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A stretchable and biodegradable strain and pressure sensor for orthopaedic application


The ability to monitor, in real time, the mechanical forces on tendons after surgical repair could allow personalized rehabilitation programmes to be developed for recovering patients. However, the development of devices capable of such measurements has been hindered by the strict requirements of biocompatible materials and the need for sensors with satisfactory performance. Here we report an implantable pressure and strain sensor made entirely of biodegradable materials. The sensor is designed to degrade after its useful lifetime, eliminating the need for a second surgery to remove the device. It can measure strain and pressure independently using two vertically isolated sensors capable of discriminating strain as small as 0.4% and the pressure exerted by a grain of salt (12 Pa), without them interfering with one another. The device has minimal hysteresis, a response time in the millisecond range, and an excellent cycling stability for strain and pressure sensing, respectively. We have incorporated a biodegradable elastomer optimized to improve the strain cycling performances by 54%. An in vivo study shows that the sensor exhibits excellent biocompatibility and function in a rat model, illustrating the potential applicability of the device to the real-time monitoring of tendon healing.

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C.M.B. acknowledges postdoctoral fellowship support from the Swiss National Science Foundation (Postdoc Mobility Fellowship no. P2EZP2_152118) and the European Commission (Marie-Curie International Outgoing Fellowship grant no. 622362). Part of this work was performed at the Stanford Nano Shared Facilities (SNSF), supported by the National Science Foundation under award ECCS-1542152. B.C.S. acknowledges the National Research Fund of Luxembourg for financial support (project no. 6932623).

Author information

C.M.B. is the main contributor to this work, elaborating the sensor concept, developing new fabrication processes, performing all experiments for materials investigations, device characterization, data collection for in vitro and in vivo experiments, data analysis and interpretation, and drafting of the article. B.C.S. contributed to the POMaC investigation, including polymer synthesis, chemical properties characterization, data analysis and interpretation, and provided critical revision of the article. A.C. contributed to the drafting of the article and provided critical revision. Y.K. performed all surgeries related to the in vivo studies, including design of the in vivo studies, development of the protocols, sensors implantation and operation studies, and materials biocompatibility studies. He also worked on data analysis and interpretation, and contributed to the drafting and critical revision of the article. A.L. performed all surgeries related to the tendon in vitro studies, and worked on data analysis and interpretation. Z.W., J.C. and P.F. contributed to the design of the in vivo studies, working on the protocols and data interpretation. P.F. also contributed to the drafting and critical revision of the article. Z.B. contributed to developing the sensor concept, fabrication processes and materials investigation, device characterization, data interpretation and critical revision of the article.

Competing interests

The authors declare no competing interests.

Correspondence to Paige Fox or Zhenan Bao.

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Fig. 1: A fully biodegradable and stretchable strain and pressure sensor.
Fig. 2: Investigations of the POMaC elastomer used in the strain sensor and as packaging material to improve resistance to cycling upon biodegradation.
Fig. 3: Response characteristics of the biodegradable strain and pressure sensor.
Fig. 4: In vitro and in vivo study of the biodegradable strain and pressure sensor.
Fig. 5: Biocompatibility of POMaC and silicone (control) evaluated in vivo.