-PCL shape memory polymer (SMP) scaffolds with tunable transition temperatures for enhanced utility.

Thermoresponsive shape memory polymers (SMPs) prepared from UV-curable poly(ε-caprolactone) (PCL) macromers have the potential to create self-fitting bone scaffolds, self-expanding vaginal stents, and other shape-shifting devices. To ensure tissue safety during deployment, the shape actuation temperature (, the melt transition temperature or of PCL) must be reduced from ∼55 °C that is observed for scaffolds prepared from -PCL-DA ( ∼ 10 kg mol). Moreover, increasing the rate of biodegradation would be advantageous, facilitating bone tissue healing and potentially eliminating the need for stent retrieval.

Development of Biopsy Tract Sealants Based on Shape Memory Polymer Foams.

Lung biopsies are often used to aid in the diagnosis of cancers. However, the procedure carries the dual risk of air (pneumothorax) or blood (hemothorax) filling the pleural cavity, increasing the risk of a collapsed lung and chest intubation. This work demonstrates the effectiveness of a polyurethane-based shape memory polymer foam as a biopsy tract sealant.

Technical note: The design and validation of a multi-modality lung phantom.

Background: Clinically relevant models that enable certain tasks such as calibration of medical imaging devices or techniques, device validation, training healthcare professionals, and more are vital to research throughout the medical field and are referred to as phantoms. Phantoms range in complexity from a vile of water to complex designs that emulate in vivo properties.

Purpose: Specific phantoms that model the lungs have focused on replication of tissue properties but lack replication of the anatomy.

Swellable and Thermally Responsive Hydrogel/Shape Memory Polymer Foam Composites for Sealing Lung Biopsy Tracts.

Lung tissue biopsies can result in a leakage of blood (hemothorax) and air (pneumothorax) from the biopsy tract, which threatens the patient with a collapsed lung and other complications. We have developed a lung biopsy tract sealant based on a thiol-ene-crosslinked PEG hydrogel and polyurethane shape memory polymer (SMP) foam composite. After insertion into biopsy tracts, the PEG hydrogel component contributes to sealing through water-driven swelling, whereas the SMP foam contributes to sealing via thermal actuation.

Image-Based Evaluation of In Vivo Degradation for Shape-Memory Polymer Polyurethane Foam.

Shape-memory polymer (SMP) polyurethane foams have been applied as embolic devices and implanted in multiple animal models. These materials are oxidatively degradable and it is critical to quantify and characterize the degradation for biocompatibility assessments. An image-based method using high-resolution and magnification scans of histology sections was used to estimate the mass loss of the peripheral and neurovascular embolization devices (PED, NED).

Theoretical error of sectional method for estimation of shape memory polyurethane foam mass loss.

Introduction: Measuring in vivo degradation for polymeric scaffolds is critical for analysis of biocompatibility. Traditionally, histology has been used to estimate mass loss in scaffolds, allowing for simultaneous evaluation of mass loss and the biologic response to the implant. Oxidatively degradable shape memory polyurethane (SMP) foams have been implemented in two vascular occlusion devices: peripheral embolization device (PED) and neurovascular embolization device (NED).

Controlling Morphology and Physio-Chemical Properties of Stimulus-Responsive Polyurethane Foams by Altering Chemical Blowing Agent Content.

Amorphous shape memory polymer foams are currently used as components in vascular occlusion medical devices such as the IMPEDE and IMPEDE-FX Embolization Plugs. Body temperature and moisture-driven actuation of the polymeric foam is necessary for vessel occlusion and the rate of expansion is a function of physio-chemical material properties. In this study, concentrations of the chemical blowing agent for the foam were altered and the resulting effects on morphology, thermal and chemical properties, and actuation rates were studied.

Development and Characterization of Oxidatively Responsive Thiol-Ene Networks for Bone Graft Applications.

First metatarsophalangeal joint (MPJ) arthroplasty procedures are a common podiatric procedure. However, almost one-third of cases require revision surgeries because of nonunions. Revision or salvage surgery requires more extensive hardware and bone grafts to recreate the first metatarsal.

Mechanical and Shape Memory Properties of Electrospun Polyurethane with Thiol-Ene Crosslinking.

