Journal of Biomimetics, Biomaterials and Tissue Engineering Vol. 9

Abstract: Pure titanium and titanium alloys are materials widely used in orthopaedics and dental surgery because of their mechanical properties, chemical stability and biocompatibility. Although excellent clinical results have been shown, traditional porous metals have several inherent limitations (low volumetric porosity, relatively high modulus of elasticity and low frictional characteristics, availability as a coating only). With the aim of moving beyond these limits, improving the potentiality of osteointegration and consequently the stability of prosthetic implants, a new highly porous titanium biomaterial (Trabecular Titanium™, TT) has been developed. In this in vitro study, we are testing the effects of TT on osteoblast-like cells (MG63) cultured on disks of this biomaterial by using DNA microarrays containing 20,000 genes. We identified several genes covering a broad range of functional activities whose expression was significantly up- or down-regulated. Findings from this study can give a detailed description of the genetic effects TT has on human osteoblast-like cells in vitro. We demonstrated that TT stimulates osteoblast proliferation and differentiation, and reduces osteoblast apoptosis. Moreover, TT limits osteoclastogenesis, inflammation and reduces the immunologic events against the material, modulating genes related to the immune system. Therefore, all these effects contribute to improve osseointegration and consequently survival of the prosthetic implants. These reported data encourage the clinical application of Trabecular Titanium™ to prosthetic devices.

Abstract: It is known that conventional scaffold manufacturing techniques have low reproducibility and control of the micro-architecture features. Although there have been advances in bone tissue engineering fabrication, there is no consensus on the optimized parameter designs or clear understanding of the microfluidic interactions required for tissue regeneration. In this work, we introduce a new inexpensive fabrication method of producing pore designs of 3D-elastomeric structures with high controlled geometry of orthogonal arrays. The present fabrication method utilizes a permanent and reusable micro-machined mould along with a micro-casted process to efficiently fabricate diverse 3D feature directly. This fabrication method, without multiple process steps, would be suitable to support experiments of controlled environment for flow effects in 3D bone scaffolds.

Abstract: This in vitro study compared the effects of nucleotomy alone, with nucleotomy then implantation with a novel nucleus replacement device (D3 device) in a single segment kangaroo spine model. This study utilised dynamic biaxial biomechanical testing of intact, nucleotomy and nucleus replacement implant conditions to evaluate the kinematic behaviour of the single segment kangaroo lumbar spine. Studies have examined the biomechanical efficacy of invasive treatments such as Total Disc Replacement and Intervertebral Fusion for the treatment of chronic low back pain, however no studies to date have investigated the biomechanical effects of a novel elastomeric compressive load sharing nucleus replacement device. Kangaroo lumbar spine motion segments with all musculature, ligamentous tissue and posterior elements removed, were tested in intact state prior to undergoing nucleotomy or nucleotomy then nucleus implantation using the D3 device. All specimens were tested in flexion-extension and lateral-bending; Range of motion (ROM), Neutral Zone (NZ), Hysteresis (H), and Elastic Stiffness (ES) were evaluated. Nucleotomised motion segments demonstrated a 30% to 90% increase in ROM, NZ, H, but not ES for all Flexion-Extension testing conditions and in Lateral Bending test conditions when compared to intact state. Implantation of the nucleus replacement device demonstrated no significant difference when compared to intact state except for H during Lateral Bending testing conditions when compared to the intact state. Therefore, there was a significant increase in ROM, NZ, and H after Nucleotomy during Flexion-Extension motions and an increase in ROM alone during lateral bending motions in the single segment kangaroo spine model. These changes return to that of the intact state with the placement of a novel nucleus replacement device. Our data suggest that the D3 device tested can restore the kinematic changes of a degenerated disc represented by the nucleotomised single motion segment.

Abstract: Diabetic patients are entangled to various cardiovascular diseases due to increased blood viscosity. Therefore the blood viscosity of diabetic patients is lowered by regular doses of Aspirin or the injection of saline water in order to dilute the blood. This lowers the blood pressure. In this model, the effect of non-Newtonian behaviour on blood flow through a stenosed artery using Casson’s fluid model have been studied and the results depict that the increase in blood flow characteristics are comparatively small due to the non-Newtonian behaviour of the blood. The numerical illustration presented at the end of this paper provides the results for the resistance to flow, apparent viscosity and the wall shear stress through their graphical representations. It has been shown that the resistance to flow, apparent viscosity and wall shear stress increases with the size of the stenosis but these increases are comparatively small due to the non-Newtonian behaviour of the blood indicating the usefulness of its rheological character in the functioning of diseased arterial circulation. A number of comparisons with the existing results have been made in order to validate the applicability of the present model.

