3D Fabrication with Integration Molding of a Graphene Oxide/Polycaprolactone Nanoscaffold for Neurite Regeneration and Angiogenesis

Surface-Anchored Graphene Oxide Nanosheets on Cell-Scale Micropatterned Poly(d,l-lactide-co-caprolactone) Conduits Promote Peripheral Nerve Regeneration

Regeneration and functional recovery of peripheral nerves remain formidable due to the inefficient physical and chemical cues in the available nerve guidance conduits (NGCs). Introducing micropatterns and bioactive substances into the inner wall of NGCs can effectively regulate the behavior of Schwann cells, the elongation of axons, and the phenotype of macrophages, thereby aiding the regeneration of injured nerve. In this study, linear micropatterns with ridges and grooves of 3/3, 5/5, 10/10, and 30/30 μm were created on poly(d,l-lactide-co-caprolactone) (PLCL) films following with surface aminolysis and electrostatic adsorption of graphene oxide (GO) nanosheets. The GO-modified micropatterns could significantly accelerate the collective migration of Schwann cells (SCs) and migration of SCs from their spheroids in vitro. Moreover, the SCs migrated directionally along the stripes with a fastest rate on the 3/3-GO film that had the largest cell adhesion force. The neurites of N2a cells were oriented along the micropatterns, and the macrophages tended to differentiate into the M2 type on the 3/3-GO film judged by the higher expression of Arg 1 and IL-10. The systematic histological and functional assessments of the regenerated nerves at 4 and 8 weeks post-surgery in vivo confirmed that the 3/3-GO NGCs had better performance to promote the nerve regeneration, and the CMAP, NCV, wet weight of gastrocnemius muscle, positive S100β and NF200 area percentages, and average myelinated axon diameter were more close to those of the autograft group at 8 weeks. This type of NGCs thus has a great potential for nerve regeneration.

Methylcobalamin-Loaded PLCL Conduits Facilitate the Peripheral Nerve Regeneration

The feasible fabrication of nerve guidance conduits (NGCs) with good biological performance is important for translation in clinics. In this study, poly(d,l-lactide-co-caprolactone) (PLCL) films loaded with various amounts (wt; 5%, 15%, 25%) of methylcobalamin (MeCbl) are prepared, and are further rolled and sutured to obtain MeCbl-loaded NGCs. The MeCbl can be released in a sustainable manner up to 21 days. The proliferation and elongation of Schwann cells, and the proliferation of Neuro2a cells are enhanced on these MeCbl-loaded films. The MeCbl-loaded NGCs are implanted into rats to induce the regeneration of 10 mm amputated sciatic nerve defects, showing the ability to facilitate the recovery of motor and sensory function, and to promote myelination in peripheral nerve regeneration. In particular, the 15% MeCbl-loaded PLCL conduit exhibits the most satisfactory recovery of sciatic nerves in rats with the largest diameter and thickest myelinated fibers.

The effect of oxygen plasma pretreatment on the properties of mussel-inspired polydopamine-decorated polyurethane nanofibers

In this study, polyurethane (PU) scaffolds were fabricated by electrospinning technology and modified through the deposition of polydopamine (PDA) on the activated surface under oxygen plasma treatment. Herein, the effect of the modification process on the homogeneous surface coating and the changes in the physicochemical and biological properties were evaluated. Morphological observations demonstrated decoration of the nanofibrous microstructure with PDA, while the uniformity and homogeneity of the deposited layer increased after plasma oxygen treatment. Hydrophilicity measurements and swelling ratio indicated a remarkable improvement in the interaction of scaffolds with water molecules when the PDA coating is applied on the surface of the treated nanofibers. The biomineralization of the samples was characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) images. It was found that PDA has the capability for mineralization, and the amount of deposited hydroxyapatite increased as a function of PDA content. The in vitro evaluation of constructs indicated great improvement in cell-scaffold interactions, biocompatibility, and alkaline phosphatase activity after coating the PDA on the plasma-modified matrix. These results suggest that PDA coating, especially after oxygen plasma treatment, improves the physicochemical and in vitro properties of PU scaffolds for bone tissue engineering application.

