Gas station in blood vessels: An endothelium mimicking, self-sustainable nitric oxide fueling stent coating for prevention of thrombosis and restenosis.

Stenting is the primary treatment for vascular obstruction-related cardiovascular diseases, but it inevitably causes endothelial injury which may lead to severe thrombosis and restenosis. Maintaining nitric oxide (NO, a vasoactive mediator) production and grafting endothelial glycocalyx such as heparin (Hep) onto the surface of cardiovascular stents could effectively reconstruct the damaged endothelium. However, insufficient endogenous NO donors may impede NO catalytic generation and fail to sustain cardiovascular homeostasis. Here, a dopamine-copper (DA-Cu) network-based coating armed with NO precursor L-arginine (Arg) and Hep (DA-Cu-Arg-Hep) is prepared using an organic solvent-free dipping technique to form a nanometer-thin coating onto the cardiovascular stents. The DA-Cu network adheres tightly to the surface of stents and confers excellent NO catalytic activity in the presence of endogenous NO donors. The immobilized Arg functions as a NO fuel to generate NO via endothelial nitric oxide synthase (eNOS), while Hep works as eNOS booster to increase the level of eNOS to decompose Arg into NO, ensuring a sufficient supply of NO even when endogenous donors are insufficient. The synergistic interaction between Cu and Arg is analogous to a gas station to fuel NO production to compensate for the insufficient endogenous NO donor in vivo. Consequently, it promotes the reconstruction of natural endothelium, inhibits smooth muscle cell (SMC) migration, and suppresses cascading platelet adhesion, preventing stent thrombosis and restenosis. We anticipate that our DA-Cu-Arg-Hep coating will improve the quality of life of cardiovascular patients through improved surgical follow-up, increased safety, and decreased medication, as well as revitalize the stenting industry through durable designs.

Premetastatic Niche Mimicking Bone-On-A-Chip: A Microfluidic Platform to Study Bone Metastasis in Cancer Patients.

Primary cancer modulates the bone microenvironment to sow the seeds of dormancy and metastasis in tumor cells, leading to multiple organ metastasis and death. In this study, 3D printing and bone-on-a-chip (BOC) are combined to develop a BOC platform that mimics the pre-metastatic niches (PMNs) and facilitates elucidation of the interactions between bone-resident cells and metastatic tumor cells under the influence of primary cancer. Photocrosslinkable gelatin methacrylate (GelMA) is used as a 3D culturing hydrogel to encapsulate cells, and circulate tumor culture medium (CM) adjacent to the hydrogel to verify the critical role of mesenchymal stem cells (MSCs) and osteoclasts (RAW264.7s). Three niches: the dormancy niche, the perivascular niche, and the "vicious cycle" niche, are devised to recapitulate bone metastasis in one chip with high cell viability and excellent nutrient exchange. With respect to tumor dormancy and reactivation, the invadopodia formation of A549 lung cancer cells in communication with MSCs and RAW264.7 via the cortactin pathway is researched. As a proof of concept, the functionality and practicality of the platform are demonstrated by analyzing the invadopodia formation and the influence of various cells, and the establishment of the dynamic niches paves the way to understanding PMN formation and related drug discovery.

Going below and beyond the surface: Microneedle structure, materials, drugs, fabrication, and applications for wound healing and tissue regeneration.

Microneedle, as a novel drug delivery system, has attracted widespread attention due to its non-invasiveness, painless and simple administration, controllable drug delivery, and diverse cargo loading capacity. Although microneedles are initially designed to penetrate stratum corneum of skin for transdermal drug delivery, they, recently, have been used to promote wound healing and regeneration of diverse tissues and organs and the results are promising. Despite there are reviews about microneedles, few of them focus on wound healing and tissue regeneration. Here, we review the recent advances of microneedles in this field. We first give an overview of microneedle system in terms of its potential cargos (e.g., small molecules, macromolecules, nucleic acids, nanoparticles, extracellular vesicle, cells), structural designs (e.g., multidrug structures, adhesive structures), material selection, and drug release mechanisms. Then we briefly summarize different microneedle fabrication methods, including their advantages and limitations. We finally summarize the recent progress of microneedle-assisted wound healing and tissue regeneration (e.g., skin, cardiac, bone, tendon, ocular, vascular, oral, hair, spinal cord, and uterine tissues). We expect that our article would serve as a guideline for readers to design their microneedle systems according to different applications, including material selection, drug selection, and structure design, for achieving better healing and regeneration efficacy.

