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Regulating macrophage phenotypes to reconcile the conflict between bacterial suppression and tissue regeneration is ideal for treating infectious skin wounds. Here, an injectable immunoregulatory hydrogel (SrmE20) that sequentially drives macrophage phenotypic polarization (M0 to M1, then to M2) was constructed by integrating anti-inflammatory components and proinflammatory solvents. In vitro experiments demonstrated that the proinflammatory solvent ethanol stabilized the hydrogel structure, maintained the phenolic hydroxyl group activity, and achieved macrophages' proinflammatory transition (M0 to M1) to enhance antibacterial effects. With ethanol depletion, the hydrogel's cations and phenolic hydroxyl groups synergistically regulated macrophages' anti-inflammatory transition (M1 to M2) to initiate regeneration. In the anti-contraction full-thickness wound model with infection, this hydrogel effectively eliminated bacteria and even achieved anti-inflammatory M2 macrophage accumulation at three days post-surgery, accelerated angiogenesis and collagen deposition. By sequentially driving macrophage phenotypic polarization, this injectable immunoregulatory hydrogel will bring new guidance for the care and treatment of infected wounds.

Abstract Collagen, known for its excellent biocompatibility and biological properties, has limited in vivo maintenance duration after implantation, while hyaluronic acid faces challenges such as various complications and insufficient support for cell proliferation. In this study, an injectable hyaluronic acid/collagen (HCol) hydrogel was developed to achieve enhanced cell-material interactions and accelerated skin regeneration. Physical and chemical characterizations demonstrated that the HCol hydrogel was injectable and stable after the implantation. In vitro cell culture results illustrated that the hydrogel promoted the proliferation of human dermal fibroblasts, extracellular matrix expression and angiogenesis. The subcutaneous implantation in rats showed the superior biocompatibility of HCol hydrogel and enhanced secretion and deposition of extracellular matrix, compared with commercial hyaluronic acid dermal filler. MRI analysis showed that the hydrogel stably remained in vivo for at least three months. The histological examination and SHG signals further demonstrated that the hydrogel modulated fibroblast phenotype and stimulated vascular ingrowth and collagen synthesis, without inducing significant inflammation, swelling or erythema in vivo. Graphical Abstract

Abstract The interior environment of articular cartilage in osteoarthritis (OA) presents substantial hurdles, leading to the malfunction of chondrocytes and the breakdown of collagen II-enriched hyaline cartilage matrix. Despite this, most clinical treatments primarily provide temporary relief from OA discomfort without arresting OA progression. This study aimed to alleviate OA by developing intra-articular injectable dECM-enhanced hyaluronic (HE) microgels. The HE hydrogel was engineered and shaped into uniformly sized microgels using microfluidics and photopolymerization techniques. These microgels provided a spatiotemporal cascade effect, facilitating the rapid release of growth factors and a slower release of ECM macromolecules and proteins. This process assisted in the recovery of OA chondrocytes’ function, promoting cell proliferation, matrix synthesis, and cartilage-specific gene expression in vitro. It also effectively aided repair of the collagen II-enriched hyaline cartilage and significantly reduced the severity of OA, as demonstrated by radiological observation, gross appearance, histological/immunohistochemical staining, and analysis in an OA rat model in vivo. Collectively, the HE injectable microgels with spatiotemporal release of cartilage-specific molecules have shown promise as a potential candidate for a cell-free OA therapy approach. Graphical Abstract

Abstract The effectiveness of Toll‐like 9 agonists (CpG) as an adjuvant for tumor immunotherapy is restricted due to their insufficient ability to activate anti‐tumor immunity. To address that, the common nutrient metal ions are explored (Mn2+, Cu2+, Ca2+, Mg2+, Zn2+, Fe3+, and Al3+), identifying Mn2+ as a key enhancer of CpG to mediate immune activation by augmenting the STING‐NF‐κB pathway. Mn2+ and CpG are then self‐assembled with epigallocatechin gallate (EGCG) into a nanoadjuvant MPN/CpG. Local delivery of MPN/CpG effectively inhibits tumor growth in a B16 melanoma‐bearing mouse model, reshaping the tumor microenvironment (TME) by repolarizing M2‐type tumor‐associated macrophages (TAMs) to an M1‐type and boosting intra‐tumoral infiltration of CD8+/CD4+ T lymphocytes and DCs. Furthermore, compared to free CpG, MPN/CpG exhibits heightened accumulation in lymph nodes, enhancing CpG uptake and DC activation, consequently inducing significant antigen‐specific cytotoxic CD8+ T cell immune response and humoral immunity. In a prophylactic tumor‐bearing mouse model, MPN/CpG vaccination with OVA antigen significantly delays B16‐OVA melanoma growth and extends mouse survival. These findings underscore the potential of MPN/CpG as a multifunctional adjuvant platform to drive powerful innate and adaptive immunity and regulate TME against tumors.

Abstract Extensive studies demonstrate that macrophage response plays an important role in regulating angiogenesis via a paracrine way, which is crucial for skin wound repair. This study isolated and characterized nanosized exosomes from differently polarized macrophages (MΦ), including M0 (naïve), M1 (pro-inflammatory), and M2 (anti-inflammatory) macrophages, and further assessed their impacts on angiogenesis and skin regeneration. Our results indicated that compared to M0 and M1 counterparts, M2 macrophage-derived exosomes (M2-Exos) exhibited a pronounced ability to promote angiogenic ability of of human umbilical vein endothelial cells (HUVECs) by enhancing expression of angiogenic genes and proteins, increasing cell migration, and improving tubulogenesis. Bioinformatics analyses suggested that the distinct angiogenic potentials of three MΦ-Exos might be attributed to the differentially expressed angiogenesis-related miRNAs and their target genes such as Stat3, Smad 2, and Smad4. Moreover, these isolated MΦ-Exos were integrated with gelatine methacrylate (GelMA) hydrogels to achieve the sustained delivery at murine full-thickness cutaneous wound sites. In vivo results showed that Gel/M2-Exos significantly augmented angiogenesis, accelerated re-epithelialization, promoted collagen maturity, thereby promoting wound healing. In contrary, Gel/M1-Exos showed the opposite effects. Our findings provided compelling evidence that the polarization status of macrophages significantly affected angiogenesis and wound healing via the miRNA cargos of their derived exosomes. Moreover, this study opens a new avenue for developing nano-scale, cell-free exosome-based therapies in treating cutaneous wounds. Graphical abstract

Abstract The assembly of oligopeptide and polypeptide molecules can reconstruct various ordered advanced structures through intermolecular interactions to achieve protein-like biofunction. Here, we develop a “molecular velcro”-inspired peptide and gelatin co-assembly strategy, in which amphiphilic supramolecular tripeptides are attached to the molecular chain of gelatin methacryloyl via intra-/intermolecular interactions. We perform molecular docking and dynamics simulations to demonstrate the feasibility of this strategy and reveal the advanced structural transition of the co-assembled hydrogel, which brings more ordered β-sheet content and 10-fold or more compressive strength improvement. We conduct transcriptome analysis to reveal the role of co-assembled hydrogel in promoting cell proliferation and chondrogenic differentiation. Subcutaneous implantation evaluation confirms considerably reduced inflammatory responses and immunogenicity in comparison with type I collagen. We demonstrate that bone mesenchymal stem cells-laden co-assembled hydrogel can be stably fixed in rabbit knee joint defects by photocuring, which significantly facilitates hyaline cartilage regeneration after three months. This co-assembly strategy provides an approach for developing cartilage regenerative biomaterials.

