Synthetic presentation of noncanonical Wnt5a motif promotes mechanosensing-dependent differentiation of stem cells and regeneration

Advancement in smart bone implants: the latest multifunctional strategies and synergistic mechanisms for tissue repair and regeneration

Artificial implants have consistently been recognized as the most effective clinical strategy for repairing bone fractures and defects, particularly in orthopedics and stomatology. Nowadays, the focus of bone repair has shifted from basic fixation and structural restoration to the reconstruction of multifunctional "live" tissue to mimic the natural bone microenvironment. However, developing the smart implants with ideal osteogenesis-related multi-functions remains challenging, as the effects of physicochemical properties of implant materials on intracellular signaling, stem cell niches, and tissue regeneration are not yet fully understood. Herein, we systematically explore recent advancements in innovative strategies for bone repair and regeneration, revealing the significance of the smart implants that closely mimic the natural structure and function of bone tissue. Adaptation to patient-oriented osteogenic microenvironments, dynamic osteoblastogenesis-osteoclastogenesis balance, antibacterial/bactericidal capacity, vascularization, and osteoimmunomodulatory capacity and their regulatory mechanisms achieved by biomaterials design and functional modifications are thoroughly summarized and analyzed. Notably, the popular research on multifunctional platforms with synergetic interactions between different functions and treatment of complex clinical issues, including the emerging neurogenic bone repair, is also significantly discussed for developing more intelligent implants. By summarizing recent research efforts, this review proposes the latest multifunctional strategies and synergistic mechanisms of smart bone implants, aiming to provide better bone defect repair applications that more closely mimic the natural bone tissue.

Metabolite-dependent m6A methylation driven by mechanotransduction-metabolism-epitranscriptomics axis promotes bone development and regeneration

Intramembranous ossification, a major bone development process, begins with the condensation of precursor cells through the timely structural adaption of extracellular matrix (ECM) catering to rapid cellular morphological changes. Inspired by this, we design a highly cell-adaptable hydrogel to recapitulate an ECM-dependent mechanotransduction-metabolism-epitranscriptomics axis in mesenchymal stromal cells (MSCs). This hydrogel significantly enhances the E-cadherin-mediated cell-cell interactions of MSCs and promotes glucose uptake and tricarboxylic acid (TCA) cycle activities. We further show that elevated succinate inhibits fat mass and obesity-associated protein (FTO), a N6-methyladenosine (m6A) demethylase, thereby enhancing methyltransferase-like 3 (METTL3)-driven m6A methylation. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) indicates increased m6A methylation of runt-related transcription 2 (Runx2), a key osteogenic signaling factor, promoting osteogenesis of hydrogel-delivered MSCs and bone regeneration in critical-sized bone defects. Our findings reveal the mechanism underlying the critical impact of adaptable ECM structures on tissue development and provide valuable guidance for the design of ECM-mimetic cell carriers to enhance the therapeutic outcomes of regenerative medicine.

Hydrogels with programmed spatiotemporal mechanical cues for stem cell-assisted bone regeneration

Hydrogels are extensively utilized in stem cell-based tissue regeneration, providing a supportive environment that facilitates cell survival, differentiation, and integration with surrounding tissues. However, designing hydrogels for regenerating hard tissues like bone presents significant challenges. Here, we introduce macroporous hydrogels with spatiotemporally programmed mechanical properties for stem cell-driven bone regeneration. Using liquid-liquid phase separation and interfacial supramolecular self-assembly of protein fibres, the macroporous structure of hydrogels provide ample space to prevent contact inhibition during proliferation. The rigid protein fibre-coated pore shell provides sustained mechanical cues for guiding osteodifferentiation and protecting against mechanical loads. Temporally, the hydrogel exhibits tunable degradation rates that can synchronize with new tissue deposition to some extent. By integrating localized mechanical heterogeneity, macroporous structures, surface chemistry, and regenerative degradability, we demonstrate the efficacy of these stem cell-encapsulated hydrogels in rabbit and porcine models. This marks a substantial advancement in tailoring the mechanical properties of hydrogels for stem cell-assisted tissue regeneration.

Injectable hydrogel microspheres promoting inflammation modulation and nucleus pulposus-like differentiation for intervertebral disc regeneration

Local inflammation modulation and stem cell therapy have attracted much attention in the treatment of intervertebral disc degeneration (IDD). However, severe oxidative stress and limited nucleus pulposus (NP)-like differentiation of stem cells largely impair biomaterial implantation's therapeutic efficacy. Due to their excellent performance in injectability and flowability, and minor compression to NP tissue, hydrogel microspheres have become an attractive carrier for IDD treatment. Herein, an injectable hydrogel microsphere consisting of Wnt5a-mimetic peptide Foxy5- and the antioxidative peptide-grafted gelatin methacryloyl matrix (GFA), was developed as a stem cell delivery system for IDD therapy. Being fabricated and encapsulating bone marrow-derived mesenchymal stem cells (BMSCs) using the microfluidic technology, GFA hydrogel microspheres ameliorate IDD by promoting inflammation inhibition, NP-like differentiation and extracellular matrix regeneration. They efficiently eliminated reactive oxygen species, and downregulated the inflammation level through the inhibition of interleukin-17B/nuclear factor-κB signaling pathway. Moreover, the NP-like differentiation of BMSCs was effectively stimulated by Foxy5 via the calcium/calmodulin dependent protein kinase kinase 2/protein kinase A/sex determining region Y box protein 9 signaling pathway, thereby leading to a rebalance between the generation and degradation of NP matrix. In vivo rat IDD model demonstrated that BMSC-loaded GFA hydrogel microspheres mitigated local inflammation, preserved disc height, and promoted intervertebral disc regeneration. In conclusion, this study introduces an BMSC-loaded injectable hydrogel microspheres as a promising therapy for regulating the microenvironment and alleviating the progression of IDD.

Role of Wnt5a in modulation of osteoporotic adipose-derived stem cells and osteogenesis

Osteoporosis, a condition marked by the deterioration of bone microarchitecture and increased facture risk, arises from a disruption in bone metabolism, with osteoclasts surpassing osteoblasts in bone resorption versus formation. The Wnt signalling pathway, a key regulator of bone maintenance, remains partially understood in osteoporosis. Our research delves into the role of Wnt-related molecules in this disease. In osteoporotic adipose-derived stem cells (OP-ASCs), we detected a significant decrease in Ctnnb1 and Frizzled-6 (Fzd6), contrasted by an increase in Gsk-3β and Wnt5a. Activation of the Wnt pathway by LiCl resulted in elevated Ctnnb1 and Fzd6, but decreased Gsk-3β and Wnt5a levels, promoting OP-ASCs' bone-formation capacity. In contrast, inhibition of this pathway by DKK-1 led to diminished Ctnnb1 and Fzd6, and increased Gsk-3β and Wnt5a, adversely affecting osteogenesis. Furthermore, our findings show that overexpressing Wnt5a impedes, while silencing it enhances the bone-forming capability of OP-ASCs. In a cranial bone defect model, the implantation of Wnt5a-silenced OP-ASCs with biphasic calcium phosphate scaffolds significantly promoted new bone formation. These observations indicated a repression of the canonical Wnt pathway and a stimulation of the non-canonical pathway in OP-ASCs. Silencing Wnt5a increased the osteogenic and regenerative abilities of OP-ASCs. Our study suggests targeting Wnt5a could be a promising strategy for enhancing bone regeneration in post-menopausal osteoporosis.

Magnesium Nanocomposite Hydrogel Reverses the Pathologies to Enhance Mandible Regeneration

The healing of bone defects after debridement in medication-related osteonecrosis of the jaw (MRONJ) is a challenging medical condition with impaired angiogenesis, susceptible infection, and pro-inflammatory responses. Magnesium (Mg) nanocomposite hydrogel is developed to specifically tackle multiple factors involved in MRONJ. Mg-oxide nanoparticles tune the gelation kinetics in the reaction between N-hydroxysuccinimide-functionalized hyperbranched poly (ethylene glycol) and proteins. This reaction allows an enhanced mechanical property after instant solidification and, more importantly, also stable gelation in challenging environments such as wet and hemorrhagic conditions. The synthesized hydrogel guides mandible regeneration in MRONJ rats by triggering the formation of type H vessels, activating Osterix+ osteoprogenitor cells, and generating anti-inflammatory microenvironments. Additionally, this approach demonstrates its ability to suppress infection by inhibiting specific pathogens while strengthening stress tolerance in the affected alveolar bone. Furthermore, the enhanced osteogenic properties and feasibility of implantation of the hydrogel are validated in mandible defect and iliac crest defect created in minipigs, respectively. Collectively, this study offers an injectable and innovative bone substitute to enhance mandible defect healing by tackling multiple detrimental pathologies.

