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Understanding the foreign-body response (FBR) of biomaterials is a prerequisite for the prediction of its clinical application, and the present assessments mainly rely on in vitro cell culture and in situ histopathology. However, remote organs responses after biomaterials implantation is unclear. Here, by leveraging body-wide-transcriptomics data, we performed in-depth systems analysis of biomaterials - remote organs crosstalk after abdominal implantation of polypropylene and silk fibroin using a rodent model, demonstrating local implantation caused remote organs responses dominated by acute-phase responses, immune system responses and lipid metabolism disorders. Of note, liver function was specially disturbed, defined as hepatic lipid deposition. Combining flow cytometry analyses and liver monocyte recruitment inhibition experiments, we proved that blood derived monocyte-derived Kupffer cells in the liver underlying the mechanism of abnormal lipid deposition induced by local biomaterials implantation. Moreover, from the perspective of temporality, the remote organs responses and liver lipid deposition of silk fibroin group faded away with biomaterial degradation and restored to normal at end, which highlighted its superiority of degradability. These findings were further indirectly evidenced by human blood biochemical examination from 141 clinical cases of hernia repair using silk fibroin mesh and polypropylene mesh. In conclusion, this study provided knowledge of biomaterials-body interactions. It is of great important for future development of biomaterial devices for clinical application.One Sentence SummaryAbdominal local biomaterials implantation induces remote organ fatty deposition through activated blood-derived Kupffer cells.

Mesenchymal stem cells (MSCs) have been widely used as functional components in tissue engineering. However, the immunogenicity and limited pro-angiogenic efficacy of MSCs greatly limited their pro-regenerative ability in allogenic treatment. Herein, utilizing a chemically defined cocktail in the culture system, including cytokines, small molecules, structural protein, and other essential components, we generated the immunoprivileged and pro-angiogenic cells (IACs) derived from human adipose tissues. Conventional adipose-derived MSCs (cADSCs) were used as a control in all the experiments. IACs show typical MSC properties with enhanced stemness capacity and a robust safety profile. IACs induce a significantly milder immune response of allogenic peripheral blood mononuclear cells in an H3K27me3-HLA axis-dependent manner. IACs, through superior paracrine effects, further promote nitric oxide production, anti-apoptotic ability, and the tube formation of human vein endothelial cells. Embedded in a photo-reactive hydrogel (Gel) termed as GelMA/HA-NB/LAP for tissue engineering treatment, IACs promote faster tissue regeneration in a xenogeneic full-thickness skin defect model, eliciting a milder immune response and enhanced blood vessel formation in IACs-treated defect areas. Together with its excellent pro-regenerative potential and robust safety, our findings suggest that IACs may be a promising candidate for clinically relevant stem cell and tissue engineering therapeutics.

The global incidence of bone tissue injuries has been increasing rapidly in recent years, making it imperative to develop suitable bone grafts for facilitating bone tissue regeneration. It has been demonstrated that nanomaterials/nanocomposites scaffolds can more effectively promote new bone tissue formation compared with micromaterials. This may be attributed to their nanoscaled structural and topological features that better mimic the physiological characteristics of natural bone tissue. In this review, we examined the current applications of various nanomaterial/nanocomposite scaffolds and different topological structures for bone tissue engineering, as well as the underlying mechanisms of regeneration. The potential risks and toxicity of nanomaterials will also be critically discussed. Finally, some considerations for the clinical applications of nanomaterials/nanocomposites scaffolds for bone tissue engineering are mentioned.

Cartilage adheres to subchondral bone via a specific osteochondral interface tissue where forces are transferred from soft cartilage to hard bone without conferring fatigue damage over a lifetime of load cycles. However, the fine structure and mechanical properties of the osteochondral interface tissue remain unclear. Here, we identified an ultrathin ∼20-30 μm graded calcified region with two-layered micronano structures of osteochondral interface tissue in the human knee joint, which exhibited characteristic biomolecular compositions and complex nanocrystals assembly. Results from finite element simulations revealed that within this region, an exponential increase of modulus (3 orders of magnitude) was conducive to force transmission. Nanoscale heterogeneity in the hydroxyapatite, coupled with enrichment of elastic-responsive protein-titin, which is usually present in muscle, endowed the osteochondral tissue with excellent mechanical properties. Collectively, these results provide novel insights into the potential design for high-performance interface materials for osteochondral interface regeneration.