In this paper, an implicit compact finite difference (CFD) scheme was constructed to get the numerical solution for time fractional diffusion-wave equation (TFDWE), in which the time fractional derivative was denoted by Caputo-Fabrizio (C-F) sense. We proved that the full discrete scheme is unconditionally stable. We also proved that the rate of convergence in time is near to $ O(\tau^{2}) $ and the rate of convergence in space is near to $ O(h^{4}) $. Test problem was considered for regular domain with uniform points to validate the efficiency and accuracy of the method. The numerical results can support the theoretical claims.

Abstract Drug-eluting stent implantation suppresses the excessive proliferation of smooth muscle cells to reduce in-stent restenosis. However, the efficacy of drug-eluting stents remains limited due to delayed reendothelialization, impaired intimal remodeling, and potentially increased late restenosis. Here, we show that a drug-free coating formulation functionalized with tailored recombinant humanized type III collagen exerts one-produces-multi effects in response to injured tissue following stent implantation. We demonstrate that the one-produces-multi coating possesses anticoagulation, anti-inflammatory, and intimal hyperplasia suppression properties. We perform transcriptome analysis to indicate that the drug-free coating favors the endothelialization process and induces the conversion of smooth muscle cells to a contractile phenotype. We find that compared to drug-eluting stents, our drug-free stent reduces in-stent restenosis in rabbit and porcine models and improves vascular neointimal healing in a rabbit model. Collectively, the one-produces-multi drug-free system represents a promising strategy for the next-generation of stents.

Abstract The regeneration of articular cartilage posed a formidable challenge due to the restricted treatment efficacy of existing therapies. Scaffold-based tissue engineering emerges as a promising avenue for cartilage reconstitution. However, most scaffolds exhibit inadequate mechanical characteristics, poor biocompatibility, or absent cell adhesion sites. In this study, cartilage-like protein-polysaccharide hybrid hydrogel based on DOPA-modified hyaluronic acid, bovine type I collagen (Col I), and recombinant humanized type II collagen (rhCol II), denoted as HDCR. HDCR hydrogels possessed the advantage of injectability and in situ crosslinking through pH adjustment. Moreover, HDCR hydrogels exhibited a manipulable degradation rate and favorable biocompatibility. Notably, HDCR hydrogels significantly induced chondrogenic differentiation of rabbit bone marrow mesenchymal stem cells in vitro, as demonstrated by the upregulation of crucial chondrogenic genes (type II collagen, aggrecan) and the abundant accumulation of glycosaminoglycan. This approach presented a strategy to manufacture injectable, biodegradable scaffolds based on cartilage-like protein-polysaccharide polymers, offering a minimally invasive solution for cartilage repair. Graphical abstract

Abstract Bone regeneration for large, critical-sized bone defects remains a clinical challenge nowadays. Guided bone regeneration (GBR) is a promising technique for the repair of multiple bone defects, which is widely used in oral and maxillofacial bone defects but is still unsatisfied in the treatment of long bone defects. Here, we successfully fabricated a bilayer mineralized collagen/collagen (MC/Col)-GBR membrane with excellent osteoinductive and barrier function by coating the MC particles prepared via in situ biomimetic mineralization process on one side of a sheet-like pure collagen layer. The aim of the present study was to investigate the physicochemical properties and biological functions of the MC/Col film, and to further evaluate its bone regeneration efficiency in large bone defect repair. Fourier-transform infrared spectra and X-ray diffraction patterns confirmed the presence of both hydroxyapatite and collagen phase in the MC/Col film, as well as the chemical interaction between them. stereo microscope, scanning electron microscopy and atomic force microscope showed the uniform distribution of MC particles in the MC/Col film, resulting in a rougher surface compared to the pure Col film. The quantitative analysis of surface contact angle, light transmittance and tensile strength demonstrated that the MC/Col film have better hydrophilicity, mechanical properties, light-barrier properties, respectively. In vitro macrophage co-culture experiments showed that the MC/Col film can effectively inhibit macrophage proliferation and fusion, reducing fibrous capsule formation. In vivo bone repair assessment of a rabbit critical segmental radial defect proved that the MC/Col film performed better than other groups in promoting bone repair and regeneration due to their unique dual osteoinductive/barrier function. These findings provided evidence that MC/Col film has a great clinical potential for effective bone defect repair. Graphic abstract

The development of osteoimmunology has highlighted the crucial role of biomaterial surface topography in modulating macrophage responses, subsequently affecting bone formation. However, the underlying mechanism remains largely unexplored. This study introduced two biphasic calcium phosphate (BCP) ceramics with different surface architecture, finding that compared to micron-scale counterparts (BCP2, ∼3.07 μm), BCP with submicron-scale structure (BCP1, ∼0.66 μm) enhanced ectopic bone formation and facilitated M2 macrophage polarization in vivo. Previous studies have focused predominantly on soluble cytokines secreted by macrophages, the significance of exosomes in intercellular communication has been overlooked. This study isolated exosomes from macrophages treated with either submicron- or micron-scale surfaces, designated as B1-Exos and B2-Exos, respectively. Notably, B1-Exos could significantly improve osteogenic differentiation of mesenchymal stem cells (MSCs), potentially attributable to miRNA cargos within these exosomes. SmallRNA sequencing, western blotting, qRT-PCR, and bioinformatics analyses indicated that submicron-sized BCP1 ceramic markedly elevated miR-142a-5p levels in macrophage-derived exosomes, activating the PTEN/AKT signaling pathway, and consequently guiding the differentiation of MSCs towards osteoblast lineage. These findings not only deepen our understanding of the biomaterial-mediated osteoinduction mechanism, but also inform the design of bone repair materials with specialized surface design for proper immunomodulation to initiate osteogenesis.

