Withstanding frequent steam sterilisation: Innovative technique to bond glass and stainless steel composites in biotechnology and endoscopic medicine

In order to assemble various multicomponent devices for biotechnological and endoscopic applications, the different parts are typically clamped or melted together. This, however, is complicated, time-consuming and often changes the actual geometry of the parts—thereby adversely affecting the reproducibility of experiments. Thus, the aim of this study is to investigate whether adhesives can replace these conventional glass joining techniques of melting and clamping in order to create durable and autoclavable devices of glass and glass/stainless steel parts that can withstand multiple sterilisation cycles. Twelve commercial acrylate and epoxy adhesives were screened for their capability to withstand 800 standard cycles of steam sterilisation. These adhesives were applied to different borosilicate, quartz and sapphire glass as well as stainless steel substrates pre-treated by either degreasing with 2-butanone or the surface was additionally modified by Pyrosil® or atmospheric plasma. The various physicochemical properties such as shear strength, maximum force at failure, extensibility and glass transition temperature of the best screened adhesives were examined. Furthermore, the surface topologies of the tested glass materials were characterised by Scanning Electron Microscopy (SEM). Finally, the shear strengths of the different bond combinations were quantified at 121 °C, the commonly applied sterilisation temperature in biotechnology. For every substrate combination, at least one adhesive was found, which created a durable bond capable of withstanding the maximum 800 autoclaving cycles. Here, the urethane acrylate GB 368 (Delo, Windach/Germany) was determined as the best adhesive to bond glass/glass and glass/stainless steel substrates. By comparison, the epoxy M-31 CL (Henkel-Loctite, Garching/Germany) showed comparable shear strength but only for glass/glass bonds. Most importantly, all the tested epoxy resins failed to bond glass with stainless steel. Unlike the acrylates, the epoxy adhesives displayed low extensibility. At 121 °C, the shear strengths of both the epoxy and acrylate adhesives were reduced by a factor of three to ten. Since all of the best screened acrylates proved superior extensibility, they can tolerate for the internal bond stresses resulting from different thermal expansion coefficients of glass and stainless steel. Consequently, they are the best adhesives to bond glass/glass as well as glass/stainless steel substrates for applications in biotechnology and medicine.