Biomaterials Used in Injectable Implants (Liquid Embolics) for Percutaneous Filling of Vascular Spaces

Single Component Polymers, Polymer Blends, and Polymer Composites for Interventional Endovascular Embolization of Intracranial Aneurysms

Intracranial aneurysm is the abnormal focal dilation in brain arteries. When untreated, it can enlarge to rupture points and account for subarachnoid hemorrhage cases. Intracranial aneurysms can be treated by blocking the flow of blood to the aneurysm sac with clipping of the aneurysm neck or endovascular embolization with embolics to promote the formation of the thrombus. Coils or an embolic device are inserted endovascularly into the aneurysm via a micro-catheter to fill the aneurysm. Many embolization materials have been developed. An embolization coil made of soft and thin platinum wire called the "Guglielmi detachable coil" (GDC) enables safer treatment for brain aneurysms. However, patients may experience aneurysm recurrence because of incomplete coil filling or compaction over time. Unsatisfactory recanalization rates and incomplete occlusion are the drawbacks of endovascular embolization. So, the fabrication of new medical devices with less invasive surgical techniques is mandatory to enhance the long-term therapeutic performance of existing endovascular procedures. For this aim, the current article reviews polymeric materials including blends and composites employed for embolization of intracranial aneurysms. Polymeric materials used in embolic agents, their advantages and challenges, results of the strategies used to overcome treatment, and results of clinical experiences are summarized and discussed.

Polymerisation of cyanoacrylates: The effect of sclero-embolic and contrast agents

OBJECTIVES

The objective is to investigate the interaction of sclero-embolic and contrast agents with the polymerisation of medical grade n-butyl-cyanoacrylates.

METHODS

An in vitro spectrophotometric absorbance method was developed to detect changes in light transmission to measure n-BCA polymerisation. The initiation and the rate-of-polymerisation of mixtures of n-BCA with sclero-embolic and contrast agents were investigated.

RESULTS

Initiation of polymerisation: VENABLOCK™ and HISTOACRYL® were the fastest agents to polymerise, while VENASEAL™ was the slowest. Rate of polymerisation: Hypertonic saline inhibited the polymerisation of all n-BCAs, while hypertonic glucose prolonged the polymerisation rate. ETHANOL and detergent sclerosants had no effect. Contrast agents OMNIPAQUE™ and ULTRAVIST® initiated and prolonged the polymerisation of n-BCA, but in contrast, LIPIODOL® failed to initiate the process.

CONCLUSIONS

The commercially available medical cyanoacrylates differ in their polymerisation rates. These polymerisation rates are further affected when these products are used in conjunction with other compounds, such as sclero-embolic and contrast agents.

Liquid Embolic Agents for Endovascular Embolization: A Review

Endovascular embolization (EE) has been used for the treatment of blood vessel abnormalities, including aneurysms, AVMs, tumors, etc. The aim of this process is to occlude the affected vessel using biocompatible embolic agents. Two types of embolic agents, solid and liquid, are used for endovascular embolization. Liquid embolic agents are usually injectable and delivered into the vascular malformation sites using a catheter guided by X-ray imaging (i.e., angiography). After injection, the liquid embolic agent transforms into a solid implant in situ based on a variety of mechanisms, including polymerization, precipitation, and cross-linking, through ionic or thermal process. Until now, several polymers have been designed successfully for the development of liquid embolic agents. Both natural and synthetic polymers have been used for this purpose. In this review, we discuss embolization procedures with liquid embolic agents in different clinical applications, as well as in pre-clinical research studies.

