Carbon nanotubes: their potential and pitfalls for bone tissue regeneration and engineering

Nanoparticles in Bone Regeneration: A Narrative Review of Current Advances and Future Directions in Tissue Engineering

The rising demand for effective bone regeneration has underscored the limitations of traditional methods like autografts and allografts, including donor site morbidity and insufficient biological signaling. This review examines nanoparticles (NPs) in tissue engineering (TE) to address these challenges, evaluating polymers, metals, ceramics, and composites for their potential to enhance osteogenesis and angiogenesis by mimicking the extracellular matrix (ECM) nanostructure. The methods involved synthesizing and characterizing nanoparticle-based scaffoldsand integrating hydroxyapatite (HAp) with polymers to enhance mechanical properties and osteogenic potential. The results showed that these NPs significantly promote cell growth, differentiation, and bone formation, with carbon-based NPs like graphene and carbon nanotubes showing promise. NPs offer versatile, biocompatible, and customizable scaffolds that enhance drug delivery and support bone repair. Despite promising results, challenges with cytotoxicity, biodistribution, and immune responses remain. Addressing these issues through surface modifications and biocompatible molecules can improve the biocompatibility and efficacy of nanomaterials. Future research should focus on long-term in vivo studies to assess the safety and efficacy of NP-based scaffolds and explore synergistic effects with other bioactive molecules or growth factors. This review underscores the transformative potential of NPs in advancing BTE and calls for further research to optimize these technologies for clinical applications.

Detection of carbon nanotubes in bovine raw milk through Fourier transform Raman spectroscopy

The potential use of carbon-based methodologies for drug delivery and reproductive biology in cows raises concerns about residues in milk and food safety. This study aimed to assess the potential of Fourier transform Raman spectroscopy and discriminant analysis using partial least squares (PLS-DA) to detect functionalized multiwalled carbon nanotubes (MWCNT) in bovine raw milk. Oxidized MWCNT were diluted in milk at different concentrations from 25.00 to 0.01 µg/mL. Raman spectroscopy measurements and PLS-DA were performed to identify low concentrations of MWCNT in milk samples. The PLS-DA model was characterized by the analysis of the variable importance in projection (VIP) scores. All the training samples were correctly classified by the model, resulting in no false-positive or false-negative classifications. For test samples, only one false-negative result was observed, for 0.01 µg/mL MWCNT dilution. The association between Raman spectroscopy and PLS-DA was able to identify MWCNT diluted in milk samples up to 0.1 µg/mL. The PLS-DA model was built and validated using a set of test samples and spectrally interpreted based on the highest VIP scores. This allowed the identification of the vibrational modes associated with the D and G bands of MWCNT, as well as the milk bands, which were the most important variables in this analysis.

Three-dimensional printing of cell-laden bioink for blood vessel tissue engineering: influence of process parameters and components on cell viability

Three-dimensional (3D) bioprinting is a potential therapeutic method for tissue engineering owing to its ability to prepare cell-laden tissue constructs. The properties of bioink are crucial to accurately control the printing structure. Meanwhile, the effect of process parameters on the precise structure is not nonsignificant. We investigated the correlation between process parameters of 3D bioprinting and the structural response of κ-carrageenan-based hydrogels to explore the controllable structure, printing resolution, and cell survival rate. Small-diameter (<6 mm) gel filaments with different structures were printed by varying the shear stress of the extrusion bioprinter to simulate the natural blood vessel structure. The cell viability of the scaffold was evaluated. The in vitro culture of human umbilical vein endothelium cells (HUVECs) on the κ-carrageenan (kc) and composite gels (carrageenan/carbon nanotube and carrageenan/sodium alginate) demonstrated that the cell attachment and proliferation on composite gels were better than those on pure kc. Our results revealed that the carrageenan-based composite bioinks offer better printability, sufficient mechanical stiffness, interconnectivity, and biocompatibility. This process can facilitate precise adjustment of the pore size, porosity, and pore distribution of the hydrogel structure by optimising the printing parameters as well as realise the precise preparation of the internal structure of the 3D hydrogel-based tissue engineering scaffold. Moreover, we obtained perfused tubular filament by 3D printing at optimal process parameters.

An update on the advances in the field of nanostructured drug delivery systems for a variety of orthopedic applications

Nanotechnology has made significant progress in various fields, including medicine, in recent times. The application of nanotechnology in drug delivery has sparked a lot of research interest, especially due to its potential to revolutionize the field. Researchers have been working on developing nanomaterials with distinctive characteristics that can be utilized in the improvement of drug delivery systems (DDS) for the local, targeted, and sustained release of drugs. This approach has shown great potential in managing diseases more effectively with reduced toxicity. In the medical field of orthopedics, the use of nanotechnology is also being explored, and there is extensive research being conducted to determine its potential benefits in treatment, diagnostics, and research. Specifically, nanophase drug delivery is a promising technique that has demonstrated the capability of delivering medications on a nanoscale for various orthopedic applications. In this article, we will explore current advancements in the area of nanostructured DDS for orthopedic use.

Artificial Periosteum with Oriented Surface Nanotopography and High Tissue Adherent Property

Massive periosteal defects often significantly impair bone regeneration and repair, which have become a major clinical challenge. Unfortunately, current engineered periosteal materials can hardly currently focus on achieving high tissue adhesion property, being suitable for cell growth, and inducing cell orientation concurrently to meet the properties of nature periosteum. Additionally, the preparation of oriented surface nanotopography often relies on professional equipment. In this study, inspired by the oriented collagen structure of nature periosteum, we present a composite artificial periosteum with a layer of oriented nanotopography surface containing carbon nanotubes (CNTs), cross-linked with adhesive polydopamine (PDA) hydrogel on both terminals. An oriented surface structure that can simulate the oriented alignment of periosteal collagen fibers can be quickly and conveniently obtained via a simple stretching of the membrane in a water bath. With the help of CNTs, our artificial periosteum exhibits sufficient mechanical strength and desired oriented nanotopological structure surface, which further induces the directional arrangement of human bone marrow mesenchymal stem cells (hBMSCs) on the membrane. These oriented hBMSCs express significantly higher levels of osteogenic genes and proteins, while the resultant composite periosteum can be stably immobilized in vivo in the rat model of massive calvarial defect through the PDA hydrogel, which finally shows promising bone regeneration ability. We anticipate that the developed functional artificial periosteum has great potential in biomedical applications for the treatment of composite defects of the bone and periosteum.

