Shape memory polymers (SMPs) are a class of materials that can undergo a reversible transformation between two or more distinct shapes in response to external stimuli such as temperature, light, or moisture. These polymers exhibit a unique ability to “remember” a predefined shape and return to it upon activation, making them highly versatile for a range of applications. The transition typically involves a temporary shape change induced by an external stimulus, followed by a shape recovery when the material is exposed to a specific trigger, such as heat or chemical changes.
Shape Memory Polymers as Biomaterials
At the Ecker Lab, we explore the transformative potential of shape memory polymers (SMPs) for biomedical applications. These advanced materials can change shape in response to external stimuli—such as heat, light, or moisture—allowing for innovative solutions in tissue engineering, drug delivery, and medical devices.
Our research focuses on designing biocompatible and biodegradable SMPs that respond to physiological conditions, enabling minimally invasive medical interventions. From self-tightening sutures to smart scaffolds for regenerative medicine, we aim to engineer responsive materials that enhance healing, reduce surgical complications, and improve patient outcomes.
By combining polymer chemistry, material science, and biomedical engineering, we develop next-generation SMPs tailored for clinical applications. Our interdisciplinary approach ensures that these materials are not only functional but also safe, scalable, and adaptable to the complexities of the human body.
Thiol-ene Based Shape Memory Polymers
Our research focuses on the development and characterization of a novel class of biomaterials known as thiol-ene/acrylate polymers, which hold great potential for a variety of biomedical applications due to their flexibility, softening capability, and shape memory properties. However, a common challenge with these materials is their lack of sufficient stretchability for wearable or implantable devices. To address this limitation, we have introduced di-acrylate chain extenders, such as Polyethylene Glycol Diacrylate (PEGDA), into the thiol-ene polymer system to enhance its stretchability and mechanical performance.
The synthesis of these polymers involves a combination of 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TATATO), Trimethylolpropanetris(3-mercaptopropionate) (TMTMP), and PEGDA with varying molecular weights. Fourier Transform Infrared (FTIR) spectroscopy confirms the complete reaction between the monomers, ensuring a well-defined crosslinked network. Uniaxial tensile testing demonstrates the ability of these polymers to soften and stretch, with notable reductions in Young’s Modulus and significant increases in fracture strain upon the addition of PEGDA, which contributes to the desired stretchability.
Stretchable shape memory polymers are especially useful in minimally invasive devices, as they conform to the movement of organs and reduce motion artifacts. Their shape memory properties allow them to recover their original configuration after deformation, making them ideal for surgical applications and wearable biomedical devices.
Further exploration of the thermomechanical properties of these polymers reveals that PEGDA can effectively tune the glass transition temperature (Tg), providing another level of control over the material’s behavior. These polymers exhibit shape memory properties, enhancing their versatility and suitability for various biomedical applications.
While previous research has explored thiol-ene reactions for applications in areas like wound healing, drug delivery, and tissue engineering, there remains a gap in the development of polymers that combine self-softening, flexibility, stretchability, and shape memory properties specifically tailored for biomedical uses. Our work aims to bridge this gap by synthesizing and characterizing a polymer system that meets these combined requirements.
For more details, please read our publication:
Understanding the Plasticization-Induced Shape Memory Effect
Our lab’s CAREER project focuses on uncovering the fundamental mechanisms behind the plasticization-induced shape memory effect in thiol-ene-based polymers. This research is driven by the need for biodegradable, heat-shrink biomaterials that respond to physiological conditions, with a model application in colonic anastomosis repair. The goal is to develop heat-shrink tubing that contracts at body temperature (~37°C) and in simulated body fluids, providing a self-sealing alternative to traditional sutures and staples.
Investigating the Shape Memory Cycle
To fully understand and optimize this material, our research is structured around three key objectives:
- Deciphering Structure-Property Relationships
We systematically investigate how crosslink density and chain extender length influence the plasticization-induced shape memory effect. By conducting mechanical and thermomechanical measurements in simulated body fluids, we analyze how these factors affect shape recovery, elasticity, and degradation behavior, ultimately guiding material design for biomedical applications. - Optimizing Heat Shrink Tubing Performance
A critical aspect of this project is understanding the interplay between material thickness, degree of shape programming, and radial recovery forces in tube-shaped SMPs. These parameters determine the tubing’s ability to shrink effectively and conform securely to biological tissues, ensuring a strong and reliable seal in surgical applications. - Validating Functionality in an Ex Vivo Model
To bridge the gap between material development and clinical application, we will demonstrate the functionality of our biomedical heat shrink tubing using an ex vivo colon anastomosis model. By quantifying mechanical properties and sealing performance, we aim to establish this technology as a viable alternative to conventional surgical methods.
Advancing the Field of Biomedical Shape Memory Polymers
This research will contribute to the fundamental understanding of plasticization-induced shape recovery while providing a scalable, clinically relevant solution for soft tissue repair. By addressing critical gaps in structure-property relationships, our work lays the foundation for the next generation of smart biomaterials that respond dynamically to the human body’s environment.
The specific three aims are to
- Systematically investigate the effect of crosslink density and chain extender length on the plasticization-induced shape memory effect of thiol-ene-based polymers. Mechanical and thermomechanical measurements inside simulated body fluids will be used to assess shape memory properties and structure-property relationships.
- Understand the relationship between material thickness, degree of shape-programming, and radial recovery forces of tube-shaped SMPs to determine optimal design parameters for sufficient shape recovery using the heat shrink tube model.
- Demonstrate the functionality of a biomedical heat shrink tube that utilizes the plasticization-induced shape recovery through an ex vivo colon anastomosis model and quantify mechanical and sealing properties.