Large bone defects that cannot form a callus tissue are often faced with long-time recovery. Developmental engineering-based strategies with mesenchymal stem cell (MSC) aggregates have shown enhanced potential for bone regeneration. However, MSC aggregates are different from the physiological callus tissues, which limited the further endogenous osteogenesis. This study aims to achieve engineering of osteo-callus organoids for rapid bone regeneration in cooperation with bone marrow-derived stem cell (BMSC)-loaded hydrogel microspheres (MSs) by digital light-processing (DLP) printing technology and stepwise-induction. The printed MSC-loaded MSs aggregated into osteo-callus organoids after chondrogenic induction and showed much higher chondrogenic efficiency than that of traditional MSC pellets. Moreover, the osteo-callus organoids exhibited stage-specific gene expression pattern that recapitulated endochondral ossification process, as well as a synchronized state of cell proliferation and differentiation, which highly resembled the diverse cell compositions and behaviors of developmentally endochondral ossification. Lastly, the osteo-callus organoids efficiently led to rapid bone regeneration within only 4 weeks in a large bone defect in rabbits which need 2-3 months in previous tissue engineering studies. The findings suggested that in vitro engineering of osteo-callus organoids with developmentally osteogenic properties is a promising strategy for rapid bone defect regeneration and recovery.

Critical-sized bone defects often lead to non-union and full-thickness defects of the calvarium specifically still present reconstructive challenges. In this study, we show that neurotrophic supplements induce robust in vitro expansion of mesenchymal stromal cells, and in situ transplantation of neurotrophic supplements-incorporated 3D-printed hydrogel grafts promote full-thickness regeneration of critical-sized bone defects. Single-cell RNA sequencing analysis reveals that a unique atlas of in situ stem/progenitor cells is generated during the calvarial bone healing in vivo. Notably, we find a local expansion of resident Msx1+ skeletal stem cells after transplantation of the in situ cell culture system. Moreover, the enhanced calvarial bone regeneration is accompanied by an increased endochondral ossification that closely correlates to the Msx1+ skeletal stem cells. Our findings illustrate the time-saving and regenerative efficacy of in situ cell culture systems targeting major cell subpopulations in vivo for rapid bone tissue regeneration.

Irregular partial-thickness cartilage defect is a common pathogenesis of osteoarthritis (OA) with no available treatment in clinical practice. Currently, cartilage tissue engineering is only suitable for a limited area of full-thickness cartilage defect. Here, we design a biomimetic joint paint for the intractable partial-thickness cartilage defect repair. The joint paint, composed of a bridging layer of chondroitin sulfate and a surface layer of gelatin methacrylate with hyaluronic acid, can quickly and tightly adhere to the cartilage defect by light activation. Being treated by the joint paint, the group of rabbit and pig models with partial-thickness cartilage defects showed a restoration of a smooth cartilage surface and the preservation of normal glycosaminoglycan content, whereas the untreated control group exhibited serious progressive OA development. This paint treatment functions by prohibiting chondrocyte apoptosis, maintaining chondrocyte phenotype, and preserving the content of glycosaminoglycan in the partial-thickness cartilage defects. These findings illustrated that the biomimetic joint paint is an effective and revolutionary therapeutics for the patients with noncurable partial-thickness cartilage defects.

The failure to repair critical-sized bone defects often leads to incomplete regeneration or fracture non-union. Tissue-engineered grafts have been recognized as an alternative strategy for bone regeneration due to their potential to repair defects. To design a successful tissue-engineered graft requires the understanding of physicochemical optimization to mimic the composition and structure of native bone, as well as the biological strategies of mimicking the key biological elements during bone regeneration process. This review provides an overview of engineered graft-based strategies focusing on physicochemical properties of materials and graft structure optimization from macroscale to nanoscale to further boost bone regeneration, and it summarizes biological strategies which mainly focus on growth factors following bone regeneration pattern and stem cell-based strategies for more efficient repair. Finally, it discusses the current limitations of existing strategies upon bone repair and highlights a promising strategy for rapid bone regeneration.

