Processed films showed marked improvements in stability and output. Films strained to 50% achieved a voltage peak-to-peak of 0.32 V at 30 Hz, with current outputs of 18 nA, although performance decreased at higher frequencies it still performed better than the unprocessed film. The 75% strained films demonstrated further enhancements, maintaining a stable voltage output of 0.39 V and reaching a current peak-to-peak of 36 nA at 30 Hz, with improved performance across all frequencies tested. Films strained to 100% delivered the highest outputs, with voltage peaking at 0.94 V and current reaching 62 nA at 30 Hz. However, a slight reduction in sensitivity compared to 75% strained films was noted, suggesting a trade-off between maximizing output and maintaining stability. Figure shows the declining trend in output voltage and current for both unprocessed and processed PLLA films over a range of frequencies. The high voltage and current outputs of the 100% strained PLLA films make them an excellent candidate for integration into annuloplasty rings. In addition to this, a clear improvement in voltage sensitivity is observed, as shown in Figure , highlighting the superior performance of 100% strained PLLA compared to other processing conditions. This improvement underscores the critical role of molecular alignment and enhanced crystallinity achieved through mechanical processing in optimizing the material's functionality for biomedical applications . We now consider their application in strain monitoring in the context of aortic annuloplasty. Figure compares a typical healthy heart with a normally functioning aortic valve to one with an insufficient aortic valve, illustrating the anatomical and functional disparities that aortic annuloplasty aims to resolve. To address this gap, we developed a ring-like strain sensor (Figure ) fabricated from 100% strained PLLA film. The PLLA film stretched to 100% and was cut at a 45-degree angle relative to the strain direction identified by the highest absorption peak in THz-TDS. The determination of this optimal angle is discussed in greater detail in our previous work , where we explore the correlation between strain alignment and THz-TDS results. Two silver electrodes were then screen-printed onto each side of the precut film, and the necessary wiring was connected. Finally, the device was encapsulated with Kapton tape, which also facilitated shaping the structure into a ring. This novel sensor was tested in an in vitro system replicating left heart dynamics, which subjected it to pulsatile systolic/diastolic pressures of 92/51, 123/78, and 164/114 mmHg at a flow of 5.1 L/min (Figure ). These conditions simulate a realistic range of physiological pressures. The experimental setup included mounting the PLLA sensor onto a flexible structure mimicking the aortic root, see Figure . The aortic pressure over time is shown in Figure (top), and the peak-to-peak separation of the data presented in Figure (bottom) aligns well with these defined parameters. The sensor demonstrated a clear correlation between applied pressure and voltage output: at 92/51mmHg, it generated a stable, periodic signal with a range of approximately -0.5 V to 0.5 V. At 123/78 mmHg, the voltage output increased approximately to -0,7 V to 1 V, and at 164/114 mmHg, the highest tested pressure, the range expanded further to -1.1 V to 1.3 V. These results confirmed the sensor's ability to convert mechanical deformation into electrical signals. One notable observation was the slight delay in the measured response to the maximum pressure peak in all cases. We observed a delay in the measured output relative to the peak positions of the pulsatile pressures. A potential explanation for this phenomenon is the physiological response associated with the dicrotic notch and dicrotic wave. The dicrotic notch occurs as the aortic valve closes at the end of systole, creating a brief interruption in the pressure waveform. Following this, the dicrotic wave arises due to the elastic recoil of the aorta and arteries, which transiently increases pressure in the arterial system . Additionally, this delay may be influenced by the frequency response of the sensor itself. The pressure increase during systole primarily contains lower frequency components, whereas the dicrotic notch, with its more transient nature, encompasses higher frequency content and is more broadband. If the sensor's frequency response is less sensitive to higher frequencies, it may preferentially capture the smoother, lower-frequency components of the systolic pressure increase, thereby contributing to the observed delay. This highlights the importance of understanding both physiological and sensor-related dynamics when interpreting such measurements. These effects could explain the observed delay, as the maximum pressure is generated slightly after the initial pulse, reflecting the dynamic interplay between cardiac activity and arterial elasticity The current design focuses on monitoring pulsations, representing an essential step toward developing a comprehensive tool for the biomechanical assessment of annuloplasty rings. The goal is to refine the sensor to also measure expansion due to biomechanical forces during surgery and recovery. This capability would allow precise intraoperative adjustments, improving immediate surgical outcomes, while also enabling long-term postoperative monitoring to detect mechanical failure early. By providing real-time data on the performance of annuloplasty rings, this technology could address critical gaps in current monitoring methods. Our in vitro tests have demonstrated the feasibility of using a PLLA-based strain sensor for annuloplasty monitoring, laying the groundwork for further refinement. By addressing challenges such as noise and enhancing the sensor's sensitivity, we aim to advance this technology into a fully integrated system capable of transforming how annuloplasty procedures are performed and evaluated.