The ability to treat complex medical issues often requires dynamic and versatile materials. Electrospinning is a fabrication technique which produces nano-/microfibers that can mimic the extracellular matrix of many biological tissues while shape memory polymers allow for geometric changes in devices upon implantation. Here, we present the fabrication of electrospun polyurethane which exhibits the shape memory effect.

Macrophage activation in response to shape memory polymer foam-coated aneurysm occlusion devices.

Brain aneurysms can be treated with embolic coils using minimally invasive approaches. It is advantageous to modulate the biologic response of platinum embolic coils. Our previous studies demonstrated that shape memory polymer (SMP) foam coated embolization coils (FCC) devices demonstrate enhanced healing responses in animal models compared with standard bare platinum coil (BPC) devices.

Shape memory polymer (SMP) scaffolds with improved self-fitting properties.

"Self-fitting" shape memory polymer (SMP) scaffolds prepared as semi-interpenetrating networks (semi-IPNs) with crosslinked linear-poly(ε-caprolactone)-diacrylate (PCL-DA, M∼10 kg mol) and linear-poly(l-lactic acid) (PLLA, M∼15 kg mol) [75/25 wt%] exhibited robust mechanical properties and accelerated degradation rates versus a PCL-DA scaffold control. However, their potential to treat irregular craniomaxillofacial (CMF) bone defects is limited by their relatively high fitting temperature (T∼55 °C; related to the T of PCL) required for shape recovery (i.e.

Chemical Modifications of Porous Shape Memory Polymers for Enhanced X-ray and MRI Visibility.

The goal of this work was to develop a shape memory polymer (SMP) foam with visibility under both X-ray and magnetic resonance imaging (MRI) modalities. A porous polymeric material with these properties is desirable in medical device development for applications requiring thermoresponsive tissue scaffolds with clinical imaging capabilities. Dual modality visibility was achieved by chemically incorporating monomers with X-ray visible iodine-motifs and MRI visible monomers with gadolinium content.

Shape Memory Polymer Foams Synthesized Using Glycerol and Hexanetriol for Enhanced Degradation Resistance.

Shape memory polymer foams have been used in a wide range of medical applications, including, but not limited to, vessel occlusion and aneurysm treatment. This unique polymer system has been proven to shape-fill a void, which makes it useful for occlusion applications. While the shape memory polymer foam has superior performance and healing outcomes compared to its leading competitors, some device applications may benefit from longer material degradation times, or degradation-resistant formulations with increased fibrous encapsulation.

Three-dimensional bioprinting of aneurysm-bearing tissue structure for endovascular deployment of embolization coils.

Various types of embolization devices have been developed for the treatment of cerebral aneurysms. However, it is challenging to properly evaluate device performance and train medical personnel for device deployment without the aid of functionally relevant models. Currentaneurysm models suffer from a lack of key functional and morphological features of brain vasculature that limit their applicability for these purposes.

Microscopic Assessment of Healing and Effectiveness of a Foam-Based Peripheral Occlusion Device.

The IMPEDE Embolization Plug is a catheter-delivered vascular occlusion device that utilizes a porous shape memory polymer foam as a scaffold for thrombus formation and distal coils to anchor the device within the vessel. In this study, we investigated the biological response of porcine arteries to the IMPEDE device by assessing the extent of healing and overall effectiveness in occluding the vessel at 30, 60, and 90 days. Compared to control devices (Amplatzer Vascular Plug and Nester Embolization Coils), the host response to IMPEDE showed increased cellular infiltration (accommodated by the foam scaffold), which led to advanced healing of the initial thrombus to mature collagenous connective tissue (confirmed by transmission electron microscopy (TEM)).

Improved Oxidative Biostability of Porous Shape Memory Polymers by Substituting Triethanolamine for Glycerol.

While many aromatic polyurethane systems suffer from poor hydrolytic stability, more recently proposed aliphatic systems are oxidatively-labile. The use of the renewable monomer glycerol as a more oxidatively-resistant moiety for inclusion in shape memory polymers (SMPs) is demonstrated here. Glycerol-containing SMPs and the amino alcohol control compositions are compared, with accelerated degradation testing displaying increased stability (time to complete mass loss) as a result of the inclusion of glycerol without sacrificing the shape memory, thermal transitions, or the ultralow density achieved with the control compositions.

