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Biomaterials
Built to respond F
or many conventional medical devices, a key design objective has been to minimise undesirable interactions between devices and biological tissues. Some devices use relatively inert or biocompatible materials to minimise adverse biological reactions, although many are designed to interact with cells, tissues or biological fluids. Many conventional devices are also designed to maintain a substantially fixed form during use. However, a new generation of emerging medical devices is moving away from this paradigm. These devices respond to stimuli from within or outside the body by changing their form, mechanical properties, chemical behaviour or drug-release profile. In some cases, those changes are intended to contribute to a therapeutic effect. To do so, they feature a wide range of stimuli-responsive biomaterials that respond to temperature, pH, electric fields or other signals. These include polymers such as hydrogels and
shape-memory polymers, shape-memory alloys and nanoparticle-based materials. Inspired by controlled drug-delivery systems in pharmaceuticals, some of these devices release therapeutic molecules at specific sites.
Biomaterials and what they sense Medical devices that respond to temperature variations have existed for decades. These devices, which range from braces and stents to implants, feature shape-memory alloys such as nitinol. An alloy of nickel and titanium, nitinol can recover a programmed shape when heated through its transformation-temperature range, which can be engineered to overlap with body temperature. For example, “you can insert a stent through a catheter at room temperature, and it will deploy when it reaches body temperature,” says Phillip Messersmith, chair of bioengineering at the University of California, Berkeley.
From self-deploying stents to soft robotic catheters, responsive biomaterials are turning medical devices from passive tools into active systems. Sachin Rawat speaks with Phillip Messersmith of the University of California, Berkeley, and Carmel Majidi of Carnegie Mellon University about the materials driving the shift, the applications taking shape and the barriers to clinical use.
www.medicaldevice-developments.com
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