“Thermally Responsive Shape Memory Polymer Actuator, Prosthesis Incorporating Same, And Fabrication Method” in Patent Application Approval Process (USPTO 20190160206)

2019 JUN 19 (NewsRx) -- By a News Reporter-Staff News Editor at Insurance Daily News -- A patent application by the inventors Lathers, Steven (Englewood, CO); LaBelle, Jeffrey (Tempe, AZ), filed on November 27, 2018, was made available online on May 30, 2019, according to news reporting originating from Washington, D.C., by NewsRx correspondents.

This patent application is assigned to Arizona State University (Scottsdale, Arizona, United States).

The following quote was obtained by the news editors 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 limp 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.degree. 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.”

In addition to the background information obtained for this patent application, NewsRx journalists 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(c-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(c-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, 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 molding step.

“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 subtractive manufacturing step.

“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(c-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(c-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 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 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 thermally responsive shape memory actuator comprising: 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; wherein the body comprises a plurality of fused shape memory polymer elements comprising a plurality of dots, rods, or layers.

“2. The thermally responsive shape memory actuator of claim 1, wherein the non-linear segment comprises a substantially flat zig-zag shape.

“3. The thermally responsive shape memory actuator of claim 1, wherein 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.

“4. The thermally responsive shape memory actuator of claim 1, wherein the plurality of fused shape memory polymer elements comprises a linear aliphatic thermoplastic polyester and at least one other polymer.

“5. The thermally responsive shape memory actuator of claim 4, wherein the at least one other polymer comprises a melting temperature that exceeds a melting temperature of the linear aliphatic thermoplastic polyester.

“6. The thermally responsive shape memory actuator of claim 4, wherein the linear aliphatic thermoplastic polyester comprises at least one of a poly(L-lactide)-based polymer or a poly(.epsilon.-caprolactone)-based polymer.

“7. The thermally responsive shape memory actuator of claim 4, wherein the plurality of fused shape memory polymer elements comprises (i) poly(L-lactide) or poly(.epsilon.-caprolactone) and (ii) at least one other polymer.

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

“9. 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 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; and wherein 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.

“10. The prosthetic device of claim 9, 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.

“11. The prosthetic device of claim 9, 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.

“12. The prosthetic device of claim 11, 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.

“13. The prosthetic device of claim 9, 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.

“14. The prosthetic device of claim 13, wherein the linear aliphatic thermoplastic polyester comprises at least one of a poly(L-lactide)-based polymer or a poly(.epsilon.-caprolactone)-based polymer.

“15. The prosthetic device of claim 13, wherein the shape memory polymer material of the body comprises (i) poly(L-lactide) or poly(.epsilon.-caprolactone) and (ii) at least one other polymer.

“16. The prosthetic device of claim 9, 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.

“17. 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.

“18. The method of claim 17, wherein the body comprises a plurality of fused shape memory polymer elements comprising a plurality of dots, rods, or layers.

“19. The method of claim 17, comprising at least one of the following features (i) or (ii): (i) the tension is sufficient to elongate the body in a range of from 40% to 70% relative to an initial length of the body, or (ii) the elevated temperature is within the glass transition temperature range of the shape memory polymer material.

“20. The method of claim 17, wherein 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.”

URL and more information on this patent application, see: Lathers, Steven; LaBelle, Jeffrey. Thermally Responsive Shape Memory Polymer Actuator, Prosthesis Incorporating Same, And Fabrication Method. Filed November 27, 2018 and posted May 30, 2019. Patent URL: http://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=%2220190160206%22.PGNR.&OS=DN/20190160206&RS=DN/20190160206

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