Theoretically And Experimentally Research On The Mechanical Behavior Of Needles Inserting Into Skin

The medical needles play important roles on delivering drugs through the skin into the system circulation.However,fierce pain and invasiveness would take place while a hypodermic needle was inserted into the skin.It was found that the pain and invasiveness are strongly dependent on the insertion force(IF)and insertion displacement(ID).In other word,the pain and invasiveness induced by the hypodermic needle can be considerably decreased by decreasing the IF and ID.Therefore,in the present work,great efforts were paid to seek effective approaches to decrease the IF and ID with respect to needles insertion.Two strategies including pre-stretching or vibrating the skin or the skin phantom were advanced.And then a type of in-plane metal microneedle array was fabricated and experiments were carried out to study their IF and ID.The detailed studies are as follows:(1)The effects of pre-stretch on IF and ID of the needle were experimentally studied by inserting a stainless steel needle into an isotropic silicon film as a tissue phantom and an anisotropic rabbit skin with two pre-stretch modes.The two prestretch modes are equibiaxial tension and uniaxial extension with a fixed pre-extension in another direction,respectively.(2)The effects of vibration on the IF and ID of a stainless steel needle into an isotropic silicon film were experimentally studied.In experiments,the vibration frequency,the vibration amplitude,the insertion velocity and the coupling effect of the preextension of the silicon film with different vibration modes were all studied.(3)An in-plain metal microneedles array was designed and manufactured by traditional wire cutting method.Firstly,the insertion behavior of the in-plain metal microneedle array into silicon film was experimentally studied.Then the effects of pre-extension and microneedle height arrangement on the IF and ID were studied,too.From the above studies,the following conclusions can be drawn:(1)The IF and ID of one single needle inserting into a silicone film phantom can be considerably decreased by exerting pre-extension on the film.The larger the pre-extension is,the smaller the IF and ID are.In addition,results show that equibiaxial tension has a better effect on reducing the IF and ID than the uniaxial extension mode.However,it should be pointed out that when the pre-extension in different fixed directions is applied to an anisotropic rabbit skin,the effects of pre-extension on the IF and ID are strongly related to the direction of deformation.The reason for this phenomenon is that fibers of skin tissue arrange anisotropically and there are coupling effects between the fibers arrangement with the uniaxial extension direction.(2)When the needle or silicon film is subjected to vibration,the static insertion can be transformed into a dynamic impact.Experiments show that the IF and ID can be decreased with an increase of vibration frequency or vibration amplitude.Analogously,vibrating the skin can also reduce the IF and ID.Therefore,a watch-like skin vibrator was designed and fabricated.Experiments show that such a skin vibrator can exactly reduce the IF and.Besides,the IF and ID of a needle into a silicon film can be increased by increasing the insertion velocity of the needle.Finally,It was found that the IF of a needle into a silicon film can be dramatically reduced by vibrating the film with an equibiaxial pre-extension,i.e.,the vibration and pre-extension have coupling positive effects on the IF reduction.However,the ID will firstly increase and then decrease with the increase of the vibration amplitude.(3)It was found that optimizing the height arrangement of a metal in-plane microneedle array is helpful to eliminate the phenomenon that different microneedles in the array may penetrate the skin early or late.Moreover,exerting preextension on the silicon film can reduce decrease the IF and ID of the metal in-plane microneedle array piercing the silicon film.These findings mentioned above are useful to decrease the IF and ID of one single hypodermic needle or microneedle array inserting into the skin.