Star-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 (i.e., the melt transition temperature or Tm of PCL) must be reduced from ∼55 °C that is observed for scaffolds prepared from linear-PCL-DA (Mn ∼ 10 kg mol-1). Moreover, increasing the rate of biodegradation would be advantageous, facilitating bone tissue healing and potentially eliminating the need for stent retrieval. Herein, a series of six UV-curable PCL macromers were prepared with linear or 4-arm star architectures and with Mns of 10, 7.5, and 5 kg mol-1, and subsequently fabricated into six porous scaffold compositions (10k, 7.5k, 5k, 10k★, 7.5k★, and 5k★) via solvent casting particulate leaching (SCPL). Scaffolds produced from star-PCL-tetraacrylate (star-PCL-TA) macromers produced pronounced reductions in Tm with decreased Mnversus those formed with the corresponding linear-PCL-diacrylate (linear-PCL-DA) macromers. Scaffolds were produced with the desired reduced Tm profiles: 37 °C < Tm < 55 °C (self-fitting bone scaffold), and Tm ≤ 37 °C (self-expanding stent). As macromer Mn decreased, crosslink density increased while % crystallinity decreased, particularly for scaffolds prepared from star-PCL-TA macromers. While shape memory behavior was retained and radial expansion pressure increased, this imparted a reduction in modulus but with an increase in the rate of degradation.

Fabrication and In Vivo Assessment of Oxidatively Responsive PolyHIPE Scaffolds for Use in Diabetic Orthopedic Applications.

Achieving surgical success in orthopedic patients with metabolic disease remains a substantial challenge. Diabetic patients exhibit a unique tissue microenvironment consisting of high levels of reactive oxygen species (ROS), which promotes osteoclastic activity and leads to decreased bone healing. Alternative solutions, such as synthetic grafts, incorporating progenitor cells or growth factors, can be costly and have processing constraints. Previously, the potential for thiol-methacrylate networks to sequester ROS while possessing tunable mechanical properties and degradation rates has been demonstrated. In this study, the ability to fabricate thiol-methacrylate interconnected porous scaffolds using emulsion templating to create monoliths with an average porosity of 97.0% is reported. The average pore sizes of the scaffolds range from 27 to 656 µm. The scaffolds can sequester pathologic levels of ROS via hydrogen peroxide consumption and are not impacted by sterilization. Subcutaneous implantation shows no signs of acute toxicity. Finally, in a 6-week bilateral calvarial defect model in Zucker diabetic fatty rats, ROS scaffolds increase new bone volume by 66% over sham defects. Histologic analysis identifies woven bone infiltration throughout the scaffold and neovascularization. Overall, this study suggests that porous thiol-methacrylate scaffolds may improve healing for bone grafting applications where high levels of ROS hinder bone growth.

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. The impact of diameter, length, pore size, and shape memory effect was evaluated to determine the ideal device design for tract sealing. Characterization in an in vitro benchtop lung model identified that diameter had the largest influence on sealing efficacy, while the length of the device had little to no impact. Finally, evaluation of deployment force demonstrated that devices fabricated from the shape memory polymer foams were easier to deploy than elastic foams. Following characterization, down-selected device designs were combined with radiopaque markers for use in image-guided based procedures. Furthermore, the introduction of the markers or sterilization did not impact the ability of the devices to seal the biopsy tract and led to a decrease in the deployment force. Overall, these results demonstrate the potential for polyurethane-based shape memory foam devices to serve as biopsy tract sealant devices that aim to reduce complications, such as pneumothorax, from occurring.

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. This limits the use across multiple imaging modalities and for device testing when anatomical considerations as well as tissue properties are needed. This work reports a lung phantom design utilizing materials that accurately mimic the ultrasound and magnetic resonance imaging (MRI) properties of in vivo lungs and includes relevant anatomical equivalence. METHODS: The tissue mimicking materials were selected based on published studies of the materials, through qualitative comparisons of the materials with ultrasound imaging, and quantitative MRI relaxation values. A PVC ribcage was used as the structural support. The muscle/fat combined layer and the skin layer were constructed with various types of silicone with graphite powder added as a scattering agent where appropriate. Lung tissue was mimicked with silicone foam. The pleural layer was replicated by the interface between the muscle/fat layer and the lung tissue layer, requiring no additional material. RESULTS: The design was validated by accurately mimicking the distinct tissue layers expected with in vivo lung ultrasound while maintaining tissue-mimicking relaxation values in MRI as compared to reported values. Comparisons between the muscle/fat material and in vivo muscle/fat tissue demonstrated a 1.9% difference in T1 relaxation and a 19.8% difference in T2 relaxation. CONCLUSIONS: Qualitative US and quantitative MRI analysis verified the proposed lung phantom design for accurate modeling of the human lungs.

