Super-Strong, Nonswellable, and Biocompatible Hydrogels Inspired by Human Tendons

Abstract

Fabricating artificial materials that mimic the structures and properties of tendons is of great significance. Possessing a tensile stress of approximately 10.0 MPa and a water content of around 60%, human tendons exhibit excellent mechanical properties to support daily functions. In contrast to tendons, most synthetic hydrogels with similar water content typically exclude qualified strength, swelling resistance, and biocompatibility. Herein, a facile strategy based on poly­(vinyl alcohol) (PVA) and tannic acid (TA) is demonstrated to tackle this problem via a combination of sequential steps including freezing–thawing PVA aqueous solutions to form crystalline regions, prestretching and air drying in confined conditions to induce anisotropic structures, soaking in TA solutions to form multiple hydrogen bondings between PVA and TA, and finally dialyzing against water for the removal of residual TA molecules and the rearrangements and homogenization of multiple hydrogen bonds. The obtained PVA hydrogels possess hierarchically anisotropic structures, where the alignment of PVA bundles promotes high modulus, while the hydrogen bonding between PVA and TA endows them with an energy dissipation mechanism. Benefitting from the synergy of material composition and structural engineering, the obtained hydrogel displays super-strong mechanics (a tensile stress of 19.3 MPa and a toughness of 32.1 MJ/m3), outperforming most tough hydrogels. Remarkably, this hydrogel demonstrates excellent swelling resistance. It barely expands after immersion in deionized water, phosphate-buffered saline (PBS), and SBF aqueous solutions for 7 days with the strength and volume nearly the same as their initial values. All of the features, combined with excellent cytocompatibility, make it an ideal material for biotechnological and biomedical applications.

Novel Trends in Hydrogel Development for Biomedical Applications: A Review

“…However, it has been proved by Pan et al that single PVA hydrogels do not efficiently support cell proliferation and lack antibacterial activity and elasticity [ 46 ]. Using cross-linking agents and combining PVA with natural polymers to improve their biological properties are current trends [ 46 , 47 , 48 , 49 , 138 ]. As to biological features, PVA-based hydrogels containing diphlorethohydroxycarmalol (DPHC) have been developed by Kim et al (2020) for wound healing applications, whose in vitro and in vivo evaluation on ICR mice demonstrated interesting antimicrobial properties against S. aureus and P. aeruginosa [ 50 ].…”

Janus Hydrogel to Mimic the Structure and Property of Articular Cartilage

“…The results showed that the obtained gel was suitable for cartilage substitutes (compressive strength around 10 MPa). The fracture energy and the fatigue threshold were estimated to be 47.4 kJ/m 2 and 715.3 J/m 2 for the J-HPCS-HAp gel (Figure S10), respectively, among top value of PVA hydrogels. ,− To compare our results with reported cartilage replacements, their performances were summarized in Figure d and Table S2. ,,,,, Clearly, the J-HPCS-HAp hydrogel was superior to the current hydrogels, especially in a combination of high strength, remarkable swelling resistance, low FC and osteoinductivity potential.…”

“…Mass ratios of C and O near the surface (47.88, 52.12%) were close to that at the middle (47.92, 52.08%), indicating even distribution. 7,35 Considering the ionic interactions are universal, we also immersed PVA/CS aerogel in aqueous solutions of sodium alginate (SA) and poly(acrylic acid) (PAAc). As shown in Figure S4, although the compressive strength and modulus of the PVA-CS-SA, PVA-CS-PAAc composited gels were better than the resultant HPCS pregel, their FCs were higher than the resultant HPCS pregel, due to the decline in water contents.…”

“…Since cartilage could not regenerate spontaneously, artificial replacements become alternative choices. Among those substitutes, hydrogels have been intensively studied because of their high water content, resemblance to the native extracellular matrix, good nutrition permeability, as well as a broad range of mechanic tunability. − An ideal hydrogel substitute should meet the following criteria: (i) excellent biocompatibility for surrounding cells and tissues to survive; (ii) stable mechanics and volumes in physiological environments to bear loads; (iii) low friction coefficient (FC) to minimize wear of adjacent surfaces; and (iv) osteogenesis potential to promote the combination with subchondral bone. − However, currently reported gels partially fulfill these requirements. − Consequently, it is urgent to manufacture hydrogels to integrate all these features, especially from commercially available materials.…”

Mechanical Gradients Enable Highly Stretchable Electronics Based on Nanofiber Substrates

“…Thereby, the mechanical gradient strategy of ICs (rigid)-PVA glue (high elastic modulus)-TPU nanofiber substrates (low elastic modulus)-LM (liquid) can be used to adapt the stretching of the devices. TPU is a commonly used elastic polymer in various industries due to its excellent mechanical and anti-biochemical properties. , Gallium-based LM is also favored by flexible electronics researchers due to its low toxicity, high electrical conductivity, and strong ductility. − PVA is the main ingredient in many commercial types of glue, which has excellent biocompatibility. , Its aqueous solution will become a flexible membrane with a high elastic modulus after drying. Through these mechanical gradients, we obtain ultra-stretchable (900%) flexible electronic devices with particularly stable and reliable joints, which also have good comfort, safety, and multilayer structure.…”