Specialty chemicals company Evonik and Swiss plastics specialist Samaplast are combining their expertise in developing an osteoconductive PEEK biomaterial for injection molding. As part of the collaboration, both partners are demonstrating and documenting the processing properties of the new osteoconductive high-performance polymer VESTAKEEP Fusion using the first prototypes of spinal implants. 
 
Biphasic Calcium Phosphate Accelerates Healing
Until now, it has been virtually impossible to manufacture implants from polymer compounds with bioactive particles by injection molding, because a thin polymer layer usually forms on the surface that overlays the particles, preventing the implant from growing in. But with VESTAKEEP Fusion, the functional BCP additives (biphasic calcium phosphate) are also available on the surface of injection-molded components. This is ensured by the specially configured microparticles and their homogeneous distribution.
 
"Implant manufacturers were missing a PEEK material that fuse with bone cells and thus accelerates healing, for example after spinal surgery," said Marc Knebel, head of the Medical Systems Market Segment at Evonik. "We are closing this gap in the market with VESTAKEEP Fusion and offering an alternative to titanium, stainless steel or cobalt-chromium implants right away."
 
Osteoconductive PEEK Biomaterial for Injection Molding
VESTAKEEP Fusion was developed with a goal to process in different manufacturing technologies and is initially offered as granules and semi-finished products. It can be milled, compression molded, extruded-and even injection molded. For the latter, Evonik has optimized the compound in close cooperation with Samaplast AG.
 
"We tested VESTAKEEP Fusion on injection molding machines in the clean room and found that it was very easy to process," confirmed Samaplast CEO Stefan Okle. "Thanks to the excellent exchange with Evonik, we were able to produce a prototype within ten days." Previously, tool development alone had taken eight to ten weeks. With rapid prototyping, this process can be shortened considerably.  
 
Cage Prototype Demonstrates Design Diversity
Evonik and Samaplast are demonstrating what is possible with the first prototypes of intervertebral implants, known as cages or spacers, which are used to fill the disc space in the spine following its removal due to disc degeneration. "We have produced a cage that contains all the details, such as serrations, threads, and apertures, that are relevant for spinal implants," explained Okle.
 
Thanks to the design freedom in injection molding of VESTAKEEP Fusion, specific cage variants can be produced—tailored to the anatomical conditions and different surgical techniques such as PLIF, TLIF and ALIF. The cage models show the design diversity in the interlocks and in the cavities for ossification. In addition, the design facilitates instrument guidance during surgery and also enables minimally invasive, patient-friendly surgical techniques.
 
Higher Cell Proliferation
With VESTAKEEP Fusion, Evonik is introducing a new product line of next-generation PEEK-based implant materials. The osteoconductive properties of the new PEEK material were achieved by using a special functional additive—biphasic calcium phosphate—and allow bone cells to adhere to implants more quickly, thus positively influencing fusion, so called osteointegration, at the boundary between the bone and the implant. This, in turn, will accelerate bone fusion and convalescence.
 
In-vitro studies document more than 30 percent increased cell attachment and cell proliferation. In preclinical tests, histological examination reveals a dense network of newly formed osteoblasts at the bone-implant interface. Bone histomorphometry shows an approximately twofold increase in bone apposition. And pull-out tests demonstrate a more than twofold increase in implant fixation.
 
Evonik's polymer experts are also developing a 3D-printable VESTAKEEP Fusion filament that could be processed in additive manufacturing using fused filament fabrication (FFF) technology.
 
Evonik is active in more than 100 countries around the world and generated sales of 12.2 billion euros and an operating profit (adjusted EBITDA) of 1.91 billion euros in 2020. Evonik goes far beyond chemistry to create innovative, profitable and sustainable solutions for customers. About 33,000 employees work at the company. The Smart Materials division includes businesses with innovative materials that enable resource-saving solutions and replace conventional materials. The Smart Materials division generated sales of 3.24 billion euros in 2020 with about 7,900 employees.