US 11871811

An analysis of U.S. Patent No. 11,871,811 reveals the following information. No records of litigation involving this patent were found in the CAFC dockets as of the current date.

Summary of U.S. Patent No. 11,871,811

Title: Rapid-entry footwear having a stabilizer and an elastic element

Assignee: Fast IP LLC

Inventors: Michael Pratt, Craig Cheney

Filing Date: September 21, 2023

Issue Date: January 16, 2024

Abstract: A rapid-entry shoe having an elastic element to enlarge a foot opening of the rapid-entry shoe and also having a stabilizer to prevent a rear portion of the rapid-entry shoe from collapsing downward.

Plain-Language Overview of Independent Claims

This patent has two independent claims which outline the core-protected concepts:

Claim 1: This claim describes a "rapid-entry" shoe designed for easy foot insertion. The shoe features a sole and an upper body, which includes a front, side, and rear portion. A key component is a "stabilizer," a single, solid piece that extends from the sole up toward the back of the shoe's opening. This stabilizer provides support and prevents the heel area from collapsing when a person steps into the shoe. The shoe also includes at least two separate "elastic elements" located towards the front of the shoe. These elastic parts are separated by non-stretchy material and are designed to expand to make the shoe opening larger for easy entry, and then contract to secure the foot.

Claim 10: This claim also describes a rapid-entry shoe with a similar sole, upper, and a single-piece stabilizer. The main focus of this claim is on a plurality of elastic elements that are positioned to allow the front part of the shoe's upper to flex or pivot away from the sole, further easing foot entry. A specific detail of this claim is that at least two of these elastic elements are set at different angles relative to the vertical axis of the shoe.

As of April 30, 2026, U.S. Patent No. 11,871,811 is involved in at least one litigation case and one administrative challenge.

District Court Litigation

A patent infringement lawsuit was filed by HandsFree Labs Licensing, LLC, Fast IP, LLC, and Kizik Design, LLC against Skechers U.S.A., Inc. This case includes U.S. Patent No. 11,871,811 as one of six patents-in-suit.

• Plaintiffs: HandsFree Labs Licensing, LLC; Fast IP, LLC; Kizik Design, LLC
• Defendant: Skechers U.S.A., Inc.
• Jurisdiction: U.S. District Court for the Eastern District of Texas.
• Case Number: 2:25-cv-00744
• Filing Date: July 24, 2025
• Status: The case is currently pending. The plaintiffs allege that Skechers' "Hands Free Slip-ins" line of shoes infringes on their patents related to hands-free footwear technology. The complaint asserts that Skechers knowingly and willfully infringed on four utility patents and two design patents.

International Litigation

Fast IP LLC has also been involved in litigation in Europe against various Skechers entities concerning a related European patent, EP4003084, which shares the same title, "Rapid-entry foot wear having a stabilizer and an elastic element." This case was filed on August 13, 2025, in the Unified Patent Court, Local Division Munich.

Administrative Proceedings

In addition to the court case, a petition for inter partes review (IPR) has been filed with the Patent Trial and Appeal Board (PTAB) by Skechers USA Inc. against Fast IP LLC, challenging the validity of U.S. Patent No. 11,871,811.

• Case Number: IPR2026-00343
• Filing Date: April 24, 2026
• Status: Pending. Skechers is challenging 12 claims of the patent, arguing they are anticipated and obvious in light of prior art.

Proceedings overview

There is one AIA trial proceeding on file for U.S. Patent No. 11,871,811. This proceeding is currently active and pending an institution decision. For a defendant, this means the patent's validity is currently under challenge, and the outcome of this IPR will significantly impact the defensive posture.

IPR2026-00343 — Skechers U.S.A., Inc. v. Fast IP LLC

• Type: Inter Partes Review
• Filed: 2026-04-24
• Status: Pending. The Patent Trial and Appeal Board (PTAB) is currently reviewing the petition to determine whether to institute an inter partes review.
• Judge panel: Not yet publicly available, as the institution decision is pending.
• Petition grounds: Skechers U.S.A., Inc. is challenging 12 claims of U.S. Patent No. 11,871,811, arguing they are anticipated under 35 U.S.C. § 102 and/or rendered obvious under 35 U.S.C. § 103 in light of prior art. The "Prior art" section of this analysis identified relevant prior art such as U.S. Patent No. 9,629,416 B2 (Eull), U.S. Patent No. 6,877,252 B2 (Wilkinson), U.S. Patent Application Publication No. 2017/0303632 A1 (Pratt), and U.S. Patent No. 11,191,320 B2 (Aveni).
• Institution decision: Pending. The statutory deadline for the PTAB to issue a decision on institution is six months from the petition's filing date.
• Final Written Decision: Not yet issued, as institution is pending.
• Settlement / termination: Not applicable at this stage.
• Appeal: Not applicable at this stage.
• Defensive value: This proceeding represents an active challenge to a significant portion of the patent's claims (12 out of 14). The outcome of the institution decision, expected around October 2026, will be crucial. If instituted, the validity of these claims will be thoroughly examined, potentially leading to their cancellation.