Conductive conduit small gap tubulization for peripheral nerve repair

Despite advances in surgical techniques, functional recovery following epineurial neurorrhaphy of transected peripheral nerves often remains quite unsatisfactory. Small gap tubulisation is a promising approach that has shown potential to traditional epineurial neurorrhaphy in the treatment of peripheral nerve injury. Thus, the goal of this study is to evaluate sciatic nerve regeneration after nerve transection, followed by small gap tubulization using a reduced graphene oxide-based conductive conduit. In vitro, the electrically conductive conduit could promote Schwann cell proliferation through PI3K/Akt signaling pathway activation. In vivo, the results of electrophysiological and walking track analysis suggest that the electrically conductive conduit could promote sensory and motor nerve regeneration and functional recovery, which is based on the mechanisms of selective regeneration and multiple-bud regeneration. These promising results illustrate electrically conductive conduit small gap tubulization as an alternative approach for transected peripheral nerve repair.

rGO-based conductive nerve conduit as a scaffold to bridge peripheral nerve transected injury and 2 mm gap provides a suitable microenvironment for axons selective regeneration.

Incorporation of graphene oxide into poly(ɛ-caprolactone) 3D printed fibrous scaffolds improves their antimicrobial properties

Implantable medical devices infection and consequent failure is a severe health issue, which can result from bacterial adhesion, growth, and subsequent biofilm formation at the implantation site. Graphene-based materials, namely graphene oxide (GO), have been described as potential antibacterial agents when immobilized and exposed in polymeric matrices. This work focuses on the development of antibacterial and biocompatible 3D fibrous scaffolds incorporating GO. Poly(ε-caprolactone) scaffolds were produced, with and without GO, using wet-spinning combined with additive manufacturing. Scaffolds with different GO loadings were evaluated regarding physical-chemical characterization, namely GO surface exposure, antibacterial properties, and ability to promote human cells adhesion. Antimicrobial properties were evaluated through live/dead assays performed with Gram-positive and Gram-negative bacteria. 2 h and 24 h adhesion assays revealed a time-dependent bactericidal effect in the presence of GO, with death rates of adherent S. epidermidis and E. coli reaching ~80% after 24 h of contact with scaffolds with the highest GO concentration. Human fibroblasts cultured for up to 14 days were able to adhere and spread over the fibers, independently of the presence of GO. Overall, this work demonstrates the potential of GO-containing fibrous scaffolds to be used as biomaterials that hinder bacterial infection, while allowing human cells adhesion.

(-)-Epigallocatechin gallate-loaded polycaprolactone scaffolds fabricated using a 3D integrated moulding method alleviate immune stress and induce neurogenesis

Objectives

In peripheral neuropathy, the underlying mechanisms of nerve and muscle degeneration include chronic inflammation and oxidative stress in fibrotic tissues. (‐)‐Epigallocatechin gallate (EGCG) is a major, active component in green tea and may scavenge free radical oxygen and attenuate inflammation. Conservative treatments such as steroid injection only deal with early, asymptomatic, peripheral neuropathy. In contrast, neurolysis and nerve conduit implantation work effectively for treating advanced stages.

Materials and methods

An EGCG‐loaded polycaprolactone (PCL) porous scaffold was fabricated using an integrated moulding method. We evaluated proliferative, oxidative and inflammatory activity of rat Schwann cells (RSCs) and rat skeletal muscle cells (RSMCs) cultured on different scaffolds in vitro. In a rat radiation injury model, we assessed the morphological, electrophysiological and functional performance of regenerated sciatic nerves and gastrocnemius muscles, as well as oxidative stress and inflammation state.

Results

RSCs and RSMCs exhibited higher proliferative, anti‐oxidant and anti‐inflammatory states in an EGCG/PCL scaffold. In vivo studies showed improved nerve and muscle recovery in the EGCG/PCL group, with increased nerve myelination and muscle fibre proliferation and reduced macrophage infiltration, lipid peroxidation, inflammation and oxidative stress indicators.

Conclusions

The EGCG‐modified PCL porous nerve scaffold alleviates cellular oxidative stress and repairs peripheral nerve and muscle structure in rats. It attenuates oxidative stress and inflammation in vivo and may provide further insights into peripheral nerve repair in the future.

