Developing Improved Biomaterials: Increasing Tissue Growth, Decreasing Infection, and Inhibiting Inflammation without Drugs

Thomas J. Webster, department chair, chemical engineering at Northeastern University (Boston), will speak on "Developing Improved Biomaterials: Increasing Tissue Growth, Decreasing Infection, and Inhibiting Inflammation Without Drugs" at the MD&M West MedTech Innovate Seminar taking place on Tuesday, February 12.

MPMN: Which themes do you intend to cover in your presentation at the MedTech Innovate Seminar, and why are these themes important?

Webster: One of the important emerging medical device areas is the use of nanotechnology. Nanotechnology is often defined as the creation of materials--be they particles, grain, or tubes--that have at least one dimension less than 100 nm. When you make such small materials, they essentially have much different properties than larger materials, such as micron-sized particles, grains, or tubes. The size range of nanomaterials provides unique properties, one of which is superhigh surface energy. When you think of medical devices, surface energy is a critical property for interacting with cells, tissues, and the body, since the body is primarily composed of water. If you have materials with high surface energy, you have materials that will interact better with the body.

A key feature of my presentation will be a discussion of what is happening with the field of nanotechnology and medical devices. This is a quickly changing field; there is a lot going on. FDA is incredibly interested in what this new size range of materials is doing for tissue growth, what is happening in terms of safety, how to manufacture nanomaterials, and how they are being used to help everything from hip implants to catheters. That's a lot of what my talk will summarize. Of course, the reason why I'm talking about it is because many companies and researchers at universities are reporting increased tissue growth through the use of nanomaterials--these high-surface-energy materials.

The excitement surrounding nanomaterials is also being transferred to old materials. Such older-type materials as titanium, which has been used as a hip-implant material for decades, are getting a new lease on life and being received with a new burst of excitement as manufacturers are beginning to make them out of nanoparticles or fabricate them with nanofeatures. Associated with the use of such materials is increased tissue growth, including bone growth.

MPMN: For cardio, orthopedic, or other medical device applications, what are some of the challenges facing designers and developers of biomaterials?

Webster: This is another thing I'll discuss at the seminar. An area that we have not conquered in the medical device sphere is infection control. If you look at the statistics, the entire globe is seeing an increased number of infection cases caused by medical devices. Thus, whether you're talking about orthopedics or such cardiovascular applications as stents, heart patches, or catheters that are used over a long period time, infection is a big problem. And as we know, the way we've tried to combat this problem thus far is by developing antibiotics. But bacteria are proliferating so quickly that it's easy for them to evolve and mutate, enabling them to resist antibiotics. We are constantly behind the curve. We're constantly trying to develop new antibiotics, but by the time we bring them to market, the bacteria have begun to develop resistance to them, and they aren't effective anymore.

Thus, one of the challenges that still remains and for which I'll highlight some approaches is medical device-related infection. This is an issue that we really have to get a hold on because we're spending so much time and effort in developing better orthopedic or cardiovascular implants only to see them cause infections.

We'll talk about strategies for combating this problem. One such strategy that appears to be working and that does not involve the use of antibiotics is using nanomaterials to change the surface energy of implant materials. For example, I'll highlight a study in which we have taken a catheter made from a material that is frequently associated with infection. We have created nanoscale surface features on the catheter that change the surface energy so that the device can repel bacteria. Fortunately, we are seeing no cases of infection from these catheters with nanoscale features. This is a nondrug, nonantibiotic approach; we are using surface properties to improve the functionality of the medical device.

MPMN: What do you see as the role of tissue ingrowth for fighting infection and inflammation?

Webster: Unfortunately, bacteria will proliferate if they're present in the area of the medical device. In addition, they will grow much quicker than tissue and mammalian, or tissue-forming, cells. Thus, in a sense, we're already a couple of steps behind in the competition. The bacteria will beat mammalian cells to the surface and grow.