Biodegradable shape memory polymer foams with appropriate thermal properties for hemostatic applications.

Shape memory polymer (SMP) foams are a promising material for hemostatic dressings due to their biocompatibility, high surface area, excellent shape recovery, and ability to quickly initiate blood clotting. Biodegradable SMP foams could eliminate the need for a secondary removal procedure of hemostatic material from the patients' wound, further facilitating wound healing. In this study, we developed hydrolytically and oxidatively biodegradable SMP foams by reacting polyols (triethanolamine or glycerol) with 6-aminocaproic acid or glycine to generate foaming monomers with degradable ester bonds.

Micro-CT and histopathology methods to assess host response of aneurysms treated with shape memory polymer foam-coated coils versus bare metal coil occlusion devices.

Recent studies utilizing shape memory polymer foams to coat embolizing coils have shown potential benefits over current aneurysm treatments. In the current study utilizing a rabbit-elastase aneurysm model, the performance of test article (foam-coated coil [FCC]) and control (bare platinum coils [BPCs]) devices were compared at 30, 90, and 180 days using micro-CT and histological assessments. The host response was measured by identifying the cells regionally present within the aneurysm, and assessing the degree of residual debris and connective tissue.

Computational study of clot formation in aneurysms treated with shape memory polymer foam.

To prevent aneurysmal rupture, intracranial aneurysms are often treated with endovascular metal coils that fill the aneurysm sac and stimulate thrombus formation, thereby isolating the aneurysm from the arterial flow. Despite its widespread use, this method can result in suboptimal outcomes leading to aneurysm recurrence. Recently, shape memory polymer foam has been proposed as an alternative aneurysm filler.

Shape memory polyurethane-urea foams with improved toughness.

Current vascular aneurysm treatments often require either highly invasive strategy to surgically occlude an aneurysm or endovascular occlusion via metal coils. While endovascular coils are safer, they have limited efficacy. Endovascular coils that are integrated with shape memory polymer (SMP) foams have the potential to improve occlusion and reduce coil risks; however, the mechanical performance and limited homogeneity of SMP foams can hinder their effective use.

In vivo comparison of shape memory polymer foam-coated and bare metal coils for aneurysm occlusion in the rabbit elastase model.

Shape memory polymer (SMP) foam-coated coils (FCCs) are new embolic coils coated with porous SMP designed to expand for increased volume filling and enhanced healing after implantation. The purpose of this study was to compare chronic aneurysm healing after treatment with SMP FCCs to bare platinum coil (BPC) controls in the rabbit elastase aneurysm model. BPCs or SMP FCCs were implanted in rabbit elastase-induced aneurysms for follow-up at 30 days (n = 10), 90 days (n = 5), and 180 days (n = 12 for BPCs; n = 14 for SMP FCCs).

Highly Cross-Linked Shape Memory Polymers with Tunable Oxidative and Hydrolytic Degradation Rates and Selected Products Based on Succinic Acid.

Minimally invasive medical devices are of great interest, with shape memory polymers (SMPs) representing one such possibility for producing these devices. Previous work with low density, highly porous SMPs has demonstrated oxidative degradation, while attempts to incorporate hydrolytic degradation have resulted in rapidly decreasing glass transition temperature (T ), ultimately preventing strain fixity of the materials at clinically relevant temperatures. Through esterification of the amino alcohol triethanolamine, an alcohol containing network was synthesized and incorporated into SMPs.

Light scattering by pulmonary alveoli and airway surface liquid using a concentric sphere model.

We employ a concentric sphere Mie scattering model to describe light scattering by pulmonary alveoli and airway surface liquid (ASL). Using this layered sphere model, we compare alveolar scattering at different points along the respiratory cycle and observe the effect of ASL thickness on light scattering in the lung. We have also extrapolated the model to investigate alveolar scattering in various animal models of pulmonary disease.

A computational thrombus formation model: application to an idealized two-dimensional aneurysm treated with bare metal coils.

Cardiovascular implantable devices alter the biofluid dynamics and biochemistry of the blood in which they are placed. These perturbations can lead to thrombus formation which may or may not be desired, depending on the application. In this work, a computational model is developed that couples biofluid dynamics and biochemistry to predict the clotting response of blood to such devices.