Multilayered Graphene Hydrogel Membranes for Guided Bone Regeneration

Biomimetic Membranes of Methacrylated Gelatin/Nanohydroxyapatite/Poly(l-Lactic Acid) for Enhanced Bone Regeneration

Nanofibrous poly(l-lactic acid) (PLLA) membrane-simulated extracellular matrices (ECMs) can be used in the biomedical field. However, the hydrophobic nature and poor osteoinductive property of PLLA limit its application in guided bone regeneration (GBR). In this work, a methacrylated gelatin/nano-HA (GelMA/nHA) complex was first synthesized in situ and then introduced into PLLA to fabricate biomimetic GelMA/nHA/PLLA membranes, mimicking the nanofibrous architecture and composition of ECMs by electrospinning and photocrosslinking. Compared to PLLA and GelMA/PLLA membranes, the novel GelMA/nHA/PLLA membranes demonstrated better tensile, hydrophilic, water sorption, and degradation properties. An in vitro biological evaluation indicated that the membranes promoted human bone marrow-derived mesenchymal stem cell (hBMSC) proliferation, adhesion, and osteogenic differentiation. Critical-sized defects in rat models were used to evaluate the bone regeneration performances of the three kinds of membranes in vivo, and the GelMA/nHA/PLLA membranes demonstrated excellent osteogenic regeneration potential. Therefore, GelMA/nHA/PLLA membranes have wide application prospects in bioengineering applications such as GBR treatment.

Magnesium-based layered double hydroxide nanosheets: a new bone repair material with unprecedented osteogenic differentiation performance

Osteonecrosis of femoral head (ONFH) has been one of the most common diseases, and thus the development of novel biomaterials with superior osteogenic ability is the key issue. In this work, Yb-containing MgAl-layered double hydroxide (LDH) monolayer nanosheets (MgAlYb-LDHs) were designed and synthesized and were used as a new biomaterial with outstanding osteogenic differentiation ability. The LDH monolayer nanosheets gave a high loading content (LC) of 197% for alendronate (AL) with an encapsulation efficiency (EE) of 98.6%. Notably, outstanding in vitro osteogenic differentiation performance of MgAlYb-LDHs was demonstrated in the transcriptional level of Collagen I, with a 3000-fold enhancement compared with the blank control. For in vivo tests with rabbits, the total volume of bone regeneration after treatment with the LDH group was 2.77 and 1.41 times larger than that with the negative control group and positive control group (autologous bone graft, clinical gold standard) at 8 weeks postoperatively. In addition, with the degradation of AL/LDHs, the bone mass density (BMD) of the femoral head increased by 1.52 times compared with that for the positive control group at 8 weeks postoperatively. Therefore, this work provides a new perspective for the design and preparation of 2D monolayer MgAlYb-LDHs and their drug formulation (AL/LDHs), which show great promise in ONFH accompanied by osteoporosis.

In Vivo Disintegration and Bioresorption of a Nacre-Inspired Graphene-Silk Film Caused by the Foreign-Body Reaction

Graphene-based substrates are emerging as a promising functional platform for biomedical applications. Although dispersible graphene sheets have been demonstrated to be biodegradable, their assembled macroscopic architectures are biopersistent because of strong π-π interactions. In this study, we developed a nacre-inspired graphene-silk nanocomposite film by vacuum filtration with a subsequent green chemical reduction procedure. The "brick-and-mortar" architecture not only ensures the mechanical and electrical properties of the film but also endows it with disintegrable and bioresorbable properties following rat subcutaneous implantation. Furthermore, covalent cross-linking leads to the formation of graphene with decreased interlayer spacing, which effectively prolongs the residence time in vivo. We found that enzymatic treatment created microcracks on the film surface and that the foreign-body reaction was involved in the deformation, delamination, disintegration, and phagocytosis processes of the nanocomposite films. This bioinspired strategy paves the way for the development of high-performance graphene-based macroscopic biomaterials with tunable bioresorbability.

Clinical and histological evaluations of alveolar ridge augmentation using a novel bi-layered porous polyethylene barrier membrane

Guided bone regeneration (GBR) is an effective alveolar ridge reconstruction technique used before or at implant placement. The combination of various barrier membranes and bone substitutes has been employed. This study aimed to perform a preliminarily evaluation of the safety and performance of a new nonabsorbable bi-layered porous polyethylene (PPE) membrane, in combination with a freeze-dried cortical bone allograft in posterior mandibular ridge augmentation. Fifteen adults who had combined posterior mandibular defects were included for ridge augmentation via GBR using PPE membrane and allograft before implant placement. The keratinized mucosa width (KW), ridge width (RW), ridge height (RH), distance from measurement matrix to bone (DMB), and horizontal alveolar width at 14.0 mm apical to the occlusal plane (HAW) were clinically measured at 15 intended implant sites before and after the augmentation. Fifteen biopsy specimens were harvested at the implant sites for histological analysis. All the subjects completed the whole study. The KW and RH showed minor gains by 0.2 ± 1.4 mm and 0.9 ± 2.3 mm respectively; however, no statistically significant differences were found between, before, and after the augmentation (P > 0.05). In contrast, the RW and HAW significantly increased by 4.8 ± 1.6 mm and 2.3 ± 1.7 mm, respectively, (P ≤ 0.001), while DMB significantly decreased by 1.0 ± 0.8 mm after treatment (P < 0.001). Histological analysis revealed that allograft underwent active bone remodeling. The PPE membrane was adequately safe and efficient to use with allograft in GBR for the reconstruction of combined ridge defects. Although some complications were observed, these were manageable and subsequently lead to successful implant placement for all the subjects. However, further randomized controlled trials are still needed to confirm these findings.