Three-Dimensional Printing and Injectable Conductive Hydrogels for Tissue Engineering Application

The goal of tissue engineering scaffolds is to simulate the physiological microenvironment, in which the electrical microenvironment is an important part. Hydrogel is an ideal material for tissue engineering scaffolds because of its soft, porous, water-bearing, and other extracellular matrix-like properties. However, the hydrogel matrix is usually not conductive and can hinder the communication of electrical signals between cells, which promotes researchers' attention to conductive hydrogels. Conductive hydrogels can promote the communication of electrical signals between cells and simulate the physiological microenvironment of electroactive tissues. Hydrogel formation is an important step for the application of hydrogels in tissue engineering. In situ forming of injectable hydrogels and customized forming of three-dimensional (3D) printing hydrogels represent two most potential advanced forming processes, respectively. In this review, we discuss (i) the classification, properties, and advantages of conductive hydrogels, (ii) the latest development of conductive hydrogels applied in myocardial, nerve, and bone tissue engineering, (iii) advanced forming processes, including injectable conductive hydrogels in situ and customized 3D printed conductive hydrogels, (iv) the challenges and opportunities of conductive hydrogels for tissue engineering. Impact Statement Biomimetic construction of electro-microenvironment is a challenge of tissue engineering. The development of conductive hydrogels provides possibility for the construction of biomimetic electro-microenvironment. However, the importance of conductive hydrogels in tissue engineering has not received enough attention so far. Herein, various conductive hydrogels and their tissue engineering applications are systematically reviewed. Two potential methods of conductive hydrogel forming, in situ forming of injectable conductive hydrogels and customized forming of three-dimensional printing conductive hydrogels, are introduced. The current challenges and future development directions of conductive hydrogels are comprehensively overviewed. This review provides a guideline for tissue engineering applications of conductive hydrogels.

Adaptable Microporous Hydrogels of Propagating NGF-Gradient by Injectable Building Blocks for Accelerated Axonal Outgrowth

Injectable hydrogels in regeneration medicine can potentially mimic hierarchical natural living tissue and fill complexly shaped defects with minimally invasive implantation procedures. To achieve this goal, however, the versatile hydrogels that usually possess the nonporous structure and uncontrollable spatial agent release must overcome the difficulties in low cell-penetrative rates of tissue regeneration. In this study, an adaptable microporous hydrogel (AMH) composed of microsized building blocks with opposite charges serves as an injectable matrix with interconnected pores and propagates gradient growth factor for spontaneous assembly into a complex shape in real time. By embedding gradient concentrations of growth factors into the building blocks, the propagated gradient of the nerve growth factor, integrated to the cell-penetrative connected pores constructed by the building blocks in the nerve conduit, effectively promotes cell migration and induces dramatic bridging effects on peripheral nerve defects, achieving axon outgrowth of up to 4.7 mm and twofold axon fiber intensity in 4 days in vivo. Such AMHs with intrinsic properties of tunable mechanical properties, gradient propagation of biocues and effective induction of cell migration are potentially able to overcome the limitations of hydrogel-mediated tissue regeneration in general and can possibly be used in clinical applications.

Mesoporous bioactive glass combined with graphene oxide scaffolds for bone repair

Recently there has been an increasing interest in bioactive factors with robust osteogenic ability and angiogenesis function to repair bone defects. However, previously tested factors have not achieved satisfactory results due to low loading doses and a short protein half-life. Finding a validated stable substitute for these growth factors and apply it to the construction of porous scaffolds with the dual function of osteogenesis and angiogenesis is therefore vital for bone tissue regeneration engineering. Graphene oxide (GO) has attracted increasing attention due to its good biocompatibility, osteogenic, and angiogenic functions. This study aims to design a scaffold composed of mesoporous bioactive glasses (MBG) and GO to investigate whether the composite porous scaffold promotes local angiogenesis and bone healing. Our in vitro studies demonstrate that the MBG-GO scaffolds have better cytocompatibility and higher osteogenesis differentiation ability with rat bone marrow mesenchymal stem cells (rBMSCs) than the purely MBG scaffold. Moreover, MBG-GO scaffolds promote vascular ingrowth and, importantly, enhance bone repair at the defect site in a rat cranial defect model. The new bone was fully integrated not only with the periphery but also with the center of the scaffold. From these results, it is believed that the MBG-GO scaffolds possess excellent osteogenic-angiogenic properties which will make them appealing candidates for repairing bone defects. The novelty of this research is to provide a new material to treat bone defects in the clinic.