Silk-elastinlike protein-based hydrogels for drug delivery and embolization

Silk-Elastinlike Protein-Based Polymers (SELPs) can form thermoresponsive hydrogels that allow for the generation of in-situ drug delivery matrices. They are produced by recombinant techniques, enabling exact control of monomer sequence and polymer length. In aqueous solutions SELP strands form physical crosslinks as a function of temperature increase without the addition of crosslinking agents. Gelation kinetics, modulus of elasticity, pore size, drug release, biorecognition, and biodegradation of SELP hydrogels can be controlled by placement of amino acid residues at strategic locations in the polymer backbone. SELP hydrogels have been investigated for delivery of a variety of bioactive agents including small molecular weight drugs and fluorescent probes, oligomers of glycosaminoglycans, polymeric macromolecules, proteins, plasmid DNA, and viral gene delivery systems. In this review we provide a background for use of SELPs in matrix-mediated delivery and summarize recent investigations of SELP hydrogels for controlled delivery of bioactive agents as well as their use as liquid embolics.

Angiographic Embolization with Histoacryl in Combination with Direct Injection of Bone Cement of an Intraosseous Venous Malformation of the Mandible: Report of a Case with 22-Year Follow-Up

Vascular malformations of the maxillofacial region are unusual, and they occur more rarely in bone than in soft tissue. Mandibular intraosseous vascular lesions represent 0.5-1.0% of all bone tumors, and they are classified as venous malformation, lymphatic malformation, arterial malformation, arteriovenous malformations, and arteriovenous fistulae. Venous malformation is the most common vascular malformation, accounting for 44-64% of all vascular malformations, and is considered a low-flow malformation. Endovascular therapy as selective angiographic embolization is considered as the first-choice treatment associated or not with emboli injections with a success rate of 70%, and this evades mutilating surgery and related sequelae. We report a case of mandibular venous malformation on a 45-year-old female complaining of unilateral swelling of the left body of the mandible with facial deformation. The computed tomography scan images and the T1-weighted MR images showed a lesion that expresses an expansible lesion in the spongy bone of the left of the mandible with a buccal cortical rupture. Signal voids were not identified, suggesting a low-flow vascular lesion. The T2-weighted images exposed hypersignals; accordingly, a vascular lesion was suspected. The treatment was done under locoregional analgesia; after selective angiography, direct histoacryl injection was completed, followed by bone cement injection. The patient was followed yearly since1998. Radiological images of 10-year follow-up MRI showed a stabilization of the lesion without any new extensions. The panoramic radiograph after 22 years showed a bone formation inside the body of the mandible. The long follow-up period and the absence of any complications are favorable for the adopted treatment plan.

Injectable hydrogels for vascular embolization and cell delivery: The potential for advances in cerebral aneurysm treatment

Cerebral aneurysms are vascular lesions caused by the biomechanical failure of the vessel wall due to hemodynamic stress and inflammation. Aneurysmal rupture results in subarachnoid hemorrhage often leading to death or disability. Current treatment options include open surgery and minimally invasive endovascular options aimed at secluding the aneurysm from the circulation. Cerebral aneurysm embolization with appropriate materials is a therapeutic approach to prevent rupture and the resultant clinical sequelae. Metallic platinum coils are a typical, practical option to embolize cerebral aneurysms. However, the development of an alternative treatment modality is of interest because of poor occlusion permanence, coil migration, and coil compaction. Moreover, minimizing the implanted foreign materials during therapy is of importance not just to patients, but also to clinicians in the event an open surgical approach has to be pursued in the future. Polymeric injectable hydrogels have been investigated for transcatheter embolization and cell therapy with the potential for permanent aneurysm repair. This review focuses on how the combination of injectable embolic biomaterials and cell therapy may achieve minimally invasive remodeling of a degenerated cerebral artery with promise for superior outcomes in treatment of this devastating disease.

Application of a rabbit-elastase aneurysm model for preliminary histology assessment of the PPODA-QT liquid embolic

Background

PPODA-QT is a novel liquid embolic under development for the treatment of cerebral aneurysms. We sought to test the rabbit-elastase aneurysm model to evaluate the tissue response following PPODA-QT embolization.