Evaluation of polyetheretherketone composites modified by calcium silicate and carbon nanotubes for bone regeneration: mechanical properties, biomineralization and induction of osteoblasts

Desired orthopedic implant materials must have a good biological activity and possess appropriate mechanical property that correspond to those of human bone. Although polyetheretherketone (PEEK) has displayed a promising application prospect in musculoskeletal and dentistry reconstruction thanks to its non-biodegradability and good biocompatibility in the body, the poor osseointegration and insufficient mechanical strength have significantly limited its application in the repair of load-bearing bones and surgical operations. In this study, carbon nanotubes (CNT)/calcium silicate (CS)/polyetheretherketone ternary composites were fabricated for the first time. The addition of CS was mainly aimed at improving biological activities and surface hydrophilicity, but it inevitably compromised the mechanical strength of PEEK. CNT can reinforce the composites even when brittle CS was introduced and further upgraded the biocompatibility of PEEK. The CNT/CS/PEEK composites exhibited higher mechanical strengths in tensile and bending tests, 64% and 90% higher than those of brittle CS/PEEK binary composites. Besides, after incorporation of CNT and CS into PEEK, the hydrophilicity, surface roughness and ability to induce apatite-layer deposition were significantly enhanced. More importantly, the adhesion, proliferation, and osteogenic differentiation of mouse embryo osteoblasts were effectively promoted on CNT/CS/PEEK composites. In contrast to PEEK, these composites exhibited a more satisfactory biocompatibility and osteoinductive activity. Overall, these results demonstrate that ternary CNT/CS/PEEK composites have the potential to serve as a feasible substitute to conventional metal alloys in musculoskeletal regeneration and orthopedic implantation.

Enhanced Cartilage and Subchondral Bone Repair Using Carbon Nanotube-Doped Peptide Hydrogel-Polycaprolactone Composite Scaffolds

A carbon nanotube-doped octapeptide self-assembled hydrogel (FEK/C) and a hydrogel-based polycaprolactone PCL composite scaffold (FEK/C3-S) were developed for cartilage and subchondral bone repair. The composite scaffold demonstrated modulated microstructure, mechanical properties, and conductivity by adjusting CNT concentration. In vitro evaluations showed enhanced cell proliferation, adhesion, and migration of articular cartilage cells, osteoblasts, and bone marrow mesenchymal stem cells. The composite scaffold exhibited good biocompatibility, low haemolysis rate, and high protein absorption capacity. It also promoted osteogenesis and chondrogenesis, with increased mineralization, alkaline phosphatase (ALP) activity, and glycosaminoglycan (GAG) secretion. The composite scaffold facilitated accelerated cartilage and subchondral bone regeneration in a rabbit knee joint defect model. Histological analysis revealed improved cartilage tissue formation and increased subchondral bone density. Notably, the FEK/C3-S composite scaffold exhibited the most significant cartilage and subchondral bone formation. The FEK/C3-S composite scaffold holds great promise for cartilage and subchondral bone repair. It offers enhanced mechanical support, conductivity, and bioactivity, leading to improved tissue regeneration. These findings contribute to the advancement of regenerative strategies for challenging musculoskeletal tissue defects.

Early In Vivo Osteogenic and Inflammatory Response of 3D Printed Polycaprolactone/Carbon Nanotube/Hydroxyapatite/Tricalcium Phosphate Composite Scaffolds

The development of advanced biomaterials and manufacturing processes to fabricate biologically and mechanically appropriate scaffolds for bone tissue is a significant challenge. Polycaprolactone (PCL) is a biocompatible and degradable polymer used in bone tissue engineering, but it lacks biofunctionalization. Bioceramics, such as hydroxyapatite (HA) and β tricalcium phosphate (β-TCP), which are similar chemically to native bone, can facilitate both osteointegration and osteoinduction whilst improving the biomechanics of a scaffold. Carbon nanotubes (CNTs) display exceptional electrical conductivity and mechanical properties. A major limitation is the understanding of how PCL-based scaffolds containing HA, TCP, and CNTs behave in vivo in a bone regeneration model. The objective of this study was to evaluate the use of three-dimensional (3D) printed PCL-based composite scaffolds containing CNTs, HA, and β-TCP during the initial osteogenic and inflammatory response phase in a critical bone defect rat model. Gene expression related to early osteogenesis, the inflammatory phase, and tissue formation was evaluated using quantitative real-time PCR (RT-qPCR). Tissue formation and mineralization were assessed by histomorphometry. The CNT+HA/TCP group presented higher expression of osteogenic genes after seven days. The CNT+HA and CNT+TCP groups stimulated higher gene expression for tissue formation and mineralization, and pro- and anti-inflammatory genes after 14 and 30 days. Moreover, the CNT+TCP and CNT+HA/TCP groups showed higher gene expressions related to M1 macrophages. The association of CNTs with ceramics at 10wt% (CNT+HA/TCP) showed lower expressions of inflammatory genes and higher osteogenic, presenting a positive impact and balanced cell signaling for early bone formation. The association of CNTs with both ceramics promoted a minor inflammatory response and faster bone tissue formation.

A non-invasive smart scaffold for bone repair and monitoring

Existing strategies for bone defect repair are difficult to monitor. Smart scaffold materials that can quantify the efficiency of new bone formation are important for bone regeneration and monitoring. Carbon nanotubes (CNT) have promising bioactivity and electrical conductivity. In this study, a noninvasive and intelligent monitoring scaffold was prepared for bone regeneration and monitoring by integrating carboxylated CNT into chemically cross-linked carboxymethyl chitosan hydrogel. CNT scaffold (0.5% w/v) demonstrated improved mechanical properties with good biocompatibility and electrochemical responsiveness. Cyclic voltammetry and electrochemical impedance spectroscopy of CNT scaffold responded sensitively to seed cell differentiation degree in both cellular and animal levels. Interestingly, the CNT scaffold could make up the easy deactivation shortfall of bone morphogenetic protein 2 by sustainably enhancing stem cell osteogenic differentiation and new bone tissue formation through CNT roles. This research provides new ideas for the development of noninvasive and electrochemically responsive bioactive scaffolds, marking an important step in the development of intelligent tissue engineering.

