Direct 3D Printing of High Strength Biohybrid Gradient Hydrogel Scaffolds for Efficient Repair of Osteochondral Defect

The emerging 3D printing technique allows for tailoring hydrogel‐based soft structure tissue scaffolds for individualized therapy of osteochondral defects. However, the weak mechanical strength and uncontrollable swelling intrinsic to conventional hydrogels restrain their use as bioinks. Here, a high‐strength thermoresponsive supramolecular copolymer hydrogel is synthesized by one‐step copolymerization of dual hydrogen bonding monomers, N‐acryloyl glycinamide, and N‐[tris(hydroxymethyl)methyl] acrylamide. The obtained copolymer hydrogels demonstrate excellent mechanical properties—robust tensile strength (up to 0.41 MPa), large stretchability (up to 860%), and high compressive strength (up to 8.4 MPa). The rapid thermoreversible gel ? sol transition behavior makes this copolymer hydrogel suitable for direct 3D printing. Successful preparation of 3D‐printed biohybrid gradient hydrogel scaffolds is demonstrated with controllable 3D architecture, owing to shear thinning property which allows continuous extrusion through a needle and also immediate gelation of fluid upon deposition on the cooled substrate. Furthermore, this biohybrid gradient hydrogel scaffold printed with transforming growth factor beta 1 and β‐tricalciumphosphate on distinct layers facilitates the attachment, spreading, and chondrogenic and osteogenic differentiation of human bone marrow stem cells (hBMSCs) in vitro. The in vivo experiments reveal that the 3D‐printed biohybrid gradient hydrogel scaffolds significantly accelerate simultaneous regeneration of cartilage and subchondral bone in a rat model.     

A Bifunctional Biomaterial with Photothermal Effect for Tumor Therapy and Bone Regeneration

Malignant bone tumor is one of the major bone diseases. The treatment of such a bone disease typically requires the removal of bone tumor and regeneration of tumor‐initiated bone defects simultaneously. To address this issue, it is required that implanted biomaterials should combine the bifunctions of both therapy and regeneration. In this work, a bifunctional graphene oxide (GO)‐modified β‐tricalcium phosphate (GO‐TCP) composite scaffold combining a high photothermal effect with significantly improved bone‐forming ability is prepared by 3D‐printing and surface‐modification strategies. The prepared GO‐TCP scaffolds exhibit excellent photothermal effects under the irradiation of 808 nm near infrared laser (NIR) even at an ultralow power density of 0.36 W cm^?2, while no photothermal effects are observed for pure β‐TCP scaffolds. The photothermal temperature of GO‐TCP scaffolds can be effectively modulated in the range of 40–90 °C by controlling the used GO concentrations, surface‐modification times, and power densities of NIR. The distinct photothermal effect of GO‐TCP scaffolds induces more than 90% of cell death for osteosarcoma cells (MG‐63) in vitro, and further effectively inhibits tumor growth in mice. Meanwhile, the prepared GO‐TCP scaffolds possess the improved capability to stimulate the osteogenic differentiation of rabbit bone mesenchymal stem cells (rBMSCs) by upregulating bone‐related gene expression, and significantly promote new bone formation in the bone defects of rabbits as compared to pure β‐TCP scaffolds. These results successfully demonstrate that the prepared GO‐TCP scaffolds have bifunctional properties of photothermal therapy and bone regeneration, which is believed to pave the way to design and fabricate novel implanting biomaterials in combination of therapy and regeneration functions.     

