Preparation and characterization of a novel hydroxyapatite/carbon nanotubes composite and its interaction with osteoblast-like cells

Calcium Orthophosphate (CaPO4) Containing Composites for Biomedical Applications: Formulations, Properties, and Applications

The goal of this review is to present a wide range of hybrid formulations and composites containing calcium orthophosphates (abbreviated as CaPO4) that are suitable for use in biomedical applications and currently on the market. The bioactive, biocompatible, and osteoconductive properties of various CaPO4-based formulations make them valuable in the rapidly developing field of biomedical research, both in vitro and in vivo. Due to the brittleness of CaPO4, it is essential to combine the desired osteologic properties of ceramic CaPO4 with those of other compounds to create novel, multifunctional bone graft biomaterials. Consequently, this analysis offers a thorough overview of the hybrid formulations and CaPO4-based composites that are currently known. To do this, a comprehensive search of the literature on the subject was carried out in all significant databases to extract pertinent papers. There have been many formulations found with different material compositions, production methods, structural and bioactive features, and in vitro and in vivo properties. When these formulations contain additional biofunctional ingredients, such as drugs, proteins, enzymes, or antibacterial agents, they offer improved biomedical applications. Moreover, a lot of these formulations allow cell loading and promote the development of smart formulations based on CaPO4. This evaluation also discusses basic problems and scientific difficulties that call for more investigation and advancements. It also indicates perspectives for the future.

Corrosion, mechanical and bioactivity properties of HA-CNT nanocomposite coating on anodized Ti6Al4V alloy

Hydroxyapatite-carbon nanotubes (HA-CNTs) nanocomposite coating was applied by electrophoretic method on anodized Ti alloy to investigate its stability in simulated body fluid (SBF). The biocoating was characterized by using scanning electron microscope (SEM) for microstructure, X-ray diffraction (XRD) for crystallography. The effect of CNTs concentration on the coating properties was also investigated and found out that CNTs up to 5% has various improving effect on the system. It increased corrosion resistance and adhesion of the coating to the substrate and decreased the number of cracks on the coating. The results of the in vitro test showed that the cell viability increased with increasing the concentration of CNTs to 3 wt.% CNTs. Graphical abstract.

Emerging zero-dimensional to four-dimensional biomaterials for bone regeneration

Bone is one of the most sophisticated and dynamic tissues in the human body, and is characterized by its remarkable potential for regeneration. In most cases, bone has the capacity to be restored to its original form with homeostatic functionality after injury without any remaining scarring. Throughout the fascinating processes of bone regeneration, a plethora of cell lineages and signaling molecules, together with the extracellular matrix, are precisely regulated at multiple length and time scales. However, conditions, such as delayed unions (or nonunion) and critical-sized bone defects, represent thorny challenges for orthopedic surgeons. During recent decades, a variety of novel biomaterials have been designed to mimic the organic and inorganic structure of the bone microenvironment, which have tremendously promoted and accelerated bone healing throughout different stages of bone regeneration. Advances in tissue engineering endowed bone scaffolds with phenomenal osteoconductivity, osteoinductivity, vascularization and neurotization effects as well as alluring properties, such as antibacterial effects. According to the dimensional structure and functional mechanism, these biomaterials are categorized as zero-dimensional, one-dimensional, two-dimensional, three-dimensional, and four-dimensional biomaterials. In this review, we comprehensively summarized the astounding advances in emerging biomaterials for bone regeneration by categorizing them as zero-dimensional to four-dimensional biomaterials, which were further elucidated by typical examples. Hopefully, this review will provide some inspiration for the future design of biomaterials for bone tissue engineering.

Carbon-Based Nanomaterials for Bone and Cartilage Regeneration: A Review

As the main load-bearing structure in the human body, bone and cartilage are susceptible to damage in sports and other activities. The repair and regeneration of bone and articular cartilage have been extensively studied in the past decades. Traditional approaches have been widely applied in clinical practice, but the effect varies from person to person and may cause side effects. With the rapid development of tissue engineering and regenerative medicine, various biomaterials show great potential in the regeneration of bone and cartilage. Carbon-based nanomaterials are solid materials with different structures and properties composed of allotropes of carbon, which are classified into zero-, one-, and two-dimensional ones. This Review systemically summarizes the different types of carbon-based nanomaterials, including zero-dimensional (fullerene, carbon dots, nanodiamonds), one-dimensional (carbon nanotubes), and two-dimensional (graphenic materials) as well as their applications in bone, cartilage, and osteochondral regeneration. Current limitations and future perspectives of carbon-based nanomaterials are also discussed.

