R. Ribeiro

Anthropometric measurements to design best-fit femoral stem for the Indian population

Background: The standard commercially available marketed prostheses sometimes may not be the best fit to Indian patients because of the large anatomic variation. Orthopedic surgeons always stress the need for a proper implant–patient match in hip joint replacements, in particular, for a cementless femoral stem. The complications of mismatch are aseptic loosening, improper load distribution, and discomfort. The present study was undertaken to compare the differences in dimensions between femurs of elderly Indians and those of populations from other regions in order to solve the problem of a possible geometric mismatch between a selected implant and the hip joint as far as Indian patients are concerned. Materials and Methods: Measurements were made using computer aided design techniques on computed tomography (CT) scanned images of 98 femurs (56 left and 42 right). The software used to convert the CT images into solid models was MIMICS® (Materialize, Inc., Leuven, Belgium). The geometrical parameters, viz., the femoral head offset, femoral head center (HC), femoral head diameter, femoral head relative position, position of shaft isthmus, neck-shaft angle, bow angle, femoral neck length, canal flare index, femoral length, and canal width at various locations, were chosen to design best-fit standard femoral stems for cementless insertion. These data were compared with the published data of other countries. Results: A difference of 16.8% was found in the femoral head offset between Indian and Swiss populations, which can affect soft tissue tension and range of motion. At a distance of 20 mm above the lesser trochanter (LT), the anteroposterior (AP) canal width was found to differ by 45.4%, when compared with a French population which can affect the mechanical stability of femoral stem. Femoral dimensions of Indian male and female subjects have also been compared and differences evaluated. At the LT, the aspect ratio (ratio of mediolateral canal width and AP canal width) in case of males (1.198) is approximately13% higher than that of females (1.059). Conclusions: This study indicates a need for redesign of femoral stems. The obtained anthropometric femoral dimensions can be used to design and develop indigenous hip joint prosthesis in India. The results of this study can also be used in forensic anthropometric studies.

A tribological and biomimetic study of PI–CNT composites for cartilage replacement

This article presents an investigation into the possible matching of mechanical properties of a polyimide (PI)–carbon nanotube (CNT) composite system to natural cartilage tissue. Currently used ultrahigh molecular weight polyethylene (UHMWPE) used in total joint replacements presents certain drawbacks due to a mismatch in mechanical and tribological properties with those of a natural bone joint. Natural cartilage tissue is a composite material itself, being composed of collagen fibers, hydrophilic proteoglycan molecules, cells and other constituents. The current investigation attempts to mimic the mechanical and tribological properties of natural cartilage tissue by varying the CNT concentration in a PI matrix. Nanoindentation and pin-on-flat tribological tests were conducted for this purpose. It was found that the coefficient of friction (COF) reached a minimum at a concentration of 0.5% CNT (by volume) when articulated against Ti6Al4V alloy. When articulated against Ti6Al4V alloy in the presence of a lubricant, the minimum COF was obtained at a concentration of 0.2% CNT. The maximum penetration depth under nanoindentation varied with CNT concentration and indicated that the mechanical properties could be tailored to match that of cartilage tissue. A closer investigation into this behavior was carried out using scanning electron, transmission electron, and atomic force microscopy. It was noticed that there is good bonding between the CNTs and polyimide matrix. There was a ductile to brittle transition as the concentration of CNT was increased. Competing interactions between nanotube–matrix and nanotube–nanotube are possible reasons for the deformation and friction behavior identified.

Development of echo control strategy for AK prosthesis: An embedded system approach

In spite of wide availability, the current prosthesis does not meet most of the functional requirements along with the other parameters like metabolic energy, training period and cost. This paper presents the development of a low cost Above Knee (AK) prosthesis which regulates the knee damping automatically by calculating the speed of walking from the data of the normal limb. The prosthesis uses an additional hardware of wireless transmission system, which does not add to the cost significantly, but promises a speed adaptive control of AK prosthesis and thus requires significantly less training time for the amputee.

Characterization of the Electron Beam Curing of Cationic Polymerization of Diglycidylether of Bisphenol A Epoxy Resin