Artificial cilia for soft and stable surface covalent immobilization of bone morphogenetic protein-2.

Preservation of growth factor sensitivity and bioactivity (e.g., bone morphogenetic protein-2 (BMP-2)) post-immobilization to tissue engineering scaffolds remains a great challenge. Here, we develop a stable and soft surface modification strategy to address this issue. BMP-2 (a model growth factor) is covalently immobilized onto homogeneous poly (glycidyl methacrylate) (PGMA) polymer brushes which are grafted onto substrate surfaces (Au, quartz glass, silica wafer, or common biomaterials) via surface-initiated atom transfer radical polymerization. This surface modification method multiplies the functionalized interfacial area; it is simple, fast, gentle, and has little effect on the loaded protein owing to the cilia motility. The immobilized BMP-2 (i-BMP-2) on the surface of homogeneous PGMA polymer brushes exhibits excellent bioactivity (⁓87% bioactivity of free BMP-2 in vitro and 20%-50% higher than scaffolds with free BMP-2 in vivo), with conformation and secondary structure well-preserved after covalent immobilization and ethanol sterilization. Moreover, the osteogenic activity of i-BMP-2 on the nanoline pattern (PGMA-poly (N-isopropylacrylamide)) shows ⁓110% bioactivity of free BMP-2. This is superior compared to conventional protein covalent immobilization strategies in terms of both bioactivity preservation and therapeutic efficacy. PGMA polymer brushes can be used to modify surfaces of different tissue-engineered scaffolds, which facilitates in situ immobilization of growth factors, and accelerates repair of a wide range of tissue types.

Gaussian curvature-driven direction of cell fate toward osteogenesis with triply periodic minimal surface scaffolds.

Leaf photosynthesis, coral mineralization, and trabecular bone growth depend on triply periodic minimal surfaces (TPMSs) with hyperboloidal structure on every surface point with varying Gaussian curvatures. However, translation of this structure into tissue-engineered bone grafts is challenging. This article reports the design and fabrication of high-resolution three-dimensional TPMS scaffolds embodying biomimicking hyperboloidal topography with different Gaussian curvatures, composed of body inherent ß-tricalcium phosphate, by stereolithography-based three-dimensional printing and sintering. The TPMS bone scaffolds show high porosity and interconnectivity. Notably, compared with conventional scaffolds, they can reduce stress concentration, leading to increased mechanical strength. They are also found to support the attachment, proliferation, osteogenic differentiation, and angiogenic paracrine function of human mesenchymal stem cells (hMSCs). Through transcriptomic analysis, we theorize that the hyperboloid structure induces cytoskeleton reorganization of hMSCs, expressing elongated morphology on the convex direction and strengthening the cytoskeletal contraction. The clinical therapeutic efficacy of the TPMS scaffolds assessed by rabbit femur defect and mouse subcutaneous implantation models demonstrate that the TPMS scaffolds augment new bone formation and neovascularization. In comparison with conventional scaffolds, our TPMS scaffolds successfully guide the cell fate toward osteogenesis through cell-level directional curvatures and demonstrate drastic yet quantifiable improvements in bone regeneration.

Biomimicking design of artificial periosteum for promoting bone healing.

Background: Periosteum is a vascularized tissue membrane covering the bone surface and plays a decisive role in bone reconstruction process after fracture. Various artificial periosteum has been developed to assist the allografts or bionic bone scaffolds in accelerating bone healing. Recently, the biomimicking design of artificial periosteum has attracted increasing attention due to the recapitulation of the natural extracellular microenvironment of the periosteum and has presented unique capacity to modulate the cell fates and ultimately enhance the bone formation and improve neovascularization. Methods: A systematic literature search is performed and relevant findings in biomimicking design of artificial periosteum have been reviewed and cited. Results: We give a systematical overview of current development of biomimicking design of artificial periosteum. We first summarize the universal strategies for designing biomimicking artificial periosteum including biochemical biomimicry and biophysical biomimicry aspects. We then discuss three types of novel versatile biomimicking artificial periosteum including physical-chemical combined artificial periosteum, heterogeneous structured biomimicking periosteum, and healing phase-targeting biomimicking periosteum. Finally, we comment on the potential implications and prospects in the future design of biomimicking artificial periosteum. Conclusion: This review summarizes the preparation strategies of biomimicking artificial periosteum in recent years with a discussion of material selection, animal model adoption, biophysical and biochemical cues to regulate the cell fates as well as three types of latest developed versatile biomimicking artificial periosteum. In future, integration of innervation, osteochondral regeneration, and osteoimmunomodulation, should be taken into consideration when fabricating multifunctional artificial periosteum.The Translational Potential of this Article: This study provides a holistic view on the design strategy and the therapeutic potential of biomimicking artificial periosteum to promote bone healing. It is hoped to open a new avenue of artificial periosteum design with biomimicking considerations and reposition of the current strategy for accelerated bone healing.

