Mussel-inspired extracellular matrix-mimicking hydrogel scaffold with high cell affinity and immunomodulation ability for growth factor-free cartilage regeneration

Fostering tissue engineering and regenerative medicine to treat musculoskeletal disorders in bone and muscle

The musculoskeletal system, which is vital for movement, support, and protection, can be impaired by disorders such as osteoporosis, osteoarthritis, and muscular dystrophy. This review focuses on the advances in tissue engineering and regenerative medicine, specifically aimed at alleviating these disorders. It explores the roles of cell therapy, particularly Mesenchymal Stem Cells (MSCs) and Adipose-Derived Stem Cells (ADSCs), biomaterials, and biomolecules/external stimulations in fostering bone and muscle regeneration. The current research underscores the potential of MSCs and ADSCs despite the persistent challenges of cell scarcity, inconsistent outcomes, and safety concerns. Moreover, integrating exogenous materials such as scaffolds and external stimuli like electrical stimulation and growth factors shows promise in enhancing musculoskeletal regeneration. This review emphasizes the need for comprehensive studies and adopting innovative techniques together to refine and advance these multi-therapeutic strategies, ultimately benefiting patients with musculoskeletal disorders.

Polydopamine-armored zeolitic imidazolate framework-8-incorporated zwitterionic hydrogel with multifunctional properties for infected wound healing

Diabetic skin wound healing is compromised by bacterial infections, oxidative stress, and vascular disruption, leading to delayed recovery and potential complications. This study developed an antibacterial, antioxidant, and adhesive hydrogel dressing that promotes rapid bacterial-infected diabetic wound healing using the biological macromolecule of polydopamine (PDA). This hydrogel comprised PDA-armored zeolitic imidazolate framework-8 nanoparticles (PDA@ZIF-8 NPs) combined with a second armor of zwitterionic polymer network (poly(acrylamide-co-sulfobetaine methacrylate); PAS), realizing low concentration Zn2+ release, good adhesion (14.7 kPa for porcine skin), and improved tensile strength (83.2 kPa). The hydrogel exhibited good antibacterial efficacy against both Staphylococcus aureus (S. aureus, 92.8 %), Escherichia coli (E. coli, 99.6 %) and methicillin-resistant S. aureus (MRSA, 99.2 %), which was attributed to the properties of the incorporated PDA@ZIF-8 NPs. Notably, in vitro, the PDA@ZIF-8 PAS hydrogel not only promoted fibroblast proliferation and migration but also facilitated endothelial cell angiogenesis. In vivo, the PDA@ZIF-8 PAS hydrogel retained its Zn2+-releasing function and effectively suppressed bacterial growth in infected wounds, thereby accelerating the regeneration of both normal and diabetic wounds. This multiarmored hydrogel is a promising sustained-release carrier for functional metal ions and drugs, making it applicable for not only skin healing, but potentially the regeneration of other complex tissues.

Modulation of macrophage polarization by secondary cross-linked hyaluronan-dopamine hydrogels

The inflammatory response plays a critical role in standard tissue repair processes, wherein active modulation of macrophage polarization is necessary for wound healing. Dopamine, a mussel-inspired bioactive material, is widely involved in wound healing, neural/bone/myocardial regeneration, and more. Recent studies indicated that dopamine-modified biomaterials can potentially alter macrophages polarization towards a pro-healing phenotype, thereby enhancing tissue regeneration. Nevertheless the immunoregulatory activity of dopamine on macrophage polarization remains unclear. This study introduces a novel interpenetrating hydrogel to bridge this research gap. The hydrogel, combining varying concentrations of oxidized dopamine with hyaluronic acid hydrogel, allows precise regulation of mechanical properties, antioxidant bioactivity, and biocompatibility. Surprisingly, both in vivo and in vitro outcomes demonstrated that dopamine concentration modulates macrophage polarization, but not linearly. Lower concentration (2 mg/mL) potentially decrease inflammation and facilitate M2 type macrophage polarization. In contrast, higher concentration (10 mg/mL) exhibited a pro-inflammatory tendency in the late stages of implantation. RNA-seq analysis revealed that lower dopamine concentrations induced the M1/M2 transition of macrophages by modulating the NF-κB signaling pathway. Collectively, this research offers valuable insights into the immunoregulation effects of dopamine-integrated biomaterials in tissue repair and regeneration.

