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A Coating Primer: Technologies for Orthopedic Implants

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Orthopedic implants utilize both bone on-growth and bone in-growth coatings. An implant's success is often connected to the coating's ability to increase healing, decrease friction or strengthen the material. This article explores the benefits of various orthopedic coating types.

Titanium Plasma Spray (TPS)

TPS is characterized by a rough surface of peaks and valleys and a very well connected interporosity. The open porosity provides a rough topography for bone growth. The application process of TPS will impact the porosity. When TPS coating is sprayed above 500 microns, it meets the FDA standard for porous coating, which requires a pore size greater than 100 microns.

The biggest advantage to the plasma spray process is that titanium can be applied to dissimilar materials. A newer process to come to market is spraying titanium on polymeric implants, typically PEEK (polyethertherketone). PEEK is used extensively in spinal implants. Some of the key differences of this coating is it will not be as thick as normal TPS and it is isoelastic in nature, which means that it is stiff and additional materials are added to avoid delamination from the underlying structure.


Asymmatrix® is a non-spherical bead coating with particles that are jagged to achieve higher coefficient of friction. The coating can be customized to particle size and the number of layers. The particles can be packed tightly or loosely to control both porosity and pore size. Its rough scratch-fit type coating is one of its benefits compared to spherical beads because it provides better initial fixation.

Asymmatrix® uses high temperatures which reduces the substrate strength during the sintering process.

Asymmatrix® is a proprietary Orchid Orthopedic Solutions coating.

Hydroxyapatite (HA)

Hydroxyapatite is made up of inorganic materials found naturally in bones. The process for applying the coating is similar to any thermal plasma process, the major difference is that the coating is thin and very dense.

HA’s biggest advantage is that it can be applied to a variety of substrates and can also be applied to porous substrates, incorporating the bone on-growth properties of HA with the bone in-growth properties typically coming from the porous structures.

Spherical Bead

Spherical bead coating has been around for more than 30 years and can be used for both titanium and cobalt chrome substrates. It contains various sizes that create a three-dimensional porous structure. The process is simple but uses high temperatures which can reduce the strength of the material.

One of the limitations of this type of coating is the titanium can only be used on titanium substrates and cobalt can only be used on cobalt chrome implants.

New Coating Developments

As part of Orchid’s orthopedic supply chain solutions, the company has expertise in TPS, asymmetric, HA and sintered spherical coating. Orchid continues to research and learn how to overcome the limitations of the application processes and working on technologies that will help orthopedics grow and bring new coatings to the market.

This email address is being protected from spambots. You need JavaScript enabled to view it., is Lead Engineer Product Innovation – Coatings at Orchid Orthopedic Solutions.