Porous Structures: In situ Porous Structures: A Unique Polymer Erosion Mechanism in Biodegradable Dipeptide‐Based Polyphosphazene and Polyester Blends Producing Matrices for Regenerative Engineering (Adv. Funct. Mater. 17/2010)

Synthetic biodegradable polymers serve as temporary substrates that accommodate cell infiltration and tissue in‐growth in regenerative medicine. To allow tissue in‐growth and nutrient transport, traditional three‐dimensional (3D) scaffolds must be prefabricated with an interconnected porous structure. Here we demonstrated for the first time a unique polymer erosion process through which polymer matrices evolve from a solid coherent film to an assemblage of microspheres with an interconnected 3D porous structure. This polymer system was developed on the highly versatile platform of polyphosphazene‐polyester blends. Co‐substituting a polyphosphazene backbone with both hydrophilic glycylglycine dipeptide and hydrophobic 4‐phenylphenoxy group generated a polymer with strong hydrogen bonding capacity. Rapid hydrolysis of the polyester component permitted the formation of 3D void space filled with self‐assembled polyphosphazene spheres. Characterization of such self‐assembled porous structures revealed macropores (10–100 μm) between spheres as well as micro‐ and nanopores on the sphere surface. A similar degradation pattern was confirmed in vivo using a rat subcutaneous implantation model. 12 weeks of implantation resulted in an interconnected porous structure with 82–87% porosity. Cell infiltration and collagen tissue in‐growth between microspheres observed by histology confirmed the formation of an in situ 3D interconnected porous structure. It was determined that the in situ porous structure resulted from unique hydrogen bonding in the blend promoting a three‐stage degradation mechanism. The robust tissue in‐growth of this dynamic pore forming scaffold attests to the utility of this system as a new strategy in regenerative medicine for developing solid matrices that balance degradation with tissue formation.     

Production and Potential of Bioactive Glass Nanofibers as a Next‐Generation Biomaterial

Over the past decades, bioactive glass has played a central role in the bone regeneration field, due to its excellent bioactivity, osteoconductivity, and even osteoinductivity. Herein, exploitation of bioactive glass as a one‐dimensional nanoscale fiber by employing an electrospinning process based on a sol–gel precursor is reported for the first time. Under controlled processing conditions, continuous nanofibers have been generated successfully with variable diameters. The excellent bioactivity of the nanofiber is confirmed in vitro within a simulated body fluid by the rapid induction of bonelike minerals onto the nanofiber surface. The bone‐marrow‐derived cells are observed to attach and proliferate actively on the nanofiber mesh, and differentiate into osteoblastic cells with excellent osteogenic potential. The bioactive nanofibers have been further exploited in various forms, such as bundled filament, nanofibrous membrane, 3D macroporous scaffold, and nanocomposite with biopolymer, suggesting their versatility and potential applications in bone‐tissue engineering. Based on this study, the bioactive nanofibrous matrix is regarded as a promising next‐generation biomaterial in the bone‐regeneration field.     

In Situ Porous Structures: A Unique Polymer Erosion Mechanism in Biodegradable Dipeptide-based Polyphosphazene and Polyester Blends Producing Matrices for Regenerative Engineering

Synthetic biodegradable polymers serve as temporary substrates that accommodate cell infiltration and tissue in-growth in regenerative medicine. To allow tissue in-growth and nutrient transport, traditional three-dimensional (3D) scaffolds must be prefabricated with an interconnected porous structure. Here we demonstrated for the first time a unique polymer erosion process through which polymer matrices evolve from a solid coherent film to an assemblage of microspheres with an interconnected 3D porous structure. This polymer system was developed on the highly versatile platform of polyphosphazene-polyester blends. Co-substituting a polyphosphazene backbone with both hydrophilic glycylglycine dipeptide and hydrophobic 4-phenylphenoxy group generated a polymer with strong hydrogen bonding capacity. Rapid hydrolysis of the polyester component permitted the formation of 3D void space filled with self-assembled polyphosphazene spheres. Characterization of such self-assembled porous structures revealed macropores (10-100 μm) between spheres as well as micro- and nanopores on the sphere surface. A similar degradation pattern was confirmed in vivo using a rat subcutaneous implantation model. 12 weeks of implantation resulted in an interconnected porous structure with 82-87% porosity. Cell infiltration and collagen tissue in-growth between microspheres observed by histology confirmed the formation of an in situ 3D interconnected porous structure. It was determined that the in situ porous structure resulted from unique hydrogen bonding in the blend promoting a three-stage degradation mechanism. The robust tissue in-growth of this dynamic pore forming scaffold attests to the utility of this system as a new strategy in regenerative medicine for developing solid matrices that balance degradation with tissue formation.     