Abstract: Patient anatomy specific orthopaedic implant design, fabrication and identification of the most suitable position to fix implants onto bone fractures are challenging problems for surgeons to overcome of the existing shortcomings of commercially available implants. In this work, a 3D finite element model of the left tibial bone of an adult male is developed from Computed Tomography scan images. Proximal tibial fracture type B1 (as per Association for the Study of Internal Fixation) is simulated on the bone model. A geometry specific implant is obtained in order to promote better bone ingrowths and uniform stress distribution, by extracting the surface features of the bone. Finite Element Analysis is performed to evaluate and compare the mechanical properties such as stress, strain and displacement of the bone and implant of four various thicknesses which are fixed at two different positions. The design objectives such as low stress and displacement combination is obtained through the antero-lateral position with 1.8 mm implant thickness. Various material properties are assigned to cortical, cancellous, trabecular regions of the bone and to implants made up of titanium alloy. The results obtained from the Finite Element Analysis are used to evaluate the stability and suitability of the implant for that particular fracture.

Abstract: The thermo-sensitive graft-polymer of Gleditsia Sinensis polysaccharide with N-Isopropyl Acrylamide (NIPAM) was prepared and cross linked with glutaraldehyde to form the hydrogel. The effect of reaction conditions on the graft rate and gel strength of Gleditsia Sinesis Polysaccharide-g-NIPAM was evaluated. The graft rate of Gleditsia Sinensis polysaccharide reached the highest value with temperature of 75°C, reaction time of 5 hours and initiator of 0.025% (ratio of initiator to hydrogel, w/w) respectively. The gel strength of hydrogel, generated by the graft-polymer using glutaraldehyde as a cross linker, had a negative correlation with the grafting rate of the polymer. The influence of ionic strength and concentration of cross linker on gel strength, contractibility and Equilibrium Degree of Swelling (EDS) were investigated. The contractibility and gel strength increased with increments of cross linker and NaCl concentration, while EDS decreased with the increasing amount of cross linker and NaCl concentration. FT-IR and XRD were employed to confirm the grafting reaction between NIPAM and Gleditsia Sinensis polysaccharide. There was a great difference of contracting behavior between the thermo-sensitive hydrogel and ordinary hydrogel, which was mainly manifested by the temperature reaching the Lower Critical Solution Temperature (LCST) of the polymer. The amount of water released from the thermo-sensitive hydrogel per unit time was much more than the ordinary hydrogel, which was mostly due to the conformation transition of the graft-polymer. It was found that the LCST of the polymer was obtained at 36.5°C, which indicates that the polymer has an obvious temperature dependency and could be used in living tissues as drug controlled release materials.

Abstract: The human spinal column is a highly complex and sophisticated system both from an engineering and neurological point of view, and provides a source of biomimetic inspiration for analysis of its function in trauma scenarios. A three-dimensional multi-body model of the 50th percentile male human and discretized neck were built for the study on cervical spine injuries in vehicle frontal impact. The discretized neck includes of cervical spine vertebrae, intervertebral discs, ligaments, and muscles. Following motor front crash evaluations, a finite element vehicle model was propelled straight ahead into a concrete barrier at a speed of 50 km/h. The longitudinal velocity of driver seat was decreased due to the absorbing energy function of the crumple zones. A Hybrid III adult male dummy was seated on a sled, restrained using safety belt, and longitudinal velocity measured from frontal impact was applied to simulate cervical spine injuries. The disk bending loads, interspinous ligament loads and disk shear strain of the cervical spine were analyzed in this paper.

Abstract: Intramedullary (IM) nails are routinely used to stabilize long bone fractures. They can however lead to stress shielding, pain, migration, obstruct hematopoietic tissue, become a loci for infection, and require subsequent surgical retrieval. Novel intra-osseous scaffold (IOS™) prototypes for fracture healing have been developed to function as a regenerative scaffold to enhance callous formation under mechanically stabilized conditions then resorb. Prototype fixation pins and rod systems were formed from glass-reinforced-glass. Flexion, torsion and shear tests were performed to evaluate the composite pins and rods. A modular rod design was successfully deployed and dilated while in a deformable state. When fitted and gripping the intramedullary canal then set in a rigid state. An obliquely sectioned ovine femur was used as a long bone fracture model for deployment and mechanical verification. Flexural support provided by the intramedullary scaffold was superior to multiple k-wire fixation, while the k-wire approach was more stabilizing under torsional loads. Glass reinforced glass samples were mechanically tested after soaking for up to 4 weeks in saline. Strength and modulus of the composite was reduced to approximately 25% of initial values after 2 weeks.

Abstract: The objectives of this study were to compare transport characteristics of the soluble interleukin-2 receptor (CD25) in haemodialyzers (high- and low flux) under equilibrium and sink conditions. Using an in vitro model high-flux polymethylmethacrylate (PMMA), high-flux cellulose acetate (CA), and low-flux polysulfone (PSF) dialyzer membranes were perfused with CD25 through the intracapillary space. Anti-CD25 antibodies added to the extracapillary space resulted in immunoextraction of CD25 after the system had reached steady-state. Results indicate that CD25 was efficiently cleared by both high-flux dialyzers but not the low-flux dialyzer. Furthermore, CD25 interaction with cellulose acetate membranes may promote formation of antigen-antibody lattice structures which disperse after antigen concentrations occur in excess. CD25 did not strongly adsorb to any of the membranes but its mass clearance was significantly enhanced by antibodies in the dialysate compartment. These studies demonstrated the utility of in vitro experiments to elucidate midsize molecule clearance during dialysis therapy.