Cranial flap

In most medical manufacturing, smooth, rough, and porous surfaces which are required for successful implantation into human beings are done through secondary finishing techniques, but C&A Tool and WITHIN have launched a patient-specific, metal-implant design and manufacturing program called WITHIN Medical to eliminate those secondary steps.

Free downloadable software developed by WITHIN and additive manufacturing technology via Direct Metal Laser Sintering from EOS aim to streamline the process.

Current processes use machining – often with plasma spraying or hand-sintering beads – to provide the necessary surface characteristics. DMLS can eliminate many of the additional processes, creating the necessary mix of surfaces by building the implants layer-by-layer.

A Tibial tray,  part of an implant used for Total Knee ArthroplastyOsseointegration is essentially the formation of direct interfaces between an implant and human bone which does not require soft tissue to form a bond. The critical element of the bond, pores into which osteoblasts and supporting connective tissue can migrate, was discovered in 1952 by Per-Ingvar Brånemark of Sweden. Brånemark undertook an experiment which used a titanium implant chamber to study blood flow in rabbit bone, and at the end of his study, he found that when the time came to remove the titanium chambers from the bone, bone material had integrated completely with the implant and could not be removed.

He called the phenomenon osseointegration.

WITHIN says their software, which targets medical, surgical, and orthopedic designers and manufacturers, allows those developers to create highly customized products to improve osseointegration, or bone growth. An acetabular cup is the part of a hip implant adhered to the pelvis for the ball of the joint replacement to sit in. Traditional implant designs used cement and multiple screws, but inducing osseointegration is thought to encourage a more secure fit, with larger pores favorable for stress transfer and smaller pores beneficial for initial fixation.

Acetabular cup

The WITHIN process gives designers the power to choose the pore size of the trabecular lattice and vary the porosity throughout the implant.

As the implant was manufactured in a single phase using Direct Metal Laser Sintering (DMLS) there is structural continuity between solid and porous sections. The acetabular cup implant was built in a biocompatible titanium alloy with the entire contact surface formed from trabecular lattice. Once removed from the build plate and cleaned, the implant can be coated with a hydroxylapatite bioabsorbable filler to further stimulate bony ingrowth.

"With this program, companies now have the opportunity to explore the benefits that designing for DMLS can bring to their medical products without investing in their own laser-sintering system," said John Halverson, Medical Business Unit Manager at C&A Tool. "They'll be able to discover firsthand how DMLS reduces manufacturing steps, improves product performance and allows them to tailor medical products to individual patient needs."

For orthopedic applications, the systems use biocompatible materials like medical-grade titanium cobalt-chrome and stainless steel alloys.

"WITHIN Medical design software is free, easy to use and offers a high level of design control," said Kaveh Mahdavi of WITHIN. "We focused on the end-to-end solution, everything from design to manufacturing to validation."