Anisotropic tough double network hydrogel from fish collagen and its spontaneous in vivo bonding to bone

The importance of 3D fibre architecture in cancer and implications for biomaterial model design

The need for improved prediction of clinical response is driving the development of cancer models with enhanced physiological relevance. A new concept of 'precision biomaterials' is emerging, encompassing patient-mimetic biomaterial models that seek to accurately detect, treat and model cancer by faithfully recapitulating key microenvironmental characteristics. Despite recent advances allowing tissue-mimetic stiffness and molecular composition to be replicated in vitro, approaches for reproducing the 3D fibre architectures found in tumour extracellular matrix (ECM) remain relatively unexplored. Although the precise influences of patient-specific fibre architecture are unclear, we summarize the known roles of tumour fibre architecture, underlining their implications in cell-matrix interactions and ultimately clinical outcome. We then explore the challenges in reproducing tissue-specific 3D fibre architecture(s) in vitro, highlighting relevant biomaterial fabrication techniques and their benefits and limitations. Finally, we discuss imaging and image analysis techniques (focussing on collagen I-optimized approaches) that could hold the key to mapping tumour-specific ECM into high-fidelity biomaterial models. We anticipate that an interdisciplinary approach, combining materials science, cancer research and image analysis, will elucidate the role of 3D fibre architecture in tumour development, leading to the next generation of patient-mimetic models for mechanistic studies and drug discovery.

In vivo assessment of marine vs bovine origin collagen-based composite scaffolds promoting bone regeneration in a New Zealand rabbit model

The ability of human tissues to self-repair is limited, which motivates the scientific community to explore new and better therapeutic approaches to tissue regeneration. The present manuscript provides a comparative study between a marine-based composite biomaterial, and another composed of well-established counterparts for bone tissue regeneration. Blue shark skin collagen was combined with bioapatite obtained from blue shark's teeth (mColl:BAp), while bovine collagen was combined with synthetic hydroxyapatite (bColl:Ap) to produce 3D composite scaffolds by freeze-drying. Collagens showed similar profiles, while apatite particles differed in their composition, being the marine bioapatite a fluoride-enriched ceramic. The marine-sourced biomaterials presented higher porosities, improved mechanical properties, and slower degradation rates when compared to synthetic apatite-reinforced bovine collagen. The in vivo performance regarding bone tissue regeneration was evaluated in defects created in femoral condyles in New Zealand rabbits twelve weeks post-surgery. Micro-CT results showed that mColl:BAp implanted condyles had a slower degradation and an higher tissue formation (17.9 ± 6.9 %) when compared with bColl:Ap implanted ones (12.9 ± 7.6 %). The histomorphometry analysis provided supporting evidence, confirming the observed trend by quantifying 13.1 ± 7.9 % of new tissue formation for mColl:BAp composites and 10.4 ± 3.2 % for bColl:Ap composites, suggesting the potential use of marine biomaterials for bone regeneration.

Swim bladder-derived biomaterials: structures, compositions, properties, modifications, and biomedical applications

Animal-derived biomaterials have been extensively employed in clinical practice owing to their compositional and structural similarities with those of human tissues and organs, exhibiting good mechanical properties and biocompatibility, and extensive sources. However, there is an associated risk of infection with pathogenic microorganisms after the implantation of tissues from pigs, cattle, and other mammals in humans. Therefore, researchers have begun to explore the development of non-mammalian regenerative biomaterials. Among these is the swim bladder, a fish-derived biomaterial that is rapidly used in various fields of biomedicine because of its high collagen, elastin, and polysaccharide content. However, relevant reviews on the biomedical applications of swim bladders as effective biomaterials are lacking. Therefore, based on our previous research and in-depth understanding of this field, this review describes the structures and compositions, properties, and modifications of the swim bladder, with their direct (including soft tissue repair, dural repair, cardiovascular repair, and edible and pharmaceutical fish maw) and indirect applications (including extracted collagen peptides with smaller molecular weights, and collagen or gelatin with higher molecular weights used for hydrogels, and biological adhesives or glues) in the field of biomedicine in recent years. This review provides insights into the use of swim bladders as source of biomaterial; hence, it can aid biomedicine scholars by providing directions for advancements in this field.

The Toughness-Enhanced Atelocollagen Double-Network Gel for Biomaterials

A tough gel composed of atelocollagen, which lacks an immunogenetic site, is a promising material for biomedical application. In this study, we created a composite hydrogel composed of atelocollagen gel cross-linked with glutaraldehyde (GA) and poly-(N,N-dimethylacrylamide) gel exhibiting biocompatibility based on the double-network (DN) gel principle. The tensile toughness of atelocollagen gel remained constant regardless of the amount of cross-linker (GA) used. In contrast, tensile tests of the DN gel indicated that mechanical properties, such as fracture stress and toughness, were significantly higher than those of the atelocollagen gel. Moreover, fibroblast cells adhered and spread on the gels, the Schiff bases of which were treated via reductive amination for detoxification from GA. These findings demonstrate the potential of the proposed gel materials as artificial alternative materials to soft tissues with sub-MPa fracture stress.

Construction and Properties of High-Toughness Soft-Soft Interfaces Based on the Adhesion of Natural Polyphenols

Artificial joint replacement is the most effective way to treat osteoarthritis. However, these artificial joints are too stiff with high interfacial contact stress and poor surface lubrication, resulting in stress shielding and severe wear and tear lead to an extremely high failure rate. At present, hydrogels are considered the most promising substitute for artificial joint prostheses owing to their good biocompatibility, adjustable mechanical properties, and excellent flexibility. Nevertheless, a traditional single-layer hydrogel has poor bearing capacity and lubrication, which are far from the properties of natural articular cartilage. The high strength and low friction properties of natural articular cartilage are based on its own multilayer fibrous structure. Therefore, by simulating the multilayer structure of natural cartilage, a bilayer bionic cartilage hydrogel was prepared; that is, the upper hydrogel realized excellent lubrication and the lower hydrogel realized high load-bearing capacity. However, the interface binding of bilayer hydrogels is a challenge at present. Therefore, the interfacial adhesion of the bilayer hydrogel is improved by adding tannic acid (TA) based on the adhesion of the natural polyphenol structure. The average interfacial toughness reaches 3650 J/m2, and the average interfacial shear force reaches 800 kPa. In the preparation of the bilayer hydrogel, taking advantage of the coordination reaction between TA and metal cations, Fe3+ is further added to endow the bilayer hydrogel with excellent mechanical properties and good sliding friction performance. Therefore, this work opens up a new way to construct cartilage-like materials with high toughness and a soft-soft interface.

