Enhancement of primary neuronal cell proliferation using printing‐transferred carbon nanotube sheets

Advances in 3D printing combined with tissue engineering for nerve regeneration and repair

The repair of nerve damage has long posed a challenge owing to limited self-repair capacity and the highly differentiated nature of nerves. While new therapeutic and pharmacologic interventions have emerged in neurology, their regenerative efficacy remains limited. Tissue engineering offers a promising avenue for overcoming the limitations of conventional treatments and increasing the outcomes of regenerative repair. By implanting scaffolds into damaged nerve tissue sites, the repair and functional reconstruction of nerve injuries can be significantly facilitated. The integration of three-dimensional (3D) printing technology introduces a novel approach for accurate simulation and scalably fabricating neural tissue structures. Tissue-engineered scaffolds developed through 3D printing technology are expected to be a viable therapeutic option for nerve injuries, with broad applicability and continued development. This review systematically examines recent advances in 3D printing and tissue engineering for nerve regeneration and repair. It details the basic principles and construction strategies of neural tissue engineering and explores the crucial role of 3D printing technology. Additionally, it elucidates specific applications and technical challenges associated with this integrated approach, thereby providing valuable insights into innovative strategies and pragmatic implementation within this field.

Donors for nerve transplantation in craniofacial soft tissue injuries

Neural tissue is an important soft tissue; for instance, craniofacial nerves govern several aspects of human behavior, including the expression of speech, emotion transmission, sensation, and motor function. Therefore, nerve repair to promote functional recovery after craniofacial soft tissue injuries is indispensable. However, the repair and regeneration of craniofacial nerves are challenging due to their intricate anatomical and physiological characteristics. Currently, nerve transplantation is an irreplaceable treatment for segmental nerve defects. With the development of emerging technologies, transplantation donors have become more diverse. The present article reviews the traditional and emerging alternative materials aimed at advancing cutting-edge research on craniofacial nerve repair and facilitating the transition from the laboratory to the clinic. It also provides a reference for donor selection for nerve repair after clinical craniofacial soft tissue injuries. We found that autografts are still widely accepted as the first options for segmental nerve defects. However, allogeneic composite functional units have a strong advantage for nerve transplantation for nerve defects accompanied by several tissue damages or loss. As an alternative to autografts, decellularized tissue has attracted increasing attention because of its low immunogenicity. Nerve conduits have been developed from traditional autologous tissue to composite conduits based on various synthetic materials, with developments in tissue engineering technology. Nerve conduits have great potential to replace traditional donors because their structures are more consistent with the physiological microenvironment and show self-regulation performance with improvements in 3D technology. New materials, such as hydrogels and nanomaterials, have attracted increasing attention in the biomedical field. Their biocompatibility and stimuli-responsiveness have been gradually explored by researchers in the regeneration and regulation of neural networks.

A printing-spray-transfer process for attaching biocompatible and antibacterial coatings to the surfaces of patient-specific silicone stents

An antibacterial coating with stable antibacterial properties and favorable biocompatibility is recognized as an effective method to prevent bacterial adhesion and biofilm formation on biomedical implant surfaces. In this study, a convenient and low-cost printing-spray-transfer process was proposed that enables reliably attaching antibacterial and biocompatible coatings to patient-specific silicone implant surfaces. A desktop three-dimensional printer was used to print the mold of silicone implant molds according to the characteristics of the diseased areas. Multiwalled carbon nanotubes (MWCNTs) uniformly decorated with silver nanoparticles (AgNPs/CNTs) were synthesized as the antibacterial materials for the spray process. The well-distributed AgNPs/CNT coating was anchored to the silicone surface through an in-mold transfer printing process. Stable adhesion of the coatings was assessed via tape testing and UV-vis spectra. Hardly any AgNPs/CNTs peeled off the substrate, and the adhesion was rated at 4B. Antibacterial activity, Ag release, cell viability and morphology were further assessed, revealing high antibacterial activity and great biocompatibility. The process proposed herein has potential applications for fabricating stable antibacterial coatings on silicone implant surfaces, especially for patient-specific silicone implants such as silicone tracheal stents.

Biomaterial-assisted scalable cell production for cell therapy

Cell therapy, the treatment of diseases using living cells, offers a promising clinical approach to treating refractory diseases. The global market for cell therapy is growing rapidly, and there is an increasing demand for automated methods that can produce large quantities of high quality therapeutic cells. Biomaterials can be used during cell production to establish a biomimetic microenvironment that promotes cell adhesion and proliferation while maintaining target cell genotype and phenotype. Here we review recent progress and emerging techniques in biomaterial-assisted cell production. The increasing use of auxiliary biomaterials and automated production methods provides an opportunity to improve quality control and increase production efficiency using standardized GMP-compliant procedures.

