This Small Business Innovation Research (SBIR) Phase I project aims to develop a mechanically-active soft tissue reinforcement device using a shape-memory fabric to improve the tissue quality of chronic rotator cuff tears. With chronic tears, the rotator cuff has degenerated to a point that prevents its ability to heal back to bone using standard repair procedures. The intellectual merit of this project stems from using the shape-memory effect to apply a continuous force on the atrophied rotator cuff tissue in an effort to promote tissue regeneration and improve the overall healing capacity. The research for this project will focus on evaluating (1) how the physical attributes of the fabric will impact the shape-memory properties and (2) the effect of applying a force, generated by the fabric?s shape recovery, on the quality of the rotator cuff tissue. The anticipated results of this work will be the identification of a fabric that can contract via shape recovery at body temperature over a time scale required for soft tissue reattachment to occur. This work will also demonstrate that tension can be continuously applied to cuff tissue at a magnitude representative of physiological tensile loading on the cuff.
The broader impact/commercial potential of this project is the potential to address a significant clinical problem pertaining to the treatment of chronic rotator cuff tears. Over 400,000 rotator cuff repairs are performed each year, but have a failure rate of 20%. The rotator cuff reinforcement device market is estimated to be $91 M and growing 16% annually. There are currently no reinforcement devices commercially available that can help improve tissue quality in chronic cuff tears. Thus, a reinforcement device that can apply continuous tensile force to improve tissue quality could serve as a disruptive technology in a large market and significantly impact how rotator cuff procedures are performed. From a technological/scientific standpoint, this project will provide the fundamental knowledge of how shape-memory materials can be applied to mechanically stimulate a biologic response in vivo, specifically the effect of tensile force on soft tissue regeneration. In addition, this shape-memory fabric technology could broadly lend itself to other clinical applications including Achilles tendon repair, hernia repair, battle-field/traumatic muscle injuries, and muscular disorders.
The rotator cuff is a set of tendons and their muscles used to secure the shoulder joint. Over 400,000 rotator cuff repairs are performed in the U.S. annually at a cost of nearly $474 million. Rotator cuff tears can result from a traumatic shoulder injury in the younger population, but are more often due to repetitive activities in the elderly. Due to a number of complications, such as tear size, time from injury to surgery, and tissue quality, the failure rate of rotator cuff repairs ranges from 20-57%. Chronic tears are plagued by muscle atrophy, which complicates surgical repair due to poor tissue quality, and the rotator cuff tendon cannot be repaired back to its original location. Currently, orthopedic device companies offer reinforcement patches, either made of biological or synthetic material, to try to increase healing of torn rotator cuffs. Unfortunately, current reinforcement patches have drawbacks and complications, such as mechanical failure or an unfavorable inflammatory reaction by patients. As a result, there is significant potential to introduce a novel technology into the marketplace. This Small Business Innovation Research Phase I proposal aimed to develop and prototype a rotator cuff repair device based on shape-memory fabric to improve the tissue quality of rotator cuff tear repairs. Shape-memory fabrics are a class of materials that can change from a temporary shape back to an original shape or apply a force in response to a stimulus, such as heat, light, or water. For a medical device, the surgeon would be given the device in its temporary shape. Upon implantation, body temperature would supply the heat for recovery to the original shape over days to weeks. The goal of this proposal was to determine if a shape-memory fabric would be able to tension rotator cuff tendon-muscle units, which may suggest an improvement in tissue quality of rotator cuff tears. Also, the shape-memory fabric should have biomechanical performance similar to current devices. Upon exposure to body temperature and absorption of moisture, the shape-memory fabric will gradually contract, thus applying tension to the atrophied tissue. If tensioning is possible, then muscle atrophy may be reversed and the repair may be more secure allowing improved healing. The intellectual merit of this proposal is the use of the shape-memory effect to apply a continual in vivo force on the atrophied rotator cuff tendon-muscle units. This proposal was accomplished by studying the shape-memory properties and biomechanical testing of rotator cuff tendons with shape-memory fabrics. Overall, the Phase I efforts have been successful for demonstrating the main objectives: (1) the shape-memory fabric can tension and elongate tendons and (2) the shape-memory fabric has properties within the range of current devices. Objective 1 established the relationships between fabric processing parameters, fabric structure, and shape-memory behavior (e.g. recovery speed and recovery force). Scanning electron microscopy was used to determine the fiber diameter of the shape-memory fabrics with microfiber structure (Figure 1). A specific range of processing parameters was found to give the optimal mechanical properties under immersed conditions by retaining breaking strength while maximizing elongation capacity (Figure 2). This demonstrates that the shape-memory fabric can be tailored to a variety of mechanical properties, which gives it broader potential for multiple medical applications. Objective 2 examined the biomechanical performance of the shape-memory fabric. The shape-memory fabrics could tension and elongate rotator cuff tendons several millimeters under simulated physiological conditions (Figure 3). The shape-memory fabrics were considered biocompatible as they demonstrated cell viability with adult bone and tendon cells and a high degree of tissue integration with negligible inflammatory response when implanted in vivo. In addition, the shape-memory fabrics had suture pull-out forces comparable to current devices. A supplemental award in the form of a Phase IB was granted, which allowed for further exploration of the fabric structure and interaction with adult bone and tendon cells. Micro-computed tomography is a non-destructive method to determine the 3-D structure of biomaterials, and was employed to determine how the shape-memory fabric’s structure changes during recovery (Figure 4). Changes in the fiber diameter, fiber spacing, and porosity were determined, which allows for a complete understanding of the changes during shape-memory recovery and acts as a quality control method during fabric production. Bone and tendon cells in contact with fabrics that were recovering had similar viability and calcium and collagen deposition as controls. This shape-memory fabric device may be able to improve tissue quality of atrophied rotator cuff tissue by using a novel technology without associated complications of biological reinforcement patches. Though this proposal is focused on chronic rotator cuff tears, it has the potential to broadly impact many orthopedic procedures including Achilles tendon repair, severe muscle trauma, and muscular disorders. This proposal would be the first to commercialize a shape-memory fabric device that provides an in vivo tension to improve tissue quality.