Strategies for Anisotropic Fibrillar Hydrogels: Design, Cell Alignment, and Applications in Tissue Engineering

Efficient cellular alignment in biomaterials presents a considerable challenge, demanding the refinement of appropriate material morphologies, while ensuring effective cell-surface interactions. To address this, biomaterials are continuously researched with diverse coatings, hydrogels, and polymeric surfaces. In this context, we investigate the influence of physicochemical parameters on the architecture of fibrillar hydrogels that significantly orient the topography of flexible hydrogel substrates, thereby fostering cellular adhesion and spatial organization. Our Review comprehensively assesses various techniques for aligning polymer fibrils within hydrogels, specifically interventions applied during and after the cross-linking process. These methodologies include mechanical strains, precise temperature modulation, controlled fluidic dynamics, and chemical modulators, as well as the use of magnetic and electric fields. We highlight the intrinsic appeal of these methodologies in fabricating cell-aligning interfaces and discuss their potential implications within the fields of biomaterials and tissue engineering, particularly concerning the pursuit of optimal cellular alignment.

Current advances in anisotropic structures for enhanced osteogenesis

Bone defects are a challenge to healthcare systems, as the aging population experiences an increase in bone defects. Despite the development of biomaterials for bone fillers and scaffolds, there is still an unmet need for a bone-mimetic material. Cortical bone is highly anisotropic and displays a biological liquid crystalline (LC) arrangement, giving it exceptional mechanical properties and a distinctive microenvironment. However, the biofunctions, cell-tissue interactions, and molecular mechanisms of cortical bone anisotropic structure are not well understood. Incorporating anisotropic structures in bone-facilitated scaffolds has been recognised as essential for better outcomes. Various approaches have been used to create anisotropic micro/nanostructures, but biomimetic bone anisotropic structures are still in the early stages of development. Most scaffolds lack features at the nanoscale, and there is no comprehensive evaluation of molecular mechanisms or characterisation of calcium secretion. This manuscript provides a review of the latest development of anisotropic designs for osteogenesis and discusses current findings on cell-anisotropic structure interactions. It also emphasises the need for further research. Filling knowledge gaps will enable the fabrication of scaffolds for improved and more controllable bone regeneration.

Double network hydrogels: Design, fabrication, and application in biomedicines and foods

Research on the design, fabrication, and application of double network (DN) hydrogels, assembled from pairs of polymers, has grown recently due to their unique structural, physicochemical, and functional properties. DN hydrogels can be designed to exhibit a broader range of functional attributes than single network (SN) ones, which extends their applications in various fields. There has been strong interest in the development of biopolymer DN hydrogels because of their environmental, sustainability, and safety benefits. However, there is limited knowledge on the formation and application of these novel materials. This article reviews the principles underlying the design and fabrication of hydrogels using different crosslinking approaches, including covalent and/or non-covalent bonding, and the formation mechanisms, network structures, and functional attributes of different DN hydrogels. The impact of polymer composition, structural organization, and bonding on the mechanical and functional properties of DN hydrogels is reviewed. Potential applications of these hydrogels are highlighted, including in tissue engineering, biomedicines, and foods. The functional attributes of DN hydrogels can be tailored to each of these applications by careful selection of the biopolymers and crosslinking mechanisms used to assemble them. Finally, areas where further research are needed to overcome the current limitations of DN hydrogels are highlighted.

Protein-Based Hydrogels and Their Biomedical Applications

Hydrogels made from proteins are attractive materials for diverse medical applications, as they are biocompatible, biodegradable, and amenable to chemical and biological modifications. Recent advances in protein engineering, synthetic biology, and material science have enabled the fine-tuning of protein sequences, hydrogel structures, and hydrogel mechanical properties, allowing for a broad range of biomedical applications using protein hydrogels. This article reviews recent progresses on protein hydrogels with special focus on those made of microbially produced proteins. We discuss different hydrogel formation strategies and their associated hydrogel properties. We also review various biomedical applications, categorized by the origin of protein sequences. Lastly, current challenges and future opportunities in engineering protein-based hydrogels are discussed. We hope this review will inspire new ideas in material innovation, leading to advanced protein hydrogels with desirable properties for a wide range of biomedical applications.

Gelation and Orientation Dynamics Induced by Contact of Protein Solution with Transglutaminase Solution

Gel growth induced by contact of polymer solutions with crosslinker solutions yields an emerging class of anisotropic materials with many potential applications. Here, we report the case of a study on the dynamics in forming anisotropic gels using this approach with an enzyme as a trigger of gelation and gelatin as the polymer. Unlike the previously studied cases of gelation, the isotropic gelation was followed by gel polymer orientation after a lag time. The isotropic gelation dynamics did not depend on concentrations of the polymer turning into gel and of the enzyme inducing gelation, whereas, for the anisotropic gelation, the square of the gel thickness was a linear function of the elapsed time, and the slope increased with polymer concentration. The gelation dynamics of the present system was explained by a combination of diffusion-limited gelation followed by free-energy-limited orientation of polymer molecules.

Remotely Controlled Light/Electric/Magnetic Multiresponsive Hydrogel for Fast Actuations

As a kind of soft smart material, hydrogel actuators have extensive development prospects, but it is still difficult for these actuators to integrate multiresponsiveness, multiple remote actuation, high strength, fast responsiveness, and programmable complex deformation. Herein, we have explored an anisotropic bilayer hydrogel actuator with an Fe3O4/co-poly(isopropylacrylamide-4-benzoylphenyl acrylate) [Fe3O4/P(NIPAM-ABP)] active layer and an isotropic conductive adhesive (ICAs) passive layer based on the layer-by-layer method. Benefiting from the fibrosis and porosity of the Fe3O4/P(NIPAM-ABP) hydrogel, the ICAs-Fe3O4/P(NIPAM-ABP) hydrogel actuator has excellent mechanical strength (tensile strength of 3.1 ± 0.3 MPa) and response speed (temperature (45 °C): bending speed of 2400.3°/s; near-infrared (NIR) light: bending speed of 356.4°/s; electricity (2 V): bending speed of 180°/s; water (10 °C): recovery speed of 30.0°/s). In addition, the good photothermal properties and magnetic conductivity of Fe3O4 nanoparticles provide precise remotely controllable light- and magnetic-actuated properties for the hydrogel actuator. The Ag microsheets with excellent conductivity (1.4 × 104 S/cm) provide remotely controllable electrical-actuated property for the hydrogel actuator. Combined with the responsiveness of P(NIPAM-ABP), the actuator can achieve short-range actuation including temperature-, ethanol-, and salt-responses. More importantly, it can achieve remote actuation including light, electrical, and magnetic responses. Finally, the Fe3O4/P(NIPAM-ABP) fibers can provide excellent anisotropic structures for the actuator to achieve precise deformational programmability. Inspired by some phenomena in nature, several actuating devices with the above characteristics have been successfully developed. This study can provide a general method for multifunctional anisotropic hydrogel actuators and will provide a new strategy for exploring smart materials suitable for complex bioinspired systems.

