D. Garcia-Gonzalez

On the mechanical behaviour of PEEK and HA cranial implants under impact loading

The human head can be subjected to numerous impact loadings such as those produced by a fall or during sport activities. These accidents can result in skull fracture and in some complex cases, part of the skull may need to be replaced by a biomedical implant. Even when the skull is not damaged, such accidents can result in brain swelling treated by decompressive craniectomy. Usually, after recovery, the part of the skull that has been removed is replaced by a prosthesis. In such situations, a computational tool able to analyse the choice of prosthesis material depending on the patients specific activity has the potential to be extremely useful for clinicians. The work proposed here focusses on the development and use of a numerical model for the analysis of cranial implants under impact conditions. In particular, two main biomaterials commonly employed for this kind of prosthesis are polyether-ether-ketone (PEEK) and macroporous hydroxyapatite (HA). In order to study the suitability of these implants, a finite element head model comprising scalp, skull, cerebral falx, cerebrospinal fluid and brain tissues, with a cranial implant replacing part of the skull has been developed from magnetic resonance imaging data. The human tissues and these two biocompatible materials have been independently studied and their constitutive models are provided here. A computational model of the human head under impact loading is then implemented and validated, and a numerical comparison of the mechanical impact response of PEEK and HA implants is presented. This comparison was carried out in terms of the effectiveness of both implants in ensuring structural integrity and preventing traumatic brain injury. The results obtained in this work highlight the need to take into account environmental mechanical considerations to select the optimal implant depending on the specific patient: whereas HA implants present attractive biointegration properties, PEEK implant can potentially be a much more appropriate choice in a demanding mechanical life style. Finally, a novel methodology is proposed to assess the need for further clinical evaluation in case of impact with both implants over a large range of impact conditions.

High impact velocity on multi-layered composite of polyether ether ketone and aluminium

Hybrid structures composed of multi-layer sheets of polymers and metals offer a great potential for impact protection systems in automotive and aeronautics industries. This work presents an experimental and numerical investigation on the perforation behaviour of layered polymer/metal composites. Penetration tests have been conducted on sandwich panels of aluminium 2024-T3 skins and polyether-ether-ketone (PEEK) cores, using spherical projectiles. The perforation experiment covered impact velocities in the range 250–500 m/s. The initial and residual velocities of the projectile were measured, and the ballistic limit velocity was obtained. The impact mechanical behaviour of PEEK core is compared with Ti6Al4V titanium core, for the same areal density of protection. It has been shown high perforation efficiency of PEEK polymer and a promised application for aeronautical protections. A numerical modelling is presented and validated with experimental data.