Hassan S. Hedia

Cell and nanoparticle transport in tumour microvasculature: the role of size, shape and surface functionality of nanoparticles

Through nanomedicine, game-changing methods are emerging to deliver drug molecules directly to diseased areas. One of the most promising of these is the targeted delivery of drugs and imaging agents via drug carrier-based platforms. Such drug delivery systems can now be synthesized from a wide range of different materials, made in a number of different shapes, and coated with an array of different organic molecules, including ligands. If optimized, these systems can enhance the efficacy and specificity of delivery compared with those of non-targeted systems. Emerging integrated multiscale experiments, models and simulations have opened the door for endless medical applications. Current bottlenecks in design of the drug-carrying particles are the lack of knowledge about the dispersion of these particles in the microvasculature and of their subsequent internalization by diseased cells (Bao et al. 2014 J. R. Soc. Interface 11, 20140301 (doi:10.1098/rsif.2014.0301)). We describe multiscale modelling techniques that study how drug carriers disperse within the microvasculature. The immersed molecular finite-element method is adopted to simulate whole blood including blood plasma, red blood cells and nanoparticles. With a novel dissipative particle dynamics method, the beginning stages of receptor-driven endocytosis of nanoparticles can be understood in detail. Using this multiscale modelling method, we elucidate how the size, shape and surface functionality of nanoparticles will affect their dispersion in the microvasculature and subsequent internalization by targeted cells.

Improved Stress Shielding on a Cementless Tibia Tray using Functionally Graded Material

Abstract Aseptic loosening of the tibial component is a primary concern of total knee replacement (TKR), which may be caused by stress shielding in cancellous bone of tibia and may require subsequent revision surgery. There is no doubt that materials and design are important issues within general product development and even more in biomedical products. In this study, a 2D axisymmetric finite element model of the tibia and tibial prosthesis is designed to find the optimal functionally graded material (FGM) constituents as well as the optimal gradation direction. The results showed that the optimal design of a tibia tray material is represented by grading it vertically from hydroxyapatite at the end of stem tibia to collagen at the upper layers of the tibia plate. This new design is found to reduce stress shielding in cancellous epiphyseal and diaphyseal bone by 78 % and 68 %, respectively, compared to cementless titanium tibia tray. However, the interface shear stress in cancellous diapyseal bone is reduced by 24 % using FGM tibia tray, which will reduce the pain at the end of stem after the surgery. It is concluded that the new tibial design will increase the life of the knee prosthesis.

Effect of agglomeration and dispersion on the elastic properties of polymer nanocomposites: A Monte Carlo finite element analysis

Abstract Owing to their superior mechanical and physical properties, carbon nanotubes (CNT) seem to hold a great promise as an ideal reinforcing material for composites of high-strength and low-density. In most of the experimental results up to date, however, only modest improvements in the strength and stiffness have been achieved by incorporating carbon nanotubes in polymers. In the present paper, the influence of single wall carbon nanotube agglomeration on the effective stiffness is analyzed by using an Eshelbys inclusion model. Analytical expressions are derived for the effective elastic stiffness of single wall carbon nanotube-reinforced composites with the effects of agglomeration. The present study not only provides the important relationship between the effective properties and the morphology of CNT-reinforced composites, but also may be useful for improving and tailoring their mechanical properties. In addition, a multiscale Monte Carlo finite element method (MCFEM) was used for determining mechanical properties of polymer nanocomposites (PNC) that consist of polymers reinforced with single-walled carbon nanotubes (SWCNT). Specifically, the method uses a multiscale homogenization approach to link the structural variability at the nano/micro scales with the local constitutive behavior. Subsequently, the method incorporates a FE scheme to determine the Youngs modulus and Poisson ratio of PNC. The use of the computed properties in macroscale modeling is validated by comparison with experimental tensile test data.

Design, Manufacture and Analysis of Composite Epoxy Material with Embedded MWCNT Fibers