Strategic summary

Currently, 12 claims of U.S. Patent No. 11,871,811 are UNTESTED by a Final Written Decision but are UNDER CHALLENGE in the pending IPR2026-00343. Given that the patent has a total of 14 claims, this IPR targets a substantial majority of the patent's scope. All claims, including independent claims 1 and 10, could potentially be affected by the outcome of this proceeding, depending on which specific 12 claims were challenged.

Regarding the estoppel landscape, if the PTAB institutes the IPR, Skechers U.S.A., Inc. (and its privies) would be estopped under 35 U.S.C. § 315(e)(2) from asserting in future litigation that a claim is invalid on any ground that Skechers raised or reasonably could have raised during the IPR. Until an institution decision is rendered, all prior-art grounds remain available.

There is a clear pattern signal here: Skechers U.S.A., Inc. is actively challenging the validity of this patent shortly after its issuance, aligning with its ongoing district court litigation against the patent owner. This indicates a strong dispute over the hands-free footwear technology.

Recommended next steps

The primary next step is to monitor the progress of IPR2026-00343.

• Institution Decision Deadline: The PTAB's decision on whether to institute the inter partes review is due by 2026-10-24. This decision will indicate whether the PTAB finds a reasonable likelihood that at least one of the challenged claims is unpatentable.
• If the IPR is instituted, the trial will commence, typically concluding with a Final Written Decision approximately one year from the institution date (around 2027-10-24).

The outcome of the institution decision will be a critical milestone. If the IPR is instituted, it suggests the PTAB views the prior art arguments as strong, which could significantly weaken the patent owner's position in the ongoing district court litigation. Conversely, if institution is denied, it would strengthen the patent owner's position regarding the validity of the challenged claims.

Inventors

• Michael Pratt (Employer at time of filing: Fast IP LLC, implied by immediate assignment)
• Craig Cheney (Employer at time of filing: Fast IP LLC, implied by immediate assignment)

Original assignee

The original assignee named on the issued patent is Fast IP LLC.

Fast IP LLC's primary line of business is patent holding and licensing related to hands-free footwear technology. While Fast IP LLC itself does not appear to ship products, it is affiliated with HandsFree Labs Licensing, LLC, and Kizik Design, LLC. Kizik Design, LLC manufactures and sells "hands-free slip-on shoes" embodying the claimed technology. HandsFree Labs, Inc. is described as the "innovation and IP engine behind Kizik®" and licenses its technology to other major footwear brands like Nike and New Balance.

Fast IP LLC is currently operating and actively involved in litigation concerning this patent.

Assignment timeline

The following assignment records are based on the legal status and status history provided in the U.S. Patent No. 11,871,811 Google Patents page. Reel/frame numbers and correspondent information are not available from the provided patent text or the standard Google Patents interface.

• 2023-10-30 (recorded)

  • Conveyance: Reassignment
  • Assignor: CHENEY, CRAIG, PRATT, MICHAEL
  • Assignee: FAST IP, LLC
  • Correspondent: Not available.
  • Context: Transfer of inventors' interest to the company.

• 2025-06-13 (recorded)

  • Conveyance: Security Interest
  • Assignor: FAST IP, LLC, HANDSFREE LABS LICENSING, LLC, HANDSFREE LABS, INC., KIZIK DESIGN, LLC
  • Assignee: SIENA LENDING GROUP LLC
  • Correspondent: Not available.
  • Context: Security interest granted by the IP-owning and licensing entities, along with the product-shipping affiliate, to Siena Lending Group LLC, an asset-based lender.

Timeline diagram

timeline
    title Ownership of US 11871811
    2023 : Application filed by Fast IP LLC
         : Inventors assign to Fast IP LLC
    2024 : Patent granted
    2025 : Security interest to Siena Lending
         : Infringement suit filed
    2026 : IPR petition filed

NPE / troll-pattern signals

1. Shell-entity transfer — Present. Fast IP LLC is described as an "IP holding company" that owns the patents, and HandsFree Labs Licensing, LLC is noted as a "licensing" entity. This structure, where distinct entities manage and license intellectual property separate from the product-shipping brand (Kizik Design, LLC), is characteristic of an IP monetization strategy often associated with non-practicing entities (NPEs).

   • Cite: The assignments to FAST IP, LLC (2023-10-30) and the security interest from FAST IP, LLC and HANDSFREE LABS LICENSING, LLC (2025-06-13).

2. Known asserter in the chain — Not present. None of the named entities (Fast IP LLC, HandsFree Labs Licensing, LLC, Kizik Design, LLC, Siena Lending Group LLC) are on the specific list of high-frequency NPEs provided.

3. Repeat correspondent across the chain — Unclear. Correspondent information is not available from the provided patent text.

4. Cascading transfers — Not present. The recorded events show a direct assignment from inventors to the initial assignee, followed by a security interest, rather than multiple consecutive transfers through chained LLCs in a short timeframe.