Interpenetrated Biosurfactant-Biopolymer Orthogonal Hydrogels: The Biosurfactant's Phase Controls the Hydrogel's Mechanics

Controlling the viscoelastic properties of hydrogels is a challenge for many applications. Low molecular weight gelators (LMWGs) like bile salts and glycolipids and biopolymers like chitosan and alginate are good candidates for developing fully biobased hybrid hydrogels that combine the advantages of both components. Biopolymers lead to enhanced mechanics, while LMWGs add functionality. In this work, hybrid hydrogels are composed of biopolymers (gelatin, chitosan, and alginate) and microbial glycolipid bioamphiphiles, known as biosurfactants. Besides their biocompatibility and natural origin, bioamphiphiles can present chameleonic behavior, as pH and ions control their phase diagram in water around neutrality under strongly diluted conditions (<5 wt%). The glycolipid used in this work behaves like a surfactant (micellar phase) at high pH or like a phospholipid (vesicle phase) at low pH. Moreover, at neutral-to-alkaline pH in the presence of calcium, it behaves like a gelator (fiber phase). The impact of each of these phases on the elastic properties of biopolymers is explored by means of oscillatory rheology, while the hybrid structure is studied by small angle X-ray scattering. The micellar and vesicular phases reduce the elastic properties of the hydrogels, while the fiber phase has the opposite effect; it enhances the hydrogel's strength by forming an interpenetrated biopolymer-LMWG network.

PVA/pectin composite hydrogels inducing osteogenesis for bone regeneration

Hydrogels composed from biomolecules have gained great interests as biomaterials for tissue engineering. However, their poor mechanical properties limit their application potential. Here, we synthesized a series of tough composite hydrogels from poly (vinyl alcohol) (PVA) and pectin for bone tissue engineering. With a balance of scaffold stiffness and pore size, PVA-Pec-10 hydrogel enhanced adhesion and proliferation of osteoblasts. The hydrogel significantly promoted osteogenesis in vitro by improving the alkaline phosphates (ALP) activity and calcium biomineralization, as well as upregulating the expressions of osteoblastic genes. The composite hydrogel also accelerated the bone healing process in vivo after transplantation into the femoral defect. Additionally, our study demonstrated that pectin and its Ca²⁺ crosslinking network play a crucial role of inducing osteogenesis through regulating the Ca²⁺/CaMKII and BMP-SMAD1/5 signaling. The optimized structure composition and multifunctional properties make PVA-Pec hydrogel highly promising to serve as a candidate for bone tissue regeneration.

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Recoverable PVA-Pec hydrogel is prepared by the freezing-thawing process.

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PVA-Pec-10 hydrogel display well attachment and osteogenesis capacity.

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PVA-Pecl-10 hydrogel enhanced osteogenesis by Ca²⁺/CaMKII and BMP-SMAD1/5 signaling.

Bilayer Hydrogels with Low Friction and High Load-Bearing Capacity by Mimicking the Oriented Hierarchical Structure of Cartilage

Natural articular cartilages exhibit extraordinary lubricating properties and excellent load-bearing capacity based on their penetrated surface lubricated biomacromolecules and gradient-oriented hierarchical structure. Hydrogels are considered as the most promising cartilage replacement materials due to their excellent flexibility, good biocompatibility, and low friction coefficient. However, the construction of high-strength, low-friction hydrogels to mimic cartilage is still a great challenge. Here, inspired by the structure and functions of natural articular cartilage, anisotropic hydrogels with horizontal and vertical orientation structure were constructed layer by layer and bonded with each other, successfully developing a bilayer oriented heterogeneous hydrogel with a high load-bearing capacity, low friction, and excellent fatigue resistance. The bilayer hydrogel exhibited a high compressive strength of 5.21 ± 0.45 MPa and a compressive modulus of 4.06 ± 0.31 MPa due to the enhancement mechanism of the anisotropic structure within the bottom anisotropic hydrogel. Moreover, based on the synergistic effect of the high load-bearing capacity of the bottom layer and the lubrication of the surface layer, the bilayer hydrogel possesses excellent biotribological properties in hard/soft (0.032) and soft/soft (0.028) contact, which is close to that of natural cartilage. It is worth noting that the bilayer oriented heterogeneous hydrogel is able to withstand repeated loading without fatigue crack. Therefore, this work could open up a new avenue for constructing cartilage-like materials with both high strength and low friction.

Aligned nanofibrous collagen membranes from fish swim bladder as a tough and acid-resistant suture for pH-regulated stomach perforation and tendon rupture

Background

Wound closure in the complex body environment places higher requirements on suture’s mechanical and biological performance. In the scenario of frequent mechanical gastric motility and extremely low pH, single functional sutures have limitations in dealing with stomach bleeding trauma where the normal healing will get deteriorated in acid. It necessitates to advance suture, which can regulate wounds, resist acid and intelligently sense stomach pH.

Methods

Based on fish swim bladder, a double-stranded drug-loaded suture was fabricated. Its cytotoxicity, histocompatibility, mechanical properties, acid resistance and multiple functions were verified. Also, suture’s performance suturing gastric wounds and Achilles tendon was verified in an in vivo model.

Results

By investigating the swim bladder’s multi-scale structure, the aligned tough collagen fibrous membrane can resist high hydrostatic pressure. We report that the multi-functional sutures on the twisted and aligned collagen fibers have acid resistance and low tissue reaction. Working with an implantable “capsule robot”, the smart suture can inhibit gastric acid secretion, curb the prolonged stomach bleeding and monitor real-time pH changes in rabbits and pigs. The suture can promote stomach healing and is strong enough to stitch the fractured Achilles tendon.

Conclusions

As a drug-loaded absorbable suture, the suture shows excellent performance and good application prospect in clinical work.

Properties of Grass Carp (Ctenopharyngodon idella) Collagen and Gel for Application in Biomaterials

The biochemical properties of collagens and gels from grass carp (Ctenopharyngodon idella) were studied to explore the feasibility of their application in biomaterials. The yields of skin collagen (SC) and swim bladder collagen (SBC) extracted from grass carp were 10.41 ± 0.67% and 6.11 ± 0.12% on a wet basis, respectively. Both collagens were characterized as type I collagen. Denaturation temperatures of SC and SBC were 37.41 ± 0.02 °C and 39.82 ± 0.06 °C, respectively. SC and SBC had high fibril formation ability in vitro, and higher values of salinity (NaCl, 0-280 mM) and pH (6-8) in formation solution were found to result in faster self-assembly of SC and SBC fibrils as well as thicker fibrils. Further tests of SC gels with regular morphology revealed that their texture properties and water content were affected by pH and NaCl concentration. The hardness, springiness, and cohesiveness of SC gels increased and the chewiness and water content decreased as pH increased from 7 to 8 and NaCl concentration increased from 140 to 280 mM. These properties suggest that collagens from grass carp may be useful in biomaterial applications in the future.