Inverted‐Colloidal‐Crystal Hydrogel Matrices as Three‐Dimensional Cell Scaffolds

Successful engineering of functional tissues requires the development of three‐dimensional (3D) scaffolds that can provide an optimum microenvironment for tissue growth and regeneration. A new class of 3D scaffolds with a high degree of organization and unique topography is fabricated from polyacrylamide hydrogel. The hydrogel matrix is molded by inverted colloidal crystals made from 104 μm poly(methyl methacrylate) spheres. The topography of the scaffold can be described as hexagonally packed 97 μm spherical cavities interconnected by a network of channels. The scale of the long‐range ordering of the cavities exceeds several millimeters. In contrast to analogous material in the bulk, hydrogel shaped as an inverted opal exhibits much higher swelling ratios; its swelling kinetics is an order of magnitude faster as well. The engineered scaffold possesses desirable mechanical and optical properties that can facilitate tissue regeneration while allowing for continuous high‐resolution optical monitoring of cell proliferation and cell–cell interaction within the scaffold. The scaffold biocompatibility as well as cellular growth and infiltration within the scaffold were observed for two distinct human cell lines which were seeded on the scaffold and were tracked microscopically up to a depth of 250 μm within the scaffold for a duration of up to five weeks. Ease of production, a unique 3D structure, biocompatibility, and optical transparency make this new type of hydrogel scaffold suitable for most challenging tasks in tissue engineering.     

3D Fiber‐Deposited Electrospun Integrated Scaffolds Enhance Cartilage Tissue Formation

Despite the periodical and completely interconnected pore network that characterizes rapid prototyped scaffolds, cell seeding efficiency remains still a critical factor for optimal tissue regeneration. This can be mainly attributed to the current resolution limits in pore size. We present here novel three‐dimensional (3D) scaffolds fabricated by combining 3D fiber deposition (3DF) and electrospinning (ESP). Scaffolds consisted of integrated 3DF periodical macrofiber and random ESP microfiber networks (3DFESP). The 3DF scaffold provides structural integrity and mechanical properties, while the ESP network works as a “sieving” and cell entrapment system and offers?at the same time?cues at the extracellular matrix (ECM) scale. Primary bovine articular chondrocytes were isolated, seeded, and cultured for four weeks on 3DF and 3DFESP scaffolds to evaluate the influence of the integrated ESP network on cell entrapment and on cartilage tissue formation. 3DFESP scaffolds enhanced cell entrapment as compared to 3DF scaffolds. This was accompanied by a higher amount of ECM (expressed in terms of sulphated glycosaminoglycans or GAG) and a significantly higher GAG/DNA ratio after 28 days. SEM analysis revealed rounded cell morphology on 3DFESP scaffolds. Spread morphology was observed on 3DF scaffolds, suggesting a direct influence of fiber dimensions on cell differentiation. Furthermore, the ESP surface topology also influenced cell morphology. Thus, the integration of 3DF and ESP techniques provide a new set of “smart” scaffolds for tissue engineering applications.     

The Implications of Polymer Selection in Regenerative Medicine: A Comparison of Amorphous and Semi‐Crystalline Polymer for Tissue Regeneration

Biodegradable polymeric scaffolds are being investigated as scaffolding materials for use in regenerative medicine. While the in vivo evaluation of various three‐dimensional (3D), porous, biodegradable polymeric scaffolds has been reported, most studies are ≤3 months in duration, which is typically prior to bulk polymer degradation, a critical event that may initiate an inflammatory response and inhibit tissue formation. Here, a 6 month in vitro degradation and corresponding in vivo studies that characterized scaffold changes during complete degradation of an amorphous, 3D poly(lactide‐co‐glycolide)(3D‐PLAGA) scaffold and near‐complete degradation of a semi‐crystalline3D‐PLAGA scaffold are reported. Using sintered microsphere matrix technology, constructs were fabricated in a tubular shape, with the longitudinal axis void and a median pore size that mimicked the architecture of native bone. Long‐term quantitative measurements of molecular weight, mechanical properties, and porosity provided a basis for theorization of the scaffold degradation process. Following implantation in a critical size ulnar defect model, histological analysis and quantitative microCT indicated early solubilization of the semi‐crystalline polymer created an acidic microenvironment that inhibited mineralized tissue formation. Thus, the use of amorphous over semi‐crystalline PLAGA materials is advocated for applications in regenerative medicine.     

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.     

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.     