Methods

Experimental elastase-induced aneurysms were created in fourteen New Zealand White Rabbits. Eight animals were used for aneurysm model and endovascular embolization technique development. Six PPODA-QT-treated animals were enrolled in the study. Control and aneurysm tissues were harvested at acute (n = 2), 1-month (n = 2), and 3-month (n = 2) timepoints and the tissues were prepared for histology assessment.

Results

All fourteen rabbit-elastase aneurysms resulted in small and medium aneurysm heights (<10 mm dome height) with highly variable neck morphologies, small midline dome diameters, and beyond-wide dome-to-neck (d: n) ratios. Histological evaluation of four aneurysms, treated with PPODA-QT, demonstrated reorganization of aneurysm wall elastin into a smooth muscle layer, and observed as early as the 1-month survival timepoint. At the aneurysm neck, a homogenous neointimal layer (200-300 μm) formed at the PPODA-QT interface, sealing off the parent vessel from the aneurysm dome. No adverse immune response was evident at 1- and 3-month survival timepoints.

Conclusion

PPODA-QT successfully embolized the treated aneurysms. Following PPODA-QT embolization, neointimal tissue growth and remodeling were noted with minimal immunological response. The experimental aneurysms created in rabbits were uniformly small with inconsistent neck morphology. Further testing of PPODA-QT will be conducted in larger aneurysm models for device delivery optimization and aneurysm healing assessment before human clinical investigation.

Safety and Efficacy of Peripheral Embolization with EASYX Liquid Embolic Agent: A Multicenter Prospective Study

PURPOSE

To evaluate the clinical safety and efficacy of EASYX, a new nonadhesive precipitating liquid embolic agent based on a polyvinyl alcohol ether polymer labeled with iodine molecules, for peripheral embolization.

MATERIALS AND METHODS

This open-label prospective multicenter study was conducted on 50 consecutive patients treated with embolization using EASYX in 3 academic hospitals from April 2018 to July 2019. Indications for embolization were symptomatic varicocele (n = 15), type II endoleak (n = 8), acute hemorrhage (n = 16), portal vein embolization (PVE; n = 9), or angiomyolipoma (AML; n = 2). Patient characteristics, technical and clinical success rates, pain at injection, and satisfaction of the interventional radiologists were assessed. Follow-up imaging was performed using ultrasound for varicoceles (at 1 month) and computed tomography (CT) for the other indications (at 3 or 6 months).

RESULTS

The immediate technical success rate was 98%. The clinical success rates were 100% for acute hemorrhage and type II endoleaks, 89% for PVE, 86% for varicoceles, and 50% for AMLs. Patients who underwent PVE showed significant hypertrophy of the future liver remnant at follow-up (P < .001), and 55.6% of patients proceeded to hepatectomy. The absence of artifacts on imaging allowed improved monitoring of the aneurysmal sac in patients with type II endoleaks. The satisfaction rate of the interventional radiologists was >90% for 5 of 7 items.

CONCLUSIONS

EASYX as a novel copolymer liquid embolic agent was safe and efficient for peripheral embolization. The absence of tantalum allowed reduced CT artifacts on imaging follow-up, which was especially useful in patients with type II endoleaks.

Treatment of experimental aneurysms with a GPX embolic agent prototype: preliminary angiographic and histological results

Background

Recently, liquid embolic agents have emerged for the endovascular treatment of cerebral aneurysms. Here we describe the in vivo performance of a novel liquid embolization agent (GPX Embolic Device).

Methods

Elastase-induced aneurysms were embolized with a GPX prototype under balloon assistance. Digital subtraction angiography was performed pre-deployment and immediately after, and at 5, 10, and 30 min post-deployment in 10 rabbits and at 1 month in 8 rabbits. The early post-deployment intra-aneurysmal flow was graded as unchanged, moderately diminished, or completely absent. At 1 month the status of aneurysm occlusion was evaluated. Adhesion to catheter material and migration of GPX was assessed.

