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Researchers at the University of Chicago’s Pritzker School of Molecular Engineering have created a groundbreaking hydrogel that doubles as a semiconductor. The material combines the soft, flexible properties of biological tissues with the electronic capabilities of semiconductors, making it ideal for advanced medical devices.
In a study published in Science, the research team, led by Sihong Wang, developed a stretchy, jelly-like material that provides the robust semiconducting properties necessary for use in devices such as pacemakers, biosensors and drug delivery systems.
Hydrogels are ideal for many biomedical applications because they are soft, flexible and water-absorbent – just like human tissues. Material scientists, long recognizing the vast potential of hydrogels, have pushed the boundaries of this class of material. One way is to create hydrogels with semiconducting abilities that can be useful for transmitting information between living tissues and bioelectronic device interfaces – in other words, a hydrogel semiconductor.
Imparting semiconducting properties to hydrogels is no easy task, however. Semiconductors, while known for their remarkable electronic properties, are typically rigid, brittle and water-repellent, making them inherently incompatible with hydrogels. By overcoming this fundamental mismatch, Wang and his team have created a material that could revolutionize the way medical devices interface with the human body.
Traditional hydrogels are made by dissolving hydrogel precursors (monomers or polymers) in water and adding chemicals to crosslink the polymers and form a water-swelled state. Since most polymers are inherently insulating, creating a hydrogel with semiconducting properties requires a special class of semiconducting polymers. The challenges do not stop there, however. These polymers typically only dissolve in organic solvents, not in water.
“The question becomes how to achieve a well-dispersed distribution of these semiconducting materials within a hydrogel matrix,” says first author Yahao Dai, a PhD student in the Wang lab. “This isn’t just about randomly dispersing particles into the matrix. To achieve strong electrical performance, a 3D interconnected network is essential for effective charge transport. So, the fundamental question is: how do you build a hydrophobic, 3D interconnected network within the hydrogel matrix?”
To address this challenge, the researchers first dissolved the polymer in an organic solvent that is miscible with water, forming an organogel – a gel-like material composed of an organic liquid phase in a 3D gel network. They then immersed the organogel in water and allowed the water to gradually replace the organic solvent, transforming it into a hydrogel.
The researchers point out that this versatile solvent exchange process can be adapted to a variety of semiconducting polymers, opening up new possibilities for hydrogel semiconductors with diverse applications.
The result is a hydrogel semiconductor material that’s soft enough to match the feel of human tissue. With a Young’s modulus as low as 81 kPa – comparable to that of jelly – and the ability to stretch up to 150% of its original length, this material mimics the flexibility and softness of living tissue. These tissue-like characteristics allow the material to seamlessly interface with the human body, reducing the inflammation and immune responses that are often triggered by rigid medical implants.
The material also has a high charge carrier mobility, a measure of its ability to efficiently transmit electrical signals, of up to 1.4 cm2/V/s. This makes it suitable for biomedical devices that require effective semiconducting performance.
The potential applications extend beyond implanted devices. The material’s high hydration and porosity enable efficient volumetric biosensing and mass transport throughout the entire thickness of the semiconducting layer, which is useful for biosensing, tissue engineering and drug delivery applications. The hydrogel also responds to light effectively, opening up possibilities for light-controlled therapies, such as light-activated wireless pacemakers or wound dressings that use heat to accelerate healing.
The research team’s hydrogel material is now patented and being commercialized through UChicago’s Polsky Center for Entrepreneurship and Innovation. “Our goal is to further develop this material system and enhance its performance and application space,” says Dai. While the immediate focus is on enhancing the electrical and light modulation properties of the hydrogel, the team envisions future work in biochemical sensing.
“An important consideration is how to functionalize various bioreceptors within the hydrogel semiconductor,” explains Dai. “As each biomarker requires a specific bioreceptor, the goal is to target as many biomarkers as possible.”
The team is already exploring new methods to incorporate bioreceptors, such as antibodies and aptamers, within the hydrogels. With these advances, this class of semiconductor hydrogels could act as next-generation interfaces between human tissues and bioelectronic devices, from sensors to tailored drug-delivery systems. This breakthrough material may soon bridge the gap between living systems and electronics in ways once thought impossible.
The post Tissue-like hydrogel semiconductors show promise for next-generation bioelectronics appeared first on Physics World.
A team of scientists based in the US has developed a non-invasive headset device designed to track changes in blood flow and assess a patient’s stroke risk. The device could make it easier to detect early signs of stroke, offering patients and physicians a direct, cost-effective approach to stroke prevention.
