Enhancing Polymethyl Methacrylate Prostheses for Cranioplasty with Ti mesh Inlays

Biocompatible polymers such as polymethyl methacrylate (PMMA), despite fulfilling biomedical aspects, lack the mechanical strength needed for hard-tissue implant applications. This gap can be closed by using composites with metallic reinforcements, as their adaptable mechanical properties can overcome this problem. Keeping this in mind, novel Ti-mesh-reinforced PMMA composites were developed. The influence of the orientation and volume fraction of the mesh on the mechanical properties of the composites was investigated. The composites were prepared by adding Ti meshes between PMMA layers, cured by hot-pressing above the glass transition temperature of PMMA, where the interdiffusion of PMMA through the spaces in the Ti mesh provided sufficient mechanical clamping and adhesion between the layers. The increase in the volume fraction of Ti led to a tremendous improvement in the mechanical properties of the composites. A significant anisotropic behaviour was analysed depending on the direction of the mesh. Furthermore, the shaping possibilities of these composites were investigated via four-point bending tests. High shaping possibility was found for these composites when they were shaped at elevated temperature. These promising results show the potential of these materials to be used for patient-specific implant applications

Deep drawing behaviour of steel-glass fibre-reinforced and non-reinforced polyamide-steel sandwich materials

Thermoplastic-based fibre metal laminates (FMLs) have gained increasing interest in the automotive industry due to their forming potential—especially at higher temperatures—into complex components compared to thermoset-based ones. However, several challenges arise while processing thermoplastic-based FMLs. One the one hand, forming at room temperature (RT) leads to early failure modes, e.g., fracture and delamination. On the other hand, warm forming can extend their forming limits, although further defects arise, such as severe thickness irregularities and wrinkling problems. Therefore, this study focuses on developing different approaches for deep drawing conditions to deliver a promising, feasible, and cost-effective method for deep-drawn FML parts. We also describe the defects experimentally and numerically via the finite element method (FEM). The FMLs based on steel/glass fibre-reinforced polyamide 6 (GF-PA6/steel) are studied under different deep drawing conditions (temperatures, punch, and die dimensions). In addition, mono-materials and sandwich materials without fibre reinforcement are investigated as benchmarks. The results showed that the best deep drawing condition was at a temperature of 200 ◦C and a die/punch radius ratio of 0.67, with a gap/thickness ratio of ≤2.0. The FEM simulation via Abaqus 6.14 was able to successfully replicate the anisotropic properties and wrinkling of the GF-PA6 core in an FML, resembling the experimental results

Stretching and forming limit curve of steel-glass fibre reinforced and non-reinforced polyamide-steel sandwich materials

This paper focuses on investigating the forming behaviour of sandwich materials composed of steel sheets and glass fibre-reinforced polyamide 6 (GF-PA6), i.e., thermoplastic-based fibre metal laminates (FML). Stretching and forming limit curve (FLC) determination of FML with different cover/core layer thickness ratios at various forming temperatures, i.e., at room temperature (RT), 200 and 235 ◦C, are the main approaches for characterizing their formability. In addition, the formability of mono-materials and non-reinforced sandwich materials is investigated as a reference. For a successful test and reliable results, several technical issues are considered, such as the suitable lubrication configuration and digital image correlation at elevated forming temperatures. The results revealed that the formability of non-reinforced sandwich materials with different core layer thicknesses exhibited compared formability to their monolithic steel sheet and no remarkable improvement in their formability with increasing the temperature up to 200 ◦C. Conversely, the formability of FML shows significant improvement (approx. 300%) with increasing temperature with a forming depth of about 33 mm at 235 ◦C compared to only 12 mm at RT

