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Irregular bone defects, characterized by unpredictable size, shape, and depth, pose a major challenge to clinical treatment. Although various bone grafts are available, none can fully meet the repair needs of the defective area. Here, this study fabricates a dough-type hydrogel (DR-Net), in which the first dynamic network is generated by coordination between thiol groups and silver ions, thereby possessing kneadability to adapt to various irregular bone defects. The second rigid covalent network is formed through photocrosslinking, maintaining the osteogenic space under external forces and achieving a better match with the bone regeneration process. In vitro, an irregular alveolar bone defect is established in the fresh porcine mandible, and the dough-type hydrogel exhibits outstanding shape adaptability, perfectly matching the morphology of the bone defect. After photocuring, the storage modulus of the hydrogel increases 8.6 times, from 3.7 kPa (before irradiation) to 32 kPa (after irradiation). Furthermore, this hydrogel enables effective loading of P24 peptide, which potently accelerates bone repair in Sprague–Dawley (SD) rats with critical calvarial defects. Overall, the dough-type hydrogel with kneadability, space-maintaining capability, and osteogenic activity exhibits exceptional potential for clinical translation in treating irregular bone defects.

The crosstalk between immune cells and the neurovascular unit plays a pivotal role in neural regeneration following central nervous system (CNS) injury. Maintaining brain immune homeostasis is crucial for restoring neurovascular function. In this study, an interactive bridge was developed via an immunomodulatory hydrogel microsphere to link the interaction network between microglia and the neurovascular unit, thereby precisely regulating immune-neurovascular crosstalk and achieving neural function recovery. This immunomodulatory crosstalk microsphere (MP/RIL4) was composed of microglia-targeted RAP12 peptide-modified interleukin-4 (IL-4) nanoparticles and boronic ester-functionalized hydrogel using biotin-avidin reaction and air-microfluidic techniques. We confirmed that the immunomodulatory microspheres reduced the expression of pro-inflammatory factors including IL-1β, iNOS, and CD86, while upregulating levels of anti-inflammatory factors such as IL-10, Arg-1, and CD206 in microglia. In addition, injection of the MP/RIL4 significantly mitigated brain atrophy volume in a mouse model of ischemic stroke, promoted neurobehavioral recovery, and enhanced the crosstalk between immune cells and the neurovascular unit, thus increasing angiogenesis and neurogenesis of stroke mice. In summary, the immunomodulatory microspheres, capable of orchestrating the interaction between immune cells and neurovascular unit, hold considerable therapeutic potential for ischemic stroke and other CNS diseases.

After rotator cuff injuries, uncontrolled inflammation hinders tendon–bone junction regeneration and induces scar formation in situ. Therefore, precisely controlling inflammation could be a solution to accelerate tendon–bone junction regeneration. In this study, we synthesized a peptide–metal ion complex hydrogel with thermosensitive capability that can be used as a hydrogel chemical regulator. By the coordination complex between Mg2+and BMP-12, the free and coordinated Mg2+can be programmability released from the hydrogel. The fast release of free Mg2+can prevent inflammation at the early stage of injuries, according to the results of RT-qPCR and immunofluorescence staining. Then, the coordinated Mg2+was slowly released from the hydrogel and provided an anti-inflammatory environment for tendon–bone junction regeneration in the long term. Finally, the hydrogel demonstrated enhanced therapeutic effects in a rat rotator cuff tear model. Overall, the Mg2+/BMP-12 peptide–metal ion complex-based hydrogel effectively addresses the regenerative requirements of the tendon–bone junction across various stages by graded modulating inflammation.

Inspired by the imbalance between extrinsic and intrinsic tendon healing, this study fabricated a new biofilter scaffold with a hierarchical structure based on a melt electrowriting technique. The outer multilayered fibrous structure with connected porous characteristics provides a novel passageway for vascularization and isolates the penetration of scar fibers, which can be referred to as a biofilter process. In vitro experiments found that the porous architecture in the outer layer can effectively prevent cell infiltration, whereas the aligned fibers in the inner layer can promote cell recruitment and growth, as well as the expression of tendon-associated proteins in a simulated friction condition. It was shown in vivo that the biofilter process could promote tendon healing and reduce scar invasion. Herein, this novel strategy indicates great potential to design new biomaterials for balancing extrinsic and intrinsic healing and realizing scarless tendon healing.

Extracellular vesicles (EVs) are potential gene therapy platforms, yet their therapeutic use is hindered by low encapsulation efficiency and weak targeting specificity. A recent Nature Biomedical Engineeringstudy reports the retrovirus-like EVs for efficient mRNA delivery to the CNS, showing considerable promise for systematic, targeted, and efficient gene therapy.

Intervertebral disc degeneration (IVDD) is rising worldwide and leading to significant health issues and financial strain for patients. Traditional treatments for IVDD can alleviate pain but do not reverse disease progression, and surgical removal of the damaged disc may be required for advanced disease. The inflammatory microenvironment is a key driver in the development of disc degeneration. Suitable anti-inflammatory substances are critical for controlling inflammation in IVDD. Several treatment options, including glucocorticoids, non-steroidal anti-inflammatory drugs, and biotherapy, are being studied for their potential to reduce inflammation. However, anti-inflammatories often have a short half-life when applied directly and are quickly excreted, thus limiting their therapeutic effects. Biomaterial-based platforms are being explored as anti-inflammation therapeutic strategies for IVDD treatment. This review introduces the pathophysiology of IVDD and discusses anti-inflammatory therapeutics and the components of these unique biomaterial platforms as comprehensive treatment systems. We discuss the strengths, shortcomings, and development prospects for various biomaterials platforms used to modulate the inflammatory microenvironment, thus providing guidance for future breakthroughs in IVDD treatment.