Review of Hybrid Materials Based on Polyhydroxyalkanoates for Tissue Engineering Applications

This review is focused on hybrid polyhydroxyalkanoate-based (PHA) biomaterials with improved physico-mechanical, chemical, and piezoelectric properties and controlled biodegradation rate for applications in bone, cartilage, nerve and skin tissue engineering. PHAs are polyesters produced by a wide range of bacteria under unbalanced growth conditions. They are biodegradable, biocompatible, and piezoelectric polymers, which make them very attractive biomaterials for various biomedical applications. As naturally derived materials, PHAs have been used for multiple cell and tissue engineering applications; however, their widespread biomedical applications are limited due to their lack of toughness, elasticity, hydrophilicity and bioactivity. The chemical structure of PHAs allows them to combine with other polymers or inorganic materials to form hybrid composites with improved structural and functional properties. Their type (films, fibers, and 3D printed scaffolds) and properties can be tailored with fabrication methods and materials used as fillers. Here, we are aiming to fill in a gap in literature, revealing an up-to-date overview of ongoing research strategies that make use of PHAs as versatile and prospective biomaterials. In this work, a systematic and detailed review of works investigating PHA-based hybrid materials with tailored properties and performance for use in tissue engineering applications is carried out. A literature survey revealed that PHA-based composites have better performance for use in tissue regeneration applications than pure PHA.

Mineralized paper scaffolds for bone tissue engineering

Mineralized polymer scaffolds have proven to be effective biomaterials for inducing osteoinductivity in bone tissue engineering. Sequential mineralization is a promising technique for depositing minerals in three-dimensional (3D) scaffolds. Paper, which is made of cellulose fibers, can be used as a tissue scaffold due to its highly porous structure and flexibility, as well as its excellent ability to wick fluids and support the growth of bone cells. In this study, paper-based, mineralized scaffolds were fabricated using sequential mineralization. We conducted experiments with two groups of scaffolds based on different incubation times in the mineralization solutions (30 min and 24 h). Ten cycles of mineralization were performed for each group. We found that the mineral content increased as the cycle number increased and that the 24-h group scaffolds consistently had more mineralization than did the 30-min group scaffolds when measured at the same cycle number. A quantitative reverse transcription-polymerase chain reaction was performed for two osteogenic differentiation markers of the preosteoblasts that were grown on the mineralized paper scaffolds. The gene expression results for bone-specific markers revealed that the mineralized scaffolds were osteoinductive. Subcutaneous implantation of the scaffolds in rats demonstrated favorable biocompatibility, high vascularization, and non-immunogenicity in vivo. The overall results suggest that the sequentially mineralized paper scaffolds are promising materials for use in bone tissue engineering.

Tailoring Cu substituted hydroxyapatite/functionalized multiwalled carbon nanotube composite coating on 316L SS implant for enhanced corrosion resistance, antibacterial and bioactive properties

The aim of the present work is to study the potential change in the antibacterial properties of Cu-hydroxyapatite/functionalized multiwall carbon nanotube (HA/f-MWCNT) composite coated heterogeneous implant surfaces against Gram positive and Gram-negative microorganism and to reveal the possible contribution of surface corrosion effects arising in stimulated body fluid. Novel spray pyrolysis instrument designed with double nozzle was used for the fabrication of Cu-hydroxyapatite/f-MWCNT film on 316L stainless steel (SS). The Cu-hydroxyapatite/MWCNT coated bioimplant was characterized by a series of techniques to identify the crystallinity, chemical bonds, surface morphology and elemental composition. The results disclose that the coated implants exhibit highly crystalline nature with the space group of P6_3mc and spherical shaped morphology. The corrosion current density revealed a remarkable decrease from 6.8 to 3.8 μA suggesting that the Cu substituted hydroxyapatite/f-MWCNT composite coating provided higher barrier properties which is beneficial to achieve higher corrosion protection of 316L SS implant. The hybrid Cu-hydroxyapatite-MWCNT composite revealed better antibacterial ability than HA/MWCNT for both gram positive and gram-negative bacteria with a maximum inhibition zone of 13-17 mm, compared with hydroxyapatite/f-MWCNT. The antibacterial ability of the Cu-hydroxyapatite/f-MWCNT nanocomposites was effective against Escherichia coli compared with other microorganisms. The Cu-hydroxyapatite/f-MWCNT nanocomposite exhibited that the coated material is nontoxic, biocompatible and suitable for biomedical application.