One of two things can happen if bacteria are present on the medical device. Either they will grow at an incredible rate and form a biofilm, preventing tissue from growing. Or, if they grow at a slow rate, tissue will grow in the midst of the bacteria, causing tissue infection. And if bone gets infected, it becomes very weak. Thus, if someone has a hip implant and the bacteria on the implant intermingle with the bone, you will have very weak bone surrounding the implant. That's most likely where the bone will fracture, forcing the patient to undergo replacement surgery. Unfortunately, the current solution to an infection is to remove the implant. That's the last-resort situation you want to be in, but that's commonly what has to happen because we have no way of stopping the bacteria from growing once they reach a certain population density.

Combating this problem is where approaches such as nanotechnology are really needed. We need to keep bacteria from attaching to medical devices in the first place, but if they do attach and grow on the medical device, can we use nanoparticles to combat them? Yes, we can actually direct nanoparticles to go into the biofilm, into the bacteria, and kill them without having to remove the implant. We're seeing indications that we can create nanoparticles that could be injected around an infected implant to kill the bacteria and remove the infection so that you don't have to ask the patient to go through a costly, time-consuming, and detrimental surgery. This is another topic that I will cover in my presentation.

MPMN: How close to commercialization are the nanotechnology applications you are addressing here? And what about the potential cytotoxicity dangers associated with nanotechnology?

Webster: Let me preface this by saying that many of us in this field view nanotechnology as having two parts. One part is nanoparticles. Many people are using nanoparticles to fight cancer or improve disease detection. That's one part of nanotechnology. Another part that is actually closer to commercialization is using nanotechnology to create nanofeatures on implants. This application does not have to involve nanoparticles. There are ways that you can create nanodimensional features on existing implants that do not involve the use or the shedding of nanoparticles.

One such nanotechnology surface-modification technique is called anodization. Already employed in the medical device community, anodization is a process that manufacturing companies often use to color code their medical devices. It's an electrochemical process that changes surface roughness. Thus, an orthopedic screw can have a greenish tint if it's anodized one way and a blue tine if it's anodized a different way. What people are doing in the nanotechnology field is changing this electrochemistry so that you produce nanofeatures rather than micron-size features that change the color of an object.

Furthermore, anodizing orthopedic implants to create nanofeatures is close to commercialization. There are a couple of efforts in which companies have submitted applications for FDA 510(k) approval because they are not changing chemistry by using this approach. They still start with titanium, but they're changing its roughness characteristics, and that's a much easier way to get FDA approval.

In terms of commercialization, I might also add that we have tested a silicon nitride product with nanoscale features offered by a company called Amedica (Salt Lake City). This product almost looks as if it has little blades of grass growing on the surface. We performed a number of animal and in vitro studies showing that this material does a better job of improving bone growth than titanium. But more importantly, it decreases bacterial function, and it does this without the use of antibiotics. The material's surface energy and surface roughness decrease bacterial function. Amedica is selling this material commercially, and it's being used in spinal implantations. In addition, FDA recently granted the company expanded claims for antiinfection properties. It's the first FDA-approved material that I know with an antiinfection claim that does not involve releasing a drug.

MPMN: What conclusions do you hope attendees at the MedTech Innovate Seminar will draw from your presentation?

Webster: One conclusion that I hope attendees will draw from my talk is that we don't have to give up on the materials that we are inserting into the body today. Many companies, academicians, and clinicians think that we need brand-new chemistries to improve the performance of our medical devices. I don't think that this is true. By highlighting this new material size, by highlighting nanotechnology, we open the door again to all of the chemistries that we've been inserting into the body for a long time. However, we may need to change small things about them to make them perform better. I think that's a valuable thing for people to hear. At the same time, this approach can also accelerate the process of commercializing new medical implant technologies.

One criticism of nanotechnology and regenerative medicine is that the next material that we will develop, get approved, and use in people is still decades away. But again, by concentrating on the old chemistries and using old materials with different dimensions, we can speed up the FDA approval process, accelerate commercialization, and really help people faster.