Novel elastic gel pad

Abstract

A method of making a thermoplastic gel prosthetic pad for use with a prosthetic assembly that acts as an interface between a stump of an amputee and a socket assembly. A prosthetic pad includes an open proximal end, a closed distal end, and a sidewall including an inner layer of a molded thermoplastic gel. A thermoplastic gel is molded on a mandrel that has been blasted at 100 psi using # 36 sand grains and optionally # 320 sand grains in order to form dimples and reduce the coefficient of static friction.

Description

[0001] Cross - Reference to Related Applications

[0002] This application is a partial continuation of application Ser. No. 17 / 742,721, filed on May 12, 2022, entitled "New Silicone Liner", which is a partial continuation of application Ser. No. 16 / 868,776, filed on May 7, 2020, entitled "New Silicone Liner", which claims the benefit of provisional application No. 62 / 844,253, filed on May 7, 2019, and provisional application No. 62 / 844,296, filed on May 7, 2019. The disclosures of these applications are incorporated herein by reference. Technical Field

[0003] The present invention relates to liners for use in prosthetic components. Specifically, the described invention relates to liners having a thermoplastic elastomer lining that is smooth to the touch through the use of surface modification of the mold used to produce the liner. Background Art

[0004] Since the 1980s, silicone liners have been used in the prosthetics industry, such as those described in U.S. Patent No. 4,923,474 to Klasson and Kristinsson. Other examples of these liners include U.S. Patent No. 5,728,168 to Laghi et al., U.S. Patent No. 5,830,237 to Kania, U.S. Patent No. 5,507,834 to Laghi et al., U.S. Patent No. 5,443,525 to Laghi et al., and U.S. Patent No. 5,728,168 to Laghi et al.

[0005] However, due to the high coefficient of static friction of silicone, silicone liners have historically been difficult to don and doff. As a result, they tend to adhere to the skin of the residual limb. This prevents relative movement at the skin / liner interface, so that when ground reaction forces during walking are transmitted through the silicone interface and skin to the bone, the local skin of the residual limb is subjected to significant shear forces. These resulting shear forces increase the likelihood of skin blistering, especially for patients with sensitive skin. Therefore, it is desirable to develop silicone liners with reduced frictional effects such that users can easily don and doff their prosthetic liners.

[0006] In addition, most amputees are amputated due to vascular reasons rather than trauma. This means that the amputation is due to poor circulation. Most amputees are also elderly. Therefore, most amputees have thinner, more fragile skin that is prone to injury and has reduced blood flow to the extremities, making their ability to heal sores and wounds lower. Some elderly amputees have ultimately had a re - amputation due to skin damage and infection of their residual limbs.

[0007] To address these issues, a method has been developed that includes an additive that exudes from the silicone matrix and serves as a lubricant between the liner and the skin. The problem with this solution is that the exudate can collect dirt on the inner surface of the liner, exacerbating skin damage. The exudate also requires more thorough cleaning and makes the liner slippery.

[0008] Similarly, it is known in the art to use thermoplastic elastomer gels instead of silicone for prosthetic liners, such as those described in Laghi et al., 11,179,252. Such thermoplastic elastomer gels typically comprise a styrene triblock copolymer mixed with a plasticizer, which forms a composite material with an outer fabric layer. One problem with gel liners is that some users may find them sticky, which can prevent relative movement at the interface between the skin and the liner.

[0009] The present invention utilizes a novel surface modification technique to create "micro-pits" in the silicone or elastomer gel used for a prosthetic liner during the molding of the prosthetic liner, which makes the liner easy to don and doff and skin-friendly. The method described herein is particularly effective for silicone liners because silicone has a low surface tension in its liquid state, which allows it to penetrate tiny pores and cracks and thus create micro-pits. The viscosity of silicone is also inversely proportional to temperature, which makes silicone more fluid when it is closer to the hot mold surface. Thus, silicone creates a faithful mirror image of the pitted mold surface. Although having different molding processes, elastomer gels commonly used for prosthetic liners have similar properties when using the method described herein.

[0010] Accordingly, an object of the present invention is to provide an improvement that overcomes the above deficiencies of the prior art devices and provides an improvement that makes an important contribution to the development of the field of liners.

[0011] Another object of the present invention is to provide a silicone liner having a more comfortable inner silicone lining.

[0012] Another object of the present invention is to provide a method of manufacturing a silicone liner having reduced frictional properties.

[0013] Another object of the present invention is to provide a liner having micro-pits.

[0014] Another object of the present invention is to describe a method of manufacturing a silicone liner by molding the liner using a sandblasted mold mandrel.

[0015] Another object of the present invention is to provide a method of manufacturing a thermoplastic elastomer gel liner having reduced frictional properties.