Polyhedral Oligomeric Silsesquioxane-Incorporated Gelatin Hydrogel Promotes Angiogenesis during Vascularized Bone Regeneration

Many approaches have been made toward the development of scaffolds with good biocompatibility and appreciable physicochemical properties to facilitate stem cell adhesion, osteogenic differentiation, and vascularization in tissue engineering. Nowadays, vascularization is a main bottleneck in tissue engineering strategies that is needed to be overcome and developed. Herein, we construct a series of polyhedral oligomeric silsesquioxane (POSS)-modified porous gelatin hydrogels with different POSS concentrations from 0 to 5 wt %, defined as X% POSS hydrogels (X = 0, 1, 2, 3, 4, 5) to support vascularized bone repair. The introduction of POSS into gelatin effectively promoted adhesive protein adsorption and integrin α5β1 expression, subsequently leading to enhanced adhesion of both rat bone marrow mesenchymal stem cells and human umbilical vein endothelial cells (HUVECs). In vitro experiments further demonstrated that POSS-containing hybrid hydrogels more effectively support the angiogenic tube and network formation in HUVECs than the 0% POSS hydrogel. Besides, POSS-containing hybrid hydrogels showed desirable performance as a sustained release system of vascular endothelial growth factor (VEGF) and bone morphogenetic protein-2 (BMP-2), and they further accelerated vascular network establishment and the formation of a new bone in defect regions. When the hydrogels were implanted into critical-sized rat calvarial defects in vivo, the VEGF/BMP-2-coupled 3% POSS group gained a higher blood vessel volume in the bone defect regions (5.49 ± 0.35 mm³) than the 3% POSS group (3.12 ± 0.20 mm³) and the 0% POSS group (1.57 ± 0.25 mm³), suggesting that the 3% POSS hydrogel with VEGF/BMP-2 would expedite vascularization. Based on these evaluations, our results indicated that the POSS-incorporated gelatin hydrogel would provide a promising bone graft scheme in potential clinical application of large bone defect repair.

Hydrogel membranes: A review

Hydrogel membranes (HMs) are defined and applied as hydrated porous media constructed of hydrophilic polymers for a broad range of applications. Fascinating physiochemical properties, unique porous architecture, water-swollen features, biocompatibility, and special water content dependent transport phenomena in semi-permeable HMs make them appealing constructs for various applications from wastewater treatment to biomedical fields. Water absorption, mechanical properties, and viscoelastic features of three-dimensional (3D) HM networks evoke the extracellular matrix (ECM). On the other hand, the porous structure with controlled/uniform pore-size distribution, permeability/selectivity features, and structural/chemical tunability of HMs recall membrane separation processes such as desalination, wastewater treatment, and gas separation. Furthermore, supreme physiochemical stability and high ion conductivity make them promising to be utilised in the structure of accumulators such as batteries and supercapacitors. In this review, after summarising the general concepts and production processes for HMs, a comprehensive overview of their applications in medicine, environmental engineering, sensing usage, and energy storage/conservation is well-featured. The present review concludes with existing restrictions, possible potentials, and future directions of HMs.

Bone Tissue Engineering via Carbon-Based Nanomaterials

Bone tissue engineering (BTE) has received significant attention due to its enormous potential in treating critical-sized bone defects and related diseases. Traditional materials such as metals, ceramics, and polymers have been widely applied as BTE scaffolds; however, their clinical applications have been rather limited due to various considerations. Recently, carbon-based nanomaterials attract significant interests for their applications as BTE scaffolds due to their superior properties, including excellent mechanical strength, large surface area, tunable surface functionalities, high biocompatibility as well as abundant and inexpensive nature. In this article, recent studies and advancements on the use of carbon-based nanomaterials with different dimensions such as graphene and its derivatives, carbon nanotubes, and carbon dots, for BTE are reviewed. Current challenges of carbon-based nanomaterials for BTE and future trends in BTE scaffolds development are also highlighted and discussed.

Electrospun poly(3-hydroxybutyrate-co-4-hydroxybutyrate) /Octacalcium phosphate Nanofibrous membranes for effective guided bone regeneration

Membranes used in guided bone regeneration (GBR) are required to exhibit high mechanical strength, biocompatibility, biodegradation, osteogenic and osteoinductive potential. In our study, poly(3-hydroxybutyrate-co-4-hydroxybutyrate)(P(3HB-co-4HB))/octacalcium phosphate (OCP) (P(3HB-co-4HB)/OCP) nanofibrous membranes were fabricated by electrospinning with two different P(3HB-co-4HB) to OCP ratios (P(3HB-co-4HB):OCP = 95:5 wt% and 90:10 wt%, termed P(3HB-co-4HB)/OCP(5)and P(3HB-co-4HB)/OCP (10), respectively) for GBR. The developed P(3HB-co-4HB)/OCP nanofibrous membranes were analysed for their osteogenic and osteoinductive properties using mesenchymal stem cells (MSCs) in vitro and in a calvarial bone defect rat model. The composite P(3HB-co-4HB)/OCP nanofibrous membranes showed decreased fibre size and enhanced tensile strength compared with those of P(3HB-co-4HB) nanofibrous membranes. In the in vitro studies, the P(3HB-co-4HB)/OCP membranes facilitated cell growth and osteoblastic differentiation of MSCs and were superior to P(3HB-co-4HB) membranes. After covered on the calvarial bone defects, P(3HB-co-4HB)/OCP membranes facilitated greater neobone formation than P(3HB-co-4HB) membranes did, as the result of histological evaluation and micro-CT analysis with higher bone volume/total volume (BV/TV) ratio and bone mineral density (BMD). P(3HB-co-4HB)/OCP(10) membranes with higher OCP content showed greater stiffness and osteoinductivity than P(3HB-co-4HB)/OCP (5)membranes, demonstrating the role of OCP in the composite membranes. These results indicated that electrospun P(3HB-co-4HB)/OCP nanofibrous membranes hold promise for the clinical application of GBR.