Interbody fusion devices are critical in spinal surgery to restore spinal stability, reduce pain and improve function. Polyetheretherketone (PEEK) has become a commonly used alternative material for fusion cages owing to its excellent mechanical properties and biocompatibility, but its biological inertness limits bone regeneration and may lead to poor fusion. In this study, a novel strategy for preparing bioactive biomineralized PEEK cages was developed using a unique combination of osteoinductive CaP bioceramic fillings in the cage window, acid sulfonation and simulated body fluid incubation. In vitro experiments showed that biomineralized PEEK cages and CaP bioceramics regulate immunity and promote angiogenesis and bone integration via activation of hypoxia-inducible factor 1-alpha and cyclic guanosine monophosphate/protein kinase G signaling pathways. In vivo goat spinal fusion experiments demonstrated that PEEK cages filled with CaP bioceramics resulted in good bone growth and spinal fusion. Therefore, the high mechanical strength and good biocompatibility of biomineralized PEEK cages, together with the excellent bioactivity and degradation properties of CaP bioceramics, provide an ideal microenvironment for bone fusion. The development of this composite material not only addresses some of the limitations of existing fusion devices but also will facilitate the development of spinal fusion technology.

The strategy of coupling the micro-vibration mechanical field with Ca/P ceramics to optimize the osteogenic microenvironment and enhance the functional activity of the cells can significantly improve the bone regeneration of the graft. However, the regulation mode and mechanism of this coupling strategy are not fully understood at present. This study investigated the influence of different waveforms of the electrical signals driving Microvibration Stimulation (MVS) on this coupling effect. The results showed that there were notable variances in calcium phosphate dissolution and redeposition, protein adsorption, phosphorylation of ERK1/2 and FAK signal pathways and activation of calcium channels such as TRPV1/Piezo1/Piezo2 in osteogenic microenvironment under the coupling action of hydroxyapatite (HA) ceramics and MVS driven by different electrical signal waveforms. Ultimately, these differences affected the osteogenic differentiation process of cells by a way of time-sequential regulation. Square wave-MVS coupled with HA ceramic can significantly delay the high expression time of characteristic genes (such as Runx2, Col-I and OCN) in MC3T3-E1 cells during in vitro the early, middle and late stage of differentiation, while maintain the high proliferative activity of MC3T3-E1 cells. Triangle wave signal-MVS coupled with HA ceramic promoted the osteogenic differentiation of cells in the early and late stages. Sine wave-MVS shows the effect on the process of osteogenic differentiation in the middle stage (such as the up-regulation of ALP synthesis and Col-I gene expression in the early stage of stimulation). In addition, Square wave-MVS showed the best coupling effect. The bone graft constructed under square wave-MVS formed new bone tissue and mature blood vessels only 2 weeks after subcutaneous implantation in nude mice. Our study provides a new non-invasive regulation model for precisely optimizing the osteogenic microenvironment, which can accelerate bone regeneration in bone grafts more safely, accurately and reliably.

Osteoimmunology is a concept involving molecular and cellular crosstalk between the skeletal and immune systems. Toll-like receptors (TLRs) are widely expressed both on mesenchymal stromal cells (MSCs), the hematopoietic cells, and immune cells in the osteogenic microenvironment for bone development or repair. TLRs can sense both exogenous pathogen-associated molecular patterns (PAMPs) derived from microorganisms, and damage-associated molecular patterns (DAMPs) derived from normal cells subjected to injury, inflammation, or cell apoptosis under physiological or pathological conditions. Emerging studies reported that TLR signaling plays an important role in bone remodeling by directly impacting MSC osteogenic differentiation or osteoimmunology. However, how to regulate TLR signaling is critical and remains to be elucidated to promote the osteogenic differentiation of MSCs and new bone formation for bone tissue repair. This review outlines distinct TLR variants on MSCs from various tissues, detailing the impact of TLR pathway activation or inhibition on MSC osteogenic differentiation. It also elucidates TLR pathways’ interplay with osteoclasts, immune cells, and extracellular vesicles (EVs) derived from MSCs. Furthermore, we explore biomaterial-based activation to guide MSCs’ osteogenic differentiation. Therefore, understanding TLRs’ role in this context has significant implications for advancing bone regeneration and repair strategies.

Acquiring high-performance calcium phosphate (CaP) ceramics via 3D printing is critical for their applications in bone regenerative repair. In current study, a complete process study of 3D printed CaP ceramics based on digital light processing (DLP) technology was performed to get the ideal implant for the regenerative repair of calvarial defects. The smaller particle size of initial powder would be more favorable to getting slurry with high solid content and low viscosity. CaP green body with high precision and high curing rate could be fabricated at the exposure energy density and exposure time of 6.20 mJ cm−2 and 2 s, respectively. Moreover, the post-curing treatment could eliminate the interlayer cracks and increase the curing rate from 69.78% to 93.91% of green body. After that, the mechanical strength of CaP ceramics increased by 46.34%. In-vitro cellular experiments showed that 3D printed CaP ceramics had good biocompatibility, and could promote the osteoblastic differentiation of BMSCs. In-vivo rat cranial defect implantation revealed 3D printed CaP ceramics exhibited better osteogenic ability than the commercial ones (BAM®), reaching the close level with the autografts. Overall, this study could provide a closed-loop solution for 3D printed CaP ceramics with high-precision and low-defect to induce bone regeneration.

Healing of an anterior cruciate ligament (ACL) autologous graft in a bone tunnel occurs through the formation of fibrovascular scar tissue, which is structurally and compositionally inferior to normal fibrocartilaginous insertion and thus may increase the reconstruction failure and the rate of failure recurrence. In this study, an injectable hydroxyapatite/type I collagen (HAp/Col Ⅰ) paste was developed to construct a suitable local microenvironment to accelerate the healing of bone-tendon interface. Physicochemical characterization demonstrated that the HAp/Col Ⅰ paste was injectable, uniform and stable. The in vitro cell culture illustrated that the paste could promote MC3T3-E1 cells proliferation and osteogenic expression. The results of a canine ACL reconstruction study showed that the reconstructive ACL had similar texture and color as the native ACL. The average width of the tunnel, total bone volume, bone volume/tissue volume and trabecular number acquired from micro-CT analysis suggested that the healing of tendon-bone interface in experimental group was better than that in control group. The biomechanical test showed the maximal loads in experimental group achieved approximately half of native ACL's maximal load at 24 weeks. According to histological examination, Sharpey fibers could be observed as early as 12 weeks postoperatively while a typical four-layer transitional structure of insertion site was regenerated at 48 weeks in the experimental group. The injectable HAp/Col Ⅰ paste provided a biomimetic scaffold and microenvironment for early cell attachment and proliferation, further osteogenic expression and extracellular matrix deposition, and in vivo structural and functional regeneration of the tendon-bone interface.