Harnessing the potential of hyaluronic acid methacrylate (HAMA) hydrogel for clinical applications in orthopaedic diseases

The treatment of orthopaedic diseases, such as fractures and osteoarthritis, remains a significant challenge due to the complex requirements for mechanical strength and tissue repair. Hydrogels based on hyaluronic acid methacrylate (HAMA) show promise as tissue engineering materials for these conditions. Hyaluronic acid (HA) is a natural component of the extracellular matrix, known for its good compatibility. The mechanical strength of HAMA-based hydrogels can be adjusted through crosslinking and by combining them with other materials. This review provides an overview of recent research on HAMA-based hydrogels for tissue engineering applications in orthopaedic diseases. First, we summarize the techniques for the preparation and characterization of HAMA hydrogels. Next, we offer a detailed review of the use of HAMA-based hydrogels in treating conditions such as cartilage injuries, bone defects, and meniscus injuries. Additionally, we discuss the applications of HAMA-based hydrogels in other diseases related to orthopaedics. Finally, we point out the challenges and propose future directions for the clinical translation of HAMA-based hydrogels.

Translational potential statement

HAMA-based hydrogels show strong translational potential in orthopaedics due to their biocompatibility, adjustable mechanical properties, and regenerative capabilities. With ongoing research, these hydrogels are well-positioned for clinical applications, particularly in cartilage repair, meniscus injuries, and osteoarthritis treatment.

Advances in ligand-based surface engineering strategies for fine-tuning T cell mechanotransduction toward efficient immunotherapy

T cell-based immunotherapy has recently emerged as a promising strategy to treat cancer, requiring the activation of antigen-directed cytotoxicity to eliminate cancer cells. Mechanical signaling, although often overshadowed by its biochemical counterpart, plays a crucial role in T cell anticancer responses, from activation to cytolytic killing. Rapid advancements in the fields of chemistry, biomaterials, and micro/nanoengineering offer an interdisciplinary approach to incorporating mechano- and immunomodulatory ligands, including but not limited to synthetic peptides, small molecules, cytokines, and artificial antigens, onto the biomaterial-based platforms to modulate mechanotransducive processes in T cells. The surface engineering of these immunomodulatory ligands with optimization of ligand density, geometrical arrangement, and mobility has been proven to better mimic the natural ligation between immunoreceptors and ligands to directly enhance or inhibit mechanotransduction pathways in T cells, through triggering upstream mechanosensitive channels, adhesion molecules, cytoskeletal components, or downstream mechanoimmunological regulators. Despite its tremendous potential, current research on this new biomaterial surface engineering approach for mechanomodulatory T cell activation and effector functions remains in a nascent stage. This review highlights the recent progress in this new direction, focusing on achievements in mechanomodulatory ligand-based surface engineering strategies and underlying principles, and outlooks the further research in the rapidly evolving field of T cell mechanotransduction engineering for efficient immunotherapy.

Heraclenin promotes the osteogenic differentiation of bone marrow stromal cells by activating the RhoA/ROCK pathway

BACKGROUND

Osteoporosis is a devastating skeletal disease, the pathogenesis of which is related to abnormal bone metabolism, featured by the imbalance between osteoblastic bone formation and osteoclastic bone resorption. Stem cell-based therapies have been demonstrated to improve osteoporosis treatment. Previously, the linear furanocoumarin heraclenin was reported to enhance osteoblast differentiation and mineralization in mouse mesenchymal stem cells (MSCs), suggesting its potential for osteogenic differentiation and bone regeneration. Our study was designed to confirm the promotive role of heraclenin on osteogenic differentiation of human bone MSCs (BMSCs) and explore the underlying mechanisms.

METHODS

Human BMSCs were treated for 24, 48, and 72h with heraclenin (5, 10, 20, 40, and 80 μM), and cell viability was determined by Cell Counting Kit-8 (CCK-8) assay. To further evaluate the cytotoxicity of heraclenin, cell suspension obtained from BMSCs treated with heraclenin (5, 10, and 20 μM) for 72h was subjected to a MUSE™ cell analyzer for cell viability and count assay. BMSCs were incubated in osteogenic induction medium for 7 days. Then, osteogenic differentiation and mineralization of BMSCs were assessed through alkaline phosphatase (ALP) and Alizarin Red S staining. The expression of osteogenesis markers including ALP, osteocalcin (OCN), osterix (OSX), and runt-related transcription factor 2 (RUNX2) was detected via reverse transcription quantitative polymerase chain reaction (RT-qPCR) and western blotting. The effects of heraclenin on the RhoA/ROCK pathway were estimated through western blotting. Y-27632, the ROCK inhibitor, was used to confirm the role of the RhoA/ROCK pathway in heraclenin-mediated osteogenic differentiation of BMSCs.

RESULTS

Heraclenin (5-80 μM) was non-toxic on human BMSCs. Heraclenin treatment (5-20 μM) dose-dependently enhanced ALP activity and calcium deposition. Furthermore, heraclenin promoted ALP, OCN, OSX, and RUNX2 mRNA and protein expression. Mechanically, heraclenin treatment increased RhoA and ROCK1 mRNA expression, stimulated the translocation of ROCK from the cytosolic to the membrane fraction, and elevated the protein levels of phosphorylated cofilin (p-cofilin) and active RhoA. Additionally, treatment with Y-27632 overturned the promotion of heraclenin on ALP activity, calcium deposition, the expression of osteogenesis markers, and the RhoA/ROCK signaling pathway.

CONCLUSION

Heraclenin facilitates the osteogenic differentiation of human BMSCs through the activation of the RhoA/ROCK pathway.

Biomimetic Hydrogels as the Inductive Endochondral Ossification Template for Promoting Bone Regeneration

Repairing critical size bone defects (CSBD) is a major clinical challenge and requires effective intervention by biomaterial scaffolds. Inspired by the fact that the cartilaginous template-based endochondral ossification (ECO) process is crucial to bone healing and development, developing biomimetic biomaterials to promote ECO is recognized as a promising approach for repairing CSBD. With the unique highly hydrated 3D polymeric network, hydrogels can be designed to closely emulate the physiochemical properties of cartilage matrix to facilitate ECO. In this review, the various preparation methods of hydrogels possessing the specific physiochemical properties required for promoting ECO are introduced. The materiobiological impacts of the physicochemical properties of hydrogels, such as mechanical properties, topographical structures and chemical compositions on ECO, and the associated molecular mechanisms related to the BMP, Wnt, TGF-β, HIF-1α, FGF, and RhoA signaling pathways are further summarized. This review provides a detailed coverage on the materiobiological insights required for the design and preparation of hydrogel-based biomaterials to facilitate bone regeneration.

Cellular Scale Curvature in Bioceramic Scaffolds Enhanced Bone Regeneration by Regulating Skeletal Stem Cells and Vascularization

Critical-sized segmental bone defects cannot heal spontaneously, leading to disability and significant increase in mortality. However, current treatments utilizing bone grafts face a variety of challenges from donor availability to poor osseointegration. Drugs such as growth factors increase cancer risk and are very costly. Here, a porous bioceramic scaffold that promotes bone regeneration via solely mechanobiological design is reported. Two types of scaffolds with high versus low pore curvatures are created using high-precision 3D printing technology to fabricate pore curvatures radius in the 100s of micrometers. While both are able to support bone formation, the high-curvature pores induce higher ectopic bone formation and increased vessel invasion. Scaffolds with high-curvature pores also promote faster regeneration of critical-sized segmental bone defects by activating mechanosensitive pathways. High-curvature pore recruits skeletal stem cells and type H vessels from both the periosteum and the marrow during the early phase of repair. High-curvature pores have increased survival of transplanted GFP-labeled skeletal stem cells (SSCs) and recruit more host SSCs. Taken together, the bioceramic scaffolds with defined micrometer-scale pore curvatures demonstrate a mechanobiological approach for orthopedic scaffold design.