A sericin/ graphene oxide composite scaffold as a biomimetic extracellular matrix for structural and functional repair of calvarial bone

Bone defects affect millions of people worldwide each year, leading to severe disabilities. Biomimetic scaffolds mediated tissue regeneration represents a promising alternative for bone repair. However, the major problem associated with most currently clinical available artificial bone substitutes (scaffolds) is that they mainly possess filling function but lack of osteo-induction abilities. Therefore, development of biomaterials with osteo-induction property for effective bone regeneration is highly desired. Methods: We report the design and fabrication of a photo-crosslinked sericin methacryloyl (SerMA)/ graphene oxide (GO) hydrogel (SMH/GO) as a biomimetic scaffold for the functional repair of the bone. The mechanical strength, degradation and biocompatibility behavior of SMH/GO hydrogel were measured in vitro. The effect of SMH/GO hydrogel on BMSCs proliferation, migration, osteogenesis differentiation was assessed. After that, SMH/GO-2 was used as an artificial bone substitute for bone regeneration after calvarial defects and effect on bone repair was evaluated by histological, X-Ray and microCT analysis. Furthermore, the potential mechanism of SMH/GO hydrogel regulating BMSCs migration and differentiation was investigated by RNA sequencing. Results: This scaffold has good biocompatibility, cell adhesive property, proliferation- and migration-promoting effects, and osteogenic induction property. After being implanted in a rat calvarial defect model, this SMH/GO scaffold effectively promotes new bone regeneration and achieves structural and functional repair within 12 weeks by inducing autologous bone marrow-derived mesenchymal stem cells (BMSCs) differentiation. By utilizing cell-biological assays and RNA sequencing, we reveal its possible regeneration mechanisms: the SMH/GO hydrogel regulates BMSCs migration and osteo-differentiation via activating MAPK, TNF, and chemokine signaling for bone regeneration. Conclusion: Aiming to meet clinical demands and overcome current limitations of existing artificial bones, we have developed a new type of sericin/ graphene oxide composite scaffold and provided histological, functional, and molecular evidence demonstrating that it is capable of effectively repairing defective bones by inducing autologous BMSCs directional migration and osteogenic differentiation.

Multilayered Titanium Carbide MXene Film for Guided Bone Regeneration

Purpose

MXenes are two-dimensional (2D) materials that are increasingly being applied in biomedical fields. This is ascribed to their good physiochemical properties, unique structure and high biological compatibility. However, the osteogenic activity and suitability of these materials for bone tissue engineering are not clearly understood. Thus, the aim of this study is to evaluate the biocompatibility, osteoinductivity and guided bone regeneration ability of Ti₃C₂T_x MXene in vitro and in vivo.

Methods

Multilayered Ti₃C₂T_x MXene films were prepared and characterized by XRD and SEM. In vitro experiments were performed to evaluate the effect of MXene films on cell adhesion and morphology with SEM and fluorescence microscopy. The cytotoxicity of MXene films was detected with the Live/Dead double-staining tests. The EdU assay was employed to evaluate cell proliferation on MXene films and ALP activity was tested to determine the effect of the films on osteogenic differentiation in vitro. The mRNA expression of osteogenic differentiation-related markers was measured using qRT-PCR. In vivo animal studies were performed in which the MXene films were implanted subcutaneously in rats to evaluate biocompatibility and host tissue response in vivo. In addition, a rat calvarial defect model was established to examine the bone regeneration performance of the Ti₃C₂T_x MXene films. The specimens were analyzed with micro-CT evaluation and histological tests.

Results

The XRD and SEM analyses revealed that the Ti₃C₂T_x MXene film was successfully synthesized. The cellular experiments showed that MXene films were highly cytocompatible and enhanced osteogenic differentiation in vitro. When implanted into subcutaneous sites and calvarial defect sites in rats, MXene films showed good biocompatibility, osteoinductivity and bone regeneration activity in vivo.

Conclusion

In summary, this study presents new applications of MXenes in bone tissue engineering and in guided bone regeneration therapy.

Two-dimensional nanomaterials: fascinating materials in biomedical field

Due to their high anisotropy and chemical functions, two-dimensional (2D) nanomaterials have attracted increasing interest and attention from various scientific fields, including functional electronics, catalysis, supercapacitors, batteries and energy materials. In the biomedical field, 2D nanomaterials have made significant contributions to the field of nanomedicine, especially in drug/gene delivery systems, multimodal imaging, biosensing, antimicrobial agents and tissue engineering. 2D nanomaterials such as graphene/graphene oxide (GO)/reduced graphene oxide (rGO), silicate clays, layered double hydroxides (LDHs), transition metal dichalcogenides (TMDs), transition metal oxides (TMOs), black phosphorus (BP), graphitic carbon nitride (g-C₃N₄), hexagonal boron nitride (h-BN), antimonene (AM), boron nanosheets (B NSs) and tin telluride nanosheets (SnTe NSs) possess excellent physical, chemical, optical and biological properties due to their uniform shapes, high surface-to-volume ratios and surface charge. In this review, we first introduce the properties, structures and synthetic strategies of different configurations of 2D nanomaterials. Recent advances and paradigms of 2D nanomaterials in a variety of biomedical applications, ranging from drug delivery, cancer treatment, bioimaging and tissue engineering to biosensing are discussed afterwards. In the final part, we foresee the development prospects and challenges of 2D nanomaterials after summarizing the research status of ultrathin 2D nanomaterials.