Excellency of Hydroxyapatite Composite Scaffolds for Bone Tissue Engineering

The hydroxyapatite [HAp, Ca10(PO4)6(OH)2] has a variety of applications in bone fillers and replacements due to its excellent bioactivity and osteoconductivity. It comprises the main inorganic component of hard tissues. Among the various approaches, a composite approach using several components like biopolymer, gelatin, collagen, and chitosan in the functionalization of scaffolds with HAp has the prospective to be an engineered biomaterial for bone tissue engineering. HAp composite scaffolds have been developed to obtain a material with different functionalities such as surface reactivity, bioactivity, mechanical strength, and capability of drug or growth factor delivery. Several techniques and processes for the synthesis and fabrication of biocompatible HAp composite scaffolds suitable for bone regeneration are addressed here. Further, this chapter described the excellences of various HAp composite scaffolds used in in vitro and in vivo experiments in bone tissue engineering.

Wettability and pre-osteoblastic behavior evaluations of a dense bovine hydroxyapatite ceramics

In this study, the wettability, cell viability, and roughness of an experimental dense bovine hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂] ceramic block were evaluated so that, in the future, it could be used as a base material for dental implants. The results to commercial zirconia and a commercially pure titanium (Ti) alloy were compared. The surface roughness and contact angles were measured. An in vitro evaluation was conducted by means of tests in which pre-osteoblastic MC3T3-E1 cells were placed in indirect and direct contact with these materials. For cell viability, a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and crystal violet test were conducted. A qualitative analysis was conducted using variable pressure scanning electron microscopy (SEM). No statistically significant differences were observed in wettability and roughness tests among the groups. In both the MTT assay and crystal violet test, all groups demonstrated satisfactory results without cytotoxicity. SEM showed cell adhesion and cell proliferation results on the material surfaces after 24 h and 48 h. In conclusion, this dense Ca₁₀ (PO₄)₆(OH)₂ ceramic can be considered as a potential biocompatible material.

Bone Tissue Engineering via Carbon-Based Nanomaterials

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

Incorporating silica-coated graphene in bioceramic nanocomposites to simultaneously enhance mechanical and biological performance

The applications of a variety of bioactive ceramics such as hydroxyapatite (HA) in orthopedics are limited by their insufficient mechanical properties, especially poor fracture toughness. Thus, further extending the clinical applications of these materials warrants the enhancement of their mechanical properties. Although the reinforcement of ceramics by 2D nanomaterials has been well recognized, integrated structural, mechanical, and functional considerations have been neglected in the design and synthesis of such composite materials. Herein, we report the first use of silica-coated reduced graphene oxide (S-rGO) hybrid nanosheets to create bioceramic-based composites with simultaneously enhanced mechanical and biological properties. In the representative HA-based bioceramic systems prepared by spark plasma sintering, S-rGO incorporation was found to be more effective for increasing the Young's modulus, hardness, and fracture toughness than the incorporation of uncoated reduced GO (rGO). Furthermore, when assessed with osteoblast-like MG-63 cells, such novel materials led to faster cell proliferation and higher cell viability and alkaline phosphatase activity than are generally observed with pure HA; additionally, cells demonstrate stronger affinity to S-rGO/HA than to rGO/HA composites. The S-rGO/bioceramic composites are therefore promising for applications in orthopedic tissue engineering, and this research provides valuable insights into the fabrication of silica-coated hybrid nanosheet-reinforced ceramics.

