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Development of Composite Technology for Apatite Particles to Stainless-Steel Surface Using Ozone Water
~Chemical Bonding Between Metal Surface and Materials with Affinity for Biological Body & Application to Medical Devices like Stent and Dental Field~

Recently SofSera Corporation, with head office located in Tokyo, CEO Kazushige Karl Kawabe and capital stock of JPY 66 million has developed the composite technology to bond nanoparticles of hydroxyapatite as materials with affinity for biological bodies to stainless-steel surface chemically, collaborating with Iwatani Corporation setting out gas business and industrial machines, with head office located in Osaka and Tokyo, President Akiji Makino and capital stock of JPY 20,000 million.

SofSera Corporation had already built up technology to coat apatite particles on polymer-based material collaborating with National Cerebral and Cardiovascular Center. Moreover, SofSera Corporation has succeeded in developing the coating technology for steel surface that was used to be difficult to complete through the collaborative research with Iwatani Corporation. Hydroxyapatite is a material with affinity for biological bodies as a base of teeth and bones to diminish the risk of infectious diseases. Therefore, it is expected that hydroxyapatite can be applied as medical devices such as stent expanding from within lumens like blood vessels and countermeasure against metal allergy.

Features of the Technology

The hydroxyapatite is a mineral ceramic called calcium phosphate compound, Ca10(PO4)6(OH)2 and compared with polymer-based materials it is more difficult to be bonded chemically to stainless-steel surface. SofSera Corporation and Iwatani Corporation discovered that by operating highly-concentrated ozone water to stainless surface it becomes possible to form functional group, hydroxyl effectively needed for bonding the stainless surface with hydroxyapatite. Also, not only the process of ozone water along with the technologies having been developed at National Cerebral and Cardiovascular Center but defragmenting each process and condition built up the effective coating technology meditating even high-volume production.

As a method without using ozone using strong acid like nitric acid and drug solution with extremely strong odor like thiol, which is an organic compound with sulfur terminally-connected have been proposed for researching. However, these methods are not so effective in bonding evenly and effectively as the ones SofSera Corporation and Iwatani Corporation developed, and using hazardous chemicals can lead big defects.

Prospective Application Fields

  1. Various medical fields typified by stent.
  2. Application of orthopedic field like artificial joints & dental field with implant treatments.
  3. Reaction prevention for metal allergy to pierced earring, necklace and watch.

Details of the Process

Metal surface of stainless is usually coated by naturally oxidized membrane (② in below image.) The naturally oxidized membrane is too stable to coat nanoparticles of hydroxyapatite. First, after precision cleaning by using highly-concentrated ozone water with strong oxidation power hydroxyl, hydroxyl group (-OH) with reaction activity for steel surface is introduced (③ in the image.) Finally, this hydroxyl becomes a basic point in compositing the hydroxyapatite. Secondly, a compound, silane coupling agent as an intermediary is reacted to bond inorganic materials with organic materials (④ in the image.) And, graft polymer is formed by graft-polymerizing reactive monomer to the silane coupling agent (⑤ in the image.) This graft polymer increases the number of hands to bond with hydroxyapatite particles, and it also plays a role in strengthening the bonding as a binder. The surface the graft polymer is formed on is treated by disperse solution of hydroxyapatite particles. At last, by chemically bonding, called condensation reaction alkoxyl group, -Si(OR)3 group as a side chain functional group of the graft polymer with the hydroxyl, hydroxyl group (-OH) of hydroxyapatite, calcium phosphate hydroxide, Ca10(PO4)6(OH)2), hydroxyapatite and base material are bonded chemically to complete the compositing process(⑥ in the image.)

Coating Process for Apatite Particles to Stainless Surface

As seen above, since chemically bonded apatite is coated extreme solidly it cannot be dropped off easily.
Stainless surface bonded with apatite is shown in below images.
It seems to be coated very evenly.

SUS surface BEFORE coating apatite  SUS surface AFTER coating apatite

Signification of the Technological Development & Future Objectives

The technological development has been evolved based on surface-modifying technology which GM Tsutomu Furuzono at National Cerebral and Cardiovascular Center Research Institute, currently Kinki University engaged. This technology widely expands application for medical devices since it can coat metal surface with apatite particles with affinity for biological bodies, developed from existing organic polymer-based material. For a typical example of applying for stent, by inhibiting inflammation reactions after implanting the stent without being recognized as a foreign substance it is expected that it can improve QOL, Quality of Life of patients and reduce their burden. Moreover, application for orthopedic and dental field is also anticipated. From now on, we are planning to build up the compositing process of apatite for not only SUS304 stainless tested this time but all sorts of metals and mixed metals used for medical devices. And, mainly SofSera Corporation will start animal experimentations in the US soon in order to acquire medical authorization to lead its practical realization after clinical trials.


Hydroxyapatite is a base material of bones and teeth, also easy to relate to bodies. However, it is too solid and fragile to be fit to soft parts of the body. To redeem the defect, the apatite should be converted into fine and small particles of nano-scale* so that it can be bonded to surface of soft and flexible materials strongly resulting in overcoming its friability and expressing its affinity function for biological bodies instead. SofSera Corporation possesses the technology to manufacture nanoparticles of apatite with high quality.
  • Question that is often

We can offer other applications of SHAp and the composition to meet your demands.Please feel free to contact us for details.