Calcium Phosphate Nanocluster-Loaded Injectable Hydrogel for Bone Regeneration

Bone is a hierarchical tissue in which the extracellular matrix consists of hydroxyapatite (HAP) crystals embedded in the collagen matrix. Artificial bone regeneration remains a great challenge due to the difficulty of balancing the chemical composition, biological compatibility, and mechanical performance of the implant. Biomineralization starts from the formation of a hydrogel-like biomacromolecule matrix in many cases, while the mineralization of HAP often builds from amorphous calcium phosphate (ACP) nanoclusters. Inspired by these discoveries, here we use a hydrogel loaded with ∼1 nm sized polymer-stabilized ACP nanoclusters (cluster-loaded hydrogel) as an injectable bone regeneration material. The hydrogel is biocompatible and stabilizes the ACP clusters such that they could efficiently infiltrate into collagen fibrils leading to intrafibrillar mineralization of HAP nanocrystals. Ex vivo results reveal that the cluster-loaded hydrogel has an excellent bone affinity as well as provides a suitable environment for the proliferation and differentiation of bone cells. In vivo experiments with rat bone show that the cluster-loaded hydrogel can generate HAP-based fillings within bone defects with perfect bonding to the surrounding tissue and a mechanical performance comparable with native bone. The fluidity of the hydrogel is further beneficial by providing a feasible minimally invasive bone healing procedure via syringe injection. The discovery and utilization of the cluster-loaded hydrogel described here provide a promising bioinspired approach for bone tissue regeneration.

Osteoporotic Bone Recovery by a Highly Bone-Inductive Calcium Phosphate Polymer-Induced Liquid-Precursor

Osteoporosis is an incurable chronic disease characterized by a lack of mineral mass in the bones. Here, the full recovery of osteoporotic bone is achieved by using a calcium phosphate polymer-induced liquid-precursor (CaP-PILP). This free-flowing CaP-PILP material displays excellent bone inductivity and is able to readily penetrate into collagen fibrils and form intrafibrillar hydroxyapatite crystals oriented along the c-axis. This ability is attributed to the microstructure of the material, which consists of homogeneously distributed ultrasmall (≈1 nm) amorphous calcium phosphate clusters. In vitro study shows the strong affinity of CaP-PILP to osteoporotic bone, which can be uniformly distributed throughout the bone tissue to significantly increase the bone density. In vivo experiments show that the repaired bones exhibit satisfactory mechanical performance comparable with normal ones, following a promising treatment of osteoporosis by using CaP-PILP. The discovery provides insight into the structure and property of biological nanocluster materials and their potential for hard tissue repair.

Structurally Tunable Reduced Graphene Oxide Substrate Maintains Mouse Embryonic Stem Cell Pluripotency

Culturing embryonic stem cells (ESCs) in vitro usually requires animal-derived trophoblast cells, which may cause pathogenic and immune reactions; moreover, the poor repeatability between batches hinders the clinical application of ESCs. Therefore, it is essential to synthesize a xenogeneic-free and chemically well-defined biomaterial substrate for maintaining ESC pluripotency. Herein, the effects of structurally tunable reduced graphene oxide (RGO) substrates with different physicochemical properties on ESC pluripotency are studied. Colony formation and CCK-8 assays show that the RGO substrate with an average 30 µm pore size promotes cell survival and proliferation. The unannealed RGO substrate promotes ESC proliferation significantly better than the annealed substrate due to the interfacial hydrophilic groups. The RGO substrate can also maintain ESC for a long time. Additionally, immunofluorescence staining shows that ESCs cultured on an RGO substrate highly express E-cadherin and β-catenin, whereas after being modified by Dickkopf-related protein 1, the RGO substrate is unable to sustain ESC pluripotency. Furthermore, the cell line that interferes with E-cadherin is also unable to maintain pluripotency. These results confirm that the RGO substrate maintains ESC pluripotency by promoting E-cadherin-mediated cell-cell interaction and Wnt signaling.

Development of Polyhydroxyalkanoate-Based Polyurethane with Water-Thermal Response Shape-Memory Behavior as New 3D Elastomers Scaffolds

In this study, we report the synthesis of a novel bio-based material from polyhydroxyalkanoate (PHA) with good shape-memory effect (SME) and rapid recovery. In this PHA-based polyurethane (PHP), telechelic-hydroxylated polyhydroxyalkanoate (PHA-diols) and polyethylene glycol (PEG) were used as soft segments, providing thermo-responsive domains and water-responsive regions, respectively. Thus, PHP possesses good thermal-responsive SME, such as high shape fixing (>99%) and shape recovery ratio (>90%). Upon immersing in water, the storage modulus of PHP decreased considerably owing to disruption of hydrogen bonds in the PHP matrix. Their water-responsive SME is also suitable for rapid shape recovery (less than 10 s). Furthermore, these outstanding properties can trigger shape-morphing, enabling self-folding and self-expansion of shapes into three-dimensional (3D) scaffolds for potential biomedical applications.