Regulating macrophage activation precisely is crucial in treating chronic inflammation in osteoarthritis (OA). However, the stable pro-inflammatory state and deep distribution of macrophages in vivo pose a great challenge to treatment. In this study, inspired by the innate immune, immune cell mobilized hydrogel microspheres were constructed by microfluidic methods and load chemokines, macrophage antibodies and engineered cell membrane vesicles (sEVs) via covalent and non-covalent junctions. The immune cell mobilized hydrogel microspheres, based on a mixture of streptavidin grafted hyaluronic acid methacrylate (HAMA-SA) and Chondroitin sulfate methacrylate (ChSMA) microspheres (HCM), can recruit, capture and reprogram proinflammatory macrophages in the joint cavity to improve the joint inflammatory microenvironment. In vitro experiments demonstrated that immune cell mobilized hydrogel microspheres had excellent macrophage recruitment, capture, and reprogramming abilities. Pro-inflammatory macrophages can be transformed into anti-inflammatory macrophages with an efficiency of 88.5 %. Animal experiments also revealed significant reduction in synovial inflammation and cartilage matrix degradation of OA. Therefore, the immune cell mobilized hydrogel microspheres may be an effective treatment of OA inflammation for the future.

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Graphical abstract: The oxygen-rich characteristics of short fibrous sponges with aggregational oxygen atoms can optimize the water absorption performance of short fibers, effectively regulate cell respiration and improve tissue oxidation metabolism by improving the ability of cells to adapt to oxygen, and provide important application value for tissue damage repair in collaboration with ADSCs.

Protein hydrogels are often used to mimic biological load-bearing tissues due to their excellent biocompatibility. However, protein hydrogels are usually too soft to achieve the unique mechanical properties of high stiffness and toughness of articular cartilage. This preview introduces the strategies that use chain entanglement to enhance the stiffness for engineering biomedical hydrogels with high stiffness, toughness, and compression resistance.

Extracellular vesicles (EVs) are nano-scale vesicles derived by cell secretion with unique advantages such as promoting cell proliferation, anti-inflammation, promoting blood vessels and regulating cell differentiation, which benefit their wide applications in regenerative medicine. However, the in vivotherapeutic effect of EVs still greatly restricted by several obstacles, including the off-targetability, rapid blood clearance, and undesired release. To address these issues, biomedical engineering techniques are vastly explored. This review summarizes different strategies to enhance EV functions from the perspective of drug loading, modification, and combination of biomaterials, and emphatically introduces the latest developments of functionalized EV-loaded biomaterials in different diseases, including cardio-vascular system diseases, osteochondral disorders, wound healing, nerve injuries. Challenges and future directions of EVs are also discussed.

Due to the lack of sufficient elasticity and strain sensing capability, protein-based ultrafine fibrous tissue engineering scaffolds, though favorable for skin repair, can hardly fulfill on-spot wound monitoring during healing. Herein, we designed highly elastic corn protein ultrafine fibrous smart scaffolds with a three-layer structure for motion tracking at an unpackaged state. The densely cross-linked protein networks were efficiently established by introducing a highly reactive epoxy and provided the fiber substrates with wide-range stretchability (360% stretching range) and ultrahigh elasticity (99.91% recovery rate) at a wet state. With the assistance of the polydopamine bonding layer, a silver conductive sensing layer was built on the protein fibers and endowed the scaffolds with wide strain sensing range (264%), high sensitivity (gauge factor up to 210.55), short response time (<70 ms), reliable cycling stability, and long-lasting duration (up to 30 days). The unpackaged smart scaffolds could not only support cell growth and accelerate wound closure but also track motions on skin and in vivoand trigger alarms once excessive wound deformations occurred. These features not only confirmed the great potential of these smart scaffolds for applications in tissue reconstruction and wound monitoring but also proved the possibility of employing various plant protein ultrafine fibers as flexible bioelectronics.

CRISPR/Cas9 is a revolutionary genome editing technology with the tremendous advantages such as precisely targeting/shearing ability, low cost and convenient operation, becoming an efficient and indispensable tool in biological research. As a disruptive technique, CRISPR/Cas9 genome editing has a great potential to realize a future breakthrough in the clinical bone and cartilage repairing as well. This review highlights the research status of CRISPR/Cas9 system in bone and cartilage repair, illustrates its mechanism for promoting osteogenesis and chondrogenesis, and explores the development tendency of CRISPR/Cas9 in bone and cartilage repair to overcome the current limitations.

Arterial vasospasm after microsurgery can cause severe obstruction of blood flow manifested as low tissue temperature, leading to tissue necrosis. The timely discovery and synchronized treatment become pivotal. In this study, a reversible, intelligent, responsive thermosensitive hydrogel system is constructed employing both the gel–sol transition and the sol–gel transition. The “reversible thermosensitive (RTS)” hydrogel loaded with verapamil hydrochloride is designed to dynamically and continuously regulate the extravascular microenvironment by inhibiting extracellular calcium influx. After accurate implantation and following in situ gelation, the RTS hydrogel reverses to the sol state causing massive drug release to inhibit vasospasm when the tissue temperature drops to the predetermined transition temperature. Subsequent restoration of the blood supply alleviates further tissue injury. Before the temperature drops, the RTS hydrogel maintains the gel state as a sustained-release reservoir to prevent vasospasm. The inhibition of calcium influx and vasospasm in vitroand in vivois demonstrated using vascular smooth muscle cells, mice mesenteric arterial rings, and vascular ultrasonic Doppler detection. Subsequent animal experiments demonstrate that RTS hydrogel can promote tissue survival and alleviate tissue injury responding to temperature change. Therefore, this RTS hydrogel holds therapeutic potential for diseases requiring timely detection of temperature change.

The 3D printing technique is suitable for patient-specific implant preparation for bone repair after bone tumor resection. However, improving the survival rate due to tumor recurrence remains a challenge for implants. The macrophage polarization induction to M2-type tumor-associated macrophages (TAMs) by the tumor microenvironment is a key factor of immunosuppression and tumor recurrence. In this study, a regenerative scaffold regulating the macrophage immune microenvironment and promoting bone regeneration in a dual-stage process for the postoperative treatment of bone tumors was constructed by binding a colony-stimulating factor 1 receptor (CSF-1R) inhibitor GW2580 onto in situ cosslinked hydroxybutylchitosan (HBC)/oxidized chondroitin sulfate (OCS) hydrogel layer covering a 3D printed calcium phosphate scaffold based on electrostatic interaction. The hydrogel layer on scaffold surface not only supplied abundant sulfonic acid groups for stable loading of the inhibitor, but also acted as the cover mask protecting the bone repair part from exposure to unhealthy growth factors in the microenvironment at the early treatment stage. With local prolonged release of inhibitor being realized via the functional material design, CSF-1R, the main pathway that induces polarization of TAMs, can be efficiently blocked, thus regulating the immunosuppressive microenvironment and inhibiting tumor development at a low therapeutic dose. At the later stage of treatment, calcium phosphate component of the scaffold can facilitate the repair of bone defects caused by tumor excision. In conclusion, the difunctional 3D printed bone repair scaffold regulating immune microenvironment in stages proposed a novel approach for bone tumor postoperative treatment.