Forming potential of low-density laminates

Metal/polymer/metal sandwich laminates show a rising rate in a variety of applications, for instance in automotive and aircraft industry. Due to the dissimilarity between the metal skin sheets and the polymer core, characterizing the forming potential of such laminates is a necessity. In this study, steel skin sheets and polypropylene-polyethylene copolymer as core sheet – called sandwich laminates - were used. They were produced in a roll bonding process using an adhesive agent. One major research point in IMET is investigating the effect of core and skin thicknesses on the forming behavior and mechanical properties of the sandwich laminates. Forming behavior is evaluated using deep drawing in addition to determining the forming limit curves (FLC). Bonding strength is evaluated by lap shear tests. More-over, the durability of the steel/polymer joints are evaluated under hydrothermal ageing conditions following heating/cooling regime cycles. Basically, the mechanical properties were determined using tensile testing. The adhesion test results show good adhesion strength and a cohesive failure mode. The lap shear strength after ageing shows no remarkable deterioration. The deep drawability of the sandwich laminates depends on the thicknesses of the layers and their volume fraction. With increasing the core thickness, the limiting drawing ratio (LDR) decreases and the probability of wrinkling in the flange area and cracking is higher as well. In case of different skin thicknesses in one sandwich, the best setting condition is to position the thinner skin in contact with the forming tool (punch) if acceptable by design

Experimental Investigation on Local and Global Texture Evolution in Drawing Seamless Copper Tubes

Mass flow inequality in the initial stage of tube processing can lead to eccentricity and micro- and nano-structural changes that affect residual stress and texture development. In this study, the macro- and micro-texture development of copper tubes drawn with a tilted die was investigated using three methods: synchrotron, neutron diffraction, and electron backscatter diffraction, in the positions of maximum and minimum wall thickness of the tubes. Understanding how a tilted die can affect the texture development in copper tubes is the main aim of this study. The micro-texture results of EBSD examinations showed the same behavior at the maximum and minimum sides of the as-received tube, as observed using the synchrotron diffraction method as well as macro-texture measurements. The cube texture component was found to be the predominant orientation in the as-received tube. However, it almost disappeared after drawing with −5° tilting. By contrast, the Cu texture component increased significantly. Before drawing, the cube component varied strongly across the wall thickness. After drawing, however, there was no noticeable texture gradient across the wall thickness. The analyses showed that tilting is not creating an inhomogeneous texture development over the circumference

Adhesion Behavior of Ti–PMMA–Ti Sandwiches for Biomedical Applications

International audienceAbstract The “stress-shielding” problem, common with metallic implants, may be solved by using biocompatible sandwiches with a polymeric core between two metallic skin sheets. To achieve such sandwiches, a process route has been developed, beginning with the grafting of poly-(methyl-methacrylate) (PMMA) on titanium (Ti) sheets via the “grafting from” technique. Grafting resulted in variable thicknesses of PMMA on the Ti sheets. Hot-pressing was used to prepare semi-finished Ti–PMMA–Ti sandwiches. The adhesion was achieved by the interpenetration between PMMA sheet and the grafted PMMA chains. Investigation was carried out to understand the influence of the grafted PMMA thickness on the adhesion strength. Similar adhesion strengths were found for the sandwiches despite variable grafted PMMA thicknesses, indicating a successful grafting of PMMA on large-scale Ti sheets. The adhesion followed the autohesion theory, where a time-dependent increase in adhesion strength was found for the sandwiches

Double functionalization for the design of innovative craniofacial prostheses

International audienceTitanium (Ti) is the most commonly used material for cranial prostheses. However, this material does not exhibit the same mechanical properties as the bone. Incorporating polymers onto Ti by combining both their properties is a solution to overcome this issue. Thus, sandwich materials made of two Ti skin sheets and a poly(methyl methacrylate) (PMMA) core are promising structures to design biomedical prostheses. The "grafting to" and "grafting from" procedures to functionalize the Ti/PMMA interface are described in this paper as two strategies for chemically connecting PMMA chains on Ti surfaces. The advantage of the first approach is the capacity to control the architecture of the grafted PMMA on Ti. Moreover, a method for selectively grafting a bioactive polymer such as poly(sodium styrene sulfonate) (PNaSS) on one side of the Ti and PMMA on the other side is developed. This contribution presents efficient ways of functionalizing Ti for biomedical applications