Researchers Submit Patent Application, “Thermally Responsive Shape Memory Polymer Actuator, Prosthesis Incorporating Same, And Fabrication Method”, for Approval (USPTO 20210322646): Arizona State University

2021 NOV 09 (NewsRx) -- By a News Reporter-Staff News Editor at Insurance Daily News -- From Washington, D.C., NewsRx journalists report that a patent application by the inventors LaBelle, Jeffrey (Tempe, AZ, US); Lathers, Steven (Englewood, CO, US), filed on June 30, 2021, was made available online on October 21, 2021.

The patent’s assignee is Arizona State University (Scottsdale, Arizona, United States).

News editors obtained the following quote from the background information supplied by the inventors: “In the United States, about two million people have lost a limb, and about 185,000 people each year lose a limb, with hospital costs for amputations of approximately $8.3 billion each year. 54% of limb losses are attributable to vascular diseases, including diabetes and peripheral arterial disease; about 45% of limb losses are attributable to physical trauma; and fewer than 2% of limb losses are attributable to cancer, with a ratio of upper limb loss to lower limb loss of 1:4. Prosthetics can cost up to $50,000 per limb, and a significant number (possibly a majority) are not covered by insurance. Additionally, many prosthetics need to be replaced as the user grows, and health insurance frequently does not cover the cost of continual replacement and/or modification of prosthetics.

“For upper limb amputations, conventional functional prosthetics include categories of body-powered systems and electric/intelligent systems. Body-powered prosthetics typically use cables and harnesses strapped to the individual to mechanically maneuver the artificial limb with the use of an intact anatomical system. Body-powered systems are lightweight, inexpensive, and lack complexity; however, such systems lack feedback, are unable to provide high force output, and can be fatiguing to operate. Conventional electric prosthetic systems use high powered direct current and/or servo motors in conjunction with a feedback/control system that collects input from electrodes monitoring muscular (EMG) activity or neural (EEG) activity. Downsides of electric systems are that they are expensive, heavy, and noisy. Regarding the weight issue, for example, EMG control hands can weigh 32%-87% more than an average human hand, making EMG hands difficult and uncomfortable to wear since the weight of such hands is applied to soft tissue instead of the skeletal system.

“Conventional body and electric powered systems cannot provide actuated motion that mimics bulk skeletal muscle. This is due to linear output by motors associated with electric/intelligent systems, and linear output provided by body-powered systems that use rigid cables to transfer force and motion.

“This is in contrast to bulk skeletal muscle, which generates a non-linear output under contraction/active movements and passive movements.

“To overcome the issues associated with conventional actuators, academic research has developed many different types of actuators that include pneumatic or soft robotic actuators, shape memory alloys, large thermal expansion materials, combination mechanical and tissue engineered systems, thin films, and nanofibers.

“Pneumatic or soft robotic actuators use compressed air or fluid to transfer into specific chambers within an actuation system, where the chambers are independent of one another. This allows the system to fill specific chambers with fluid and creates a structure that deforms to grasp and/or move objects. The downside is that these systems are complex, require a source of compressed fluid, and can be heavy relative to their size.

“Shape memory alloys (SMA) and thermal expansion materials can generate high force per weight characteristics with heat by changing microstructure orientation/phase or by reversible, directional thermal expansion. A shape memory alloy is a metal alloy that “remembers” its original shape and that, when deformed, returns to its pre-deformed state when actuated (e.g., by application of electric current, heat, magnetic field, etc.).

“Both SMAs and thermal expansion materials require high temperatures (e.g., up to 120° C.) for actuation/displacement, wherein such temperatures can hinder actuation response time. Such materials also exhibit low strain recovery, wherein SMAs can typically achieve a maximum strain recovery of only eight percent. Additionally, thermal expansion materials require a load to be applied to hold such materials in a deformed position so such materials can recover a shape when heated.

“Additionally, mechanical/tissue engineered, thin films, nanofibers, or shape deposition manufactured actuators have been used to create actuators, but require one or more of living skeletal muscle cells, complex nanowire/fiber manufacturing and structure, or embedded electronic components. Actuators with living cells or nanofibers can generate high or physiological comparable strain rates, but have living cells that need nutrients and require complex manufacturing. Moreover, current shape deposition manufactured actuators require the use of embedded electronics during the printing process to create an actuator, but these actuators still provide a linear output response.

“In consequence of the foregoing considerations, the art continues to seek improved actuators and prosthetic systems incorporating same.”

As a supplement to the background information on this patent application, NewsRx correspondents also obtained the inventors’ summary information for this patent application: “Disclosed herein are novel thermally responsive shape memory polymer (SMP) actuators, and prosthetic devices incorporating multiple thermally responsive SMP actuators, as well as methods for their fabrication and use. SMP actuators may be used to provide movement and force to joints within a prosthetic device.