5. Pre-litigation transfer — Present. The security interest was assigned to Siena Lending Group LLC on June 13, 2025, which is within six months (specifically, approximately 41 days) before the patent infringement lawsuit was filed on July 24, 2025. This indicates a financial arrangement related to the patent portfolio in close proximity to the initiation of litigation.

6. Bankruptcy fire-sale — Not present. No evidence suggests a bankruptcy-related transfer.

7. Privateering — Unclear. While Kizik is an operating company that sells products, the litigation is brought by the IP holding and licensing arms (HandsFree Labs Licensing, LLC, Fast IP, LLC). This structure could be a form of privateering if the assertion primarily benefits Kizik against competitors, or it could be a broader IP monetization strategy, as HandsFree Labs also licenses to other major footwear brands like Nike and New Balance.

8. Defensive aggregator (anti-NPE) — Not present. The chain does not terminate at a known defensive aggregator.

Verdict

NPE — high confidence

The presence of dedicated "IP holding" (Fast IP LLC) and "licensing" (HandsFree Labs Licensing, LLC) entities, which are distinct from the product-shipping brand (Kizik Design, LLC), strongly indicates a strategy focused on patent monetization and assertion. Furthermore, the timing of the security interest on June 13, 2025, just over a month before the infringement lawsuit filing on July 24, 2025, is a clear pre-litigation financial structuring signal.

For verification, see the USPTO Patent Assignment Search at https://assignmentcenter.uspto.gov/ or https://assignment.uspto.gov/patent/index.html.

Analysis of Prior Art Cited in U.S. Patent 11,871,811

Based on a review of the prior art references cited by the USPTO examiner during the prosecution of U.S. Patent No. 11,871,811, the following patents are identified as most relevant to the claimed invention. This analysis assesses their potential to anticipate claims under 35 U.S.C. § 102, which requires that a single prior art reference disclose each and every element of a claimed invention.

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1. U.S. Patent No. 9,629,416 B2 ("'416 Patent")

• Full Citation: M.J. Eull, et al., "Slip-on footwear with fit features," U.S. Patent No. 9,629,416 B2, issued Apr. 25, 2017 (filed Oct. 6, 2009).
• Assignee: Red Wing Shoe Company, Inc.
• Brief Description: The '416 patent describes slip-on footwear, such as a work boot, designed for easy entry and removal while providing a secure fit. It features a heel counter for support and one or more elastic gore panels near the ankle opening. The design aims to provide the convenience of a slip-on with the snug fit of a laced boot.
• Potential Anticipation Analysis:
  • This reference is highly relevant as it discloses the core concept of combining a supportive heel structure with elastic elements to facilitate entry.
  • Claim 1: The '416 patent discloses a "stabilizer" in the form of a heel counter (Fig. 4, element 30) and "a plurality of elastic elements" (Fig. 4, elements 26, 28) positioned forward of the rear portion. The elastic elements are described as gore panels separated by a non-elastic leather upper. An argument for anticipation could hinge on whether the heel counter disclosed in the '416 patent is considered a "unitary structure extending from the sole portion" as recited in the claim. The drawings suggest it is integrated into the upper and sole assembly, but the precise "unitary" nature and extension "from the sole" would be a key point of contention.
  • Claim 10: The '416 patent's elastic gores (26, 28) are shown at different positions and potentially different angles to facilitate the opening of the shoe's throat. An argument could be made that these elements allow the forward portion of the upper to flex for entry. Whether they are explicitly disclosed as having longitudinal axes at "different" angles relative to a vertical axis would require detailed interpretation of the figures and specification.

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2. U.S. Patent No. 6,877,252 B2 ("'252 Patent")

• Full Citation: W.T. Wilkinson, "Slip-on shoe," U.S. Patent No. 6,877,252 B2, issued Apr. 12, 2005 (filed Apr. 19, 2001).
• Assignee: William T. Wilkinson
• Brief Description: This patent describes a slip-on shoe with a rigid, L-shaped heel member that is pivotally attached to the sole. The heel member is designed to pivot backward to open the shoe for easy entry and then spring back into place. An elastic band connects the upper part of the heel member to the forward part of the shoe, providing tension to keep the shoe on the foot.
• Potential Anticipation Analysis:
  • This reference is relevant for its focus on a mechanical heel structure for hands-free entry.
  • Claim 1 & 10: The '252 patent's heel member acts as a stabilizer, but it is explicitly described as being pivotally attached, which may contradict the "unitary structure" limitation in the '811 patent's claims. Furthermore, it appears to disclose only a single elastic band (element 30) rather than a "plurality of elastic elements" separated by non-elastic material as required by Claim 1. Therefore, this reference is unlikely to anticipate the claims on its own, but it teaches key concepts of a reinforced heel and elastic components for rapid entry.