Biomimetic Elastomeric Bioactive Siloxane‐Based Hybrid Nanofibrous Scaffolds with miRNA Activation: A Joint Physico‐Chemical‐Biological Strategy for Promoting Bone Regeneration

Rapid and efficient disease‐induced or critical‐size bone regeneration remains a challenge in tissue engineering due to the lack of highly bioactive biomaterial scaffolds. Physical structures such as nanostructures, chemical components such as silicon elements, and biological factors such as genes have shown positive effects on bone regeneration. Herein, a bioactive photoluminescent elastomeric silicate‐based nanofibrous scaffold with sustained miRNA release is reported for promoting bone regeneration based on a joint physico‐chemical‐biological strategy. Bioactive nanofibrous scaffolds are fabricated by cospinning poly (ε‐caprolactone) (PCL), elastomeric poly (citrates‐siloxane) (PCS), and bioactive osteogenic miRNA nanocomplexes (denoted PPM nanofibrous scaffolds). The PPM scaffolds possess uniform nanostructures, significantly enhanced tensile stress (≈15 MPa) and modulus (≈32 MPa), improved hydrophilicity (30–60°), controlled biodegradation, and strong blue fluorescence. Bioactive miRNA complexes are efficiently loaded into the nanofibrous matrix and exhibit long‐term release for up to 70 h. The PPM scaffolds significantly promote the adhesion, proliferation, and osteoblast differentiation of bone marrow stem cells in vitro and enhanced rat cranial defect restoration (12 weeks) in vivo. This work reports an attractive joint physico‐chemical‐biological strategy for the design of novel cell/protein‐free bioactive scaffolds for synergistic tissue regeneration.     

A Bi‐Lineage Conducive Scaffold for Osteochondral Defect Regeneration

Because cartilage and bone tissues have different lineage‐specific biological properties, it is challenging to fabricate a single type of scaffold that can biologically fulfill the requirements for regeneration of these two lineages simultaneously within osteochondral defects. To overcome this challenge, a lithium‐containing mesoporous bioglass (Li‐MBG) scaffold is developed. The efficacy and mechanism of Li‐MBG for regeneration of osteochondral defects are systematically investigated. Histological and micro‐CT results show that Li‐MBG scaffolds significantly enhance the regeneration of subchondral bone and hyaline cartilage‐like tissues as compared to pure MBG scaffolds, upon implantation in rabbit osteochondral defects for 8 and 16 weeks. Further investigation demonstrates that the released Li+ ions from the Li‐MBG scaffolds may play a key role in stimulating the regeneration of osteochondral defects. The corresponding mechanistic pathways involve Li+ ions enhancing the proliferation and osteogenic differentiation of bone mesenchymal stem cells (BMSCs) through activation of the Wnt signalling pathway, as well as Li+ ions protecting chondrocytes and cartilage tissues from the inflammatory osteoarthritis (OA) environment through activation of autophagy. These findings suggest that the incorporation of Li+ ions into bioactive MBG scaffolds is a viable strategy for fabricating bi‐lineage conducive scaffolds that enhance regeneration of osteochondral defects.     

Three Dimensional Graphene Foam/Polymer Hybrid as a High Strength Biocompatible Scaffold

Graphene foam (GrF)/polylactic acid–poly‐ε‐caprolactone copolymer (PLC) hybrid (GrF‐PLC) scaffold is synthesized in order to utilize both the desirable properties of graphene and that of foams such as excellent structural characteristics and a networked 3‐D structure for cells to proliferate in. The hybrid scaffold is synthesized by a dip‐coating method that enables retention of the porous 3D structure. The excellent wettability of PLC with graphene foam along with the formation of PLC bridges leads to a ≈3700% enhancement in strength and a ≈3100% increase in ductility in the GrF‐PLC scaffold. Biocompatibility of both graphene foam and GrF‐PLC scaffold is demonstrated by culturing of human mesenchymal stem cells (hMSCs) for 28 days, a period over which cell proliferation is robust. The hMSCs are differentiated in chondrogenic media and supported chondrogenesis in both scaffolds. The demand for aggrecan extracellular matrix protein synthesis is reduced in hybrids due to improved bearing of cell‐induced loads, this may be critical for ensuring adequate cellular distribution and layering of extracellular matrix. Hence, the unique mechanical and biotolerant properties of the GrF‐PLC scaffold are suited for musculoskeletal tissue engineering applications, such as the growth of de novo cartilage to replace cartilage lost due to injury or osteoarthritis.     