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Existing strategies for bone defect repair are difficult to monitor.

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In this study, a noninvasive and intelligent monitoring scaffold was prepared for bone regeneration and monitoring.

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This scaffold was a combination of CNT integrated into a chemically cross-linked carboxymethyl chitosan hydrogel.

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CNT scaffold showed improved mechanical properties with biocompatibility and electrochemical responsiveness.

Single-Walled Carbon Nanotube Membranes Accelerate Active Osteogenesis in Bone Defects: Potential of Guided Bone Regeneration Membranes

Carbon nanotubes (CNTs) are potentially important biomaterials because of their chemical, physical, and biological properties. Our research indicates that CNTs exhibit high compatibility with bone tissue. The guided bone regeneration (GBR) technique is commonly applied to reconstruct alveolar bone and treat peri-implant bone defects. In GBR, bone defects are covered with a barrier membrane to prevent the entry of nonosteogenic cells such as epithelial cells and fibroblasts. The barrier membrane also maintains a space for new bone formation. However, the mechanical and biological properties of materials previously used in clinical practice sometimes delayed bone regeneration. In this study, we developed a CNT-based membrane for GBR exhibiting high strength to provide a space for bone formation and provide cellular shielding to induce osteogenesis. The CNT membrane was made via the dispersion of single-walled CNTs (SWCNTs) in hyaluronic acid solution followed by filtration. The CNT membrane assumed a nanostructure surface due to the bundled SWCNTs and exhibited high strength and hydrophilicity after oxidation. In addition, the membrane promoted the proliferation of osteoblasts but not nonosteogenic cells. CNT membranes were used to cover experimental bone defects made in rat calvaria. At 8 weeks after surgery, more extensive bone formation was observed in membrane-covered defects compared with bone defects not covered with membrane. Almost no diffusion of CNTs was observed around the membrane. These results indicate that the CNT membrane has adequate strength, stability, and surface characteristics for osteoblasts, and its shielding properties promote bone formation. Demonstration of the safety and osteogenic potential of the CNT membranes through further animal studies should facilitate their clinical application in GBR.

Laser Technology for the Formation of Bioelectronic Nanocomposites Based on Single-Walled Carbon Nanotubes and Proteins with Different Structures, Electrical Conductivity and Biocompatibility

A laser technology for creating nanocomposites from alternating layers of albumin/collagen proteins with two types of single-walled carbon nanotubes (SWCNT) at concentrations of 0.001 and 0.01 wt.% was proposed. For this purpose, a setup with a diode laser (810 nm) and feedback system for controlling the temperature of the area affected by the radiation was developed. Raman spectroscopy was used to determine a decrease in the defectiveness of SWCNT with an increase in their concentration in the nanocomposite due to the formation of branched 3D networks with covalent bonds between nanotubes. It was revealed that adhesion of proteins to branched 3D networks from SWCNT occurred. The specific electrical conductivity of nanocomposites based on large SWCNT nanotubes was 3.2 and 4.3 S/m compared to that for nanocomposites based on small SWCNT with the same concentrations—1.1 and 1.8 S/m. An increase in the concentration and size of nanotubes provides higher porosity of nanocomposites. For small SWCNT-based nanocomposites, a significant number of mesopores up to 50 nm in size and the largest specific surface area and specific pore volume were found. Nanocomposites with small SWCNT (0.001 wt.%) provided the best cardiac fibroblast viability. Such technology can be potentially used to create bioelectronic components or scaffolds for heart tissue engineering.

Carbon nanomaterials for cardiovascular theranostics: Promises and challenges

Cardiovascular diseases (CVDs) are the leading cause of death worldwide. Heart attack and stroke cause irreversible tissue damage. The currently available treatment options are limited to "damage-control" rather than tissue repair. The recent advances in nanomaterials have offered novel approaches to restore tissue function after injury. In particular, carbon nanomaterials (CNMs) have shown significant promise to bridge the gap in clinical translation of biomaterial based therapies. This family of carbon allotropes (including graphenes, carbon nanotubes and fullerenes) have unique physiochemical properties, including exceptional mechanical strength, electrical conductivity, chemical behaviour, thermal stability and optical properties. These intrinsic properties make CNMs ideal materials for use in cardiovascular theranostics. This review is focused on recent efforts in the diagnosis and treatment of heart diseases using graphenes and carbon nanotubes. The first section introduces currently available derivatives of graphenes and carbon nanotubes and discusses some of the key characteristics of these materials. The second section covers their application in drug delivery, biosensors, tissue engineering and immunomodulation with a focus on cardiovascular applications. The final section discusses current shortcomings and limitations of CNMs in cardiovascular applications and reviews ongoing efforts to address these concerns and to bring CNMs from bench to bedside.

An Overview of Antimicrobial Properties of Carbon Nanotubes-Based Nanocomposites

The development of carbon-based nanomaterials has extensively facilitated new discoveries in various fields. Carbon nanotube-based nanocomposites (CNT-based nanocomposites) have lately recognized as promising biomaterials for a wide range of biomedical applications due to their unique electronic, mechanical, and biological properties. Nanocomposite materials such as silver nanoparticles (AgNPs), polymers, biomolecules, enzymes, and peptides have been reported in many studies, possess a broad range of antibacterial activity when incorporated with carbon nanotubes (CNTs). It is crucial to understand the mechanism which governs the antimicrobial activity of these CNT-based nanocomposite materials, including the decoupling individual and synergistic effects on the cells. In this review, the interaction behavior between microorganisms and different types of CNT-based nanocomposites is summarized to understand the respective antimicrobial performance in different conditions. Besides, the current development stage of CNT-based nanocomposite materials, the technical challenges faced, and the exceptional prospect of implementing potential antimicrobial CNT-based nanocomposite materials are also discussed.

Development of Porous Photopolymer Resin-SWCNT Produced by Digital Light Processing Technology Using for Bone Femur Application

BACKGROUND

Although bone tissue has the unique characteristic of self-repair in fractures, bone grafting is needed in some situations. The synthetic substances that are used in such situations should bond to the porous bones, be biocompatible and biodegradable, and do not stimulate the immune responses. Biomaterial engineering is the science of finding and designing novel products. In principle, the most suitable biodegradable matrix should have adequate compressive strength of more than two megapascals. At this degradation rate, the matrix can eventually be replaced by the newly formed bone, and the osteoprogenitor cells migrate into the scaffold. This study aimed to evaluate the fabrication of a scaffold made of polymer-ceramic nanomaterials with controlled porosity resembling that of spongy bone tissue.