It is still a challenge for existing bioprinting technologies to fabricate organs suitable for implantation, mainly due to the inability to recapitulate the organs' complex anatomical structures, mechanical properties, and biological functions. Additionally, the failure to create 3D constructs with interconnected microchannels for long-range mass transportation that limits the clinical applications of 3D printing technologies. Here, a new method was developed to print functional living skin (FLS) using a newly designed biomimetic bioink (GelMA/HA-NB/LAP) and digital light processing (DLP)-based 3D printing technology. The FLS possess interconnected microchannels that facilitates cell migration, proliferation and neo-tissue formation. The GelMA/HA-NB/LAP bioink, composed of gelatin methacrylate (GelMA), N-(2-aminoethyl)-4-(4-(hydroxymethyl)-2-methoxy-5-nitrosophenoxy) butanamide (NB) linked hyaluronic acid (HA-NB) and photo-initiator lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP). The bioink demonstrated its rapid gelation kinetics, tunable mechanical properties, good biocompatibility and tissue adhesion. The DLP-based 3D printing technology provides a rapid method to precisely position clusters of human skin fibroblasts (HSFs) and human umbilical vein endothelial cells (HUVECs) with high cell viability to form FLS. The FLS promotes skin regeneration and efficient neovascularization by mimicking the physiological structure of natural skin, and it can also be easily handled and implanted onto the wound site due to its strong mechanical and bio-adhesive properties. Moreover, in vivo study demonstrated that the living skin exhibited instant defense function and had superior performance in promoting dermal regeneration with skin appendages in large animals. This study provides a rapid and mass production method of functional living organs for future clinical applications.

Articular cartilage repair still remains a major challenge in today's clinical practice due to its poor self-healing capacity. Therefore, it is essential to develop a promising strategy to achieve a one-step cartilage repair for patients suffering from joint diseases and traumas. Inspired by the complex composition and microscopic architecture of native articular cartilage, an injectable hydrogel (M-O-G) with tough mechanical property and strong tissue adhesiveness is developed. All hydrogel material compositions are natural polymers or their derivatives resemble the normal cartilage extracellular matrix (ECM). This hydrogel showed superior tunable mechanical properties (mechanical strength ≈270 kPa, compressibility ≈70%) and rapid recovery ability. Moreover, it exhibited strong adhesiveness and enhanced integration with tissues. Further studies demonstrated that the hydrogel had good biocompatibility and superior performance in cartilage defect regeneration. Thus, the presented hydrogel is a promising biomaterial for clinical cartilage regeneration and other biomedical applications.

Corneal injury-induced inflammation may result in permanent vision loss. In situ forming adhesive hydrogels offer a promising tissue substitute for repair of partial-thickness corneal wounds, but the uncertainty of biodegradation rate potentially fails to form new tissues in vivo. To overcome this problem, a methacrylated collagen (ColMA) hydrogel is newly developed as a wound dressing to repair partial-thickness corneal defects using a two-stage approach. Such a hydrogel can maintain the viability and adhesion of human corneal epithelial cells (HCECs) as well as promoting their migration in vitro. During surgery, we initially photopolymerized ColMA hydrogel to form a in situ coating at defects. The hydrogel is further designed to be dislodged off after implantation and thus avoid the potential risks from the uncontrollable gel biodegradation. In both rabbit and pig corneal defect models, this collagen hydrogel not only serves as a physical barrier to prevent bacterial penetration and corneal wound dehydration, but also produces nanogranules to highly promote re-epithelization, thereby contributing to the decrease of scar formation and improvement of corneal epithelial-stromal regeneration via reducing myofibroblast activation. This study presents a useful platform system that can be adapted and extended towards the repair of diverse tissues or organs through the addition of bioactive molecules, encouraging the ColMA hydrogel wound dressing to be translated into advanced regenerative therapies.