Abstract The weight and fuel savings offered by composite materials make them attractive not only to the military, but also to the civilian aircraft, space, and automobile industries. In these industries, bolted and riveted joints are extensively used as a primary method for structural joining. Bolted joints in composite materials have complex failure modes, and hence the demand for improving their performance exists. The main objective of this work is to improve the performance of bolted joints in composite structures by introducing nanoparticles/fibers around the expected failure zone. The literature on this issue showed shortcomings in the investigations of such materials. Most of the investigations in this field aimed to enhance the mechanical properties of epoxy materials, which cannot be used alone for high performance structural applications due to their low mechanical properties. In the present work, epoxy resin was modified with different types of nanofillers including multi walled carbon nanotubes (MWCNT). Nano-phased epoxy was used to fabricate different types of nanocomposites as well as nano-hybridized glass fiber reinforced composite laminates. Therefore, six different advanced materials were fabricated including a nanocomposite material (MWCNT/E), a quasi-isotropic nano-hybridized composite laminate (QI-GFR/MWCNT/E), a unidirectional nano-hybridized composite laminate (UD-GFR/MWCNT/E) and a control panel manufactured without nano-fillers (neat epoxy, QI-GFR/E, UD-GFR/E). The materials were characterized by tension and compression tests. The obtained properties are essential for the validation of respective finite element analysis. The results showed improvements in the tensile and compressive properties (strength and modulus) of the fabricated nanocomposites (MWCNT/E) compared with neat epoxy. The hybridized composite laminate with MWCNT showed high improvements in their mechanical properties compared to the composite laminates without nanofillers.

A New Design of Dental Implant Coating Using Functionally Graded Material

Abstract Dental implantation treatment has developed into one of the most successful prosthetic technologies. A critical progress made in this area was the development of biocompatible materials to enable an engineered device (implant) to integrate within its surrounding bony tissues. Titanium and its alloys have been widely adopted as such materials due to their excellent biocompatibility. However, their mechanical properties largely differ from those in host bony tissues, which is problematical in osseointegration and bone remodeling. The challenge to face in prosthetics is to develop both biologically and mechanically compatible biomaterials for this purpose. Few existing research has been reported to develop an optimized design of functionally graded material (FGM) dental implant for promoting a long-term success. One of the authors of the present Contributions has previously designed a new FGM dental implant coating graded in axial direction from titanium at the apex to collagen at the basis of the dental implant. The aim of this investigation is to design a new gradation direction of FGM dental implant coating as well as studying the effect of coating thickness on the maximum von Mises stresses in bone adjacent to the coating layer. The gradation of the elastic modulus is changed along the longitudinal direction. Stress analysis using a finite element method showed that using a coating of 150 μm thickness, which is functionally graded from titanium at the outer shell adjacent to the bone to collagen at the inner shell adjacent to the implant, will reduce the maximum von Mises stress by 16 % and 13 % compared with the common conventional coating materials such as collagen and hydroxyapatite coatings, respectively. However, using FGM coating graded from hydroxyapatite at the outer shell to titanium at the inner shell reduces the maximum von Mises stress by 8 % and 5 % compared with collagen and hydroxyapatite coatings, respectively, but this gradation can improve the biocompatibility and can also achieve a full integration of the implant within the living bone, which increases the life of the implant.

Design, manufacture and analysis of composite epoxy material with embedded silicon carbide (SiC) and alumina (Al2O3) nanoparticles/fibers

Abstract The main objective of the presented study is to improve the performance of composite structures by introducing nanoparticles/fibers in the epoxy resin. The literature on this issue showed shortcomings in the investigations of such materials. Most of the investigations in this field are to enhance the mechanical properties of epoxy materials, which cannot be used alone for high performance structural applications due to their low mechanical properties. In the present work, the epoxy resin was modified with these different types of nanofillers such as silicon carbide (SiC) and alumina (Al2O3) nanoparticles. The nanophased epoxy was used to fabricate different types of nanocomposites as well as nano-hybridized glass fiber reinforced composite laminates. Therefore, nine different advanced materials have been fabricated including two nanocomposite materials (SiC/E and Al2O3/E), two quasi-isotropic nano-hybridized composite laminates (QI-GFR/SiC/E and QI-GFR/Al2O3/E), two unidirectional nano-hybridized composite laminates (UD-GFR/SiC/E and UD-GFR/Al2O3/E), and three control panels manufactured without nanofillers (neat epoxy, QI-GFR/E, UD-GFR/E). The materials were characterized under tension and compression. The results showed improvements in the tensile and compressive properties (strength and modulus) of the fabricated nanocomposites (SiC/E, and Al2O3/E) compared with neat epoxy. The hybridized composite laminate with Al2O3 showed high improvements in its mechanical properties compared to the composite laminates without nanofillers. In contrast, discouraging mechanical properties were observed for SiC hybridized composite laminate. Due to the many variables studied in the present work, the literature list will be long. The investigated parameters include nanofillers, nanocomposites, nano-hybridized advanced composite laminates, mechanical properties, glass transition temperature (Tg), bolted joint parameters and sonication parameters.