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. The gelation kinetics, swelling properties, and rheological properties of various hydrogel formulations were studied to determine the optimal formulation for composite fabrication. Composites were then fabricated via vacuum infiltration of the PEG hydrogel precursors into the SMP foam followed by thermal curing. After drying, the composites were crimped to enable insertion into biopsy tracts. Characterization revealed that the composites exhibited a slight delay in shape recovery compared to control SMP foams. However, the composites were still able to recover their shape in a matter of minutes. Cytocompatibility testing showed that leachable byproducts can be easily removed by washing and washed composites were not cytotoxic to mouse lung fibroblasts (L929s). Benchtop testing demonstrated that the composites can be easily deployed through a cannula, and the working time for deployment after exposure to water was 2 min. Furthermore, testing in an in vitro lung model demonstrated that the composites were able to effectively seal a lung biopsy tract and prevent air leakage. Collectively, these results show that the PEG hydrogel/SMP foam composites have the potential to be used as lung biopsy tract sealants to prevent pneumothorax post-lung biopsy.

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). Detailed analysis of foam microarchitecture (i.e., struts and membranes) was used to estimate total relative mass loss over time. PED foams implanted in porcine arteries showed a degradation rate of ~0.11% per day as evaluated at 30-, 60-, and 90-day explant timepoints. NED foams implanted in rabbit carotid elastase aneurysms showed a markedly faster rate of degradation at ~1.01% per day, with a clear difference in overall degradation between 30- and 90-day explants. Overall, membranes degraded faster than the struts. NEDs use more hydrophobic foam with a smaller pore size (~150-400 µm) compared to PED foams (~800-1200 µm). Previous in vitro studies indicated differences in the degradation of the two polymer systems, but not to the magnitude seen in vivo. Implant location, animal species, and local tissue health are among the hypothesized reasons for different degradation rates.

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. Lower concentration of chemical blowing agent yielded foams with thick foam struts due to less bubble formation during the foaming process. Foams with thicker struts also had high tensile modulus and lower strain at break values compared to the foams made with higher blowing agent concentration. Additionally, less blowing agent resulted in foams with a lower glass transition temperature due to less urea formation during the foaming reaction. This exploratory study provides an approach to control thermo-mechanical foam properties and morphology by tuning concentrations of a foaming additive. This work aims to broaden the applications of shape memory polymer foams for medical use.

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. Unfortunately, salvage surgeries have a similar rate of failure attributed to delayed healing, bone graft dissolution, and the lack of bone ingrowth. Furthermore, patients who suffer from neuropathic comorbidities such as diabetes suffer from a diminished healing capacity. An increase in proinflammatory factors and the high presence of reactive oxygen species (ROS) present in diabetics are linked to lower fusion rates. To this end, there is a need for a clinically relevant bone graft to promote bone fusions in patients with neuropathic comorbidities. Incorporating thiol-ene networks for bone scaffolds has demonstrated increased osteogenic biomarkers over traditional polymeric materials. Furthermore, thiol-ene networks can act as antioxidants. Sulfide linkages within the network have an inherent ability to consume radical oxygen to create sulfoxide and sulfone groups. These unique properties of thiol-ene networks make them a promising candidate as bone grafts for diabetic patients. In this work, we propose a thiol-ene biomaterial to address the current limitations of MPJ fusion in diabetics by characterizing mechanical properties, degradation rates under accelerated conditions, and oxidative responsiveness under pathophysiologic conditions. We also demonstrated that thiol-ene-based materials could reduce the number of hydroxyl radicals associated with neuropathic comorbidities.

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). This work explores the errors introduced when using histological sections to evaluate mass loss. METHODS: Models of the SMP foams were created to mimic the device geometry and the tetrakaidekahedral structure of the foam pore. These models were degraded in Blender for a wide range of possible degradation amounts and the mass loss was estimated using m sections. RESULTS: As the number of sections (m) used to estimate mass loss for a volume increased the sampling error decreased and beyond m = 5, the decrease in error was insignificant. NED population and sampling errors were higher than for PED scenarios. When m ≥ 5, the averaged sampling error was below 1.5% for NED and 1% for PED scenarios. DISCUSSION/CONCLUSION: This study establishes a baseline sampling error for estimating randomly degraded porous scaffolds using a sectional method. Device geometry and the stage of mass loss influence the sampling error. Future studies will use non-random degradation to further investigate in vivo mass loss scenarios.

