1 Bioceramic coating of hydroxyapatite on titanium substrate with Nd-YAG laser Reference: Materials Science and Engineering: C, Volume 25, Issue 4, June 2005, Pages Gary J. Cheng, Daniel Pirzada, M. Cai, Pravansu Mohanty, Amit Bandyopadhyay Instructor: T.Y.Kuo Student: W.D.Dai Date:

2 Outline Introduction Experimental method Coating Schemes Conclusions 2

3 Introduction Compatible with various tissue types Outstanding osteoconductivity Since titanium has poor osteoinductive properties, the concept of applying HA onto metallic implants as a surface coating was developed Although HA has good mechanical properties and osteoinductive.but brittleness, low tensile strength, and poor impact resistance. 3 Hydroxyapatite (HA):

4 Experimental method(1/2) In Fig.1 its shows HA very low absorption to Nd-YAG laser-stay at low temperature. Most laser power is transmitted and scattered by HA until its finally absorbed by Ti powder and the substrate. HA powders are kept in low temperature before the powders are entrapped into metallic layer and form a strong bonding with the metallic substrate. The absorption of metal to laser is the highest in infrared range, while HA is transparent to infrared light but opaque to UV light. 4 Fig. 1. Spectrum of HAp at UV-Near Infrared range

5 Experimental method(2/2) Thin plate of Titanium (10mm) is spray-coated with mixture of the precursor and organic solvent (acetone) After drying use Nd:YAG coating HA on substrate. After coating,use SEM the coating is analyzed by EDS attached to the SEM. The measurement of hardness and modulus by nanoindentation The determination of the interfacial toughness of this HA/Ti substrate system by Vickers indentation 5

6 Coating Schemes(1/6) Since HA does not absorb laser, HA powders will stay at low temperature before they are entrapped into metallic layer Result in 3 layers: porous HA layer, dense HA/Ti bonded structure layer and Ti substrate.(Fig.2) 6 Fig. 2. Schematic representation of monolayer HAp ceramic coating on Ti substrates. (a)Laser coating of HAp powders. (b) Composite microstructure Monolayer porous coating after laser coating.

7 Coating Schemes(2/6) The top layer is a less dense HA coating. The less dense and porous HA layer is preferred for cell growth by forming a strong bonding between HA and body cell The mid-layer is a composite structure where HA powders are entrapped in Ti molten zone. The density of HA decreases with the depth increasing. 7 Fig. 3. Cross-sectional SEM micrograph of HAp coated Ti6a14V substrate using an Nd:YAG laser with power of 100W and scanning velocity of 1 mm/s

8 Coating Schemes(3/6) In Fig. 4(a) that HA powders are entrapped in Ti molten zone forming a composite structure with a solid HA/Ti bonding. Fig.4(b) shows another area with a further depth from the surface than Fig. 4(a) HA/Ti composite structures were also found in Fig. 4(b), however the density of HA is less than that in Fig. 4(a) 8 Fig. 4. The SEM micrograph and chemical analysis by EDS on the cross-section of coating (a) HAp/Ti composites at interface (b) HAp/Ti composites with depth increasing

9 Coating Schemes(4/6) The substrate layer of Ti, is shown in Fig. 4(c) The elastic modulus from nanoindentation test From Fig. 5 that porous HA coatings near the top surface has low elastic modulus. The elastic modulus increases gradually 9 (c) Titanium substrate Fig. 5. The elastic constant results of the HAp coating on Titanium substrate from nanoindentation test.

10 Coating Schemes(5/6) Hardness test Fig. 6(a) shows the hardness of many points on the coating surface. Near the top surface, porous HA coatings has low hardness. The hardness is highest right below the porous coatings. the highest hardness (7¨9GPa) Fig. 6(b) It shows that the hardness of HA/Ti interface decrease continuously to 2.5¨3GPa a Fig. 6. The hardness results of the HAp coating on Titanium substrate from nanoindentation test. (a) Hardness distribution near the coating surface. (b)Hardness from nanoindentation at a larger depth scale.

11 Coating Schemes(6/6) Fig. 7 There is no apparent crack on the edges and corners of the indent. This is because the ductility of the coating is enhanced by the HA/Ti composite structure. Fig. 7. Image of indentation after microhardness testing with Loading applied normal to the coating surface

12 Conclusions This process is presented in this paper to coat HA powders on Ti substrates at low temperature by laser surface engineering. HA has very low absorption to Nd-YAG laser, therefore most laser power is transmitted and scattered by HA powders and finally absorbed by Ti powders and Ti substrate. In this fast heating and cooling process, HA powders are kept in low temperature. This proves use HA to coating,coz good interfacial mechanical properties has been achieved by using LSE technique. 12