Developing a Strontium-Releasing Graphene Oxide-/Collagen-Based Organic-Inorganic Nanobiocomposite for Large Bone Defect Regeneration via MAPK Signaling Pathway

Significant efforts have been dedicated to fabricating favorable biomaterial-based bone substitutes for the repair of large bone defects. However, the development of bone biomaterials with suitable physiochemical and osteoinductive properties remains a challenge. Here, novel strontium-graphene oxide (Sr-GO) nanocomposites that allow long-term release of Sr ions are fabricated, which are used to reinforce collagen (Col) scaffolds through covalent cross-linking. The prepared Sr-GO-Col scaffold demonstrates significantly high water retention rates and excellent mechanical properties compared with unmodified Col scaffolds. The Sr-GO-modified Col scaffolds display a strong effect on adipose-derived stem cells by facilitating cell adhesion and osteogenic differentiation and by promoting the secretion of angiogenic factors to stimulate the in vitro tube formation of endothelial cells. Additionally, the secretion of angiogenic VEGF and osteogenic BMP-2 proteins is increased, which may be attributed to the synergistic effects of GO and Sr on the activation of the MAPK signaling pathway. The Sr-GO-Col constructs were then transplanted into rat critical-size calvarial bone defects, which showed the best bone regeneration and angiogenesis outcome at 12 weeks. Moreover, histological staining results show that the Sr-GO-Col group achieved complete defect bridging with the newly formed bone tissue and the residual Sr-GO nanoparticles are phagocytosed and degraded by multinucleated giant cells. These findings reveal that the incorporation of inorganic Sr-GO nanocomposites into biocompatible Col scaffolds is a viable strategy for fabricating favorable substitutes that enhance the regeneration of large bone defects.

Roles of electrical stimulation in promoting osteogenic differentiation of BMSCs on conductive fibers

The strategy of using conductive materials in regenerating bone defects is attractive, benefiting from the bioelectricity feature of natural bone tissues. Thereby, POP conductive fibers were fabricated by coating polypyrrole (PPY) onto electrospun poly(l-lactide) (PLLA) fibers, and their potentials in promoting osteogenic differentiation of bone mesenchymal stromal cells (BMSCs) were investigated. Different from the smooth-surfaced PLLA fibers, POP fibers were rough-surfaced and favorable for protein adsorption and mineralization nucleation. When electrical stimulation (ES) was applied, the surface charges on the conductive POP fibers further promoted the protein adsorption and the mineral deposition, while the non-conductive PLLA fibers displayed no such promotion. When BMSCs were cultured on these fibers, strong cell viability was detected, indicating their good biocompatibility and cell affinity. In osteogenic differentiation studies, BMSCs demonstrated the strongest ability in differentiating toward osteoblasts when they were cultured on the POP fibers under ES, followed by the case without ES. In comparison with the conductive POP fibers, the non-conductive PLLA fibers displayed significantly weaker ability in inducing the osteogenic differentiation of BMSCs with ES being applied or not. Alongside the differentiation, both the calcium deposition on BMSC/material complexes and the intracellular Ca²⁺ concentration were identified the most abundant when BMSCs grew on the POP fibers under ES. These findings suggested that the surface charges of conductive fibers played roles in regulating protein adsorption, ion migration and nucleation, particularly under ES, which contributed much to the increased intracellular Ca²⁺ ions, and thus accelerated the osteogenic differentiation of the seeded cells. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2019.

Recent advances in functional nanostructured materials for bone-related diseases

Bone-related diseases seriously threaten people's health and research studies have been dedicated towards searching for new and effective treatment methods. Nanotechnologies have opened up a new field in recent decades and nanostructured materials, which exist in a variety of forms, are considered to be promising materials in this field. This article reviews the most recent progress in the development of nanostructured materials for bone-related diseases, including osteoporosis, osteoarthritis, bone metastasis, osteomyelitis, myeloma, and bone defects. We highlight the advantages and functions of nanostructured materials, including sustained release, bone targeting, scaffolding in bone tissue engineering, etc., in bone-related diseases. We also include the remaining challenges of these emerging materials.

A mechanically robust and flexible PEGylated poly(glycerol sebacate)/β-TCP nanoparticle composite membrane for guided bone regeneration

A PEGS/β-TCP composite membrane was fabricated by a simple prepolymer mixing-in situ crosslinking method for guided bone regeneration.

Chitosan-based asymmetric topological membranes with cell-like features for healthcare applications

Chitosan-based guided tissue regeneration (GTR) membranes are extensively used in orthopedic/stomatological regenerative medicine since chitosan shares many chemical and structural similarities with glycosaminoglycans (GAGs) in the extracellular matrix.

Engineering natural matrices with black phosphorus nanosheets to generate multi-functional therapeutic nanocomposite hydrogels

Natural matrices are engineered with black phosphorus nanosheets to generate therapeutic nanocomposite hydrogels with promising multi-functions, providing a facile and efficient therapeutic strategy for bone tissue engineering.

Incorporation of Conductive Materials into Hydrogels for Tissue Engineering Applications

In the field of tissue engineering, conductive hydrogels have been the most effective biomaterials to mimic the biological and electrical properties of tissues in the human body. The main advantages of conductive hydrogels include not only their physical properties but also their adequate electrical properties, which provide electrical signals to cells efficiently. However, when introducing a conductive material into a non-conductive hydrogel, a conflicting relationship between the electrical and mechanical properties may develop. This review examines the strengths and weaknesses of the generation of conductive hydrogels using various conductive materials such as metal nanoparticles, carbons, and conductive polymers. The fabrication method of blending, coating, and in situ polymerization is also added. Furthermore, the applications of conductive hydrogel in cardiac tissue engineering, nerve tissue engineering, and bone tissue engineering and skin regeneration are discussed in detail.