Preparation of Nano-Hydroxyapatite Coated Carbon Nanotube Reinforced Hydroxyapatite Composites

Uniform and dense nano-hydroxyapatite (nHA) coating with nanorod-shaped structure was fabricated on carbon nanotubes (CNTs) by combining electrodeposition with biomineralization. The CNTs with nHA coating (nHA–CNTs) were used as reinforcement to improve the mechanical properties of HA. Firstly, a mixed acid solution of nitric acid and sulfuric acid was used to treat CNTs (NS–CNTs). The dispersion of NS–CNTs was obviously improved, and O-containing functional groups were grafted on the surfaces of NS–CNTs by treatment. Then, calcium phosphate (CaP) was deposited on NS–CNTs by electrodeposition, and NS–CNTs were provided with numerous active nucleation sites for the next coating preparation process. Then nanorod-shaped HA crystals were obtained on the surfaces of NS–CNTs by biomineralization. Using the CNTs with nHA coating (nHA–CNTs) as reinforcement, HA-based composites reinforced with CNTs and nHA–CNTs (nHA–CNTs/HA) were fabricated by pressure-less process. Bending strength and fracture toughness of 1.0 wt % nHA–CNTs reinforced HA composites (HAnC1) reaches a maximum (30.77 MPa and 2.59 MPa), which increased by 26.94% and 7.02% compared with 1.0 wt % CNTs reinforced HA composites, respectively. Importantly, the fracture toughness of HAnC1 is within the range of that to compact bone. This work provides theoretical and practical guidance for preparing nHA coating on nanomaterials. It also contributes to the potential application of nHA–CNTs/HA composites for artificial bone implants.

Electrochemically grown functionalized -Multi-walled carbon nanotubes/hydroxyapatite hybrids on surgical grade 316L SS with enhanced corrosion resistance and bioactivity

Coatings using functionalized multi-walled carbon nanotubes (f-MWCNTs)/hydroxyapatite (HAP) on 316 L Stainless Steel by electrodeposition at the parameter of "-1.5 V" for 30 min. with three electrode set-up configuration and optimization of various concentrations of f-MWCNTs from 1 to 5% were done to improve the coating characteristics for future biomedical applications. The obtained coatings were characterized by Fourier Transformed-Infra Red spectroscopy (FT-IR) and X-ray diffractometer (XRD) to reveal the phase formation in the composites. With various additions of f-MWCNTs, the HAP phase was found to be retained. The growth of HAP on f-MWCNTs was analyzed by High-resolution Transmission Electron Microscope (HR-TEM) and the morphology of composite was found to be of the needle and flower-like particles. To understand the corrosion resistance effect of the developed HAP/f-MWCNTs composite in SBF, electrochemical investigations were carried out using Impedance and Tafel polarization analysis. From the results, it was observed that the coatings have enhanced corrosion resistance behavior and bioactivity. In addition, the Vickers Hardness study proved that the prepared HAP/fMWCNTs composite coating was found to have improved hardness value of (H_v) 390.2 ± 8.0. Thus, the electrodeposited composite coating on 316 L SS substrate can be effectively deployed for biomedical applications.

Physicomechanical properties of spark plasma sintered carbon nanotube-containing ceramic matrix nanocomposites

Recently, a wide variety of research works have focused on carbon nanotube (CNT)-ceramic matrix nanocomposites. In many cases, these novel materials are produced through conventional powder metallurgy methods including hot pressing, conventional sintering, and hot isostatic pressing. However, spark plasma sintering (SPS) as a novel and efficient consolidation technique is exploited for the full densification of high-temperature ceramic systems. In these binary nanocomposites, CNTs are added to ceramic matrices to noticeably modify their inferior properties and SPS is employed to produce fully dense compacts. In this review, a broad overview of these systems is provided and the potential influences of CNTs on their functional and structural properties are addressed. The technical challenges are then mentioned and the ongoing debates over overcoming these drawbacks are fully highlighted. The structural classification used is material-oriented. It helps the readers to easily find the material systems of interest. The SPSed CNT-containing ceramic matrix nanocomposites are generally categorized into four main classes: CNT-oxide systems; CNT-nitride systems, CNT-carbide systems, and CNT-boride systems. A large number of original curves and bubble maps are provided to fully summarize the experimental results reported in the literature. They pave the way for obviously selecting the ceramic systems required for each industrial application. The properties in consideration include the relative density, hardness, yield strength, fracture toughness, electrical and thermal conductivities, modulus, and flexural strength. These unique graphs facilitate the comparison between reported results and help the reader to easily distinguish the best method for producing the ceramic systems of interest and the optimal conditions under which the superior properties can be reached. The authors have concentrated on the microstructure evolution-physicomechanical property relationship and tried to relate each property to pertinent microstructural phenomena and address why the properties are degraded or enhanced with the variation of SPS conditions or material parameters.

