Mechanical characterization and comparison of different NiTi/silicone rubber interfaces

Abstract

International audienceThis paper investigates the effects of different surface treatments on the mechanical resistance of interface between wires of NiTi shape memory alloy and silicone rubber. Three different treatments were used; primer, plasma and combination of both. The wires deoxidation effects have also been studied. In order to characterize the interface properties in such composite material, pull-out tests were carried out by means of a home-made device. This test allows us to evaluate the mechanical resistance of the interface in terms of the maximum force reached during the test. First, results show that the debonding force is not higher after the wires deoxidation. This preparation is therefore not necessary. Second, using a primer PM820 and plasma separately leads to a significant improvment of the mechanical resistance. Third, the combination of these treatments (primer followed by plasma) and a longer time of exposure to the plasma alone get the debonding force higher. Consequently, NiTi/silicone rubber interface improved only by means of plasma offers a new way to obtain biocompatible interfaces in such composite material

An original architectured NiTi silicone rubber structure for biomedical applications

“…Thinner NiTi wires with dimensions of 0.1 mm diameter were used to fabricate the composite. Characteristic temperatures were previously identified by DSC [19]. The austenite to rhombohedral (A to R) transformation occurs during cooling at a temperature equal to 30 • C and the reverse transformation (R to A) occurs at a temperature equal to 34 • C. Like previously, the rhombohedral to martensite (R to M) transformation was not observable on the DSC.…”

“…The adhesion between NiTi and silicone rubber was performed by using a plasma treatment without any chemical substances [18,19]: a gas under low pressure is subjected to a high frequency oscillating electromagnetic field and the accelerated ions in the gas collide with the gas molecules, ionizing them and forming plasma. The ionized gas particles in the plasma interact with solid surfaces placed in the same environment by removing organic contamination from surfaces and modifying or enhancing the physical and chemical surfaces characteristics [25].…”

“…The treatment was performed under vacuum conditions, with operation pressure set equal to 10 −1 kPa and 2.10 −2 kPa for the RIE 300 and the Harrick Plasma Cleaner, respectively. Once the wire surface was treated by plasma, it was placed into a self-developed mold, already used in a previous paper of the authors [19]. The mold was then closed, and the silicone was blended to a curing agent and degassed, before injected into the mold using a medical syringe.…”

“…This type of test is classically used in the literature [16,17,18,19,27] to evaluate the mechanical resistance of the interfaces. For this test, the increase of the adhesion strength is defined by the increase of the maximum required force to pull-out the NiTi wire from the polymer matrix.…”

“…Each treatment presents its own disadvantages: the mechanical treatments are not applicable for every geometries and chemical treatments such as adhesion promoters are often unsuitable for biocompatibility. For these reasons, the use of plasma treatment seems to benefit both of the interface resistance [18,19] and the interface biocompatibility [20]. It was also used in polymeric materials to improve the efficacy of voice prosthesis [22] or to fulfill the requirements medical in medical applications [23].…”