Abstract Supramolecular peptides exhibit obvious similarities with collagen fibers in terms of self-assembly characteristics, nanofibrous structure, and responsiveness to external stimuli. Here, a series of supramolecular peptides were developed by altering the amino acid sequence, enabling the self-assembly of three types of 4-biphenylacetic acid (BPAA)-tripeptides into fibrous hydrogel through hydrogen bonding and π–π stacking under the influence of ion induction. Transmission electron and scanning electron microscopies revealed that the diameter of the fiber within nanofibrous hydrogels was ~ 10 and ~ 40 nm, respectively, which was similar with the self-assembled collagen fibers. For this reason, these hydrogels could be considered as a biomimetic extracellular substitute. Meanwhile, the gelation concentration induced by ions was even lower than 0.66 wt%, with an elastic modulus of ~ 0.27 kPa, corresponding to a water content of 99.34 wt%. In addition, the three supramolecular hydrogels were found to be good substrates for L929 cell adhesion and MC-3T3 cell proliferation. The overall results implied that BPAA-based hydrogels have a lucrative application potential as cell carriers. Graphical Abstract

The rapid degradation of magnesium (Mg)-based implants in physiological environment limits its clinical applications, and alloying treatment is an effective way to regulate the degradation rate of Mg-based materials. In the present study, three Mg alloys, including Mg-0.8Ca (denoted as ZQ), Mg-0.8Ca-5Zn-1.5Ag (denoted as ZQ71) and Mg-0.8Ca-5Zn-2.5Ag (denoted as ZQ63), were fabricated by alloying with calcium (Ca), zinc (Zn) and silver (Ag). The results obtained from electrochemical corrosion tests and in vitro degradation evaluation demonstrated that the three Mg alloys exhibited distinct corrosion resistance, and ZQ71 exhibited the lowest degradation rate in vitro among them. After addition of Zn and Ag, the antibacterial potential of Mg alloys was also enhanced. The in vitro cell experiments showed that all the three Mg alloys had good biocompatibility. After implantation in a rat femoral defect, ZQ71 showed significantly higher osteogenic activity and bone substitution rate than ZQ63 and ZQ, due to its higher corrosion resistance as well as the stimulatory effects of the released metallic ions. In addition, the average daily degradation rate of each Mg alloy in vivo was significantly higher than that in vitro, as could be due to the implantation site located in the highly vascularized trabecular region. Importantly, the correlations between the in vitro and in vivo degradation parameters of the Mg alloys were systematically analyzed to find out the potential predictors of the in vivo degradation performance of the materials. The current work not only evaluated the clinical potential of the three biodegradable Mg alloys as bone grafts but also provided a feasible approach for predicting the in vivo degradation behavior of biodegradable materials.

Abstract Collagen made a tremendous impact in the field of regenerative medicine as a bioactive material. For decades, collagen has been used not only as a scaffolding material but also as an active component in regulating cells' biological behavior and phenotype. However, animal-derived collagen as a major source suffered from problems of immunogenicity, risk of viral infection, and the unclear relationship between bioactive sequence and function. Recombinant humanized collagen (rhCol) provided alternatives for regenerative medicine with more controllable risks. However, the characterization of rhCol and the interaction between rhCol and cells still need further investigation, including cell behavior and phenotype. The current study preliminarily demonstrated that recombinant humanized collagen type III (rhCol III) conformed to the theoretical amino acid sequence and had an advanced structure resembling bovine collagen. Furthermore, rhCol III could facilitate basal biological behaviors of human skin fibroblasts, such as adhesion, proliferation and migration. rhCol III was beneficial for some extracellular matrix-expressing cell phenotypes. The study would shed light on the mechanism research of rhCol and cell interactions and further understanding of effectiveness in tissue regeneration. Graphical abstract

The improved corrosion resistance, osteogenic activity, and antibacterial ability are the key factors for promoting the large-scale clinical application of magnesium (Mg)-based implants. In the present study, a novel nanocomposite coating composed of inner magnesium hydroxide, middle graphene oxide, and outer hydroxyapatite (Mg(OH)2/GO/HA) is constructed on the surface of Mg-0.8Ca–5Zn-1.5Ag by a combined strategy of hydrothermal treatment, electrophoretic deposition, and electrochemical deposition. The results of material characterization and electrochemical corrosion test showed that all the three coatings have high bonding strength, hydrophilicity and corrosion resistance. In vitro studies show that Mg(OH)2 indeed improves the antibacterial activity of the substrate. The next GO and GO/HA coating procedures both promote the osteogenic differentiation of MC3T3-E1 cells and show no harm to the antibacterial activity of Mg(OH)2 coating, but the latter exhibits the best promoting effect. In vivo studies demonstrate that the Mg alloy with the composite coating not only ameliorates osteolysis induced by bacterial invasion but also promotes bone regeneration under both normal and infected conditions. The current study provides a promising surface modification strategy for developing multifunctional Mg-based implants with good corrosion resistance, antibacterial ability and osteogenic activity to enlarge their biomedical applications.

Abstract In tissue engineering, bioactive materials play an important role, providing structural support, cell regulation and establishing a suitable microenvironment to promote tissue regeneration. As the main component of extracellular matrix, collagen is an important natural bioactive material and it has been widely used in scientific research and clinical applications. Collagen is available from a wide range of animal origin, it can be produced by synthesis or through recombinant protein production systems. The use of pure collagen has inherent disadvantages in terms of physico-chemical properties. For this reason, a processed collagen in different ways can better match the specific requirements as biomaterial for tissue repair. Here, collagen may be used in bone/cartilage regeneration, skin regeneration, cardiovascular repair and other fields, by following different processing methods, including cross-linked collagen, complex, structured collagen, mineralized collagen, carrier and other forms, promoting the development of tissue engineering. This review summarizes a wide range of applications of collagen-based biomaterials and their recent progress in several tissue regeneration fields. Furthermore, the application prospect of bioactive materials based on collagen was outlooked, aiming at inspiring more new progress and advancements in tissue engineering research. Graphical Abstract

The blossoming Chinese medical device market calls for a science-based regulatory system in China. Consistent efforts have been made to advance the medical device regulatory reforms for innovation, translation and industry development. In this article, we report both the latest regulatory requirements which aim to ensure safety and efficacy for patients while encouraging innovation of the medical device industry, and the key programs on medical devices covered in the Regulatory Science Action Plan (RSAP) of the National Medical Products Administration of China (NMPA). The main features of the revised regulations are first elucidated before the opportunities for translational research are interpreted, including those for additive manufacturing and customized devices, drug–device combination products, artificial intelligence-powered software and surgical robots, and nanomaterials for medical devices. Finally, a regulatory perspective is provided to researchers who expect to translate their technologies in the Chinese medical device market. Important issues including early attention to critical market and clinical needs, understanding the true principle and spirit underlying the changing regulations and standards, and protecting intellectual property rights with comprehensive measures, are discussed. These developments warrant further investigations into the distinct role of regulatory science in shaping medical devices research and development.