Fructose-mineralized black phosphorus for syncretic bone regeneration and tumor suppression

Black phosphorus (BPs) nanosheets with their inherent and selective chemotherapeutic effects have recently been identified as promising cancer therapeutic agents, but challenges in surface functionalization hinder satisfactory enhancement of their selectivity between tumors and normal cells. To address this issue, we developed a novel biomineralization-inspired strategy to synthesize CaBPs-Na2FDP@CaCl2 nanosheets, aiming to achieve enhanced and selective anticancer bioactivity along with accelerated osteoblast activity. Benefiting from the in situ mineralization and fructose modification, CaBPs-Na2FDP@CaCl2 exhibited improved pH-responsive degradation behavior and targeted therapy for osteosarcoma. The in vitro results indicated that CaBPs-Na2FDP@CaCl2 exhibited efficient uptake and quick degradation by GLUT5-positive 143B osteosarcoma cells, enhancing BPs-driven chemotherapeutic effects through ATP level disturbance-mediated apoptosis of tumor cells. Moreover, CaBPs-Na2FDP@CaCl2 underwent gradual degradation into PO43-, Ca2+ and fructose in MC3T3-E1 cells, eliminating systemic toxicity. Intracellular Ca2+ bound to calmodulin (CaM), activating Ca2+/CaM-dependent signaling cascades, thereby enhancing osteoblast differentiation and mineralization in pro-osteoblastic cells. In vivo experiments affirmed the anti-tumor capability, inhibition of tumor recurrence and bone repair promotion of CaBPs-Na2FDP@CaCl2. This study not only broadens the application of BPs in bone tumor therapy but also provides a versatile surface functionalization strategy for nanotherapeutic agents.

Human dental pulp stem cells derived extracellular matrix promotes mineralization via Hippo and Wnt pathways

Extracellular matrix (ECM) is an intricate structure providing the microenvironment niche that influences stem cell differentiation. This study aimed to investigate the efficacy of decellularized ECM derived from human dental pulp stem cells (dECM_DPSCs) and gingival-derived mesenchymal stem cells (dECM_GSCs) as an inductive scaffold for osteogenic differentiation of GSCs. The proteomic analysis demonstrated that common and signature matrisome proteins from dECM_DPSCs and dECM_GSCs were related to osteogenesis/osteogenic differentiation. RNA sequencing data from GSCs reseeded on dECM_DPSCs revealed that dECM_DPSCs upregulated genes related to the Hippo and Wnt signaling pathways in GSCs. In the inhibitor experiments, results revealed that dECM_DPSCs superiorly promoted GSCs osteogenic differentiation, mainly mediated through Hippo and Wnt signaling. The present study emphasizes the promising translational application of dECM_DPSCs as a bio-scaffold rich in favorable regenerative microenvironment for tissue engineering.

PRX1-positive mesenchymal stem cells drive molar morphogenesis

Mammalian teeth, developing inseparable from epithelial-mesenchymal interaction, come in many shapes and the key factors governing tooth morphology deserve to be answered. By merging single-cell RNA sequencing analysis with lineage tracing models, we have unearthed a captivating correlation between the contrasting morphology of mouse molars and the specific presence of PRX1+ cells within M1. These PRX1+ cells assume a profound responsibility in shaping tooth morphology through a remarkable divergence in dental mesenchymal cell proliferation. Deeper into the mechanisms, we have discovered that Wnt5a, bestowed by mesenchymal PRX1+ cells, stimulates mesenchymal cell proliferation while orchestrating molar morphogenesis through WNT signaling pathway. The loss of Wnt5a exhibits a defect phenotype similar to that of siPrx1. Exogenous addition of WNT5A can successfully reverse the inhibited cell proliferation and consequent deviant appearance exhibited in Prx1-deficient tooth germs. These findings bestow compelling evidence of PRX1-positive mesenchymal cells to be potential target in regulating tooth morphology.

Bioactive Scaffolds as a Promising Alternative for Enhancing Critical-Size Bone Defect Regeneration in the Craniomaxillofacial Region

Reconstruction of critical-size bone defects (CSDs) in the craniomaxillofacial (CMF) region remains challenging. Scaffold-based bone-engineered constructs have been proposed as an alternative to the classical treatments made with autografts and allografts. Scaffolds, a key component of engineered constructs, have been traditionally viewed as biologically passive temporary replacements of deficient bone lacking intrinsic cues to promote osteogenesis. Nowadays, scaffolds are functionalized, giving rise to bioactive scaffolds promoting bone regeneration more effectively than conventional counterparts. This review focuses on the three approaches most used to bioactivate scaffolds: (1) conferring microarchitectural designs or surface nanotopography; (2) loading bioactive molecules; and (3) seeding stem cells on scaffolds, providing relevant examples of in vivo (preclinical and clinical) studies where these methods are employed to enhance CSDs healing in the CMF region. From these, adding bioactive molecules (specifically bone morphogenetic proteins or BMPs) to scaffolds has been the most explored to bioactivate scaffolds. Nevertheless, the downsides of grafting BMP-loaded scaffolds in patients have limited its successful translation into clinics. Despite these drawbacks, scaffolds containing safer, cheaper, and more effective bioactive molecules, combined with stem cells and topographical cues, remain a promising alternative for clinical use to treat CSDs in the CMF complex replacing autografts and allografts.

Convergence of Calcium Channel Regulation and Mechanotransduction in Skeletal Regenerative Biomaterial Design

Cells are known to perceive their microenvironment through extracellular and intracellular mechanical signals. Upon sensing mechanical stimuli, cells can initiate various downstream signaling pathways that are vital to regulating proliferation, growth, and homeostasis. One such physiologic activity modulated by mechanical stimuli is osteogenic differentiation. The process of osteogenic mechanotransduction is regulated by numerous calcium ion channels-including channels coupled to cilia, mechanosensitive and voltage-sensitive channels, and channels associated with the endoplasmic reticulum. Evidence suggests these channels are implicated in osteogenic pathways such as the YAP/TAZ and canonical Wnt pathways. This review aims to describe the involvement of calcium channels in regulating osteogenic differentiation in response to mechanical loading and characterize the fashion in which those channels directly or indirectly mediate this process. The mechanotransduction pathway is a promising target for the development of regenerative materials for clinical applications due to its independence from exogenous growth factor supplementation. As such, also described are examples of osteogenic biomaterial strategies that involve the discussed calcium ion channels, calcium-dependent cellular structures, or calcium ion-regulating cellular features. Understanding the distinct ways calcium channels and signaling regulate these processes may uncover potential targets for advancing biomaterials with regenerative osteogenic capabilities.

Matrix stiffness regulates osteoclast fate through integrin-dependent mechanotransduction

Osteoclasts ubiquitously participate in bone homeostasis, and their aberration leads to bone diseases, such as osteoporosis. Current clinical strategies by biochemical signaling molecules often perturb innate bone metabolism owing to the uncontrolled management of osteoclasts. Thus, an alternative strategy of precise regulation for osteoclast differentiation is urgently needed. To this end, this study proposed an assumption that mechanic stimulation might be a potential strategy. Here, a hydrogel was created to imitate the physiological bone microenvironment, with stiffnesses ranging from 2.43kPa to 68.2kPa. The impact of matrix stiffness on osteoclast behaviors was thoroughly investigated. Results showed that matrix stiffness could be harnessed for directing osteoclast fate in vitro and in vivo. In particular, increased matrix stiffness inhibited the integrin β3-responsive RhoA-ROCK2-YAP-related mechanotransduction and promoted osteoclastogenesis. Notably, preosteoclast development is facilitated by medium-stiffness hydrogel (M-gel) possessing the same stiffness as vessel ranging from 17.5 kPa to 44.6 kPa by partial suppression of mechanotransduction, which subsequently encouraged revascularization and bone regeneration in mice with bone defects. Our works provide an innovative approach for finely regulating osteoclast differentiation by selecting the optimum matrix stiffness and enable us further to develop a matrix stiffness-based strategy for bone tissue engineering.

Advances and Prospects in Materials for Craniofacial Bone Reconstruction

The craniofacial region is composed of 23 bones, which provide crucial function in keeping the normal position of brain and eyeballs, aesthetics of the craniofacial complex, facial movements, and visual function. Given the complex geometry and architecture, craniofacial bone defects not only affect the normal craniofacial structure but also may result in severe craniofacial dysfunction. Therefore, the exploration of rapid, precise, and effective reconstruction of craniofacial bone defects is urgent. Recently, developments in advanced bone tissue engineering bring new hope for the ideal reconstruction of the craniofacial bone defects. This report, presenting a first-time comprehensive review of recent advances of biomaterials in craniofacial bone tissue engineering, overviews the modification of traditional biomaterials and development of advanced biomaterials applying to craniofacial reconstruction. Challenges and perspectives of biomaterial development in craniofacial fields are discussed in the end.

