Embolization of the false lumen using IMPEDE-FX embolization plugs as part of treatment of an infrarenal post-dissection aneurysm: a case report

Shape memory polymer technology in peripheral vascular embolization

OBJECTIVES

Porous, radiolucent, shape memory polymer is a new technology available in discrete peripheral vascular embolization devices. Shape memory polymers can exist in two stable shapes; crimped for catheter delivery and expanded for vessel embolization. The expanded shape memory polymer in these new devices is hemostatic, and the porous polymeric scaffold has been shown to support tissue ingrowth and eventually bioabsorbs in preclinical animal studies. This report describes clinical experience with this novel material in vascular plug devices.

METHODS

a prospective, single-arm, safety study at a single center in New Zealand with longer term follow-up via retrospective imaging review. The study device was a pushable shape memory polymer vascular plug with a distal nitinol anchor coil and a proximal radiopaque marker.

RESULTS

Ten male patients were each implanted with a single shape memory polymer vascular plug. Three inferior mesenteric arteries and an accessory renal artery were embolized during endovascular aneurysm repair. An internal iliac artery was treated prior to the open surgical repair of aorto-iliac aneurysms. An internal iliac artery and a subclavian artery were embolized to treat/prophylactically address potential endoleaks. A profunda branch was embolized prior to tumor resection, and two testicular veins were embolized to treat varicoceles. Acute technical success of target vessel embolization was achieved in all implantation cases. Patients were followed for 30 days as part of the study, and no serious adverse events with a relationship to the study device occurred. No recurrent clinical symptoms attributable to treated vessel embolization or recanalization were documented. There was no evidence of recanalization on retrospective review of follow-up imaging through a mean of 22.2 months (range, <1-44 months) post-procedure.

CONCLUSIONS

Shape memory polymer vascular embolization devices were safe and effective over the follow-up period of this small safety study. Further experience and longer term follow-up will assess further applicability.

Degrees of macrophage-facilitated healing in aneurysm occlusion devices

Insufficient healing of aneurysms following treatment with vascular occlusion devices put patients at severe risk of fatal rupture. Therefore, promoting healing and not just occlusion is vital to enhance aneurysm healing. Following occlusion device implantation, healing is primarily orchestrated by macrophage immune cells, ending with fibroblasts depositing collagen to stabilize the aneurysm neck and dome, preventing rupture. Several modified occlusion devices are available currently on-market. Previous in vivo work demonstrated that modifications of occlusion devices with a shape memory polymer foam had enhanced aneurysm healing outcomes. To better understand cellular response to occlusion devices and improve aneurysm occlusion device design variables, we developed an in vitro assay to isolate prominent interactions between devices and key healing players: macrophages and fibroblasts. We used THP-1 monocyte derived macrophages and human dermal fibroblasts in our cell culture models. Macrophages were allowed device contact with on-market competitor aneurysm occlusion devices for up to 96 h, to allow for any spontaneous device-driven macrophage activation. Macrophage secreted factors were captured in the culture media, in response to device-specific activation. Fibroblasts were then exposed to device-conditioned macrophage media (with secreted factors alone), to determine if there were any device-induced changes in collagen secretion. Our in vitro studies were designed to test the direct effect of devices on macrophage activation, and the indirect effect of devices on collagen secretion by fibroblasts to promote aneurysm healing and stabilization. Over 96 h, macrophages displayed significant migration toward and interaction with all tested devices. As compared to other devices, shape memory polymer foams (SMM, Shape Memory Medical) induced significant changes in gene expression indicating a shift toward an anti-inflammatory pro-healing M2-like phenotype. Similarly, macrophages in contact with SMM devices secreted more vascular endothelial growth factor (VEGF) compared with other devices. Macrophage conditioned media from SMM-contacted macrophages actively promoted fibroblast secretion of collagen, comparable to amounts observed with exogenous stimulation via VEGF supplementation. Our data indicate that SMM devices may promote good aneurysm healing outcomes, because collagen production is an essential step to ultimately stabilize an aneurysm.

Active aortic aneurysm sac treatment with shape memory polymer during endovascular aneurysm repair

Preprocedural image analysis and intraprocedural techniques to fully treat infrarenal abdominal aortic aneurysm sacs outside of the endograft with shape memory polymer (SMP) devices during endovascular aneurysm repair were developed. Prospective, multicenter, single-arm studies were performed. SMP is a porous, self-expanding polyurethane polymer material. Target lumen volumes (aortic flow lumen volume minus endograft volume) were estimated from the preprocedural imaging studies and endograft dimensions. SMP was delivered immediately after endograft deployment via a 6F sheath jailed in a bowed position in the sac. Technical success was achieved in all cases, defined as implanting enough fully expanded SMP volume to treat the actual target lumen volume.