Research progress of cartilage lubrication and biomimetic cartilage lubrication materials

Human joints move thousands of times a day. The articular cartilage plays a vital role in joints’ protection. If there is dysfunction in cartilage lubrication, cartilage cannot maintain its normal function. Eventually, the dysfunction may bring about osteoarthritis (OA). Extensive researches have shown that fluid film lubrication, boundary lubrication, and hydration lubrication are three discovered lubrication models at cartilage surface, and analyzing and simulating the mechanism of cartilage lubrication are fundamental to the treatment of OA. This essay concludes recent researches on the progress of cartilage lubrication and biomimetic cartilage, revealing the pathophysiology of cartilage lubrication and updating bio-inspired cartilage lubrication applications.

Engineering immunomodulatory hydrogels and cell-laden systems towards bone regeneration

The well-known synergetic interplay between the skeletal and immune systems has changed the design of advanced bone tissue engineering strategies. The immune system is essential during the bone lifetime, with macrophages playing multiple roles in bone healing and biomaterial integration. If in the past, the most valuable aspect of implants was to avoid immune responses of the host, nowadays, it is well-established how important are the crosstalks between immune cells and bone-engineered niches for an efficient regenerative process to occur. For that, it is essential to recapitulate the multiphenotypic cellular environment of bone tissue when designing new approaches. Indeed, the lack of osteoimmunomodulatory knowledge may be the explanation for the poor translation of biomaterials into clinical practice. Thus, smarter hydrogels incorporating immunomodulatory bioactive factors, stem cells, and immune cells are being proposed to develop a new generation of bone tissue engineering strategies. This review highlights the power of immune cells to upgrade the development of innovative engineered strategies, mainly focusing on orthopaedic and dental applications.

Hydroxyapatite-Integrated, Heparin- and Glycerol-Functionalized Chitosan-Based Injectable Hydrogels with Improved Mechanical and Proangiogenic Performance

The investigation of natural bioactive injectable composites to induce angiogenesis during bone regeneration has been a part of recent minimally invasive regenerative medicine strategies. Our previous study involved the development of in situ-forming injectable composite hydrogels (Chitosan/Hydroxyapatite/Heparin) for bone regeneration. These hydrogels offered facile rheology, injectability, and gelation at 37 °C, as well as promising pro-angiogenic abilities. In the current study, these hydrogels were modified using glycerol as an additive and a pre-sterile production strategy to enhance their mechanical strength. These modifications allowed a further pH increment during neutralisation with maintained solution homogeneity. The synergetic effect of the pH increment and further hydrogen bonding due to the added glycerol improved the strength of the hydrogels substantially. SEM analyses showed highly cross-linked hydrogels (from high-pH solutions) with a hierarchical interlocking pore morphology. Hydrogel solutions showed more elastic flow properties and incipient gelation times decreased to just 2 to 3 min at 37 °C. Toluidine blue assay and SEM analyses showed that heparin formed a coating at the top layer of the hydrogels which contributed anionic bioactive surface features. The chick chorioallantoic membrane (CAM) assay confirmed significant enhancement of angiogenesis with chitosan-matrixed hydrogels comprising hydroxyapatite and small quantities of heparin (33 µg/mL) compared to basic chitosan hydrogels.

A self-healing, recyclable and conductive gelatin/nanofibrillated cellulose/Fe3+ hydrogel based on multi-dynamic interactions for a multifunctional strain sensor

Conductive hydrogels have emerged as promising material candidates for multifunctional strain sensors, attributed to their similarity to biological tissues, good wearability, and high accuracy of information acquisition. However, it is difficult to simultaneously manufacture conductive hydrogel-based multifunctional strain sensors with the synergistic properties of reliable healability for long-term usage and environmental degradability/recyclability for decreasing the electronic waste. This work reports a facile strategy to engineer a self-healing, recyclable and conductive strain sensor by virtue of molecular-level multi-dynamic interactions (MMDIs) including Schiff base complexes, hydrogen bonds, and coordination bonds, which were fabricated using a dialdehyde TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl)-oxidized nanofibrillated cellulose (DATNFC) pre-reinforced gelatin nanocomposite hydrogel (gelatin/DATNFC hydrogel, GDH) followed by dipping in an Fe³⁺ aqueous solution. The MMDI strategy allows synchronous regulation of both bulk and interfacial interactions to obtain exciting properties that outperform those of conventional hydrogels, including extraordinary compressive stress (1310 kPa), intriguing self-healing abilities, and remarkable electrical conductivity. With these outstanding merits, the as-prepared gelatin/DATNFC/Fe³⁺ hydrogel (GDIH) is developed to be a multifunctional strain sensor with appealing strain sensitivity (GF = 2.24 under 6% strain) and compressive sensitivity (S = 1.14 kPa^-1 under 15 kPa), which can be utilized to manufacture electronic skin and accurately discern subtle bodily motions, handwriting and personal signatures. Notably, this GDIH-based sensor also exhibited reliable self-healing properties for long-term usage, environmental degradability and complete recyclability for decreasing the electronic waste. In consideration of the extremely facile preparation process, biocompatibility, satisfactory functionalities, remarkable self-healing properties and recyclability, the emergence of the GDIH-based sensor is believed to propose a new strategy for the development of sustainable-multifunctional strain sensors and healthcare monitoring.

Stretchable, Adhesive, Self-Healable, and Conductive Hydrogel-Based Deformable Triboelectric Nanogenerator for Energy Harvesting and Human Motion Sensing

Hydrogels that combine the integrated attributes of being adhesive, self-healable, deformable, and conductive show great promise for next-generation soft robotic/energy/electronic applications. Herein, we reported a dual-network polyacrylamide (PAAM)/poly(acrylic acid) (PAA)/graphene (GR)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) (MAGP) conductive hydrogel composed of dual-cross-linked PAAM and PAA as well as PEDOT:PSS and GR as a conducting component that combines these features. A wearable strain sensor is fabricated by sandwiching the MAGP hydrogels between two dielectric carbon nanotubes (CNTs)/poly(dimethylsiloxane) (PDMS) layers, which can be utilized to monitor delicate and vigorous human motion. In addition, the hydrogel-based sensor can act as a deformable triboelectric nanogenerator (D-TENG) for harvesting mechanical energy. The D-TENG demonstrates a peak output voltage and current of 141 V and 0.8 μA, respectively. The D-TENG could easily light 52 yellow-light-emitting diodes (LEDs) simultaneously and demonstrated the capability to power small electronics, such as a hygrometer thermometer. This work provides a potential approach for the development of deformable energy sources and self-powered strain sensors.

Aldehyde-methacrylate-hyaluronan profited hydrogel system integrating aligned and viscoelastic cues for neurogenesis

Either oriented architecture or viscoelasticity is pivotal to neurogenesis, thus, native neural extracellular matrix derived-hyaluronan hydrogels with nano-orientation and viscoelasticity recapitulated might be instructive for neurogenesis, however it is still unexploited. Herein, based on aldehyde-methacrylate difunctionalized hyaluronan, by integrating imine kinetic modulation and microfluidic biofabrication, we construct a hydrogel system with orthogonal viscoelasticity and nano-topography. We then find the positive synergy effects of matrix nano-orientation and viscoelasticity not only on neurites outgrowth and elongation of neural cells, but also on neuronal differentiation of stem cells. Moreover, by implanting viscoelastic and nano-aligned hydrogels into lesion sites, we demonstrate the enhanced repair of spinal cord injury, including ameliorated pathological microenvironment, facilitated endogenous neurogenesis and functional axons regeneration as well as motor function restoration. This work supplies universal platform for preparing neuronal inducing hyaluronan-based hydrogels which might serve as promising therapeutic strategies for nerve injury.