3D Printing of Conductive Tissue Engineering Scaffolds Containing Polypyrrole Nanoparticles with Different Morphologies and Concentrations

Inspired by electrically active tissues, conductive materials have been extensively developed for electrically active tissue engineering scaffolds. In addition to excellent conductivity, nanocomposite conductive materials can also provide nanoscale structure similar to the natural extracellular microenvironment. Recently, the combination of three-dimensional (3D) printing and nanotechnology has opened up a new era of conductive tissue engineering scaffolds exhibiting optimized properties and multifunctionality. Furthermore, in the case of two-dimensional (2D) conductive film scaffolds such as periosteum, nerve membrane, skin repair, etc., the traditional preparation process, such as solvent casting, produces 2D films with defects of unequal bubbles and thickness frequently. In this study, poly-l-lactide (PLLA) conductive scaffolds incorporated with polypyrrole (PPy) nanoparticles, which have multiscale structure similar to natural tissue, were prepared by combining extrusion-based low-temperature deposition 3D printing with freeze-drying. Furthermore, we creatively integrated the advantages of 3D printing and solvent casting and successfully developed a 2D conductive film scaffold with no bubbles, uniform thickness, and good structural stability. Subsequently, the effects of concentration and morphology of PPy nanoparticles on electrical properties and mechanical properties of 3D conductive scaffolds and 2D conductive films scaffolds have been studied, which provided a new idea for the design of both 2D and 3D electroactive tissue engineering scaffolds.

Graphene-based 3D scaffolds in tissue engineering: fabrication, applications, and future scope in liver tissue engineering

Tissue engineering embraces the potential of recreating and replacing defective body parts by advancements in the medical field. Being a biocompatible nanomaterial with outstanding physical, chemical, optical, and biological properties, graphene-based materials were successfully employed in creating the perfect scaffold for a range of organs, starting from the skin through to the brain. Investigations on 2D and 3D tissue culture scaffolds incorporated with graphene or its derivatives have revealed the capability of this carbon material in mimicking in vivo environment. The porous morphology, great surface area, selective permeability of gases, excellent mechanical strength, good thermal and electrical conductivity, good optical properties, and biodegradability enable graphene materials to be the best component for scaffold engineering. Along with the apt microenvironment, this material was found to be efficient in differentiating stem cells into specific cell types. Furthermore, the scope of graphene nanomaterials in liver tissue engineering as a promising biomaterial is also discussed. This review critically looks into the unlimited potential of graphene-based nanomaterials in future tissue engineering and regenerative therapy.

In vitro and in vivo studies of electroactive reduced graphene oxide-modified nanofiber scaffolds for peripheral nerve regeneration

