Inspired by insect wings that kill bacteria on contact, researchers from the Indian Institute of Science in Bangalore have developed a method to treat the surface of titanium orthopaedic implants at nano-scales so that they resist bacterial infection. Study leader Kaushik Chatterjee and postdoctoral research fellow Jafar Hasan talk to OPN about the research.
Q: Tell us a little about your background and education in the orthopaedic industry?
A: I studied materials engineering at college level and subsequently for a PhD in bioengineering. As a PhD student at Penn State University I worked on surface engineering of materials used in cardiovascular devices. Thereafter, I completed a postdoctoral fellowship jointly at the National Institute of Standards and Technology and the National Institutes of Health, working on developing biomaterials for use as scaffolds for bone tissue engineering. Since 2011, I joined the faculty of the Indian Institute of Science in Bangalore where we started a new laboratory for biomaterials research. In our group we work on engineering materials for biomedical applications and focus primarily on orthopaedics.
Q: Could you tell us more about your recent work on the nanotopography on titanium and what you discovered?
A: A major interest in our lab is to engineer titanium alloys for developing the next generation of orthopaedic implants. In that context, we have been exploring surface engineering strategies for enhanced biological performance. Two common clinical challenges associated with biomedical implants are bacterial infections and poor osseointegration. We were inspired by recent studies that reported on the presence of unique nanostructures on the surface of insect wings and set out to mimic these structures on the surface of titanium. Using reactive ion etching, a popular technique in the world of microelectronics, we prepared anisotropic nanostructures like a bed of nanoscale pins. We observed that if the dimensions of the pillar were optimised by controlling the etching time, the nanostructures impart several benefits. This nanoengineered surface can kill a wide variety of bacterial cells on contact but not human stem cells. In fact, this surface was more effective in the osteogenic differentiation of the human stem cells than the unmodified smooth surface.
Q: How were you inspired by the insect wings that kill bacteria on contact?
A: There have been several studies in recent years that show how the surface of wings of certain insects such as dragonfly and cicada exhibit a unique bactericidal property, wherein bacterial cells are killed on contact through mechanical rupture of the cell in contrast to chemical means that form the basis of antibiotics. This mechanism has evolved likely to survive bacterial infections. Other surfaces found in nature such as shark skin also exhibit microscale surface features to resist formation of bacterial biofilms, but this mediated by resistance to attachment and are therefore antibiofouling surfaces. In contrast, the insect wings with the nanostructures are bactericidal. We were inspired to mimic these structures on titanium for biomedical use.
Q: How could this help surgeons and benefit patients?
A: Implant-associated infections are a major clinical challenge and with the growing menace of drug-resistant bacteria there is a need for novel strategies. Use of such nanostructures on implant surfaces may offer a new route to minimizing bacterial infections. In addition, the nanoscale roughness could facilitate bone growth around the implant by promoting osteogenic differentiation of the osteoprogenitor cells, thereby helping in fixation.
Q: What stage of development are you currently at? What is the next step in your research?
A: In our published study, we described the preparation of the surface and described the response of bacterial cells and bone marrow derived stem cells, in vitro. Now we are testing the ability of such a surface to resist infection and promote bone formation in animal models, which will be essential towards the long-term goal of using such surfaces for implants in human patients. We have been in regular discussions with orthopaedic surgeons to discuss our work and how best to develop it further to tackle challenges encountered in the clinic.
SEM images showing bacterial cells with ruptured membrane on the titanium surface with nanopillars.
Q: Are you currently working with any medical device companies?
A: Not yet but are hoping to work with medical device companies. We welcome contact from interested companies to partner with us.
Q: What could your research mean for the future of orthopaedic implants?
A: Biology and medicine have conventionally depended on the use of chemical and biomolecular-based approaches to control cells and address clinical challenges of human physiology. There is now a growing recognition of using physical cues to influence human physiology. I believe our work is part of this burgeoning field of research and offers a novel approach to control the interaction of both bacterial and human cells with material surface. Inspired by nature we have used topography to kill bacterial cells on contact and differentiate stem cells to bone cells. Patients could benefit with such technologies incorporated into the next generation of implants to tackle clinical challenges of the current implants including the risk of microbial infections and poor host integration.
Article reference: Jafar Hasan and others; Nanoscale Topography on Black Titanium Imparts Multi-biofunctional Properties for Orthopedic Applications, Scientific Reports 7, Article number: 41118 (2017). doi:10.1038/srep41118