Elastomeric Fibrous Hybrid Scaffold Supports In Vitro and In Vivo Tissue Formation

Biomimetic materials with biomechanical properties resembling those of native tissues while providing an environment for cell growth and tissue formation, are vital for tissue engineering (TE). Mechanical anisotropy is an important property of native cardiovascular tissues and directly influences tissue function. This study reports fabrication of anisotropic cell‐seeded constructs while retaining control over the construct's architecture and distribution of cells. Newly synthesized poly‐4‐hydroxybutyrate (P4HB) is fabricated with a dry spinning technique to create anelastomeric fibrous scaffold that allows control of fiber diameter, porosity, and rate ofdegradation. To allow cell and tissue ingrowth, hybrid scaffolds with mesenchymalstem cells (MSCs) encapsulated in a photocrosslinkable hydrogel were developed. Culturing the cellularized scaffolds in a cyclic stretch/flexure bioreactor resulted in tissue formation and confirmed the scaffold's performance under mechanical stimulation. In vivo experiments showed that the hybrid scaffold is capable of withstanding physiological pressures when implanted as a patch in the pulmonary artery. Aligned tissue formation occurred on the scaffold luminal surface without macroscopic thrombus formation. This combination of a novel, anisotropic fibrous scaffold and a tunable native‐like hydrogel for cellular encapsulation promoted formation of 3D tissue and provides a biologically functional composite scaffold for soft‐tissue engineering applications.     

Microribbon‐Like Elastomers for Fabricating Macroporous and Highly Flexible Scaffolds that Support Cell Proliferation in 3D

Hydrogel‐based scaffolds are widely used for culturing cells in three dimensions due to their tissue‐like water content and tunable biochemical and physical properties. Most conventional hydrogels lack the macroporosity desirable for efficient cell proliferation and migration and have limited flexibility when subject to mechanical load. Here microribbon‐like elastomers that, when photocrosslinked, can form macroporous and highly flexible scaffolds that support cell proliferation in 3D are developed. These microribbons are produced by wet‐spinning gelatin solution into microfibers, followed by drying in acetone, which causes asymmetrical collapse of microfibers to form microribbon‐like structures. Gelatin microribbons are then modified using methacrylate anhydride to allow further photocrosslinking into 3D scaffolds. The macroporosity and mechanical properties of the microribbon‐based scaffold may be tuned by varying wet‐spinning rate, drying temperature, choice of drying agent, level of glutaraldehyde crosslinking, and microribbon density. When encapsulated in the microribbon‐based scaffold, human adipose‐derived stromal cells proliferated up to 30‐fold within 3 weeks. Furthermore, microribbons‐based scaffold demonstrate great flexibility and can sustain up to 90% strain and 3 MPa stress without failing. The unique mechanical properties of microribbon‐based scaffolds make them promising tools for engineering shock‐absorbing tissues such as cartilage and intervertebral discs.     

Cocrystal Strategy toward Multifunctional 3D‐Printing Scaffolds Enables NIR‐Activated Photonic Osteosarcoma Hyperthermia and Enhanced Bone Defect Regeneration

Malignant bone tumors are one of the major serious diseases in clinic. Inferior reconstruction of new bone and rapid propagation of residual tumor cells are the main challenges to surgical intervention. Herein, a bifunctional DTC@BG scaffold for near‐infrared (NIR)‐activated photonic thermal ablation of osteosarcoma and accelerated bone defect regeneration is engineered by in situ growth of NIR‐absorbing cocrystal (DTC) on the surface of a 3D‐printing bioactive glass (BG) scaffold. The prominent photothermal conversion performance and outstanding bone regeneration capability of DTC@BG scaffolds originate from the precise tailoring of the bandgap between the electron donors and acceptors of DTC and promote new bone growth performance of BG scaffolds. DTC@BG scaffolds not only significantly promote tumor cell ablation in vitro, but also effectively facilitate bone tumor suppression in vivo. In particular, DTC@BG scaffolds exhibit excellent capability in stimulating osteogenic differentiation and angiogenesis, and finally promote newborn bone formation in the bone defects. This research represents the first paradigm for ablating osteosarcoma and facilitating new bone formation through precise modulation of electron donors and acceptors in the cocrystal, which offers a new avenue to construct high‐efficiency therapeutic platforms based on cocrystal strategy for ablation of malignant bone tumor.     