The proposed research will advance science by filling the gap in the structure-property relationship of thiol-ene-based SMPs that utilize plasticization for their shape recovery, which is essential for designing future devices.
In addition, this innovative biomaterial will allow the broader research community to develop novel biomedical devices tailored to specific tissues and applications. Educational and outreach activities will be implemented to raise excitement, awareness, and interest in the emerging field of smart polymeric biomaterials. These will include a gender- and ethnicity-matched mentor-mentee program, training students from underrepresented groups in the PI’s laboratory, incorporating research discoveries into coursework, and communicating research to the general public at local science slam events.
Biomedical Heat Shrink Tubing
One of our lab’s key innovations is the development of biomedical heat shrink tubing using a biocompatible, biodegradable, and shape memory polymer that shrinks at body temperature. This novel material is designed to provide minimally invasive solutions for surgical applications, particularly in soft tissue repair.
Polymer Design: Thiol-Ene Chemistry for Precision Control
Our biomedical heat shrink tubing is based on a thiol-ene polymer system, a highly tunable crosslinked network that allows for precise control over mechanical properties, degradation rates, and responsiveness to physiological conditions. Thiol-ene chemistry enables the fabrication of highly uniform and defect-free polymer networks, offering advantages such as:
- Low polymerization shrinkage, reducing stress on surrounding tissues.
- Cytocompatibility, ensuring safe integration into biological environments.
- Tailorable degradation, allowing the tubing to resorb naturally after the tissue has healed.
By adjusting the monomer ratios and crosslinking density, we can fine-tune the tubing’s thermal and mechanical behavior, ensuring optimal performance in biomedical applications.
Shape Memory via Plasticization: Activation at Body Temperature
A unique feature of our heat shrink tubing is its ability to undergo plasticization-induced shape memory activation. Unlike traditional heat shrink materials that require high temperatures or external activation, our polymer system is designed to shrink at body temperature (~37°C) due to the presence of physiological fluids acting as plasticizers.
This effect is achieved through:
- Hydrophilic functional groups that allow controlled absorption of water, lowering the glass transition temperature (Tg).
- Strategic polymer network design, ensuring a transition from a temporarily expanded shape to its original, contracted form when exposed to moisture and warmth.
This mechanism enables conformal sealing around tissues without the need for external heating devices, making it particularly attractive for delicate surgical applications such as vascular and gastrointestinal repairs.
Key Applications:
- Intestinal Anastomosis: Provides a self-sealing alternative to sutures and staples, reducing the risk of leaks and post-surgical complications.
- Vascular Repair: Forms a tight, supportive seal around damaged blood vessels while gradually degrading as healing progresses.
- Nerve Regeneration: Serves as a protective conduit for nerve repair, maintaining alignment and minimizing scarring.
Our goal is to translate this technology from lab to clinic, providing a biodegradable, off-the-shelf solution that simplifies procedures and improves patient outcomes. Through ongoing collaborations with clinicians and biomedical engineers, we are optimizing the material properties for scalability, manufacturability, and regulatory approval to bring this breakthrough technology closer to real-world applications.
SMP Bandage to prevent Colonic Anastomotic Leak
After colonic resections that may be necessary in case of cancer or diverticulitis, the two parts of the colon need to be reattached after the procedure. This procedure is called anastomosis and can be done through manual sutures or staples. In any case, there are rates between 1% and 30% of anastomotic dehiscence reported in the literature.1 Anastomotic Leak is defined as a “leak of luminal contents from a surgical join between two hollow viscera.”2 If contents from the inside of the colon leak into the abdominal area, the consequences are various clinical signs like peritonitis; feculent wound, drain discharge, abscess, or fever. “Anastomotic leakage remains today a major cause of postoperative mortality and morbidity in colorectal surgery.”3
In order to minimize the risk of anastomotic leakage, we propose to develop a bandage made of SMP, which can wrap around the colon to seal the reconnected parts from the outside and, therefore, prevent any fluids from getting into the abdominal cavity. The SMP will be fabricated into a tube shape that has a slightly smaller radius than the colon. The tube will then be radially expanded to a radius that is 1.5 times the radius of the colon. The device will be placed at the outside of the colon, covering the part where the anastomosis took place. The polymer will recover its shape due to the plasticization-induced shape memory effect and will wrap tightly around it to seal the colonic part against leakage after surgery. The SMP will be designed to be biodegradable in order to dissolve over the course of 3 to 6 months so that a second surgical procedure will not be necessary. The biodegradability and time span of degradation can be tuned by the number of ester groups in the polymeric backbone and the crosslink density of the polymeric network.
In addition, anti-inflammatory drugs and bioactive compounds that promote wound healing will be loaded into the polymer. This study will serve as a model to test the hypothesis that polymers loaded with bioactive compounds reveal positive effects on the healing process and can serve as a platform technology capable of concurrent drug delivery.
[1] Kingham, T. P.; Pachter, H. L., Colonic Anastomotic Leak: Risk Factors, Diagnosis, and Treatment. Journal of the American College of Surgeons 2009, 208 (2), 269-278.
[2] Peel, A. L.; Taylor, E. W., Proposed definitions for the audit of postoperative infection: a discussion paper. Surgical Infection Study Group. Annals of The Royal College of Surgeons of England 1991, 73 (6), 385-388.
[3] Alves, A.; Panis, Y.; Trancart, D.; Regimbeau, J.-M.; Pocard, M.; Valleur, P., Factors Associated with Clinically Significant Anastomotic Leakage after Large Bowel Resection: Multivariate Analysis of 707Patients. World Journal of Surgery 2002,26 (4), 499-502