Hydroxyapatite–-Past, Present, and Future in Bone Regeneration

Hydroxyapatite (HA) is an essential element required for bone regeneration. Different forms of HA have been used for a long time. The essence of bone regeneration always revolves around the healthy underlying bone or it may be the surroundings that give enough strength. HA is well known for bone regeneration through conduction or by acting as a scaffold for filling of defects from ancient times, but emerging trends of osteoinductive property of HA are much promising for new bone regeneration. Emerging technology has made the dreams of clinicians to realize the use of HA in different forms for various regenerative purposes both in vivo and in vitro. The nanostructured calcium apatite plays an important role in the construction of calcified tissues. The nanostructured material has the ability to attach biological molecules such as proteins, which can be used as functional materials in many aspects, and the capability of synthesizing controlled structures of apatite to simulate the basic structure of bone and other calcified tissues. The process of regeneration requires a biomimetic and biocompatible nanostructured novel material. The nanostructured bioceramic particles are of interest in synthetic bone grafts and bone cements both injectable and controlled setting, so that such composites will reinforce the strength of bioceramics. Extensive research is being carried out for bone regeneration using nanotechnology. Artificial bone formation is not far from now. Nanotechnology has made many dreams come true. This paper gives comprehensive insights into the history and evolution with changing trends in the use of HA for various regenerative purposes.

Enhanced bone regeneration with carbon nanotube reinforced hydroxyapatite in animal model

In order to improve the inherently poor mechanical properties of hydroxyapatite (HAp) and to increase its feasibility as load bearing implant material, in the present investigation, functionalised (HFC1 and HFC2) and non-functionalized (HC1 and HC2) multi-walled carbon nanotubes were used as reinforcing material with HAp. Significant improvement with respect to fracture toughness, flexural strength and impact strength of the composites was noticed. In vitro biological properties of HAp-carbon nanotube (CNT) biocomposites have also favored uniform and systematic apatite growth on their surface. Subsequently, in vivo osseous ingrowth at bone defect of rabbit femur was evaluated and compared using radiology, push out test, fluorochrome labeling, histology and scanning electron microscopy after 2 and 4 months respectively. The results demonstrated growth of web like soft callus from the host bone towards the implant, ensuring strong host bone interaction. Toxicological studies of the liver and kidney cells exhibited no abnormality, thereby confirming non-toxicity of the CNT in the animal body. Host-implant biomechanical strength showed high interfacial strength of the composites, indicating their high potentials to be used for bone remodeling applications.

Decorated multi-walled carbon nanotubes with Sm doped fluorapatites: synthesis, characterization and catalytic activity

Novel and sustainable heterogeneous catalysts, namely, multi-walled carbon nanotubes (MWCNT) decorated with Sm doped fluorapatite nanocomposites (MWCNT/Sm-FAp) were prepared with different loadings of Sm (1%, 2%, 3%, 5%, and 7%).

High strength chitosan rod reinforced by non-covalent functionalized multiwalled carbon nanotubes via an in situ precipitation method

High strength CS/MWCNTs composite rods preparedvia in situprecipitation & PaPA functionalization, with a 3D sophisticated structure and uniformly dispersed MWCNTs.