Integrated and Bifunctional Bilayer 3D Printing Scaffold for Osteochondral Defect Repair

Bioinspired scaffolds with two distinct regions resembling stratified anatomical architecture provide potential strategies for osteochondral defect repair and are studied in preclinical animals. However, delamination of the two layers often causes tissue disjunction between the regenerated cartilage and subchondral bone, leading to few commercially available clinical applications. This study develops an integrated poly(ε-caprolactone) (PCL)-based scaffold for repairing osteochondral defects. An extracellular matrix (ECM)-incorporated 3D printing composite scaffold (ECM/PCL) coated with ECM hydrogel (E-co-E/PCL) is fabricated as the upper layer, and magnesium oxide nanoparticles coated with polydopamine (MgO@PDA)-incorporated composite scaffold (MD/PCL) is fabricated using 3D printing as the bottom layer. The physicochemical and mechanical properties of the bilayer scaffold meet the requirements in designing and fabricating the osteochondral scaffold, especially a strong interface possessed between the two layers. By in vitro study, the integrated scaffold stimulates proliferation, chondrogenic differentiation, and osteogenic differentiation of human bone mesenchymal stem cells. Moreover, the integrated bilayer scaffold exhibits well repair ability to facilitate simultaneous regeneration of cartilage and subchondral bone after implanting into the osteochondral defect in rats. In addition, cartilage “tidemarks” completely regenerated after 12 weeks of implantation of the bilayer scaffold, which indicates no tissue disjunctions formed between the regenerated cartilage and subchondral bone.     

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.     

Engineered 3D Silk‐Based Metastasis Models: Interactions Between Human Breast Adenocarcinoma,Mesenchymal Stem Cells and Osteoblast‐Like Cells

Bone metastasis occurs in 70% of breast cancer patients and is a frequent cause of morbidity in cancer patients. A delicate balance exists in the bone microenvironment, but the functional dynamics underlying the tumor cell‐microenvironment interactions remain poorly understood. 3D in vitro model systems of metastasis can throw new light on this phenomenon. Silk protein fibroin scaffolds, are cytocompatible for 3D cancer cell culture. They are structurally more resistant to protease degradation than other native biomaterials making these matrices suitable for cancer modeling. In this report, human breast adenocarcinoma cells, human osteoblast like cells and mesenchymal stem cells are co‐cultered. Cancer cells and osteoblast‐like cells are found to interact through secreted products. Decreased population of osteoblast‐like cells and mineralization of extracellular matrix are observed as a result of co‐culture. Significantly increased migration of breast cancer cells is observed in the bone‐like constructs than in non‐seeded scaffolds. The co‐culture constructs show significant increase in drug resistance, invasiveness and angiogenicity. Co‐culture of breast cancer cells with osteoblast like cells and mesenchymal stem cells also indicate that the interaction of cancer cells with bone microenvironment varies with spatial organization, presence of osteogenic factors as well as stromal cell type. Here, results show that 3D in vitro co‐culture models is possibly a better system to study and target cancer progression.     

Osteoconductive Performance of Carbon Nanotube Scaffolds Homogeneously Mineralized by Flow‐Through Electrodeposition

The treatment of bone lesions, including fractures, tumor resection and osteoporosis, is a common clinical practice where bone healing and repair are pursued. It is widely accepted that calcium phosphate‐based materials improve integration of biomaterials with surrounding bone tissue and further serve as a template for proper function of bone‐forming cells. Within this context, mineralization on preformed substrates appears as an interesting and successful alternative for mineral surface functionalization. However, mineralization of “true” 3D scaffolds –in which the magnitude of the third dimension is within the same scale as the other two– is by no means a trivial issue because of the difficulty to obtain a homogeneous mineral layer deposited on the entire internal surface of the scaffold. Herein, a “flow‐through” electrodeposition process is applied for mineralization of 3D scaffolds composed of multiwall carbon nanotubes and chitosan. It is demonstrated that, irrespective of the experimental conditions used for electrodeposition (e.g., time, temperature and voltages), the continuous feed of salts provided by the use of a flow‐through configuration is the main issue if one desires to coat the entire internal structure of 3D scaffolds with a homogeneous mineral layer. Finally, mineralized scaffolds not only showed a remarkable biocompatibility when tested with human osteoblast cells, but also enhanced osteoblast terminal differentiation (as early as 7 days in calcifying media).     

Unprecedentedly Tough,Folding‐Endurance,and Multifunctional Graphene‐Based Artificial Nacre with Predesigned 3D Nanofiber Network as Matrix

Mimicking the hierarchical brick‐and‐mortar architecture of natural nacre provides great opportunities for the design and synthesis of multifunctional artificial materials. The crucial challenge to push nacre‐mimetic functional materials toward practical applications is to achieve ample ductility, toughness, and folding endurance with simultaneously maintaining high‐level functional properties. In this study, the microstructure of nacre‐mimetics is reformed through predesigning a 3D nanofiber network to replace conventional polymer matrices. A unique sol–gel–film transformation approach is developed to fabricate a graphene‐based artificial nacre containing a preforming 3D, interconnective, inhomogeneous poly(p‐phenylene benzobisoxazole) nanofiber network. The fabulous coupling of the extensive sliding of graphene nanoplatelets and intensive stretching of the 3D nanofiber network over a large scale enables the artificial nacre to display natural nacre‐like deformation behavior, achieving ultralarge strain‐to‐failure (close to 35%), unprecedented toughness (close to 50 MJ m^?3), and fold endurance (no decrease in tensile properties after folding for 10 000 times or folding at increasing stress). The new levels of ductility, toughness, and folding endurance are integrated with outstanding thermal properties, including thermal conductivity (≈130 W m^?1 K^?1), thermal stability (520 °C) and nonflammability, rendering the lightweight nacre‐mimetics promising in flexible electronic devices, particularly for aerospace electronics.     