Research Progress in Hydrogels for Cartilage Organoids

The repair and regeneration of cartilage has always been a hot topic in medical research. Cartilage organoids (CORGs) are special cartilage tissue created using tissue engineering techniques outside the body. These engineered organoids tissues provide models that simulate the complex biological functions of cartilage, opening new possibilities for cartilage regenerative medicine and treatment strategies. However, it is crucial to establish suitable matrix scaffolds for the cultivation of CORGs. In recent years, utilizing hydrogel to culture stem cells and induce their differentiation into chondrocytes has emerged as a promising method for the in vitro construction of CORGs. In this review, the methods for establishing CORGs are summarized and an overview of the advantages and limitations of using matrigel in the cultivation of such organoids is provided. Furthermore, the importance of cartilage tissue ECM and alternative hydrogel substitutes for Matrigel, such as alginate, peptides, silk fibroin, and DNA derivatives is discussed, and the pros and cons of using these hydrogels for the cultivation of CORGs are outlined. Finally, the challenges and future directions in hydrogel research for CORGs are discussed. It is hoped that this article provides valuable references for the design and development of hydrogels for CORGs.

One-Pot Construction of Articular Cartilage-Like Hydrogel Coating for Durable Aqueous Lubrication

Articular cartilage has an appropriate multilayer structure and superior tribological properties and provides a structural paradigm for design of lubricating materials. However, mimicking articular cartilage traits on prosthetic materials with durable lubrication remains a huge challenge. Herein, an ingenious three-in-one strategy is developed for constructing an articular cartilage-like bilayer hydrogel coating on the surface of ultra-high molecular weight polyethylene (BH-UPE), which makes full use of conceptions of interfacial interlinking, high-entanglement crosslinking, and interface-modulated polymerization. The hydrogel coating is tightly interlinked with UPE substrate through hydrogel-UPE interchain entanglement and bonding. The hydrogel chains are highly entangled with each other to form a dense tough layer with negligible hysteresis for load-bearing by reducing the amounts of crosslinker and hydrophilic initiator to p.p.m. levels. Meanwhile, the polymerization of monomers in the top surface region is suppressed via interface-modulated polymerization, thus introducing a porous surface for effective aqueous lubrication. As a result, BH-UPE exhibits an ultralow friction coefficient of 0.0048 during 10 000 cycles under a load of 0.9 MPa, demonstrating great potential as an advanced bearing material for disc prosthesis. This work may provide a new way to build stable bilayer coatings and have important implications for development of biological lubricating materials.

Injectable and Self-Curing Single-Component Hydrogel for Stem Cell Encapsulation and In Vivo Bone Regeneration

An ideal hydrogel for stem cell therapy would be injectable and efficiently promote stem cell proliferation and differentiation in body. Herein, an injectable, single-component hydrogel with hyaluronic acid (HA) modified with phenylboronic acid (PBA) and spermidine (SM) is introduced. The resulting HAps (HA-PBA-SM) hydrogel is based on the reversible crosslinking between the diol and the ionized PBA, which is stabilized by the SM. It has a shear-thinning property, enabling its injection through a syringe to form a stable hydrogel inside the body. In addition, HAps hydrogel undergoes a post-injection "self-curing," which stiffens the hydrogel over time. This property allows the HAps hydrogel to meet the physical requirements for stem cell therapy in rigid tissues, such as bone, while maintaining injectability. The hydrogel enabled favorable proliferation of human mesenchymal stem cells (hMSCs) and promoted their differentiation and mineralization. After the injection of hMSCs-containing HAps into a rat femoral defect model, efficient osteogenic differentiation of hMSCs and bone regeneration is observed. The study demonstrates that simple cationic modification of PBA-based hydrogel enabled efficient gelation with shear-thinning and self-curing properties, and it would be highly useful for stem cell therapy and in vivo bone regeneration.

