Conductive layer formed strain gauge and method of making same
Inventors
Majerus, Steve J A • Dunning, Jeremy • Bogie, Katherine M. • Potkay, Joseph A.
Assignees
Case Western Reserve University • US Department of Veterans Affairs
Publication Number
US-10694999-B2
Publication Date
2020-06-30
Expiration Date
2038-10-12
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Abstract
A sensor apparatus includes at least one substrate layer of an elastically deformable material, the substrate layer extending longitudinally between spaced apart ends thereof. A conductive layer is attached to and extends longitudinally between the spaced apart ends of the at least one substrate layer. The conductive layer includes an electrically conductive material adapted to form a strain gauge having an electrical resistance that varies based on deformation of the conductive layer in at least one direction.
Core Innovation
The invention provides a sensor apparatus comprising at least one substrate layer of an elastically deformable material extending longitudinally between spaced apart ends. A conductive layer is attached to and extends longitudinally between the ends of the substrate layer. The conductive layer includes an electrically conductive material adapted to form a strain gauge with electrical resistance that varies based on deformation of the conductive layer in at least one direction.
The sensor apparatus can include multiple substrate layers with the conductive layer sandwiched between at least two substrate layers, the materials can be biocompatible and elastically deformable such as polydimethylsiloxane (PDMS) with conductive particles embedded in the PDMS. The layers are fabricated with parallel strands extending in directions that allow the apparatus to have anisotropic compliance, enabling strain sensitivity along a predetermined direction while inhibiting deformation transverse to that direction.
The conductive layer and substrate structure can be fabricated using additive manufacturing depositing strands in various orientations and spacing to achieve desired elasticity, compliance, and strain sensitivity. The sensor apparatus may be mounted around a tubular structure, such as a vascular graft, to detect deformation caused by blood flow pulsation externally without contacting the bloodstream, thereby avoiding adverse biological effects associated with prior sensors.
Claims Coverage
The patent includes multiple independent claims covering the sensor apparatus structure and methods of making and using the sensor apparatus. Main inventive features span structural configurations, anisotropic compliance, material compositions, measurement systems, and methods of manufacture and application.
sensor apparatus with elastically deformable substrate and conductive strain gauge
A sensor apparatus with at least one elastically deformable substrate layer extending longitudinally between spaced ends and a conductive layer attached to and extending between the substrate ends. The conductive layer forms a piezoresistive strain gauge whose electrical resistance varies based on deformation in at least a longitudinal direction.
multi-layer sensor structure with anisotropic compliance
The substrate includes multiple elastically deformable layers, with the conductive layer sandwiched between at least two substrate layers. The substrate and conductive layers are arranged with parallel strands oriented parallel or transverse to a given direction to provide anisotropic compliance, enabling deformation along a given direction and inhibiting it transversely.
conductive layer configured as strain gauge with conductive strips and contacts
The conductive layer includes at least one conductive strip extending along a path between spaced ends with electrical contacts at strip ends, allowing electrical connection for resistance measurement.
sensor apparatus configured for radial strain sensing when wrapped around tubular structures
The sensor layers are arranged to circumscribe a central axis forming a cylindrical sensor body that measures radial expansion or contraction. The sensor apparatus can be attached circumferentially along a graft's annular sidewall.
method of sensing biological function using the sensor apparatus
Mounting the sensor apparatus to circumscribe a tubular structure such that the conductive layer deformation corresponds to radial expansion or contraction responsive to a biological function, where the tubular structure is a graft or biological tissue.
method of making sensor device by providing substrate and forming conductive strain gauge layer
Providing an elastically deformable substrate layer extending longitudinally between spaced ends and forming a conductive layer on the substrate surface extending longitudinally between the ends. The conductive layer forms a piezoresistive strain gauge with resistance varying based on deformation in at least a longitudinal direction.
method of forming multi-layer sensor structure with anisotropic compliance
Forming at least one other substrate layer over the conductive layer so that the conductive layer is sandwiched between at least two substrate layers. Each layer is formed by extruding substantially parallel strands oriented parallel or transverse to the given direction, with direction and spacing determining anisotropic compliance.
method of mounting sensor apparatus on biological tissue or vascular graft
Mounting the resulting sensor apparatus to an outer surface of biological tissue or around a cylindrical sidewall of an annular vascular graft. The substrate can also be the graft itself with the conductive layer disposed directly on its surface.
These inventive features provide a deformable sensor apparatus with anisotropic compliance and piezoresistive strain sensing capabilities, methods of forming layered structures with controlled strand orientation and spacing, and methods for mounting to biological tissues or grafts to enable monitoring biological function through strain measurement.
Stated Advantages
The sensor apparatus deforms commensurately with biological tissues or grafts enabling sensitive strain measurement without adversely affecting tissue function or blood flow.
Anisotropic compliance allows strain sensitivity in desired directions while inhibiting deformation transversely, improving measurement accuracy and mechanical matching with the substrate.
Additive manufacturing of strands with configurable orientations and spacing enables customized sensor geometry, size, and compliance for specific applications.
Electrical resistance changes correlate with biological flow and pressure providing real-time monitoring capabilities with potential wireless communication.
Mounting externally to grafts or tissues avoids direct contact with blood, reducing risks of hypercellular processes or graft failure.
Documented Applications
Monitoring graft function by mounting the sensor apparatus around vascular grafts to detect blood flow and graft wall motion.
Measuring deformation of biological tissue surfaces for sensing biological functions such as pressure and flow changes.
Integrating the sensor apparatus directly on graft surfaces by 3D printing conductive layers onto the graft.
Utilizing the sensor data to detect graft dysfunction such as occlusion or stenosis and generate alerts for early intervention.
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