METHODS

A compound of resin polymer, single-walled carbon nanotube (SWCNT) as reinforcement, and hydroxyapatite (HA) were dissolved using an ultrasonic and magnetic stirrer. A bio-nano-composite scaffold model was designed in the SolidWorks software and built using the digital light processing (DLP) method. Polymer-HA scaffolds with the solvent system were prepared with similar porosity to that of human bones.

RESULTS

HA-polymer scaffolds had a random irregular microstructure with homogenizing porous architecture. The SWCNT improved the mechanical properties of the sample from 25 MPa to 36 MPa besides having a proper porosity value near 55%, which can enhance the transformation and absorption of protein in human bone.

CONCLUSION

The combined bio-nanocomposite had a suitable porous structure with acceptable strength that allowed it to be used as a bone substitute in orthopedic surgery.

[Advantages and challenges of carbon nanotubes as bone repair materials]

With the in-depth research on bone repair process, and the progress in bone repair materials preparation and characterization, a variety of artificial bone substitutes have been fully developed in the treatment of bone related diseases such as bone defects. However, the current various natural or synthetic biomaterials are still unable to achieve the structure and properties of natural bone. Carbon nanotubes (CNTs) have provided a new direction for the development of new materials in the field of bone repair due to their excellent structural stability, mechanical properties, and functional group modifiability. Moreover, CNTs and their composites have broad prospects in the design of bone repair materials and as drug delivery carriers. This paper describes the advantages of CNTs related to bone tissue regeneration from the aspects of morphology, chemistry, mechanics, electromagnetism, and biosafety, as well as the application of CNTs in drug delivery carriers and reinforcement components of scaffold materials. In addition, the potential problems and prospects of CNTs in bone regenerative medicine are discussed.

The effect of carbon nanotubes on osteogenic functions of adipose-derived mesenchymal stem cells in vitro and bone formation in vivo compared with that of nano-hydroxyapatite and the possible mechanism

It has been well recognized that the development and use of artificial materials with high osteogenic ability is one of the most promising means to replace bone grafting that has exhibited various negative effects. The biomimetic features and unique physiochemical properties of nanomaterials play important roles in stimulating cellular functions and guiding tissue regeneration. But efficacy degree of some nanomaterials to promote specific tissue formation is still not clear. We hereby comparatively studied the osteogenic ability of our treated multi-walled carbon nanotubes (MCNTs) and the main inorganic mineral component of natural bone, nano-hydroxyapatite (nHA) in the same system, and tried to tell the related mechanism. In vitro culture of human adipose-derived mesenchymal stem cells (HASCs) on the MCNTs and nHA demonstrated that although there was no significant difference in the cell adhesion amount between on the MCNTs and nHA, the cell attachment strength and proliferation on the MCNTs were better. Most importantly, the MCNTs could induce osteogenic differentiation of the HASCs better than the nHA, the possible mechanism of which was found to be that the MCNTs could activate Notch involved signaling pathways by concentrating more proteins, including specific bone-inducing ones. Moreover, the MCNTs could induce ectopic bone formation in vivo while the nHA could not, which might be because MCNTs could stimulate inducible cells in tissues to form inductive bone better than nHA by concentrating more proteins including specific bone-inducing ones secreted from M2 macrophages. Therefore, MCNTs might be more effective materials for accelerating bone formation even than nHA.

Paramagnetic Functionalization of Biocompatible Scaffolds for Biomedical Applications: A Perspective

The burst of research papers focused on the tissue engineering and regeneration recorded in the last years is justified by the increased skills in the synthesis of nanostructures able to confer peculiar biological and mechanical features to the matrix where they are dispersed. Inorganic, organic and hybrid nanostructures are proposed in the literature depending on the characteristic that has to be tuned and on the effect that has to be induced. In the field of the inorganic nanoparticles used for decorating the bio-scaffolds, the most recent contributions about the paramagnetic and superparamagnetic nanoparticles use was evaluated in the present contribution. The intrinsic properties of the paramagnetic nanoparticles, the possibility to be triggered by the simple application of an external magnetic field, their biocompatibility and the easiness of the synthetic procedures for obtaining them proposed these nanostructures as ideal candidates for positively enhancing the tissue regeneration. Herein, we divided the discussion into two macro-topics: the use of magnetic nanoparticles in scaffolds used for hard tissue engineering for soft tissue regeneration.

Exploring the effectiveness of incorporating carbon nanotubes into bioengineered scaffolds to improve cardiomyocyte function

INTRODUCTION

Carbon nanotubes are effective in improving scaffolds to enhance cardiomyocyte function and hold great promise in the field of cardiac tissue engineering.

AREAS COVERED

A PubMed and Google Scholar search was performed to find relevant literature. 18 total studies were used as primary literature. The literature revealed that the incorporation of carbon nanotube into biocompatible scaffolds that mimic myocardial extracellular matrix enhanced the ability to promote cell functions by improving physical profiles of scaffolds. Several studies showed improved scaffold conductance, mechanical strength, improvements in cell properties such as viability, and beating behavior of cells grown on carbon nanotube incorporated scaffolds. Carbon nanotubes present a unique opportunity in the world of tissue engineering through reparation and regeneration of the myocardium, an otherwise irreparable tissue.

EXPERT OPINION

The high burden of cardiovascular disease has prompted research into cardiac tissue engineering applications. Carbon-nanotube incorporation into extracellular matrix-mimicking-scaffolds has shown to improve cardiomyocyte conductivity, viability, mechanical strength, beating behavior, and have protected them from damage to a certain degree. These are promising findings that have the potential of becoming the focus of future cardiac tissue engineering research.

Mimicking the electrophysiological microenvironment of bone tissue using electroactive materials to promote its regeneration

The process of bone tissue repair and regeneration is complex and requires a variety of physiological signals, including biochemical, electrical and mechanical signals, which collaborate to ensure functional recovery. The inherent piezoelectric properties of bone tissues can convert mechanical stimulation into electrical effects, which play significant roles in bone maturation, remodeling and reconstruction. Electroactive materials, including conductive materials, piezoelectric materials and electret materials, can simulate the physiological and electrical microenvironment of bone tissue, thereby promoting bone regeneration and reconstruction. In this paper, the structures and performances of different types of electroactive materials and their applications in the field of bone repair and regeneration are reviewed, particularly by providing the results from in vivo evaluations using various animal models. Their advantages and disadvantages as bone repair materials are discussed, and the methods for tuning their performances are also described, with the aim of providing an up-to-date account of the proposed topics.