High-Strength Smart Microneedles with "Offensive and Defensive" Effects for Intervertebral Disc Repair

Intervertebral disc degeneration (IVDD) is a global public health issue. The injury of annulus fibrosus (AF) caused by acupuncture or discectomy can trigger IVDD again. However, there is currently no suitable method for treating AF injury. In this study, the high-strength smart microneedles (MNs) which can penetrate the AF tissue through a local and minimally invasive method, and achieve remote control of speeded-up release of the drug and hyperthermia by the Near Infrared is developed. The PDA/GelMA composite MNs loaded with diclofenac sodium are designed to extracellularly "offend" the inflammatory microenvironment and mitigate damage to cells, and intracellularly increase the level of cytoprotective heat shock proteins to enhance the defense against the hostile microenvironment, achieving "offensive and defensive" effects. In vitro experiments demonstrate that the synergistic treatment of photothermal therapy and anti-inflammation effectively reduces inflammation, inhibits cell apoptosis, and promotes the synthesis of the extracellular matrix (ECM). In vivo experiments show that the MNs mitigate the inflammatory response, promote ECM deposition, reduce the level of apoptosis, and restore the biomechanical properties of the intervertebral disc (IVD) in rats. Overall, this high-strength smart MNs display promising "offensive and defensive" effects that can provide a new strategy for IVD repair.

An Exploration of Organoid Technology: Present Advancements, Applications, and Obstacles

BACKGROUND

Organoids are in vitro models that exhibit a three-dimensional structure and effectively replicate the structural and physiological features of human organs. The capacity to research complex biological processes and disorders in a controlled setting is laid out by these miniature organ-like structures.

OBJECTIVES

This work examines the potential applications of organoid technology, as well as the challenges and future directions associated with its implementation. It aims to emphasize the pivotal role of organoids in disease modeling, drug discovery, developmental biology, precision medicine, and fundamental research.

METHODS

The manuscript was put together by conducting a comprehensive literature review, which involved an in-depth evaluation of globally renowned scientific research databases.

RESULTS

The field of organoids has generated significant attention due to its potential applications in tissue development and disease modelling, as well as its implications for personalised medicine, drug screening, and cell-based therapies. The utilisation of organoids has proven to be effective in the examination of various conditions, encompassing genetic disorders, cancer, neurodevelopmental disorders, and infectious diseases.

CONCLUSION

The exploration of the wider uses of organoids is still in its early phases. Research shall be conducted to integrate 3D organoid systems as alternatives for current models, potentially improving both fundamental and clinical studies in the future.

Mussel-inspired cortical bone-adherent bioactive composite hydrogels promote bone augmentation through sequential regulation of endochondral ossification

Endochondral ossification (ECO) plays an integral part in bone augmentation, which undergoes sequential processes including mesenchymal stem cells (MSC) condensation, chondrocyte differentiation, chondrocyte hypertrophy, and mineralized bone formation. Thus, accelerating these steps will speed up the osteogenesis process through ECO. Herein, inspired by the marine mussels' adhesive mechanism, a bioactive glass-dopamine (BG-Dopa) hydrogel was prepared by distributing the micro-nano BG to aldehyde modified hyaluronic acid with dopamine-modified gelatin. By in vitro and in vivo experiments, we confirm that after implanting in the bone augmentation position, the hydrogel can adhere to the cortical bone surface firmly without sliding. Moreover, the condensation and hypertrophy of stem cells were accelerated at the early stage of ECO. Whereafter, the osteogenic differentiation of the hypertrophic chondrocytes was promoted, which lead to accelerating the late stage of ECO process to achieve more bone augmentation. This experiment provides a new idea for the design of bone augmentation materials.

A Metal-Organic Framework-Incorporated Hydrogel for Delivery of Immunomodulatory Neobavaisoflavone to Promote Cartilage Regeneration in Osteoarthritis