Growth factor-loaded sulfated microislands in granular hydrogels promote hMSCs migration and chondrogenic differentiation

Cell-based therapies for articular cartilage lesions are expensive and time-consuming; clearly, a one-step procedure to induce endogenous repair would have significant clinical benefits. Acellular heterogeneous granular hydrogels were explored for their injectability, cell-friendly cross-linking, and ability to promote migration, as well as to serve as a scaffold for depositing cartilage extracellular matrix. The hydrogels were prepared by mechanical sizing of bulk methacrylated hyaluronic acid (HAMA) and bulk HAMA incorporating sulfated HAMA (SHAMA). SHAMA's negative charges allowed for the retention of positively charged growth factors (GFs) (e.g., TGFB3 and PDGF-BB). Mixtures of HAMA and GF-loaded SHAMA microgels were annealed by enzymatic cross-linking, forming heterogeneous granular hydrogels with GF deposits. The addition of GF loaded sulfated microislands guided cell migration and enhanced chondrogenesis. Granular heterogeneous hydrogels showed increased matrix deposition and cartilage tissue maturation compared to bulk or homogeneous granular hydrogels. This advanced material provides an ideal 3D environment for guiding cell migration and differentiation into cartilage. STATEMENT OF SIGNIFICANCE: Acellular materials which promote regeneration are of great interest for repair of cartilage defects, and they are more cost- and time-effective compared to current cell-based therapies. Here we develop an injectable, granular hydrogel system which promotes cell migration from the surrounding tissue, facilitating endogenous repair. The hydrogel architecture and chemistry were optimized to increase cell migration and extracellular matrix deposition. The present study provides quantitative data on the effect of microgel size and chemical modification on cell migration, growth factor retention and tissue maturation.

Functionalized hydrogel-microsphere composites stimulating neurite outgrowth for vascularized bone regeneration

Neurovascularized bone regeneration remains an enormous challenge in the clinic. Biomaterials mimicking the developmental microenvironment might be promising tools to enhance tissue regeneration. In this study, functionalized hydrogel-microsphere composites are developed to enhance bone regeneration via a recapitulating neurovascularized microenvironment. RGD peptide and the porous structure generated by the degradation of gelatin microspheres (GMs) are beneficial for the proliferation and migration of human mesenchymal stem cells (hMSCs); mesoporous silica nanoparticles (MSNs) promote osteogenic differentiation of hMSCs through the delivery of BFP-1 peptide; the QK peptide from the GMs is sustained-released to recruit endogenous endothelial cells (ECs), and IK19 peptide grafted on the hydrogel guides the neurite outgrowth. The in vivo results show that the hydrogel-microsphere composites not only promote new bone formation, but also facilitate nerve infiltration and angiogenesis. Furthermore, the neurovascularized niche created by this composite stimulated neurite growth through MAPK, PI3K, IL17 and TNF signaling pathways, enabling vascularized bone regeneration. The findings suggest a novel bioengineering approach to guide the construction of neurovascularized bone repair materials, which is beneficial for achieving functional bone regeneration and repair.

Biomimetic Nanofibrillar Hydrogel with Cell-Adaptable Network for Enhancing Cellular Mechanotransduction, Metabolic Energetics, and Bone Regeneration

The natural extracellular matrix, with its heterogeneous structure, provides a stable and dynamic biophysical framework and biochemical signals to guide cellular behaviors. It is challenging but highly desirable to develop a synthetic matrix that emulates the heterogeneous fibrous structure with macroscopic stability and microscopical dynamics and contains inductive biochemical signals. Herein, we introduce a peptide fiber-reinforced hydrogel in which the stiff ß-sheet fiber functions as a multivalent cross-linker to enhance the hydrogel's macroscopic stability. The dynamic imine cross-link between the peptide fiber and polymer network endows the hydrogel with a microscopically dynamic network. The obtained fibrillar nanocomposite hydrogel, with its cell-adaptable dynamic network, enhances cell-matrix and cell-cell interactions and therefore significantly promotes the mechanotransduction, metabolic energetics, and osteogenesis of encapsulated stem cells. Furthermore, the hydrogel can codeliver a fiber-attached inductive drug to further enhance osteogenesis and bone regeneration. We believe that our work provides valuable guidance for the design of cell-adaptive and bioactive biomaterials for therapeutic applications.

Engineering Strategies to Move from Understanding to Steering Renal Tubulogenesis

Rebuilding the kidney in the context of tissue engineering offers a major challenge as the organ is structurally complex and has a high variety of specific functions. Recreation of kidney function is inherently connected to the formation of tubules since the functional subunit of the kidney, the nephron, is based on tubular structures. In vivo, tubulogenesis culminates in a perfectly shaped, patterned, and functional renal tubule via different morphogenic processes that depend on delicately orchestrated chemical, physical, and mechanical interactions between cells and between cells and their microenvironment. This review summarizes the current understanding of the role of the microenvironment in the morphogenic processes involved in in vivo renal tubulogenesis. We highlight the current state-of-the-art of renal tubular engineering and provide a view on the design elements that can be extracted from these studies. Next, we discuss how computational modeling can aid in specifying and identifying design parameters and provide directions on how these design parameters can be incorporated in biomaterials for the purpose of engineering renal tubulogenesis. Finally, we propose that a step-by-step reciprocal interaction between understanding and engineering is necessary to effectively guide renal tubulogenesis. Impact statement Tubular tissue engineering lies at the foundation of regenerating kidney tissue function, as the functional subunit of the kidney, the nephron, is based on tubular structures. Guiding renal tubulogenesis toward functional renal tubules requires in-depth knowledge of the developmental processes that lead to the formation of native tubules as well as engineering approaches to steer these processes. In this study, we review the role of the microenvironment in the developmental processes that lead to functional renal tubules and give directions how this knowledge can be harnessed for biomaterial-based tubular engineering using computational models.

Bioactive peptides for boosting stem cell culture platform: Methods and applications

Peptides, short protein fragments, can emulate the functions of their full-length native counterparts. Peptides are considered potent recombinant protein alternatives due to their specificity, high stability, low production cost, and ability to be easily tailored and immobilized. Stem cell proliferation and differentiation processes are orchestrated by an intricate interaction between numerous growth factors and proteins and their target receptors and ligands. Various growth factors, functional proteins, and cellular matrix-derived peptides efficiently enhance stem cell adhesion, proliferation, and directed differentiation. For that, peptides can be immobilized on a culture plate or conjugated to scaffolds, such as hydrogels or synthetic matrices. In this review, we assess the applications of a variety of peptides in stem cell adhesion, culture, organoid assembly, proliferation, and differentiation, describing the shortcomings of recombinant proteins and their full-length counterparts. Furthermore, we discuss the challenges of peptide applications in stem cell culture and materials design, as well as provide a brief outlook on future directions to advance peptide applications in boosting stem cell quality and scalability for clinical applications in tissue regeneration.

Light-controlled scaffold- and serum-free hard palatal-derived mesenchymal stem cell aggregates for bone regeneration

Cell aggregates that mimic in vivo cell-cell interactions are promising and powerful tools for tissue engineering. This study isolated a new, easily obtained, population of mesenchymal stem cells (MSCs) from rat hard palates named hard palatal-derived mesenchymal stem cells (PMSCs). The PMSCs were positive for CD90, CD44, and CD29 and negative for CD34, CD45, and CD146. They exhibited clonogenicity, self-renewal, migration, and multipotent differentiation capacities. Furthermore, this study fabricated scaffold-free 3D aggregates using light-controlled cell sheet technology and a serum-free method. PMSC aggregates were successfully constructed with good viability. Transplantation of the PMSC aggregates and the PMSC aggregate-implant complexes significantly enhanced bone formation and implant osseointegration in vivo, respectively. This new cell resource is easy to obtain and provides an alternative strategy for tissue engineering and regenerative medicine.