A novel self-expanding shape memory polymer coil for intracranial aneurysm embolization: 1 year follow-up in Chile

BACKGROUND

Aneurysm recurrence remains a challenge when coiling cerebral aneurysms. Development of next generation coils has focused on accelerating thrombus maturation and increasing coil packing density. Ultra low density shape memory polymer is a novel embolic material designed for this purpose. The polymer is crimped over a platinum-tungsten coil for catheter delivery and self-expands to a predefined volume on contact with blood.

METHODS

This prospective study in humans evaluated aneurysms 5-16 mm (inclusive) in diameter that were indicated for endovascular coil embolization. At least 70% coil volume was required to be shape memory polymer coils. Patients were followed-up according to standard of care for 12 months.

RESULTS

Nine patients (89% women, mean age 55.8±11.7 years) were treated with shape memory polymer coils and completed 12 months of follow-up. Aneurysms were all unruptured and were in the ophthalmic segment of the internal carotid artery (n=7), posterior communicating artery, and anterior cerebral artery A1-A2 segment. Aneurysms were a mean of 7.8±2.9 mm in diameter (range 5.2-14.9 mm). The mean packing density based on unexpanded polymer was 17±6%. Packing density based on expanded polymer was 43±13%. At 12 months, no recurrence had occurred, and a Raymond-Roy occlusion classification of 1 (n=5) or 2 (n=4) was observed. No serious adverse events related to the study device occurred over the 12 months after the procedure.

CONCLUSIONS

Shape memory polymer coils were safe and effective in treating intracranial aneurysms over 12 months in this first study in human subjects.

Feasibility of aortic aneurysm sac embolization using a novel shape memory polymer embolic device

BACKGROUND

We investigated the feasibility of aneurysm sac embolization using a novel self-expanding porous shape memory polymer (SMP) device during endovascular aortic abdominal or thoracic aneurysm repair (EVAR).

METHODS

Retrospective analysis of consecutive patients treated at 2 centers in Germany. Patients were treated from January 2019 to July 2021 with follow-up at 7 days and 3, 6, and 12 months. Aneurysm sacs were implanted with SMP devices immediately following endograft placement during the same procedure. Primary endpoint was technically successful SMP-device deployment into the aneurysm sac outside the endograft. Secondary endpoints were changes in aneurysm volume and associated complications (e.g., endoleaks).

RESULTS

We included 18 patients (16 males), aged 72 ± 9 years, achieving 100% technical success. Mean preprocedure aortic aneurysm sac volume was 195 ± 117 mL with a perfused aneurysm volume of 97 ± 60 mL. A mean of 24 ± 12 SMP devices per patient were used (range 5-45, corresponding to 6.25-56.25 mL expanded embolic material volume). All evaluable patients exhibited sac regression except 2 patients yet to reach 3-month follow-up. At mean 11 ± 7 months (range 3-24), change in aneurysm volume from baseline was -30 ± 21 mL (p < 0.001). In 8 patients, aneurysm regression was observed despite type 2 endoleaks in 6 and type 1A endoleaks in 2, none of them requiring further intervention to date. No morbidity or mortality related to this treatment occurred.

CONCLUSIONS

SMP devices for aortic aneurysm sac embolization during endovascular repair appear feasible and safe in this small case series. Prospective studies are needed.

KEY POINTS

• Shape memory polymer is a novel, self-expanding, porous, and radiolucent embolic device material. • Aortic aneurysm sacs were treated with polymer devices immediately following endograft placement. • Aortic aneurysm sac regression was observed in all patients with over 3-month follow-up. • Aortic aneurysm sac regression was observed even in the presence of endoleaks.

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.

Smart scaffolds: shape memory polymers (SMPs) in tissue engineering

Smart scaffolds based on shape memory polymer (SMPs) have been increasingly studied in tissue engineering. The unique shape actuating ability of SMP scaffolds has been utilized to improve delivery and/or tissue defect filling. In this regard, these scaffolds may be self-deploying, self-expanding, or self-fitting. Smart scaffolds are generally thermoresponsive or hydroresponsive wherein shape recovery is driven by an increase in temperature or by hydration, respectively. Most smart scaffolds have been directed towards regenerating bone, cartilage, and cardiovascular tissues. A vast variety of smart scaffolds can be prepared with properties targeted for a specific tissue application. This breadth of smart scaffolds stems from the variety of compositions employed as well as the numerous methods used to fabricated scaffolds with the desired morphology. Smart scaffold compositions span across several distinct classes of SMPs, affording further tunability of properties using numerous approaches. Specifically, these SMPs include those based on physically cross-linked and chemically cross-linked networks and include widely studied shape memory polyurethanes (SMPUs). Various additives, ranging from nanoparticles to biologicals, have also been included to impart unique functionality to smart scaffolds. Thus, given their unique functionality and breadth of tunable properties, smart scaffolds have tremendous potential in tissue engineering.