Graphical Abstract: TOC figure: The electrospun double-layer sponge fabricated by electrospinning simulated the microstructure of the urethra. The sponge can deliver the exosomes through a physical absorption style. The P(LLA-CL)/SF/VitB5 bilayer sponge has great potential to promote vascular regeneration and wound healing and can effectively inhibit fibrosis.

Balancing osteoblast‐osteoclast (OB‐OC) cross‐talk is crucial for restoring bone tissue structure and function. Current clinical drugs targeting either osteogenesis or osteoclastogenesis fail to effectively regulate cross‐talk, impeding efficient bone repair in osteoporosis patients. Ubiquitin‐specific protease 26 (USP26) is shown to coordinate OB‐OC cross‐talk by independently regulating β‐catenin and Iκb‐α. However, effective drugs for activating USP26 are still lacking. Here, they constructed bone homeostasis repair microcarriers (BHRC) that encapsulate Usp26mRNA‐loaded lipid nanoparticles (mRNA@LNP) within MMPs‐responsive GelMA hydrogel microspheres. These microcarriers target the osteoporotic microenvironment and regulate OB‐OC cross‐talk, thereby facilitating intervertebral fusion in osteoporotic rats. Results demonstrate that mRNA@LNP exhibits uniform particle size and high transfection efficiency, while GelMA hydrogel microspheres possess excellent biocompatibility and MMP responsiveness, providing favorable cell survival space and controllable release of mRNA@LNP. The released LNP upregulates USP26 protein expression, effectively promoting osteogenesis while suppressing osteoclast formation. In vivo experiments show that injecting BHRC into the defect site of intervertebral discs in osteoporotic rats significantly promotes tail vertebrae fusion by responding to the microenvironment and regulating cell‐to‐cell cross‐talk. Thus, the BHRC holds great potential in regulating osteoporotic homeostasis, particularly in challenging bone defects such as intervertebral fusion in osteoporotic environments. Due to the existence of OB‐OC cross‐talk, the effect of clinical fusion treatment for IVDD patients with osteoporosis is poor. Based on the coordination function of USP26, this study proposes an innovative mRNA@LNP hydrogel microsphere to promote osteogenic differentiation of BMSC and inhibit osteoclast differentiation of BMDM in response to the MMP microenvironment of osteoporosis, thereby promoting intervertebral fusion.

Activated fibroblast-like synovial (FLS) cells are regarded as an important target for rheumatoid arthritis (RA) treatment via starvation therapy mediated by glucose oxidase (GOx). However, the hypoxic RA-FLS environment greatly reduces the oxidation process of glucose and leads to a poor therapeutic effect of the GOx-based starvation therapy. In this work, we designed a hollow mesoporous copper sulfide nanoparticles (CuS NPs)-based smart GOx/atovaquone (ATO) codelivery system (named as V-HAGC) targeting RA-FLS cells to realize a O2-economized dual energy inhibition strategy to solve the limitation of GOx-based starvation therapy. V-HAGC armed with dual multi-stimuli-responsive “doorkeepers” can guard drugs intelligently. Once under the stimulation of photothermal and acidic conditions at the targeted area, the dual intelligent responsive “doors” would orderly open to realize the controllable release of drugs. Besides, the efficacy of V-HAGC would be much improved by the additional chemodynamic therapy (CDT) and photothermal therapy (PTT) stimulated by CuS NPs. Meanwhile, the upregulated H2O2and acid levels by starvation therapy would promote the Fenton-like reaction of CuS NPs under O2-economized dual energy inhibition, which could enhance the PTT and CDT efficacy as well. In vitroand in vivoevaluations revealed V-HAGC with much improved efficacy of this combination therapy for RA. In general, the smart V-HAGC based on the O2-economized dual energy inhibition strategy combined with enhanced CDT and PTT has the potential to be an alternative methodology in the treatment of RA.

Lipid-based boundary layers formed on liposome-containing hydrogels can facilitate lubrication. However, these boundary layers can be damaged by shear, resulting in decreased lubrication. Here, a shear-responsive boundary-lubricated drug-loaded hydrogel is created by incorporating celecoxib (CLX)-loaded liposomes within dynamic covalent bond-based hyaluronic acid (HA) hydrogels (CLX@Lipo@HA-gel). The dynamic cross-linked network enables the hydrogel to get restructured in response to shear, and the HA matrix allows the accumulation of internal liposome microreservoirs on the sliding surfaces, which results in the formation of boundary layers to provide stable lubrication. Moreover, hydration shells formed surrounding the hydrogel can retard the degradation process, thus helping in sustaining lubrication. Furthermore, in vitro and in vivo experiments found that CLX@Lipo@HA-gels can maintain anabolic-catabolic balance, alleviate cartilage wear, and attenuate osteoarthritis progression by delivering CLX and shear-responsive boundary lubrication. Overall, CLX@Lipo@HA-gels can serve as shear-responsive boundary lubricants and drug-delivery vehicles to alleviate friction-related diseases like osteoarthritis.

ABSTRACTIntroductionGene therapy is becoming increasingly common in clinical practice, giving hope for the correction of a wide range of human diseases and defects. The CRISPR/Cas9 system, consisting of the Cas9 nuclease and single-guide RNA (sgRNA), has revolutionized the field of gene editing. However, efficiently delivering the CRISPR-Cas9 to the target organ or cell remains a significant challenge. In recent years, with rapid advances in nanoscience, materials science, and medicine, researchers have developed various technologies that can deliver CRISPR-Cas9 in different forms for in vitroand in vivogene editing. Here, we review the development of the CRISPR-Cas9 and describe the delivery forms and the vectors that have emerged in CRISPR-Cas9 delivery, summarizing the key barriers and the promising strategies that vectors currently face in delivering the CRISPR-Cas9.Areas coveredWith the rapid development of CRISPR-Cas9, delivery methods are becoming increasingly important in the in vivodelivery of CRISPR-Cas9.Expert opinionCRISPR-Cas9 is becoming increasingly common in clinical trials. However, the complex nuclease and protease environment is a tremendous challenge for in vivoclinical applications. Therefore, the development of delivery methods is highly likely to take the application of CRISPR-Cas9 technology to another level.