Zonally Stratified Decalcified Bone Scaffold with Different Stiffness Modified by Fibrinogen for Osteochondral Regeneration of Knee Joint Defect

Articular cartilage is generally known to be a complex tissue with multiple layers. Each layer has different composition, structure, and mechanical properties, making regeneration after knee joint defects a troubling clinical problem. A novel integrated stratified decalcified bone matrix (SDBM) scaffold with different stiffness to mimic the mechanical properties of articular cartilage is presented herein. This SDBM scaffold was modified using fibrinogen (Fg) (Fg + SDBM) to enhance its vascularization ability and improve its repair efficiency for osteochondral defects of knee joints. A Fg + SDBM scaffold with different elastic modulus in each layer (high-stiffness DBM (HDBM) layer, 174.208 ± 44.330 MPa (Fg + HDBM); medium-stiffness DBM (MDBM) layer, 21.214 ± 6.922 MPa (Fg + MDBM); and low-stiffness DBM (LDBM) layer, 0.678 ± 0.269 MPa (Fg + LDBM)) was constructed by controlling the stratified decalcification time with layered embedding paraffin (0, 3, and 5 days). The low- and medium-stiffness layers of the Fg + SDBM scaffold remarkably promoted the cartilage differentiation of bone marrow mesenchymal stem cells in vitro. Subcutaneous transplantation and rabbit knee joint osteochondral defect repair experiments revealed that the low- and medium-stiffness layers of the Fg + SDBM scaffold exhibited wonderful cartilage capacity, whereas the high-stiffness layer of Fg + SDBM scaffold exhibited good osteogenesis ability. Furthermore, this scaffold could promote blood vessel formation in subchondral bone area. This study presents a feasible strategy for osteochondral regeneration of defective knee joints, which is of great clinical value for tissue repair.

Immunomodulatory Blood-Derived Hybrid Hydrogels as Multichannel Microenvironment Modulators for Augmented Bone Regeneration

Autologous blood-derived protein hydrogels have shown great promise in the field of personalized regenerative medicine. However, the inhospitable regenerative microenvironments, especially the unfavorable immune microenvironment, are closely associated with their limited tissue-healing outcomes. Herein, novel immunomodulatory blood-derived hybrid hydrogels (PnP-iPRF) are rationally designed and constructed for enhanced bone regeneration via multichannel regulation of the osteogenic microenvironment. Such double-network hybrid hydrogels are composed of clinically approved injectable platelet-rich fibrin (i-PRF) and polycaprolactone/hydroxyapatite composite nanofibers by using enriched polydopamine (PDA) as the anchor. The polycaprolactone component in PnP-iPRF provides a reinforced structure to stimulate osteoblast differentiation in a proper biomechanical microenvironment. Most importantly, the versatile PDA component in PnP-iPRF can not only offer high adhesion capacity to the growth factors of i-PRF and create a suitable biochemical microenvironment for sustained osteogenesis but also reprogram the osteoimmune microenvironment via the induction of M2 macrophage polarization to promote bone healing. The present study will provide a new paradigm to realize enhanced osteogenic efficacy by multichannel microenvironment regulations and give new insights into engineering high-efficacy i-PRF hydrogels for regenerative medicine.

Actions of WNT family member 5A to regulate characteristics of development of the bovine preimplantation embryo†

WNT signaling is important for regulation of embryonic development. The most abundant WNT gene expressed in the bovine endometrium during the preimplantation period is WNT5A. One objective was to determine whether WNT5A regulates competence of the bovine preimplantation embryo to become a blastocyst and alters the number of cells in the inner cell mass and trophectoderm. A second objective was to delineate features of the cell-signaling mechanisms involved in WNT5A actions. WNT5A caused a concentration-dependent increase in the proportion of embryos developing to the blastocyst stage and in the number of inner cell mass cells in the resultant blastocysts. A concentration of 200 ng/mL was most effective, and a higher concentration of 400 ng/mL was not stimulatory. Bovine serum albumin in culture reduced the magnitude of effects of WNT5A on development to the blastocyst stage. WNT5A affected expression of 173 genes at the morula stage; all were upregulated by WNT5A. Many of the upregulated genes were associated with cell signaling. Actions of WNT5A on development to the blastocyst stage were suppressed by a Rho-associated coiled-coil kinase (ROCK) signaling inhibitor, suggesting that WNT5A acts through Ras homology gene family member A (RhoA)/ROCK signaling. Other experiments indicated that actions of WNT5A are independent of the canonical β-catenin signaling pathway and RAC1/c-Jun N-terminal kinase (JNK) signaling. This is the first report outlining the actions of WNT5A to alter the development of the mammalian embryo. These findings provide insights into how embryokines regulate maternal-embryonic communication.

Vascular Endothelial Growth Factor Mimetic Peptide and Parathyroid Hormone (1-34) Delivered via a Blue-Light-Curable Hydrogel Synergistically Accelerate Bone Regeneration

Safe and effective biomaterials are in urgent clinical need for tissue regeneration and bone repair. While numerous advances have been made on hydrogels promoting osteogenesis in bone formation, co-stimulation of the angiogenic pathways in this process remains to be exploited. Here, we have developed a gelatin-based blue-light-curable hydrogel system, functionalized with an angiogenic vascular endothelial growth factor (VEGF) mimetic peptide, KLTWQELYQLKYKGI (KLT), and an osteoanabolic peptide, parathyroid hormone (PTH) 1-34. We have discovered that the covalent modification of gelatin scaffold with peptides can modulate the physical properties and biological activities of the produced hydrogels. Furthermore, we have demonstrated that those two peptides orchestrate synergistically and promote bone regeneration in a rat cranial bone defect model with remarkable efficacy. This dual-peptide-functionalized hydrogel system may serve as a promising lead to functional biomaterials in bone repair and tissue engineering.

Engineering the viscoelasticity of gelatin methacryloyl (GelMA) hydrogels via small “dynamic bridges” to regulate BMSC behaviors for osteochondral regeneration

The dynamic extracellular matrix (ECM) constantly affects the behaviors of cells. To mimic the dynamics of ECM with controllable stiffness and energy dissipation, this study proposes a strategy in which a small molecule, 3,4-dihydroxybenzaldehyde (DB), was used as fast "dynamic bridges'' to construct viscoelastic gelatin methacryloyl (GelMA)-based hydrogels. The storage modulus and loss modulus of hydrogels were independently adjusted by the covalent crosslinking density and by the number of dynamic bonds. The hydrogels exhibited self-healing property, injectability, excellent adhesion and mechanical properties. Moreover, the in vitro results revealed that the viscous dissipation of hydrogels favored the spreading, proliferation, osteogenesis and chondrogenesis of bone marrow mesenchymal stem cells (BMSCs), but suppressed their adipogenesis. RNA-sequencing and immunofluorescence suggested that the viscous dissipation of hydrogels activated Yes-associated protein (YAP) by stabilizing integrin β1, and further promoted nuclear translocation of smad2/3 and β-catenin to enhance chondrogenesis and osteogenesis. As a result, the viscoelastic GelMA hydrogels with highest loss modulus showed best effect in cartilage and subchondral bone repair. Taken together, findings from this study reveal an effective strategy to fabricate viscoelastic hydrogels for modulating the interactions between cells and dynamic ECM to promote tissue regeneration.

Non-canonical Wnt signaling participates in Jagged1-induced osteo/odontogenic differentiation in human dental pulp stem cells

Osteoblast differentiation requires the interaction of various cell signaling pathways to modulate cell responses. Notch and Wnt signaling are among the crucial pathways that control numerous biological processes, including osteo/odontogenic differentiation. The aim of the present study was to examine the involvement of Wnt signaling in the Jagged1-induced osteo/odontogenic differentiation in human dental pulp stem cells (hDPSCs). The Wnt-related gene expression was analyzed from publicly available data of Jagged1-treated human dental pulp cells. The mRNA expression of Wnt ligands (WNT2B, WNT5A, WNT5B, and WNT16) and Wnt inhibitors (DKK1, DKK2, and SOST) were confirmed using real-time polymerase chain reaction. Among the Wnt ligands, WNT2B and WNT5A mRNA levels were upregulated after Jagged1 treatment. In contrast, the Wnt inhibitors DKK1, DKK2, and SOST mRNA levels were downregulated. Recombinant WNT5A, but not WNT2B, significantly promoted in vitro mineral deposition by hDPSCs. Wnt signaling inhibition using IWP-2, but not DKK1, inhibited Jagged1-induced alkaline phosphatase (ALP) activity, mineralization, and osteo/odontogenic marker gene expression in hDPSCs. In conclusion, Jagged1 promoted hDPSC osteo/odontogenic differentiation by modulating the non-canonical Wnt pathway.

