Hydrothermal Synthesis and Characterisation of Bioactive Glass-Ceramic Nanorods

In this study fabrication of rod-like bioactive glass-ceramics (BGCs) using hydrothermal treatment based on a sol-gel precursor is reported for the first time. BGCs with composition 58 wt% SiO2, 33 wt% CaO and 9 wt% P2O5 were synthesized in different thermal conditions (200 and 220 °C) and characterised with regard to morphology, chemical composition and crystallinity. The bioactivity of the materials was assessed by immersion in simulated body fluid for up to 7 days. The results revealed that as the reaction temperature increased from 200 to 220 °C, the diameter of rods was reduced from microscale to nanoscale and the crystallinity was enhanced. It was also found that the BGC nanorods have higher surface area and consequently enhanced bioactivity than BGC microrods. This technique provides a facile method for rapid production of BGC nanorods at relatively low temperature which may have the potential to be used as bioactive composite reinforcement or for bone grafting applications

Comparison of various functionally graded femoral prostheses by finite element analysis

This study is focused on finite element analysis of a model comprising femur into which a femoral component of a total hip replacement was implanted. The considered prosthesis is fabricated from a functionally graded material (FGM) comprising a layer of a titanium alloy bonded to a layer of hydroxyapatite. The elastic modulus of the FGM was adjusted in the radial, longitudinal, and longitudinal-radial directions by altering the volume fraction gradient exponent. Four cases were studied, involving two different methods of anchoring the prosthesis to the spongy bone and two cases of applied loading. The results revealed that the FG prostheses provoked more SED to the bone. The FG prostheses carried less stress, while more stress was induced to the bone and cement. Meanwhile, less shear interface stress was stimulated to the prosthesis-bone interface in the noncemented FG prostheses. The cement-bone interface carried more stress compared to the prosthesis-cement interface. Stair climbing induced more harmful effects to the implanted femur components compared to the normal walking by causing more stress. Therefore, stress shielding, developed stresses, and interface stresses in the THR components could be adjusted through the controlling stiffness of the FG prosthesis by managing volume fraction gradient exponent

Development of calcium silicate-based composites for load-bearing implants / Seyed Farid Seyed Shirazi

The essential requirements for successful bone repair and regeneration using synthetic-based hard tissues are: (i) mechanical stability; (ii) bioactivity; (iii) biodegradability and (iv) interconnectivity to allow for efficient migration of bone cell precursors and for the vascularization necessary for bone formation. In the case of large, critical-size bone defects, the synthetic materials currently available fall short of meeting the combined requirements for high porosity and interconnectivity while maintaining mechanical properties and bioactivity. Therefore, fabrication of a tissue that maintains architectural support throughout the duration of the healing phase under load-bearing conditions has been a huge challenge in the field. During the past 30 years, a variety of synthetic bone graft substitutes based on bioactive ceramics and glasses have become available, including bioglasses, hydroxyapatite (HA), calcium silicates (CS, CaSiO3) and biphasic calcium silicate (α/β-CS). A major drawback of currently available bioactive ceramics is inadequate mechanical properties (low strength, toughness and high brittleness) for load-bearing applications. One way to address this has been addition of biocompatible materials such as polymers and bioinert ceramics as the reinforcement agents to cover the weak points of bioactive ceramics while maintaining the shine points of biological properties. The aim of this thesis is to develop synthetic bioactive tissues for the repair and regeneration of large bone defects in load-bearing applications. Major advances have been achieved in this thesis through the development of materials with the right balance between material properties, implant architecture and bioactivity to satisfy the functional and regenerative requirements of bone. Fabrication of new biocomposites based on CS matrix and using appropriate synthesis strategies for doping CS with the cations can turn brittle and weak ceramics into tough, elastic and strong bone tissues for load-bearing applications. CS/Alumina composites sintered at 1250°C showed significant enhancement in hardness and fracture toughness compared to pure CS due to the presence of hardener agent as alumina. Moreover, Doping the CS structure with the cations can increase the mechanical properties while keeping or improving the biological characteristics. CS nanopowders doped with monovalent (Ag+) and pentavalent (Ta5+) cations showed an improvement in hardness and fracture toughness. However, hFOB cell proliferation was increased at each time point in higher concentration of Ta, the results showed no significant differences in proliferation in the presence or absence of higher amount of Ag in the CS structure. The new composites of CS/ poly(1.8-octanediol citrate) (POC) were developed with the aim of controlling the weight loss and improving the biological and mechanical properties for fixation device applications. The reports confirmed a very high improvement in mechanical strength and biological properties with incorporation of 40 wt% POC. In conclusion, the approach adapted in this thesis is the rational combination of many validated individual elements, which act synergistically to produce for the very first time biomaterials which can substitute for lost bone, both by allowing bone formation and in the meantime withstanding load. These newly developed ceramics have the potential to have a significant contribution in existing therapies to provide a superior clinical result