“In one aspect of the disclosure, a thermally responsive shape memory actuator comprises a body including a first end, a second end, and at least one non-linear segment disposed between the first end and the second end. The body comprises a plurality of fused shape memory polymer elements comprising a plurality of dots, rods, or layers.

“In certain embodiments, the non-linear segment comprises a substantially flat zig-zag shape.

“In certain embodiments, the body comprises a first substantially straight segment proximate to the first end and a second substantially straight segment proximate to the second end, with the at least one non-linear segment being arranged between the first substantially straight segment and the second substantially straight segment.

“In certain embodiments, the plurality of fused shape memory polymer elements comprises a linear aliphatic thermoplastic polyester and at least one other polymer. In certain embodiments, the at least one other polymer comprises a melting temperature that exceeds a melting temperature of the linear aliphatic thermoplastic polyester.

“In certain embodiments, the linear aliphatic thermoplastic polyester comprises at least one of a poly(L-lactide)-based polymer or a poly(e-caprolactone)-based polymer. In certain embodiments, the plurality of fused shape memory polymer elements comprises poly(L-lactide) and thermoplastic polyurethane.

“In certain embodiments, the plurality of fused shape memory polymer elements comprises poly(e-caprolactone) and at least one other polymer. In certain embodiments, the at least one other polymer comprises polyhedral oligosilsesquioxane.

“In certain embodiments, the body is pre-strained by heating and elongation in a range of 140% to 170% of an initial length of the body.

“In another aspect of the disclosure, a prosthetic device comprises a plurality of thermally responsive shape memory actuators, a movable joint connected between first and second structural members, and multiple anchors associated with the structural members. Each thermally responsive shape memory actuator comprises a body including a non-linear segment disposed between two body ends, and the body comprises a shape memory polymer material. The movable joint is configured to permit pivotal movement between the first structural member and the second structural member. A first anchor element and a second anchor element are associated with the first structural member, and a third anchor element and a fourth anchor element are associated with the second structural member. A first group of thermally responsive shape memory actuators is coupled between the first anchor element and the third anchor element, and is configured to promote pivotal movement between the first structural member and the second structural member in a first direction. Additionally, a second group of thermally responsive shape memory actuators is coupled between the second anchor element and the fourth anchor element, and is configured to promote pivotal movement between the first structural member and the second structural member in a second direction that differs from the first direction.

“In certain embodiments, the body of each thermally responsive shape memory actuator of the plurality of thermally responsive shape memory actuators is produced by a method including at least one additive manufacturing step. In certain embodiments, the body of each thermally responsive shape memory actuator of the plurality of thermally responsive shape memory actuators comprises a plurality of fused shape memory polymer elements comprising a plurality of dots, rods, or layers.

“In certain embodiments, for each thermally responsive shape memory actuator of the plurality of thermally responsive shape memory actuators, the body includes a first end, a second end, and at least one non-linear segment disposed between the first end and the second end. In certain embodiments, the non-linear segment comprises a substantially flat zig-zag shape.

“In certain embodiments, for each thermally responsive shape memory actuator of the plurality of thermally responsive shape memory actuators, the body comprises a first substantially straight segment proximate to the first end and a second substantially straight segment proximate to the second end, with the at least one non-linear segment being arranged between the first substantially straight segment and the second substantially straight segment.

“In certain embodiments, for each thermally responsive shape memory actuator of the plurality of thermally responsive shape memory actuators, the shape memory polymer material of the body comprises a linear aliphatic thermoplastic polyester and at least one other polymer. In certain embodiments, the at least one other polymer comprises a melting temperature that exceeds a melting temperature of the linear aliphatic thermoplastic polyester.

“In certain embodiments, the linear aliphatic thermoplastic polyester comprises at least one of a poly(L-lactide)-based polymer or a poly(e-caprolactone)-based polymer.

“In certain embodiments, the shape memory polymer material of the body comprises poly(L-lactide) and thermoplastic polyurethane.

“In certain embodiments, the shape memory polymer material of the body comprises poly(e-caprolactone) and at least one other polymer. In certain embodiments, the at least one other polymer comprises polyhedral oligosilsesquioxane.

“In certain embodiments, the body of each thermally responsive shape memory actuator of the plurality of thermally responsive shape memory actuators is pre-strained by heating and elongation in a range of 140% to 170% of an initial length of the body.

“In another aspect of the disclosure, a method of fabricating a thermally responsive shape memory actuator, the method comprising: forming a body by additive manufacturing, the body comprising a shape memory polymer material, a first end, a second end, and at least one non-linear segment disposed between the first end and the second end; following formation of the body, heating the body into a glass transition temperature range of the shape memory polymer material; applying tension to the body while the body is at an elevated temperature due to said heating of the body, wherein the tension is sufficient to elongate the body by at least partial straightening of the at least one non-linear segment; and cooling the body.

“In certain embodiments, the additive manufacturing comprises fused filament fabrication.

“In certain embodiments, the additive manufacturing comprises stereolithography, selective laser sintering, or selective laser melting.