The treatment of osteoarthritis (OA)-related cartilage defects is a great clinical challenge due to the complex pathogenesis of OA and poor self-repair ability of cartilage tissue. Combining local and long-term anti-inflammatory therapies to promote cartilage repair is an effective method to treat OA. In this study, a zinc-organic framework-incorporated extracellular matrix (ECM)-mimicking hydrogel platform was constructed for the inflammatory microenvironment-responsive delivery of neobavaisoflavone (NBIF) to promote cartilage regeneration in OA. The NBIF was encapsulated in situ in zeolitic imidazolate frameworks (ZIF-8 MOFs). The NBIF@ZIF-8 MOFs were decorated with polydopamine and incorporated into a methacrylate gelatin/hyaluronic acid hybrid network to form the NBIF@ZIF-8/PHG hydrogel. The hydrogel featured excellent cell/tissue affinity, providing a favorable microenvironment for recruiting cells and cytokines to the defect sites. The hydrogel enabled the on-demand NBIF released in response to a weakly acidic microenvironment at the injured joint site to resolve inflammatory responses during the early stages of OA. Consequently, the cooperativity of the loaded NBIF and hydrogel synergistically modulated the immune response and assisted in cartilage defect repair. In summary, the NBIF@ZIF-8/PHG hydrogel delivery platform represents an effective treatment strategy for OA-related cartilage defects and may attract attentions for applications in other inflammatory diseases.

A Biomimetic Adhesive and Robust Janus Patch with Anti-Oxidative, Anti-Inflammatory, and Anti-Bacterial Activities for Tendon Repair

Early stage oxidative stress, inflammatory response, and infection after tendon surgery are highly associated with the subsequent peritendinous adhesion formation, which may diminish the quality and function of the repaired tendon. Although various anti-inflammatory and/or antibacterial grafts have been proposed to turn the scale, most of them suffer from the uncertainty of drug-induced adverse effects, low mechanical strength, and tissue adhesiveness. Here, inspired by the tendon anatomy and pathophysiology of adhesion development, an adhesive and robust dual-layer Janus patch is developed, whose inner layer facing the operated tendon is a multifunctional electrospun hydrogel patch (MEHP), encircled further by a poly-l-lactic acid (PLLA) fibrous outer layer facing the surrounding tissue. Specifically, MEHP is prepared by gelatin methacryloyl (GelMA) and zinc oxide (ZnO) nanoparticles, which are co-electrospun first and then treated by tannic acid (TA). The inner MEHP exhibits superior mechanical performance, adhesion strength, and outstanding antioxidation, anti-inflammation, and antibacterial properties, and it can adhere to the injury site offering a favorable microenvironment for tendon regeneration. Meanwhile, the outer PLLA acts as a physical barrier that prevents extrinsic cells and tissues from invading the defect site, reducing peritendinous adhesion formation. This work presents a proof-of-concept of a drug-free graft with anisotropic adhesive and biological functions to concert the healing phases of injured tendon by alleviating incipient inflammation and oxidative damage but supporting tissue regeneration and reducing tendon adhesion in the later phase of repair and remodeling. It is envisioned that this Janus patch could offer a promising strategy for safe and efficient tendon therapy.

Engineered biochemical cues of regenerative biomaterials to enhance endogenous stem/progenitor cells (ESPCs)-mediated articular cartilage repair

As a highly specialized shock-absorbing connective tissue, articular cartilage (AC) has very limited self-repair capacity after traumatic injuries, posing a heavy socioeconomic burden. Common clinical therapies for small- to medium-size focal AC defects are well-developed endogenous repair and cell-based strategies, including microfracture, mosaicplasty, autologous chondrocyte implantation (ACI), and matrix-induced ACI (MACI). However, these treatments frequently result in mechanically inferior fibrocartilage, low cost-effectiveness, donor site morbidity, and short-term durability. It prompts an urgent need for innovative approaches to pattern a pro-regenerative microenvironment and yield hyaline-like cartilage with similar biomechanical and biochemical properties as healthy native AC. Acellular regenerative biomaterials can create a favorable local environment for AC repair without causing relevant regulatory and scientific concerns from cell-based treatments. A deeper understanding of the mechanism of endogenous cartilage healing is furthering the (bio)design and application of these scaffolds. Currently, the utilization of regenerative biomaterials to magnify the repairing effect of joint-resident endogenous stem/progenitor cells (ESPCs) presents an evolving improvement for cartilage repair. This review starts by briefly summarizing the current understanding of endogenous AC repair and the vital roles of ESPCs and chemoattractants for cartilage regeneration. Then several intrinsic hurdles for regenerative biomaterials-based AC repair are discussed. The recent advances in novel (bio)design and application regarding regenerative biomaterials with favorable biochemical cues to provide an instructive extracellular microenvironment and to guide the ESPCs (e.g. adhesion, migration, proliferation, differentiation, matrix production, and remodeling) for cartilage repair are summarized. Finally, this review outlines the future directions of engineering the next-generation regenerative biomaterials toward ultimate clinical translation.

