslinking cations. The subsequent reswelling results in a high water content (&gt;80%) similar to that of natural tendons while high strength, modulus, and toughness are maintained. The optimized anisotropic hybrid hydrogel exhibits a tensile modulus of 7.2 MPa, strength of 1.3 MPa, and toughness of 1.4 MJ m−3 even in the swollen state, which is 451‐, 27‐, and 2.2 times higher than that observed in the non‐swollen tough DN hydrogel. This study suggests a new strategy for fabricating anisotropic hydrogels with superior mechanical properties to develop new biomaterials for artificial tendons or ligaments.

Poly(vinyl alcohol co-vinyl acetate) as a novel scaffold for mammalian cell culture and controlled drug release

Tissue engineering requires novel smart materials to sustain cell growth, tissue regeneration and in situ drug release in a controlled mode. Also, biocompatible synthesis methods are needed to immobilize biologically active compounds. Poly(vinyl alcohol co-vinyl acetate) (PAcVA) was synthesized at 37 °C using glutaraldehyde (GA) as a crosslinking agent. The mechanical characteristics of the polymer were manipulated by varying crosslinking degrees using different GA concentrations. Materials with Young’s modules similar to soft tissues, adequate for tissue engineering, were obtained. PAcVA was a pH-responsive material with maximum swelling at pH 5.8. When hydrated, PAcVA was electro-responsive. Fluorescein was used as a model molecule to characterize the releasing properties of the polymer. Effective diffusivities were a function of the crosslinking degree. Release rates were proportional to temperature and were faster at lower GA contents. According to a fit to the Korsmeyer–Peppas’ model, diffusion at 5 and 10% GA was Fickian, but at 20% GA, diffusion was abnormal. To promote cell attachment and neutralize free aldehyde groups, PAcVA hydrogels were covered with poly-l-lysine and laminin, which supported growth of lung carcinoma and mouse hypothalamic cells without signs of cytotoxicity or oxidative stress. An intelligent low-cost hydrogel with properties that can be easily modulated was synthesized and fully characterized. Its properties make it suitable for tissue engineering applications, as they mimic the mechanical properties of natural tissues.

Recent Progress of Fabrication of Cell Scaffold by Electrospinning Technique for Articular Cartilage Tissue Engineering.

As a versatile nanofiber manufacturing technique, electrospinning has been widely employed for the fabrication of tissue engineering scaffolds. Since the structure of natural extracellular matrices varies substantially in different tissues, there has been growing awareness of the fact that the hierarchical 3D structure of scaffolds may affect intercellular interactions, material transportation, fluid flow, environmental stimulation, and so forth. Physical blending of the synthetic and natural polymers to form composite materials better mimics the composition and mechanical properties of natural tissues. Scaffolds with element gradient, such as growth factor gradient, have demonstrated good potentials to promote heterogeneous cell growth and differentiation. Compared to 2D scaffolds with limited thicknesses, 3D scaffolds have superior cell differentiation and development rate. The objective of this review paper is to review and discuss the recent trends of electrospinning strategies for cartilage tissue engineering, particularly the biomimetic, gradient, and 3D scaffolds, along with future prospects of potential clinical applications.

Design and characterization of dexamethasone-loaded poly (glycerol sebacate)-poly caprolactone/gelatin scaffold by coaxial electro spinning for soft tissue engineering

The aim of this research was to fabricate dexamethasone (Dex)-loaded poly (glycerol sebacate) (PGS)-poly (caprolactone) (PCL)/gelatin (Gt) (PGS-PCL/Gt-Dex) fibrous scaffolds in the form of core/shell structure which have potential application in soft tissues. In this regard, after synthesize and characterizations of PGS, PGS-PCL and gelatin fibrous scaffolds were separately developed in order to optimize the electrospinning parameters. In the next step, coaxial electrospun fibrous scaffold of PGS-PCL/Gt fibrous scaffold with PGS-PCL as core and Gt as shell was developed and its mechanical, physical and chemical properties were characterized. Moreover, degradability, hydrophilicity and biocompatibility of PGS-PCL/Gt fibrous scaffold were evaluated. In addition, Dex was encapsulated in PGS-PCL/Gt fibrous scaffold and drug release was assessed for tissue engineering application. Results demonstrated the formation of coaxial fibrous scaffold with average porosity of 79% and average fiber size of 294nm. Moreover, PGS-PCL/Gt fibrous scaffold revealed lower elastic modulus, ultimate tensile and ultimate elongation than those of PGS-PCL scaffold and more close to mechanical properties of natural tissue. Furthermore, lower contact angle of PGS-PCL/Gt than that of PGS-PCL demonstrated improved surface hydrophilicity of scaffold. DEX release was sustained over a period time of 30days from the scaffolds via three steps consisting of an initial burst release, secondary linear phase release pattern with slower rate over 20days followed by an apparent zero-order release phase. MTT observations demonstrated that there was no evidence of toxicity in the samples with and without Dex. Our findings indicated that core/shell PGS-PCL/Gt-Dex fibrous could be used as a carrier for the sustained release of drugs relevant for tissue engineering which makes it appropriate for soft tissue engineering.