Microfluidic 3D Printing Responsive Scaffolds with Biomimetic Enrichment Channels for Bone Regeneration

Tissue-engineered scaffolds have been extensively explored for treating bone defects; however, slow and insufficient vascularization throughout the scaffolds remains a key challenge for further application. Herein, a versatile microfluidic 3D printing strategy to fabricate black phosphorus (BP) incorporated fibrous scaffolds with photothermal responsive channels for improving vascularization and bone regeneration is proposed. The thermal channeled scaffolds display reversible shrinkage and swelling behavior controlled by near-infrared irradiation, which facilitates the penetration of suspended cells into the scaffold channels and promotes the prevascularization. Furthermore, the embedded BP nanosheets exhibit intrinsic properties for in situ biomineralization and improve in vitro cell proliferation and osteogenic differentiation. Following transplantation in vivo, these channels also promote host vessel infiltration deep into the scaffolds and effectively accelerate the healing process of bone defects. Thus, it is believed that these near-infrared responsive channeled scaffolds are promising candidates for tissue/vascular ingrowth in diverse tissue engineering applications.     

Black‐Phosphorus‐Incorporated Hydrogel as a Conductive and Biodegradable Platform for Enhancement of the Neural Differentiation of Mesenchymal Stem Cells

Conductive hydrogel scaffolds have important applications for electroactive tissue repairs. However, the development of conductive hydrogel scaffolds tends to incorporate nonbiodegradable conductive nanomaterials that will remain in the human body as foreign matters. Herein, a biodegradable conductive hybrid hydrogel is demonstrated based on the integration of black phosphorus (BP) nanosheets into the hydrogel matrix. To address the challenge of applying BP nanosheets in tissue engineering due to its intrinsic instability, a polydopamine (PDA) modification method is developed to improve the stability. Moreover, PDA modification also enhances interfacial bonding between pristine BP nanosheets and the hydrogel matrix. The incorporation of polydopamine‐modified black phosphorous (BP@PDA) nanosheets into the gelatin methacryloyl (GelMA) hydrogels significantly enhances the electrical conductivity of the hydrogels and improves the cell migration of mesenchymal stem cells (MSCs) within the 3D scaffolds. On the basis of the gene expression and protein level assessments, the BP@PDA‐incorporated GelMA scaffold can significantly promote the differentiation of MSCs into neural‐like cells under the synergistic electrical stimulation. This strategy of integrating biodegradable conductive BP nanomaterials within a biocompatible hydrogel provides a new insight into the design of biomaterials for broad applications in tissue engineering of electroactive tissues, such as neural, cardiac, and skeletal muscle tissues.     

3D Molecularly Functionalized Cell‐Free Biomimetic Scaffolds for Osteochondral Regeneration

Clinically, cartilage damage is frequently accompanied with subchondral bone injuries caused by disease or trauma. However, the construction of biomimetic scaffolds to support both cartilage and subchondral bone regeneration remains a great challenge. Herein, a novel strategy is adopted to realize the simultaneous repair of osteochondral defects by employing a self‐assembling peptide hydrogel (SAPH) FEFEFKFK (F, phenylalanine; E, glutamic acid; K, lysine) to coat onto 3D‐printed polycaprolactone (PCL) scaffolds. Results show that the SAPH‐coated PCL scaffolds exhibit highly improved hydrophilicity and biomimetic extracellular matrix (ECM) structures compared to PCL scaffolds. In vitro experiments demonstrate that the SAPH‐coated PCL scaffolds promote the proliferation and osteogenic differentiation of rabbit bone mesenchymal stem cells (rBMSCs) and maintain the chondrocyte phenotypes. Furthermore, 3% SAPH‐coated PCL scaffolds significantly induce simultaneous regeneration of cartilage and subchondral bone after 8‐ and 12‐week implantation in vivo, respectively. Mechanistically, by virtue of the enhanced deposition of ECM in SAPH‐coated PCL scaffolds, SAPH with increased stiffness facilitates and remodels the microenvironment around osteochondral defects, which may favor simultaneous dual tissue regeneration. These findings indicate that the 3% SAPH provides efficient and reliable modification on PCL scaffolds and SAPH‐coated PCL scaffolds appear to be a promising biomaterial for osteochondral defect repair.     

