Hydrophilic Coating for Medical Implant Materials from Promimic

By AZoNano.com Staff Writers

Topics Covered

Introduction - HAnano Surface
HAnano Surface on Metals
HAnano Surface on Ceramics
HAnano Surface on Polymers
HAnano Surface on Porous Materials
HAnano Surface on Pyrocarbon
About Promimic AB

Introduction - HAnano Surface

The HAnano Surface from Promimic is a 20 nanometer thin coating composed of nanocrystalline Hydroxyapatite (HA) particles, which are the key element of teeth and bone. The HAnano Surface particles  resemble the size, shape and crystallinity of human bone and when applied as a coating they produce a super-hydrophilic surface. This enables the implant to interact more intimately with the body so that osseointegration is accelerated to provide stronger anchoring to the bone.

The HAnano Surface can be applied over all commercial implants irrespective of their material and structure. Compared to traditional coatings like the micrometer thick plasma-sprayed HA, the HAnano Surface is only 20 nanometres, thereby protecting the micron-structure/micro-roughness of the implant surface with improved osteoconductivity. In addition, the thinness of the HAnano Surface prevents the use of new implant instrumentation, including drills and screwing taps.

 

Figure 1. The coating technology of the HAnano Surface is very simple and cost-effective. The coating liquid can be applied in three different ways; through spraying (a), dripping (b) or dipping (c), followed by a short heat treatment step which finalizes the surface.

Production of the HAnano Surface is based on a wet chemical process. It is easy to integrate this simple and cost-effective technology to any implant manufacturer’s internal production lines. There are three different ways - spraying, dripping and dipping - to apply the coating liquid, as shown in Figure 1. Excess coating solution can be removed by spinning and pressurized gas followed by a short heat treatment.

 

HAnano Surface on Metals

The most commonly used implant materials such as stainless steel, titanium, and cobalt-chrome alloys exhibit superior chemical stability and mechanical properties in the human body. In several in vivo and in vitro studies, the surface modification by the HAnano Surface has proven to improve the bone-to-implant attachment strength as well as the amount of bone attached to the implant surface.

 

Figure 2. The comparison of unmodified and HAnano Surface coated titanium implant.

In addition, osseointegration is accelerated in the presence of the HAnano Surface without triggering any toxic/inflammatory response or implant rejection. Moreover, there is no observation of cracking or release of particles from the HAnano Surface in any of the performed pre-clinical studies, two issues often related to micrometer thick coatings. The comparison of unmodified and HAnano Surface modified titanium implants is shown in Figure 2. The following are the advantages of the HAnano Surface on metals:

  • Coating layer from 20 nm
  • Improves anchoring strength
  • Forms an osteoconductive surface
  • Accelerates osseointegration
  • Generates a super hydrophilic implant surface
  • Produces an implant with bone-like chemistry and optimal surface roughness

HAnano Surface on Ceramics

Ceramic and zirconia-based implants exhibit high resistance to corrosion, fractures and wear, which make them a promising alternative to metal implants. In addition, their bone-like color makes them more attractive to meet specific aesthetic requirements. However, one major disadvantage is the low response to bone cell growth, when compared to titanium.

Figure 3. The comparison of unmodified and HAnano Surface coated zirconia implant

This issue can be addressed with the application of the HAnano Surface coating as it shows high compatibility with ceramic surfaces and has proven to improve bone growth on ceramic implants. This, in turn, accelerates osseointegration and increases the anchoring strength of the implant. The HAnano Surface transforms the ceramic implant surfaces from bioinert to osteoconductive. The comparison of unmodified and HAnano Surface modified zirconia implants is illustrated in Figure 3. The following are the advantages of the HAnano Surface on ceramics:

 

  • Coating layer from 20 nm
  • Accelerates osseointegration
  • Improves anchoring strength
  • Generates a super-hydrophilic implant surface
  • Converts the ceramic surface from bioinert to osteoconductive
  • Larger interfacial contact area

HAnano Surface on Polymers

During the past decades, polymeric materials have increasingly been used as alternatives to conventional implant materials in many different applications. PEEK is most commonly used as replacement to titanium-based implants, particularly in orthopedics and spinal fusion, due to its several favorable properties, including thermal stability, biocompatibility, radiolucency, and similarity to the mechanical properties of bone.