Scale-out production of extracellular vesicles derived from natural killer cells via mechanical stimulation in a seesaw-motion bioreactor for cancer therapy.

Extracellular vesicles (EVs) derived from immune cells have shown great anti-cancer therapeutic potential. However, inefficiency in EV generation has considerably impeded the development of EV-based basic research and clinical translation. Here, we developed a seesaw-motion bioreactor (SMB) system by leveraging mechanical stimuli such as shear stress and turbulence for generating EVs with high quality and quantity from natural killer (NK) cells. Compared to EV production in traditional static culture (229 ± 74 particles per cell per day), SMB produced NK-92MI-derived EVs at a higher rate of 438 ± 50 particles per cell per day and yielded a total number of 2 × 1011EVs over two weeks via continuous dynamic fluidic culture. In addition, the EVs generated from NK-92MI cells in SMB shared a similar morphology, size distribution, and protein profile to EVs generated from traditional static culture. Most importantly, the NK-92MI-derived EVs in SMB were functionally active in killing melanoma and liver cancer cells in both 2D and 3D culture conditionsin vitro, as well as in suppressing melanoma growthin vivo. We believe that SMB is an attractive approach to producing EVs with high quality and quantity; it can additionally enhance EV production from NK92-MI cells and promote both the basic and translational research of EVs.

Shedding light on 3D printing: Printing photo-crosslinkable constructs for tissue engineering.

3D printing has emerged as a pivotal fabrication technique for preparing scaffolds for engineering tissues and tissue models. Among different 3D printing platforms, photo-crosslinking-based 3D printing techniques like digital light processing and stereolithography have become most popular as they enable the construction of complex architecture with improved spatial resolution, reliable pattern fidelity, and high printing speed. In addition, by selecting appropriate ink combinations or modulating the photo-crosslinking printing parameters (e.g., the types or concentrations of photoinitiators and crosslinkers, light exposure time or intensity, as well as the 3D printing techniques used), the structures and properties (e.g., swelling and mechanical properties) of the resultant printed scaffolds can be finely tailored to meet the practical application requirements. Here, recent advances on the promising development of photo-crosslinkable materials for 3D printing with a focus on their biomedical applications for repairing damaged organs and developing in vitro tissue models are reviewed. Firstly, an overview of commonly used photo-crosslinkable materials, as well as insights on how the printing outcomes of these materials can be improved are provided. Then, the diverse regulation strategies of the photo-polymerization process and the 3D printing parameters to improve the performances of the printed structures are summarized. The existing challenges and future directions are finally discussed from the technical and application perspectives of photo-crosslinking-based 3D printing.

Electrosprayed Regeneration-Enhancer-Element Microspheres Power Osteogenesis and Angiogenesis Coupling.

Electrosprayed microspheres for bone regeneration are conventionally restricted by the lack of osteogenic modulation for both encapsulated stem cells and surrounding cells at the defect site. Here, sodium alginate microspheres encapsulating L-arginine doped hydroxyapatite nanoparticles (Arg/HA NPs) and bone mesenchymal stem cells (BMSCs) as regeneration-enhancer-element reservoirs (Arg/HA-SA@BMSC) for bone healing are electrosprayed. The Arg/HA NPs serve as a container of L-arginine and Ca2+ and the BMSCs inside the microspheres metabolize the released L-arginine into bioactive gas nitric oxide (NO) in the presence of Ca2+ to activate the nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) signaling pathway. Meanwhile, the generated NO diffuses out of the microspheres together with the Ca2+ and L-arginine as exterior enhancers to promote the osteogenesis-angiogenesis coupling of surrounding BMSCs and endothelial cells (ECs) at the bone defect site, generating an internal/external modulation loop between the encapsulated cells and surrounding native cells. It is demonstrated that such regeneration-enhancer-element reservoirs could effectively increase the bone tissue formation and neovasculature using rat calvarial defect models. It is envisioned that the microsphere system could streamline vascularized bone regeneration therapy as a high throughput, minimally invasive yet highly effective strategy to accelerate bone healing.