Wet chemistry approach to the preparation of tantalum-doped hydroxyapatite: Dopant content effects

Tantalum-doped hydroxyapatite (Ta-doped HA) nanopowders with different Ta contents were synthesized by a wet-chemical precipitation route. The structure modification and charge compensation mechanism were investigated by various characterization techniques. Due to the smaller size of tantalum ions compared to the Ca2+ size, it was assumed that the tantalum ions occupy either the Ca2+ and/or the interstitial positions in the HA lattice, where the charge imbalance from to this substitution was compensated by the Ca2+ vacancies. From the XRD patterns, the as-synthesized nanopowders were poorly crystalline apatite in the absence and presence of different dopant contents. The hexagonal HA and tricalcium phosphate (β-TCP) phases as biphasic calcium phosphate mixtures were formed after heating at 900 °C. In addition to the β-TCP phase, minor extra phases such as calcium oxide (CaO) and calcium pyrophosphate (Ca2P2O7) were identified from the HA decomposition. The FTIR results indicated that the decrease of structural hydroxyl groups depended on both tantalum oxyanions and carbonate contents. In the XPS profile, the Ta 4 f peak of the doped sample could be decomposed into four main components, which showed different oxidation states for tantalum (TaO2 oxide). According to the TEM observations, the doped calcined powder at 900 °C was composed of uniform nanoneedles with an average length and width of 120 ± 50 and 10 ± 5 nm, respectively

A Comparison in Mechanical Properties of Cermets of Calcium Silicate with Ti-55Ni and Ti-6Al-4V Alloys for Hard Tissues Replacement

This study investigated the impact of calcium silicate (CS) content on composition, compressive mechanical properties, and hardness of CS cermets with Ti-55Ni and Ti-6Al-4V alloys sintered at 1200°C. The powder metallurgy route was exploited to prepare the cermets. New phases of materials of Ni16Ti6Si7, CaTiO3, and Ni31Si12 appeared in cermet of Ti-55Ni with CS and in cermet of Ti-6Al-4V with CS, the new phases Ti5Si3, Ti2O, and CaTiO3, which were emerged during sintering at different CS content (wt%). The minimum shrinkage and density were observed in both groups of cermets for the 50 and 100 wt% CS content, respectively. The cermets with 40 wt% of CS had minimum compressive Young’s modulus. The minimum of compressive strength and strain percentage at maximum load were revealed in cermets with 50 and 40 wt% of CS with Ti-55Ni and Ti-6Al-4V cermets, respectively. The cermets with 80 and 90 wt% of CS showed more plasticity than the pure CS. It concluded that the composition and mechanical properties of sintered cermets of Ti-55Ni and Ti-6Al-4V with CS significantly depend on the CS content in raw cermet materials. Thus, the different mechanical properties of the cermets can be used as potential materials for different hard tissues replacements

Effect of Geometrical Parameters on the Performance of Longitudinal Functionally Graded Femoral Prostheses

This study aimed to assess the performance of different longitudinal functionally graded femoral prostheses. This study was also designed to develop an appropriate prosthetic geometric design for longitudinal functionally graded materials. Three-dimensional models of the femur and prostheses were developed and analyzed. The elastic modulus of these prostheses in the sagittal plane was adjusted along a gradient direction from the distal end to the proximal end. Furthermore, these prostheses were composed of titanium alloy and hydroxyapatite. Results revealed that strain energy, interface stress, and developed stress in the femoral prosthesis and the bone were influenced by prosthetic geometry and gradient index. In all of the prostheses with different geometries, strain energy increased as gradient index increased. Interface stress and developed stress decreased. The minimum principal stress and the maximum principal stress of the bone slightly increased as gradient index increased. Hence, the combination of the femoral prosthetic geometry and functionally graded materials can be employed to decrease stress shielding. Such a combination can also be utilized to achieve equilibrium in terms of the stress applied on the implanted femur constituents; thus, the lifespan of total hip replacement can be prolonged. 2014 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.Scopu

Comparison of Various Functionally Graded Femoral Prostheses by Finite Element Analysis

