Centre for Excellence in Nanomedicine

Coatings for Implants

The nidation of biomaterials into the human organic structure allows it to re-establish biological and mechanical maps and hence to increase the quality of life. Biomaterials are man-made stuffs intended to work suitably in contact with a life tissue and organic structure fluids. Metallic elements, ceramics, polymers and complexs are used as biomaterials. These stuffs entirely can non fulfill all the demands for bio-implant applications such as superior mechanical belongingss, wear opposition, corrosion opposition from the organic structure plasma and, biocompatibility etc. Hence tremendous research work is being carried out on biocompatible coatings with superior mechanical, tribological and biocompatible belongingss towards developing bioceramic and biomimetic coating on both metallic and non-metallic substrates. A assortment of medical devices, such as coronary stents, intraocular lenses, bosom valves, hip and articulatio genus articulations, bio-chips, dental implants and pacesetters are implanted in the human organic structure. The stuffs of the implants are exposed to the interaction with the organic structure cells and fluids and to possible caustic activity from the stuffs of the organic structure. The organic structure fluid contains 1 % Na chloride and constitutes a caustic environment for the implants. Joint implants are exposed to skiding wear. The interactions of the implants with the organic structure cells, the merchandises of the corrosion, and of the wear dust can hold inauspicious effects on the organic structure and on the implants. These effects can include cellular harm, infections, blood curdling ( potentially taking to thrombosis ) and failure of the implants. In order to carry through their map the implants should non do infections, prevent uncontrolled cell growing, maintain their unity inside the organic structure, and avoid formation of dust. In certain instances it is utile to hold the implants interact in a governable manner with the biological environment, e.g. to advance growing of bone cells on implants. The biological behavior of an implant is strongly influenced by the chemical state of affairs nowadays at the implant surface. Therefore, bio reactions can be tuned by tuning the surface chemical science of an implant, particularly the elemental composing, to make a specific surface giving a defined biological response. Metallic implants can let go of metal ions and wear dust into the environing tissue and these can take to osteolysis ( bone reabsorption, loss ) and loosening and failure of the implant. Hip and articulatio genus implants are exposed to skiding motions, which can do wear of the surfaces in contact. Ti and its metals are among the most biocompatible metals but their wear opposition is comparatively low. The dust atoms generated by the wear can do rednesss of the tissue and can take to osteolysis around the implant. Coating the implants with protective movies, which can cut down corrosion and wear, may forestall or relieve the jobs described above and widen the life-time of implants to the benefit of the patients. Hence a coating to be used for implants should hold the undermentioned belongingss

  • Excellent Mechanical Properties
  • Low Coefficient of Friction
  • Low Wear
  • Low Surface Roughness
  • Low Internal Stress ( Compressive Stress )
  • Good Adhesion towards both Metallic and Non-metallic Surfaces
  • Hemocompatibility and
  • Longer Life Time

Extensive research work has been carried out in the field of biocompatible coatings based on metal coatings, diamond-like C coatings ( DLC ) and heteroxyapatite ( HA ) coatings. During the past two decennaries, DLC movies have attracted an overpowering involvement from both industry and the research community. These movies offer a broad scope of exceeding physical, mechanical, biomedical and tribological belongingss that make them scientifically really absorbing and commercially indispensable for legion industrial applications. DLC movies are chiefly made of C atoms that are extracted or derived from carbon-containing beginnings, such as solid C marks and liquid and gaseous signifiers of hydrocarbons and fullerenes. Depending on the type of C beginning being used during the movie deposition, the type of bonds ( i.e. sp1, sp2, sp3 ) that hold C atoms together in DLC may change a great trade and can impact their mechanical, electrical, optical and tribological belongingss. The major disadvantage of the deposition of ace difficult diamond-like C movies and therefore of the realisation of proficient applications is frequently a comparatively low adhesion of DLC-films on metallic and ceramic substrates caused by really high internal compressive emphasis of these coatings. In the instance of ion-beam-assisted deposition characteristic belongingss of the coatings like hardness, elastic modulus and residuary emphasis are strongly correlated with the sum of sp3 bonding in C movies. This job has now been overcome by guaranting that there are no stress concentrations near the coating/substrate interface. A often used method trades with a design of a trim interface in the signifier of a chemically gradient interlayer or a multilayer coating between the substrate stuff and the C movie. On a multilayer interface with an optimized bed sequence of Ti, TiN, TiCN, TiC, DLC to cut down residuary emphasis and increase the critical burden of failure in the scratch-test of the DLC movies. An interesting method to diminish the internal emphasis in the DLC coating is to present metal nanoparticles in between the DLC matrix.

In an earlier work ( M. Sridharan et al. , Surface and Coating Technology, 202 ( 2007 ) 920 ) , g-alumina nanoparticles have been embedded in the formless aluminum oxide matrix yielded increased hardness and decreased internal emphasis in the aluminum oxide movies. The movies were deposited by ionised magnetron spatter ( inductively coupled plasma magnetron sputtering ) . The magnetron was powered with a pulsed DC power supply, and the substrate was negatively biased with a pulsed DC electromotive force supply. An RF powered spiral was located above the substrate to change the ion flux hitting the substrate.

As measured with transmittal negatron microscopy and X-ray diffraction, the movies were formless in the temperature scope 200 to 600 & A ; deg ; C, when merely a low flux of ions hit the movie during growing. At 200 & A ; deg ; C, with increasing ion barrage, 100 nm big bunchs of little crystalline grains of g-alumina with sizes of the order of 5 nanometers were embedded in the formless stage. Increasing the flux of ions and/or the temperature further enabled us to do movies dwelling merely of crystalline g-alumina. A systematic survey was carried out of the dependance of the nanostructure on a ) the RF power of the spiral making the ions pelting the turning movie, on B ) the bias electromotive force, and on degree Celsius ) the substrate temperature. The hardness values of the movies were measured and correlated to the movie nanostructure. The hardness increased with the crystalline-volume fraction. The hardness values of the formless aluminum oxide movies were 7-9 GPa and for the wholly crystalline gamma alumnus films the hardness value was 22 GPa. When the substrate temperature was increased farther resulted in decrease of hardness value caused by the larger grain sizes.

Work to be carried out:

DLC nanocomposite coatings with superior mechanical, tribological and biocompatible belongingss will be synthesised towards run intoing the demands for implants ( bosom valves and hip and articulatio genus articulations ) . The coatings will be deposited by magnetron spatter ( inductively coupled plasma magnetron sputtering ) onto steel and Si substrates. The metal marks ( for illustration Cr and Ti ) will be sputtered ( sputtering gas: Ar ; reactive gas: methane or ethyne ) to acquire metal nanoparticle embedded DLC coatings ( nc-DLC ) . The deposition parametric quantities, such as, gas flow rate, partial force per unit area, substrate prejudice, substrate temperature and power applied to the cathode will be consistently varied and the nanoparticle concentration, grain size and grain distribution will be varied to obtain nc-DLC coatings with superior mechanical, tribological and biocompatible belongingss. Besides coatings / multilayers based on Ti and Cr will be deposited onto steel and Si substrates by magnetron sputtering taking towards the applications for implants. Besides the hydroxyapatite coatings will be synthesised by magnetron spatter, which is really much used in orthopedic and dental implants. These nc-DLC coatings, Ti and Cr based coatings and the hydroxyapatite coatings with superior belongingss will be used for bosom valves, dental implants and other protective coatings to be used for the implants.