Guided bone regeneration using a hydrophilic membrane made of unsintered hydroxyapatite and poly(L-lactic acid) in a rat bone-defect model

The effectiveness of a previously developed unsintered hydroxyapatite (uHA) and poly(L-lactic acid) (PLLA) hydrophilic membrane as a resorbable barrier for guided bone regeneration (GBR) was evaluated. Critical-size 8-mm diameter bone defects were surgically generated in the parietal bones of 24 12-week-old male Wistar rats, which were then divided into three groups in which either a uHA/PLLA or a collagen membrane or no membrane (control) was placed onto the bone defect. Following sacrifice of the animals 2 or 4 weeks after surgery, bone defects were examined using microcomputed tomography and histological analysis. Bone mineral density, bone mineral content, and relative bone growth area values 2 or 4 weeks after surgery were highest in the uHA/PLLA group. Four weeks after surgery, the relative bone growth area in the uHA/PLLA group was larger than that in the collagen group. The resorbable uHA/PLLA membrane is thus potentially effective for GBR.

Effects of thermal treatment on the adhesion strength and osteoinductive activity of single-layer graphene sheets on titanium substrates

In recent years, dental implants have become the preferred approach for the restoration of missing teeth. At present, most dental implants are made of pure titanium, and are affected by peri-implantitis and bone resorption, which usually start from the implant neck, due to the complex environment in this region. To address these issues, in this study we modified the surface of titanium (Ti) implants to exploit the antibacterial and osteoinductive effects of single-layer graphene sheets. Chemical vapor deposition (CVD)-grown single-layer graphene sheets were transferred to titanium discs, and a method for improving the adhesion strength of graphene on Ti was developed due to compromised adhesion strength between graphene and titanium surface. A thermal treatment of 2 h at 160 °C was found to enhance the adhesion strength of graphene on Ti to facilitate clinical transformation. Graphene coatings of Ti enhanced cell adhesion and osteogenic differentiation, and imparted antibacterial activity to Ti substrate; these favorable effects were not affected by the thermal treatment. In summary, the present study elucidated the effects of a thermal treatment on the adhesion strength and osteoinductive activity of single-layer graphene sheets on titanium substrates.

Porous Graphene Films with Unprecedented Elastomeric Scaffold-Like Folding Behavior for Foldable Energy Storage Devices

The development of fully foldable energy storage devices is a major science and engineering challenge, but one that must be overcome if next-generation foldable or wearable electronic devices are to be realized. To overcome this challenge, it is necessary to develop new electrically conductive materials that exhibit superflexibility and can be folded or crumpled without plastic deformation or damage. Herein, a graphene film with engineered microvoids is prepared by reduction (under confinement) of its precursor graphene oxide film. The resultant porous graphene film can be single folded, double folded, and even crumpled, but springs back to its original shape without yielding or plastic deformation akin to an elastomeric scaffold after the applied stress is removed. Even after thermal annealing at ≈1300 °C, the folding performance of the porous graphene film is not compromised and the thermally annealed film exhibits complete foldability even in liquid nitrogen. A solid-state foldable supercapacitor is demonstrated with the porous graphene film as the device electrode. The capacitance performance is nearly identical after 2000 cycles of single-folding followed by another 2000 cycles of double folding.

Urethane-based low-temperature curing, highly-customized and multifunctional poly(glycerol sebacate)-co-poly(ethylene glycol) copolymers

Poly (glycerol sebacate) (PGS), a tough elastomer, has been widely explored in tissue engineering due to the desirable mechanical properties and biocompatibility. However, the complex curing procedure (high temperature and vacuum) and limited hydrophilicity (∼90° of wetting angle) greatly impede its functionalities. To address these challenges, a urethane-based low-temperature setting, PEGylated PGS bioelastomer was developed with and without solvent. By simultaneously tailoring PEG and hexamethylene diisocyanate (HDI) contents, the elastomers X-P-mUs (X referred to the PEG content and m referred to HDI content) with a broad ranging mechanical properties and customized hydrophilicity were constructed. The X-P-mUs synthesized exhibited adjustable tensile Young's modulus, ultimate tensile strength and elongation at break in the range of 1.0 MPa-14.2 MPa, 0.3 MPa-7.6 MPa and 53.6%-272.8%, with the water contact angle varying from 28.6° to 71.5°, respectively. Accordingly, these elastomers showed favorable biocompatibility in vitro and mild host response in vivo. Furthermore, the potential applications of X-P-mU elastomers prepared with solvent-base and solvent-free techniques in biomedical fields were investigated. The results showed that these X-P-mU elastomers with high molding capacity at mild temperature could be easily fabricated into various shapes, used as reinforcement for fragile materials, and controllable delivery of drugs and proteins with excellent bioactivity, demonstrating that the X-P-mU elastomers could be tailored as potential building blocks for diverse applications in biomedical research.

STATEMENT OF SIGNIFICANCE

Poly(glycerol sebacate) (PGS), a tough biodegradable elastomer, has received great attentions in biomedical field. But the complex curing procedure and limited hydrophilicity greatly hamper its functionality. Herein, a urethane-based low-temperature setting, PEGylated PGS (PEGS-U) bioelastomer with highly-customized mechanical properties, hydrophilicity and biodegradability was first explored. The synthesized PEGS-U showed favorable biocompatibility both in vitro and in vivo. Furthermore, the PEGS-U elastomer could be easily fabricated into various shapes, used as reinforcement for fragile materials, and controllable delivery of drugs and proteins with excellent bioactivity. This versatile, user-tunable bioelastomers should be a promising biomaterials for biomedical applications.