This study is focused on finite element analysis of a model comprising femur into which a femoral component of a total hip replacement was implanted. The considered prosthesis is fabricated from a functionally graded material (FGM) comprising a layer of a titanium alloy bonded to a layer of hydroxyapatite. The elastic modulus of the FGM was adjusted in the radial, longitudinal, and longitudinal-radial directions by altering the volume fraction gradient exponent. Four cases were studied, involving two different methods of anchoring the prosthesis to the spongy bone and two cases of applied loading. The results revealed that the FG prostheses provoked more SED to the bone. The FG prostheses carried less stress, while more stress was induced to the bone and cement. Meanwhile, less shear interface stress was stimulated to the prosthesis-bone interface in the noncemented FG prostheses. The cement-bone interface carried more stress compared to the prosthesis-cement interface. Stair climbing induced more harmful effects to the implanted femur components compared to the normal walking by causing more stress. Therefore, stress shielding, developed stresses, and interface stresses in the THR components could be adjusted through the controlling stiffness of the FG prosthesis by managing volume fraction gradient exponent

Self‐Healing Polyester Urethane Supramolecular Elastomers Reinforced with Cellulose Nanocrystals for Biomedical Applications

Stretchable self-healing urethane-based biomaterials have always been crucial for biomedical applications; however, the strength is the main constraint of utilization of these healable materials. Here, a series of novel, healable, elastomeric, supramolecular polyester urethane nanocomposites of poly(1,8-octanediol citrate) and hexamethylene diisocyanate reinforced with cellulose nanocrystals (CNCs) are introduced. Nanocomposites with various amounts of CNCs from 10 to 50 wt% are prepared using solvent casting technique followed by the evaluation of their microstructural features, mechanical properties, healability, and biocompatibility. The synthesized nanocomposites indicate significantly higher tensile modulus (approximately 36–500-fold) in comparison to the supramolecular polymer alone. Upon exposure to heat, the materials can reheal, but nevertheless when the amount of CNC is greater than 10 wt%, the self-healing ability of nanocomposites is deteriorated. These materials are capable of rebonding ruptured parts and fully restoring their mechanical properties. In vitro cytotoxicity test of the nanocomposites using human dermal fibroblasts confirms their good cytocompatibility. The optimized structure, self-healing attributes, and noncytotoxicity make these nanocomposites highly promising for tissue engineering and other biomedical applications

The effect of nanocrystalline cellulose on flow properties of fiber crop aqueous suspension

Nanocrystalline cellulose (NCC) a nature-based material, has gained significant attentions for its unique properties. The present study aims to investigate the flow behavior of cellulosic suspension containing non-wood pulp fibers and NCC, by means of rheological and pressure drop measurements. The NCC sample was prepared by sulfuric acid hydrolysis from Acacia mangium fibers. The rheological properties of kenaf/NCC suspensions were studied using viscosity and yield stress measurements. The pressure drop properties of the suspension flow were studied with respect to variation in flow velocity (0.4 m/s–3.6 m/s) and the NCC concentration (70 mg/l and 150 mg/l). The pressure drop results showed that the pulp suspension containing 150 mg/l NCC had higher drag reduction than kenaf suspension alone. The present insights into the flow of pulp/NCC suspension provide a new data and promote the application of NCC in industries

Mechanical and in vitro biological performance of graphene nanoplatelets reinforced calcium silicate composite.

Calcium silicate (CaSiO3, CS) ceramic composites reinforced with graphene nanoplatelets (GNP) were prepared using hot isostatic pressing (HIP) at 1150°C. Quantitative microstructural analysis suggests that GNP play a role in grain size and is responsible for the improved densification. Raman spectroscopy and scanning electron microscopy showed that GNP survived the harsh processing conditions of the selected HIP processing parameters. The uniform distribution of 1 wt.% GNP in the CS matrix, high densification and fine CS grain size help to improve the fracture toughness by ∼130%, hardness by ∼30% and brittleness index by ∼40% as compared to the CS matrix without GNP. The toughening mechanisms, such as crack bridging, pull-out, branching and deflection induced by GNP are observed and discussed. The GNP/CS composites exhibit good apatite-forming ability in the simulated body fluid (SBF). Our results indicate that the addition of GNP decreased pH value in SBF. Effect of addition of GNP on early adhesion and proliferation of human osteoblast cells (hFOB) was measured in vitro. The GNP/CS composites showed good biocompatibility and promoted cell viability and cell proliferation. The results indicated that the cell viability and proliferation are affected by time and concentration of GNP in the CS matrix