Self-crosslinkable hyaluronate-based hydrogels as a soft tissue filler

Supramolecular assembly of multi-purpose tissue engineering platforms from human extracellular matrix

Recapitulating the biophysical and biochemical complexity of the extracellular matrix (ECM) remains a major challenge in tissue engineering. Hydrogels derived from decellularized ECM provide a unique opportunity to replicate the architecture and bioactivity of native ECM, however, they exhibit limited long-term stability and mechanical integrity. In turn, materials assembled through supramolecular interactions have achieved considerable success in replicating the dynamic biophysical properties of the ECM. Here, we merge both methodologies by promoting the supramolecular assembly of decellularized human amniotic membrane (hAM), mediated by host-guest interactions between hAM proteins and acryloyl-β-cyclodextrin (AcβCD). Photopolymerization of the cyclodextrins results in the formation of soft hydrogels that exhibit tunable stress relaxation and strain-stiffening. Disaggregation of bulk hydrogels yields an injectable granular material that self-reconstitutes into shape-adaptable bulk hydrogels, supporting cell delivery and promoting neovascularization. Additionally, cells encapsulated within bulk hydrogels sense and respond to the biophysical properties of the surrounding matrix, as early cell spreading is favored in hydrogels that exhibit greater susceptibility to applied stress, evidencing proper cell-matrix interplay. Thus, this system is shown to be a promising substitute for native ECM in tissue repair and modelling.

Development and Characterization of Hyaluronic Acid Graft-Modified Polydopamine Nanoparticles for Antibacterial Studies

The problem of antibiotic abuse and drug resistance is becoming increasingly serious. In recent years, polydopamine (PDA) nanoparticles have been recognized as a potential antimicrobial material for photothermal therapy (PTT) due to their excellent photothermal conversion efficiency and unique antimicrobial ability. PDA is capable of rapidly converting light energy into heat energy under near-infrared (NIR) light irradiation to kill bacteria efficiently. In order to solve the problem of PDA's tendency to aggregate and precipitate, this study improved its stability by grafting hyaluronic acid (HA) onto the surface of PDA. Using dopamine and hyaluronic acid as raw materials, hyaluronic acid (HA) was grafted onto polydopamine (PDA) nanoparticles via self-polymerization and Michael addition reactions under alkaline conditions to obtain PDA-HA-modified nanoparticles. We confirmed the successful grafting of hyaluronic acid via scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR), nuclear magnetic hydrogen spectroscopy (¹H NMR), ultraviolet-visible spectroscopy (UV-vis), Raman spectroscopy (Raman), and dynamic light scattering (DLS) methods. Scanning electron microscopy (SEM) was used to observe the surface morphology and nanostructure of the grafted materials, providing information on the morphology and size distribution of the materials. Near-infrared performance experiments showed that the temperature of the PDA-HA solution increased rapidly under near-infrared light irradiation, demonstrating an excellent photothermal conversion performance. Antimicrobial properties were assessed via the colony counting method, and typical Gram-positive bacteria S. aureus and Gram-negative bacteria E. coli were selected as model strains. The experimental groups were tested under dark conditions and near-infrared (NIR) light irradiation. PDA/HA showed significant photothermal properties under NIR light irradiation, resulting in a rapid increase in the surrounding temperature to a level sufficient to kill bacteria. Under NIR light irradiation, PDA/HA exhibited 100% antimicrobial efficacy against both S. aureus and E. coli, while antimicrobial efficacy was limited under dark conditions. This indicates that the antibacterial activity of PDA/HA is highly dependent on NIR light activation.

Tailoring biomaterials for skin anti-aging

Skin aging is the phenomenon of degenerative changes in the structure and function of skin tissues over time and is manifested by a gradual loss of skin elasticity and firmness, an increased number of wrinkles, and hyperpigmentation. Skin anti-aging refers to a reduction in the skin aging phenomenon through medical cosmetic technologies. In recent years, new biomaterials have been continuously developed for improving the appearance of the skin through mechanical tissue filling, regulating collagen synthesis and degradation, inhibiting pigmentation, and repairing the skin barrier. This review summarizes the mechanisms associated with skin aging, describes the biomaterials that are commonly used in medical aesthetics and their possible modes of action, and discusses the application strategies of biomaterials in this area. Moreover, the synergistic effects of such biomaterials and other active ingredients, such as stem cells, exosomes, growth factors, and antioxidants, on tissue regeneration and anti-aging are evaluated. Finally, the possible challenges and development prospects of biomaterials in the field of anti-aging are discussed, and novel ideas for future innovations in this area are summarized.