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. To improve the mechanical and shape memory properties of this system, we incorporate vinyl side chains in the polymer backbone which enable crosslinking via thiol-ene click chemistry post fabrication. We also discuss a novel technique to improve photoinitiated crosslinking for electrospun materials. A material with these properties is potentially beneficial for various medical applications, such as vascular anastomosis, and the characterization of this material will be valuable in directing those applications.

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. Macrophages are the most prevalent immune cell type that coordinate the greater immune response to implanted materials. Hence, we hypothesized that the highly porous SMP foam coatings on embolic coils activate a pro-regenerative healing phenotype. To test this hypothesis, we analyzed the number and type of infiltrating macrophages in FCC or BPC devices implanted in a rabbit elastase aneurysm model. FCC devices elicited a great number of infiltration macrophages, skewed significantly to a pro-regenerative M2-like phenotype 90 days following implantation. We devised an in vitro assay, where monocyte-derived macrophages were placed in close association with FCC or BPC devices for 6-72 h. Macrophages encountering SMP FCC-devices demonstrated highly mixed activation phenotypes at 6 h, heavily skewing toward an M2-like phenotype by 72 h, compared with macrophages encountering BPC devices. Macrophage activation was evaluated using gene expression analysis, and secreted cytokine evaluation. Together, our results demonstrate that FCC devices promoted a pro-regenerative macrophage activation phenotype, compared with BPC devices. Our in vitro findings corroborate with in vivo observations that SMP-based modification of embolic coils can promote better healing of the aneurysm site, by sustaining a pro-healing macrophage phenotype.

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, Mn∼10 kg mol-1) and linear-poly(l-lactic acid) (PLLA, Mn∼15 kg mol-1) [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 (Tfit∼55 °C; related to the Tm of PCL) required for shape recovery (i.e. expansion) and subsequent shape fixation during press fitting of the scaffold, which can be harmful to surrounding tissue. Additionally, the viscosity of the solvent-based precursor solutions, cast over a fused salt template during fabrication, can limit scaffold size. Thus, in this work, analogous semi-IPN SMP scaffolds were formed with a 4-arm star-PCL-tetracryalate (star-PCL-TA) (Mn∼10 kg mol-1) and star-PLLA (Mn∼15 kg mol-1). To assess the impact of a star-polymer architecture, four semi-IPN compositions were prepared: linear-PCL-DA/linear-PLLA (L/L), linear-PCL-DA/star-PLLA (L/S), star-PCL-TA/linear-PLLA (S/L) and star-PCL-TA/star-PLLA (S/S). Two PCL controls were also prepared: LPCL (i.e. 100% linear-PCL-DA) and SPCL (i.e. 100% star-PCL-TA). The S/S semi-IPN scaffold exhibited particularly desirable properties. In addition to achieving a lower, tissue-safe Tfit (∼45 °C), it exhibited the fastest rate of degradation which is anticipated to more favourably permit neotissue infiltration. The radial expansion pressure exerted by the S/S semi-IPN scaffold at Tfit was greater than that of LPCL, which is expected to enhance osseointegration and mechanical stability. The intrinsic viscosity of the S/S semi-IPN macromer solution was also reduced such that larger scaffold specimens could be prepared.

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. Physical and thermomechanical characterization showed the effect of increased gadopentetic acid (GPA) on shape memory behavior. Multiple compositions showed brightening effects in pilot, T1-weighted MR imaging. There was a correlation between the polymeric density and X-ray visibility on expanded and compressed SMP foams. Additionally, extractions and indirect cytocompatibility studies were performed to address toxicity concerns of gadolinium-based contrast agents (GBCAs). This material platform has the potential to be used in a variety of medical devices.

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. In this study, biostable shape memory polymer foams were synthesized, and their physical and chemical properties were characterized as an initial evaluation of feasibility for vascular occlusion applications. After characterizing their shape memory behavior in an aqueous environment, degradation of this polymer system was studied in vitro using accelerated oxidative and hydrolytic solutions. Results indicated that the foams did not lose mass under oxidative or hydrolytic conditions, and they maintained high shape recovery in aqueous in vitro models. These degradation-resistant systems have potential for use in vascular occlusion and other wound healing applications that benefit from permanent, space-filling shape memory behavior.