Immune system activation is usually based on the difference between the body’s self and non-self. However, cancer is a result of genetic mutation in host cells characterized by uncontrolled cell proliferation, metastasis, and escape from immune surveillance. Vaccines have great potential in cancer immunotherapy because they stimulate the body’s immune response. Although encouraging, most of the reported cancer vaccines only work for a small number of patients because of tumor heterogeneity and the immunosuppressive tumor microenvironment. Nanovaccines hold the potential to enhance immunotherapeutic efficacy, considering their co-delivery capabilities of antigens and therapeutic agents and enhanced solid tumor accumulation and penetration efficacy.

Diabetes patients often suffer from fractures despite normal or high bone mineral density, a phenomenon known as the diabetic bone paradox. Gao et al.1identify AGEs as disrupting bone quality and compromising skeletal integrity in diabetic bone disease.

The effective osteointegration of orthopedic implants is a key factor for the success of orthopedic surgery. However, local metabolic imbalance around implants under osteoporosis condition could jeopardize the fixation effect. Inspired by the bone structure and the composition around implants under osteoporosis condition, alendronate (A) was grafted onto methacryloyl hyaluronic acid (H) by activating the carboxyl group of methacryloyl hyaluronic acid to be bonded to inorganic calcium phosphate on trabecular bone, which is then integrated with aminated bioactive glass (AB) modified by oxidized dextran (O) for further adhesion to organic collagen on the trabecular bone. The hybrid hydrogel could be solidified on cancellous bone in situunder UV irradiation and exhibits dual adhesion to organic collagen and inorganic apatite, promoting osteointegration of orthopedic implants, resulting in firm stabilization of the implants in cancellous bone areas. In vitro, the hydrogel was evidenced to promote osteogenic differentiation of embryonic mouse osteoblast precursor cells (MC3T3-E1) as well as inhibit the receptor activator of nuclear factor-κ B ligand (RANKL)-induced osteoclast differentiation of macrophages, leading to the upregulation of osteogenic-related gene and protein expression. In a rat osteoporosis model, the bone-implant contact (BIC) of the hybrid hydrogel group increased by 2.77, which is directly linked to improved mechanical stability of the orthopedic implants. Overall, this organic-inorganic, dual-adhesive hydrogel could be a promising candidate for enhancing the stability of orthopedic implants under osteoporotic conditions.

Despite the clinical evidence underpinning the efficacy of prescribing mechanical loads for combating specific diseases, the lack of simple platforms that generate forces with a stimuli-delivering interface to the tissue effectively seems to stifle the potential of mechanotherapy. In a recent study, a new mechanically active tissue adhesive that generates and delivers mechanical stimulation to the muscle tissue with programmed strength and frequency is proposed. This newly reported device holds a broad application prospect for mechanotherapy.

The SARS-CoV-2 pandemic spread worldwide unabated. However, achieving protection from the virus in the whole respiratory tract, avoiding blood dissemination, and calming the subsequent cytokine storm remains a major challenge. Here, we develop an inhaled microfluidic microsphere using dual camouflaged methacrylate hyaluronic acid hydrogel microspheres with a genetically engineered membrane from angiotensin-converting enzyme II (ACE2) receptor-overexpressing cells and macrophages. By timely competing with the virus for ACE2 binding, the inhaled microspheres significantly reduce SARS-CoV-2 infective effectiveness over the whole course of the respiratory system in vitroand in vivo. Moreover, the inhaled microspheres efficiently neutralize proinflammatory cytokines, cause an alternative landscape of lung-infiltrated immune cells, and alleviate hyperinflammation of lymph nodes and spleen. In an acute pneumonia model, the inhaled microspheres show significant therapeutic efficacy by regulation of the multisystem inflammatory syndrome and reduce acute mortality, suggesting a powerful synergic strategy for the treatment of patients with severe COVID-19 via non-invasive administration.

Herein, a smart nanohydrogel with endogenous microRNA-21 toehold is developed to encapsulate gemcitabine-loaded mesoporous silica nanoparticles for targeted pancreatic cancer therapy. This toehold mediated strand displacement method can simultaneously achieve specific drug release and miRNA-21 silencing, resulting in the up-regulation of the expression of tumor suppressor genes PTEN and PDCD4.

Living cells and active factors are the two core elements of tissue repair, directly affecting the healing efficiency of damaged tissue. Nanofat (NF) can release living cells, such as adipose-derived stem cells (ADSCs), as well as active growth factors to promote angiogenesis, thus realizing cell-based wound healing. Herein, a novel living electrospun short fibrous sponge is constructed by modifying three-dimensional (3D) bionic short fibers with engineered NF. The uniform distribution of the polydopamine (PDA) modification endows the living sponges with stable mechanical properties, reversible water absorption and excellent adhesion even after repeated compression by an external force and long-term aqueous immersion. Meanwhile, the living electrospun short fibrous sponges with uniform NF modification contain living cells such as ADSCs and active growth factors such as vascular endothelial growth factor (VEGF), which can effectively promote the tube formation of human umbilical vein endothelial cells (HUVECs). In vivo,the living sponges can effectively and continuously act on wounds and act as a bionic living skin to prevent the loss of internal nutrients, creating a comfortable and favorable microenvironment for tissue regeneration and promoting the healing of diabetic wounds. Therefore, living electrospun short fibrous sponges via engineered NF are expected to achieve continuous wound healing with in situ living cells and active factors in injured tissues.

Soft tissue remodeling is a sophisticated process that sequentially provides dynamic biological signals to guide cell behavior. However, capturing these signals within hydrogel and directing over time has still been unrealized owing to the poor comprehension of physiological processes. Here, a bio-mimicking hydrogel is designed via thiol-ene click reaction to capture the early physical signal triggered by inflammation, and the chemical signals provided with chemokine and natural adhesion sites, which guaranteed the precise soft tissue remodeling. This bio-mimicking hydrogel efficiently facilitated cell anchoring, migration, and invasion in the 3D matrix due to the permissive space and the interaction with integrin receptors. Besides, the covalently grafted chemokine-like peptide is optimal for colonization and functional differentiation of endothelial cells through a HIF-1α dependent signal pathway. Furthermore, the early polarization of macrophages, collagen deposition and angiogenesis in rat acute wound model, and the increased blood perfusion in mouse skin flap model have confirmed that the bio-mimicking hydrogel realized precise soft tissue remodeling and opens new avenues for the phased repair of different tissues such as nerve, myocardium, and even bone.