3D Superelastic Scaffolds Constructed from Flexible Inorganic Nanofibers with Self‐Fitting Capability and Tailorable Gradient for Bone Regeneration

Repair of bone defects with irregular shapes or at soft tissue insertion sites faces a huge challenge. Scaffolds capable of adapting to bone cavities, generating stiffness gradients, and inducing osteogenesis are necessary. Herein, a superelastic 3D ceramic fibrous scaffold is developed by assembly of intrinsically rigid, structurally flexible electrospun SiO₂ nanofibers with chitosan as bonding sites (SiO₂ NF‐CS) via a lyophilization technique. SiO₂ NF‐CS scaffolds exhibit excellent elasticity (full recovery from 80% compression), fast recovery rate (>500 mm min^?1), and good fatigue resistance (>10 000 cycles of compression) in an aqueous medium. SiO₂ NF‐CS scaffolds induce human mesenchymal stem cell (hMSC) elongation and differentiation into osteoblasts. In vivo self‐fitting capability is demonstrated by implanting compressed SiO₂ NF‐CS scaffolds into different shaped mandibular defects in rabbits, with a spontaneous recovery and full filling of defects. Rat calvarial defect repair validates enhanced bone formation and vascularization by cell (hMSC) histomorphology analysis. Further, subchondral bone scaffolds with gradations in SiO₂ nanofibers are developed, leading to a stiffness gradient and spatially chondrogenic and osteogenic differentiation of hMSCs. This work presents a type of 3D ceramic fibrous scaffold, which can closely match bone defects with irregular shapes or at different implant sites, and is promising for clinical translation.     

Injection and Self‐Assembly of Bioinspired Stem Cell‐Laden Gelatin/Hyaluronic Acid Hybrid Microgels Promote Cartilage Repair In Vivo

In this paper, a novel bioinspired stem cell‐laden microgel and related in vivo cartilage repair strategy are proposed. In particular, herein the preparation of new stem cell‐laden microgels, which can be injected into the chondral defect site in a minimally invasive way, and more importantly, capable of in situ self‐assembly into 3D macroporous scaffold without external stimuli, is presented. Specifically, thiolated gelatin (Gel‐SH) and vinyl sulfonated hyaluronic acid (HA‐VS) are first synthesized, and then stem cell‐laden gelatin/hyaluronic acid hybrid microgels (Gel‐HA) are generated by mixing Gel‐SH, HA‐VS, and bone mesenchymal stem cells (BMSCs) together via droplet‐based microfluidic approach, followed by gelation through fast and efficient thiol‐Michael addition reaction. The encapsulated BMSCs show high viability, proliferation, and chondrogenic differentiation potential in the microgels. Moreover, the in vitro test proves that BMSC‐laden Gel‐HA microgels are injectable without sacrificing BMSC viability, and more importantly, can self‐assemble into cartilage‐like scaffolds via cell–cell interconnectivity. In vivo experiments further confirm that the self‐assembled microgels can inhibit vascularization and hypertrophy. The Gel‐HA microgels and relevant cartilage repair strategy, i.e., injecting BMSC‐laden microgels separately and reconstructing chondral defect structure by microgel self‐assembly, provides a simple and effective method for cartilage tissue engineering and regenerative medicine.     