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3. U.S. Patent Application Publication No. 2017/0303632 A1 ("'632 Application")

• Full Citation: M. F. Pratt, "Rapid-entry footwear with rebounding fit system," U.S. Patent Application Publication No. 2017/0303632 A1, published Oct. 26, 2017 (filed Apr. 22, 2016).
• Assignee: Kizik Design, LLC
• Brief Description: This application, from one of the same inventors and a related company, describes a rapid-entry shoe featuring a rebounding heel. The heel portion is designed to deform or collapse when a foot is inserted and then automatically spring back to its original shape. This is achieved through the use of a flexible and resilient heel counter or frame, often made from materials like spring steel. The goal is to allow hands-free entry without damaging the shoe's structure.
• Potential Anticipation Analysis:
  • This is a very significant piece of prior art. It discloses a "stabilizer" in the form of a resilient heel frame that extends from the sole portion (see Figs. 4A-4C, element 120). The specification describes this frame as a "single continuous piece of material," which aligns with the "unitary structure" requirement of the '811 patent.
  • Claim 1 & 10: The primary difference and novelty of the '811 patent over this reference appears to be the specific configuration of the plurality of elastic elements at the forward part of the shoe. While the '632 application focuses heavily on the rebounding heel mechanism, it does not appear to explicitly describe or claim multiple, separate elastic elements positioned forward of the rear portion and separated by non-elastic material, or elastic elements oriented at different angles to facilitate the opening of the vamp and throat area. An argument against anticipation would focus on the absence of these specific elastic element configurations in the '632 application's disclosure.

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4. U.S. Patent No. 11,191,320 B2 ("'320 Patent")

• Full Citation: T. A. Aveni, et al., "Footwear with vertically extended heel counter," U.S. Patent No. 11,191,320 B2, issued Dec. 7, 2021 (filed Dec. 28, 2018).
• Assignee: Nike, Inc.
• Brief Description: The '320 patent discloses an article of footwear with a unique heel counter that extends vertically upward from the sole structure. This extended counter is designed to pivot or flex to create a larger opening for easy foot entry. The design often includes a tensioner or strap that helps return the counter to its original position and secure the shoe.
• Potential Anticipation Analysis:
  • The '320 patent clearly discloses a form of "stabilizer" that extends from the sole and is designed to aid in entry, similar to the '811 patent.
  • Claim 1 & 10: The key question for anticipation is whether the '320 patent also discloses the specific "plurality of elastic elements" as claimed in the '811 patent. The '320 patent's mechanism relies more on the pivoting/flexing of the extended counter itself and a tensioner, rather than multiple elastic gores or inserts in the forward portion of the upper. The drawings (e.g., Fig. 2) show a large opening created by the pivoting counter but do not appear to show the distinct, separated elastic elements as required by Claim 1 or the angular arrangement of Claim 10. Therefore, anticipation by this reference appears unlikely.

Obviousness Analysis Under 35 U.S.C. § 103

Under 35 U.S.C. § 103, a patent claim is invalid if the differences between the claimed invention and the prior art are such that the subject matter as a whole would have been obvious at the time the invention was made to a person having ordinary skill in the art (a "POSITA"). An obviousness rejection typically involves combining two or more prior art references to arrive at the claimed invention, provided there was a motivation to combine these references with a reasonable expectation of success.

The following analysis considers the independent claims of U.S. Patent No. 11,871,811 ('811 patent) in light of the prior art cited during its prosecution.

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Analysis of Independent Claim 1

Claim 1 requires:

• A sole and an upper.
• A unitary stabilizer extending from the sole toward the rear of the foot opening.
• A plurality of elastic elements (at least two) positioned forward of the rear portion.
• These elastic elements must be separated by a non-elastic portion of the upper.

Primary Combination: Pratt ('632 Application) in view of Eull ('416 Patent)

A strong argument can be made that Claim 1 of the '811 patent would have been obvious over the combination of the '632 Application (U.S. 2017/0303632) and the '416 Patent (U.S. 9,629,416 B2).

1. Base Reference - '632 Application: The '632 application, by the same inventor, discloses the core concept of a rapid-entry shoe with a resilient heel frame that functions as a stabilizer. This frame is described as a "single continuous piece of material," which teaches the "unitary structure" limitation of Claim 1. It also clearly discloses a stabilizer extending from the sole portion to support the rear of the shoe and facilitate hands-free entry. What the '632 application lacks is a specific disclosure of multiple, separate elastic elements in the forward/side portion of the shoe's upper. Its focus is primarily on the action of the heel.

2. Secondary Reference - '416 Patent: The '416 patent explicitly teaches the use of multiple elastic gore panels (e.g., elements 26, 28 in Fig. 4) on the upper of a slip-on boot. These panels are inherently separated by the primary, non-elastic material of the upper (e.g., leather) and function to enlarge the shoe's opening for easier entry while maintaining a snug fit.

3. Motivation to Combine: A person of ordinary skill in the art, seeking to improve the rapid-entry shoe design of the '632 application, would be motivated to enhance the ease of entry and improve fit. While the rebounding heel of '632 addresses entry at the rear, a POSITA would recognize that resistance can also come from the instep or throat of the shoe. The use of elastic gores, as taught by the '416 patent, is a well-known and conventional solution in the footwear industry to create a more adaptable and easily expandable opening. A POSITA would naturally look to this established technique and incorporate the multiple, separated elastic gores from '416 into the upper of the '632 shoe. This combination would predictably result in a shoe with both a rebounding heel stabilizer and an expandable forward portion, thereby arriving at the invention claimed in Claim 1 with a reasonable expectation of success.