Carbon nanotubes and their polymeric composites: the applications in tissue engineering

Carbon nanotubes (CNTs), with unique graphitic structure, superior mechanical, electrical, optical and biological properties, has attracted more and more interests in biomedical applications, including gene/drug delivery, bioimaging, biosensor and tissue engineering. In this review, we focus on the role of CNTs and their polymeric composites in tissue engineering applications, with emphasis on their usages in the nerve, cardiac and bone tissue regenerations. The intrinsic natures of CNTs including their physical and chemical properties are first introduced, explaining the structure effects on CNTs electrical conductivity and various functionalization of CNTs to improve their hydrophobic characteristics. Biosafety issues of CNTs are also discussed in detail including the potential reasons to induce the toxicity and their potential strategies to minimise the toxicity effects. Several processing strategies including solution-based processing, polymerization, melt-based processing and grafting methods are presented to show the 2D/3D construct formations using the polymeric composite containing CNTs. For the sake of improving mechanical, electrical and biological properties and minimising the potential toxicity effects, recent advances using polymer/CNT composite the tissue engineering applications are displayed and they are mainly used in the neural tissue (to improve electrical conductivity and biological properties), cardiac tissue (to improve electrical, elastic properties and biological properties) and bone tissue (to improve mechanical properties and biological properties). Current limitations of CNTs in the tissue engineering are discussed and the corresponded future prospective are also provided. Overall, this review indicates that CNTs are promising “next-generation” materials for future biomedical applications.

Nanomaterial-based scaffolds for bone tissue engineering and regeneration

The global incidence of bone tissue injuries has been increasing rapidly in recent years, making it imperative to develop suitable bone grafts for facilitating bone tissue regeneration. It has been demonstrated that nanomaterials/nanocomposites scaffolds can more effectively promote new bone tissue formation compared with micromaterials. This may be attributed to their nanoscaled structural and topological features that better mimic the physiological characteristics of natural bone tissue. In this review, we examined the current applications of various nanomaterial/nanocomposite scaffolds and different topological structures for bone tissue engineering, as well as the underlying mechanisms of regeneration. The potential risks and toxicity of nanomaterials will also be critically discussed. Finally, some considerations for the clinical applications of nanomaterials/nanocomposites scaffolds for bone tissue engineering are mentioned.

Injectable Electrical Conductive and Phosphate Releasing Gel with Two-Dimensional Black Phosphorus and Carbon Nanotubes for Bone Tissue Engineering

Injectable hydrogels have unique advantages for the repair of irregular tissue defects. In this study, we report a novel injectable carbon nanotube (CNT) and black phosphorus (BP) gel with enhanced mechanical strength, electrical conductivity, and continuous phosphate ion release for tissue engineering. The gel utilized biodegradable oligo(poly(ethylene glycol) fumarate) (OPF) polymer as the cross-linking matrix, with the addition of cross-linkable CNT-poly(ethylene glycol)-acrylate (CNTpega) to grant mechanical support and electric conductivity. Two-dimensional (2D) black phosphorus nanosheets were also infused to aid in tissue regeneration through the steady release of phosphate that results from environmental oxidation of phosphorus in situ. This newly developed BP-CNTpega-gel was found to enhance the adhesion, proliferation, and osteogenic differentiation of MC3T3 preosteoblast cells. With electric stimulation, the osteogenesis of preosteoblast cells was further enhanced with elevated expression of several key osteogenic pathway genes. As monitored with X-ray imaging, the BP-CNTpega-gel demonstrated excellent in situ gelation and cross-linking to fill femur defects, vertebral body cavities, and posterolateral spinal fusion sites in the rabbit. Together, these results indicate that this newly developed injectable BP-CNTpega-gel owns promising potential for future bone and broad types of tissue engineering applications.

Carbon Nanotube/Poly(dimethylsiloxane) Composite Materials to Reduce Bacterial Adhesion

Different studies have shown that the incorporation of carbon nanotubes (CNTs) into poly(dimethylsiloxane) (PDMS) enables the production of composite materials with enhanced properties, which can find important applications in the biomedical field. In the present work, CNT/PDMS composite materials have been prepared to evaluate the effects of pristine and chemically functionalized CNT incorporation into PDMS on the composite's thermal, electrical, and surface properties on bacterial adhesion in dynamic conditions. Initial bacterial adhesion was studied using a parallel-plate flow chamber assay performed in conditions prevailing in urinary tract devices (catheters and stents) using Escherichia coli as a model organism and PDMS as a control due to its relevance in these applications. The results indicated that the introduction of the CNTs in the PDMS matrix yielded, in general, less bacterial adhesion than the PDMS alone and that the reduction could be dependent on the surface chemistry of CNTs, with less adhesion obtained on the composites with pristine rather than functionalized CNTs. It was also shown CNT pre-treatment and incorporation by different methods affected the electrical properties of the composites when compared to PDMS. Composites enabling a 60% reduction in cell adhesion were obtained by CNT treatment by ball-milling, whereas an increase in electrical conductivity of seven orders of magnitude was obtained after solvent-mediated incorporation. The results suggest even at low CNT loading values (1%), these treatments may be beneficial for the production of CNT composites with application in biomedical devices for the urinary tract and for other applications where electrical conductance is required.