The balance of redox homeostasis is key to stem cell maintenance and differentiation. However, this balance is disrupted by the overproduced reactive oxygen species (ROS) in pathological conditions, which seriously impair the therapeutic efficacy of stem cells. In the present study, highly dispersed fullerol nanocrystals with enhanced bioreactivity were incorporated into hydrogel microspheres using one-step innovative microfluidic technology to construct fullerol-hydrogel microfluidic spheres (FMSs) for in situregulating the redox homeostasis of stem cells and promoting refractory bone healing. It was demonstrated that FMSs exhibited excellent antioxidant activity to quench both intracellular and extracellular ROS, sparing stem cells from oxidative stress damage. Furthermore, these could effectively promote the osteogenic differentiation of stem cells with the activation of FoxO1 signaling, indicating the intrinsically osteogenic property of FMSs. By injecting the stem cells-laden FMSs into rat calvarial defects, the formation of new bone was remarkably reinforced, which is a positive synergic effect from modulating the ROS microenvironment and enhancing the osteogenesis of stem cells. Collectively, the antioxidative FMSs, as injectable stem cell carriers, hold enormous promise for refractory bone healing, which can also be expanded to deliver a variety of other cells, targeting diseases that require in situredox regulation.

Metal ions are important trace elements in the human body, which directly affect the human metabolism and the regeneration of damaged tissues. For instance, the advanced combination of magnesium ions (Mg2+) and bone repair materials make the composite materials have the function of promoting vascular repair and enhancing the adhesion of osteoblasts. Herein, inspired by magnets to attract metals, we utilized the coordination reaction of metal ion ligand to construct a bisphosphonate-functionalized injectable hydrogel microsphere (GelMA-BP-Mg) which could promote cancellous bone reconstruction of osteoporotic bone defect via capturing Mg2+. By grafting bisphosphonate (BP) on GelMA microspheres, GelMA-BP microspheres could produce powerful Mg2+capture ability and sustained release performance through coordination reaction, while sustained release BP has bone-targeting properties. In the injectable GelMA-BP-Mg microsphere system, the atomic percentage of captured Mg2+was 0.6%, and the captured Mg2+could be effectively released for 18 days. These proved that the composite microspheres could effectively capture Mg2+and provided the basis for the composite microspheres to activate osteoblasts and endothelial cells and inhibit osteoclasts. Both in vivoand in vitroexperimental results revealed that the magnet-inspired Mg2+-capturing composite microspheres are beneficial to osteogenesis and angiogenesis by stimulating osteoblasts and endothelial cells while restraining osteoclasts, and ultimately effectively promote cancellous bone regeneration. This study could provide some meaningful conceptions for the treatment of osteoporotic bone defects on the basis of metal ions.

In the field of bone defect repair, 3D printed scaffolds have the characteristics of personalized customization and accurate internal structure. However, how to construct a well-structured vascular network quickly and effectively inside the scaffold is essential for bone repair after transplantation. Herein, inspired by the unique biological structure of “lotus seedpod”, hydrogel microspheres encapsulating deferoxamine (DFO) liposomes were prepared through microfluidic technology as “lotus seeds”, and skillfully combined with a three-dimensional (3D) printed bioceramic scaffold with biomimetic “lotus” biological structure which can internally grow blood vessels. In this composite scaffold system, DFO was effectively released by 36% in the first 6 h, which was conducive to promote the growth of blood vessels inside the scaffold quickly. In the following 7 days, the release rate of DFO reached 69%, which was fundamental in the formation of blood vessels inside the scaffold as well as osteogenic differentiation of bone mesenchymal stem cells (BMSCs). It was confirmed that the composite scaffold could significantly promote the human umbilical vein endothelial cells (HUVECs) to form the vascular morphology within 6 h in vitro. In vivo, the composite scaffold increased the expression of vascularization and osteogenic related proteins Hif1-α, CD31, OPN, and OCN in the rat femoral defect model, significantly cutting down the time of bone repair. To sum up, this “lotus seedpod” inspired porous bioceramic 3D printed scaffold with internal vascularization functionality has broad application prospects in the future.

The simultaneous differentiation of human-induced pluripotent stem cells (hiPSCs) into different cell types is the basis for obtaining organoids and tissues with complex cell components, structures, and functions. Lewis and colleagues' latest work published in Nature Biomedical Engineering presented a new one-pot orthogonally differentiation strategy combined with a multi-material 3D bioprinting method to generate programmatic patterned organoids and bioprinted tissues. This approach will provide a new roadmap to developing engineered tissues for extensive biomedical applications.

Conditioned medium (CM) contains variety of factors secreted by cells, which directly regulate cellular processes, showing tremendous potential in regenerative medicine. Here, for the first time, we proposed a novel regenerative therapy mediated by biodegradable micro-nano electrospun fibers loaded with highly active conditioned medium of adipose-derived stem cells (ADSC-CM). ADSC-CM was successfully loaded into the nanofibers with biological protection and controllable sustained-release properties by emulsion electrospinning and protein freeze-drying technologies. In vitro, ADSC-CM released by the fibers accelerated the migration rate of fibroblasts; inhibited the over proliferation of fibroblasts by inducing apoptosis and damaging cell membrane; in addition, ADSC-CM inhibited the transformation of fibroblasts into myofibroblasts and suppressed excessive production of extracellular matrix (ECM). In vivo, the application of CM-biomaterials significantly accelerated wound closure and improved regeneration outcome, showing superior pro-regenerative performance. This study pioneered the application of CM-biomaterials in regenerative medicine, and confirmed the practicability and significant biological effects of this innovative biomaterials.