Platelet-rich plasma-hyaluronic acid/chondrotin sulfate/carboxymethyl chitosan hydrogel for cartilage regeneration

In this study, the chondrogenic potential of hyaluronic acid/chondrotin sulfate/carboxymethyl chitosan hydrogels with adipose-derived mesenchymal stem cells (ADMSCs) was evaluated. Here, hyaluronic acid, chondrotin sulfate, and carboxymethyl chitosan were used as the substrate for cartilage tissue engineering in which the hydrogel is formed due to electrostatic and hydrogen bonds through mixing the polymers. Because of the instability of this hydrogel in the biological environment, 1-ethyl-3-(3-dimethylaminopropyl-carbodiimide hydrochloride/N-hydroxy-succinimide was used as a crosslinker to increase the hydrogel stability. The hydrogels showed reasonable stability due to the combined effect of self-crosslinking and chemical crosslinking. The cells were treated with the prepared hydrogel samples for 14 and 21 days in nondifferentiation medium for evaluation of the cellular behavior of ADMSCs. Gene expression evaluation was performed, and expression of specific genes involved in differentiation was shown in the crosslinked hydrogel with platelet-rich plasma (PRP) (H-EN-P) had increased the gene expression levels. Quantification of immunofluorescence intensity indicated the high level of expression of SOX9 in H-EN-P hydrogel. Based on the results, we confirmed that the presence of PRP and the similarity of the hydrogel constituents to the cartilage extracellular matrix could have positive effects on the differentiation of the cells, which is favorable for cartilage tissue engineering approaches.

ROCK ‘n TOR: An Outlook on Keratinocyte Stem Cell Expansion in Regenerative Medicine via Protein Kinase Inhibition

Keratinocyte stem cells play a fundamental role in homeostasis and repair of stratified epithelial tissues. Transplantation of cultured keratinocytes autografts provides a landmark example of successful cellular therapies by restoring durable integrity in stratified epithelia lost to devastating tissue conditions. Despite the overall success of such procedures, failures still occur in case of paucity of cultured stem cells in therapeutic grafts. Strategies aiming at a further amplification of stem cells during keratinocyte ex vivo expansion may thus extend the applicability of these treatments to subjects in which endogenous stem cells pools are depauperated by aging, trauma, or disease. Pharmacological targeting of stem cell signaling pathways is recently emerging as a powerful strategy for improving stem cell maintenance and/or amplification. Recent experimental data indicate that pharmacological inhibition of two prominent keratinocyte signaling pathways governed by apical mTOR and ROCK protein kinases favor stem cell maintenance and/or amplification ex vivo and may improve the effectiveness of stem cell-based therapeutic procedures. In this review, we highlight the pathophysiological roles of mTOR and ROCK in keratinocyte biology and evaluate existing pre-clinical data on the effects of their inhibition in epithelial stem cell expansion for transplantation purposes.

Osteogenic peptides in periodontal ligament stem cell-containing three-dimensional bioscaffolds promote bone healing

Bone tissue engineering shows great potential in bone regeneration; however, the lack of bone growth factors with high biocompatibility and efficiency is a major concern. Oligopeptides have drawn great attention due to their high biological efficacy, low toxicity, and low molecular weight. The oligopeptide SDSSD promotes the osteogenesis of human periodontal ligament stem cells (hPDLSCs) in vitro. The SDSSD-modified three-dimensional (3D) bioscaffolds promote osteogenesis and bone formation in the subcutaneous pockets of BALB/c nude mice and facilitate bone healing in vivo. Mechanistically, SDSSD promoted bone formation by binding to G protein-coupled receptors and regulating the AKT signaling pathway. 3D-printing bioscaffolds with SDSSD may be potential bone tissue engineering materials for treating bone defects.

Biomaterial-Mediated Presentation of Jagged-1 Mimetic Ligand Enhances Cellular Activation of Notch Signaling and Bone Regeneration

The development from stem cells to adult tissues requires the delicate presentation of numerous crucial inductive cues and the activation of associated signaling pathways. The Notch signaling pathways triggered by ligands such as Jagged-1 have been demonstrated to be essential in various development processes especially in osteogenesis and ossification. However, few studies have capitalized on the osteoinductivity of the Jagged-1 mimetic ligands to enhance the osteogenesis and skeleton regeneration. In this study, we conjugate the porous hyaluronic acid hydrogels with a Jagged-1 mimetic peptide ligand (Jagged-1) and investigate the efficacy of such biomimetic functionalization to promote the mechanotransduction and osteogenesis of human mesenchymal stem cells by activating the Notch signaling pathway. Our findings indicate that the immobilized Jagged-1 mimetic ligand activates Notch signaling via the upregulation of NICD and downstream MSX2, leading to the enhanced mechanotransduction and osteogenesis of stem cells. We further demonstrate that the functionalization of the Jagged-1 ligand in the porous scaffold promotes angiogenesis, regulates macrophage recruitment and polarization, and enhances in situ regeneration of rat calvarial defects. Our findings provide valuable guidance to the design of development-inspired bioactive biomaterials for diverse biomedical applications.

Biomaterial-mediated presentation of wnt5a mimetic ligands enhances chondrogenesis and metabolism of stem cells by activating non-canonical Wnt signaling

The presentation of development-relevant bioactive cues by biomaterial scaffolds is essential to the guided differentiation of seeded human mesenchymal stem cells (hMSCs) and subsequent tissue regeneration. Wnt5a is a critical non-canonical Wnt signaling ligand and plays a key role in the development of musculoskeletal tissues including cartilage. Herein we investigate the efficacy of biofunctionalizing the hyaluronic acid hydrogel with a synthetic Wnt5a mimetic ligand (Foxy5 peptide) to promote the chondrogenesis of hMSCs and the potential underlying molecular mechanism. Our findings show that the conjugation of Foxy5 peptide in the hydrogels activates non-canonical Wnt signaling of encapsulated hMSCs via the upregulation expression of PLCE1, CaMKII-β, and downstream NFATc1, leading to enhanced expression of chondrogenic markers such as SOX9. The decoration of Foxy5 peptide also promotes the metabolic activities of encapsulated hMSCs as evidenced by upregulated gene expression of mitochondrial complex components and glucose metabolism biomarkers, leading to enhanced ATP biosynthesis. Furthermore, the conjugation of Foxy5 peptide activates the non-canonical Wnt, PI3K-PDK-AKT and IKK/NF-κB signaling pathways, thereby inhibiting the hypertrophy of the chondrogenically induced hMSCs in the hydrogels under both in vitro and in vivo conditions. This enhanced chondrogenesis and attenuated hypertrophy of hMSCs by the biomaterial-mediated bioactive cue presentation facilitates the potential clinical translation of hMSCs for cartilage regeneration. Our work provides valuable guidance to the rational design of bio-inductive scaffolds for various applications in regenerative medicine.

Surface presentation of the noncanonical Wnt5a motif to cytotoxic CD8+ T-cells promotes their mechanotransduction and activation

We report here strategic functionalization of the Wnt5a mimetic peptide ligand Foxy5 on a polydimethylsiloxane elastomer substrate to enhance the mechanotransduction and activation of cytotoxic CD8⁺ T cells by triggering the noncanonical Wnt signaling. This new mechanoregulatory ligand platform can be widely applied in the fundamental research of mechano-immunology and further the development of novel immunotherapies.

Immobilization of bioactive vascular endothelial growth factor onto Ca-deficient hydroxyapatite-coated Mg by covalent bonding using polydopamine

BACKGROUND

Bone tissue engineering (BTE) is considered a promising technology for repairing bone defects. Mg2+ promotes osteogenesis, which makes Mg-based scaffolds popular for research on orthopedic implant materials. Angiogenesis plays an important role in the process of bone tissue repair and regeneration, and it is one of the important problems in BTE urgently needs to be solved.

METHODS

Mg was firstly coated with Ca-deficient hydroxyapatite (CDHA) via hydrothermal treatment, and polydopamine (DOPA) was then used as the connecting medium to immobilize vascular endothelial growth factor (VEGF) on the CDHA coating. The physicochemical properties of the coatings were characterized by SEM, EDS, XPS, FTIR and immersion experiment in SBF. The ahesion, proliferation, and angiogenesis potential of the coatings were determined in vitro.