While most bone defects can be repaired spontaneously, the healing process can be complicated due to insufficient bone regeneration when osteoporosis occurs. Synthetic materials that intrinsically stimulate bone formation without inclusion of exogenous cells or growth factors represent a highly desirable alternative to current grafting strategies for the management of osteoporotic defects. Herein, we developed a series of hydroxyapatite bioceramics composed of a microwhiskered scaffold (wHA) reinforced with multiple layers of releasable hydroxyapatite nanoparticles (nHA). These novel bioceramics (nwHA) are tunable to optimize the loading amount of nHA for osteoporotic bone formation. The utility of nwHA bioceramics for the proliferation or differentiation of osteoporotic osteoblasts in vitro is demonstrated. A much more compelling response is seen when bioceramics are implanted in critical-sized femur defects in osteoporotic rats, as nwHA bioceramics promote significantly higher bone regeneration and delay adjacent bone loss. Moreover, the nwHA bioceramics loaded with a moderate amount of nHA can induce new bone formation with a higher degree of ossification and homogenization. Two types of osteogenesis inside the nwHA bioceramic pores were discovered for the first time, depending on the direction of growth of the new bone. The current study recommends that these tailored hybrid micro/nanostructured bioceramics represent promising candidates for osteoporotic bone repair.

The fast development of biomaterials science and engineering has generated significant number of studies and publications as well as tremendous amount of research data. A methodology is needed to translate such research data and results to validated scientific evidence. This article for the first time proposes the concept and methodology of evidence-based biomaterials research, which is to use evidence-based research approach represented by systematic reviews to generate evidence for answering scientific questions related to biomaterials. After briefly introducing the advancement of biomaterials since 1950s, the scientific and engineering nature of biomaterials are discussed along with the roadmap of biomaterials translation from basic research to commercialized medical products, and the needs of scientific evidence. Key information of the evidence-based approach such as its origination from evidence-based medicine, levels of evidence, systematic review and meta-analysis, differences between systematic and narrative reviews is then highlighted. Applications with a step-by-step procedure of conducting evidence-based biomaterials research, three examples of biomaterials research using evidence-based approach to generate scientific evidence, and opportunities and challenges of evidence-based biomaterials research are presented. With its notable impact on the practice of medicine, the evidence-based approach is also expected to make influential contributions to the biomaterials field.

Abstract Hydroxyapatite (HA) bioceramics have been extensively employed as bone tissue scaffolds owing to their biodegradability and osteoinductivity. In our work, HA, a significant component of natural bone tissue used as the raw material to produce porous scaffolds employing three‐dimensional (3D)‐printing technology. Physical and chemical properties, porosity, and compression resistance of the scaffolds were investigated in vitro. The scaffold was confirmed to have a large number of interconnected pore structures on the surface and inside HA scaffolds showed good cell compatibility and cell adhesion in cell text. To analyze the effect of the scaffold on bone repair and regeneration in vivo, the large‐size defect of beagle skull was repaired with a 3D printing group and an autologous bone group (ABG) for 8 months. Images and histological analysis of the 3D printing group indicated better integration with adjacent tissues. However, there were obvious gaps in the ABG, which indicates weak bone regeneration ability of this group due to unmatched implant dimension. Immunohistochemistry and immunofluorescence results showed that 3D‐printed scaffolds had a highly vascularized structure. This study indicates that 3D‐printed bioceramics scaffolds that are osteoinductivity and biodegradable have great potential in maxillofacial bone regeneration.

Mitral regurgitation (MR) was the most common heart valve disease. Surgical repair with artificial chordal replacement had become one of the standard treatments for mitral regurgitation. Expanded polytetrafluoroethylene (ePTFE) was currently the most commonly used artificial chordae material due to its unique physicochemical and biocompatible properties. Interventional artificial chordal implantation techniques had emerged as an alternative treatment option for physicians and patients in treating mitral regurgitation. Using either a transapical or a transcatheter approach with interventional devices, a chordal replacement could be performed transcatheter in the beating heart without cardiopulmonary bypass, and the acute effect on the resolution of mitral regurgitation could be monitored in real-time by transesophageal echo imaging during the procedure. Despite the in vitro durability of the expanded polytetrafluoroethylene material, artificial chordal rupture occasionally occurred. In this article, we reviewed the development and therapeutic results of interventional devices for chordal implantation and discuss the possible clinical factors responsible for the rupture of the artificial chordal material.

Abstract Pure titanium is widely used in clinical implants, but its bioinert properties (poor strength and mediocre effect on bone healing) limit its use under load‐bearing conditions. Modeling on the structure of collagen fibrils and specific nanocrystal plane arrangement of hydroxyapatite in the natural bone, a new type of titanium (Ti) with a highly aligned fibrous‐grained (FG) microstructure is constructed. The improved attributes of FG Ti include high strength (≈950 MPa), outstanding affinity to new bone growth, and tight bone‐implant contact. The bone‐mimicking fibrous grains induce an aligned surface topological structure conducive to forming close contact with osteoblasts and promotes the expression of osteogenic genes. Concurrently, the predominant Ti(0002) crystal plane of FG Ti induces the formation of hydrophilic anatase titanium oxide layers, which accelerate biomineralization. In conclusion, this bioinspired FG Ti not only proves to show mechanical and bone‐regenerative improvements but it also provides a new strategy for the future design of metallic biomaterials.

Abstract Nanostructured biomaterials that replicate natural bone architecture are expected to facilitate bone regeneration. Here, nanohydroxyapatite (nHAp) with vinyl surface modification is acquired by silicon‐based coupling agent and photointegrated with methacrylic anhydride‐modified gelatin to manufacture a chemically integrated 3D‐printed hybrid bone scaffold (75.6 wt% solid content). This nanostructured procedure significantly increases its storage modulus by 19.43‐fold (79.2 kPa) to construct a more stable mechanical structure. Furthermore, biofunctional hydrogel with biomimetic extracellular matrix is anchored onto the filament of 3D‐printed hybrid scaffold (HGel‐g‐nHAp) by polyphenol‐mediated multiple chemical reactions, which contributes to initiate early osteogenesis and angiogenesis by recruiting endogenous stem cells in situ. Significant ectopic mineral deposition is also observed in subcutaneously implanted nude mice with storage modulus enhancement of 25.3‐fold after 30 days. Meanwhile, HGel‐g‐nHAp realizes substantial bone reconstruction in the rabbit cranial defect model, achieving 61.3% breaking load strength and 73.1% bone volume fractions in comparison to natural cranium 15 weeks after implantation. This optical integration strategy of vinyl modified nHAp provides a prospective structural design for regenerative 3D‐printed bone scaffold.