Effect of the addition CNTs on performance of CaP/chitosan/coating deposited on magnesium alloy by electrophoretic deposition

CaP/chitosan/carbon nanotubes (CNTs) coating on AZ91D magnesium alloy was prepared via electrophoretic deposition (EPD) followed by conversion in a phosphate buffer solution (PBS). The bonding between the layer and the substrate was studied by an automatic scratch instrument. The phase compositions and microstructures of the composite coatings were determined by using X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FTIR), Raman spectroscopy and scanning electron microscope (SEM). The element concentration and gentamicin concentration were respectively determined by inductively coupled plasma optical emission spectrometer (ICP-OES) test and ultraviolet spectrophotometer (UV). The cell counting kit (CCK) assay was used to evaluate the cytotoxicity of samples to SaOS-2 cells. The results showed that a few CNTs with their original tubular morphology could be found in the CaP/chitosan coating and they were beneficial for the crystal growth of phosphate and improvement of the coating bonding when the addition amount of CNTs in 500 ml of electrophoretic solution was from 0.05 g to 0.125 g. The loading amount of gentamicin increased and the releasing speed of gentamicin decreased after CNTs was added into the CaP/chitosan coating for immersion loading and EPD loading. The cell viability of Mg based CaP/chitosan/CNTs was higher than that of Mg based CaP/chitosan from 16 days to 90 days.

Calcium Orthophosphate-Containing Biocomposites and Hybrid Biomaterials for Biomedical Applications

The state-of-the-art on calcium orthophosphate (CaPO4)-containing biocomposites and hybrid biomaterials suitable for biomedical applications is presented. Since these types of biomaterials offer many significant and exciting possibilities for hard tissue regeneration, this subject belongs to a rapidly expanding area of biomedical research. Through the successful combinations of the desired properties of matrix materials with those of fillers (in such systems, CaPO4 might play either role), innovative bone graft biomaterials can be designed. Various types of CaPO4-based biocomposites and hybrid biomaterials those are either already in use or being investigated for biomedical applications are extensively discussed. Many different formulations in terms of the material constituents, fabrication technologies, structural and bioactive properties, as well as both in vitro and in vivo characteristics have been already proposed. Among the others, the nano-structurally controlled biocomposites, those containing nanodimensional compounds, biomimetically fabricated formulations with collagen, chitin and/or gelatin, as well as various functionally graded structures seem to be the most promising candidates for clinical applications. The specific advantages of using CaPO4-based biocomposites and hybrid biomaterials in the selected applications are highlighted. As the way from a laboratory to a hospital is a long one and the prospective biomedical candidates have to meet many different necessities, the critical issues and scientific challenges that require further research and development are also examined.

Surface modification of hydroxyapatite crystals by Mg–Al–CO3-layered double hydroxides in HA/Mg–Al–CO3–LDH nanocomposite

Bioactivity and improved mechanical properties of hydroxyapatite/Mg–Al-layered double hydroxide nanocomposite are reported for the first time.

Processing strategies for smart electroconductive carbon nanotube-based bioceramic bone grafts

Electroconductive bone grafts have been designed to control bone regeneration. Contrary to polymeric matrices, the translation of the carbon nanotube (CNT) electroconductivity into oxide ceramics is challenging due to the CNT oxidation during sintering. Sintering strategies involving reactive-bed pressureless sintering (RB + P) and hot-pressing (HP) were optimized towards prevention of CNT oxidation in glass/hydroxyapatite (HA) matrices. Both showed CNT retentions up to 80%, even at 1300 °C, yielding an increase of the electroconductivity in ten orders of magnitude relative to the matrix. The RB + P CNT compacts showed higher electroconductivity by ∼170% than the HP ones due to the lower damage to CNTs of the former route. Even so, highly reproducible conductivities with statistical variation below 5% and dense compacts up to 96% were only obtained by HP. The hot-pressed CNT compacts possessed no acute toxicity in a human osteoblastic cell line. A normal cellular adhesion and a marked orientation of the cell growth were observed over the CNT composites, with a proliferation/differentiation relationship favouring osteoblastic functional activity. These sintering strategies offer new insights into the sintering of electroconductive CNT containing bioactive ceramics with unlimited geometries for electrotherapy of the bone tissue.

