Around 1 in 3 robotic prosthetics are abandoned due to weight or limited movement (Biddiss and Chau, 2007). However, researchers Hao Yang, Zhe Tao and Jian Yang from the University of Science and Technology of China (USTC) aim to change that and provide better options to amputees. Their team has built an arm that is capable of a larger range of motion, while being as lightweight as a human hand. It can comb hair, pour a drink or even use a smartphone. A paper published in Nature in January this year has outlined their results with a 60-year-old amputee participant, proving highly successful (Yang et al., 2025).  

Current prosthetics can lead to discomfort that develops into health issues like arthritis (Pasquina et al., 2015). Most products can currently move in about 10 directions (degrees of freedom, or DOF). This is less than the human hand with 23 DOF, and the USTC device with an impressive 19 DOF (Yang et al., 2025). This technology has the potential to revolutionise prosthetics. Having access to fine motor skills can provide users with a new level of independence and confidence. 

When it comes to electric prosthetics, there is a trade-off between the complexity of the device and its weight. Electric motors can be heavy, and users are much less likely to be open to integrating a device into their lifestyle if it is physically taxing. This prosthetic weighs only 370g while the average human hand weighs 400g (Yirka, 2023) - the secret to this is the use of shape-memory alloy (SMA) actuators.  

The actuators work by using wires that can change shape in response to temperature (Cambridge Mechatronics, 2023). They can be as thin as a human hair, producing proportionally large movements. These properties make them ideal for mimicking muscles. Having a high power density of 1000W/kg means that SMA actuators can deliver a lot of energy in a small amount of time, suitable for quick movements.  

Figure 1. A diagram comparing the prosthetic produced at the University of Science and Technology in China to the human hand. It shows the location of the actuators in the wrist and forearm. 

The casing is soft silicone with the wires just underneath the surface. Their motions are controlled through heating/cooling, but the temperature never exceeds 27.2 °C. The test subject was able to use it confidently in less than a day. In addition, the arm also has an AI voice command operated by the iFLYTEK Large Language Model. This feature controls the prosthetic in more than 60 languages (Yang, 2025). It even works in noisy indoor environments of up to 70dB, which is about as loud as a washing machine (DecibelPro, 2021).   

Figure 2. Gestures produced by the prosthetic compared to a human hand, both showing numbers 1-10 in Chinese sign language.  

One drawback is that for very rapid movements, there is a time delay (Yang, 2025). Additionally, there is a lack of long-term data for this device, which makes its serviceability hard to predict for other users. With all these developments, SMA actuators could be key to solving issues with prosthetic limbs today. With more research and more development, hopefully, these prosthetic limbs can be fully integrated into healthcare globally.

Sources 

1. Biddiss, E.A. and Chau, T.T. (2007). Upper limb prosthesis use and abandonment: A survey of the last 25 years. Prosthetics and Orthotics International, 31(3), pp.236– 257. doi: https://doi.org/10.1080/03093640600994581.  
2. Cambridgemechatronics.com. (2023). Controlling Shape Memory Alloy actuators. [online] Available at: https://www.cambridgemechatronics.com/en/news/resources-blogs/controllingshape-memory-alloy-actuators/ 
3. Decibel Meter App | Best Digital Sound Level Meter For Your Smartphone. (2021). How Loud Is 70 decibels | What is a 70 dB equivalent. [online] Available at: https://decibelpro.app/blog/how-loud-is-70-db/.  
4. Pasquina, P.F., Perry, B.N., Miller, M.E., Ling, G.S.F. and Tsao, J.W. (2015). Recent advances in bioelectric prostheses. Neurology: Clinical Practice, 5(2), pp.164–170. doi: https://doi.org/10.1212/cpj.0000000000000132.  
5. Yang, H., Tao, Z., Yang, J., Ma, W., Zhang, H., Xu, M., Wu, M., Sun, S., Jin, H., Li, W., Wang, L. and Zhang, S. (2025). A lightweight prosthetic hand with 19-DOF dexterity and human-level functions. Nature Communications, 16(1). doi: https://doi.org/10.1038/s41467-025-56352-5. Abstract, Discussion, Figures 1C and 5C.  
6. Yirka, B. (2023). Experiments show people dramatically underestimate how much their hands weigh. [online] medicalxpress.com. Available at: https://medicalxpress.com/news/2023-07-people-underestimate.html.