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.     

Electrospun Extracellular Matrix: Paving the Way to Tailor‐Made Natural Scaffolds for Cardiac Tissue Regeneration

Biomimetic scaffolds generally aim at structurally and compositionally imitating native tissue, thus providing a supportive microenvironment to the transplanted or recruited cells in the tissue. Native decellularized porcine extracellular matrix (ECM) is becoming the ultimate bioactive material for the regeneration of different organs. Particularly for cardiac regeneration, ECM is studied as a patch and injectable scaffolds, which improve cardiac function, yet lack reproducibility and are difficult to control or fine‐tune for the desired properties, like most natural materials. Seeking to harness the natural advantages of ECM in a reproducible, scalable, and controllable scaffold, for the first time, a matrix that is produced from whole decellularized porcine cardiac ECM using electrospinning technology, is developed. This unique electrospun cardiac ECM mat preserves the composition of ECM, self‐assembles into the same microstructure of cardiac ECM ,and ,above all, preserves key cardiac mechanical properties. It supports cell growth and function, and demonstrates biocompatibility in vitro and in vivo. Importantly, this work reveals the great potential of electrospun ECM‐based platforms for a wide span of biomedical applications, thus offering the possibility to produce complex natural materials as tailor‐made, well‐defined structures.     

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.     

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.     

Biomimetic Ultralight,Highly Porous,Shape‐Adjustable,and Biocompatible 3D Graphene Minerals via Incorporation of Self‐Assembled Peptide Nanosheets

Hybrid nanomaterials with tailored functions, consisting of self‐assembled peptides, are intensively applied in nanotechnology, tissue engineering, and biomedical applications due to their unique structures and properties. Herein, a peptide‐mediated biomimetic strategy is adopted to create the multifunctional 3D graphene foam (GF)‐based hybrid minerals. First, 2D peptide nanosheets (PNSs), obtained by self‐assembling a motif‐specific peptide molecule (LLVFGAKMLPHHGA), are expected to exhibit biofunctionality, such as the biomimetic mineralization of hydroxyapatite (HA) minerals. Subsequently, the noncovalent conjugation of PNSs onto GF support is utilized to form 3D GF‐PNSs hybrid scaffolds, which are suitable for the growth of HA minerals. The fabricated biomimetic 3D GF‐PNSs‐HA minerals exhibit adjustable shape, superlow weight (0.017 g cm^?3), high porosity (5.17 m² g^?1), and excellent biocompatibility, proving potential applications in both bone tissue engineering and biomedical engineering. To the best of the authors' knowledge, it is the first time to combine 2D PNSs and GF to fabricate 3D organic–inorganic hybrid scaffold. Further development of these hybrid GF‐PNSs scaffolds can potentially lead to materials used as matrices for drug delivery or bone tissue engineering as proven via successful 3D scaffold formation exhibiting interconnected pore‐size structures suitable for vascularization and medium transport.     

Autologous Versatile Vesicles‐Incorporated Biomimetic Extracellular Matrix Induces Biomineralization

Restoring extracellular matrix (ECM) with supportive and osteoinductive abilities is of great significance for bone tissue regeneration. Current approaches involving cell‐based scaffolds or nanoparticle‐modified biomimic‐ECM have been met with additional biosafety concerns. Herein, the natural biomineralization process is first analyzed and is found that mesenchymal stem cells‐derived extracellular vesicles (EVs) from early and late stages of osteoinduction play different roles during the mineralization process. The functional EVs hierarchically with blood‐derived autohydrogel (AH) are then incorporated to form an osteoinductive biomimetic extracellular matrix (BECM). The alkaline phosphatase‐rich EVs are released from the outer layers to induce osteoblast differentiation during early stages. Thereafter, as the degradation of AH occurred, calcium/phosphorus (Ca/P)‐rich EVs are liberated to promote the nucleation of extracellular mineral crystals. Additionally, BECM contains considerable collagen fibrils that provide additional nucleation sites for crystallites deposition, thus reaching self‐mineralization in situ. In conclusion, this research provides a promising, versatile mineralization‐instructive platform to tackle the challenges faced in bone‐tissue engineering.     

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.