Oxide ceramic implant materials
Ceramic implant materials for hip replacements must meet a whole range of requirements. In addition to excellent abrasion strength, adequate fracture strength and biocompatibility of the abrasion are required. ELEC® (high-purity alumina) and ELEC®plus (zirconia-toughened alumina) from HiPer Medical meet all relevant requirements for implants subjected to high load - as defined by ISO 6474-1 and ISO 6474-2, for example - and are therefore well-suited for the production of surface bearing components of modular hip replacement systems. High-purity alumina in accordance with ISO 6471-1 and zirconia-toughened alumina in accordance with ISO 6474-2 have been used successfully in clinical routine for decades.
ELEC®: High-purity Alumina
ELEC® alumina features a nearly defect-free, fine-grained structure and high flexural strength. ELEC® components tempered by hot-isostatic pressing (HIP) permit the manufacture of hip replacement components with only minimal surface roughness. The high surface integrity and extreme hardness of ELEC® ensure extremely little abrasion on the sliding partner. ELEC® is also biocompatible in its finest distributed form, such as abrasion particles. ELEC® is used exclusively for manufacturing femoral heads.
ELEC®plus: Zirconia-toughened Alumina (ZTA)
ELEC®plus (zirconia-toughened alumina, ZTA) is an oxide-ceramic composite from a main alumina phase in which fine yttria-partially stabilized zirconia particles are homogeneously distributed. In the alumina embedding, the zirconia particles reinforce the resistance to mechanical stress. ELEC®plus therefore has even higher flexural strength than ELEC® and can be used as a material for thin-walled hip replacement components subjected to complex load conditions. The abrasion resistance and biocompatibility of ELEC® and ELEC®plus are almost identical. ELEC®plus is manufactured without admixtures of strontium oxide or chromium oxide and meets all requirements of the ISO 6474-2 standard. ELEC®plus is used for all hip replacement components offered by HiPer Medical.
Surface Bearing and Abrasion
Hip joint articulation requires the sliding partner of a hip replacement system to meet the highest demands for mechanical and abrasion resistance. In the articulation of a ceramic femoral head against a polyethylene acetabular component used over time, the polyethylene component is subjected to a far higher degree of wear. To minimize abrasion of the polyethylene, ELEC® and ELEC®plus femoral heads are manufactured with extremely low surface roughness. The service life of this type of hip replacement therefore depends on the abrasion resistance of the polyethylene cup and the surface integrity and hardness of the femoral component, in addition to many other factors.
The volume and nature of the abrasion of an implanted hip replacement have long been considered to be the relevant factors for aseptic loosening, which often requires premature revision hip arthroplasty. In this context, polyethylene particles are considered to be especially critical and can only be excluded if hard-on-hard bearings are used. All-ceramic bearings comprising ELEC® femoral heads or ELEC®plus femoral heads and ELEC®plus acetabular components offer a suitable alternative to polyethylene acetabular components due to their extremely low abrasion and the biocompatibility of the abraded material.
Biokompatibility of ELEC® and ELEC®plus
ELEC® alumina and ELEC®plus ZTA have been tested for biocompatibility at our affiliate Zellwerk GmbH - www.zellwerk.biz - in a wide range of cell culture models (L929 mouse fibroblasts, human umbilical cord blood stem cells, human bone marrow mesenchymal stem cells, human HepG9-hepatic cell line). No signs of cytotoxicity, reduction in viability or other cell-damaging properties of the material were found in any of these models. There is no need to add admixtures of chromium, nickel, strontium or other non-constituent element oxides to either ELEC® or ELEC®plus to improve fracture mechanical or tribological properties.