So far, how to achieve the optimal regenerative repair of large load-bearing bone defects using artificial bone grafts is a huge challenge in clinic. In this study, a strategy of combining osteoinductive biphasic calcium phosphate (BCP) bioceramic scaffolds with intramedullary nail fixation for creating stable osteogenic microenvironment was applied to repair large segmental bone defects (3.0 cm in length) in goat femur model. The material characterization results showed that the BCP scaffold had the initial compressive strength of over 2.0 MPa, and total porosity of 84%. The cell culture experiments demonstrated that the scaffold had the excellent ability to promote the proliferation and osteogenic differentiation of rat bone marrow-derived mesenchymal stem cells (BMSCs). The in vivo results showed that the intramedullary nail fixation maintained the initial stability and structural integrity of the implants at early stage, promoting the osteogenic process both guided and induced by the BCP scaffolds. At 9 months postoperatively, good integration between the implants and host bone was observed, and a large amount of newborn bones formed, accompanying with the degradation of the material. At 18 months postoperatively, almost the complete new bone substitution in the defect area was achieved. The maximum bending strength of the repaired bone defects reached to the 100% of normal femur at 18 months post-surgery. Our results demonstrated the good potential of osteoinductive BCP bioceramics in the regenerative repair of large load-bearing bone defects. The current study could provide an effective method to treat the clinical large segmental bone defects.

The application of medical devices to repair skin damage is clinically accepted and natural polymer enjoys an important role in this field, such as collagen or hyaluronic acid, etc. However, the biosafety and efficacy of these implants are still challenged. In this study, a skin damage animal model was prepared by UV-photoaging and recombinant humanized type III collagen (rhCol III) was applied as a bioactive material to implant in vivo to study its biological effect, comparing with saline and uncrosslinked hyaluronic acid (HA). Animal skin conditions were non-invasively and dynamically monitored during the 8 weeks experiment. Histological observation, specific gene expression and other molecular biological methods were applied by the end of the animal experiment. The results indicated that rhCol III could alleviate the skin photoaging caused by UV radiation, including reduce the thickening of epidermis and dermis, increase the secretion of Collagen I (Col I) and Collagen III (Col III) and remodel of extracellular matrix (ECM). Although the cell-material interaction and mechanism need more investigation, the effect of rhCol III on damaged skin was discussed from influence on cells, reconstruction of ECM, and stimulus of small biological molecules based on current results. In conclusion, our findings provided rigorous biosafety information of rhCol III and approved its potential in skin repair and regeneration. Although enormous efforts still need to be made to achieve successful translation from bench to clinic, the recombinant humanized collagen showed superiorities from both safety and efficacy aspects.

Osteoinductivity is a crucial factor to determine the success and efficiency of posterolateral spinal fusion (PLF) by employing calcium phosphate (Ca-P) bioceramics. In this study, three kinds of Ca-P ceramics with microscale to nanoscale gain size (BCP-control, BCP-micro and BCP-nano) were prepared and their physicochemical properties were characterized. BCP-nano had the spherical shape and nanoscale gain size, BCP-micro had the spherical shape and microscale gain size, and BCP-control (BAM®) had the irregular shape and microscale gain size. The obtained BCP-nano with specific nanotopography could well regulate in vitro protein adsorption and osteogenic differentiation of MC3T3 cells. In vivo rabbit PLF procedures further confirmed that nanotopography of BCP-nano might be responsible for the stronger bone regenerative ability comparing with BCP-micro and BCP-control. Collectedly, due to nanocrystal similarity with natural bone apatite, BCP-nano has excellent efficacy in guiding bone regeneration of PLF, and holds great potentials to become an alternative to standard bone grafts for future clinical applications.

Limited stem cells and mismatched interface fusion have plagued biomaterial-mediated cranial reconstruction. Here, the authors engineer an instantly fixable and self-adaptive scaffold to promote calcium chelation and interface integration, regulate macrophage M2 polarization, and recruit endogenous stem cells.

Combination products with a wide range of clinical applications represent a unique class of medical products that are composed of more than a singular medical device or drug/biological product. The product research and development, clinical translation as well as regulatory evaluation of combination products are complex and challenging. This review firstly introduced the origin, definition and designation of combination products. Key areas of systematic regulatory review on the safety and efficacy of device-led/supervised combination products were then presented. Preclinical and clinical evaluation of combination products was discussed. Lastly, the research prospect of regulatory science for combination products was described. New tools of computational modeling and simulation, novel technologies such as artificial intelligence, needs of developing new standards, evidence-based research methods, new approaches including the designation of innovative or breakthrough medical products have been developed and could be used to assess the safety, efficacy, quality and performance of combination products. Taken together, the fast development of combination products with great potentials in healthcare provides new opportunities for the advancement of regulatory review as well as regulatory science.

Supramolecular nanofiber peptide assemblies had been used to construct functional hydrogel biomaterials and achieved great progress. Here, a new class of biphenyl-tripeptides with different C-terminal amino acids sequences transposition were developed, which could self-assemble to form robust supramolecular nanofiber hydrogels from 0.7 to 13.8 kPa at ultra-low weight percent (about 0.27 wt%). Using molecular dynamics simulations to interrogate the physicochemical properties of designed biphenyl-tripeptide sequences in atomic detail, reasonable hydrogen bond interactions and “FF” brick (phenylalanine-phenylalanine) promoted the formation of supramolecular fibrous hydrogels. The biomechanical properties and intermolecular interactions were also analyzed by rheology and spectroscopy analysis to optimize amino acid sequence. Enhanced L929 cells adhesion and proliferation demonstrated good biocompatibility of the hydrogels. The storage modulus of BPAA-AFF with 10 nm nanofibers self-assembling was around 13.8 kPa, and the morphology was similar to natural extracellular matrix. These supramolecular nanofiber hydrogels could effectively support chondrocytes spreading and proliferation, and specifically enhance chondrogenic related genes expression and chondrogenic matrix secretion. Such biomimetic supramolecular short peptide biomaterials hold great potential in regenerative medicine as promising innovative matrices because of their simple and regular molecular structure and excellent biological performance.

As cancer is increasingly considered a metabolic disorder, it is postulated that serum metabolite profiling can be a viable approach for detecting the presence of cancer. Here, the authors report a machine learning model using mass spectrometry-based liquid biopsy data for pan-cancer screening and classification.

In nature, many natural porous tissues of animals or plants follow heterogeneous structures pattern. Including turtle back pattern, leaf veins, wood porous fiber and porous cancellous bone are classic heterogeneous structures. In order to better design bionic microenvironment porous bone implants, herein, a bionic porous structure based on Voronoi-Thiessen diagram to create heterogeneous topology microenvironment promoting bone regeneration were proposed. Porous structures with tunable heterogeneity were built and achieved by selective laser melting (SLM). The topology analysis revealed the introduce of heterogeneity brought wide pore size distribution and irregular topology. The mechanical and hydrodynamics properties were predesigned and simulated by finite element analysis (FEA). The heterogeneity hardly influenced the overall strength, stiffness and permeability but the irregular stress and fluid shear rate distribution in FEA results indicated fluctuating local stiffness and permeability. In vitro and in vivo experimental results indicated that Quasi-homogeneous structure had irregular topology mimicking that of the natural bone structure and semi-heterogenous structure shown better osteogenesis. It is found that the scaffold heterogeneous microenvironment factors play important roles for bone regeneration, and which is crucial for the development of new orthopedic implants.