Injectable mineralized Sr-hydroxyapatite nanoparticles-loaded ɛ-polylysine-hyaluronic acid composite hydrogels for bone regeneration

In this study, multifunctional injectable mineralized antibacterial nanocomposite hydrogels were prepared by a homogenous distribution of high content of (up to 60 wt%) Sr-substituted hydroxyapatite (Sr-HAp) nanoparticles into covalently cross-linked ɛ-polylysine (ɛ-PL) and hyaluronic acid (HA) hydrogel network. The developed bone-targeted nanocomposite hydrogels were to synergistically combine the functional properties of bioactive Sr-HAp nanoparticles and antibacterial ɛ-PL-HA hydrogels for bone tissue regeneration. Viscoelasticity, injectability, structural parameters, degradation, antibacterial activity, and in vitro biocompatibility of the fabricated nanocomposite hydrogels were characterized. Physical performances of the ɛ-PL-HA hydrogels can be tailored by altering the mass ratio of Sr-HAp. The nanocomposite hydrogels revealed good stability against enzymatic degradation, which increased from 5 to 19 weeks with increasing the mass ratio of Sr-HAp from 40 % to 60 %. The loading of the Sr-HAp at relatively high mass ratios did not suppress the fast-acting and long-term antibacterial activity of the ɛ-PL-HA hydrogels against S. aureus and E. coli. The cell studies confirmed the cytocompatibility and pre-collagen I synthesis-promoting activity of the fabricated nanocomposite hydrogels.

Injectable and biodegradable collagen-chitosan microspheres for enhanced skin regeneration

Skin aging is influenced by both external environmental factors and intrinsic biological mechanisms. Traditional microsphere implants aim to rejuvenate aging skin through collagen regeneration, yet their non-biodegradability and risk of granuloma formation often limit their effectiveness. In this study, we developed novel, injectable, highly bioactive, and degradable collagen-chitosan double-crosslinked composite microspheres for skin rejuvenation. The microspheres demonstrated excellent injectability, requiring an injection force of only 0.9 N, and significant biodegradability, effectively degraded in solutions containing phosphate buffer, type I collagenase, and pepsin. In addition, the microspheres exhibited excellent biocompatibility and bioactivity, significantly promoting the proliferation, adhesion, and migration of human foreskin fibroblast-1 (HFF-1) cells. In a photoaged mouse skin model, the implantation of microspheres significantly enhanced dermal density and skin elasticity while reducing transepidermal water loss. Importantly, the implant promoted the regeneration of collagen fibers. This study suggests that collagen-chitosan double-crosslinked composite microspheres hold significant potential for skin rejuvenation treatments.

Advances in enhancing the mechanical properties of biopolymer hydrogels via multi-strategic approaches

The limited mechanical properties of biopolymer-based hydrogels have hindered their widespread applications in biomedicine and tissue engineering. In recent years, researchers have shown significant interest in developing novel approaches to enhance the mechanical performance of hydrogels. This review focuses on key strategies for enhancing mechanical properties of hydrogels, including dual-crosslinking, double networks, and nanocomposite hydrogels, with a comprehensive analysis of their underlying mechanisms, benefits, and limitations. It also introduces the classic application scenarios of biopolymer-based hydrogels and the direction of future research efforts, including wound dressings and tissue engineering based on 3D bioprinting. This review is expected to deepen the understanding of the structure-mechanical performance-function relationship of hydrogels and guide the further study of their biomedical applications.

Synthesis and Properties of Injectable Hydrogel for Tissue Filling

Hydrogels with injectability have emerged as the focal point in tissue filling, owing to their unique properties, such as minimal adverse effects, faster recovery, good results, and negligible disruption to daily activities. These hydrogels could attain their injectability through chemical covalent crosslinking, physical crosslinking, or biological crosslinking. These reactions allow for the formation of reversible bonds or delayed gelatinization, ensuring a minimally invasive approach for tissue filling. Injectable hydrogels facilitate tissue augmentation and tissue regeneration by offering slow degradation, mechanical support, and the modulation of biological functions in host cells. This review summarizes the recent advancements in synthetic strategies for injectable hydrogels and introduces their application in tissue filling. Ultimately, we discuss the prospects and prevailing challenges in developing optimal injectable hydrogels for tissue augmentation, aiming to chart a course for future investigations.