Biocompatible chitin/carbon nanotubes composite hydrogels as neuronal growth substrates

In the past decades, extensive studies have demonstrated that carbon nanotubes (CNTs) could promote cell adhesion, proliferation and differentiation of neuronal cells. However, the potential cytotoxicity in biological systems severely restricted the utilization of CNTs as substrates for neural growth. In this study, biocompatible chitin/carbon nanotubes (Ch/CNT) composite hydrogels were developed via blending modified CNTs with chitin solution in 11wt% NaOH/4wt% urea aqueous system, and subsequently regenerating in ethanol. As the CNTs were dispersed homogeneously in chitin matrix and combined with chitin nanofibers to form a compact and neat Ch/CNT nanofibrous network through intermolecular interactions, such as electrostatic interactions, hydrogen bonding and amphiphilic interaction, etc. The tensile strength and elongation at break of the Ch/CNT composite hydrogels were obviously enhanced, and the swelling ratio decreased. In addition, the Ch/CNT hydrogels exhibited good hemocompatibility, biodegradation in vitro and biocompatibility without cytotoxicity and neurotoxicity nature to neuronal and Schwann cells (PC12 cells and RSC96 cells). Especially, the Ch/CNT3 composite hydrogels exhibited significant enhancement of the neuronal cell adhesion, proliferation and neurite outgrowth of neuronal cells with a great increase in both the percentage and the length of neurites. Therefore, we provide a simple and efficient approach to construct the novel Ch/CNT hydrogels as neuronal growth substrates for the potential application in nerve regeneration.

In vivo feasibility test using transparent carbon nanotube-coated polydimethylsiloxane sheet at brain tissue and sciatic nerve

Carbon nanotubes, with their unique and outstanding properties, such as strong mechanical strength and high electrical conductivity, have become very popular for the repair of tissues, particularly for those requiring electrical stimuli. Polydimethylsiloxane (PDMS)-based elastomers have been used in a wide range of biomedical applications because of their optical transparency, physiological inertness, blood compatibility, non-toxicity, and gas permeability. In present study, most of artificial nerve guidance conduits (ANGCs) are not transparent. It is hard to confirm the position of two stumps of damaged nerve during nerve surgery and the conduits must be cut open again to observe regenerative nerves after surgery. Thus, a novel preparation method was utilized to produce a transparent sheet using PDMS and multiwalled carbon nanotubes (MWNTs) via printing transfer method. Characterization of the PDMS/MWNT (PM) sheets revealed their unique physicochemical properties, such as superior mechanical strength, a certain degree of electrical conductivity, and high transparency. Characterization of the in vitro and in vivo usability was evaluated. PM sheets showed high biocompatibility and adhesive ability. In vivo feasibility tests of rat brain tissue and sciatic nerve revealed the high transparency of PM sheets, suggesting that it can be used in the further development of ANGCs. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1736-1745, 2017.

Covalent crosslinking of graphene oxide and carbon nanotube into hydrogels enhances nerve cell responses

Healing of nerve injuries is a critical medical issue. Biodegradable polymeric conduits are a promising therapeutic solution to provide guidance for axon growth in a given space, thus helping nerve heal. Extensive studies in the past decade reported that conductive materials could effectively increase neurite and axon extension in vitro and nerve regeneration in vivo. In this study, graphene oxide and carbon nanotubes were covalently functionalized with double bonds to obtain crosslinkable graphene oxide acrylate (GOa) sheets and carbon nanotube poly(ethylene glycol) acrylate (CNTpega). An electrically conductive reduced GOa-CNTpega-oligo(polyethylene glycol fumarate) (OPF) hydrogel (rGOa-CNTpega-OPF) was successfully fabricated by chemically crosslinking GOa sheets and CNTpega with OPF chains followed by in situ chemical reduction in l-ascorbic acid solution. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging showed homogenous distribution of GOa/CNTpega carbon content in the rGOa-CNTpega-OPF composite hydrogel, resulting in a significant increase of electrical conductivity compared with neutral OPF without carbon content. Cell studies showed excellent biocompatibility and distinguished PC12 cell proliferation and spreading on the rGOa-CNTpega-OPF composite hydrogel. Fluorescent microscopy imaging demonstrated robustly stimulated neurite development in these cells on a conductive rGOa-CNTpega-OPF composite hydrogel compared with that on neutral OPF hydrogels. These results illustrated a promising potential for the rGOa-CNTpega-OPF composite hydrogel to serve as conduits for neural tissue engineering.