Human epidermal growth factor receptor-2 (HER-2) positive breast cancer is highly invasive with poor clinical outcomes and high risk of recurrence. Here, trastuzumab functionalized pullulan-doxorubicin nanoparticles (Tz-P-Dox) were developed and characterized as a new anticancer formulation for active targeting HER-2 overexpression of breast cancer cells. The obtained nanoparticles had the hydrodynamic diameter of 66.7 ± 2.0 nm and PDI of 0.218 ± 0.012. And the in vitro results showed significant difference of cell uptake and cytotoxic effect between Tz-P-Dox and non-targeted P-Dox against HER-2 positive cell lines (BT474 and MCF-7 cells). However, the differences between Tz-P-Dox and P-Dox were not observed in HER-2 negative cell lines (MDA-MB-231 cells). These results suggested that trastuzumab functionalized nanoparticles had great potential to be considered as a candidate drug for HER-2 positive breast cancer treatment.

Scientific research originates from curiosity and interests. Translational research of biomaterials should always focus on addressing specific needs of the targeted clinical applications. The guest editors of this special issue hope that the included articles have provided cutting-edge biomaterials research as well as insights of the translation of biomaterials from bench to clinic.

Early neovascularization and osteoinductivity are two key factors to determine the regenerative abilities of biphasic calcium phosphate (BCP) bioceramics in bone repair. Due to the uncontrolled pore structure and large grain size, the biological performances of the conventional BCP bioceramics is restricted to a large extent. Herein, this study attempted to fabricate BCP bioceramics with appropriately uniform macropores and abundant micropores by combining the advantages of the H2O2 foaming method with the microsphere-sintering method, and different sintering methods were adopted to adjust the micro-nano topography. Due to the optimal design of macropore distribution and nano topography, the obtained BCP bioceramics could well trigger and regulate in vitro biological responses, such as degradation, bone-like apatite formation, protein adsorption, cell spreading, angiogenic and osteogenic differentiation. In vivo canine intramuscular implantation further revealed that the nano topography and appropriately uniform macropores might be responsible for the early neovascularization and osteoinductivity of the prepared BCP bioceramics. Collectedly, the neovascularization and osteoinductivity of BCP bioceramics were further enhanced by optimally designing the pore structure and micro-nano topography, which hold huge potential to be an alternative to the gold standard of autogenous bone in bone repairing applications.

Recent studies on osteoimmunology have revealed the indispensable role of immune cells in osteogenesis. The surface topography of biomaterials plays a critical role in regulating cellular behaviors; however, little attention is paid to its effects on the immune response. Three dense hydroxyapatite (HA) disks with grain size in nano-scale (∼100 nm) to submicron (∼500 nm) range were prepared to investigate their role in macrophage polarization and functional status. It was found that HA ceramics with nano-topography promoted macrophage phenotypic switching from the pro-inflammatory M1 type to the pro-healing M2 type. A reduction in grain size could significantly inhibit the secretion of pro-inflammatory cytokine and increase the proportion of CD206+ M2 population in vitro. Meanwhile, nano-topography could reduce tissue inflammation, up-regulate gene expression of M2 phenotypic marker, and raise the fraction of ARG+ M2 macrophages in vivo. This might be attributed to the differential integrin expression to regulate the activation of intracellular signaling cascades. These findings indicate that the surface topography of HA ceramics regulates macrophage responses, thereby adjusting inflammation and subsequent tissue regeneration. An improved understanding of the relationship between material features and its immunomodulatory potential may help to design bone substitute materials with good biological performance.

Abstract Although a promising strategy, the mesenchymal stem cell (MSC)‐based therapy of cartilage defects is sometimes accompanied with chronic inflammation during the remodeling status, which may hinder cartilage regeneration. During this process, the inflammatory cytokine tumor necrosis factor α (TNFα) plays an important role and may be a potential target. In this study, we investigated the effect of Tnfα RNA interference by introducing a functional and highly safe carbon dot (CD)‐SMCC nanovector synthesized by bioconjugation of CDs with a protein crosslinker, sulfosuccinimidyl‐4‐(N‐maleimidomethyl) cyclohexane‐1‐carboxylate (sulfo‐SMCC), as the vehicle of the silenced TNFα (siTnfα) on chondrogenesis of MSCs. The results showed that CD‐SMCC displayed intense fluorescence with well‐dispersed and positively charged properties, which favored effective binding and delivering of siTnfα into the MSCs. CD‐SMCC‐siTnfα nanoformula also exhibited considerably high transfection efficiency and nearly no cytotoxicity, which is preferred over commercial polyethyleneimine. Interference of Tnfα by CD‐SMCC‐siTnfα markedly promoted the chondrogenesis of MSCs, as indicated by upregulating cartilage‐specific markers. Furthermore, in vivo exploration indicated that CD‐SMCC‐siTnfα transfected MSCs accelerated cartilage regeneration. In conclusion, this study demonstrated that in combination with the novel CD‐SMCC nanovector, targeting Tnfα may facilitate stem cell‐based therapy of cartilage defects. Stem Cells Translational Medicine 2019;8:724&736

Polylactic acid/Hydroxyapatite (PLA/HA) composite was widely studied and applied in the field of biomaterials for its good processability, bioactivity, and mechanical properties. In addition to traditional preparation methods, additive manufacturing has also been adopted to prepare PLA/HA composites with customized geometries. This work combined the comprehensive optimized PLLA (L-polylactic acid)/nano-HA (nHA) composite with the low-cost and stable Fused deposition modeling (FDM) technology to successfully prepare PLLA/nHA porous bone repair scaffolds. The results showed that PLLA/nHA composite ink satisfied the smoothness of printing, and the accuracy also met the requirements of personalized bone repair application. The high loaded nHA scaffold had suitable compressive strength was significantly higher than those of pure HA ceramic scaffold and cancellous bone. Besides, in vitro bone-like apatite formation on the surface in the degradation process and in vivo evaluations further verified its good osteogenic property. Compared with other complex and cutting-edge 3D printing technologies, this study provides a low-cost, stable, simple and fast way to realize personalized printing of bone repair scaffolds, which is undoubtedly conductive to the improvement and rapid deployment of personalized biomaterials in clinical applications.