Facilely printed silk fibroin hydrogel microparticles as injectable long-lasting fillers

There is a high demand from aging people for facial fillers with desirable biocompatibility and lasting filling effects to overcome facial depression. Novel injectable regenerated silk fibroin (RSF) microparticles were facilely printed from a glycidyl methacrylate-modified silk fibroin hydrogel to address this issue. The β-sheet content and mechanical properties of the RSF hydrogel can be simply modulated by the number of freeze-thawing cycles, and the swelling rate of the RSF hydrogel in saline was negligible. The printed RSF microparticles were uniform, and their diameter was about 300-500 μm, which could be adjusted by the pore sizes of the printed screens. After the injection with a 26-gauge needle, the size distribution of RSF microparticles had no noticeable variation, suggesting that the microparticles could bear the shear strain without breaking during the injection. The in vitro experiments demonstrated that RSF not only had desirable biocompatibility but also facilitated fibroblast migration. The subcutaneous injection experiments demonstrated that the RSF microparticles formed a lasting spot in the injected site. The tissue sections revealed that the RSF microparticles were still distinct on week 8, and blood vessels formed around the microparticles. These promising data demonstrate that the printed RSF microparticles have great potential for facial rejuvenation.

Injectable fillers: current status, physicochemical properties, function mechanism, and perspectives

With the increasing understanding of the aging process and growing desire for minimally invasive treatments, injectable fillers have great potential for correcting and rejuvenating facial wrinkles/folds and contouring the face. However, considering the increasing availability of multiple soft tissue fillers, it is important to understand their inherent biophysical features and specific mechanism. Thus, in this review, we aim to provide an update on the current injectable filler products and analyze and compare their critical physicochemical properties and function mechanisms for volume-filling. Additionally, future trends and development processes for injectable fillers are also proposed.

Photo-crosslinkable hyaluronic acid microgels with reactive oxygen species scavenging capacity for mesenchymal stem cell encapsulation

Mesenchymal stem cells (MSCs) have gained increasing attention in various biomedical applications. However, conventional therapeutic approaches, such as direct intravenous injection, are associated with low cell survival due to the shear force during injection and the oxidative stress microenvironments in the lesion area. Herein, a photo-crosslinkable antioxidant hydrogel based on tyramine- and dopamine-modified hyaluronic acid (HA-Tyr/HA-DA) was developed. Meanwhile, human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) were encapsulated in HA-Tyr/HA-DA hydrogel using a microfluidic system to create size-controllable microgels (hUC-MSCs@microgels). The HA-Tyr/HA-DA hydrogel was demonstrated to have good rheology, biocompatibility, and antioxidant properties for cell microencapsulation. The hUC-MSCs encapsulated in microgels showed a high viability and a significantly improved the survival rate under oxidative stress conditions. Therefore, the presented work provides a promising platform for MSCs microencapsulation, which may further improve the stem cell-based biomedical applications.

Prospective bacterial and fungal sources of hyaluronic acid: A review

The unique biological and rheological properties make hyaluronic acid a sought-after material for medicine and cosmetology. Due to very high purity requirements for hyaluronic acid in medical applications, the profitability of streptococcal fermentation is reduced. Production of hyaluronic acid by recombinant systems is considered a promising alternative. Variations in combinations of expressed genes and fermentation conditions alter the yield and molecular weight of produced hyaluronic acid. This review is devoted to the current state of hyaluronic acid production by recombinant bacterial and fungal organisms.

Self-Healing Injectable Hydrogels for Tissue Regeneration

Biomaterials with the ability to self-heal and recover their structural integrity offer many advantages for applications in biomedicine. The past decade has witnessed the rapid emergence of a new class of self-healing biomaterials commonly termed injectable, or printable in the context of 3D printing. These self-healing injectable biomaterials, mostly hydrogels and other soft condensed matter based on reversible chemistry, are able to temporarily fluidize under shear stress and subsequently recover their original mechanical properties. Self-healing injectable hydrogels offer distinct advantages compared to traditional biomaterials. Most notably, they can be administered in a locally targeted and minimally invasive manner through a narrow syringe without the need for invasive surgery. Their moldability allows for a patient-specific intervention and shows great prospects for personalized medicine. Injected hydrogels can facilitate tissue regeneration in multiple ways owing to their viscoelastic and diffusive nature, ranging from simple mechanical support, spatiotemporally controlled delivery of cells or therapeutics, to local recruitment and modulation of host cells to promote tissue regeneration. Consequently, self-healing injectable hydrogels have been at the forefront of many cutting-edge tissue regeneration strategies. This study provides a critical review of the current state of self-healing injectable hydrogels for tissue regeneration. As key challenges toward further maturation of this exciting research field, we identify (i) the trade-off between the self-healing and injectability of hydrogels vs their physical stability, (ii) the lack of consensus on rheological characterization and quantitative benchmarks for self-healing injectable hydrogels, particularly regarding the capillary flow in syringes, and (iii) practical limitations regarding translation toward therapeutically effective formulations for regeneration of specific tissues. Hence, here we (i) review chemical and physical design strategies for self-healing injectable hydrogels, (ii) provide a practical guide for their rheological analysis, and (iii) showcase their applicability for regeneration of various tissues and 3D printing of complex tissues and organoids.