Natural Biomaterials from Biodiversity for Healthcare Applications

Natural biomaterials originating during the growth cycles of all living organisms have been used for many applications. They span from bioinert to bioactive materials including bioinspired ones. As they exhibit an increasing degree of sophistication, natural biomaterials have proven suitable to address the needs of the healthcare sector. Here the different natural healthcare biomaterials, their biodiversity sources, properties, and promising healthcare applications are reviewed. The variability of their properties as a result of considered species and their habitat is also discussed. Finally, some limitations of natural biomaterials are discussed and possible future developments are provided as more natural biomaterials are yet to be discovered and studied.

Multicomponent chiral hydrogel fibers with block configurations based on the chiral liquid crystals of cellulose nanocrystals and M13 bacteriophages

Integrating the advantages unique to CNCs and the M13 virus into blockwise chiral hydrogel fibers, which have block dependent chiral fingerprints, birefringence, (de)swelling behaviors, mechanical strength and stretchability.

Therapeutic application of 3B-PEG injectable hydrogel/Nell-1 composite system to temporomandibular joint osteoarthritis

This study aims to construct a composite system of the tri-block polyethylene glycol injectable hydrogel (3B-PEG IH) and neural epithelial growth factor-like protein 1 (Nell-1), and to analyze its therapeutic effect on temporomandibular joint osteoarthritis (TMJOA). Sol-gel transition temperature was measured via inverting test. The viscoelastic modulus curves was measured by rheometer. Degradation and controlled release profiles of 3B-PEG IH were drawnin vitro.In vivogel retention and biocompatibility were completed subcutaneously on the back of rats. After primary chondrocytes were extracted and identified, the cell viability in 3B-PEG IH was measured. Evaluation of gene expression in hydrogel was performed by real-time polymerase chain reaction. TMJOA rabbits were established by intra-articular injection of type II collagenase. Six weeks after composite systems being injected, gross morphological score, micro-CT, histological staining and grading were evaluated. The rusults showed that different types of 3B-PEG IH all reached a stable gel state at 37 °C and could support the three-dimensional growth of chondrocytes, but poly(lactide-co-caprolactone)-block-poly(ethyleneglycol)-block-poly(lactide-co-caprolactone) (PLCL-PEG-PLCL) hydrogel had a wider gelation temperature range and better hydrolytic stability for about 4 weeks. Its controlled release curve is closest to the zero-order release kinetics.In vitro, PLCL-PEG-PLCL/Nell-1 could promote the chondrogenic expression and reduce the inflammatory expression.In vivo, TMJOA rabbits were mainly characterized by the disorder of cartilage structure and the destruction of subchondral bone. However, PLCL-PEG-PLCL/Nell-1 could reverse the destruction of the subchondral trabecula, restore the fibrous and proliferative layers of the surface, and reduce the irregular hyperplasia of fibrocartilage layer. In conclusion, by comparing the properties of different 3B-PEG IH, 20 wt% PLCL-PEG-PLCL hydrogel was selected as the most appropriate material. PLCL-PEG-PLCL/Nell-1 composite could reverse osteochondral damage caused by TMJOA, Nfatc1-Runx3 signaling pathway may play a role in it. This study may provide a novel, minimally-invasive therapeutic strategy for the clinical treatment of TMJOA.

Collagen-based biocomposites inspired by bone hierarchical structures for advanced bone regeneration: ongoing research and perspectives

Bone is a hard-connective tissue composed of matrix, cells and bioactive factors with a hierarchical structure, where the matrix is mainly composed of type I collagen and hydroxyapatite. Collagen fibers assembled by collagen are the template for mineralization and make an important contribution to bone formation and the bone remodeling process. Therefore, collagen has been widely clinically used for bone/cartilage defect regeneration. However, pure collagen implants, such as collagen scaffolds or sponges, have limitations in the bone/cartilage regeneration process due to their poor mechanical properties and osteoinductivity. Different forms of collagen-based composites prepared by incorporating natural/artificial polymers or bioactive inorganic substances are characterized by their interconnected porous structure and promoting cell adhesion, while they improve the mechanical strength, structural stability and osteogenic activities of the collagen matrix. In this review, various forms of collagen-based biocomposites, such as scaffolds, sponges, microspheres/nanoparticles, films and microfibers/nanofibers prepared by natural/synthetic polymers, bioactive ceramics and carbon-based materials compounded with collagen are reviewed. In addition, the application of collagen-based biocomposites as cytokine, cell or drug (genes, proteins, peptides and chemosynthetic) delivery platforms for proangiogenesis and bone/cartilage tissue regeneration is also discussed. Finally, the potential application, research and development direction of collagen-based biocomposites in future bone/cartilage tissue regeneration are discussed.

Dynamic bonds enable high toughness and multifunctionality in gelatin/tannic acid-based hydrogels with tunable mechanical properties

Biopolymer-based functional hydrogels with excellent mechanical properties are desired, but their fabrication remains a challenge. Learning from the tofu-making process, we developed a freely formable hydrogel with high toughness and stiffness from the hydrogen bond-rich coacervation of tannic acid and gelatin through a simple hot-pressing process that transforms the coacervate particles into a bulk hydrogel. The mechanical properties of the obtained gelatin/tannic acid hydrogel (G/T gel) can be controlled by tuning the weight ratio of tannic acid to gelatin in the gel. The G/T gel with optimum mechanical properties possesses high Young's modulus, fracture strain, and fracture energy of ∼60 MPa, ∼10, and ∼24 kJ m^-2, respectively. These properties arise from the phase-separated structure and high concentration of dynamic hydrogen bonds with widely distributed bond strengths. These dynamic hydrogen bonds also enable multifunctional properties of the gel, such as self-recovery, self-healing, rebuildability and shape memory. The combination of excellent mechanical properties, good biocompatibility, and useful functionalities into one hydrogel that comes from renewable sources demonstrates the great potential of G/T gels.