The regeneration of bone defects in osteoporotic patients presents a big challenge. Icariin (Ica), which is the main active component of traditional Chinese medicine - herba epimedii, has been widely loaded to scaffolds for the treatment of bone fracture and osteoporosis. To increase drug loading capacity, and meanwhile achieve a stable and safe drug delivery, in present study, a novel icariin derivative - thiolated icariin (Ica-SH) molecule with good cytocompatibility and bioactivity was incorporated into biphasic calcium phosphate (BCP) ceramic scaffold through Ica-SH intermolecular disulfide bonds (abbr., Ica-SH/BCP) to form film coating. Compared with Ica-loaded BCP scaffolds via physical adsorption (abbr., Ica/BCP), the formation of Ica-SH intermolecular disulfide bonds in Ica-SH/BCP scaffolds led to a decreased real-time drug release concentration, and a reduced drug release rate. The released drug from Ica-SH/BCP scaffolds could promote the proliferation, migration, and osteoblastic differentiation of ovariectomized rat bone mesenchymal stem cells (OVX-rBMSCs), and up-regulate the angiogenic gene expression in human umbilical vein endothelial cells (HUVECs) in vitro. The OVX-rat femoral condyle defect model also demonstrated that Ica-SH/BCP scaffolds promoted a superior bone regeneration in osteoporotic animals than BCP ones. These findings suggest that Ica-SH is a promising drug, which can be facilely incorporated into a variety of scaffolds for repairing bone defects of patients, in particular the ones with osteoporosis.

Jaw bone repair requires scaffold with bone regeneration, antibacterial function and personalized size. This study proposed 3D printed degradable calcium phosphate scaffolds with antibacterial functions for regeneration of jaw bone. Calcium phosphate powders and berberine were combined to modulate the printing inks. Porous scaffolds were fabricated by direct extrusion 3D printing and cross-linked with sodium alginate in situ. The dimensional size, shape and porosity of scaffolds were precisely customized by 3D printing. Berberine-loaded scaffolds show sustained release of antimicrobial drugs. By adjusting the concentration and cross-linking time of calcium chloride, the cross-linking degree of the scaffold can be adjusted and the drug load of the scaffold can be controlled. The young's modulus of 3DP scaffold was about 1.3 MPa. After freeze-drying, the shrinkage was about 24.4% and less swelling was observed, indicating that the scaffold had sufficient structural stability. In vitro biological test showed that the 3DP scaffold had low cytotoxicity and it was beneficial to MC3T3 cell adhesion and proliferation. 3D printed calcium phosphate scaffolds with controlled-release antibacterial properties is a promising biomaterials for jaw repair. Keywords: 3D printing, Bone tissue engineering, Calcium phosphate, scaffolds, Antibacterial functions

Abstract In vitro expansion of mesenchymal stem cells (MSCs) has been implicated in loss of multipotency, leading to impaired chondrogenic potential and an eventual therapeutic effect, as reported in our previous study. However, the precise regulatory mechanism is still unclear. Here, we demonstrate that endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) were involved in transformation of MSCs induced by in vitro culture based on the comparative profiling of in vitro cultured bone marrow MSCs at passage 3 (P3 BMSCs) vs. fresh P0 BMSCs by microarray analysis. Indeed, RT-PCR and Western blot analysis showed significantly lower expression levels of three key UPR-related molecules, ATF4, ATF6 and XBP1, in P3 BMSCs than P0 BMSCs. Further, we found that UPR suppression by 4-phenylbutyrate (4-PBA) reduced the chondrogenic potential of P0 BMSCs and further cartilage regeneration. Conversely, UPR induction by tunicamycin (TM) enhanced the chondrogenic differentiation of P3 BMSCs and the therapeutic effect on cartilage repair. Thus, the decline in the chondrogenic potential of stem cells after in vitro culture and expansion may be due to changes in ER stress and the UPR pathway.

It is well known that stem cells reside within tissue engineering functional microenvironments that physically localize them and direct their stem cell fate. Recent efforts in the development of more complex and engineered scaffold technologies, together with new understanding of stem cell behavior in vitro, have provided a new impetus to study regulation and directing stem cell fate. A variety of tissue engineering technologies have been developed to regulate the fate of stem cells. Traditional methods to change the fate of stem cells are adding growth factors or some signaling pathways. In recent years, many studies have revealed that the geometrical microenvironment played an essential role in regulating the fate of stem cells, and the physical factors of scaffolds including mechanical properties, pore sizes, porosity, surface stiffness, three-dimensional structures, and mechanical stimulation may affect the fate of stem cells. Chemical factors such as cell-adhesive ligands and exogenous growth factors would also regulate the fate of stem cells. Understanding how these physical and chemical cues affect the fate of stem cells is essential for building more complex and controlled scaffolds for directing stem cell fate.

With significant improvements in living standards in China and the aging population that accompanies these improvements, the market demand for high-quality orthopaedic biomaterials for clinical applications is tremendous and growing rapidly. There are major efforts to promote cooperation between different scientific institutes with complementary strengths for the further development of the biomaterial industry in China to achieve the technological level of developed countries. An excellent example is that the Ministry of Science and Technology of the People's Republic of China (MOST; Beijing, China) established the Chinese National Engineering Research Centres (CNERCs), which serve as a major initiative in driving basic and applied technological research and development (R&D) in mainland China. To create a win-win situation with Hong Kong, the MOST and the Hong Kong Innovation and Technology Commission are jointly establishing the Hong Kong Branch of the CNERCs. Through an amicable arrangement, the Chinese University of Hong Kong (CUHK; Shatin, Hong Kong) and the Chinese National Engineering Research Centre for Biomaterials (i.e., Main Centre) in Chengdu, People's Republic of China have decided to apply to establish the Hong Kong Branch of the CNERC for Biomaterials at the CUHK. The effort in establishing the Hong Kong Branch of Biomaterials seeks to promote further collaboration with the Main Centre with the goals of promoting synergy and a win-win cooperation between mainland China and Hong Kong in scientific research, talent cultivation, clinically driven novel biomaterials product design, and preclinical and clinical testing. It will thus become a model for the successful collaboration between the Hong Kong research institutions and the mainland CNERCs in the area of biomaterials. Such initiatives will facilitate close collaboration in translational medicine associated with biomaterial development and application.

In the process of bone regeneration, new bone formation is largely affected by physico-chemical cues in the surrounding microenvironment. Tissue cells reside in a complex scaffold physiological microenvironment. The scaffold should provide certain circumstance full of structural cues to enhance multipotent mesenchymal stem cell (MSC) differentiation, osteoblast growth, extracellular matrix (ECM) deposition, and subsequent new bone formation. This article reviewed advances in fabrication technology that enable the creation of biomaterials with well-defined pore structure and surface topography, which can be sensed by host tissue cells (esp., stem cells) and subsequently determine cell fates during differentiation. Three important cues, including scaffold pore structure (i.e., porosity and pore size), grain size, and surface topography were studied. These findings improve our understanding of how the mechanism scaffold microenvironmental cues guide bone tissue regeneration.