[0016] Some related objectives of the present invention have been outlined above. These objectives should be construed as merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be obtained by applying the disclosed invention in different ways or modifying the invention within the scope of this disclosure. Therefore, in addition to the scope of the present invention as defined by the claims in conjunction with the accompanying drawings, other objectives and a more complete understanding of the present invention can be obtained by referring to the summary of the invention and the detailed description of the preferred embodiments of the present invention. Summary of the Invention

[0017] The present invention generally relates to a liner for use in a prosthetic component, the liner having a thermoplastic elastomeric gel interior that includes micro-pits by sandblasting a mandrel with #36 grit at 100 psi. Using a sandblasted mold mandrel, a prosthetic liner with improved frictional properties can be manufactured. The liner of the present invention may optionally include a fabric cover bonded to the outer surface.

[0018] The more relevant and important features of the present invention have been outlined rather extensively above so as to provide a better understanding of the detailed description of the present invention that follows and, thus, a more complete appreciation of the contribution to the art. Additional features of the present invention will be described below, and these features form the subject matter of the claims of the present invention. Those of ordinary skill in the art should understand that the disclosed concepts and specific embodiments can be readily used as a basis for modifying or designing other structures for achieving the same purposes of the present invention. Those of ordinary skill in the art should also recognize that such equivalent constructions do not depart from the spirit and scope of the present invention as set forth in the appended claims. Brief Description of the Drawings

[0019] To fully understand the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

[0020] Figure 1 is a front view of an improved prosthetic liner.

[0021] Figure 2 is a cross-sectional view of a silicone or thermoplastic gel sheet formed using an un-sandblasted mandrel.

[0022] Figure 3 is a cross-sectional view of a silicone or thermoplastic gel sheet formed using a mandrel sandblasted with #36 grit at 100 psi.

[0023] Figure 4 is a cross-sectional view of a silicone or thermoplastic gel sheet formed using a mandrel sandblasted with 20 grit at 100 psi #3.

[0024] Figure 5 is a graph showing the effect of sandblasting on the pull force required to remove a silicone sheet from a steel substrate, thus showing the effect on the coefficient of static friction.

[0025] In several views of the drawings, like reference numerals refer to like components. DETAILED DESCRIPTION

[0026] The following description is the best mode currently contemplated for carrying out the invention. The description is not to be construed as limiting, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims.

[0027] The present invention relates to a liner 100 for a prosthetic device. As Figure 1 shown, the liner 100 for a prosthetic assembly includes an open upper end 12 for receiving a stump (not shown), a closed bottom end 14, and a sidewall 16 of a predetermined thickness. When worn on the stump, the liner is sealed. The preferred thickness of the sidewall 16 is from about 1.5 mm to 3.0 mm. Note that the thickness of the bottom end is greater than the thickness of the sidewall; the preferred thickness of the silicone at the bottom end 14 is from about 3.0 mm to 12.0 mm. The sidewall 16 has an inner layer 18 of the improved silicone described herein. The sidewall 16 can be a fabric or another layer of more durable and higher friction silicone.

[0028] Before molding the silicone, the mandrel is sandblasted with #36 grit at 100 psi. The particular grit and pressure used provide the beneficial properties of the present invention. Other grits and pressures do not produce the benefits of reduced friction retention and reduced opportunity for skin irritation. After sandblasting the mandrel, silicone is molded thereon, allowing the silicone to penetrate into the micro-pits formed by the sandblasting. As Figures 2 - 4 shown, the grit size used during the sandblasting process has a significant effect.

[0029] Figure 2 A silicone sheet 20 without sandblasting is depicted. As shown in cross-section 2-2, not sandblasting the mandrel results in a smooth outer surface 22, which retains the high friction properties of the silicone. On the other hand, Figure 3 and Figure 4 show a microscopic view of the outer surface 22 after sandblasting the mandrel. Figure 3 shows micro-pitting of the outer surface 22 with #36 grit at 100 psi, thereby creating micro-pits 24. Along line 3-3, the depth of the micro-pits is typically about 0.0195 mm. Figure 4 shows micro-pitting of the outer surface 22 with #320 grit at 100 psi. The sandblasting with #320 grit can be carried out alone or after the mandrel has already been sandblasted with #36 grit. Along line 4-4, the depth of the resulting micro-pits is typically about 0.0100 mm. The deeper micro-pits create a lower coefficient of static friction for the silicone because the surface area in contact with the outer surface 22 is smaller, as in the sheet in Figure 3 compared to Figure 4It can be seen when comparing the sheets therein. Sandblasting between #36 and #320 grit can also be performed.