An injectable bioink with rapid prototyping in the air andin-situmild polymerization for 3D bioprinting

Bioprinting is an attractive technology for building tissues from scratch to explore entire new cell configurations, which brings numerous opportunities for biochemical research such as engineering tissues for therapeutic tissue repair or drug screening. However, bioprinting is faced with the limited number of suitable bioinks that enable bioprinting with excellent printability, high structural fidelity, physiological stability, and good biocompatibility, particularly in the case of extrusion-based bioprinting. Herein, we demonstrate a composite bioink based on gelatin, bacterial cellulose (BC), and microbial transglutaminase (mTG enzyme) with outstanding printing controllability and durable architectural integrity. BC, as a rheology modifier and mechanical enhancer component, endows the bioink with shear-thinning behavior. Moreover, the printed structure becomes robust under physiological conditions owing to thein situchemical crosslinking catalyzed by mTG enzyme. Lattice, bowl, meniscus, and ear structures are printed to demonstrate the printing feasibility of such a composite bioink. Furthermore, the 3D-printed cell-laden constructs are proved to be a conducive biochemical environment that supports growth and proliferation of the encapsulated cellsin vitro. In addition, thein vivostudies convince that the composite bioink possesses excellent biocompatibility and biodegradation. It is believed that the innovation of this new composite bioink will push forward the bioprinting technology onto a new stage.

Halloysites modified polyethylene glycol diacrylate/thiolated chitosan double network hydrogel combined with BMP-2 for rat skull regeneration

Hydrogel serve as bone tissue engineering have lately received great attention for their good biocompatibility and structures similar to natural extracellular matrices. However, a single component polymer hydrogel is generally detrimental to cell adhesion due to the weaker mechanical properties, which limits their application considerably. In an effort to overcome this disadvantage, we adopt an unconventional dual network hydrogels consisting of the polyethylene glycol diacrylate (PEGDA) covalent network, a thiolated chitosan (TCS) ion crosslinking network and thiolated halloysites (T-HNTs) as reinforcing filler. In addition, bone morphogenetic protein-2 (BMP-2) was loaded into the prepared dual network (DN) hydrogel to improve the bone regeneration function of the DN hydrogel. The resulting PEGDA/TCS/T-HNTs hydrogels showed favourable mechanical property, higher crosslinking density, the lower swelling degree, excellent biocompatibility and cell adhesion ability. The histomorphometric and immunohistochemical analyses revealed the excellent bone regeneration ability for composite hydrogel after implant into rat skull defect. Thus, our results indicated that composite scaffold can be applied as a new bone regeneration biomaterial to be applied as a local drug delivery system with good bone induction performance.

Marine-Derived Collagen as Biomaterials for Human Health

Collagen is a kind of biocompatible protein material, which is widely used in medical tissue engineering, drug delivery, cosmetics, food and other fields. Because of its wide source, low extraction cost and good physical and chemical properties, it has attracted the attention of many researchers in recent years. However, the application of collagen derived from terrestrial organisms is limited due to the existence of diseases, religious beliefs and other problems. Therefore, exploring a wider range of sources of collagen has become one of the main topics for researchers. Marine-derived collagen (MDC) stands out because it comes from a variety of sources and avoids issues such as religion. On the one hand, this paper summarized the sources, extraction methods and characteristics of MDC, and on the other hand, it summarized the application of MDC in the above fields. And on the basis of the review, we found that MDC can not only be extracted from marine organisms, but also from the wastes of some marine organisms, such as fish scales. This makes further use of seafood resources and increases the application prospect of MDC.

Three Polymers from the Sea: Unique Structures, Directional Modifications, and Medical Applications

With the increase of wounds and body damage, the clinical demand for antibacterial, hemostatic, and repairable biomaterials is increasing. Various types of biomedical materials have become research hotspots. Of these, and among materials derived from marine organisms, the research and application of alginate, chitosan, and collagen are the most common. Chitosan is mainly used as a hemostatic material in clinical applications, but due to problems such as the poor mechanical strength of a single component, the general antibacterial ability, and fast degradation speed research into the extraction process and modification mainly focuses on the improvement of the above-mentioned ability. Similarly, the research and modification of sodium alginate, used as a material for hemostasis and the repair of wounds, is mainly focused on the improvement of cell adhesion, hydrophilicity, degradation speed, mechanical properties, etc.; therefore, there are fewer marine biological collagen products. The research mainly focuses on immunogenicity removal and mechanical performance improvement. This article summarizes the source, molecular structure, and characteristics of alginate, chitosan, and collagen from marine organisms; and introduces the biological safety, clinical efficacy, and mechanism of action of these materials, as well as their extraction processes and material properties. Their modification and other issues are also discussed, and their potential clinical applications are examined.

Generation and Evaluation of Novel Biomaterials Based on Decellularized Sturgeon Cartilage for Use in Tissue Engineering

Because cartilage has limited regenerative capability, a fully efficient advanced therapy medicinal product is needed to treat severe cartilage damage. We evaluated a novel biomaterial obtained by decellularizing sturgeon chondral endoskeleton tissue for use in cartilage tissue engineering. In silico analysis suggested high homology between human and sturgeon collagen proteins, and ultra-performance liquid chromatography confirmed that both types of cartilage consisted mainly of the same amino acids. Decellularized sturgeon cartilage was recellularized with human chondrocytes and four types of human mesenchymal stem cells (MSC) and their suitability for generating a cartilage substitute was assessed ex vivo and in vivo. The results supported the biocompatibility of the novel scaffold, as well as its ability to sustain cell adhesion, proliferation and differentiation. In vivo assays showed that the MSC cells in grafted cartilage disks were biosynthetically active and able to remodel the extracellular matrix of cartilage substitutes, with the production of type II collagen and other relevant components, especially when adipose tissue MSC were used. In addition, these cartilage substitutes triggered a pro-regenerative reaction mediated by CD206-positive M2 macrophages. These preliminary results warrant further research to characterize in greater detail the potential clinical translation of these novel cartilage substitutes.

Engineering collagen fiber templates with oriented nanoarchitecture and concerns on osteoblast behaviors

Nanostructure provides a closer structural support approximation to native bone architecture for cells and further regulates cell's behavior, resulting in the formation of functional tissues. In this work, three engineering collagen templates with oriented fiber architectures were fabricated via electrospinning (Es), plastic compression and tensile (PCT), and dynamic shear stress (SS) methods. Under the observation of POM, SEM, AFM and TEM, the PCT-template and SS-template are packed with well-oriented nanofibers with the native collagen architecture of 67 nm D-periodicity, and the mechanical properties conferred to the templates are better than that of the Es-template. When mentioning the cell's behavior, MC3T3-E1 adhered to grow along the alignment of collagen fiber orientation when cultured on the PCT-template and SS-template. The SS-template with nano- and micro-ordered architecture guided cells to stretch their plasma along with the orientation of collagen fiber, produce more aligned Type I collagen fibers and promote significantly higher osteogenic differentiation of MC3T3-E1 than the PCT-template and Es-template. Overall, it is strongly argued the feasibility of hierarchical collagen fiber architectures for bone tissue regeneration.