Stroke remains the leading cause of death and long-term disability, affecting 15 million people worldwide every year. In the United States, someone dies from a stroke roughly every 3 min. Those who survive are often left physically and cognitively impaired.
About 80% of strokes occur when a blood clot blocks an artery that carries blood to the brain (ischaemic stroke). In other cases, a blood vessel can rupture and bleed into the brain (haemorrhagic stroke). In both types of stroke, deprived of oxygen from the loss of blood flow, millions of brain cells rapidly die every minute, causing devastating disability and even death.
As debilitating as stroke is, current methods for assessing stroke risk remain limited. Physicians typically use a questionnaire that assesses factors such as demographics, blood test results and pre-existing medical conditions to estimate a patient’s risk. While non-invasive techniques exist to detect changes after the onset of a stroke, by the time a stroke is suspected and patients are rushed to the emergency room, critical damage may have already been done.
Consequently, there remains an acute need for tools that can proactively monitor and quantify stroke risk before an event occurs.
Seeking to bridge this gap, in a study published in Biomedical Optics Express, a research team, led by Charles Liu of the Keck School of Medicine at the University of Southern California and Changhuei Yang of California Institute of Technology, developed a headset device to monitor changes in the brain’s blood flow and volume while a patient holds their breath.
“Stroke is essentially a brain attack. The stroke world has been trying to draw a parallel between a heart attack and a brain attack,” explains Liu. “When you have a heart disease, under normal circumstances – like sitting on the couch or walking to the kitchen – your heart may seem fine. But if you start walking uphill, you might experience chest pain. For heart diseases, we have the cardiac stress test. During this test, a doctor puts you on a treadmill and monitors your heart with EKG leads. For stroke, we do not have a scalable and practical equivalent to a cardiac stress test.”
Indeed, breath holding temporarily stresses the brain, similar to the way that walking uphill or running on a treadmill would stress the heart in a cardiac stress test. During breath holding, blood volume and blood flow increase in response to lower oxygen and higher carbon dioxide levels. In turn, blood vessels dilate to mitigate the pressure of this increase in blood flow. In patients with higher stroke risk, less flexible blood vessels would impede dilation, causing distinct changes in blood flow dynamics.
Researchers have long had access to various imaging techniques to measure blood dynamics in the brain. However, these methods are often expensive, invasive and impractical for routine screening. To circumvent these limitations, the team built a device comprising a laser diode and a camera that can be placed on the head with no external optical elements, making it lightweight, portable, and cost-effective.
The device transmits infrared light through the skull and brain. A camera positioned elsewhere on the head captures the transmitted light through the skull. By tracking how much the light intensity decreases as it travels through the skull and into the camera, the device can measure changes in blood volume.
When a coherent light source such as a laser scatters off a moving sample (i.e., flowing blood), it creates a type of granular interference pattern, known as a speckle pattern. These patterns fluctuate as blood moves through the brain – the faster the blood flow, the quicker the fluctuations. This technique, called speckle contrast optical spectroscopy (SCOS), enables the researchers to non-invasively measure the blood flow rate in the brain.
The researchers tested the device on 50 participants, divided into low- and high-risk groups based on a standard stroke-risk calculator. During a breath-holding exercise, they found significant differences in blood dynamic changes between people with high stroke risk and those at lower risk.
Specifically, the high-risk group exhibited a faster blood flow rate but a lower volume of blood in response to the brain’s oxygen demands, suggesting restricted blood flow through the stiff vessels. Overall, these findings establish physiological links between stroke risk and blood dynamics measurements, highlighting the technology’s potential for stroke diagnosis and prevention.
The team plans to expand these studies to a broader population to reinforce the validity of the results. “Our goal is to further develop this concept to ensure it remains portable, compact, and easy to operate without requiring specialized technicians. We believe the design is scalable, aligning well with our vision of accessibility, allowing diverse and underrepresented communities to benefit from this technology,” says co-lead author Simon Mahler, a postdoctoral scholar in the Yang lab at Caltech.
The researchers also aim to integrate machine learning into data analysis and conduct clinical trials in a hospital setting, testing their approach’s effectiveness in stroke prevention. They are also excited about the applications of their device in other neurological conditions, including brain injuries, seizures, and headaches.
The post Laser-based headset assesses stroke risk using the brain’s blood flow appeared first on Physics World.
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