Biomaterials optimally suited as scaffolds for tissue regeneration and reconstructive surgery have remained an elusive goal for material scientists and bioengineers. A collaboration between the College of Dentistry and College of Engineering at the University of Illinois at Chicago has led to a new technique for improving the properties of one of the oldest and most widely used structural biomaterials, collagen.
The most abundant protein in mammals, collagen has been employed as a biomaterial since sutures made from cat intestines were used to close the wounds of Roman gladiators. Strong, flexible, and unlikely to provoke an immune response, collagen membranes are utilized today in many medical applications, including tissue engineering and dental bone grafting.
Seven years ago, bioengineering and chemical engineering professor Christos Takoudis, PhD, was working on atomic layer deposition (ALD), which allows nanometer-thin layers of a metal or metal oxide to be uniformly and conformally applied to a substrate’s surface with 2-D or 3-D complex topography. That’s when he met associate professor of restorative dentistry Cortino Sukotjo, DDS, PhD, MS, who was interested in improving dental implant materials.
Together, they investigated how they could modify and enhance the surface properties of a biological substrate. They imagined that the biocompatibility and bioactivity of commercially available collagen membranes could be improved by coating them with an ultra-thin layer of titanium dioxide, which is used in cosmetics, sunscreens, and dental/orthopedic implants.
Also, the professors envisioned using the ALD process to apply a nanolayer of the metal oxide to these complex nanostructured membranes. But the challenge is that biological materials like collagen cannot withstand the heat of industrial ALD treatment, which often is higher than 200°C, or nearly 400°F.
“Seventy degrees C is the lowest others had gotten, especially for the ALD process of titanium dioxide on biological fibrous substrate,” said Arghya Bishal, a doctoral student in the Richard and Loan Hill Department of Bioengineering. “We had to work at lower and lower temperatures until we finally got to room-temperature ALD of titanium dioxide.”
The researchers achieved room-temperature ALD by using a custom apparatus they devised along with tetrakis (dimethylamido) titanium as the titanium metal source and ozone as the oxidizing agent to generate titanium dioxide. The components were introduced one after the other, with an argon pulse in between, into a low-pressure chamber that held the collagen-membrane ALD substrate.
Next, the researchers repeated the ALD cycle 150, 300, and 600 times to grow titanium-oxide films of increasing thickness that each could be compared to uncoated collagen membranes. Now, they plan to begin pre-clinical in vivo experiments and try to create or modify new materials using other metals and/or ALD metal oxides to cater to the specific needs of different clinical applications.