Results

The mean aneurysm neck diameter, width, and height were 3.6±1.0 mm, 3.0±0.8 mm, and 7.4±1.4 mm, respectively. The mean dome-to-neck ratio was 0.9±0.2. Complete stagnation of intra-aneurysmal flow was observed in 9 of 10 aneurysms (90%) within 30 min of device deployment. One aneurysm showed moderately diminished intra-aneurysmal flow at 30 min. At 1 month, 8 aneurysms were completely occluded. There was no evidence of GPX adhesion to the catheter material. Histologically, a leukocyte and foreign body reaction to GPX was detectable 28 days after embolization.

Conclusions

This is the first preclinical study reporting the performance of a protype version of the GPX Embolic Device in a wide-neck aneurysm model. GPX showed promising results by achieving and maintaining high rates of complete angiographic occlusion, but may induce an inflammatory reaction.

Embolization of Vascular Malformations via In Situ Photocrosslinking of Mechanically Reinforced Alginate Microfibers using an Optical-Fiber-Integrated Microfluidic Device

Embolization, which is a minimally invasive endovascular treatment, is a safe and effective procedure for treating vascular malformations (e.g., aneurysms). Hydrogel microfibers obtained via spatiotemporally controllable in situ photocrosslinking exhibit great potential for embolizing aneurysms. However, this process is challenging because of the absence of biocompatible and morphologically stable hydrogels and the difficulty in continuously spinning the microfibers via in situ photocrosslinking in extreme endovascular environments such as those involving a tortuous geometry and high absorbance. A double-crosslinked alginate-based hydrogel with tantalum nanopowder (DAT) that exploits the synergistic effect of covalent crosslinking by visible-light irradiation and ionic crosslinking using Ca2+ , which is present in the blood, is developed in this study. Furthermore, an effective strategy to design and produce an optical-fiber-integrated microfluidic device (OFI-MD) that can continuously spin hydrogel microfibers via in situ photocrosslinking in extreme endovascular environments is proposed. As an embolic material, DAT exhibits promising characteristics such as radiopacity, nondissociation, nonswelling, and constant mechanical strength in blood, in addition to excellent cyto- and hemo-compatibilities. Using OFI-MD to spin DAT microfibers continuously can help fill aneurysms safely, uniformly, and completely within the endovascular simulator without generating microscopic fragments, which demonstrates its potential as an effective embolization strategy.

Thermo-sensitive composite hydrogels based on poloxamer 407 and alginate and their therapeutic effect in embolization in rabbit VX2 liver tumors

Interventional embolization therapy is an effective, most widely used method for inoperable liver tumors. Blood-vessel-embolic agents were essential in transarterial embolization (TAE). In this work, thermo-sensitive composite hydrogels based on poloxamer 407, sodium alginate, hydroxymethyl cellulose and iodixanol (PSHI), together with Ca2+ (PSHI-Ca2+) were prepared as liquid embolic agents for TAE therapy to liver cancer. With increasing temperature, PSHI exhibited two phase states: a flowing sol and a shrunken gel. Rheology tests showed good fluidity and excellent viscoelastic behavior with a gelation temperature (GT) of 26.5°C. The studies of erosion indicated that PSHI had calcium ion-related erosion characteristics and showed a slow erosion rate in an aqueous environment. When incubated with L929 cells, the thermo-sensitive composite hydrogels had low cytotoxicity in vitro. The results of analyzing the digital subtraction angiography and computed tomography images obtained from in vitro and in vivo assays indicated a good embolic effect in the renal arteries of normal rabbits. Angiography and histological studies on VX2 tumor-bearing rabbits indicated that PSHI-Ca2+ successfully occluded the tumors, including the peripheral vessels. In conclusion, PSHI-Ca2+ was a promising embolic agent for transarterial embolization therapy.