[0030] Alternative methods for creating micro-pits 24 of different depths include, but are not limited to, modifying the mandrel surface by rolling, pressing a mold against a textured surface, chemical etching, laser engraving, computer numerical control (CNC) engraving, electro-erosion (i.e., electrical discharge machining), electro-deposition, laser micro-melting, shot peening, air peening, and pinwheel rotation. Similar methods equivalent to the methods included (i.e., methods for creating micro-pits in the outer surface of a silicone liner in a prosthetic liner) that are now known or will be discovered are intended to be included in the above list.

[0031] Three tests were conducted to demonstrate the beneficial characteristics of the present invention, and the results are shown in Figure 5 In the first test, the mold was sandblasted with #36 grit at 100 psi, and a force of 1.6 N was required in terms of tensile resistance, i.e., before tearing. In the second test, the mold was sandblasted with #320 grit. The result was that a force of 2.33 N was required in terms of tensile resistance. In the last test, the mold was not sandblasted at all and a force of 9.33 N was required. This test was conducted using a silicone strip that was 1 inch wide and 7 inches long, while applying a 100-gram weight on a smooth stainless steel.

[0032] The present invention can also be modified to improve the functionality of the thermoplastic elastomer gel liner. Using thermoplastic molding techniques (such as pressure molding or compression molding) in combination with the methods described herein, the inner layer 18 of the liner 100 can be made of a micro-pitted thermoplastic elastomer gel that includes a styrene triblock copolymer (such as those described in Chen's U.S. Patent No. 6,552,109), polyurethane, polybutene, or polypropylene. Different from silicone, the sidewalls 16 of the gel liner are generally thicker, and the thickness can be in the range of 3 to 12 mm, with a preferred thickness at the bottom end 14 of 3 to 15 mm.

[0033] The present disclosure includes what is contained in the appended claims as well as the foregoing description. Although the present invention has been described in its preferred form to a certain degree of particularity, it should be understood that the present disclosure of the preferred form has been by way of example only, and various changes can be made to the details of the construction and the combination and arrangement of the components without departing from the spirit and scope of the present invention.

[0034] The present invention has now been described.

Claims

1. A method of manufacturing a thermoplastic gel pad, the method comprising: modifying the mandrel surface using a method selected from the group consisting of: sandblasting, rolling, chemical etching, laser engraving, computer numerical control engraving, electrocorrosion, electrodeposition, laser micromelting, shot peening, peening, and pinwheel rotation; molding a styrene triblock copolymer gel on the mandrel; forming a fabric sidewall on the styrene triblock copolymer gel to produce a composite material, wherein the composite material further comprises an open upper end, a closed bottom end, and a fabric sidewall having a thickness, wherein the sidewall further comprises an inner layer of styrene triblock copolymer gel having a gel thickness, and wherein the styrene triblock copolymer gel has micropits with a depth of 0.0100 to 0.0195 millimeters.

2. The method of manufacturing a thermoplastic gel pad according to claim 1, wherein the thickness of the sidewall is 3 to 12 millimeters.

3. The method of manufacturing a thermoplastic gel pad according to claim 1, wherein the thickness of the styrene triblock copolymer gel at the bottom end is 3 to 15 millimeters.

4. The method of manufacturing a thermoplastic gel pad according to claim 1, the method further comprising a force with a tensile resistance of less than 2.4 N before fracture.

5. The method of manufacturing a thermoplastic gel pad according to claim 1, wherein the micropits are further formed by pressing the styrene triblock copolymer gel against a textured surface after molding but before cooling.

6. A method of manufacturing a thermoplastic gel pad, the method comprising: modifying the mandrel surface using a method selected from the group consisting of: sandblasting, rolling, chemical etching, laser engraving, computer numerical control engraving, electrocorrosion, electrodeposition, laser micromelting, shot peening, peening, and pinwheel rotation; molding an elastomer gel on the mandrel; forming a fabric sidewall on the styrene triblock copolymer gel to produce a composite material, wherein the composite material further comprises an open upper end, a closed bottom end, and a fabric sidewall having a thickness, wherein the sidewall further comprises an inner layer of elastomer gel having a gel thickness, and wherein the elastomer gel has micropits with a depth of 0.0100 to 0.0195 millimeters.

7. The method of manufacturing a thermoplastic gel pad according to claim 1, wherein the thickness of the sidewall is 3 to 12 millimeters.

8. The method of manufacturing a thermoplastic gel pad according to claim 1, wherein the gel thickness at the bottom end is 3 to 15 millimeters.

9. The method of manufacturing a thermoplastic gel pad according to claim 1, the method further comprising a force with a tensile resistance of less than 2.4 N before fracture.

10. The method of manufacturing a thermoplastic gel pad according to claim 1, wherein the micropits are further formed by pressing the elastomer gel against a textured surface after molding but before cooling.

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