SLIPS technology is an approach to coating medical surfaces that creates a material that is highly lyophobic to various liquids including blood. It is mainly inspired by the pitcher plant. In the past, SLIPS has been fabricated through the creation of porous microstructures, low-surface-energy modification, and the infusion of the lubricant liquid. A liquid lubricating layer forms on the SLIPS as the lubricant is infused into the porous microstructure; thereby, a proper porous microstructure is the key to prepare the SLIPS. In medicine, hemocompatibility defines the measure of the thrombotic response induced by a material or device in contact with blood that will lead to the activation of the blood coagulation cascade, including platelet response, complement activation, and coagulation cascade initiation. Medical implants and blood containing devices save countless lives in the medical field; however, most of these devices suffer a hemocompatibility problem caused by the blood-implant interaction. NiTi (Nickel Titanium) alloys are an ideal bioengineering material that is widely used as the interventional medical scaffold in the modern medical field because of their excellent shape memory property, super elasticity, and biocompatibility.
Despite this, it is considered incredibly difficult to form an abundant porous microstructure on hard metal especially NiTi alloys. To date, it has still been a substantial challenge to create slippery porous microstructures on medical metal materials and then improve the hemocompatibility of those implantable materials. On this account, researchers from the Xi’an Jiaotong University in China: Yang Cheng (PhD candidate, Professor Qing Yang, Dr. Yu Lu Professor Jiale Yong, Dr. Yao Fang, Dr. Xun Hou and Professor Feng Chen carried out a research that sought out to improve on the hemocompatibility of the NiTi alloy by preparing the SLIPS using a cone shaped Bessel beam instead of a Gaussian Laser beam. Their work is currently published in the research journal, Biomaterials Science.
In comparison with the general Gaussian Laser beam, the Bessel laser beam has a longer depth of the focal field and a smaller focal spot. Therefore, the Bessel laser beam was considered more suitable for preparing deep micro hole structures than the Gaussian laser beam. A uniform deep porous microstructure was directly created on the surface of the NiTi alloy. Afterwards, the porous surface was stored in air for seven days to lower the surface energy. After the infusion of perfluorodecalin into the porous microstructure to form a lubricant layer, the SLIPS was successfully fabricated on the NiTi alloy. Lastly, the researchers conducted experiments on the SLIPS to confirm hemocompatibility, antibacterial rates, hemolysis rates and anti-coagulation.
The authors reported that adhesion of fibrinogen on the SLIPS was significantly reduced by 12 times compared to that on the untreated NiTi alloy. It was also seen that the formation of the SLIPS decreased the hemolysis rate on the NiTi alloy from 4.69% to 1.56%, which was remarkably lower than the Chinese national standard (5%). In addition, the SLIPS could effectively inhibit the adhesion of bacteria on the NiTi alloy and enhance the bacterial repellency of the NiTi alloy. The antibacterial rates of the resultant SLIPS reach 98.14% and 99.32% for E. coli and S. aureus bacteria, respectively.
In summary, the study presented a novel method to fabricate a SLIPS on an implantable NiTi alloy based on femtosecond laser processing, which improves the hemocompatibility of the NiTi alloy. Remarkably, the as-prepared SLIPS was nontoxic because the surface energy of the porous microstructure was lowered by the absorption of hydrocarbon groups from the atmosphere rather than traditional fluoroalkylsilane modification. In a statement to Advances in Engineering, the authors believe their approach could potentially endow various metal implantable substrates with slippery properties and allow implantable medical materials to be applied in a healthier and safer way.
Yang Cheng, Qing Yang, Yu Lu, Jiale Yong, Yao Fang, Xun Hou, Feng Chen. A femtosecond Bessel laser for preparing a nontoxic slippery liquid-infused porous surface (SLIPS) for improving the hemocompatibility of NiTi alloys. Biomaterials Science 2020 ,8, 6025.2020.