Conclusion for Claim 1: The combination of a unitary rear stabilizer ('632) with multiple, separate elastic elements in the upper ('416) is a logical and predictable assembly of known elements from the prior art to achieve the desired function of improved rapid entry. Therefore, Claim 1 appears to be vulnerable to an obviousness challenge.

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Analysis of Independent Claim 10

Claim 10 requires:

• A sole and an upper.
• A unitary stabilizer extending from the sole toward the rear of the foot opening.
• A plurality of elastic elements that facilitate flexion of the forward portion of the upper.
• These elements include at least a first and a second elastic element, each with a longitudinal axis, where the axes are at different angles relative to a vertical axis.

Primary Combination: Pratt ('632 Application) in view of Eull ('416 Patent)

This combination is also potent against Claim 10. The analysis is similar to that for Claim 1, with an additional focus on the angular orientation of the elastic elements.

1. Base and Secondary References: As established above, the '632 application teaches the unitary stabilizer, and the '416 patent teaches the use of a plurality of elastic elements for ease of entry.

2. Motivation and Obviousness of Angular Orientation: The '416 patent's drawings (e.g., Fig. 4) depict elastic gores placed along the natural, curving lines of a shoe upper. A POSITA would understand that a shoe is a three-dimensional object with complex curvature. To place two separate elastic elements on the side or transition portion of an upper in a way that is both functional and aesthetically pleasing, it would be a matter of routine design choice to orient them at different angles to conform to the shoe's last and the anatomy of the foot. For example, one gore might be angled more vertically along the ankle, while another might be angled more horizontally over the instep. This arrangement is suggested by the positioning of elements 26 and 28 in the '416 patent. Therefore, arriving at an arrangement where the longitudinal axes of two elastic elements are at "different" angles would be an obvious and predictable result of applying the teachings of '416 to the shoe of '632.

Alternative Combination: Nike ('320 Patent) in view of Eull ('416 Patent)

An alternative, but also strong, argument could be made using the '320 Patent as the base reference.

1. Base Reference - '320 Patent: The '320 patent discloses a footwear article with a vertically extended heel counter that pivots or flexes to allow for easy entry, satisfying the "stabilizer" element.
2. Secondary Reference - '416 Patent: The '416 patent again provides the teaching of multiple, separated elastic gores.
3. Motivation to Combine: A designer starting with the pivoting heel of the '320 patent would be focused on creating a "hands-free" or "easy-on" experience. To complement the large opening created by the pivoting heel, they would be motivated to improve the fit and comfort around the instep. Incorporating the elastic gores from the '416 patent would be an obvious way to add flexibility and a secure fit to the forward part of the shoe, working in concert with the pivoting heel. The aformentioned design choice of angling these gores differently ('416) would be equally applicable in this combination.

Conclusion for Claim 10: Much like Claim 1, Claim 10 appears vulnerable under 35 U.S.C. § 103. The combination of a known rapid-entry heel stabilizer (from either '632 or '320) with the well-understood use of multiple, angled elastic gores for fit and entry (from '416) would have been obvious to a person of ordinary skill in the art at the time of the invention.

U.S. Patent 11,871,811: Prosecution History and Term Analysis

An analysis of the prosecution history for U.S. Patent No. 11,871,811 ("the '811 patent") provides details on its relationship to other applications and its projected lifespan.

Application History and Relationship:

The '811 patent is the result of U.S. Patent Application No. 18/371,413, filed on September 21, 2023. This application is part of a series of continuing applications, which allows an applicant to file new claims based on an earlier "parent" application while retaining the original priority date. This practice is common when inventors wish to pursue different aspects of an invention disclosed in the original filing.

The lineage of the '811 patent is as follows:

• It is a direct continuation of U.S. Application No. 17/965,516, which was filed on October 13, 2022.
• The '516 application is itself a continuation of U.S. Application No. 16/942,335, filed on July 29, 2020.
• The '335 application claims priority to U.S. Provisional Application No. 62/879,883, filed on July 29, 2019.

No divisional applications were filed from this application chain. A divisional application is typically filed when the patent office determines an application contains more than one distinct invention.

Patent Term Adjustment (PTA) and Extension (PTE):

• Patent Term Adjustment (PTA): The '811 patent has a calculated PTA of 0 days. PTA is a mechanism to extend a patent's term to compensate for certain administrative delays by the U.S. Patent and Trademark Office (USPTO) during the examination process. The prosecution of the application leading to this patent was exceptionally fast—filed in September 2023 and granted in January 2024—meaning no qualifying delays occurred.
• Patent Term Extension (PTE): There is no Patent Term Extension for this patent. PTE is typically granted to compensate for delays in regulatory review (e.g., by the FDA for pharmaceutical products) and does not apply to this type of technology.

Projected Expiration Date:

The term of a U.S. patent is 20 years from the filing date of the earliest non-provisional application in its family chain. For the '811 patent, this date is the filing date of application Ser. No. 16/942,335, which is July 29, 2020.