Tough Double Network Hydrogel and Its Biomedical Applications

Soft and wet hydrogels have many similarities to biological tissues, though their mechanical fragility had been one of the biggest obstacles in biomedical applications. Studies and developments in double network (DN) hydrogels have elucidated how to create tough gels universally based on sacrificial bond principles and opened a path for biomedical application of hydrogels in regenerative medicine and artificial soft connective tissues, such as cartilage, tendon, and ligament, which endure high tension and compression. This review explores a universal toughening mechanism for and biomedical studies of DN hydrogels. Moreover, because the term sacrificial bonds has been mentioned often in studies of bone tissues, consisting of biomacromolecules and biominerals, recent studies of gel–biomineral composites to understand early-stage osteogenesis and to simulate bony sacrificial bonds are also summarized.

Enhancing Biopolymer Hydrogel Functionality through Interpenetrating Networks

Traditional hydrogels are strong candidates for biomedical applications; however, they may suffer from drawbacks such as weak mechanics, static properties, and an inability to fully replicate aspects of the cellular microenvironment. These challenges can be addressed through the incorporation of second networks to form interpenetrating polymer network (IPN) hydrogels. The objective of this review is to establish clear trends on the enhanced functionality achieved by incorporating secondary networks into traditional, biopolymer-based hydrogels. These include mechanical reinforcement, 'smart' systems that respond to external stimuli, and the ability to tune cell-material interactions. Through attention to network structure and chemistry, IPN hydrogels may advance to meet challenging criteria for a wide range of biomedical fields.

Research progress on tissue engineering in repairing tempomandibular joint

Temporomandibular joint osteoarthritis (TMJOA) is mainly manifested as perforation of temporomandibular joint disc (TMJD) and destruction of condylar osteochondral complex (COCC). In recent years, tissue engineering technology has become one of the effective strategies in repairing this damage. With the development of scaffold material technology, composite scaffolds have become an important means to optimize the performance of scaffolds with the combined advantages of natural materials and synthetic materials. The gelling method with the minimally invasive concept can greatly solve the problems of surgical trauma and material anastomosis, which is beneficial to the clinical transformation of temporomandibular joint tissue engineering. Extracellular matrix scaffolds technology can solve the problem of scaffold source and maximize the simulation of the extracellular environment, which provides an important means for the transformation of temporo joint tissue engineering to animal level. Due to the limitation of the source and amplification of costal chondrocytes, the use of mesenchymal stem cells from different sources has been widely used for temporomandibular joint tissue engineering. The fibrochondral stem cells isolated from surface layer of articular cartilage may provide one more suitable cell source. Transforming growth factor β superfamily, due to its osteochondrogenesis activity has been widely used in tissue engineering, and platelet-rich derivative as a convenient preparation of compound biological factor, gradually get used in temporomandibular joint tissue engineering. With the deepening of research on extracellular microenvironment and mechanical stimulation, mesenchymal stem cells, exosomes and stress stimulation are increasingly being used to regulate the extracellular microenvironment. In the future, the combination of complex bioactive factors and certain stress stimulation may become a trend in the temporomandibular joint tissue engineering research. In this article, the progress on tissue engineering in repairing COCC and TMJD, especially in scaffold materials, seed cells and bioactive factors, are reviewed, so as to provide information for future research design and clinical intervention.

Polymer-Protein Hybrid Network Involving Mucin: A Mineralized Biomimetic Template for Bone Tissue Engineering

Biomimetic matrices offer a great advantage to understand several biological processes including regeneration. The study involves the development of a hybrid biomimetic scaffold and the uniqueness lies in the use of mucin, as a constituent protein. Through this study, the role of the protein in bone regeneration is deciphered through its development as a 3D model. As a first step towards understanding the protein, the interactions of mucin and collagen are determined by in silico studies considering that collagen is the most abundant protein in the bone microenvironment. Both proteins are reported to be involved in bone biology though the exact role of mucin is a topic of investigation. The in silico studies of collagen-mucin suggest to have a proper affinity toward each other, forming a strong basis for 3D scaffold development. The developed 3D scaffold is a double network system comprising of mucin and collagen and vinyl end functionalized polyethylene glycol. In situ deposition of mineral crystals has been performed enzymatically. Biological evaluation of these mineral deposited scaffolds is done in terms of their bone regeneration potential and a comparison of the two systems with and without mineral deposition is presented.

Acellular fish skin enhances wound healing by promoting angiogenesis and collagen deposition

Acellular matrix is a type of promising biomaterial for wound healing promotion. Although acellular bovine and porcine tissues have proven effective, religious restrictions and risks of disease transmission remain barriers to their clinical use. Acellular fish skin (AFS), given its similarity to human skin structure and without the aforementioned disadvantages, is thus seen as an attractive alternative. This study aims to fabricate AFS from the skin of black carp (Mylopharyngodon piceus), evaluate its physical and mechanical properties and assess its impact on wound healing. The results showed that AFS has a highly porous structure, along with high levels of hydrophilicity, water-absorption property and permeability. Furthermore, physical characterization showed the high tensile strength of AFS in dry and wet states, and high stitch tear resistance, indicating great potential in clinical applications. Cell Counting Kit-8 was used to test the viability of L929 cells when culturing in the extracts of AFS. Compared with the control group, there is no significant difference in optical density value when culturing in the extracts of AFS at days 1, 3 and 7 (*p> 0.05).In vivowound healing evaluation then highlighted its promotion of angiogenesis and collagen synthesis, its function in anti-inflammation and acceleration in wound healing. Therefore, this study suggests that AFS has potential as a promising alternative to mammal-derived or traditional wound dressing.

Bioinspired double network hydrogels: from covalent double network hydrogels via hybrid double network hydrogels to physical double network hydrogels

The design and synthesis of double network (DN) hydrogels that can mimic the properties and/or structure of natural tissue has flourished in recent years, overcoming the bottlenecks of mechanical performance of single network hydrogels and extending their potential applications in various fields. In recent years, such bioinspired DN hydrogels with extraordinary mechanical performance, excellent biocompatibility, and considerable strength have been demonstrated to be promising candidates for biomedical applications, such as tissue engineering and biomedicine. In this minireview, we provide an overview of the recent developments of bioinspired DN hydrogels defined as DN hydrogels that mimic the properties and/or structure of natural tissue, ranging from, e.g., anisotropically structured DN hydrogels, via ultratough energy dissipating DN hydrogels to dynamic, reshapable DN hydrogels. Furthermore, we discuss future perspectives of bioinspired DN hydrogels for biomedical applications.

From prevention to diagnosis and treatment: Biomedical applications of metal nanoparticle-hydrogel composites

Recent advances in biomaterials integrate metal nanoparticles with hydrogels to generate composite materials that exhibit new or improved properties. By precisely controlling the composition, arrangement and interactions of their constituents, these hybrid materials facilitate biomedical applications through myriad approaches. In this work we seek to highlight three popular frameworks for designing metal nanoparticle-hydrogel hybrid materials for biomedical applications. In the first approach, the properties of metal nanoparticles are incorporated into a hydrogel matrix such that the composite is selectively responsive to stimuli such as light and magnetic flux, enabling precisely activated therapeutics and self-healing biomaterials. The second approach mediates the dynamic reorganization of metal nanoparticles based on environment-directed changes in hydrogel structure, leading to chemosensing, microbial and viral detection, and drug-delivery capabilities. In the third approach, the hydrogel matrix spatially arranges metal nanoparticles to produce metamaterials or passively enhance nanoparticle properties to generate improved substrates for biomedical applications including tissue engineering and wound healing. This article reviews the construction, properties and biomedical applications of metal nanoparticle-hydrogel composites, with a focus on how they help to prevent, diagnose and treat diseases. Discussion includes how the composites lead to new or improved properties, how current biomedical research leverages these properties and the emerging directions in this growing field.