“In certain embodiments, the body comprises a plurality of fused shape memory polymer elements comprising a plurality of dots, rods, or layers.

“In certain embodiments, the tension is sufficient to elongate the body by 40% to 70% relative to an initial length of the body, to yield an aggregate (elongated) length of 140% to 170% of the initial length.

“In certain embodiments, the elevated temperature is within the glass transition temperature range of the shape memory polymer material. In certain embodiments, the elevated temperature is within about 10% of the glass transition temperature range of the shape memory polymer when the glass transition temperature range is expressed in Kelvin.

“In another aspect, any one or more aspects or features described herein may be combined with any one or more other aspects or features for additional advantage.”

The claims supplied by the inventors are:

“1. A prosthetic device comprising: a plurality of thermally responsive shape memory actuators, wherein each thermally responsive shape memory actuator of the plurality of thermally responsive shape memory actuators comprises a body including a non-linear segment disposed between two body ends, and the body comprises a shape memory polymer material; a first structural member, a second structural member, and a movable joint connected between the first structural member and the second structural member, wherein the movable joint is configured to permit pivotal movement between the first structural member and the second structural member; a first anchor element and a second anchor element associated with the first structural member; a third anchor element and a fourth anchor element associated with the second structural member; wherein at least one first thermally responsive shape memory actuator of the plurality of thermally responsive shape memory actuators is coupled between the first anchor element and the third anchor element, and is configured to promote pivotal movement between the first structural member and the second structural member in a first direction; and wherein at least one second thermally responsive shape memory actuator of the plurality of thermally responsive shape memory actuators is coupled between the second anchor element and the fourth anchor element, and is configured to promote pivotal movement between the first structural member and the second structural member in a second direction that differs from the first direction.

“2. The prosthetic device of claim 1, wherein the body of each thermally responsive shape memory actuator of the plurality of thermally responsive shape memory actuators comprises a plurality of fused shape memory polymer elements comprising a plurality of dots, rods, or layers.

“3. The prosthetic device of claim 1, wherein the body of each thermally responsive shape memory actuator of the plurality of thermally responsive shape memory actuators is produced by a fused filament fabrication process.

“4. The prosthetic device of claim 1, wherein for each thermally responsive shape memory actuator of the plurality of thermally responsive shape memory actuators, the body includes a first end, a second end, and at least one non-linear segment disposed between the first end and the second end.

“5. The prosthetic device of claim 4, wherein for each thermally responsive shape memory actuator of the plurality of thermally responsive shape memory actuators, the body comprises a first substantially straight segment proximate to the first end and a second substantially straight segment proximate to the second end, with the at least one non-linear segment being arranged between the first substantially straight segment and the second substantially straight segment.

“6. The prosthetic device of claim 1, wherein for each thermally responsive shape memory actuator of the plurality of thermally responsive shape memory actuators, the shape memory polymer material of the body comprises a linear aliphatic thermoplastic polyester and at least one other polymer.

“7. The prosthetic device of claim 6, wherein the linear aliphatic thermoplastic polyester comprises at least one of a poly(L-lactide)-based polymer or a poly(e-caprolactone)-based polymer.

“8. The prosthetic device of claim 6, wherein the shape memory polymer material of the body comprises (i) poly(L-lactide) or poly(e-caprolactone) and (ii) at least one other polymer.

“9. The prosthetic device of claim 1, wherein the body of each thermally responsive shape memory actuator of the plurality of thermally responsive shape memory actuators is pre-strained by heating and elongation in a range of 140% to 170% of an initial length of the body.

“10. The prosthetic device of claim 1, wherein: the at least one first thermally responsive shape memory actuator comprises a plurality of first thermally responsive shape memory actuators; and the at least one second thermally responsive shape memory actuator comprises a plurality of second thermally responsive shape memory actuators.

“11. The prosthetic device of claim 1, wherein: at least one first flexible tube or jacket is provided around the at least one first thermally responsive shape memory actuator; and at least one first flexible tube or jacket is provided around the at least one first thermally responsive shape memory actuator.

“12. The prosthetic device of claim 1, further comprising an outer tube or covering element containing the plurality of thermally responsive shape memory actuators, the first and second structural members, the movable joint, and the first through fourth anchor elements.

“13. The prosthetic device of claim 1, further comprising a pump and a thermal source, wherein the prosthetic device is configured to circulate warm fluid through one or more of the at least one first flexible tube or jacket and the at least one second flexible tube or jacket.”

For additional information on this patent application, see: LaBelle, Jeffrey; Lathers, Steven. Thermally Responsive Shape Memory Polymer Actuator, Prosthesis Incorporating Same, And Fabrication Method. Filed June 30, 2021 and posted October 21, 2021. Patent URL: https://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.html&r=1&f=G&l=50&s1=%2220210322646%22.PGNR.&OS=DN/20210322646&RS=DN/20210322646

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