Polymeric materials for embolic and chemoembolic applications

Percutaneous transcatheter embolization procedures involve the selective occlusion of blood vessels. Occlusive agents, referred to as embolics, vary in material characteristics including chemical composition, mechanical properties, and the ability to concurrently deliver drugs. Commercially available polymeric embolics range from gelatin foam to synthetic polymers such as poly(vinyl alcohol). Current systems under investigation include tunable, bioresorbable microspheres composed of chitosan or poly(ethylene glycol) derivatives, in situ gelling liquid embolics with improved safety profiles, and radiopaque embolics that are trackable in vivo. This article reviews commercially available materials used for embolization as well as polymeric materials that are under investigation.

Controlled Release of Hepatocyte Growth Factor from MPEG-b-(PCL-ran-PLLA) Diblock Copolymer for Improved Vocal Fold Regeneration

An in situ-forming gel system comprised of diblock copolymer formed from polyethylene glycol (PEG) and polycaprolactone (PCL) {MPEG-b-(PCL-ran-PLLA)} could be used in controlled drug delivery for tissue remodeling. The purpose of this study is to demonstrate favorable vocal folds (VF) regeneration by using MPEG-b-(PCL-ran-PLLA) diblock copolymers (C97L3; CL/LA ratio 97:3) incorporating hepatocyte growth factor (HGF). Gradual release of HGF from C97L3 is detected and biochemical properties of released HGF are maintained. A scar is made with microscissors on both VFs in 32 rabbits, followed by injection of HGF-only, C97L3-only, or HGF-C97L3 composite gel in the left side VF, while the right side VF is left untreated. In vivo fluorescence live imaging system demonstrates that C97L3 enables the sustained release of injected HGF in the scarred VF for 12 weeks. The histological analysis shows increased glycosaminoglycan including hyaluronic acid accumulation and decreased collagen deposition. Videokymographic analysis shows more favorable vibrations of HGF-C97L3 treated VF mucosa, compared to other treatment groups. In conclusion, the controlled HGF release helps to regulate extracellular matrix synthesis, and leads to the eventual functional improvement of the scarred VF.

Novel Hydrogel Material as a Potential Embolic Agent in Embolization Treatments

We report a novel graphene-oxide (GO) enhanced polymer hydrogel (GPH) as a promising embolic agent capable of treating cerebrovascular diseases and malignant tumors, using the trans-catheter arterial embolization (TAE) technique. Simply composed of GO and generation five poly(amidoamine) dendrimers (PAMAM-5), our rheology experiments reveal that GPH exhibits satisfactory mechanical strength, which resist the high pressures of blood flow. Subcutaneous experiments on Sprague-Dawley (SD) rats demonstrate the qualified biocompatibility of GPH. Finally, our in vivo experiments on New Zealand rabbits, which mix GPH with the X-ray absorbing contrast agent, Iohexol, reveal complete embolization of the artery. We also note that GPH shortens embolization time and exhibits low toxicity in follow-up experiments. Altogether, our study demonstrates that GPH has many advantages over the currently used embolic agents and has potential applications in clinical practice.

Design and biocompatibility of endovascular aneurysm filling devices

The rupture of an intracranial aneurysm, which can result in severe mental disabilities or death, affects approximately 30,000 people in the United States annually. The traditional surgical method of treating these arterial malformations involves a full craniotomy procedure, wherein a clip is placed around the aneurysm neck. In recent decades, research and device development have focused on new endovascular treatment methods to occlude the aneurysm void space. These methods, some of which are currently in clinical use, utilize metal, polymeric, or hybrid devices delivered via catheter to the aneurysm site. In this review, we present several such devices, including those that have been approved for clinical use, and some that are currently in development. We present several design requirements for a successful aneurysm filling device and discuss the success or failure of current and past technologies. We also present novel polymeric-based aneurysm filling methods that are currently being tested in animal models that could result in superior healing.

Temperature-sensitive poly(N-isopropylacrylamide-co-butyl methylacrylate) nanogel as an embolic agent: distribution, durability of vascular occlusion, and inflammatory reactions in the renal artery of rabbits

BACKGROUND AND PURPOSE

We have developed a new thermosensitive liquid embolic agent, PIB nanogel, that can be solidified at body temperature. We thus further investigated the distribution, durability of vascular occlusion, and inflammatory reactions of PIB in embolization of the renal artery of rabbits.