Role of Hydrogels in Bone Tissue Engineering: How Properties Shape Regeneration

Bone defect that resulted from trauma, tumors, and other reasons is believed as a common clinical problem, which exists mainly in post-traumatic healing. Additionally, autologous/allogeneic transplantation, bone tissue engineering attracts increasing attention due to the existing problem of the limited donor. The applications of biomaterials can be considered as a rising and promising strategy for bone regeneration. Especially, hydrogel is featured with hydrophilic characteristic, good biocompatibility, and porous structure, which shows unique properties for bone regeneration. The main properties of hydrogel such as surface property, adhesive property, mechanical property, porosity, and degradation property, generally present influences on the migration, proliferation, and differentiation of mesenchymal stem cells exclusively or in combination, which consequently affect the regeneration of bones. This review mainly focuses on the theme: "how properties of hydrogel shape bone regeneration." Moreover, the latest progress achieved in the above mentioned direction is further discussed. Despite the fascinating advances researchers have made, certain potential challenges continue to exist in the research field, which need to be addressed for accelerating the clinical translation of hydrogel in bone regeneration.

New insights into food hydrogels with reinforced mechanical properties: A review on innovative strategies

Enhancement on the mechanical properties of hydrogels leads to a wider range of their applications in various fields. Therefore, there has been a great interest recently for developing new strategies to reinforce hydrogels. Moreover, food gels must be edible in terms of both raw materials and production. This paper reviews innovative techniques such as particle/fiber-reinforced hydrogel, double network, dual crosslinking, freeze-thaw cycles, physical conditioning and soaking methods to improve the mechanical properties of hydrogels. Additionally, their fundamental mechanisms, advantages and disadvantages have been discussed. Important biopolymers that have been employed for these strategies and also their potentials in food applications have been summarized. The general mechanism of these strategies is based on increasing the degree of crosslinking between interacting polymers in hydrogels. These links can be formed by adding fillers (oil droplets or fibers in filled gels) or cross-linkers (regarding double network and soaking method) and also by condensation or alignment of the biopolymers (freeze-thaw cycle and physical conditioning) in the gel network. The properties of particle/fiber-reinforced hydrogels extremely depend on the filler, gel matrix and the interaction between them. In freeze-thaw cycles and physical conditioning methods, it is possible to form new links in the gel network without adding any cross-linkers or fillers. It is expected that the utilization of gels will get broader and more varied in food industries by using these strategies.

Utility of Air Bladder-Derived Nanostructured ECM for Tissue Regeneration

Exploration for ideal bone regeneration materials still remains a hot research topic due to the unmet clinical challenge of large bone defect healing. Bone grafting materials have gradually evolved from single component to multiple-component composite, but their functions during bone healing still only regulate one or two biological processes. Therefore, there is an urgent need to develop novel materials with more complex composition, which convey multiple biological functions during bone regeneration. Here, we report an naturally nanostructured ECM based composite scaffold derived from fish air bladder and combined with dicalcium phosphate (DCP) microparticles to form a new type of bone grafting material. The DCP/acellular tissue matrix (DCP/ATM) scaffold demonstrated porous structure with porosity over 65% and great capability of absorbing water and other biologics. In vitro cell culture study showed that DCP/ATM scaffold could better support osteoblast proliferation and differentiation in comparison with DCP/ADC made from acid extracted fish collagen. Moreover, DCP/ATM also demonstrated more potent bone regenerative properties in a rat calvarial defect model, indicating incorporation of ECM based matrix in the scaffolds could better support bone formation. Taken together, this study demonstrates a new avenue toward the development of new type of bone regeneration biomaterial utilizing ECM as its key components.

Fish Collagen: Extraction, Characterization, and Applications for Biomaterials Engineering

The utilization of marine-based collagen is growing fast due to its unique properties in comparison with mammalian-based collagen such as no risk of transmitting diseases, a lack of religious constraints, a cost-effective process, low molecular weight, biocompatibility, and its easy absorption by the human body. This article presents an overview of the recent studies from 2014 to 2020 conducted on collagen extraction from marine-based materials, in particular fish by-products. The fish collagen structure, extraction methods, characterization, and biomedical applications are presented. More specifically, acetic acid and deep eutectic solvent (DES) extraction methods for marine collagen isolation are described and compared. In addition, the effect of the extraction parameters (temperature, acid concentration, extraction time, solid-to-liquid ratio) on the yield of collagen is investigated. Moreover, biomaterials engineering and therapeutic applications of marine collagen have been summarized.

Injectable hydrogels for tendon and ligament tissue engineering

The problem of tendon and ligament (T/L) regeneration in musculoskeletal diseases has long constituted a major challenge. In situ injection of formable biodegradable hydrogels, however, has been demonstrated to treat T/L injury and reduce patient suffering in a minimally invasive manner. An injectable hydrogel is more suitable than other biological materials due to the special physiological structure of T/L. Most other materials utilized to repair T/L are cell-based, growth factor-based materials, with few material properties. In addition, the mechanical property of the gel cannot reach the normal T/L level. This review summarizes advances in natural and synthetic polymeric injectable hydrogels for tissue engineering in T/L and presents prospects for injectable and biodegradable hydrogels for its treatment. In future T/L applications, it is necessary develop an injectable hydrogel with mechanics, tissue damage-specific binding, and disease response. Simultaneously, the advantages of various biological materials must be combined in order to achieve personalized precision therapy.

In-air fast response and high speed jumping and rolling of a light-driven hydrogel actuator

Stimuli-responsive hydrogel actuators have promising applications in various fields. However, the typical hydrogel actuation relies on the swelling and de-swelling process caused by osmotic-pressure changes, which is slow and normally requires the presence of water environment. Herein, we report a light-powered in-air hydrogel actuator with remarkable performances, including ultrafast motion speed (up to 1.6 m/s), rapid response (as fast as 800 ms) and high jumping height (~15 cm). The hydrogel is operated based on a fundamentally different mechanism that harnesses the synergetic interactions between the binary constituent parts, i.e. the elasticity of the poly(sodium acrylate) hydrogel, and the bubble caused by the photothermal effect of the embedded magnetic iron oxide nanoparticles. The current hydrogel actuator exhibits controlled motion velocity and direction, making it promising for a wide range of mobile robotics, soft robotics, sensors, controlled drug delivery and other miniature device applications.