Surgery is the final choice for most patients with intervertebral disc degeneration (IDD). Operation-caused trauma will cause inflammation in the intervertebral disc. Serious inflammation will cause tissue defects and induce tissue degeneration, IDD recurrence and the occurrence of other diseases. Therefore, we proposed a scheme to treat recurrence after discectomy by inhibiting inflammation with an aspirin (ASP)-loaded hydrogel to restore the mechanical stability of the spine and relieve local inflammation. ASP-liposomes (ASP-Lips) were incorporated into a photocrosslinkable gelatin-methacryloyl (GelMA) via mixing. This material can effectively alleviate inflammation by inhibiting the release of high mobility group box 1 (HMGB1) from the nucleus to the cytoplasm. We further assessed the expression of inflammatory cytokines, such as interleukin 6 (IL-6) and tumor necrosis factor-α (TNF-α), and degeneration-related factors, such as type II collagen (COL-2), Aggrecan, matrix metallopeptidases-3 (MMP-3), MMP-13, a disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS-4) and ADAMTS-5 in rat nucleus pulpous cells. The level of IDD was analyzed through H&E, safranin-O staining and immunohistochemistry in rabbit samples. In vitro, we found that ASP-Lip@GelMA treatment significantly decreased inflammatory cytokines, MMP-3 and -13, and ADAMTS-4 and -5 and up-regulated COL-2 and Aggrecan via the inhibited release of HMGB-1 from the nucleus. In vivo,ASP-Lip@GelMA can effectively inhibit inflammation of local tissue after disc surgery and fill local tissue defects. This composite hydrogel system is a promising way to treat the recurrence of IDD after surgery without persistent complications.

Since their discovery, Black Phosphorus (BP)-based nanomaterials have received extensive attentions in the fields of electromechanics, optics and biomedicine, due to their remarkable properties and excellent biocompatibility. The most essential feature of BP is that it is composed of a single phosphorus element, which has a high degree of homology with the inorganic components of natural bone, therefore it has a full advantage in the treatment of bone defects. This review will first introduce the source, physicochemical properties, and degradation products of BP, then introduce the remodeling process of bone, and comprehensively summarize the progress of BP-based materials for bone therapy in the form of hydrogels, polymer membranes, microspheres, and three-dimensional (3D) printed scaffolds. Finally, we discuss the challenges and prospects of BP-based implant materials in bone immune regulation and outlook the future clinical application.

Recently, there has been an increasing interest for utilizing the host immune system to fight against cancer. Moreover, cancer vaccines, which can stimulate the host immune system to respond to cancer in the long term, are being investigated as a promising approach to induce tumor-specific immunity. In this work, we prepared an effective cancer vaccine (denoted as “vacosome”) by reconstructing the cancer cell membrane, monophosphoryl lipid A as a toll-like receptor 4 agonist, and egg phosphatidylcholine. The vacosome triggered and enhanced bone marrow dendritic cell maturation as well as stimulated the antitumor response against breast cancer 4T1 cells in vitro. Furthermore, an immune memory was established in BALB/c mice after three-time preimmunization with the vacosome. After that, the immunized mice showed inhibited tumor growth and prolonged survival period (longer than 50 days). Overall, our results demonstrate that the vacosome can be a potential candidate for clinical translation as a cancer vaccine.

Photothermal therapy (PTT) and photodynamic therapy (PDT) have emerged as highly prospective therapeutic modalities in cancer therapy. Notwithstanding, a critical challenge still remains in the exploration of an effective strategy to maximize the synergistic efficacy of PTT and PDT due to low photoconversion efficiency. Herein, inspired by the phospholipid bimolecular structure of the cell membrane, bionic cell membrane polymeric vesicles with photothermal/photodynamic synergy for prostate cancer therapy at one wavelength’s excitation are constructed in one step by the coordination of hexadecyl trimethyl ammonium bromide (CTAB) from the surface of hydrophobic gold nanorods (AuNRs) with indocyanine green (ICG) and polycaprolactone (PCL), achieving their self-assembly in aqueous solutions. Importantly, the aggregation of the assembly improves the stability of the vesicles, realizing the synergistic effect of PTT and PDT for prostate cancer therapy. After being assembled within polymeric vesicles, bifunctional photosensitizer ICG can generate reactive oxygen species (ROS) and photothermal effect under light treatment. Their ROS not only induce PDT efficacy but also destroy the integrity of the lysosomal membrane, promoting the translocation of ICG and another photosensitizer called gold nanorods (AuNRs) into the cytosol. Moreover, their photothermal effects produced by both photosensitizers are able to engender greater damage to the tumor cells because of the close distance with organelles. This structure manifests good cellular uptake, highly effective tumor accumulation, high photothermal conversion efficiency, and excellent properties of enhanced photobleaching resistance, which are beneficial to ICG-based fluorescence tumor imaging. Using the same near-infrared (NIR) wavelength for excitation, the AuNR/ICG vesicles can reduce the side effect rate of photodamage on the skin. In addition, by generating reactive oxygen species (ROS) and double photothermal effect, the vesicles under NIR excitation can promote the apoptosis of PC3 tumor cells. Taken together, the spontaneous self-assembled AuNR/ICG vesicles exhibit huge potential in advanced-stage prostate cancer therapy, especially for the prostate-specific membrane antigen (PSMA)-negative castration-resistant subtype.

Inspired by the superlubricated surface (SLS) of ice, which consists of an ultrathin and contiguous layer of surface-bound water, we built a SLS on the polycaprolactone (PCL)/poly(2-methacryloxyethylphosphorylcholine) (PMPC) composite nanofibrous membrane via electrospinning under controlled relative humidity (RH). The zwitterionic PMPC on the nanofiber provided a surface layer of bound water, thus generating a hydration lubrication surface. Prepared under 20% RH, electrospun PCL/PMPC nanofibers reached a minimum coefficient of friction (COF) of about 0.12 when the weight ratio of PMPC to PCL was 0.1. At a higher RH, a SLS with an ultralow COF of less than 0.05 was formed on the composite nanofibers. The high stability of the SLS hydration layer on the engineered nanofibrous membrane effectively inhibited fibroblast adhesion and markedly reduced tissue adhesion during tendon repair in vivo. This work demonstrates the great potential of this ice-inspired SLS approach in tissue adhesion–prevention applications.

