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.
In this work, we present the conceptual design of a 3.5mm outside diameter cable-driven hyper-redundant robotic manipulator with an attached micro-force sensor at the tip for application in transurethral palpation of any targeted area of the bladder interior wall tissue. The stain-gauge based micro-force sensor is designed using finite element analysis (safety factor > 3.5 and load capacity of 0.8N) and subsequently prototyped using additive manufacturing. Sensor components were prototyped using additive and traditional manufacturing, assembled and characterized using a data acquisition environment. The performance of the finite element and prototyped sensor was almost identical. The characterized sensor was used to evaluate tissue properties. The concept of a hyper-redundant 10-joint 6-DOF manipulator comprising of a 5-DOF rigid and a 5-DOF continuum segment is presented along with the forward and inverse kinematics analyses. The inverse kinematics is performed using a Jacobian based formulation to limit the possibilities of singularities. Studies employing the proposed inverse kinematics analysis demonstrated the ability of the manipulator to engage with any area in the bladder and especially the difficult to reach trigone area while attaining a normal pose at the point of contact. A normal pose is required for properly interrogating the tissue with the uniaxial force sensor. The proposed manipulator and force sensor system as presented suggest a probable solution for quantitatively evaluating localized biomechanical properties of the bladder interior wall tissue as a means towards improving treatment and providing better patient care. An initial limited functionality prototype demonstrates capabilities of the proposed concept and provides confidence for further research to fully realize the proposed concept.
We present the conceptual design and limited functionality prototype and characterization of a system for application in transurethral palpation of any targeted area of the bladder interior wall tissue consisting of a robotic manipulator and a micro-force sensor attached at its tip all less than 3.5mm in diameter. A hyper-redundant 10-joint 6-DOF manipulator (5-DOF rigid and 5-joint continuum segments) is presented along with the forward and inverse kinematics analyses based on a Jacobian formulation to prevent configuration singularities. Simulated motion studies demonstrate the ability of the proposed manipulator to attain a desired pose (normal to the tissue) with any area in the bladder including the difficult to reach trigone area. A strain gauge-based micro-force sensor is designed using finite element analysis (safety factor >3), prototyped using additive manufacturing, and characterized. The characterized sensor was used to acquire in vivo measurements to evaluate human palm tissue viscoelastic properties. A single module of the continuum segment is designed and prototyped using additive manufacturing, and used to characterize its tension-bend angle behavior. Finite element analysis is used to improve structurally weak regions of the vertebra. A 3-joint 4-vertebrae prototype was successfully actuated to reach a bend state using tendons. The developed robot and sensor prototypes demonstrate capabilities of the proposed concept which could be a possible solution to quantitatively evaluate localized biomechanical properties of the bladder tissue to improve treatment and provide better patient care.
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