Direct‐Write Assembly of Microperiodic Silk Fibroin Scaffolds for Tissue Engineering Applications

Three–dimensional, microperiodic scaffolds of regenerated silk fibroin have been fabricated for tissue engineering by direct ink writing. The ink, which consisted of silk fibroin solution from the Bombyx mori silkworm, was deposited in a layer‐by‐layer fashion through a fine nozzle to produce a 3D array of silk fibers of diameter 5 µm. The extruded fibers crystallized when deposited into a methanol‐rich reservoir, retaining a pore structure necessary for media transport. The rheological properties of the silk fibroin solutions were investigated and the crystallized silk fibers were characterized for structure and mechanical properties by infrared spectroscopy and nanoindentation, respectively. The scaffolds supported human bone marrow‐derived mesenchymal stem cell (hMSC) adhesion, and growth. Cells cultured under chondrogenic conditions on these scaffolds supported enhanced chondrogenic differentiation based on increased glucosaminoglycan production compared to standard pellet culture. Our results suggest that 3D silk fibroin scaffolds may find potential application as tissue engineering constructs due to the precise control of their scaffold architecture and their biocompatibility.     

Stimuli‐Responsive Scaffold for Breast Cancer Treatment Combining Accurate Photothermal Therapy and Adipose Tissue Regeneration

Development of new therapeutic scaffolds to selectively destruct tumors under gentle conditions meanwhile promoting adipose tissue formation would be a promising strategy for clinical treatment of breast cancer. Herein, a stimuli‐responsive scaffold composed of polyacrylic acid‐g‐polylactic acid (PAA‐g‐PLLA) modified graphene oxide (GO) with a cleavable bond in between (GO‐PAA‐g‐PLLA), gambogic acid (GA), and polycaprolactone (PCL) is fabricated and then preseeded on adipose‐derived stem cells (ADSCs) for breast cancer treatment. This GO–GA‐polymer scaffold is able to simultaneously perform pH‐triggered low temperature (45 °C) photothermal therapy to selectively induce the apoptosis of tumor cells and significantly improve ADSCs growth without any photothermal damage. The low‐temperature photothermal therapy of the scaffolds can induce more than 95% of cell death for human breast cancer (MCF‐7) in vitro, which further completely inhibits tumor growth and finally eliminates tumor tissue in mice. Meanwhile, the prepared GO–GA‐polymer scaffold possesses the improved capability to stimulate the differentiation of ADSCs into adipocytes by upregulating adipo‐related gene expression, and significantly promotes new adipose tissue formation whether with or without NIR irradiation. These results successfully demonstrate that the prepared GO–GA‐polymer scaffolds with bifunctional properties will be a promising candidate for clinical cases involving both tumor treatment and tissue engineering.     

Injectable Stem Cell‐Laden Photocrosslinkable Microspheres Fabricated Using Microfluidics for Rapid Generation of Osteogenic Tissue Constructs

Direct injection is a minimally invasive method of stem cell transplantation for numerous injuries and diseases. However, despite its promising potential, its clinical translation is difficult due to the low cell retention and engraftment after injection. With high versatility, high‐resolution control and injectability, microfabrication of stem‐cell laden biomedical hydrogels holds great potential as minimally invasive technology. Herein, a strategy of microfluidics‐assisted technology entrapping bone marrow‐derived mesenchymal stem cells (BMSCs) and growth factors in photocrosslinkable gelatin (GelMA) microspheres to ultimately generate injectable osteogenic tissue constructs is presented. Additionally, it is demonstrated that the GelMA microspheres can sustain stem cell viability, support cell spreading inside the microspheres and migration from the interior to the surface as well as enhance cell proliferation. This finding shows that encapsulated cells have the potential to directly and actively participate in the regeneration process. Furthermore, it is found that BMSCs encapsulated in GelMA microspheres show enhanced osteogenesis in vitro and in vivo, associated with a significant increase in mineralization. In short, the proposed strategy can be utilized to facilitate bone regeneration with minimum invasiveness, and can potentially be applied along with other matrices for extended applications.     