ABSTRACTIntroductionThe treatment performances of current surgical therapeutic materials for injuries caused by high-energy trauma, such as prolonged bone defects, nerve-fiber disruptions, and repeated spasms or adhesions of vascular tendons after repair, are poor. Drug-loaded electrospun fibers have become a novel polymeric material for treating orthopedic diseases owing to their three-dimensional structures, thus providing excellent controlled drug-release responses and high affinity with local tissues. Herein, we reviewed the morphology of electrospun nanofibers, methods for loading drugs on the fibers, and modification methods to improve drug permeability and bioavailability. We highlight innovative applications of drug-loaded electrospun fibers in different treatments, including bone and cartilage defects, tendon and soft-tissue adhesion, vascular remodeling, skin grafting, and nervous-system injuries.Areas coveredWith the rapid development of electrospinning technologies and advancement of tissue engineering, drug-loaded electrospun fibers are becoming increasingly important in controlled drug release, wound closure, and tissue regeneration and repair.Expert opinionDrug-loaded electrospun fibers exhibit a broad range of application prospects and great potential in treating orthopedic diseases. Accordingly, a plethora of novel treatments utilizing the different morphological features of electrospun fibers, the distinctive pharmacokinetics, pharmacodynamics characteristics of different drugs, and the diverse onset characteristics of different diseases, is proposed.

Recombinant human bone morphogenetic protein-2 (rhBMP-2) and bioceramic are the widely used bioactive factors in treatment of bone defects, but these easily cause side effects because of uncontrollable local concentration. In this study, rhBMP-2 was grafted on the surface of mesoporous bioglass nanoparticles (MBGNs) with an amide bond and then photo-cross-linked together with methacrylate gelatin (GelMA); in this way, a GelMA/MBGNs-rhBMP-2 hydrogel membrane was fabricated to release rhBMP-2 in a controllable program during the early bone regeneration period and then release calcium and silicon ions to keep promoting osteogenesis instead of rhBMP-2 in a long term. In this way, rhBMP-2 can keep releasing for 4 weeks and then the ions keep releasing after 4 weeks; this process is matched to early and late osteogenesis procedures. In vitro study demonstrated that the early release of rhBMP-2 can effectively promote local cell osteogenic differentiation in a short period, and then, the inorganic ions can promote cell adhesion not only in the early stage but also keep promoting osteogenic differentiation for a long period. Finally, the GelMA/MBGNs-rhBMP-2 hydrogel shows a superior capacity in long-term osteogenesis and promoting bone tissue regeneration in rat calvarial critical size defect. This GelMA/MBGNs-rhBMP-2 hydrogel demonstrated a promising strategy for the controllable and safer use of bioactive factors such as rhBMP-2 in artificial periosteum to accelerate bone repairing.

Adipose tissue-derived stem cell-derived apoptotic bodies (ADSC-ABs) have shown great potential for immunomodulation and regeneration, particularly in diabetic wound therapy. However, their local application has been limited by unclear regulatory mechanisms, rapid clearance, and short tissue retention times.

Bone defects stemming from tumorous growths, traumatic events, and diverse conditions present a profound conundrum in clinical practice and research. While bone has the inherent ability to regenerate, substantial bone anomalies require bone regeneration techniques. Bone organoids represent a new concept in this field, involving the 3D self‐assembly of bone‐associated stem cells guided in vitro with or without extracellular matrix material, resulting in a tissue that mimics the structural, functional, and genetic properties of native bone tissue. Within the scientific panorama, bone organoids ascend to an esteemed status, securing significant experimental endorsement. Through a synthesis of current literature and pioneering studies, this review offers a comprehensive survey of the bone organoid paradigm, delves into the quintessential architecture and ontogeny of bone, and highlights the latest progress in bone organoid fabrication. Further, existing challenges and prospective directions for future research are identified, advocating for interdisciplinary collaboration to fully harness the potential of this burgeoning domain. Conclusively, as bone organoid technology continues to mature, its implications for both clinical and research landscapes are poised to be profound. Bone organoids present a novel paradigm in the field, featuring the 3D self‐assembly of bone‐associated stem cells. This innovative approach prompts a critical examination of current hurdles and charts potential trajectories for future investigations. The imperative of interdisciplinary collaboration to unlock the full potential of the bone organoids domain is emphasized.

Bioelectrical stimulation is a powerful technique used to promote tissue regeneration, but it can be hindered by an “electrical overload” phenomenon in the core region of stimulation. We develop a threaded microneedle electrode system that protects against “electrical overload” by delivering medicinal hydrogel microspheres into the core regions. The threaded needle body is coated with polydopamine and chitosan to enhance the adhesion of microspheres, which are loaded into the threaded grooves, allowing for their stereoscopic release in the core regions. After the electrode is inserted, the microspheres can be delivered three-dimensionally through physical swelling and the shear-thinning effect of chitosan, mitigating the electrical damage. Microspheres are designed to release alkylated vitamin B12 and vitamin E, providing antioxidant and cell protection effects upon in-situactivation, reducing reactive oxygen species (ROS) by 72.8% and cell death by 59.5%. In the model of peripheral nerve injury, the electrode system improves the overall antioxidant capacity by 78.5% and protects the surrounding cells. Additionally, it leads to an improved nerve conduction velocity ratio of 41.9% and sciatic nerve function index of 12.1%, indicating enhanced neuroregeneration. The threaded microneedle electrode system offers a promising approach for nerve repair by inhibiting “electrical overload”, potentially improving outcomes for tissue regeneration.

Stem cell tissue engineering is a potential treatment for osteoarthritis. However, the number of stem cells that can be delivered, loss of stem cells during injection, and migration ability of stem cells limit applications of traditional stem cell tissue engineering. Herein, kartogenin (KGN)‐loaded poly(lactic‐co‐glycolic acid) (PLGA) porous microspheres is first engineered via emulsification, and then anchored with chitosan through the amidation reaction to develop a new porous microsphere (PLGA‐CS@KGN) as a stem cell expansion vector. Following 3D co‐culture of the PLGA‐CS@KGN carrier with mesenchymal stem cells (MSCs), the delivery system is injected into the capsule cavity in situ. In vivo and in vitro experiments show that PLGA‐CS microspheres have a high cell‐carrying capacity up to 1 × 104mm−3and provide effective protection of MSCs to promote their controlled release in the osteoarthritis microenvironment. Simultaneously, KGN loaded inside the microspheres effectively cooperated with PLGA‐CS to induce MSCs to differentiate into chondrocytes. Overall, these findings indicate that PLGA‐CS@KGN microspheres held high cell‐loading ability, adapt to the migration and expansion of cells, and promote MSCs to express markers associated with cartilage repair. Thus, PLGA‐CS@KGN can be used as a potential stem cell carrier for enhancing stem cell therapy in osteoarthritis treatment. A bioadhesive porous microsphere is developed as a cell carrier for accelerating articular cartilage regeneration through the utilization of chitosan‐based cell adhesion. After injection into the joint cavity, the microspheres expedite the release of mesenchymal stem cells (MSCs) in the microenvironment of arthritis inflammation, while using kartogenin to promote the differentiation of MSCs into chondrocytes, thereby accelerating articular cartilage regeneration.