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. Currentin vitroaneurysm models suffer from a lack of key functional and morphological features of brain vasculature that limit their applicability for these purposes. These features include the physiologically relevant mechanical properties and the dynamic cellular environment of blood vessels subjected to constant fluid flow. Herein, we developed three-dimensionally (3D) printed aneurysm-bearing vascularized tissue structures using gelatin-fibrin hydrogel of which the inner vessel walls were seeded with human cerebral microvascular endothelial cells (hCMECs). The hCMECs readily exhibited cellular attachment, spreading, and confluency all around the vessel walls, including the aneurysm walls. Additionally, thein vitroplatform was directly amenable to flow measurements via particle image velocimetry, enabling the direct assessment of the vascular flow dynamics for comparison to a 3D computational fluid dynamics model. Detachable coils were delivered into the printed aneurysm sac through the vessel using a microcatheter and static blood plasma clotting was monitored inside the aneurysm sac and around the coils. This biomimeticin vitroaneurysm model is a promising method for examining the biocompatibility and hemostatic efficiency of embolization devices and for providing hemodynamic information which would aid in predicting aneurysm rupture or healing response after treatment.

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)). Over time, the host response to the IMPEDE device included degradation of the foam by multinucleated giant cells, which promoted fibrin and polymer degradation and advanced the healing response. Device effectiveness, in terms of vessel occlusion, was evaluated histologically by assessing the degree of recanalization. Although instances of recanalization were often observed at all time points for both control and test articles, the mature connective tissue within the foam scaffold of the IMPEDE devices improved percent vessel occlusion; when recanalization was observed in IMPEDE-treated vessels, channels were exclusively peri-device rather than intradevice, as often observed in the controls, and the vessels mostly remained >75% occluded. Although total vessel occlusion provides the optimal ischemic effect, in cardiovascular pathology, there is a progressive ischemic effect on the downstream vasculature as a vessel narrows. As such, we expect a sustained ischemic therapeutic effect to be observed in vessels greater than 75% occluded. Overall, the current study suggests the IMPEDE device presents advantages over controls by promoting an enhanced degree of healing within the foam scaffold, which decreases the likelihood of intradevice recanalization and ultimately may lead to a sustained ischemic therapeutic effect.

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. These monomers were used in foam synthesis to provide highly crosslinked SMP foam structures. The ester-containing foams showed clinically relevant thermal properties that were comparable to controls and excellent shape recovery within eight min. Triethanolamine-based ester-containing foams showed interconnected porous structure along with increased mechanical strength. Faster hydrolytic and oxidative biodegradation rates were achieved in ester-containing foams in comparison to controls. These biodegradable SMP foams with clinically applicable thermal properties possess great potential as an effective hemostatic device for use in hospitals or on battlefields.

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. The 3D reconstructions of aneurysms provided context for histologic findings, and aided in the overall aneurysm assessment. At all time points, >75% of the cells categorized in each aneurysm were associated with a bioactive yet biocompatible host response (vs. the remainder of cells that were associated with acute inflammation). The extracellular matrix exhibited a transition from residual fibrin at 30 days to a greater degree of connective tissue at 90 and 180 days. Although the control BPC-treated aneurysms exhibited a greater degree of connective tissue at the earliest time point examined (30 days), by 180 days, the FCC-treated aneurysms had more connective tissue and less debris overall than the control aneurysms. When considering cell types and extracellular matrix composition, the overall host response scores were significantly better in FCC-treated aneurysms at the later time point. Based on the results of these metrics, the FCC device may lead to an advanced tissue remodeling response over BPC occlusion devices.

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. In this work, a computational thrombus model is used to predict the clotting response within idealized 2D aneurysms virtually treated with foam. The results are compared to previously reported clot formation predictions in identical 2D aneurysm geometries filled with simplified endovascular metal coil shapes. Each of the foam-filled aneurysms reached at least 94% thrombus occlusion regardless of foam pore size or orientation, whereas the final thrombus occlusion within the coil-filled aneurysms varied from 80.8 to 92.2% with many of the cases leaving large areas in the aneurysm neck unfilled. Based on the simulations presented here, shape memory polymer foams may be able to produce more predictable, uniform, and complete clotting results than bare metal coils, independent of foam geometry or orientation.

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). Aneurysm occlusion and histologic healing, including a qualitative healing score, neointima thickness, collagen deposition, and inflammation were compared between the two groups. The mean neointima thickness was significantly greater in groups treated with SMP FCCs for all three time points. Histologic healing scores and collagen deposition quantification suggested that aneurysms treated with SMP FCCs experience more complete healing of the dome by 90 days, but the differences were not statistically significant. More progressive occlusion and recanalization were observed in aneurysms treated with SMP FCCs, but neither difference was statistically significant. Additionally, the SMP foam used in the FCCs was found to degrade faster in the rabbit elastase model than expected based on previous studies in a porcine sidewall aneurysm model. This study suggests that SMP FCCs can promote neointima formation along the aneurysm neck, and may lead to more complete healing of the dome and neck. These findings indicate potential benefits of this device for aneurysm occlusion procedures. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B:2466-2475, 2019.