A Hydrophilic Surface

The first stage of implant integration is the adsorption of blood and extracellular fluids onto the implant surface.  These body fluids, which contain around 90 % water, carry proteins and ions which adsorb on the surface, and most of these components are hydrophilic. A hydrophobic surface, i.e. a surface which repels water, will be a bad substrate for adsorption of water soluble components. Later on, the adsorbed proteins serve as the substrate for bone cell growth. Because of this, a hydrophilic surface is a better substrate for bone cell growth than a hydrophobic one.

The interaction between an implant and the hydrophilic body liquids becomes even more important for porous structures, such as for example metal foams for spinal fusion, or implants with a layer of plasma sprayed titanium. For these types of structures capillary forces become more dominant and will augment the difference between hydrophilic and hydrophobic surfaces. A drop of water placed on a hydrophobic porous foam will stay on top of the foam without penetrating its inner structure.

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The chart shows the surface energy for Titanium, PEEK and Zirconia, untreated and treated with HAnano Surface.

 

  

The videos show how porous tantalum is transformed from hydrophobic (left) to hydrophilic (right) when coated with HAnano Surface.

 

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Left image: dyed water drop on unmodified PEEK. Right image: water on HAnano Surface treated PEEK. 


High Surface Energy

The surface energy can be described as the force required to create a new surface of a certain material. Surface energy depends on chemistry and topography – poly(ethylene) has lower surface energy than titanium, and a rough titanium surface has a higher surface energy than a polished one. Increasing the surface energy for a material increases the number of contact points for bone cells to attach to, which in turn leads to a better osseointegration and mechanical stability. Nanoparticles deposited on a surface increases the surface energy of a substrate.

Measuring the surface energy gives a broader information on the characteristics of an implant surface. The surface energy can be calculated by measuring the contact angle between the test surface and for different liquids with known surface energies. Hydrophilicity and surface energy are closely linked, a hydrophilic surface also has a high surface energy.