The demand of favorable scaffolds has increased for the emerging cartilage tissue engineering. Chondroitin sulfate (CS) and silk fibroin have been investigated and reported with safety and excellent biocompatibility as tissue engineering scaffolds. However, the rapid degradation rate of pure CS scaffolds presents a challenge to effectively recreate neo-tissue similar to natural articular cartilage. Meanwhile the silk fibroin is well used as a structural constituent material because its remarkable mechanical properties, long-lasting in vivo stability and hypoimmunity. The application of composite silk fibroin and CS scaffolds for joint cartilage repair has not been well studied. Here we report that the combination of silk fibroin and CS could synergistically promote articular cartilage defect repair. The silk fibroin (silk) and silk fibroin/CS (silk-CS) scaffolds were fabricated with salt-leaching, freeze-drying and crosslinking methodologies. The biocompatibility of the scaffolds was investigated in vitro by cell adhesion, proliferation and migration with human articular chondrocytes. We found that silk-CS scaffold maintained better chondrocyte phenotype than silk scaffold; moreover, the silk-CS scaffolds reduced chondrocyte inflammatory response that was induced by interleukin (IL)-1β, which is in consistent with the well-documented anti-inflammatory activities of CS. The in vivo cartilage repair was evaluated with a rabbit osteochondral defect model. Silk-CS scaffold induced more neo-tissue formation and better structural restoration than silk scaffold after 6 and 12 weeks of implantation in ICRS histological evaluations. In conclusion, we have developed a silk fibroin/ chondroitin sulfate scaffold for cartilage tissue engineering that exhibits immuno-inhibition property and can improve the self-repair capacity of cartilage. Statement of Significance Severe cartilage defect such as osteoarthritis (OA) is difficult to self-repair because of its avascular, aneural and alymphatic nature. Current scaffolds often focus on providing sufficient mechanical support or bio-mimetic structure to promote cartilage repair. Thus, silk has been adopted and investigated broadly. However, inflammation is one of the most important factors in OA. But few scaffolds for cartilage repair reported anti-inflammation property. Meanwhile, chondroitin sulfate (CS) is a glycosaminoglycan present in the natural cartilage ECM, and has exhibited a number of useful biological properties including anti-inflammatory activity. Thus, we designed this silk-CS scaffold and proved that this scaffold exhibited good anti-inflammatory effects both in vitro and in vivo , promoted the repair of articular cartilage defect in animal model.

Meniscal injury is one of the most common knee joint injuries, which remains an intractable challenge in clinical practice to date. Aberrant epidermal growth factor receptor (EGFR) activation levels in both human and mice menisci following injury, prompted us to investigate the functional role of EGFR by utilizing an inducible cartilage-specific EGFR-deficient mouse model. We demonstrated that conditional EGFR deletion in mice resulted in increased partial meniscectomy-induced ECM production within the meniscus, which is comparable to utilization of the small molecule EGFR inhibitor, gefitinib, to block EGFR activity. Here, we combined intra-articular delivery of gefitinib with an implanted customized collagen scaffold to substitute for lost meniscal tissue, as well as to promote meniscal regeneration and prevent osteoarthritis (OA) progression in a rabbit meniscectomy model. Statement of Significance The main novelty of this study is the finding of a new application for small molecule EGFR inhibitor in meniscal injury therapy. This study also highlights the importance of using a customized collagen scaffold to provide robust mechanical strength and effectively promote meniscus regeneration. In summary, our study finds that intra-articular delivery of gefitinib together with implantation of a customized, multi-layer collagen scaffold not only enhanced meniscal regeneration, but also protected articular cartilage from degeneration in rabbit model. These results provide valuable insight for meniscal tissue engineering studies and clinical practice.

Summary Articular cartilage injury and degeneration causing pain and loss of quality-of-life has become a serious problem for increasingly aged populations. Given the poor self-renewal of adult human chondrocytes, alternative functional cell sources are needed. Direct reprogramming by small molecules potentially offers an oncogene-free and cost-effective approach to generate chondrocytes, but has yet to be investigated. Here, we directly reprogrammed mouse embryonic fibroblasts into PRG4+ chondrocytes using a 3D system with a chemical cocktail, VCRTc (valproic acid, CHIR98014, Repsox, TTNPB, and celecoxib). Using single-cell transcriptomics, we revealed the inhibition of fibroblast features and activation of chondrogenesis pathways in early reprograming, and the intermediate cellular process resembling cartilage development. The in vivo implantation of chemical-induced chondrocytes at defective articular surfaces promoted defect healing and rescued 63.4% of mechanical function loss. Our approach directly converts fibroblasts into functional cartilaginous cells, and also provides insights into potential pharmacological strategies for future cartilage regeneration., Graphical Abstract, Highlights • A chemical method to derive functional murine articular chondrocytes from fibroblasts • Chemical-induced chondrocytes promote in vivo regeneration of articular defects • In single-cell analysis, intermediate reprogramming events resemble cartilage development, In this article, Ouyang and colleagues develop a chemical-driven direct reprogramming of mouse embryonic fibroblasts into PRG4+ chondrocytes, with a screen-defined cocktail VCRTc. Their induced chondrocytes promote in vivo cartilage functional regeneration. The dynamical cellular phenotypes were analyzed by single-cell RNA sequencing, illustrating the inhibition of fibroblast features and activation of chondrogenesis pathways in early reprogramming.