A New Design of Hip Prosthesis Coating using Functionally Graded Material

Abstract Titanium and its alloys which have been widely used in many prostheses carry the major joint load and cause stress shielding. Thus, the bone might become osteoporotic due to lack of physiological stress flow in common hip replacement. Therefore, the optimization of hip joint materials is one of the most challenging tasks in prosthetic design. It is found in the literature that there is a great contradiction regarding the use of hydroxyapatite (HAP) coating. In this study a finite element analysis (FEA) and optimization techniques have been carried out in order to find a new design of hip stem coating using functionally graded material (FGM) to reduce stress shielding at the proximal medial part of the femur, as well as reducing the interface shear stress at the interface between the coating and the bone which directly affects the implantation and long-term stability. This work is divided into two parts: in the first part, the gradation of the elastic modulus of the coating material has been changed in the vertical direction, while the second part changes the elastic modulus in the horizontal direction. The optimal design of the first and second models was compared with HAP coating and with homogenous uncoated titanium stem. The design optimization of the first model revealed, using a coating material consisting of HAP at the upper layer of the coating graded to collagen at the lower layer, increases the maximum von Mises stress in bone at the proximal medial part of the femur by 65% and 19% compared to titanium stem and titanium coated with HAP, respectively. The maximum lateral interface shear stress in the bone at the bone/coating interface is reduced by 23% and 12%, respectively. However, the maximum medial interface shear stress in the bone at the bone/coating interface is reduced by 39% and 14% compared to titanium stem and titanium coated with HAP, respectively. The design optimization of the second model revealed, using a coating material consisting of collagen at the inner layer adjacent to stem graded to HAP at the outer layer adjacent to bone, increases the maximum von Mises stress at the proximal medial part of the femur by 60% and 15% compared to titanium stem and titanium coated with HAP, respectively. The maximum lateral interface shear stress is reduced by 18% and 6%, respectively. However, the maximum medial interface shear stress is reduced by 35% and 8% compared to titanium stem and titanium coated with HAP, respectively.

Fatigue Life Behaviour of Nanocomposite Coated Carbon Steel

Abstract Recently, nano-materials have received increasingly more attention for their potential applications as structural and functional materials. The unique mechanical properties of CNTs, their high strength and stiffness and the enormous aspect ratio provide potentials for the improvement of the mechanical properties of structural materials. The aim of this research is to investigate experimentally the effect of nanocomposite coating on the fatigue life of carbon steel AISI 1045 specimens with different surface finishes. Nanoadhesives of epoxy resin are synthesized and evaluated. They are originally modified by multiwalled carbon nanotubes (MWCNT) with 0.5 wt.-% as reinforcement. Fatigue tests are conducted on the respective specimens by a rotating bending machine of the cantilever type. Comparing the results for specimens coated with 0.5 wt.-% MWCNT-epoxy composition with the base materials it is found that fatigue life increased five times for a roughness of 0.3 µm and three times for an average specimen roughness of 0.8, 1.6 and 2.5 µm, respectively.

Material optimization of a cemented tibia tray using functionally graded material

Abstract Joint replacement surgeries are doubtlessly the gift of science and technology for human welfare. In the cemented knee replacement joint, the stiffer implant carries the majority of the load, which is actually carried by the bone itself before implantation. The resulting implant induced stress-shielding and subsequent bone remodeling causes bone resorption at the proximal bone under the tibia tray. The aim of this study is to optimize the material of the cemented tibia tray using functionally graded material FGM. The target is to find the optimal material and the optimal gradation direction for the cemented tibia tray. The results showed that the optimal vertical FGM changed from titanium at the lower tibia stem to bioglass at the upper layers of the tibia tray. The vertical FGM reduced the stress shielding by 56 and 80 % in cancellous epiphyseal and diaphyseal bone, respectively, compared to cemented titanium tibia tray. However, the optimal horizontal FGM changes from titanium at the stem core to bioglass at the rim of tibia tray layers. This horizontal gradation reduced the stress shielding in cancellous epiphyseal bone by 62 %. However, the stress shielding in cancellous diaphyseal bone did not change compared to cemented titanium tibia tray.

Effect of Nanocomposite Coating with Different Concentrations on the Fatigue Life of Stainless Steel316 with Different Surface Roughness

Abstract Many experimental researches succeeded to improve fatigue properties of materials by treating their surfaces. In this study, the benefits of nanocomposite material are used to investigate the fatigue life of stainless steel specimens with different surface roughness. Nanocomposite coating was prepared with different concentrations (0.3 %, 0.5 %, and 0.7 %) of multi wall carbon nano tubes MWCNT. This coating was applied on stainless steel test specimens with four different values of the surface roughness (0.3, 0.8, 1.6, and 2.5). It turned out that fatigue life increased more than four times compared to the original material when using 0.5 % and 0.7 % MWCNT concentration in coating composition with the 0.3 surface roughness, while no significant difference was detected at another roughness.