Polydopamine nanoparticles and hyaluronic acid hydrogels for mussel-inspired tissue adhesive nanocomposites

Bioadhesives are intended to facilitate the fast and efficient reconnection of tissues to restore their functionality after surgery or injury. The use of mussel-inspired hydrogel systems containing pendant catechol moieties is promising for tissue attachment under wet conditions. However, the adhesion strength is not yet ideal. One way to overcome these limitations is to add polymeric nanoparticles to create nanocomposites with improved adhesion characteristics. To further enhance adhesiveness, polydopamine nanoparticles with controlled size prepared using an optimized process, were combined with a mussel-inspired hyaluronic acid (HA) hydrogel to form a nanocomposite. The effects of sizes and concentrations of polydopamine nanoparticles on the adhesive profiles of mussel-inspired HA hydrogels were investigated. Results show that the inclusion of polydopamine nanoparticles in nanocomposites increased adhesion strength, as compared to the addition of poly (lactic-co-glycolic acid) (PLGA), and PLGA-(N-hydroxysuccinimide) (PLGA-NHS) nanoparticles. A nanocomposite with demonstrated cytocompatibility and an optimal lap shear strength (47 ± 3 kPa) was achieved by combining polydopamine nanoparticles of 200 nm (12.5% w/v) with a HA hydrogel (40% w/v). This nanocomposite adhesive shows its potential as a tissue glue for biomedical applications.

Polyphenol-based hydrogels: Pyramid evolution from crosslinked structures to biomedical applications and the reverse design

As a kind of nature-derived bioactive materials, polyphenol-based hydrogels possess many unique and outstanding properties such as adhesion, toughness, and self-healing due to their specific crosslinking structures, which have been widely used in biomedical fields including wound healing, antitumor, treatment of motor system injury, digestive system disease, oculopathy, and bioelectronics. In this review, starting with the classification of common polyphenol-based hydrogels, the pyramid evolution process of polyphenol-based hydrogels from crosslinking structures to derived properties and then to biomedical applications is elaborated, as well as the efficient reverse design considerations of polyphenol-based hydrogel systems are proposed. Finally, the existing problems and development prospects of these hydrogel materials are discussed. It is hoped that the unique perspective of the review can promote further innovation and breakthroughs of polyphenol-based hydrogels in the future.

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Polyphenol-based hydrogels combine advantages of polyphenols with common hydrogels.

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Cognition of such hydrogels underwent from structures to properties to applications.

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Various crosslinked structures of such hydrogels can derive outstanding properties.

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Such hydrogels can be widely used in biomedicine due to the outstanding properties.

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Reverse design thought from applications to properties to structures is promising.

A Review on the Design of Hydrogels With Different Stiffness and Their Effects on Tissue Repair

Tissue repair after trauma and infection has always been a difficult problem in regenerative medicine. Hydrogels have become one of the most important scaffolds for tissue engineering due to their biocompatibility, biodegradability and water solubility. Especially, the stiffness of hydrogels is a key factor, which influence the morphology of mesenchymal stem cells (MSCs) and their differentiation. The researches on this point are meaningful to the field of tissue engineering. Herein, this review focus on the design of hydrogels with different stiffness and their effects on the behavior of MSCs. In addition, the effect of hydrogel stiffness on the phenotype of macrophages is introduced, and then the relationship between the phenotype changes of macrophages on inflammatory response and tissue repair is discussed. Finally, the future application of hydrogels with a certain stiffness in regenerative medicine and tissue engineering has been prospected.

Hyaluronic acid/tannic acid hydrogel sunscreen with excellent anti-UV, antioxidant, and cooling effects

Excessive exposure to UV radiation is one of the major factors that causes skin aging, erythema, burns, and skin cancer. Recently, the usage of sunscreens for skin protection has increased because the amount of UV radiation reaching the Earth's surface has increased owing to the destruction of the ozone layer that blocks UV radiation. Hydrogels with a three-dimensional network structure exhibit physical and chemical properties that are similar to those of the extracellular matrix in the human body, a high water content, flexibility, and biocompatibility. Therefore, they are applied in a wide range of fields, such as in cosmetics, medicines, and pharmaceuticals. However, conventional hydrogel-based sunscreens have drawbacks such as complicated process conditions, high cost, and low biocompatibility. In this study, a novel hydrogel-type sunscreen with excellent UV protection and cooling effects was prepared by a very simple process using two natural materials, hyaluronic acid (HA) and tannic acid (TA). The HA/TA hydrogels exhibited broad-spectrum UV protection in the UVA and UVB regions (280-360 nm). In addition, they showed excellent adhesion to the skin surface, antioxidative activity, cooling effect, and high moisture content, demonstrating great application potential as a hydrogel-type sunscreen.