Gene therapy is capable of efficiently regulating the expression of abnormal genes in diseased tissues and expected to be a therapeutic option for refractory diseases. However, unidirectional targeting gene therapy is always desired at the tissue interface. In this study, inspired by the principle that like charges repulse each other, a positively charged micro-nano electrospun fibrous membrane with dual-layer structure was developed by electrospinning technology to achieve unidirectional delivery of siRNA-loaded cationic nanocarriers, thus realizing unidirectional gene therapy at the tendon-paratenon interface. Under the charge repulsion of positively charged layer, more cationic COX-2 siRNA nanocarriers were enriched in peritendinous tissue, which not only improved the bioavailability of the gene drug to prevent the peritendinous adhesion formation, but also avoided adverse effects on the fragile endogenous healing of tendon itself. In summary, this study provides an innovative strategy for unidirectional targeting gene therapy of tissue interface diseases by utilizing charge repulsion to facilitate unidirectional delivery of gene drugs.

Tendinopathy is a common disorder that causes local dysfunction and reduces quality of life. Recent research has indicated that alterations in the inflammatory microenvironment play a vital role in the pathogenesis of tendinopathy. Herein, injectable methacrylate gelatin (GelMA) microspheres (GM) were fabricated and loaded with heparin-dopamine conjugate (HDC) and hepatocyte growth factor (HGF). GM@HDC@HGF were designed to balance the inflammatory microenvironment by inhibiting oxidative stress and inflammation, thereby regulating extracellular matrix (ECM) metabolism and halting tendon degeneration. Combining growth factors with heparin was expected to improve the encapsulation rate and maintain the long-term efficacy of HGF. In addition, the catechol groups on dopamine have adhesion and antioxidant properties, allowing potential attachment at the injured site, and better function synergized with HGF. GM@HDC@HGF injected in situin rat Achilles tendinopathy (AT) models significantly down-regulated oxidative stress and inflammation, and ameliorated ECM degradation. In conclusion, the multifunctional platform developed presents a promising alternative for the treatment of tendinopathy.

Under pathological conditions, the joint is not well lubricated, which inevitably leads to osteoarthritis. Currently, in clinics injection of hyaluronic acid (HA) as an intra-articular viscosupplement is one of the main methods for alleviation of osteoarthritis. However, the viscosity of HA reduces dramatically under high shear rate due to the shear-thinning effect. Therefore, it is crucial to enhance the lubrication property of HA in order to treat osteoarthritis effectively. In this study, we successfully grafted 2-methacryloyloxyethyl phosphorylcholine (MPC), which is a zwitterionic biomaterial with excellent hydration lubrication, onto the HA with two different molecular weights (HAMPC) to enhance lubrication. The lubrication test performed using an atomic force microscope showed that, compared with HA, the friction coefficient of HAMPC was greatly reduced under various conditions. The in vitrotest demonstrated that HAMPC was biocompatible and could upregulate cartilage anabolic genes while simultaneously downregulating cartilage catabolic proteases and pain-related genes. Importantly, high molecular weight HAMPC exhibited improved the capability to regulate these genes compared with low molecular weight HAMPC. In conclusion, the high molecular weight HAMPC developed herein, with enhanced lubrication and anti-inflammation, may be a promising polymer for the treatment of osteoarthritis.

Significance:Spinal cord injury (SCI) is a neurological disorder that resulted from destroyed long axis of spinal cord, affecting thousands of people every year. With the occurrence of SCI, the lesions can form cystic cavities and produce glial scar, myelin inhibitor, and inflammation that negatively impact repair of spinal cord. Therefore, SCI remains a difficult problem to overcome with present therapeutics. This review of cell therapeutics in SCI provides a systematic review of combinatory therapeutics of SCI and helps the realization of regeneration of spinal cord in the future.Recent Advances:With major breakthroughs in neurobiology in recent years, present therapeutic strategies for SCI mainly aim at nerve regeneration or neuroprotection. For nerve regeneration, the application approaches are tissue engineering and cell transplantation, while drug therapeutics is applied for neuroprotection. Cell therapeutics is a new approach that treats SCI by cell transplantation. Cell therapeutics possesses advantages of neuroprotection, immune regulation, axonal regeneration, neuron relay formation, and remyelination.Critical Issues:Neurons cannot regenerate at the site of injury. Therefore, it is essential to find a repair strategy for remyelination, axon regeneration, and functional recovery. Cell therapeutics is emerging as the most promising approach for treating SCI.Future Directions:The future application of SCI therapy in clinical practice may require a combination of multiple strategies. A comprehensive treatment of injury of spinal cord is the focus of the present research. With the combination of different cell therapy strategies, future experiments will achieve more dramatic success in spinal cord repair.

Electrospun fibers are excellent drug carriers and tissue engineering scaffolds. However, approaches to promote drug permeation in tissues with such carriers remain of great interest. Here, we propose a Quality-by-Design strategy to enhance drug permeation with self-nanoemulsifying electrospun fibers. Owing to the nanoemulsion which formed spontaneously when the polymer contacts aqueous solution such as body fluid, the resulting drug-laden fibrous membrane exhibits an outstanding drug permeation and therapeutic enhancement effect in a Franz cell experiment with ex vivo abdomen skin of rats, an artificial connective tissue model, and an in vivo rheumatoid arthritis model in rats. Meanwhile, the material also shows the capacity of rational regulation on the rate of drug release. These features of the present strategy establish our material as a new efficient approach for various clinical conditions calling for cure.