Silymarin effect on experimental bone defect repair in rat following implantation of the electrospun PLA/carbon nanotubes scaffold associated with Wharton's jelly mesenchymal stem cells

In this study, the ability of silymarin to heal rat calvarial bone critical defects with mesenchymal stem cells isolated from human Wharton's jelly (HWJMSC) cultured on the electrospun scaffold of poly (lactic acid)/carbon nanotube (PLA/CNT) has been examined. In this study, 20 adult male Wistar rats were divided into four groups of five each. Under general anesthesia, 8 mm defects were created in the calvarial bone of the rats. Then, study groups were defined as no treatment group, the scaffold alone, the scaffold and HWJMSCs, and the scaffold/cells plus oral silymarin, respectively. The histomorphometric study was performed using H&E staining and Goldner's Masson trichrome as specific staining. The results of this study showed that the electrospun PLA/CNT scaffold is a biocompatible scaffold and HWJMSCs can considerably attach and proliferate on this scaffold, and the scaffold itself is also a suitable option for improving the bone repair process. The results of the histomorphometric analysis also showed a significantly higher amount of recently formed bone in the silymarin group plus scaffold/cells compared to the scaffold and cell group alone (p < .05). Utilizing silymarin plus HWJMSCs cultured on PLA/CNT scaffold can be used as a suitable method for the process of osteogenesis and bone repair.

Study on osteogenesis of zinc-loaded carbon nanotubes/chitosan composite biomaterials in rat skull defects

Chitosan with hydroxyapatite composition, a natural polymer, may be a biomaterial of importance for bone regeneration. Carbon nanotube, a nanoscale material, has been another focus for bone restoration. Zinc, an essential trace element, contributes to the development and growth of skeletal system. The purpose of the current research was to investigate the effects of Zinc-loaded Carbon Nanotubes/Chitosan composite biomaterials in the restoration of rat skull defects, and to verify the hypothesis that these zinc ions of appropriate concentration would strengthen the osteogenesis of rat defects. Four different groups of composite biomaterials were fabricated from no Zinc Carbon nanotubes/Chitosan (GN), 0.2% Zinc-Carbon nanotubes/Chitosan (GL), 1% Zinc-Carbon nanotubes/Chitosan (GM) and 2% Zinc-Carbon nanotubes/Chitosan (GH). After characterizations, these composite biomaterials were then transplanted into rat skull defects. The experimental animals were executed at 12 weeks after transplanted surgeries, and the rat skull defects were removed for related analyses. The results of characterizations suggested the Zinc-loaded composite biomaterials possessed good mechanical and osteoinductive properties. An important finding was that the optimal osteogenic effect appeared in rat skull defects transplanted with 1% Zinc-Carbon nanotubes/Chitosan. Overall, these composite biomaterials revealed satisfactory osteogenesis, nevertheless, there was a requirement to further perfect the zinc ion concentrations to achieve the better bone regeneration.

Aligned multi-walled carbon nanotubes with nanohydroxyapatite in a 3D printed polycaprolactone scaffold stimulates osteogenic differentiation

The development of highly biomimetic scaffolds in terms of composition and structures, to repair or replace damaged bone tissues, is particularly relevant for tissue engineering. This paper investigates a 3D printed porous scaffold containing aligned multi-walled carbon nanotubes (MWCNTs) and nano-hydroxyapatite (nHA), mimicking the natural bone tissue from the nanoscale to macroscale level. MWCNTs with similar dimensions as collagen fibres are coupled with nHA and mixed within a polycaprolactone (PCL) matrix to produce scaffolds using a screw-assisted extrusion-based additive manufacturing system. Scaffolds with different material compositions were extensively characterised from morphological, mechanical and biological points of views. Transmission electron microscopy and polarised Raman spectroscopy confirm the presence of aligned MWCNTs within the printed filaments. The PCL/HA/MWCNTs scaffold are similar to the nanostructure of native bone and shows overall increased mechanical properties, cell proliferation, osteogenic differentiation and scaffold mineralisation, indicating a promising approach for bone tissue regeneration.

Nanomaterials for bone tissue regeneration: updates and future perspectives

Joint replacement and bone reconstructive surgeries are on the rise globally. Current strategies for implants and bone regeneration are associated with poor integration and healing resulting in repeated surgeries. A multidisciplinary approach involving basic biological sciences, tissue engineering, regenerative medicine and clinical research is required to overcome this problem. Considering the nanostructured nature of bone, expertise and resources available through recent advancements in nanobiotechnology enable researchers to design and fabricate devices and drug delivery systems at the nanoscale to be more compatible with the bone tissue environment. The focus of this review is to present the recent progress made in the rationale and design of nanomaterials for tissue engineering and drug delivery relevant to bone regeneration.

Applications of Carbon Nanotubes in Bone Tissue Regeneration and Engineering: Superiority, Concerns, Current Advancements, and Prospects

With advances in bone tissue regeneration and engineering technology, various biomaterials as artificial bone substitutes have been widely developed and innovated for the treatment of bone defects or diseases. However, there are no available natural and synthetic biomaterials replicating the natural bone structure and properties under physiological conditions. The characteristic properties of carbon nanotubes (CNTs) make them an ideal candidate for developing innovative biomimetic materials in the bone biomedical field. Indeed, CNT-based materials and their composites possess the promising potential to revolutionize the design and integration of bone scaffolds or implants, as well as drug therapeutic systems. This review summarizes the unique physicochemical and biomedical properties of CNTs as structural biomaterials and reinforcing agents for bone repair as well as provides coverage of recent concerns and advancements in CNT-based materials and composites for bone tissue regeneration and engineering. Moreover, this review discusses the research progress in the design and development of novel CNT-based delivery systems in the field of bone tissue engineering.

Electrically Conductive Materials: Opportunities and Challenges in Tissue Engineering

Tissue engineering endeavors to regenerate tissues and organs through appropriate cellular and molecular interactions at biological interfaces. To this aim, bio-mimicking scaffolds have been designed and practiced to regenerate and repair dysfunctional tissues by modifying cellular activity. Cellular activity and intracellular signaling are performances given to a tissue as a result of the function of elaborated electrically conductive materials. In some cases, conductive materials have exhibited antibacterial properties; moreover, such materials can be utilized for on-demand drug release. Various types of materials ranging from polymers to ceramics and metals have been utilized as parts of conductive tissue engineering scaffolds, having conductivity assortments from a range of semi-conductive to conductive. The cellular and molecular activity can also be affected by the microstructure; therefore, the fabrication methods should be evaluated along with an appropriate selection of conductive materials. This review aims to address the research progress toward the use of electrically conductive materials for the modulation of cellular response at the material-tissue interface for tissue engineering applications.