3D Bioprinting Photo-Crosslinkable Hydrogels for Bone and Cartilage Repair.

Three-dimensional (3D) bioprinting has become a promising strategy for bone manufacturing, with excellent control over geometry and microarchitectures of the scaffolds. The bioprinting ink for bone and cartilage engineering has thus become the key to developing 3D constructs for bone and cartilage defect repair. Maintaining the balance of cellular viability, drugs or cytokines' function, and mechanical integrity is critical for constructing 3D bone and/or cartilage scaffolds. Photo-crosslinkable hydrogel is one of the most promising materials in tissue engineering; it can respond to light and induce structural or morphological transition. The biocompatibility, easy fabrication, as well as controllable mechanical and degradation properties of photo-crosslinkable hydrogel can meet various requirements of the bone and cartilage scaffolds, which enable it to serve as an effective bio-ink for 3D bioprinting. Here, in this review, we first introduce commonly used photo-crosslinkable hydrogel materials and additives (such as nanomaterials, functional cells, and drugs/cytokine), and then discuss the applications of the 3D bioprinted photo-crosslinkable hydrogel scaffolds for bone and cartilage engineering. Finally, we conclude the review with future perspectives about the development of 3D bioprinting photo-crosslinkable hydrogels in bone and cartilage engineering.

Bone-a-Petite: Engineering Exosomes towards Bone, Osteochondral, and Cartilage Repair.

Recovery from bone, osteochondral, and cartilage injuries/diseases has been burdensome owing to the damaged vasculature of large defects and/or avascular nature of cartilage leading to a lack of nutrients and supplying cells. However, traditional means of treatment such as microfractures and cell-based therapy only display limited efficacy due to the inability to ensure cell survival and potential aggravation of surrounding tissues. Exosomes have recently emerged as a powerful tool for this tissue repair with its complex content of transcription factors, proteins, and targeting ligands, as well as its unique ability to home in on target cells thanks to its phospholipidic nature. They are engineered to serve specialized applications including enhancing repair, anti-inflammation, regulating homeostasis, etc. via means of physical, chemical, and biological modulations in its deriving cell culture environments. This review focuses on the engineering means to functionalize exosomes for bone, osteochondral, and cartilage regeneration, with an emphasis on conditions such as osteoarthritis, osteoporosis, and osteonecrosis. Finally, future implications for exosome development will be given alongside its potential combination with other strategies to improve its therapeutic efficacy in the osteochondral niche.

Biomimetic, Stiff, and Adhesive Periosteum with Osteogenic-Angiogenic Coupling Effect for Bone Regeneration.

Current periosteal grafts have limitations related to low mechanical strength, tissue adhesiveness, and poor osteogenesis and angiogenesis potential. Here, a periosteum mimicking bone aid (PMBA) with similar structure and function to natural periosteum is developed by electrospinning photocrosslinkable methacrylated gelatin (GelMA), l-arginine-based unsaturated poly(ester amide) (Arg-UPEA), and methacrylated hydroxyapatite nanoparticles (nHAMA). Such combination of materials enhances the material mechanical strength, favors the tissue adhesion, and guarantees the sustained activation of nitric oxide-cyclic guanosine monophosphate (NO-cGMP) signaling pathway, with well-coordinated osteogenic-angiogenic coupling effect for accelerated bone regeneration. This work presents a proof-of-concept demonstration of thoroughly considering the progression of implant biomaterials: that is, the initial material components (i.e., GelMA, Arg-UPEA, and nHAMA) equip the scaffold with suitable structure and function, while its degradation products (i.e., Ca2+ and l-arginine) are involved in long-term mediation of physiological activities. It is envisioned that the strategy will inspire the design of high-performance bioscaffolds toward bone and periosteum tissue engineering.

Human-on-Leaf-Chip: A Biomimetic Vascular System Integrated with Chamber-Specific Organs.