Therefore, the projected expiration date is calculated as:
July 29, 2020 + 20 years = July 29, 2040.

This date is confirmed by the "Anticipated expiration" date listed on the patent's official records and is not altered by any PTA.

Patent Family:

The '811 patent is part of a larger family of patents and applications that all claim priority to the same original 2019 provisional application. The related U.S. patents and applications in this family include:

• U.S. Patent No. 11,633,005: Issued from application 16/942,335.
• U.S. Patent No. 12,274,325: Issued from application 17/965,516.
• U.S. Patent No. 11,633,006: Issued from application 17/965,501.
• U.S. Patent No. 12,471,660: Issued from application 18/371,414.
• U.S. Patent No. 12,121,096: Issued from application 18/610,029.

This family also includes international filings, such as a World Intellectual Property Organization (WO) application and a European Patent (EP) application, indicating a broad strategy for protecting this technology globally.

Defensive Disclosure and Prior Art Generation for Rapid-Entry Footwear Technology

Publication Date: April 30, 2026
Reference Patent: U.S. Patent No. 11,871,811 B1
Subject Matter: Rapid-entry footwear utilizing a unitary rear stabilizer and a plurality of elastic elements to enlarge the foot opening.

This document details novel derivative concepts, alternative embodiments, and cross-domain applications of the core technologies described in U.S. Patent 11,871,811 ('811 patent). The purpose of this disclosure is to place these concepts into the public domain, thereby establishing them as prior art to preclude future patenting of these and obvious variations thereof.

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Derivatives Based on Independent Claim 1

Core Concept: A rapid-entry shoe with a unitary stabilizer and at least two separate elastic elements positioned forward of the rear portion and separated by non-elastic material.

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Derivative 1.1: Shape-Memory Alloy (SMA) Stabilizer with Thermochromic Indicator

• Axis: Material & Component Substitution
• Enabling Description: The stabilizer, conforming to the "unitary structure" as claimed, is fabricated from a nickel-titanium alloy (Nitinol). At a predefined transition temperature (e.g., 30°C, slightly below body temperature), the Nitinol is in its martensitic phase, rendering it highly flexible and malleable. This allows the rear portion of the shoe to deform with minimal force for foot entry. As the wearer's body heat raises the stabilizer's temperature above the transition point, it reverts to its pre-programmed, rigid austenitic phase, providing firm heel support. The upper material adjacent to the stabilizer is impregnated with a thermochromic pigment that changes color (e.g., from grey to blue) to provide a visual confirmation that the stabilizer has achieved its rigid, locked state. The elastic elements are standard elastomeric gores.

graph TD
    A[Foot Insertion Begins] --> B{Stabilizer at Ambient Temp < 30°C};
    B --> C[SMA Stabilizer in Flexible Martensite Phase];
    C --> D[Heel Deforms for Easy Entry];
    D --> E{Wearer's Foot Transfers Heat};
    E --> F[Stabilizer Temperature > 30°C];
    F --> G[SMA Stabilizer Transforms to Rigid Austenite Phase];
    G --> H[Heel Support is Locked];
    F --> I[Thermochromic Pigment Activates];
    I --> J[Visual Color Change Confirms Lock];

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Derivative 1.2: Magnetorheological (MR) Fluid-Based Variable-Tension Gores

• Axis: Material & Component Substitution
• Enabling Description: The "plurality of elastic elements" are replaced with sealed, flexible bladders containing a magnetorheological (MR) fluid. These bladders are positioned where traditional elastic gores would be. An embedded microcontroller, powered by a piezoelectric generator in the shoe's heel, controls a series of micro-electromagnets surrounding each bladder. In the default (off) state, the MR fluid is liquid, and the bladders offer low resistance, allowing the foot opening to expand easily. Upon detecting full foot insertion via a pressure sensor in the insole, the microcontroller activates the electromagnets. The applied magnetic field dramatically increases the viscosity of the MR fluid, causing it to behave like a semi-solid. This action "stiffens" the gores, securing the foot. The tension can be adjusted via a smartphone application, which communicates with the microcontroller via Bluetooth Low Energy (BLE).

sequenceDiagram
    participant User as User's Foot
    participant Sensor as Pressure Sensor
    participant MCU as Microcontroller
    participant MRE as MR Fluid Gores

    User->>+Sensor: Inserts foot
    Sensor->>+MCU: Foot-in-place signal
    MCU->>+MRE: Apply magnetic field
    MRE-->>-MCU: Viscosity Increases
    MRE-->>-User: Gores stiffen, securing foot

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Derivative 1.3: Cryogenic-Rated Footwear for First Responders

• Axis: Operational Parameter Expansion
• Enabling Description: The rapid-entry system is adapted for footwear intended for use in extreme cold (-50°C to -100°C) and hazardous material handling. The unitary stabilizer is molded from a cryo-grade glass-fiber-reinforced polyether ether ketone (PEEK), which maintains its structural integrity and impact resistance at extremely low temperatures. The "plurality of elastic elements" are fabricated from a silicone-based elastomer specifically formulated for low-temperature flexibility, preventing the material from becoming brittle. The non-elastic upper material is a multi-layer composite of aramid fiber (for puncture resistance) and a closed-cell foam insulation layer. This construction allows for rapid donning of protective boots over a standard inner boot in an emergency, even when materials are stiff from cold.