Versatile Biomaterial Platform Enriched with Graphene Oxide and Carbon Nanotubes for Multiple Tissue Engineering Applications

Carbon-based nanomaterials, such as graphene oxide (GO) or carbon nanotubes (CNTs) are currently used in various medical applications due to their positive influence on biocompatibility, adhesion, proliferation, and differentiation, as well as their contribution to modulating cell behavior in response to nanomaterial substrates. In this context, in this study, novel flexible membranes based on cellulose acetate (CA) enriched with CNT and GO in different percentages were tested for their versatility to be used as substrates for soft or hard tissue engineering (TE), namely, for their ability to support human adipose-derived stem cells (hASCs) adhesion during adipogenic or osteogenic differentiation. For this purpose, differentiation markers were assessed both at gene and protein levels, while histological staining was performed to show the evolution of the processes in response to CA-CNT-GO substrates. Micro-CT analysis indicated porous morphologies with open and interconnected voids. A slightly lower total porosity was obtained for the samples filled with the highest amount of GO and CNTs, but thicker walls, larger and more uniform pores were obtained, providing beneficial effects on cell behavior and increased mechanical stability. The addition of 1 wt% GO and CNT to the biocomposites enhanced hASCs adhesion and cytoskeleton formation. The evolution of both adipogenic and osteogenic differentiation processes was found to be augmented proportionally to the GO-CNT concentration. In conclusion, CA-CNT-GO biomaterials displayed good properties and versatility as platforms for cell differentiation with potential as future implantable materials in TE applications.

Carbon Nanotubes and Graphene as Nanoreinforcements in Metallic Biomaterials: a Review

Current challenges in existing metallic biomaterials encourage undertaking research in the development of novel materials for biomedical applications. This paper critically reviews the potential of carbon nanotubes (CNT) and graphene as nanoreinforcements in metallic biomaterials for bone tissue engineering. Unique and remarkable mechanical, electrical, and biological properties of these carbon nanomaterials allow their use as secondary-phase reinforcements in monolithic biomaterials. The nanoscale dimensions and extraordinarily large surface areas of CNT and graphene make them suitable materials for purposeful reaction with living organisms. However, the cytocompatibility of CNT and graphene is still a controversial issue that impedes advances in utilizing these promising materials in clinical orthopedic applications. The interaction of CNT and graphene with biological systems including proteins, nucleic acids, and human cells is critically reviewed to assess their cytocompatibity in vitro and in vivo. It is revealed that composites reinforced with CNT and graphene show enhanced adhesion of osteoblast cells, which subsequently promotes bone tissue formation in vivo. This potential is expected to pave the way for developing ground-breaking technologies in regenerative medicine and bone tissue engineering. In addition, current progress and future research directions are highlighted for the development of CNT and graphene reinforced implants for bone tissue engineering.

Fabrication and characterisation of 3D printed MWCNT composite porous scaffolds for bone regeneration

Carbon nanotubes (CNTs) with exceptional physical and chemical properties are attracting significant interest in the field of tissue engineering. Several reports investigated CNTs biocompatibility and their impact in terms of cell attachment, proliferation and differentiation mainly using polymer/CNTs membranes. However, these 2D membranes are not able to emulate the complex in vivo environment. In this paper, additive manufacturing (3D printing) is used to create composite 3D porous scaffolds containing different loadings of multi-walled carbon nanotubes (MWCNT) (0.25, 0.75 and 3 wt%) for bone tissue regeneration. Pre-processed and processed materials were extensively characterised in terms of printability, morphological and topographic characteristics and thermal, mechanical and biological properties. Scaffolds with pore sizes ranging between 366 μm and 397 μm were successfully produced and able to sustain early-stage human adipose-derived mesenchymal stem cells attachment and proliferation. Results show that MWCNTs enhances protein adsorption, mechanical and biological properties. Composite scaffolds, particularly the 3 wt% loading of MWCNTs, seem to be good candidates for bone tissue regeneration.

Evaluation of in vitro bioactivity and in vitro biocompatibility of Polycaprolactone/Hyaluronic acid/Multiwalled Carbon Nanotubes/Extract from Mimosa tenuiflora composites

BACKGROUND

The development of biomaterial scaffolds and implementation of tissue engineering techniques are necessary. Therefore, Polycaprolactone/Sodium Hyaluronate/Multiwalled Carbon Nanotubes/Extract of Mimosa tenuiflora composites have been produced by a thermally-induced phase separation method.

OBJECTIVE

The objective of this research was to evaluate the in vitro bioactivity and in vitro biocompatibility of the composites.

METHODS

The in vitro bioactivity of the composites was assessed by soaking them in simulated body fluid for 7, 14, 21, and 28 days. The structure and composition of the composites were analyzed using scanning electron microscopy coupled with energy dispersive spectroscopy and Fourier transform infrared spectroscopy. Also, the in vitro biocompatibility of the composites was evaluated by means of alkaline phosphatase activity of the osteoblasts and by measuring the metabolic activity of the cells using MTT assay.

RESULTS

The results show a porous and interconnected morphology with enhanced bioactivity. It was observed that the incorporation of Mimosa tenuiflora in the composites promotes increased viability of osteoblasts in the scaffolds.

CONCLUSIONS

The results show the efficiency of bioactive and biocompatible composites and their potential as candidates for tissue engineering applications.

[Recent research progress of bioactivity mechanism and application of bone repair materials]

Large bone defect repair is a difficult problem to be solved urgently in orthopaedic field, and the application of bone repair materials is a feasible method to solve this problem. Therefore, bone repair materials have been continuously developed, and have evolved from autogenous bone grafts, allograft bone grafts, and inert materials to highly active and multifunctional bone tissue engineering scaffold materials. In this paper, the related mechanism of bone repair materials, the application of bone repair materials, and the exploration of new bone repair materials are introduced to present the research status and advance of the bone repair materials, and the development direction is also prospected.

Carbon Nanomaterials for Treating Osteoporotic Vertebral Fractures

PURPOSE OF REVIEW

To identify the use of carbon nanomaterials in bone regeneration and present new data on the regenerative capacity of bone tissue in osteopenic rats treated with graphene nanoribbons (GNRs).

RECENT FINDINGS

The results show that the physical and chemical properties of the nanomaterials are suitable for the fabrication of scaffolds intended for bone regeneration. The in vitro tests suggested a non-toxicity of the GNRs as well as improved biocompatibility and bone mineralization activity. Here, for the first time, we evaluated the potential of GNRs in remodeling and repairing bone defects in osteoporotic animal models in vivo. Interestingly, bone mineralization and the initiation of the remodeling cycle by osteoclasts/osteoblasts were observed after the implantation of GNRs, thus implying healthy bone remodeling when using GNRs. This study, therefore, has opened our perspectives and certainly calls for more attention to the use of carbon nanomaterials for a wide range of osteoporosis applications.