The vascular network is a central component of the organ-on-a-chip system to build a 3D physiological microenvironment with controlled physical and biochemical variables. Inspired by ubiquitous biological systems such as leaf venation and circulatory systems, a fabrication strategy is devised to develop a biomimetic vascular system integrated with freely designed chambers, which function as niches for chamber-specific vascularized organs. As a proof of concept, a human-on-leaf-chip system with biomimetic multiscale vasculature systems connecting the self-assembled 3D vasculatures in chambers is fabricated, mimicking the in vivo complex architectures of the human cardiovascular system connecting vascularized organs. Besides, two types of vascularized organs are built independently within the two halves of the system to verify its feasibility for conducting comparative experiments for organ-specific metastasis studies in a single chip. Successful culturing of human hepatoma G2 cells (HepG2s) and mesenchymal stem cells (MSCs) with human umbilical vein endothelial cells (HUVECs) shows good vasculature formation, and organ-specific metastasis is simulated through perfusion of pancreatic cancer cells and shows distinct cancer encapsulation by MSCs, which is absent in HepG2s. Given good culture efficacy, study design flexibility, and ease of modification, these results show that the bioinspired human-on-leaf-chip possesses great potential in comparative and metastasis studies while retaining organ-to-organ crosstalk.

Generation of Cost-Effective Paper-Based Tissue Models through Matrix-Assisted Sacrificial 3D Printing.

Due to the combined advantages of cellulose and nanoscale (diameter 20-60 nm), bacterial cellulose possesses a series of attractive features including its natural origin, moderate biosynthesis process, good biocompatibility, and cost-effectiveness. Moreover, bacterial cellulose nanofibers can be conveniently processed into three-dimensional (3D) intertwined structures and form stable paper devices after simple drying. These advantages make it suitable as the material for construction of organ-on-a-chip devices using matrix-assisted sacrificial 3D printing. We successfully fabricated various microchannel structures embedded in the bulk bacterial cellulose hydrogels and retained their integrity after the drying process. Interestingly, these paper-based devices containing hollow microchannels could be rehydrated and populated with relevant cells to form vascularized tissue models. As a proof-of-concept demonstration, we seeded human umbilical vein endothelial cells (HUVECs) into the microchannels to obtain the vasculature and inoculated the MCF-7 cells onto the surrounding matrix of the paper device to build a 3D paper-based vascularized breast tumor model. The results showed that the microchannels were perfusable, and both HUVECs and MCF-7 cells exhibited favorable proliferation behaviors. This study may provide a new strategy for constructing simple and low-cost in vitro tissue models, which may find potential applications in drug screening and personalized medicine.

Graphene-Based Nanocomposites for Neural Tissue Engineering.

Graphene has made significant contributions to neural tissue engineering due to its electrical conductivity, biocompatibility, mechanical strength, and high surface area. However, it demonstrates a lack of biological and chemical cues. Also, it may cause potential damage to the host body, limiting its achievement of efficient construction of neural tissues. Recently, there has been an increasing number of studies showing that combining graphene with other materials to form nano-composites can provide exceptional platforms for both stimulating neural stem cell adhesion, proliferation, differentiation and neural regeneration. This suggests that graphene nanocomposites are greatly beneficial in neural regenerative medicine. In this mini review, we will discuss the application of graphene nanocomposites in neural tissue engineering and their limitations, through their effect on neural stem cell differentiation and constructs for neural regeneration.

Polymer-Brush-Grafted Mesoporous Silica Nanoparticles for Triggered Drug Delivery.

Mesoporous silica nanoparticles (MSNs) have been demonstrated to be one of the most promising drug-delivery systems (DDSs) to transport a variety of drugs/biomolecules. Functionalization of MSN surfaces with responsive polymer brushes leads to intelligent and controllable drug-delivery properties, that is, the encapsulated drugs/biomolecules will only be released upon certain stimuli including pH, temperature, light, enzyme, ultrasound, or redox, thus maximizing their therapeutic efficiency and minimizing side effects. These polymer brushes can also increase the stability and extend the release period of the loaded cargoes. This Minireview presents an overview of recent research progress on stimuli-responsive controlled DDSs based on polymer-brush-grafted MSNs. Utilizing the switching abilities of the grafted responsive polymer brushes, the smart DDSs show great potential for biomedical applications, especially for cancer therapy.