Nano-crosslinked dynamic hydrogels for biomedical applications

Hydrogels resemble natural extracellular matrices and have been widely studied for biomedical applications. Nano-crosslinked dynamic hydrogels combine the injectability and self-healing property of dynamic hydrogels with the versatility of nanomaterials and exhibit unique advantages. The incorporation of nanomaterials as crosslinkers can improve the mechanical properties (strength, injectability, and shear-thinning properties) of hydrogels by reinforcing the skeleton and endowing them with multifunctionality. Nano-crosslinked functional hydrogels that can respond to external stimuli (such as pH, heat, light, and electromagnetic stimuli) and have photothermal properties, antimicrobial properties, stone regeneration abilities, or tissue repair abilities have been constructed through reversible covalent crosslinking strategies and physical crosslinking strategies. The possible cytotoxicity of the incorporated nanomaterials can be reduced. Nanomaterial hydrogels show excellent biocompatibility and can facilitate cell proliferation and differentiation for biomedical applications. This review introduces different nano-crosslinked dynamic hydrogels in the medical field, from fabrication to application. In this review, nanomaterials for dynamic hydrogel fabrication, such as metals and metallic oxides, nanoclays, carbon-based nanomaterials, black phosphorus (BP), polymers, and liposomes, are discussed. We also introduce the dynamic crosslinking method commonly used for nanodynamic hydrogels. Finally, the medical applications of nano-crosslinked hydrogels are presented. We hope that this summary will help researchers in the related research fields quickly understand nano-crosslinked dynamic hydrogels to develop more preparation strategies and promote their development and application.

Alginate/Gelatin Hydrogel Scaffold Containing nCeO2 as a Potential Osteogenic Nanomaterial for Bone Tissue Engineering

Background

Clinicians frequently face difficulties when trying to fix bone abnormalities. Gelatin-Alginate (GA) is frequently employed as a carrier because it is non-toxic, biodegradable, and has a three-dimensional network structure. Meanwhile, cerium oxide nanoparticles (nCeO₂) demonstrated high antioxidant enzyme simulation activity. Therefore, in order to develop a porous hydrogel scaffold for the application of bone tissue engineering, an appropriate-type GA-nCeO₂ hydrogel scaffold was developed and evaluated.

Methods

 GA-nCeO₂ hydrogel scaffold was prepared by the lyophilized method and characterized. The surface morphology and cell adhesion of the scaffold were observed by the scanning electron microscope. CCK8 and live-dead staining methods were used to evaluate its biological safety and cell proliferation. Then the osteogenic differentiation in early and late stages was discussed. The expression of osteogenic genes was also detected by RT-PCR. Finally, a bone defect model was made in SD rats, and bone formation in vivo was detected.

Results

 The results showed that GA-nCeO₂ hydrogel scaffold exhibited a typical three-dimensional porous structure with a mean pore ratio of 70.61 ± 1.94%. The GA-nCeO₂ hydrogel was successfully endowed with simulated enzyme activity including superoxide dismutase (SOD) and catalase (CAT) after the addition of nCeO₂. Osteoblasts demonstrated superior cell proliferation and adhesion on composite scaffolds, and both mineralization test and gene expression demonstrated the strong osteogenic potential of GA-nCeO₂ hydrogel. The outcomes of hematoxylin and eosin (H&E) staining and Masson trichrome staining in the femoral defect model of SD rats further supported the scaffold's favorable biocompatibility and bone-promoting capacity.

Conclusion

Due to its favorable safety, degradability, and bone formation property, GA-nCeO₂ hydrogel was anticipated to be used as a potential bone defect healing material.