Rheological and Mechanical Properties of Thermoresponsive Methylcellulose/Calcium Phosphate-Based Injectable Bone Substitutes

In this study, a novel injectable bone substitute (IBS) was prepared by incorporating a bioceramic powder in a polymeric solution comprising of methylcellulose (MC), gelatin and citric acid. Methylcellulose was utilized as the polymeric matrix due to its thermoresponsive properties and biocompatibility. 2.5 wt % gelatin and 3 wt % citric acid were added to the MC to adjust the rheological properties of the prepared IBS. Then, 0, 20, 30 and 50 wt % of the bioceramic component comprising tetracalcium phosphate/hydroxyapatite (TTCP/HA), dicalcium phosphate dehydrate (DCPD) and calcium sulfate dehydrate (CSD) were added into the prepared polymeric component. The prepared IBS samples had a chewing gum-like consistency. IBS samples were investigated in terms of their chemical structure, rheological characteristics, and mechanical properties. After that, in vitro degradation studies were carried out by measurement of pH and % remaining weight. Viscoelastic characteristics of the samples indicated that all of the prepared IBS were injectable and they hardened at approximately 37 °C. Moreover, with increasing wt % of the bioceramic component, the degradation rate of the samples significantly reduced and the mechanical properties were improved. Therefore, the experimental results indicated that the P50 mix may be a promising candidates to fill bone defects and assist bone recovery for non-load bearing applications.

Carbon Nanotube Reinforced Collagen/Hydroxyapatite Scaffolds Improve Bone Tissue Formation In Vitro and In Vivo

Current bone regeneration strategies faced major challenges in fabricating the bionic scaffolds with nano-structure, constituents and mechanical features of native bone. In this study, we developed a new porous scaffold by adding the multi-walled carbon nanotube (MWCNT) into collagen (Col)/hydroxyapatite (HA) composites. Data showed that 0.5%CNT/Col/HA (0.5%CNT) group was approximately tenfolds stiffer than Col-HA, and it was superior in promoting bone marrow mesenchymal stem proliferation and spreading, mRNA and protein expressions of bone sialoprotein (BSP) and osteocalcin (OCN) than Col-HA group. Moreover, we utilized 0.5%CNT composite to repair the rat calvarial defects (8 mm diameter) in vivo, and observed the new bone formation by 3D reconstruction of micro CT, HE and Masson staining, and BSP, OCN by immunohistochemical analysis. Results showed that newly formed bone in 0.5%CNT group was significantly higher than that in Col-HA group at 12 weeks. These findings highlighted a promising strategy in healing of large area bone defect with MWCNT added into the Col-HA scaffold as they possessed the combined effects of mechanical strength and osteogenicity.

Scaffolds containing chitosan, gelatin and graphene oxide for bone tissue regeneration in vitro and in vivo

Critical-sized bone defects are augmented with cell free and cell loaded constructs to bridge bone defects. Improving the properties of three-dimensional scaffolds with multiple polymers and others is of growing interest in recent decades. Chitosan (CS), a natural biopolymer has limitations for its use in bone regeneration, and its properties can be enhanced with other materials. In the present study, the composite scaffolds containing CS, gelatin (Gn) and graphene oxide (GO) were fabricated through freeze-drying. These scaffolds (GO/CS/Gn) were characterized by the SEM, Raman spectra, FT-IR, EDS, swelling, biodegradation, protein adsorption and biomineralization studies. The inclusion of GO in the CS/Gn scaffolds showed better physico-chemical properties. The GO/CS/Gn scaffolds were cyto-friendly to rat osteoprogenitor cells, and they promoted differentiation of mouse mesenchymal stem cells into osteoblasts. The scaffolds also accelerated bridging of the rat tibial bone defect with increased collagen deposition in vivo. Hence, these results strongly suggested the potential nature of GO/CS/Gn scaffolds for their application in bone tissue regeneration.

Preparation and characterization of novel functionalized multiwalled carbon nanotubes/chitosan/β-Glycerophosphate scaffolds for bone tissue engineering

A major limitation in current tissue engineering scaffolds is that some of the most important characteristics of the intended tissue are ignored. As piezoelectricity and high mechanical strength are two of the most important characteristics of the bone tissue, carbon nanotubes are getting a lot of attention as a bone tissue scaffold component in recent years. In the present study, composite scaffolds comprised of functionalized Multiwalled Carbon Nanotubes (f-MWCNT), medium molecular weight chitosan and β-Glycerophosphate were fabricated and characterized. Biodegradability and mechanical tests indicate that while increasing f-MWCNT content can improve electrical conductivity and mechanical properties, there are some limitations for these increases, such as a decrease in mechanical properties and biodegradability in 1w/v% content of f-MWCNTs. Also, MTT cytotoxicity assay was conducted for the scaffolds and no significant cytotoxicity was observed. Increasing f-MWCNT content led to higher alkaline Phosphatase activity. The overall results show that composites with f-MWCNT content between 0.1w/v% and 0.5w/v% are the most suitable for bone tissue engineering application. Additionally, Preliminary cell electrical tests proved the efficiency of the prepared scaffolds for cell electrical applications.

Carbon Nanostructures in Bone Tissue Engineering

BACKGROUND

Recent advances in developing biocompatible materials for treating bone loss or defects have dramatically changed clinicians' reconstructive armory. Current clinically available reconstructive options have certain advantages, but also several drawbacks that prevent them from gaining universal acceptance. A wide range of synthetic and natural biomaterials is being used to develop tissue-engineered bone. Many of these materials are currently in the clinical trial stage.

METHODS

A selective literature review was performed for carbon nanostructure composites in bone tissue engineering.

RESULTS

Incorporation of carbon nanostructures significantly improves the mechanical properties of various biomaterials to mimic that of natural bone. Recently, carbon-modified biomaterials for bone tissue engineering have been extensively investigated to potentially revolutionize biomaterials for bone regeneration.

CONCLUSION

This review summarizes the chemical and biophysical properties of carbon nanostructures and discusses their functionality in bone tissue regeneration.