Figure 4. Unmodified and HAnano Surface coated PEEK implant

However, the downside with PEEK is chemical and biological inertness, which may affect its integration in the body. In addition, most polymers have poor wettability as they are relatively hydrophobic, which makes bone cell growth on the surface difficult. Nevertheless, the coating of HAnano Surface transforms a polymeric implant surface from hydrophobic to hydrophilic, thereby facilitating osseointegration. Unmodified and HAnano Surface coated PEEK implants are compared in Figure 4. The advantages of HAnano Surface on polymers are as follows:

  • Coating layer from 20nm
  • Accelerates osseointegration
  • Improves anchoring strength
  • Does not affect the polymer strength
  • Forms a hydrophilic implant surface
  • Produces a material with mechanical properties and chemistry analogous to bone
  • Larger interfacial contact area
  • Customization of coating method is possible based on polymer type
  • Converts the polymer surface from bioinert to osteoconductive

HAnano Surface on Porous Materials

Porous materials have been increasingly used in implants as they enable interpenetration and creation of blood vessels, an essential process for natural bone growth into the implant. Porous structures can be effectively surface treated with the HAnano Surface coating, which homogeneously covers the surface even inside the cavities without blocking the pores due to its nanometer thickness. It is easy to adapt this technique to protect the underlying surface structures, even that have a specific surface topology/roughness.

 

Figure 5. Unmodified and HAnano Surface coated porous material

Furthermore, the application of the HAnano Surface coating improves the hydrophilicity of porous materials, which enables them to absorb body fluids more effectively. The comparison of unmodified and HAnano Surface coated porous material implants is illustrated in Figure 5. The following are the benefits of the HAnano Surface on porous materials:

  • Coating with nanometer thin HA
  • Maintains porosity
  • Produces an osteoconductive surface
  • Creates a super hydrophilic implant material
  • Retains flexibility
  • Produces a material with bone-like structure and chemistry

HAnano Surface on Pyrocarbon

Pyrocarbon, a biochemically inert material, exhibits favourable mechanical properties for orthopedic implants and is gaining traction for orthopedic applications due to its biocompatibility, high wear resistance and low friction coefficient characteristics. It is a promising material for implant-bone stress transfer as its elasticity modulus is similar to cortical bone.

Figure 6. Pyrocarbon implant

Press-fitting is used for stabilizing pyrocarbon implants (Figure 6). After initial insertion, appositional bone grows around the prosthetic stem subsequent to the mechanical stabilization by the surrounding cortical bone. The application of a bone-like surface, such as the HAnano Surface coating transforms a pyrocarbon implant into an implant with properties analogous to that of human bone, thereby enabling better integration of the implant. The following are the benefits of HAnano Surface on pyrocarbon:

  • Coating layer from 20 nm
  • Creates a super hydrophilic implant surface
  • Does not affect the strength of the material
  • Larger interfacial contact area
  • Produces a material with bone-like chemistry and mechanical properties
  • Transforms the surface from bioinert to osteoconductive

About Promimic AB

Promimic is a biomaterial company founded in 2004 as a spin-off from research performed at Chalmers University of Technology in Gothenburg, Sweden. The company develops and markets a new generation of implant surface modifications and synthetic bone based on a patented method for production of nano sized hydroxyapatite. Promimic has an innovative and experienced organization that continuously is working on new ways to improve surface modification and coating of new materials.

  • HAnano Surface is a unique implant surface which dramatically accelerates osseointegration. The surface can be applied onto various types of materials - including metals, ceramics and polymers - regardless of its dimensions and structure. The HAnano Surface has received 510(k) approval by the FDA (American Food and Drug Administration), which applies to the area of dental implants.
  • HAnano Bone is a new generation of synthetic bone. The unique composition of HAnano Bone allows it to be mouldable over extended periods of time.

This information has been sourced, reviewed and adapted from materials provided by Promimic AB.

For more information on this source, please visit Promimic AB.

Date Added: Aug 29, 2013 | Updated: Sep 5, 2013
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