The role of the immune microenvironment in bone, cartilage, and soft tissue regeneration: from mechanism to therapeutic opportunity

Bone, cartilage, and soft tissue regeneration is a complex spatiotemporal process recruiting a variety of cell types, whose activity and interplay must be precisely mediated for effective healing post-injury. Although extensive strides have been made in the understanding of the immune microenvironment processes governing bone, cartilage, and soft tissue regeneration, effective clinical translation of these mechanisms remains a challenge. Regulation of the immune microenvironment is increasingly becoming a favorable target for bone, cartilage, and soft tissue regeneration; therefore, an in-depth understanding of the communication between immune cells and functional tissue cells would be valuable. Herein, we review the regulatory role of the immune microenvironment in the promotion and maintenance of stem cell states in the context of bone, cartilage, and soft tissue repair and regeneration. We discuss the roles of various immune cell subsets in bone, cartilage, and soft tissue repair and regeneration processes and introduce novel strategies, for example, biomaterial-targeting of immune cell activity, aimed at regulating healing. Understanding the mechanisms of the crosstalk between the immune microenvironment and regeneration pathways may shed light on new therapeutic opportunities for enhancing bone, cartilage, and soft tissue regeneration through regulation of the immune microenvironment.

A critical review on polydopamine surface-modified scaffolds in musculoskeletal regeneration

Increasing concern about age-related diseases, particularly musculoskeletal injuries and orthopedic conditions, highlights the need for strategies such as tissue engineering to address them. Surface modification has been developed to create pro-healing interfaces, personalize scaffolds and provide novel medicines. Polydopamine, a mussel-inspired adhesive polymer with highly reactive functional groups that adhere to nearly all substrates, has gained attention in surface modification strategies for biomaterials. Polydopamine was primarily developed to modify surfaces, but its effectiveness has opened up promising approaches for further applications in bioengineering as carriers and nanoparticles. This review focuses on the recent discoveries of the role of polydopamine as a surface coating material, with focus on the properties that make it suitable for tackling musculoskeletal disorders. We report the evolution of using it in research, and discuss papers involving the progress of this field. The current research on the role of polydopamine in bone, cartilage, muscle, nerve, and tendon regeneration is discussed, thus giving comprehensive overview about the function of polydopamine both in-vitro and in-vivo. Finally, the report concludes presenting the critical challenges that must be addressed for the clinical translation of this biomaterial while exploring future perspectives and research opportunities in this area.

The effects of process parameters on polydopamine coatings employed in tissue engineering applications

The biomaterials’ success within the tissue engineering field is hinged on the capability to regulate tissue and cell responses, comprising cellular adhesion, as well as repair and immune processes’ induction. In an attempt to enhance and fulfill these biomaterials’ functions, scholars have been inspired by nature; in this regard, surface modification via coating the biomaterials with polydopamine is one of the most successful inspirations endowing the biomaterials with surface adhesive properties. By employing this approach, favorable results have been achieved in various tissue engineering-related experiments, a significant one of which is the more rapid cellular growth observed on the polydopamine-coated substrates compared to the untreated ones; nonetheless, some considerations regarding polydopamine-coated surfaces should be taken into account to control the ultimate outcomes. In this mini-review, the importance of coatings in the tissue engineering field, the different types of surfaces requiring coatings, the significance of polydopamine coatings, critical factors affecting the result of the coating procedure, and recent investigations concerning applications of polydopamine-coated biomaterials in tissue engineering are thoroughly discussed.

Inflammation-mediated matrix remodeling of extracellular matrix-mimicking biomaterials in tissue engineering and regenerative medicine

Extracellular matrix (ECM)-mimicking biomaterials are considered effective tissue-engineered scaffolds for regenerative medicine because of their biocompatibility, biodegradability, and bioactivity. ECM-mimicking biomaterials preserve natural microstructures and matrix-related bioactive components and undergo continuous matrix remodeling upon transplantation. The interaction between host immune cells and transplanted ECM-mimicking biomaterials has attracted considerable attention in recent years. Transplantation of biomaterials may initiate injuries and early pro-inflammation reactions characterized by infiltration of neutrophils and M1 macrophages. Pro-inflammation reactions may lead to degradation of the transplanted biomaterial and drive the matrix into a fetal-like state. ECM degradation leads to the release of matrix-related bioactive components that act as signals for cell migration, proliferation, and differentiation. In late stages, pro-inflammatory cells fade away, and anti-inflammatory cells emerge, which involves macrophage polarization to the M2 phenotype and leukocyte activation to T helper 2 (Th2) cells. These anti-inflammatory cells interact with each other to facilitate matrix deposition and tissue reconstruction. Deposited ECM molecules serve as vital components of the mature tissue and influence tissue homeostasis. However, dysregulation of matrix remodeling results in several pathological conditions, such as aggressive inflammation, difficult healing, and non-functional fibrosis. In this review, we summarize the characteristics of inflammatory responses in matrix remodeling after transplantation of ECM-mimicking biomaterials. Additionally, we discuss the intrinsic linkages between matrix remodeling and tissue regeneration. STATEMENT OF SIGNIFICANCE: Extracellular matrix (ECM)-mimicking biomaterials are effectively used as scaffolds in tissue engineering and regenerative medicine. However, dysregulation of matrix remodeling can cause various pathological conditions. Here, the review describes the characteristics of inflammatory responses in matrix remodeling after transplantation of ECM-mimicking biomaterials. Additionally, we discuss the intrinsic linkages between matrix remodeling and tissue regeneration. We believe that understanding host immune responses to matrix remodeling of transplanted biomaterials is important for directing effective tissue regeneration of ECM-mimicking biomaterials. Considering the close relationship between immune response and matrix remodeling results, we highlight the need for studies of the effects of clinical characteristics on matrix remodeling of transplanted biomaterials.