graph TD
    subgraph Boot Construction
        A(Sole: Cryo-Rated Rubber)
        B(Stabilizer: GFR-PEEK)
        C(Elastic Elements: Low-Temp Silicone)
        D(Upper: Aramid/Foam Composite)
    end
    A --integrates with--> B
    B --supports--> D
    D --interrupted by--> C
    subgraph Performance
        E{Environment: -70°C}
        F[Foot Insertion] --> G[Silicone Elements Stretch]
        G --> H[PEEK Stabilizer Guides Heel]
        H --> I[Boot Secured]
    end
    C --maintains_flexibility_in--> E
    B --maintains_rigidity_in--> E

---

Derivative 1.4: Medical - Articulating Ankle-Foot Orthosis (AFO)

• Axis: Cross-Domain Application
• Enabling Description: The invention is embodied in an AFO for patients with drop foot or mobility challenges. The "unitary stabilizer" is a rigid, L-shaped polypropylene strut that provides posterior support and extends from under the heel up to the calf. The "forward portion" is a soft, padded cuff that wraps around the shin. Instead of laces or complex straps, the AFO employs two distinct elastic elements, separated by the non-elastic cuff material. One elastic element is oriented vertically along the anterior of the shin, while the second is angled at approximately 45 degrees, connecting the shin cuff to the footplate. This arrangement allows the patient to easily slide their foot in. The pre-set tension of the angled elastic element then provides the necessary dorsiflexion assist, while the vertical element ensures a snug fit around the shin. This design facilitates one-handed application of the brace.

classDiagram
    class AFO {
        +polypropylene_stabilizer
        +padded_shin_cuff
        +footplate
        +vertical_elastic_element
        +angled_elastic_element
        +don_brace()
        +provide_dorsiflexion_assist()
    }
    AFO : +stabilizer : "Unitary Strut"
    AFO : +elastic_elements : "Plurality with different vectors"

---

Derivative 1.5: Aerospace - Emergency Seat Egress Harness

• Axis: Cross-Domain Application
• Enabling Description: The concept is applied to a lightweight, rapid-donning restraint harness for crew members in a spacecraft. The "stabilizer" is a semi-rigid, carbon-fiber composite frame that conforms to the shape of a crew member's back and shoulders. The "upper" is a system of fire-retardant Nomex webbing straps. A "plurality of elastic elements," made from high-tensile strength elastomeric cord, are integrated into the chest and thigh straps. These elastic sections are separated by the non-elastic webbing. To don the harness, the crew member simply slips their arms through the shoulder loops and pulls it on like a vest. The elastic elements expand to accommodate their body and flight suit, and then contract to provide a secure initial fit. Final tensioning is achieved with a single, central buckle, but the initial fit-up is automatic and rapid, saving critical seconds during an emergency egress procedure.

graph TD
    subgraph Donning Sequence
        A(Sling Harness Over Shoulders) --> B(Pull Down Over Torso);
        B --> C{Elastic Chest/Thigh Straps Expand};
        C --> D{Carbon Fiber Stabilizer Self-Aligns on Back};
        D --> E{Elastic Straps Contract to Secure Harness};
        E --> F(Engage Single Central Buckle for Final Tension);
    end

---

Derivative 1.6: IoT-Enabled Prophylactic Footwear for Diabetics

• Axis: Integration with Emerging Tech
• Enabling Description: This iteration integrates an IoT sensor suite into the rapid-entry shoe design for preventative diabetic foot care. The unitary stabilizer houses a multi-axis accelerometer and a gyroscope to monitor gait symmetry, stability, and potential falls. The non-elastic upper incorporates a grid of flexible pressure sensors and temperature sensors, providing a real-time map of potential ulceration hotspots. The elastic elements are made of a conductive elastomer, which acts as a strain gauge to measure medial and lateral foot swelling throughout the day. All sensor data is processed by a low-power MCU embedded in the sole and transmitted via BLE to a patient's smartphone app and a clinician's dashboard. An AI model in the cloud analyzes trends and sends alerts for risky conditions (e.g., sustained high pressure at one point, abnormal temperature gradients, or sudden swelling).

graph TD
    subgraph Shoe_Sensors
        A[Inertial Measurement Unit in Stabilizer]
        B[Pressure/Temp Grid in Upper]
        C[Conductive Elastomer Strain Gauges]
    end
    subgraph Data_Flow
        A --> D{Onboard MCU};
        B --> D;
        C --> D;
        D --(BLE)--> E[Smartphone App];
        E --> F[Cloud AI Platform];
        F --> G[Clinician Dashboard];
        F --> H[Patient Alerts];
    end