RESULTS

The composite coating significantly improved the corrosion resistance of Mg and prohibited excessively high local alkalinity. VEGF could be firmly immobilized on Mg via polydopamine. The CCK-8, live/dead staining and adhesion test results showed that the VEGF-DOPA-CDHA coating exhibited excellent biocompatibility and could significantly improve the adhesion and proliferation of MC3T3-E1 cells on Mg. Microtubule formation, immunofluorescence and Quantitative Real-Time PCR (qRT-PCR) experiments showed that VEGF immobilized on Mg still possessed bioactivity in promoting the differentiation of rat mesenchymal stem cells into endothelial cells.

CONCLUSION

In this study, we enabled the angiogenic biological activity of Mg by immobilizing VEGF on Mg. Mg was successfully coated with a functional VEGF-DOPA-CDHA composite coating. The CDHA coating significantly increased the corrosion resistance of Mg and prohibited the negative effect of excessively high local alkalinity on the biological activity of VEGF. As an intermediate layer, the DOPA coating protects Mg, and DOPA provides a binding site for VEGF so that VEGF can be firmly immobilized on Mg and give Mg angiogenic bioactivity during the initial period of implantation.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

The treatment of large bone defect is still one of the orthopedic trauma diseases that are difficult to be completely treated in clinic. The development of tissue engineering technology provides a new option for the treatment of large bone defects. The regeneration of blood vessels is of great significance for the repair of bone defects. In this study, VEGF was connected on the surface of degradable magnesium by covalent bonding. Vascular biofunctionalized magnesium scaffolds are expected to regenerate bone tissue with blood transport and be used in the clinical treatment of large bone defects.

Carbohydrate-Based Macromolecular Biomaterials

Carbohydrates are the most abundant and one of the most important biomacromolecules in Nature. Except for energy-related compounds, carbohydrates can be roughly divided into two categories: Carbohydrates as matter and carbohydrates as information. As matter, carbohydrates are abundantly present in the extracellular matrix of animals and cell walls of various plants, bacteria, fungi, etc., serving as scaffolds. Some commonly found polysaccharides are featured as biocompatible materials with controllable rigidity and functionality, forming polymeric biomaterials which are widely used in drug delivery, tissue engineering, etc. As information, carbohydrates are usually referred to the glycans from glycoproteins, glycolipids, and proteoglycans, which bind to proteins or other carbohydrates, thereby meditating the cell-cell and cell-matrix interactions. These glycans could be simplified as synthetic glycopolymers, glycolipids, and glycoproteins, which could be afforded through polymerization, multistep synthesis, or a semisynthetic strategy. The information role of carbohydrates can be demonstrated not only as targeting reagents but also as immune antigens and adjuvants. The latter are also included in this review as they are always in a macromolecular formulation. In this review, we intend to provide a relatively comprehensive summary of carbohydrate-based macromolecular biomaterials since 2010 while emphasizing the fundamental understanding to guide the rational design of biomaterials. Carbohydrate-based macromolecules on the basis of their resources and chemical structures will be discussed, including naturally occurring polysaccharides, naturally derived synthetic polysaccharides, glycopolymers/glycodendrimers, supramolecular glycopolymers, and synthetic glycolipids/glycoproteins. Multiscale structure-function relationships in several major application areas, including delivery systems, tissue engineering, and immunology, will be detailed. We hope this review will provide valuable information for the development of carbohydrate-based macromolecular biomaterials and build a bridge between the carbohydrates as matter and the carbohydrates as information to promote new biomaterial design in the near future.

Salicylic acid-based nanomedicine with self-immunomodulatory activity facilitates microRNA therapy for metabolic skeletal disorders

Metabolic skeletal disorders remain a major clinical challenge. The complexity of this disease requires a strategy to address the net effects of both inflammation and impaired bone formation. microRNA-based gene therapy provides several therapeutic advantages to tackle these issues. Herein, we describe a microRNA-21 (miR-21) delivery system with an additional therapeutic effect from that of the delivery carrier itself. Poly (salicylic acid) (PSA) is, for the first time, synthesized via polycondensation of salicylic acid (SA), a bioactive ingredient widely used for anti-inflammation in medicine. PSA can self-assemble into nanoparticles (PSA-NPs) and can effectively deliver genes both in vitro and in vivo. The carrier was then attached to repetitive sequences of aspartate, serine, serine (DSS)₆ for delivering miRNAs specifically to bone-formation surfaces. In vitro studies showed that miR-21@PSA-NP could effectively realize the intracellular delivery of miR-21 with low toxicity, while in vivo results indicated that the miR-21@PSA-NP-DSS₆ prolonged blood circulation time, enhanced bone accumulation, and significantly improved the efficacy of miR-21-based bone anabolic therapy in osteoporotic mice. The constructed delivery system (miR-21@PSA-NP-DSS₆) inherited the advantages of both SA and miR-21, which could ameliorate bone-inflamed niche and rescued the impaired bone formation ability. The synergy of anti-inflammatory and pro-osteogenic effects significantly improved trabecular bone microstructure in osteoporotic mice. STATEMENT OF SIGNIFICANCE: The complexity of metabolic skeletal disorders requires a strategy to address the net effects of both inflammation and impaired bone formation. microRNA-based gene therapy provides several therapeutic advantages to tackle these issues. We develop a novel microRNA-21 delivery system with additional therapeutic effect from that of the gene carrier itself. Poly (salicylic acid) (PSA) nanoparticles, for the first time, synthesized via polycondensation of salicylic acid and can effectively deliver genes both in vitro and in vivo. The constructed delivery system (miR-21@PSA-NP-DSS₆) inherited the advantages of both SA (commonly used anti-inflammation drug in medicine) and miR-21 (a pro-osteogenic molecule), which could ameliorate bone-inflamed niche, rescued impaired bone formation ability and significantly improved trabecular bone microstructure in osteoporotic mice.

Structurally Dynamic Hydrogels for Biomedical Applications: Pursuing a Fine Balance between Macroscopic Stability and Microscopic Dynamics

Owing to their unique chemical and physical properties, hydrogels are attracting increasing attention in both basic and translational biomedical studies. Although the classical hydrogels with static networks have been widely reported for decades, a growing number of recent studies have shown that structurally dynamic hydrogels can better mimic the dynamics and functions of natural extracellular matrix (ECM) in soft tissues. These synthetic materials with defined compositions can recapitulate key chemical and biophysical properties of living tissues, providing an important means to understanding the mechanisms by which cells sense and remodel their surrounding microenvironments. This review begins with the overall expectation and design principles of dynamic hydrogels. We then highlight recent progress in the fabrication strategies of dynamic hydrogels including both degradation-dependent and degradation-independent approaches, followed by their unique properties and use in biomedical applications such as regenerative medicine, drug delivery, and 3D culture. Finally, challenges and emerging trends in the development and application of dynamic hydrogels are discussed.

Bio-inspired Incrustation Interfacial Polymerization of Dopamine and Cross-linking with Gelatin toward Robust, Biodegradable Three-Dimensional Hydrogels

In nature, laccase enzymatically catalyzes the reaction of phenolic compounds with oxygen to produce hardened surfaces known as cuticles on insects and plants. Inspired by this natural process, the present work investigated a robust, biodegradable hydrogel synthesized from dopamine and gelatin. This gel is obtained by the oxidation of dopamine dissolved in water, after which the resulting quinone compound automatically undergoes self-polymerization. The oxidized dopamine subsequently undergoes Schiff base and Michael addition reactions with gelatin, such that the exposed gelatin surface cross-links to generate a continuous hardened hydrogel film. Because gelatin transitions between sol and gel states with changes in temperature, two- and three-dimensional structures could be obtained from the gel state. This bio-inspired interfacial cross-linking reaction provides a simple means of forming complex morphologies and represents a promising technique for bio-applications.

