Bio-nanopatterning of Titanium by Electron Beam Lithography

There is a need for joint replacing implants due to osteoarthritis and trauma. For non-cemented implants made of titanium alloys, bone ingrowth is needed. However bone ingrowth is not always accomplished. Implant micro/nanotopography can be used to enhance bone ingrowth through cellular interactions. Therefore, processes to generate controlled topographies on titanium substrates are needed. The goal of this study has been to develop a method for patterning titanium in the submicron to nanoscale. The desired patterns included pits and pillars with diameters between 30 and 700 nm, a disorder (deviation from the square arrangement in a random direction) of 0 to 75 nm, and an interspacing of 300 nm and 900 nm. To achieve this goal, the electron beam lithography process has been explored. With this process, an electron beam is used to write the pattern on the resist-coated titanium substrate. Then, the pattern is transferred into the titanium. The optimum dose for writing the patterns on the positive and negative resists has been determined experimentally. For pattern transfer, reactive ion etching, and ion milling were used, either directly onto the resist mask, or through a hard mask. The resultant topographies have been evaluated by scanning electron microscopy. The results of this study indicate that the use of hard mask, in combination with the optimum dose, and reactive ion etching conditions, generates titanium pits with 320 nm and 700 nm diameter. For pillars, further optimization of the process steps is needed. With the resist mask and ion milling, pillars of 245 nm and 545 nm in diameter with heights of 50 nm and 100 nm respectively could be obtained. In this study, a new electron beam lithography process has been developed for patterning titanium in the submicron to nanoscale. The process offers control of pattern features in these scales, this enables easy change in pattern design, and ensures pattern transfer into titanium. Therefore, the processes are considered feasible for generating patterns relevant for guiding mesenchymal stem cell fate. Previous research offered precision control into polymers, or patterns with less control into titanium.