Research Bits: Dec. 20

Wearable blood tracking with light and sound; nanolaser arrays on single optical microfiber; gelbots; ornithopters.


Patch tracks blood in deep tissue

A skin-worn photoacoustic patch developed by a research team at the University of California San Diego is equipped with arrays of laser diodes and piezoelectric transducers to detect biomolecules in deep tissues, which usually would require a magnetic resonance imaging (MRI) and X-ray-computed tomography. The patch may help doctors tract hemoglobin in real time, diagnose tumors, organ malfunction, cerebral or gut hemorrhages, and more.

“The amount and location of hemoglobin in the body provide critical information about blood perfusion or accumulation in specific locations. Our device shows great potential in close monitoring of high-risk groups, enabling timely interventions at urgent moments,” said Sheng Xu, a professor of nanoengineering at UC San Diego and corresponding author of the study in a press release.

The laser diodes embedded the patch’s flexible soft silicone polymer matrix send out pulsed laser that are absorbed by biomolecules, which bounce back sound waves. Different wavelengths can be detected.

“Piezoelectric transducers receive the acoustic waves, which are processed in an electrical system to reconstruct the spatial mapping of the wave-emitting biomolecules,” said Xiaoxiang Gao, a postdoctoral researcher in Xu’s lab and co-author of the study.

“Continuous monitoring is critical for timely interventions to prevent life-threatening conditions from worsening quickly,” said Xiangjun Chen, a nanoengineering PhD student in the Xu group and study co-author. “Wearable devices based on electrochemistry for biomolecules detection, not limited to hemoglobin, are good candidates for long-term wearable monitoring applications. However, the existing technologies only achieve the ability of skin-surface detection.”

The new, flexible, low form-factor wearable patch comfortably attaches to the skin, allowing for noninvasive long-term monitoring. Photo by Xiaoxiang Gao for the Jacobs School of Engineering at UC San Diego.

Fig 1: The new, flexible, low form-factor wearable patch comfortably attaches to the skin, allowing for noninvasive long-term monitoring. Source: Photo by Xiaoxiang Gao for the Jacobs School of Engineering at UC San Diego.

To read more, see Xiaoxiang Gao, Xiangjun Chen, Hongjie Hu, Xinyu Wang, Wentong Yue, Jing Mu, Zhiyuan Lou, Ruiqi Zhang, Keren Shi, Xue Chen, Muyang Lin, Baiyan Qi, Sai Zhou, Chengchangfeng Lu, Yue Gu, Xinyi Yang, Hong Ding, Yangzhi Zhu, Hao Huang, Yuxiang Ma, Mohan Li, Aditya Mishra, Joseph Wang, Sheng Xu. A photoacoustic patch for three-dimensional imaging of hemoglobin and core temperature. Nature Communications, 2022; 13 (1) DOI: 10.1038/s41467-022-35455-3

Robots that fly and perch, gelbots

Two interesting developments in robotics mimic biology. A robot that can fly like bird — by flapping wings and perching — successfully landing . The other is a gelbot, a worm-like robot made of a water-based gel that moves when the temperature changes.

To make the gel bot move team more efficiently than previous experiments have, the team from Johns Hopkins University took advantage of how reversible thermoresponsive hydrogel swells and shrinks (deswells)depending on the temperature (30° to 60°C) to make the worm-like robot move forward and backward on a flat surface. They used specific structures of the gel, which was 3D printed, to make the movement more efficient. The gel material could be used in humanoid and fish-like robots. “It seems very simplistic but this is an object moving without batteries, without wiring, without an external power supply of any kind—just on the swelling and shrinking of gel,” said senior author David Gracias, a professor of chemical and biomolecular engineering at Johns Hopkins University said in an article on Johns Hopkins’ news page. “Our study shows how the manipulation of shape, dimensions and patterning of gels can tune morphology to embody a kind of intelligence for locomotion.”

To read more, check out the researcher’s article — Aishwarya Pantula, Bibekananda Datta, Yupin Shi, Margaret Wang, Jiayu Liu, Siming Deng, Noah J. Cowan, Thao D. Nguyen, David H. Gracias. Untethered unidirectionally crawling gels driven by asymmetry in contact forcesScience Robotics, 2022; 7 (73) DOI: 10.1126/scirobotics.add2903

An ornithopter is a robot that flies like a bird by flapping wings — the Ecole Polytechnique Fédérale de Lausanne has successfully designed an ornithopter that can land autonomously on a horizontal perch using a claw-like mechanism. The benefit of perching could make it possible for UAVs (unmanned aerial vehicles) to recharge their batteries via solar power more efficiently, which can extend the flying distance. It’s no simple feat to land a robot on branch — which involves being able to find the branch and slow flight enough to grab the branch. The wings still have to flap for a short time as the claw grabs the branch. The researchers used an on-board computer and navigation system on the ornithopter to manage all the tasks, with an external motion-capture system to help it determine its position.

The claw leg was made of carbon fiber and uses a TSL1401 line-scan sensor (1 ×128 pixels) sensor to detect the branch — a sensor used in a barcode scanning device, they are well-suited for detecting a horizontal line in controlled settings, according to the researcher’s article in Nature Communications. The ornithopter project is part of Project Griffin.

“This is the first phase of a larger project. Once an ornithopter can master landing autonomously on a tree branch, then it has the potential to carry out specific tasks, such as unobtrusively collecting biological samples or measurements from a tree. Eventually, it could even land on artificial structures, which could open up further areas of application,” said first author Raphael Zufferey, a postdoctoral fellow in the Laboratory of Intelligent Systems (LIS) and Biorobotics ab (BioRob) in the School of Engineering, in EPFL’s news brief, which shows the ornithopter landing.

To read more, see Zufferey, R., Tormo-Barbero, J., Feliu-Talegón, D. et al. How ornithopters can perch autonomously on a branch. Nat Commun 13, 7713 (2022).

A photonic crystal nanolaser array on optical microfiber

Researchers from the University of California Berkeley and Korea University demonstrated they could control densely spaced nanolaser arrays on a single optical microfiber. The all-optical programming of photonic crystal nanolaser arrays uses switchable modal interference of a pump beam. The research could lead to more efficient ways to move data in semiconductors. “We believe that our method can be readily adapted to the implementation of densely integrated on-chip WDM sources in silicon photonics and can lay the foundation for applications in other disciplines, such as biosensing, multicolor interferometry, and quantum control of optical emitters,” writes the researchers in their article in Optica magazine.

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