Adherent apatite coating on titanium substrate using chemical deposition

Abstract

Plasma-sprayed "HA" coatings on commercial orthopedic and dental implants consist of mixtures of calcium phosphate phases, predominantly a crystalline calcium phosphate phase, hydroxyapatite (HA) and an amorphous calcium phosphate (ACP) with varying HA/ACP ratios. Alternatives to the plasma-spray method are being explored because of some of its disadvantages. The purpose of this study was to deposit an adherent apatite coating on titanium substrate using a two-step method. First, titanium substrates were immersed in acidic solution of calcium phosphate resulting in the deposition of a monetite (CaHPO4) coating. Second, the monetite crystals were transformed to apatite by hydrolysis in NaOH solution. Composition and morphology of the initial and final coatings were identified using X-ray diffraction (XRD), Scanning Electron Microscopy, and Energy Dispersive Spectroscopy (EDS). The final coating was porous and the apatite crystals were agglomerated and followed the outline of the large monetite crystals. EDS revealed the presence of calcium and phosphorous elements on the titanium substrate after removing the coating using tensile or scratching tests. The average tensile bond of the coating was 5.2 MPa and cohesion failures were observed more frequently than adhesion failures. The coating adhesion measured using scratch test with a 200-microm-radius stylus was 13.1N. Images from the scratch tracks demonstrated that the coating materials were squashed without fracturing inside and/or at the border of the tracks until the failure point of the coating. In conclusion, this study showed the potential of a chemical deposition method for depositing a coating consisting of either monetite or apatite. This method has the advantage of producing a coating with homogenous composition on even implants of complex geometry or porosity. This method involves low temperatures and, therefore, can allow the incorporation of growth factors or biogenic molecules.

Historical Review of Biological Apatite Crystallography

“…Calcium phosphate based coatings have been developed and used in clinical dentistry and medicine [136][137][138] .…”

Surface Aspects of Titanium Dental Implants

“…Several studies showed that these coatings achieve a very intimate contact between the implant and bone (Hench, 1996;Rohanizadeh et al, 2005;Sun et al, 2001;Szabo et al, 1995). Clinical investigations reported a high degree of success with HAP-coated implants, reducing the healing period (Block et al, 1996).…”

Avaliação do recobrimento biomimétrico em compósitos de alumina-zircônia texturizadas superficialmente com laser de femtossegundo

“…Trilhas feitas por scratch demonstraram que o material do recobrimento foi "esmagado", "espremido", sem fratura no interior e nas bordas das trilhas até o ponto de falha do recobrimento (ROHANIZADEH, et al, 2005).…”

“…Essa carga é chamada de carga crítica (Lc) medida em Newton e corresponde à resistência de ligação entre o recobrimento e o substrato (ROHANIZADEH, et al, 2005).…”

“…As trilhas foram obtidas nas amostras por um aumento constante de carga com taxa de 100N/min enquanto as amostras foram deslocadas com uma velocidade constante de 10mm/min (ROHANIZADEH, et al, 2005).…”