The use of carbon nanotubes to reinforce 45S5 bioglass-based scaffolds for tissue engineering applications

Bioglass has been used for bone-filling material in bone tissue engineering, but its lean mechanical strength limits its applications in load-bearing positions. Carbon nanotubes (CNTs), with their high aspect ratio and excellent mechanical properties, have the potential to strengthen and toughen bioactive glass material without offsetting its bioactivity. Therefore, in this research, multiwall carbon nanotube (MWCNT)/45S5 Bioglass composite scaffolds have been successfully prepared by means of freeze casting process. 45S5 Bioglass was synthesized by the sol-gel processing method. The obtained material was characterized with X-ray powder diffraction (XRD). The mechanical properties of the scaffolds, such as compression strength and elastic modulus, were measured. Finally, compared with the scaffolds prepared by 100% 45S5 Bioglass powders, the addition of 0.25 wt.% MWCNTs increases the compressive strength and elastic modulus of 45S5 Bioglass scaffolds from 2.08 to 4.56 MPa (a 119% increase) and 111.50 to 266.59 MPa (a 139% increase), respectively.

Carbon-based nanomaterials for tissue engineering

Carbon-based nanomaterials such as graphene sheets and carbon nanotubes possess unique mechanical, electrical, and optical properties that present new opportunities for tissue engineering, a key field for the development of biological alternatives that repair or replace whole or a portion of tissue. Carbon nanomaterials can also provide a similar microenvironment as like a biological extracellular matrix in terms of chemical composition and physical structure, making them a potential candidate for the development of artificial scaffolds. In this review, we summarize recent research advances in the effects of carbon nanomaterial-based substrates on cellular behaviors, including cell adhesion, proliferation, and differentiation into osteo- or neural- lineages. The development of 3D scaffolds based on carbon nanomaterials (or their composites with polymers and inorganic components) is introduced, and the potential of these constructs in tissue engineering, including toxicity issues, is discussed. Future perspectives and emerging challenges are also highlighted.

A simple and rapid method to graft hydroxyapatite on carbon nanotubes

Herein a simple and effective approach is introduced to functionalize single walled carbon nanotubes (SWCNTs) by in-situ grafting of hydroxyapatite (HA). The pristine SWCNTs were chemically activated through introduction of carboxylic groups on their surfaces by refluxing in the mixture of H(2)SO(4) and HNO(3). The resulting carboxylated SWCNTs were further utilized for grafting of HA. The Fourier transform infrared and Raman spectroscopic studies demonstrated the formation of HA and its grafting over SWCNTs. The phase composition of HA and existence Ca(2+) and PO(4) (3-) ions were studied using X-ray diffraction and energy dispersive X-ray analyses, respectively. The surface morphology of functionalized SWCNTs was analyzed using scanning electron microscopy and transmission electron microscopy. Thermogravimetric analysis confirmed the existence of HA on SWCNTs by exhibiting different thermogram for pure HA and functionalized SWCNTs. Overall this method produced uniform grafting of low crystalline HA on carboxylated SWCNTs with strong interfacial bonding.

Nanoscale hydroxyapatite particles for bone tissue engineering

Hydroxyapatite (HAp) exhibits excellent biocompatibility with soft tissues such as skin, muscle and gums, making it an ideal candidate for orthopedic and dental implants or components of implants. Synthetic HAp has been widely used in repair of hard tissues, and common uses include bone repair, bone augmentation, as well as coating of implants or acting as fillers in bone or teeth. However, the low mechanical strength of normal HAp ceramics generally restricts its use to low load-bearing applications. Recent advancements in nanoscience and nanotechnology have reignited investigation of nanoscale HAp formation in order to clearly define the small-scale properties of HAp. It has been suggested that nano-HAp may be an ideal biomaterial due to its good biocompatibility and bone integration ability. HAp biomedical material development has benefited significantly from advancements in nanotechnology. This feature article looks afresh at nano-HAp particles, highlighting the importance of size, crystal morphology control, and composites with other inorganic particles for biomedical material development.

