Dry finishing implants

Improving surface finish can extend the functionality and lifespan of osteosynthesis implants that promote bone growth following accidents or surgery. Despite design and manufacturing improvements in recent years, implants can fail due to:

• Fretting corrosion – Fluids inside the body, mechanical stress of functionality

• Performance – Polishing, finishing processes can impact fatigue, tensile strengths; reduce biocompatibility

Medical device manufacturing demands various post-processing steps, some that require manual labor. Some parts need only slight rounding and cleaning. Others need intensive processing such as polishing. Post-processing failures can cause metal to enter patients’ bloodstreams, resulting in blood poisoning.

Eliminating and improving post-processing to improve surface finishes can improve implants and patient care. The DLyte machine range specializes in dry finishing to improve implant surface finishes.

Traditional finish technologies

Chemical-mechanical processes, such as robotized belt polishing or abrasive polishing, generate friction on the workpiece. Other procedures involve dry polishing, primarily using circular vibrators to round the edges and polish the implant’s surface. Those processes can be error prone, producing inconsistent results.

Processes that are not repeatable, generally because they involve manual labor, drive up costs by requiring rework or parts scrapping. Some processes also require costly peripheral equipment to treat water and sludge contaminated with metals.

Updated equipment

DLyte series machines, based on Drylyte technology for surface finishing metal alloys, focus on automation, simplification, and standardization. Applications include grinding, deburring, surface smoothing, and high-gloss polishing. A dry electropolishing system selectively removes a thin layer of material from a metal part to achieve shine, smoothness, and ultra-clean surfaces. The process can polish and deburr fragile parts with complex geometric forms. Using a soft, non-abrasive polish medium avoids damaging round part edges. Suitable materials for the machine include cobalt chrome, stainless steel, titanium, and Nitinol.

DLyte machines don’t leave processing marks on workpieces, delivering a mirror finish with less than 0.02µm roughness.

Testing

DLyte has extensively tested dry electropolishing machines to ensure:

Biocompatibility – Based on testing, cobalt chrome and titanium parts processed with DLyte:

• Viability better than 70% compared to blank control

• Extract at 50% of test sam- ple, greater or equal viability than extract at 100%

• Mean value no greater than 15% average value of all blanks

The processed materials can be considered non-cytotoxic, based on the study made to UNE-EN-ISO 10993-5:2009.

Corrosion resistance – Corrosion is a main factor in reducing implant lifespan. Polishing reduces the likelihood of corrosion, but abrasive mechanical polishing can embed abrasive grains in workpieces. DLyte removes roughness while reducing manufacturing processes.

Recent tests compared corrosion resistance of stainless steel (SS316) processed with DLyte or a liquid electropolishing bath. DLyte achieved better corrosion resistance, producing a test piece with:

• Lower surface roughness, more luster

• Better corrosion protection after 6-hour immersion test

• 4x-to-15x slower corrosion

Challenging parts

Finishing very small medical devices such as stents or needles requires high-quality surface finishing and cannot handle aggressive mechanical surface-finish processes that may damage components. DLyte electropolishing can perform slight deburring to high-gloss polishing as the media is non-abrasive. During the process, high vibration reduces the friction between the media and the surface, protecting fine features.

Additive manufacturing (AM) is one of the most disruptive technologies in medical implants, allowing customization and new shapes not possible with existing manufacturing technologies. However, surface finish remains a barrier to wider adoption.

A study conducted by Germany’s Fraunhofer IAPT shows that DLyte generates at least 2x better surface quality for AM parts than the next-best alternative among seven post-processing technologies.

Conclusion

Multi-step implant finishing can include grinding, tumbling, and manual buffing. Any manual process risks worker-to-worker inconsistencies, and multiple processes can be time consuming and costly. DLyte can reduce process steps, improving quality, repeatability, and labor cost per piece.

The system improves manufacturing, reduces error, decreases costs, and shortens lead times. DLyte works within automated processes, so it’s suitable for large production while delivering consistent results.

GPAINNOVA
https://www.gpainnova.com

DLyte
https://www.dlyte.com