Injectable 3D-Printed Porous Scaffolds for Adipose Stem Cell Delivery and Endometrial Regeneration

Stem-cell-based therapeutic strategies are promising in the clinical treatment of intrauterine adhesions (IUAs), while endometrial regeneration still hardly restores the structure and function of the endometrium because of the inadequate microenvironment for the grafted stem cells and subsequent limited therapeutic efficiency. Herein, an injectable porous hydrogel scaffold (PH scaffold) with customizable shapes is presented by using a microfluidic-based 3D printing technique for adipose-derived stem cells (ADSCs) delivery to enhance endometrial regeneration. These scaffolds display a controllable interconnected porous structure, which not only facilitates the encapsulation of ADSCs within the scaffold but also supports the recovery to their original shapes after injection. Furthermore, the cell viability of the laden ADSCs is well-maintained post-injection, exhibiting promotive effects on cell migration, proliferation, and tube formation. Based on these features, an ADSCs-laden PH scaffold with a hollow endometrium-mimicking morphology is designed and in situ injected into the damaged endometrium in rats of IUAs. These results show that the ADSCs-laden PH scaffolds can enhance functional endometrial regeneration by suppressing the inflammatory response, promoting cell proliferation, and improving vascularization. Thus, it is believed that such unique 3D-printed porous scaffolds are promising candidates for cell delivery, which also provides a minimally-invasive and effective strategy for endometrial regeneration.     

3D Printing Hydrogel Scaffolds with Nanohydroxyapatite Gradient to Effectively Repair Osteochondral Defects in Rats

Osteochondral (OC) defects pose an enormous challenge with no entirely satisfactory repair strategy to date. Herein, a 3D printed gradient hydrogel scaffold with a similar structure to that of OC tissue is designed, involving a pure hydrogel-based top cartilage layer, an intermediate layer for calcified cartilage with 40% (w w⁻¹) nanohydroxyapatite (nHA) and 60% (w w⁻¹) hydrogel, and a 70/30% (w w⁻¹) nHA/hydrogel-based bottom subchondral bone layer. This study is conducted to evaluate the efficacy of the scaffold with nHA gradients in terms of its ability to promote OC defect repair. The fabricated composites are evaluated for physicochemical, mechanical, and biological properties, and then implanted into the OC defects in 56 rats. Overall, bone marrow stromal cells (BMSCs)-loaded gradient scaffolds exhibit superior repair results as compared to other scaffolds based on gross examination, micro-computed tomography (micro-CT), as well as histologic and immunohistochemical analyses, confirming the ability of this novel OC graft to facilitate simultaneous regeneration of cartilage-subchondral bone.     

Capillary Network‐Like Organization of Endothelial Cells in PEGDA Scaffolds Encoded with Angiogenic Signals via Triple Helical Hybridization

Survival of tissue engineered constructs after implantation depends on proper vascularization. The differentiation of endothelial cells into mature microvasculature requires dynamic interactions between cells, scaffold, and growth factors, which are difficult to recapitulate in artificial systems. Previously, photocrosslinked poly(ethylene glycol) diacrylate (PEGDA) hydrogels displaying collagen mimetic peptides (CMPs), dubbed PEGDA‐CMP, that can be further conjugated with bioactive molecules via CMP‐CMP triple helix hybridization were reported. Here, it is shown that a bifunctional peptide featuring pro‐angiogenic domain mimicking vascular endothelial growth factor (VEGF) and a collagen mimetic domain that can fold into a triple helix conformation can hybridize with CMP side chains of the PEGDA‐CMP hydrogel, which results in presentation of insoluble VEGF‐like signals to endothelial cells. Presentation of VEGF‐like signals on the surface of micropatterned scaffolds in this way transforms cells from a quiescent state to elongated and aligned phenotype suggesting that this system could be used to engineer organized microvasculature. It is also shown that the pro‐angiogenic peptide, when applied topically in combination with modified dextran/PEGDA hydrogels, can enhance neovascularization of burn wounds in mice demonstrating the potential clinical use of CMP‐mediated matrix‐bound bioactive molecules for dermal injuries.