Aliphatic polyester elastomers derived from erythritol and α,ω-diacids

Soft polyester elastomers have emerged as a promising family of biodegradable materials for drug delivery and tissue engineering. Specifically referring to soft tissue engineering, potential biomaterials should be elastic and flexible, so as to mimic the mechanical properties of natural tissue. Herein, we report the design of several elastomers based on the polycondensation of erythritol, a sugar substitute that is approved for human consumption by the Food and Drug Administration, and one of eight dicarboxylic acids: glutaric, adipic, pimelic, suberic, azelaic, sebacic, dodecanedioic, and tetradecanedioic acids. By varying the length of the diacid and the curing conditions, several elastomers were designed with a range of physical and mechanical properties. Poly(erythritol glutarate), poly(erythritol adipate), poly(erythritol pimelate), poly(erythritol suberate), poly(erythritol azelate), poly(erythritol sebacate) poly(erythritol dodecanedioate), and poly(erythritol tetradecanedioate) achieved Young's modulus, ultimate tensile stress, and rupture strain values of 0.08–80.37 MPa, 0.14–16.65 MPa, and 22–466%, respectively. Additionally, as tissue engineering may require the use of complex 3-dimensional designs, embossed films and porous films were designed in order to demonstrate the ease of processing. Hydrolytic degradation rates ranging from 100% in 3 weeks to 6.4% in 6 weeks were obtained in phosphate-buffered saline solutions at 37 °C. Finally, in vitro cytotoxicity was studied with Swiss albino 3T3 fibroblasts and human mesenchymal stem cells. Based on these results, we believe that the poly(erythritol dicarboxylate) series are excellent candidates for potential soft biomaterials.

Reciprocal interactions between cells and extracellular matrix during remodeling of tissue constructs

Cells remodel extracellular matrix during tissue development and wound healing. Similar processes occur when cells compress and stiffen collagen gels. An important task for cell biologists, biophysicists, and tissue engineers is to guide these remodeling processes to produce tissue constructs that mimic the structure and mechanical properties of natural tissues. This requires an understanding of the mechanisms by which this remodeling occurs. Quantitative measurements of the contractile force developed by cells and the extent of compression and stiffening of the matrix describe the results of the remodeling processes. Not only do forces exerted by cells influence the structure of the matrix but also external forces exerted on the matrix can modulate the structure and orientation of the cells. The mechanisms of these processes remain largely unknown, but recent studies of the regulation of myosin-dependent contractile force and of cell protrusion driven by actin polymerization provide clues about the regulation of cellular functions during remodeling.

Biomaterials: defining the mechanical properties of natural tissues and selection of replacement materials

This article reviews the problems which are encountered in defining the mechanical properties of natural tissues, and in replacing them with synthetic materials in the human body. It describes how death, ageing, degeneration, pathology and individual variability influence the properties of natural tissues. Experimental problems arise from degradation and testing conditions; these are illustrated by the properties of the nucleus pulposus of the intervertebral disc. Replacement of natural tissues by graft materials and the products of tissue engineering is then described. Synthetic replacement materials should be biocompatible, i.e. they should not cause adverse reactions in the human body. However, polymers which hydrolyse in the body fluids may be useful for implants which are intended to have a limited life or for controlled release of drugs. Synthetic implant materials may attempt to mimic natural tissues but there may be a problem of attaching them to the surrounding tissue. Artificial ligaments provide an example of implants of this kind. Total hip replacement is used to illustrate the successful use of conventional engineering materials. Finally, safety issues are described; an implant material must be biocompatible, have the required mechanical strength, be sterile and should be incorporated into a device so that its performance in the living patient can be monitored.