Design, inverted vat photopolymerization 3D printing, and initial characterization of a miniature force sensor for localized in vivo tissue measurements

Abstract

Background Tissue healthiness could be assessed by evaluating its viscoelastic properties through localized contact reaction force measurements to obtain quantitative time history information. To evaluate these properties for hard to reach and confined areas of the human body, miniature force sensors with size constraints and appropriate load capabilities are needed. This research article reports on the design, fabrication, integration, characterization, and in vivo experimentation of a uniaxial miniature force sensor on a human forearm. Methods The strain gauge based sensor components were designed to meet dimensional constraints (diameter ≤3.5mm), safety factor (≥3) and performance specifications (maximum applied load, resolution, sensitivity, and accuracy). The sensing element was fabricated using traditional machining. Inverted vat photopolymerization technology was used to prototype complex components on a Form3 printer; micro-component orientation for fabrication challenges were overcome through experimentation. The sensor performance was characterized using dead weights and a LabVIEW based custom developed data acquisition system. The operational performance was evaluated by in vivo measurements on a human forearm; the relaxation data were used to calculate the Voigt model viscoelastic coefficient. Results The three dimensional (3D) printed components exhibited good dimensional accuracy (maximum deviation of 183μm). The assembled sensor exhibited linear behavior (regression coefficient of R2=0.999) and met desired performance specifications of 3.4 safety factor, 1.2N load capacity, 18mN resolution, and 3.13% accuracy. The in vivo experimentally obtained relaxation data were analyzed using the Voigt model yielding a viscoelastic coefficient τ=12.38sec and a curve-fit regression coefficient of R2=0.992. Conclusions This research presented the successful design, use of 3D printing for component fabrication, integration, characterization, and analysis of initial in vivo collected measurements with excellent performance for a miniature force sensor for the assessment of tissue viscoelastic properties. Through this research certain limitations were identified, however the initial sensor performance was promising and encouraging to continue the work to improve the sensor. This micro-force sensor could be used to obtain tissue quantitative data to assess tissue healthiness for medical care over extended time periods.

Development of a 3D Printed Structural Electronics Force Sensor

“…∆𝑅 𝑐 𝑅 0 ⁄ = 𝑎 + 𝑏𝐻 + 𝑐𝑇 + 𝑑𝐻 2 + 𝑒𝑇 2 + 𝑓𝐻𝑇 + 𝑔𝐻 3 + ℎ𝑇 3 + 𝑖𝐻 2 𝑇 + 𝑗𝐻𝑇 2 11 Table 4 presents the values of the coefficient in Eq.11. Within the working temperature range (10°C-25°C and 30%-90%), the accuracy of the temperature compensation (RMSE) is ±0.001 (𝑅 2 =0.998), which is comparable to the characteristics of other force sensors [37], [38].…”

Design, Prototyping, and Characterization of a Micro-Force Sensor Intended for Tissue Assessment in Confined Spaces

“…The complex features of the sensor head and base components were fabricated using additive manufacturing [17]. The Formlabs grey resin material properties were used for the structural analysis (Formlabs Inc., Somerville, MA, US).…”

“…The sensor housing subsystem was prototyped using additive manufacturing technology (low force inverted vat photopolymerization). The external diameter of the prototype sensor housing or base used in this work is 3.3 mm [17].…”

“…Alekya et al investigated a diaphragm-based tissue sensor (3.5 × 3.5 The authors are with the Department of Mechanical and Aerospace Engineering at The University of Texas at Arlington, Arlington, TX 76019 × 0.5 mm, 0-250 mN range) [16] . Along with challenges in miniaturization, these sensors can not be used to evaluate tissue viscoelastic properties for confined space applications since loads in the range of 0.2 -1.2 N are required for effective characterization [9], [17], [18], [19], [20].…”

Medical 3D Printing Using Desktop Inverted Vat Photopolymerization: Background, Clinical Applications, and Challenges

“…The use of 3D printing technology can enable rapid customization of drill guides for individual patients and has been shown to improve accuracy and reduce the risk of mispositioning during surgery [77]. A miniature force sensor using desktop inverted VP 3D printing was developed which can be inserted into living tissue without causing significant damage, unlike current methods for measuring forces in living tissue that are often invasive and can cause tissue damage [109][110][111]. The authors also noted that the use of 3D printing technology can enable rapid and low-cost production of the force sensor, which could make it more accessible for researchers and clinicians.…”