Biocomposites and hybrid biomaterials based on calcium orthophosphates

The state-of-the-art of biocomposites and hybrid biomaterials based on calcium orthophosphates that are suitable for biomedical applications is presented in this review. Since these types of biomaterials offer many significant and exciting possibilities for hard tissue regeneration, this subject belongs to a rapidly expanding area of biomedical research. Through successful combinations of the desired properties of matrix materials with those of fillers (in such systems, calcium orthophosphates might play either role), innovative bone graft biomaterials can be designed. Various types of biocomposites and hybrid biomaterials based on calcium orthophosphates, either those already in use or being investigated for biomedical applications, are extensively discussed. Many different formulations, in terms of the material constituents, fabrication technologies, structural and bioactive properties as well as both in vitro and in vivo characteristics, have already been proposed. Among the others, the nanostructurally controlled biocomposites, those containing nanodimensional compounds, biomimetically fabricated formulations with collagen, chitin and/or gelatin as well as various functionally graded structures seem to be the most promising candidates for clinical applications. The specific advantages of using biocomposites and hybrid biomaterials based on calcium orthophosphates in the selected applications are highlighted. As the way from the laboratory to the hospital is a long one, and the prospective biomedical candidates have to meet many different necessities, this review also examines the critical issues and scientific challenges that require further research and development.

Optimization of the sintering atmosphere for high-density hydroxyapatite-carbon nanotube composites

Hydroxyapatite-carbon nanotube (HA-CNT) composites have the potential for improved mechanical properties over HA for use in bone graft applications. Finding an appropriate sintering atmosphere for this composite presents a dilemma, as HA requires water in the sintering atmosphere to remain phase pure and well hydroxylated, yet CNTs oxidize at the high temperatures required for sintering. The purpose of this study was to optimize the atmosphere for sintering these composites. While the reaction between carbon and water to form carbon monoxide and hydrogen at high temperatures (known as the 'water-gas reaction') would seem to present a problem for sintering these composites, Le Chatelier's principle suggests this reaction can be suppressed by increasing the concentration of carbon monoxide and hydrogen relative to the concentration of carbon and water, so as to retain the CNTs and keep the HA's structure intact. Eight sintering atmospheres were investigated, including standard atmospheres (such as air and wet Ar), as well as atmospheres based on the water-gas reaction. It was found that sintering in an atmosphere of carbon monoxide and hydrogen, with a small amount of water added, resulted in an optimal combination of phase purity, hydroxylation, CNT retention and density.

Carbon Nanotubes: A Solution for Processing Smart Biomaterials

In the recent years the driving force for technological change in many respects has shifted towards the design and process of materials that offer a set of responses to external stimuli or environmental conditions. These materials are called “smart materials”. Such responses are designed to fulfil the range of scenarios to which a material or structure may be exposed providing them with a particular functionality. These materials are not only useful because of their structural, chemical, physical or mechanical properties; they can also perform an action within a process. It has been described that smart structures exhibit one or more of the following features; they can act as sensors or actuators within a structural material or bonded in the surface; or they have controllable capabilities that permit to respond to the stimuli according to a prescribed function. These materials become intelligent when they have the ability to respond intelligently and autonomously to changing conditions. There are lots of possibilities within the term functional “smart materials” but in all of them, the term is used to describe systems which respond to a stimulus in a useful and predictable manner. Nowadays it is widely known the useful capability of, piezoelectric, electro-optic, magnetic, electro-mechanic materials, etc…that respond to stimuli such as, electric or magnetic fields, stress, temperature, moisture or pH. These multifunctional character and capability of biomaterials makes them suitable for a big number of applications in every order of human activity, from photochromic lenses for sunglasses to military and aerospace uses. They are already a big part of the market in the engineering industry.

Carbon nanotube reinforced polylactide-caprolactone copolymer: mechanical strengthening and interaction with human osteoblasts in vitro

This study proposes the use of carbon nanotubes (CNTs) as reinforcement to enhance the mechanical properties of a polylactide-caprolactone copolymer (PLC) matrix. Biological interaction of PLC-CNT composites with human osteoblast cells is also investigated. Addition of 2 wt % CNT shows very uniform dispersion in the copolymer matrix, whereas 5 wt % CNT shows severe agglomeration and high porosity. PLC-2 wt % CNT composite shows an improvement in the mechanical properties with an increase in the elastic modulus by 100% and tensile strength by 160%, without any adverse effect on the ductility up to 240% elongation. An in vitro biocompatibility study on the composites shows an increase in the viability of human osteoblast cells compared to the PLC matrix, which is attributed to the combined effect of CNT content and surface roughness of the composite films.