Interfacing Graphene-Based Materials With Neural Cells

The scientific community has witnessed an exponential increase in the applications of graphene and graphene-based materials in a wide range of fields, from engineering to electronics to biotechnologies and biomedical applications. For what concerns neuroscience, the interest raised by these materials is two-fold. On one side, nanosheets made of graphene or graphene derivatives (graphene oxide, or its reduced form) can be used as carriers for drug delivery. Here, an important aspect is to evaluate their toxicity, which strongly depends on flake composition, chemical functionalization and dimensions. On the other side, graphene can be exploited as a substrate for tissue engineering. In this case, conductivity is probably the most relevant amongst the various properties of the different graphene materials, as it may allow to instruct and interrogate neural networks, as well as to drive neural growth and differentiation, which holds a great potential in regenerative medicine. In this review, we try to give a comprehensive view of the accomplishments and new challenges of the field, as well as which in our view are the most exciting directions to take in the immediate future. These include the need to engineer multifunctional nanoparticles (NPs) able to cross the blood-brain-barrier to reach neural cells, and to achieve on-demand delivery of specific drugs. We describe the state-of-the-art in the use of graphene materials to engineer three-dimensional scaffolds to drive neuronal growth and regeneration in vivo, and the possibility of using graphene as a component of hybrid composites/multi-layer organic electronics devices. Last but not least, we address the need of an accurate theoretical modeling of the interface between graphene and biological material, by modeling the interaction of graphene with proteins and cell membranes at the nanoscale, and describing the physical mechanism(s) of charge transfer by which the various graphene materials can influence the excitability and physiology of neural cells.

Ultra-tough injectable cytocompatible hydrogel for 3D cell culture and cartilage repair

In this work, we developed a very facile strategy, i.e. dual dynamic crosslinking, to prepare a high performance injectable hydrogel. Poly(vinyl alcohol) (PVA) was crosslinked by 4-carboxyphenylboronic acid (CPBA) through the generation of borate bonding and ionic interaction to bridge the polymer chains in the presence of calcium ions. The dynamic gathering of CPBA could induce a self-reinforcing effect inside the hydrogel matrix, leading to high tensile and compressive moduli of the hydrogel over 1.0 MPa including the highest compressive modulus up to 5.6 MPa. Meanwhile, the mechanical properties of the hydrogel can be broadly and accurately tuned. And owing to the flexible PVA network, the hydrogel is ultra-tough, showing maximum tensile strain, tensile and compressive fracture energies up to 1600%, 600 kJ m^-2 and 25 kJ m^-2, respectively. Besides, the dynamic bonding overcomes the barriers to forming an injected strong hydrogel, e.g. to obtain a modulus and a fracture energy exceeding 1.0 MPa and 40 kJ m^-2, by using a commercial dual-syringe kit under physiological conditions. Such a mild gelation procedure benefits the administration, 3D encapsulation and proliferation of cells of the hydrogels. The application of the PVA hydrogel was demonstrated by effective cartilage repair.

Triple network hydrogels (TN gels) prepared by a one-pot, two-step method with high mechanical properties

In this work, poly(vinyl alcohol) (PVA) was incorporated into the networks of polyacrylamide/polyacrylic acid (PAM/PAA) to prepare novel PAM/PAA/PVA Triple-network (TN) hydrogels by an in situ polymerization and repeated freezing-thawing (F-T) process. The TN hydrogels have not only high mechanical strength, but also a moderate swelling ability by varying the weight ratio of calcium chloride (CaCl2) and PVA and free shaping. The compressive stress of the as-prepared hydrogels could reach 11 MPa, and the highest stretching stress could reach 0.8 MPa. Upon mechanical loading, the coordination network between PAA and CaCl2 served as sacrificial bonds to efficiently dissipate energy. However, they can reform when the mechanical load is released, resulting from the fast coordination between PAA and Ca2+. Therefore, TN hydrogels have potential application in biomaterials.

Biomaterial Cues Regulate Epigenetic State and Cell Functions-A Systematic Review

Biomaterial cues can act as potent regulators of cell niche and microenvironment. Epigenetic regulation plays an important role in cell functions, including proliferation, differentiation, and reprogramming. It is now well appreciated that biomaterials can alter epigenetic states of cells. In this study, we systematically reviewed the underlying epigenetic mechanisms of how different biomaterial cues, including material chemistry, topography, elasticity, and mechanical stimulus, influence cell functions, such as nuclear deformation, cell proliferation, differentiation, and reprogramming, to summarize the differences and similarities among each biomaterial cues and their mechanisms, and to find common and unique properties of different biomaterial cues. Moreover, this work aims to establish a mechanogenomic map facilitating highly functionalized biomaterial design, and renders new thoughts of epigenetic regulation in controlling cell fates in disease treatment and regenerative medicine.

Controlled Gelation of Graphene Towards Unprecedented Superstructures

Graphene exhibits a range of exceptional physical properties and holds great promise for development of novel bulk materials for widespread applications. Properly engineering of assembled structures of graphene at multiple length scales is essential to realize its full potential in bulk forms. In this Concept article, we highlight the unique colloidal and gelation behavior of a commonly used precursor for graphene, graphene oxide (GO), and discuss how the colloidal chemistry of GO and reduced GO can enable new scalable and cost-effective approaches to construct graphene-based soft superstructures with excellent properties.