Graphene, as a promising biomaterial, has received great attention in biomedical fields due to its intriguing properties, especially the conductivity and biocompatibility. Given limited studies on the effects of graphene-based scaffolds on peripheral nerve regeneration in vitro and in vivo under electrical stimulation (ES), the present study was intended to systematically investigate how conductive graphene-based nanofibrous scaffolds regulate Schwann cell (SC) behavior including migration, proliferation and myelination, and PC12 cell differentiation in vitro via ES, and whether these conductive scaffolds could guide SC migration and promote nerve regeneration in vivo. Briefly, the reduced graphene oxide (RGO) was coated onto ApF/PLCL nanofibrous scaffolds via in situ redox reaction of the graphene oxide (GO). In vitro, RGO-coated ApF/PLCL (AP/RGO) scaffolds significantly enhanced SC migration, proliferation, and myelination including myelin-specific gene expression and neurotrophic factor secretion. The conditioned media of SCs cultured on AP/RGO scaffolds under ES could induce the differentiation of PC12 cells in a separate culture. In addition, PC12 cells cultured on the conductive AP/RGO scaffolds also showed elevated differentiation upon ES. In vivo implantation of the conductive AP/RGO nerve guidance conduits into rat sciatic nerve defects exhibited a similar healing capacity to autograft, which is the current gold standard in peripheral nerve regeneration. In view of the performance of AP/RGO scaffolds in modulating cell functions in vitro and promoting nerve regeneration in vivo, it is expected that the graphene-based conductive nanofibrous scaffolds would exhibit their potential in peripheral nerve repair and regeneration. STATEMENT OF SIGNIFICANCE: Despite the demonstrated capability of bridging the distal and proximal peripheral nerves, it remains a significant challenge with current artificial nerve conduits to achieve the desired physiological functions, e.g., the transmission of electrical stimuli. Herein, we explored the possibility of combining the conductive properties of graphene with electrospun nanofiber to create the electroactive biomimetic scaffolds for nerve tissue regeneration. In vitro and in vivo studies were carried out: (1) In vitro, the conductive nanofibrous scaffolds significantly promoted SC migration, proliferation and myelination including myelin specific gene expression and neurotrophicfactor secretion, and induced PC12 cell differentiation with electrical stimulation. (2) In vivo, the conductive nerve guidance conduit exhibited similar effects with the gold standard autograft. In view of the performance of this conductive scaffold in modulating the cell functions in vitro and promoting nerve regeneration in vivo, it is expected that the graphene-modified nanofibrous scaffolds will exhibit their potential in peripheral nerve repair and regeneration.

Asymmetrical 3D Nanoceria Channel for Severe Neurological Defect Regeneration

Inflammation and oxidative stress are major problems in peripheral nerve injury. Nanoceria can manipulate antioxidant factor expression, stimulate angiogenesis, and assist in axonal regeneration. We fabricate collagen/nanoceria/polycaprolactone (COL/NC/PCL) conduit by asymmetrical three-dimensional manufacture and find that this scaffold successfully improves Schwann cell proliferation, adhesion, and neural expression. In a 15-mm rat sciatic nerve defect model, we further confirm that the COL/NC/PCL conduit markedly alleviates inflammation and oxidative stress, improves microvessel growth, and contributes to functional, electrophysiological, and morphological nerve restoration in the long term. Our findings provide compelling evidence for future research in antioxidant nerve conduit for severe neurological defects.

•

Collagen/nanoceria/polycaprolactone conduit was prepared by asymmetrical fabrication

•

The scaffold induced proliferation, adhesion, and angiogenesis in nerve repair

•

The scaffold alleviated oxidative stress and inflammation in the microenvironment

Rational design of temperature-sensitive blood-vessel-embolic nanogels for improving hypoxic tumor microenvironment after transcatheter arterial embolization

Transcatheter arterial embolization (TAE) plays an important role in clinical tumor therapy by accomplishing vessel-casting embolization of tumor arteries at all levels and suppressing tumor collateral circulation and vascular re-canalization. In this study, we describe smart blood-vessel-embolic nanogels for improving the anti-tumor efficacy of TAE therapy on hepatocellular carcinoma (HCC). Methods: In this study, an in vitro model composed of two microfluidic chips was used for simulating the tumor capillary network and analyzing artery-embolization properties. Also, blood-vessel-casting embolization of renal arteries was evaluated in normal rabbits. Using a VX2 tumor-bearing rabbit model, the therapeutic efficacy of TAE on HCC was investigated for tumor growth, necrosis, and proliferation. Neovascularization and collateral circulation were evaluated by immunofluorescent detection of hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF), and CD31 following the TAE therapy of VX2 tumor-bearing rabbits. Results: Sufficient embolization of all eight levels of micro-channels was achieved in a tumor-vessel-mimetic model with two microfluidic chips using PIBI-2240, and was further confirmed in renal arteries of normal rabbit. Effective inhibition of tumor collateral circulation and vascular re-canalization was observed in VX2 tumor-bearing rabbits due to the reduced expression levels of HIF-1α, VEGF, and CD31. Conclusions: The exceptional anti-tumor effect of PIBI-2240 observed in this study suggested that it is an excellent blood-vessel-embolic material for tumor TAE therapy.