MATERIALS AND METHODS

The bilateral renal arteries of 9 rabbits were first embolized with PIB at different injection rates. The distribution pattern of PIB was investigated by contact radiography and histology 1 hour after embolization. The right renal arteries of 20 rabbits were then embolized with PIB at the proper injection rate. Angiography and pathologic examination of the kidneys were performed at 1 week and 1, 2, and 3 months after embolization to evaluate the long-term outcomes.

RESULTS

With the injection rate increasing, PIB could reach the more distal branch of the renal artery. The proper injection rate was chosen as 0.10 mL/s due to the homogeneous distribution of PIB from the main renal artery to the precapillary level at this rate. During a 3-month follow-up observation period, no angiographic recanalization was observed. Histologically, we found no disruption of the vessel wall or subintimal bleeding, no extravasation of PIB, and no evidence of neovascularization. Moreover, there was only a mild inflammatory response, manifested by few lymphocytic and monocellular infiltration, without foreign body granuloma formation.

CONCLUSIONS

Embolization of the renal artery with PIB was easy and controllable, which could lead to a homogeneous and persistent occlusion without severe inflammatory changes. PIB might be a suitable material for intravascular embolization.

Vitamin E triggers poly(2-hydroxyethyl methacrylate) (PHEMA) embolic potential: a proposed application for endovascular surgery

Poly(2-hydroxyethyl methacrylate) (PHEMA) is a biocompatible polymer used as embolizing agent for endovascular surgery. Blending of PHEMA with a hydrophobic and anti-oxidant agent, Vitamin E (Vit.E, 0.1-10%, w/v), modified PHEMA's haemocombatibility, evaluated measuring wettability, plasma protein adsorption along with whole blood coagulation time. The presence of Vit.E increases PHEMA's hydrophobicity and plasma protein adsorption (in particular albumin and Immunoglobulin G), while it also accelerates blood clot formation. These effects are developed due to a combination of issues such as surface hydrophobicity and plasma protein adsorption induced by the presence of Vit.E, suggesting that Vit.E blending could improve the use of PHEMA as embolizing agent.

Treatment of pseudoaneurysm of internal maxillary artery: a case report

Pseudoaneurysms are rare lesions secondary to blunt or penetrating trauma, temporomandibular joint surgery, or orthognathic surgery. Nonsurgical interventions are the treatment of choice for pseudoaneurysms. In the case reported here, endovascular injection of acrylic glue was successful in the treatment of a pseudoaneurysm of the internal maxillary artery secondary to fracture of the zygomatic bone.

Fast thermoresponsive BAB-type HEMA/NIPAAm triblock copolymer solutions for embolization of abnormal blood vessels

Thermoresponsive BAB-type HEMA/NIPAAm triblock copolymers (A = NIPAAm, B = HEMA) were prepared by atomic transfer radical polymerization (ATRP). BAB1-6 with shorter PNIPAAm blocks failed to form stable gel; while a relatively stable gel could be achieved by BAB1-8 with longer PNIPAAm blocks when copolymer aqueous solution was heated up. Introducing radiopaque agent (RA) was shown to slightly increase the transition temperature and gelation time, but the gelling ability was strengthened due to slightly weakening dehydration of copolymer in the mixture of water and RA. BAB1-8 aqueous solution about 5 wt% in the presence of RA was demonstrated to successfully occlude the cerebral rete mirabiles (RMs) and renal arteries of pigs. Within 3-month surgery, no recanalization was observed and the embolized kidney shrank considerably. Histological assay of embolized kidney demonstrated interstitial fibrosis and calcification as well as the thickening of renal small artery. This temperature sensitive copolymer with well-defined architecture holds a great potential as an embolic agent for treating arteriovenous malformations (AVMs) and renal disease due to the design flexibility of ATRP.