Deposition of Hydroxyapatite Coatings by Magnetron Sputtering

Diana María Rosario TorresWilfredo Otaño Ph.D.

RISE Program

University of Puerto Rico at Cayey

Abstract:Abstract:The project is directed toward the fabrication of a calcium

phosphate/hydroxyapatite (HA) nanocoating deposited on silicon and functionalized to overcome existing barriers of biomedical coatings commercially used with metallic implants. The calcium phosphate crystalline phase hydroxyapatite (HA) is a bioactive material with important clinical applications. HA is the main constituent of bone and teeth and shows the best bioactivity among the calcium phosphate ceramics. It has the ability to attach directly to living tissue without any intervening fibrous tissue and it is osteoconductive, forming a uniquely strong interface. The goal for this semester was the deposition of the HA thin films at different pressures and time using magnetron sputtering. A UHV Torus magnetron was used to successfully deposit calcium phosphate from a commercial hydroxyapatite (HA) target, at pressures between 5, 10 and 15 mTorr, 100 Watts of rf sputtering power, a substrate temperature of 500°C and 100% argon gas. The samples showed the same surface morphology as previous ones deposited using another target. The deposition configuration was optimized to obtain a good deposition rate. A first batch of samples was sent to UPR-Mayaguez where their ability to grow bone-forming cells is being studied.

Background and SignificanceBackground and SignificanceCaP crystalline phase Hydroxyapatite (Ca10(PO4)6(OH)2, HA).

Main constituent of bone and teethIs a bioactive materialImportant clinical applications

“Sputtering” DepositionVacuum processDeposition of coatingsExcellent adhesion of coating

Previous ResearchPrevious ResearchA UHV Torous Magnetron was used for the deposition of

calcium phosphate from an HA Commercial target.

Deposition Parameters:

600°C substrate temperature

Pressures between 5-20 mTorr

100% Ar gas

100 watts of rf sputtering power

Films presented a X-ray diffraction pattern consistent with the hydroxyapatite phase.

HA

09-0432 (I) - Hydroxylapatite, syn - Ca5(PO4)3(OH) - Y: 15.46 % - d x by: 1.000 - WL: 1.54056Operations: Displacement 0.250 | Y Scale Add 40.000 | Displacement 0.417 | Background 1.000,1.000 | ImHA 54 Frame: HA_54.unw Frame: HA_54.unw - File: HA_54.raw - Type: 2Th aloneOperations: Displacement 0.333 | Y Scale Add 32.000 | Background 1.000,1.000 | ImportHA 53 Frame: HA_53.unw Frame: HA_53.unw - File: HA_53.raw - Type: 2Th alone

Operations: Y Scale Add 2.000 | Y Scale Add 2.000 | Y Scale Add 22.000 | Background 1.000,1.000 | ImpoHA 52 Frame: HA_52.unw Frame: HA_52.unw - File: HA_52.raw - Type: 2Th aloneOperations: Y Scale Add 20.000 | Background 1.000,1.000 | Displacement 0.583 | ImportHA 51 - File: HA_51.raw - Type: 2Th alone - Start: 19.337 ° - End: 41.050 ° - Step: 0.100 ° - Step time: 800Operations: Y Scale Add 1.000 | Y Scale Add -2.000 | Y Scale Add -2.000 | Y Scale Add 7.000 | Y Scale AHA 50 - File: HA_50.raw - Type: 2Th alone - Start: 19.337 ° - End: 41.050 ° - Step: 0.100 ° - Step time: 800Operations: Y Scale Add 3.000 | Background 1.000,1.000 | Fourier 4.997 x 1 | Displacement 0.583 | ImportHA 49 - File: HA_49.raw - Type: 2Th alone - Start: 19.337 ° - End: 41.050 ° - Step: 0.100 ° - Step time: 800

Lin

(Cps

)

0

0.05

2-Theta - Scale19.1 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

HA (211

)HA (3

00)

HA (002

)

HA_52

HA_51

HA_50

HA_49

HA_53

HA_54

ProblemProblemHydroxyapatite coating used on medical implants has problems of adhesion andlongevity.

Hypothesis

Magnetron Sputtering will produce anhydroxypatite coating with good adhesionand crystallinity.

Controlled balance systemControlled balance systemTarget

Substrate

ObjectivesObjectives

Deposit hydroxyapatite (HA) thin films using the controlled balance sputtering system

The thin films will be deposited from a HA target and using in-situ heating. Deposition parameters such as deposition pressure and sputtering time will be varied to control the composition and crystallinity of the films.

MethodologyMethodology

a) Deposit HA- Thin films prepared at 5, 10, and 15 mTorrof 100% argon gas and substrate temperature of 500°C.

b) Characterization- morphology- Surface morphology studied with the SEM.

c) Send samples to UPR Mayaguez for study of bone cells adhesion and proliferation on HA surface.

SampleBase Pressure

(torr)Pressure (mtorr)

Flow Ar

(sccm) Heating

Pre-sputtering time (min)

Sputtering time (min)

dc Bias (V) Thickness Comments

HA #79 1.1x10-6 5 74 No 5 60 94 55

HA #80 1.6x10-6 5 74 5A-9V 5 120 124

HA #81 1.4x10-6 10 172 5A-9V 5 120 235

HA #82 1.7x10-6 15 284 5A-9V 5 120 212 30

HA #84Thermocouple Calibration

HA #85 2.3x10-6 5 73 509ºC ~5A 5 120 128 140Sent to UPR Mayaguez for cell growth

HA #86 2.0x10-6 10 166 509ºC ~5A 120 142

HA #87 1.6x10-6 15 284 509ºC ~5A 120 160 71

substrate distance reduced

HA #88 3.7x10-6 5 74 No 2 21.5 85

HA #89 1.2x10-6 5 No 1 180 217CaP deposition in new configuration

HA #90 1.9x10-6 10 177 No 2 180 140-160 1495A in T, not desired Temperature

HA #91 1.3x10-6 15 5A 5 180 166 298

HA#92 15.x10-6 5 77 5A-3hrs. 5 360 145-150 557After 3 hrs the heater was turned off

Data:Data:

Photos:Photos:

HA 92 at 5 mTorr

(sputtering time 360 min)

Conclusion:Conclusion:

• Impurities were acting as nuclei for the heterogeneous nucleation of nanograinsobserved at the surface and preventing the nucleation of the HA crystalline phase.

• Deposition process parameters can be used to produce HA films with controlled crystallinity.

FutureFuture ProjectionsProjections

Synthesis of a highly crystalline HA coating on silicon and Ti6Al4V substrates, with defined control of the crystalline phase(s), and with excellent adhesion to the coated surface. Begin to deposit in titanium.

ReferencesReferences

Personal Communication: Juan M. Figueroa Thesis Proposal for the UPR Cayey Honor Program.

Robert K. Waits, Thin Film Deposition and Pattering, American Vacuum Society Monograph Series, Harland.

W. Otaño, V. M. Pantojas, J. M. Figueroa, D. Hernández and A. Rodríguez-Navarro, Magnetron sputtering deposition of calcium phosphate films with nanoscale grain morphology in their surface, in Mechanics of Biological and Bio-Inspired Materials, edited by K. Katti, C. Hellmich, C. Viney, and U. Wegst ( Mater. Res. Soc. Symp.Proc. Volume 975E, Warrendale, PA, 2007) paper #0975DD06-08.

Acknowledgements Acknowledgements NAMAS LAB.RISE Program