Research On The Tribological Properties And Biocompatibility Of Laser Textured Medical Titanium Alloy Surfaces

Titanium alloy is an important structural metal developed since the 1950 s.It is applied to aerospace,automotive industry and medical fields due to its good corrosion resistance and high strength.With the development of advanced manufacturing technology,people have put forward higher requirements on the wear resistance and service life of artificial joints.In order to further meet the design requirements of new type artificial joints,this paper applies laser texturing technology to the surface of artificial joint titanium alloy materials.A series of textures with different geometric features are created on the surface of Ti-6Al-4V alloy by using a picosecond laser system,including textures with different geometric shapes(circle,square,triangle,etc.);triangular gradient texture with convergence wedge in different degrees of convergence in the horizontal direction(length to width ratio L/W=0.25-4).Triangular gradient texture with different slopes(length to depth ratio L/D=5-30)in the vertical direction.The pin-disc rotating friction and wear tester is used to execute the friction and wear test under the condition of simulating the human body environment.By comparing the friction coefficient,wear rate and wear scar of each sample,the range of geometric features of the texture surface with better tribological properties is explored.At the same time,based on the N-S equation,the numerical model of the flow field of the textured surface under hydrodynamic lubrication is established.The model is calculated by the commercial CFD analysis software Fluent.The pressure distribution in the calculation domain is obtained,and the theoretical dimensionless hydrodynamic force of the textured surface is solved by the integral method.The calculated results are compared with the experimental results.Thereby verifying the optimal range of geometrical feature values obtained.In addition,in order to verify its practical application prospects,this paper explores the biocompatibility of its implanted organisms.The cytotoxicity of the textured surface is evaluated by MTT method,and the cell surface morphology is evaluated by cell morphology to determine the range of textured surface geometry characteristic parameters with the best wear resistance,service life and biocompatibility.The experimental and simulation results show that the area density of the textures has a significant influence on the tribological properties of the textured surface,and the relatively good value range is about 19%.By setting the micro-wedge shape gradient in the horizontal and vertical directions,the tribological properties of the sample can be obviously improved.Especially when the convergence wedge with moderate convergence(L/W=1)is set in the horizontal direction,the wedge effect is more likely to occur along the lubrication direction of the texture,and the pressure at the front of the sample is obviously.It lead to the improvement of hydrodynamic force;when the micro-gradient with a moderate span(L/D=10)is set in the vertical direction,the hydrodynamic pressure effect on the surface is obtained by the micro-gradient along the vertical direction of the texture has been obvious strengthened.Therefore its carrying capacity is greatly improved.When the texture geometric characteristic parameters are within the above range of values,the friction coefficient of the textured surface is significantly decreased,and the wear between the contact surfaces is significantly reduced.At the same time,there is existence a range of optimal texture geometric features that promote cell viability.The characterization of cell adhesion behavior on textured surface shows that the presence of micro-roughness on the surface of the textured sample is beneficial to the cell preferentially adhering along the edge of the textured dimples and the "peak" region of the internal roughness,and is agglomerated in it.It has a significant promoting effect on the activity of the cells.And the cells do not preferentially adhere to the deeper textured dimple areas with respect to the surface of the substrate.In summary,the laser surface texture can effectively improve the tribological properties of the titanium alloy surface.The tribological properties and biocompatibility can be further improved by setting the convergence wedge in the horizontal direction and the vertical direction within a certain range.