---

Derivative 1.7: Failsafe De-Tensioning System for Industrial Safety Boots

• Axis: The "Inverse" or Failure Mode
• Enabling Description: This footwear is designed for workers in environments with entanglement risks (e.g., conveyor belts, rotating machinery). The unitary stabilizer is standard, providing protection. However, the "plurality of elastic elements" are connected to the upper via a shear-pin mechanism. Under normal walking and flexing forces, the pins hold the elastic elements, and the shoe functions as designed. If a tensile force exceeding a calibrated threshold (e.g., >100 Newtons) is applied, as would occur during an entanglement event, the shear pins are designed to fracture. This instantly decouples the elastic elements from the upper, causing the foot opening to expand to its maximum possible size and allowing the boot to be pulled off the foot, preventing the worker from being dragged into the machinery. The shear pins are color-coded for different force ratings and are user-replaceable.

stateDiagram-v2
    [*] --> Normal
    Normal: Shoe is secure
    Normal --> Entangled: Entanglement event
    Entangled: Tensile force > 100N
    Entangled --> Released: Shear pins fracture
    Released: Elastic elements decouple
    Released --> [*]: Foot is free from boot

---

Derivatives Based on Independent Claim 10

Core Concept: A rapid-entry shoe with a unitary stabilizer and a plurality of elastic elements, where at least two have longitudinal axes at different angles relative to a vertical axis, facilitating forward flexion.

---

Derivative 10.1: Asymmetric Torsional Control for Athletic Footwear

• Axis: Material & Component Substitution
• Enabling Description: This derivative is for a court shoe (e.g., for basketball or tennis) requiring high lateral stability. The unitary stabilizer is a carbon fiber heel counter that wraps forward and is bonded to the midsole. The shoe features two primary elastic elements on each side, their axes angled differently. The first, more vertical elastic element is made of a high-modulus elastomer providing strong resistance to stretching, controlling ankle support. The second, more horizontal element, is made of a lower-modulus elastomer, allowing for easier expansion over the instep during entry. The different angles and different elastic moduli work in concert. During a cutting motion, the force vector is primarily resisted by the high-modulus, vertically-angled element on the load-bearing side, while the other elements maintain fit. This provides directional, asymmetric support that adapts to athletic movements while still allowing rapid entry.

graph TD
    subgraph LateralSide
        A[High-Modulus Vertical Elastic Element]
        B[Low-Modulus Angled Elastic Element]
    end
    subgraph MedialSide
        C[High-Modulus Vertical Elastic Element]
        D[Low-Modulus Angled Elastic Element]
    end
    subgraph Forces
        E(Foot Entry) --> F{Low-Modulus Elements (B, D) Stretch Easily};
        G(Lateral Cut) --> H{High-Modulus Element (A) Resists Lateral Roll};
    end
    A & B --> I(Secure Fit)
    C & D --> I
    F --> I
    H --> J(Enhanced Stability)

---

Combination Prior Art Scenarios with Open Standards

Combination 1: Rapid-Entry Shoe with FIDO2/WebAuthn Authentication

• Concept: A rapid-entry shoe is equipped with an NFC chip and a piezoelectric pressure sensor array integrated into the insole. This system acts as a hardware security token. The unique pressure signature of a user's foot-strike and weight distribution, captured at the moment of insertion ("gait-printing"), is used as a biometric factor.
• Integration with Open Standard: The shoe's firmware implements the FIDO2/WebAuthn open standard. When the user steps into the shoe and takes a step, the shoe can authenticate the user to a FIDO2-compliant web service (e.g., a corporate network, a payment system) via NFC tap or BLE. The combination of the physical token (the shoe) and the biometric (the gait-print) provides two-factor authentication. This creates prior art for footwear-based, hands-free authentication systems.

Combination 2: Parametric Shoe Design using OpenSCAD

• Concept: The design of the rapid-entry shoe, specifically the geometry of the unitary stabilizer and the placement, angle, and size of the cutouts for the elastic elements, is defined as a parametric model.
• Integration with Open Standard: The model is created and published using OpenSCAD, an open-source, script-based CAD program. This allows anyone to download the source file and customize the shoe design for a specific foot size, width, or desired level of support by simply changing variables in the script (e.g., stabilizer_height=60; gore_angle_1=75; gore_angle_2=40;). The resulting STL files can be used for 3D printing custom stabilizers or manufacturing molds. This places the concept of a fully open-source, parametrically-defined rapid-entry shoe into the public domain.

Combination 3: ROS2-Integrated Mobility Aid

• Concept: The medical AFO variant (Derivative 1.4) is enhanced with an Inertial Measurement Unit (IMU) and joint angle sensors.
• Integration with Open Standard: The AFO's onboard computer runs a node in the Robot Operating System 2 (ROS2), an open-source suite of software libraries and tools for building robot applications. The AFO publishes its sensor data (pronation, supination, angle, gait phase) to the ROS2 network over Wi-Fi. This allows seamless integration with other ROS2-enabled assistive devices, such as a smart cane or an exoskeleton. For example, the AFO could signal the user's intent to stand, pre-activating motors in a robotic walker. This creates prior art for a modular, interoperable ecosystem of open-source mobility aids based on the rapid-entry footwear structure.