Polydopamine-Mediated Protein Adsorption Alters the Epigenetic Status and Differentiation of Primary Human Adipose-Derived Stem Cells (hASCs)

Polydopamine (PDA) is a biocompatible cell-adhesive polymer with versatile applications in biomedical devices. Previous studies have shown that PDA coating could improve cell adhesion and differentiation of human mesenchymal stem cells (hMSCs). However, there is still a knowledge gap in the effect of PDA-mediated protein adsorption on the epigenetic status of MSCs. This work used gelatin-coated cell culture surfaces with and without PDA underlayer (Gel and PDA-Gel) to culture and differentiate primary human adipose-derived stem cells (hASCs). The properties of these two substrates were significantly different, which, in combination with a variation in extracellular matrix (ECM) protein bioactivity, regulated cell adhesion and migration. hASCs reduced focal adhesions by downregulating the expression of integrins such as αV, α1, α2, and β1 on the PDA-Gel compared to the Gel substrate. Interestingly, the ratio of H3K27me3 to H3K27me3+H3K4me3 was decreased, but this only occurred for upregulation of AGG and BMP4 genes during chondrogenic differentiation. This result implies that the PDA-Gel surface positively affects the chondrogenic, but not adipogenic and osteogenic, differentiation. In conclusion, for the first time, this study demonstrates the sequential effects of PDA coating on the biophysical property of adsorbed protein and then focal adhesions and differentiation of hMSCs through epigenetic regulation. This study sheds light on PDA-mediated mechanotransduction.

The role of microenvironment in stem cell-based regeneration of intervertebral disc

Regenerative medicine for intervertebral disc (IVD) disease, by utilizing chondrocytes, IVD cells, and stem cells, has progressed to clinical trials in the treatment of back pain, and has been studied in various animal models of disc degeneration in the past decade. Stem cells exist in their natural microenvironment, which provides vital dynamic physical and chemical signals for their survival, proliferation and function. Long-term survival, function and fate of mesenchymal stem cells (MSCs) depend on the microenvironment in which they are transplanted. However, the transplanted MSCs and the endogenous disc cells were influenced by the complicated microenvironment in the degenerating disc with the changes of biochemical and biophysical components. It is important to understand how the MSCs and endogenous disc cells survive and thrive in the harsh microenvironment of the degenerative disc. Furthermore, materials containing stem cells and their natural microenvironment have good clinical effects. However, the implantation of tissue engineering IVD (TE-IVD) cannot provide a complete and dynamic microenvironment for MSCs. IVD graft substitutes may need further improvement to provide the best engineered MSC microenvironment. Additionally, the IVD progenitor cells inside the stem cell niches have been regarded as popular graft cells for IVD regeneration. However, it is still unclear whether actual IVD progenitor cells exist in degenerative spinal conditions. Therefore, the purpose of this review is fourfold: to discuss the presence of endogenous stem cells; to review and summarize the effects of the microenvironment in biological characteristics of MSC, especially those from IVD; to explore the feasibility and prospects of IVD graft substitutes and to elaborate state of the art in the use of MSC transplantation for IVD degeneration in vivo as well as their clinical application.