Large area skull defects accompanied by craniocerebral injury are life-threating diseases that are difficult to treat due to the large area of damage and intracranial hypertension. An autologous bone is an ideal source for the regeneration of bone, including skull defects. However, two-step treatment, including craniectomy and cranioplasty, is the main strategy in clinical practice to stabilize intracranial pressure, but still remains a huge obstacle in both the preservation of auto-bone fragments and protection of exposed brain tissue. In this study, an elastic auto-bone patch was developed to provide a new and one-step method for repairing large skull defects which are currently repaired with two stages of surgery. The elastic auto-bone patch is formed by bonding auto-bone fragments together using hydrogels, which is then re-implanted to bone defects to repair large skull defects. The auto-bone patch could adapt to changes in intracranial pressure to protect brain tissue for damage, integrate well with surrounding bone tissues, and promote bone regeneration. After 8 weeks implantation, the large-size skull defect is filled with new formed bone tissues in the group of treating with auto-bone patch. This study introduced a new procedure on the application of elastic auto-bone patch to repair large area skull defects.

Changes in the stiffness of chondrocyte extracellular matrix (ECM) are involved in the pathological progression of osteoarthritis (OA). However, the downstream responses of cartilage ECM stiffness are still unclear. YAP (Yes-associated protein) has been extensively studied as a mechanotransducer, we thus hypothesized that by targeting the downstream molecule activity of ECM stiffness could maintain chondrocyte phenotype and prevent cartilage degeneration in OA. Here, we showed that human cartilage matrix stiffened during pathological progression of OA, and the chondrocyte YAP activity was associated with ECM stiffness. We then mimicked the physiological and pathological stiffness of human cartilage by using PDMS-based substrates, and found that YAP was activated in chondrocytes seeded on stiff substrate, gradually losing their phenotype. In addition, it was observed that YAP was also significantly activated in mice OA development, and conditional knockout (cKO) of YAP in mice preserved collagen II expression and protected cartilage from degeneration in the OA model. Furthermore, intra-articular injection of YAP-selective inhibitor, Verteporfin, significantly maintained cartilage homeostasis in mice OA model. This study indicates that the application of mechanotransducer-targeted drugs could be a potential therapeutic approach for cartilage repair in OA.

One of the key problems hindering skin repair is the deficiency of dermal vascularization and difficulty of epidermis regeneration, which makes it challenging to fabricate scaffolds that can biologically fulfill the requirements for skin regeneration. To overcome this problem, three-dimensional printing was used to fabricate a gelatin-sulfonated silk composite scaffold that was incorporated with basic fibroblast growth factor 2 (FGF-2) through binding with a sulfonic acid group (SO3) (3DG-SF-SO3-FGF). The efficacy and mechanism by which the 3DG-SF-SO3-FGF scaffolds promote skin regeneration were investigated both within in vitro cell culture and in vivo with a full-thickness skin defect model. The histological results showed that the gelatin-sulfonated silk composite scaffolds promoted granulation, and that incorporation of FGF-2 significantly enhanced the regeneration of skin-like tissues after implantation in rat skin defects for 14 and 28 days. Further investigations demonstrated that 3DG-SF-SO3-FGF scaffolds might stimulate dermal vascularization. These findings thus suggest that incorporation of FGF-2 into the 3D printed scaffolds is a viable strategy for enhancing skin regeneration.

A retroreflective projection grating technique has been investigated to inspect quasi flat and specular surfaces. The method introduces the flexibility to adjust the properties of the grating to a specific application or to move it as a whole, in order to use phase shifting technology. Three types of optical configuration have been demonstrated. The method has been tested with a quantified artifact. The experiment shows that it can successfully recover the contour and amplitude of the surface waviness on the artifact. The method can be developed for industrial application in nondestructive testing and evaluation (NDTE).

Retroreflective metrology has been used to measure the 3-D surface waviness on standard artifacts. An optical configuration was constructed for the measurement, in which the grating image is produced by projection. The three-step algorithm of phase-shifting technology was applied to analyze the image. Two standard artifacts with 8.0- and 16.0-µm peak-to-peak wave amplitudes were tested. The experiments show that retroreflective metrology can successfully recover the contour and amplitude of the surface waviness on the standard artifacts. © 2000 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(00)02101-2]

An efficient system for retroreflective grating generation andanalysis has been constructed to measure the derivative and the contourof specular surfaces. In this system, a new optical configurationhas been provided to generate and capture a grating image with aretroreflective screen. Tests show that the system can detectindents and outdents with a maximum depth of less than 10mum. The method can be developed for automated industrialinspection and machine vision.