Preparation And Properties Of The Open-cell Zinc Foams For Biomedical Application

As a new type of biodegradable biomaterial,the open-cell zinc foams have gradually become the hotspot in the field of biomaterial research in recent years.However,there are few researches on the preparation process and performance of porous zinc metal materials.Therefore,it is important to study the preparation process and the optimum process parameters of the open-cell zinc foams,and to clarify the influence of the basic parameters of the pores on the mechanical properties and corrosion resistance.It is of great significance for its development and application in the field of biomaterials.In this paper,The open-cell zinc foams were prepared by the self-made vacuum infiltration casting device.The pore morphology of the open-cell zinc foams was prepared by scanning electron microscopy(SEM).The effects of pore parameters on compressive performance were investigated by compressive tests.The mechanical properties of open-cell zinc foams with different gradient structures were studied.The corrosion rate and degradation behavior of open-cell zinc foams were evaluated by immersion corrosion.Results indicate that:The optimum conditions for the preparation of calcium chloride preform are as follows:the sintered temperature is 680～720℃,the heating rate is 2℃/min,the sintered time is 5 hours,then cooling method is natural cooling.The weight of the sintering stage is adjusted in the range of 0.3～0.8 kg by the size of the filler particles.Vacuum degree of-0.090～-0.098 MPa,infiltration temperature of 580～620℃,infiltration pressure of 0.5～0.6 MPa,and keeping pressure for 5 minutes are optimum process parameters of vacuum infiltration casting.By adjusting the preform sintering process and infiltration process parameters.,the opencell zinc foams can be prepared with pore size in the range of 1～4.5 mm,porosity in the range of 55%～70%.The pore shape of the open-cell zinc foams is nearly spherical,and the pores are connected with each other.The three-dimensional structure of the pore structure is complete,which matches the porosity and pore structure of cancellous bone very well.The compressive experiments show that the elastic modulus of the open-cell zinc foams is 0.4～1.8 GPa,the compressive strength is 6.0～14.8 MPa,the elastic modulus is matched with the cancellous bone,and the compressive strength is higher than that of the human bone.Mechanical properties of open-cell zinc foams are in line with human cancellous bone very well.Therefore,the open-cell zinc foams can be regarded as one of promising bone graft material.The stress-strain curve can be divided into three stages:the elastic strain stage,the stress platform stage and the dense stage.In the stage of plastic deformation,the mesoscopic failure forms of the hole are mainly the tensile failure,shear failure of the hole edge and the tear of the hole wall after bending and folding.Local collapse is the main compression deformation mode of open-cell zinc foams.Porosity is the main factor affecting the compressive properties of open-cell zinc foams.With the increase of porosity,the elastic modulus and compressive strength of zinc foams decrease,the platform stress decreases,and the stress platform is prolonged.The pore size has little effect on the compressibility of zinc foams.The mechanical properties of gradient aperture open-cell zinc foams are improved compared with zinc foams of single pore size.The elastic modulus and compressive strength decrease with the increase of the thickness of small aperture layer.Radial gradient open-cell zinc foams are similar to human bone structure.It combines high porosity and high mechanical properties,effectively solves the contradiction between porosity and compressive strength,and has a great prospect as a bone tissue repair material.Immersion tests suggest that the open-cell zinc foams show a good corrosion resistance in simulated body fluid.Although the corrosion resistance of the open-cell zinc foams decreases with increasing porosity,the mean dissolved Zn per day for the open-cell zinc foam with a porosity of 66%is 2.5 mg/day,which is still much less than the tolerable limit of human body.In addition,the open-cell zinc foams can efficiently induce Ca-P precipitation during immersion tests and show a good bioactivity.