Surface decoration of development-inspired synthetic N-cadherin motif via Ac-BP promotes osseointegration of metal implants

Research works on the synergistic effect of surface modified bioactive molecules and bone metal implants have been highlighted. N-cadherin is regarded as a key factor in directing cell-cell interactions during the mesenchymal condensation preceding the osteogenesis in the musculoskeletal system. In this study, the N-cadherin mimetic peptide (Cad) was biofunctionalized on the titanium metal surface via the acryloyl bisphosphonate (Ac-BP). To learn the synergistic effect of N-cadherin mimetic peptide, when tethered with titanium substrates, on promoting osteogenic differentiation of the seeded human mesenchymal stem cells (hMSCs) and the osseointegration at the bone-implant interfaces. Results show that the conjugation of N-cadherin mimetic peptide with Ac-BP promoted the osteogenic gene markers expression in the hMSCs. The biofunctionalized biomaterial surfaces promote the expression of the Wnt/β-catenin downstream axis in the attached hMSCs, and then enhance the in-situ bone formation and osseointegration at the bone-implant interfaces. We conclude that this N-cadherin mimetic peptide tethered on Ti surface promote osteogenic differentiation of hMSCs and osseointegration of biomaterial implants in vitro and in vivo. These findings demonstrate the importance of the development-inspired surface bioactivation of metal implants and shed light on the possible cellular mechanisms of the enhanced osseointegration.

VE-cadherin-based matrix promoting the self-reconstruction of pro-vascularization microenvironments and endothelial differentiation of human mesenchymal stem cells

Regulating the secretion and endothelial differentiation of human mesenchymal stem cells (hMSCs) plays an important role in the vascularization in tissue engineering and regenerative medicine. In this study, a recombinant cadherin fusion protein consisting of a human vascular endothelial-cadherin extracellular domain and immunoglobulin IgG Fc region (hVE-cad-Fc) was developed as a bioartificial matrix for modulating hMSCs. The hVE-cad-Fc matrix significantly enhanced the secretion of angiogenic factors, activated the VE-cadherin-VEGFR2/FAK-AKT/PI3K signaling pathway in hMSCs, and promoted the endothelial differentiation of hMSCs even without extra VEGF. Furthermore, the hVE-cad-Fc matrix was applied for the surface modification of a poly (lactic-co-glycolic acid) (PLGA) porous scaffold, which significantly improved the hemocompatibility and vascularization of the PLGA scaffold in vivo. These results revealed that the hVE-cad-Fc matrix should be a superior bioartificial ECM for remodeling the pro-vascularization extracellular microenvironment by regulating the secretion of hMSCs, and showed great potential for the vascularization in tissue engineering.

An Engineered Biomimetic Peptide Regulates Cell Behavior by Synergistic Integrin and Growth Factor Signaling

Recreating the healing microenvironment is essential to regulate cell-material interactions and ensure the integration of biomaterials. To repair bone, such bioactivity can be achieved by mimicking its extracellular matrix (ECM) and by stimulating integrin and growth factor (GF) signaling. However, current approaches relying on the use of GFs, such as bone morphogenetic protein 2 (BMP-2), entail clinical risks. Here, a biomimetic peptide integrating the RGD cell adhesive sequence and the osteogenic DWIVA motif derived from the wrist epitope of BMP-2 is presented. The approach offers the advantage of having a spatial control over the single binding of integrins and BMP receptors. Such multifunctional platform is designed to incorporate 3,4-dihydroxyphenylalanine to bind metallic oxides with high affinity in a one step process. Functionalization of glass substrates with the engineered peptide is characterized by physicochemical methods, proving a successful surface modification. The biomimetic interfaces significantly improve the adhesion of C2C12 cells, inhibit myotube formation, and activate the BMP-dependent signaling via p38. These effects are not observed on surfaces displaying only one bioactive motif, a mixture of both motifs or soluble DWIVA. These data prove the biological potential of recreating the ECM and engaging in integrin and GF crosstalk via molecular-based mimics.

Methacrylated pullulan/polyethylene (glycol) diacrylate composite hydrogel for cartilage tissue engineering

Pullulan hydrogels are widely used in tissue engineering and drug delivery. However, these hydrogels do not meet the requirements of articular cartilage repair because of their fast degradation rate and poor mechanical strength. Herein, we fabricated a hybrid hydrogel system by combining pullulan with synthetic polymers polyethylene (glycol) diacrylate (PEGDA). In this study, pullulan was modified with methacrylic anhydride (MA) to obtain photo-crosslinkable methacrylated pullulan (PulMA). Moreover, the lithium phenyl(2,4,6-trimethylbenzoyl)phosphinate (LAP) was used as a water-soluble UV photoinitiator to form the PulMA/PEGDA hydrogel by photopolymerization strategy. Compared with the pure PulMA hydrogel, the increase of PEGDA concentration led to a slower degradation rate and an increase of residual mass from 63.9% to 86.8%. There was about 8-fold increase in storage modulus (G') (reach to 16.0 × 10³ Pa) and 13-fold increase in compressive modulus (reach to 1.17 ± 0.17 MPa) with increasing the concentration of PEGDA to 15% (w/v) in the hydrogel. In cell culture in vitro, the rabbit's mesenchymal stem cells (MSCs) encapsulated in the PulMA/PEGDA hydrogel could adhere and proliferate, indicating that the PulMA/PEGDA hydrogel had a good biocompatibility. Furthermore, the hydrogels supported glycosaminoglycan (GAG) synthesis, and chondrogenic phenotype of MSCs with TGF-β3-containing chondrogenic medium. This study demonstrated that the photo-crosslinking PulMA/PEGDA hydrogels, with good mechanical properties and slow degradation rate are promising scaffolds for cartilage repair and regeneration.

RhoA/Rock activation represents a new mechanism for inactivating Wnt/β-catenin signaling in the aging-associated bone loss

The Wnt/β-catenin signaling pathway appears to be particularly important for bone homeostasis, whereas nuclear accumulation of β-catenin requires the activation of Rac1, a member of the Rho small GTPase family. The aim of the present study was to investigate the role of RhoA/Rho kinase (Rock)-mediated Wnt/β-catenin signaling in the regulation of aging-associated bone loss. We find that Lrp5/6-dependent and Lrp5/6-independent RhoA/Rock activation by Wnt3a activates Jak1/2 to directly phosphorylate Gsk3β at Tyr216, resulting in Gsk3β activation and subsequent β-catenin destabilization. In line with these molecular events, RhoA loss- or gain-of-function in mouse embryonic limb bud ectoderms interacts genetically with Dkk1 gain-of-function to rescue the severe limb truncation phenotypes or to phenocopy the deletion of β-catenin, respectively. Likewise, RhoA loss-of-function in pre-osteoblasts robustly increases bone formation while gain-of-function decreases it. Importantly, high RhoA/Rock activity closely correlates with Jak and Gsk3β activities but inversely correlates with β-catenin signaling activity in bone marrow mesenchymal stromal cells from elderly male humans and mice, whereas systemic inhibition of Rock therefore activates the β-catenin signaling to antagonize aging-associated bone loss. Taken together, these results identify RhoA/Rock-dependent Gsk3β activation and subsequent β-catenin destabilization as a hitherto uncharacterized mechanism controlling limb outgrowth and bone homeostasis.

Preparation of a Fucoidan-Grafted Hyaluronan Composite Hydrogel for the Induction of Osteoblast Differentiation in Osteoblast-Like Cells

A suitable bone substitute is necessary in bone regenerative medicine. Hyaluronan (HA) has excellent biocompatibility and biodegradability and is widely used in tissue engineering. Additionally, research on fucoidan (Fu), a fucose- and sulfate-rich polysaccharide from brown seaweed, for the promotion of bone osteogenic differentiation has increased exponentially. In this study, HA and Fu were functionalized by grafting methacrylic groups onto the backbone of the chain. Methacrylate-hyaluronan (MHA) and methacrylate-fucoidan (MFu) were characterized by FTIR and 1H NMR spectroscopy to confirm functionalization. The degrees of methacrylation (DMs) of MHA and MFu were 9.2% and 98.6%, respectively. Furthermore, we evaluated the mechanical properties of the hydrogels formed from mixtures of photo-crosslinkable MHA (1%) with varying concentrations of MFu (0%, 0.5%, and 1%). There were no changes in the hardness values of the hydrogels, but the elastic modulus decreased upon the addition of MFu, and these mechanical properties were not significantly different with or without preosteoblastic MG63 cell culture for up to 28 days. Furthermore, the cell morphologies and viabilities were not significantly different after culture with the MHA, MHA-MFu0.5, or MHA-MFu1.0 hydrogels, but the specific activity and mineralization of alkaline phosphatase (ALP) were significantly higher in the MHA-MFu1.0 hydrogel group compared to the other hydrogels. Hence, MHA-MFu composite hydrogels are potential bone graft materials that can provide a flexible structure and favorable niche for inducing bone osteogenic differentiation.