The characterization of electron beam (E-beam) curing of diglycidyl-ether of bisphenol A-diaryliodonium hexafluoroantimonate epoxy resin-initiator system is reported as a function of (i) diaryliodonium hexafluoroantimonate catalyst (initiator) concentrations of 0.1-10 parts per hundred (phr) and (ii) total electron beam doses of 5-150 kilogray (kGy). The in situ E-beam temperature of the resin is monitored as a function of dose-time characteristics. The degree of cure is monitored after radiation exposure by Fourier transform infrared spectrometry (FTIR) and the glass transition temperatures (Tg) by differential scanning calorimetry (DSC). The degree of cure and cure rate increased with total dose exposure and initiator concentration. The maximum cure rate occurred at 5 kGy exposure and, thereafter, decreased as reactive species concentration decreased. The maximum in situ E-beam temperature of 76°C was recorded for the resin containing 10 phr of initiator, with a maximum degree of cure of 94% and a glass transition temperature of 86 C, indicating that the cure reactions under E-beam are glassy state diffusion controlled. The resin glass transition temperatures are considerably lower than the thermally cured glass transition temperatures of 170 C because of H2O termination reactions at the lower E-beam cure temperatures that result in a poor cross-linked network. In addition, the diaryliodonium hexafluoroantimonate catalytic activity for epoxide cationic polymerization is retarded by H2O. E-beam exposure causes the diaryliodonium hexafluoroantimonate to dissociate into active catalytic species, such as HSbF6, well below 100°C compared to catalytic thermal induced dissociation near 200°C. The E-beam cure reaction rate is modeled as a function of degree of cure and dose exposure by a standard autocatalytic kinetic model.

In situ observation of stress-induced Au–Si phase transformation

Nonequilibrium AuSi3 was found due to indenting contact forces at a gold and silicon interface. An in situ transmission electron microscope was used to observe interactions at the material interface during nanoindentation and to identify crystal structures. Furthermore, sliding of a gold-coated atomic-force microscope probe over a silicon substrate forms organized nanostructures. An evaluation of the observed interfacial mechanisms concluded that the contact stress triggered the phase transformation leading to the formation of a metastable interface that mediates the adhesion of contacting materials.

Effect of load distribution of the backpack- a design study

Backpack or school bag weight carried by children has raised concerns in worldwide countries over recent decades. School going children face a major problem because of the heavy weight they carry to school everyday as it leads to many problems such as a bent posture and decreased work efficiency. The prescribed weight to be carried by children has been determined to be 10–15% of their body weight; however literature shows that the majority of them carry up to 30% of their body weight. Design changes were introduced in a standard backpack to see how it would facilitate load distribution over the upper torso such that the load is not concentrated on the trunk alone. Subjects were asked to carry out trials with 0% body weight, 15% body weight with a standard backpack and 15% body weight with the modified backpack with arm straps. ECG data using Biopac MP150 was collected and the results between the three trials were compared. The results show loads of 15% of body weight or above significantly increased the amplitude of the R wave which was lower in case of carrying 15% of body weight with the arm strap. Thus the modified backpack has a potential for efficient load carriage.

A tribological comparison of pure and boronized chromium

Boronized metals are potential candidate materials for various industrial applications as well as for joint arthroplasty. This is due to their high hardness and corrosion resistance. In the present research, we investigated the tribological performance of boronized chromium when worn against bearing steel E52100. Pure chromium was used as a control material and tested under similar conditions. Three test conditions were used-dry sliding, with water, and with simulated body fluid (SBF). The highest coefficient of friction obtained was for chromium boride under dry sliding conditions. Water and SBF acted as lubricants and lowered the coefficient of friction. The friction coefficient for Cr and chromium boride was lowest under SBF conditions. SEM analysis showed that the wear modes were different under different test conditions. TEM analysis showed a layered-like structure of debris that could have acted as a lubricant and caused a very low friction coeffi.

Kinematics-coordinated walking pattern based on embedded controls

Electromechanical above-knee prosthetics are widely available, and are reliant on repetitive knee movements of fixed length/angle. This work explores the viability of developing adaptive movements on existing prototypes, through embedded controls from 8051-class 8-bit microcontroller units (MCUs). The system includes an integrated goniometer, intended for measuring the knee angle of the sound limb. The phase delay is subsequently processed to bring about kinematic coordination in the proposed echo-controlled prosthetic.

Effect of SWCNT on Tribological Behavior of Polymeric Nanocomposite

The nanoscale structure of single-walled carbon nanotubes (SWCNTs) has unique properties. These nanostructured additives can induce unusual characteristic in many polymer matrix. In one of our recent experiments, it was found that when adding SWCNTs into a polyimide (PI) matrix, friction becomes a function of the concentration of the additive. In this research, we analyze the behavior of the SWCNTs-PI nano-composite using an approximation approach. We report that the frictional behavior of the nanocomposite is dominated by the elastic and plastic deformation through randomly dispersed SWCNTs under different loading conditions. At low concentration of SWCNTs, its elasticity dominates the properties of composite while at higher concentration, plastic behavior of tubes plays a major role in describing the properties of composite.© 2008 ASME

Biocomposites: Exploring Surface Texture for Cell Adhesion

This paper discusses the principles behind effects of surface roughness and porosity of materials on cell adhesion, an important question in biocomposites. Literature provided controversial reports of surface roughness effects. We used new evidence to illustrate how cells are attached to polymeric materials.