Toward a versatile toolbox for cucurbit[n]uril-based supramolecular hydrogel networks through in situ polymerization

The success of exploiting cucurbit[n]uril (CB[n])-based molecular recognition in self-assembled systems has sparked a tremendous interest in polymer and materials chemistry. In this study, polymerization in the presence of host-guest complexes is applied as a modular synthetic approach toward a diverse set of CB[8]-based supramolecular hydrogels with desirable properties, such as mechanical strength, toughness, energy dissipation, self-healing, and shear-thinning. A range of vinyl monomers, including acrylamide-, acrylate-, and imidazolium-based hydrophilic monomers, could be easily incorporated as the polymer backbones, leading to a library of CB[8] hydrogel networks. This versatile strategy explores new horizons for the construction of supramolecular hydrogel networks and materials with emergent properties in wearable and self-healable electronic devices, sensors, and structural biomaterials. © 2017 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3105-3109.

Hierarchical Microspheres Constructed from Chitin Nanofibers Penetrated Hydroxyapatite Crystals for Bone Regeneration

Chitin exists abundantly in crab and shrimp shells as the template of the minerals, which inspired us to mineralize it for fabricating bone grafting materials. In the present work, chitin nanofibrous microspheres were used as the matrix for in situ synthesis of hydroxyapatite (HA) crystals including microflakes, submicron-needles, and submicron-spheres, which were penetrated by long chitin nanofibers, leading to the hierarchical structure. The shape and size of the HA crystals could be controlled by changing the HA synthesis process. The tight interface adhesion between chitin and HA through the noncovanlent bonds occurred in the composite microspheres, and HAs were homogeneously dispersed and bounded to the chitin nanofibers. In our findings, the inherent biocompatibilities of the both chitin and HA contributed the bone cell adhesion and osteoconduction. Moreover, the chitin microsphere with submicron-needle and submicron-sphere HA crystals remarkably promoted in vitro cell adhesion and in vivo bone healing. It was demonstrated that rabbits with 1.5 cm radius defect were almost cured completely within three months in a growth factor- and cell-free state, as a result of the unique surface microstructure and biocompatibilities of the composite microspheres. The microsphere scaffold displayed excellent biofunctions and an appropriate biodegradability. This work opened up a new avenue to construct natural polymer-based organic-inorganic hybrid microspheres for bone regeneration.

Inorganic Nanowires-Assembled Layered Paper as the Valve for Controlling Water Transportation

Layered materials with open interlayer channels enable various applications such as tissue engineering, ionic and molecular sieving, and electrochemical devices. However, most reports focus on the two-dimensional nanosheets-assembled layered materials, whose interlayer spacing is limited at the nanometer scale. Herein, we demonstrate that one-dimensional inorganic nanowires are the ideal building blocks for the construction of layered materials with open interlayer channels as well, which has not aroused much attention before. It is found that the relatively long inorganic nanowires are capable of assembling into free-standing layered paper with open interlayer channels during the filtration process. The spacings of interlayer channels between adjacent layers are up to tens of micrometers, which are much larger than those of the two-dimensional nanosheets-assembled layered materials. But the closed interlayer channels are observed when the relatively short inorganic nanowires are used as building blocks. The mechanism based on the relationship between the structural variation and the nanowires used is proposed, including the surface charge amplified effect, surface charge superimposed effect, and pillarlike supporting effect. According to the proposed mechanism, we have successfully fabricated a series of layered paper sheets whose architectures (including interlayer channels of cross section and pores on the surface) show gradient changes. The as-prepared layered paper sheets are employed as the valves for controlling water transportation. Tunable water transportation is achieved by the synergistic effect between in-plane interlayer channels (horizontal transportation) from the open to the closed states, and through-layer pores (vertical transportation) without surface modification or intercalation of any guest species.

Functional Graphene Nanomaterials Based Architectures: Biointeractions, Fabrications, and Emerging Biological Applications

Functional graphene nanomaterials (FGNs) are fast emerging materials with extremely unique physical and chemical properties and physiological ability to interfere and/or interact with bioorganisms; as a result, FGNs present manifold possibilities for diverse biological applications. Beyond their use in drug/gene delivery, phototherapy, and bioimaging, recent studies have revealed that FGNs can significantly promote interfacial biointeractions, in particular, with proteins, mammalian cells/stem cells, and microbials. FGNs can adsorb and concentrate nutrition factors including proteins from physiological media. This accelerates the formation of extracellular matrix, which eventually promotes cell colonization by providing a more beneficial microenvironment for cell adhesion and growth. Furthermore, FGNs can also interact with cocultured cells by physical or chemical stimulation, which significantly mediate their cellular signaling and biological performance. In this review, we elucidate FGNs-bioorganism interactions and summarize recent advancements on designing FGN-based two-dimensional and three-dimensional architectures as multifunctional biological platforms. We have also discussed the representative biological applications regarding these FGN-based bioactive architectures. Furthermore, the future perspectives and emerging challenges will also be highlighted. Due to the lack of comprehensive reviews in this emerging field, this review may catch great interest and inspire many new opportunities across a broad range of disciplines.

Sequential controlled-released dual-drug loaded scaffold for guided bone regeneration in a rat fenestration defect model

A 3D multifunctional scaffold, which combines the merits of osseous regeneration and local anti-inflammatory drug delivery, has been developed for GBR.

A review on the biocompatibility and potential applications of graphene in inducing cell differentiation and tissue regeneration

Advances in the biocompatibility and cell differentiation inducing capacity of graphene and its potential applications in multi-tissue regeneration.