Biomaterials and design in occlusion devices for cardiac defects: a review

Near-Infrared Remotely Controllable Shape Memory Biodegradable Occluder Based on Poly(l-lactide-co-ε-caprolactone)/Gold Nanorod Composite

Biodegradable occluders, which can efficiently eliminate the complications caused by permanent foreign implants, are considered to be the next-generation devices for the interventional treatment of congenital heart disease. However, the controllability of the deployment process of degradable occluders remains a challenge. In this work, a near-infrared (NIR) remotely controllable biodegradable occluder is explored by integrating poly(l-lactide-co-ε-caprolactone) (PLCL) with poly(ethylene glycol)-modified gold nanorods (GNR/PEG). The caprolactone structural units can effectively increase the toughness of poly(l-lactide) and reduce the shape-memory transition temperature of the occluder to a more tissue-friendly temperature. Gold nanorods endow the PLCL-GNR/PEG composite with an excellent photothermal effect. The obtained occluder can be easily loaded into a catheter for transport and spatiotemporally expanded under irradiation with near-infrared light to block the defect site. Both in vitro and in vivo biological experiments showed that PLCL-GNR/PEG composites have good biocompatibility, and the PEGylated gold nanorods could improve the hemocompatibility of the composites to a certain extent by enhancing their hydrophilicity. As a thermoplastic shape-memory polymer, PLCL-GNR/PEG can be easily processed into various forms and structures for different patients and lesions. Therefore, PLCL-GNR/PEG has the potential to be considered as a competitive biodegradable material not only for occluders but also for other biodegradable implants.

4D Printing of Overall Radiopaque Customized Bionic Occlusion Devices

Percutaneous closure of ventricular septal defect (VSD) can effectively occlude abnormal blood flow between ventricles. However, commonly used Nitinol occlusion devices have non-negligible limitations, such as nondegradability leading to life-threatening embolization; limited device size predisposing to displacement and wear; only a few radiopaque markers resulting in inaccurate positioning. Nevertheless, the exploration of customized, biodegradable, and overall radiopaque occluders is still vacant. Here, overall radiopaque, biodegradable, and dynamic reconfigurable 4D printed VSD occluders are developed. Based on wavy bionic structures, various VSD occluders are designed and manufactured to adapt to the position diversity of VSD. The customized configuration, biocompatibility, and biodegradability of the developed 4D printed bionic occluders can eliminate the series of complications caused by traditional occluders. The overall radiopacity of 4D printed VSD occluders is validated ex vivo and in vivo, whereby accurate positioning can be assured. Notably, the preparation strategies for 4D printed occluders are scalable, eliminating the barriers to mass production, and marking a meaningful step in bridging the gap between modeling and clinical application of 4D printed occlusion devices. This work opens attractive perspectives for the rapid manufacturing of customized intelligent medical devices for which overall radiopacity, dynamic reconfigurability, biocompatibility, and biodegradability are sought.

Development of Innovative Biomaterials and Devices for the Treatment of Cardiovascular Diseases

Cardiovascular diseases have become the leading cause of death worldwide. The increasing burden of cardiovascular diseases has become a major public health problem and how to carry out efficient and reliable treatment of cardiovascular diseases has become an urgent global problem to be solved. Recently, implantable biomaterials and devices, especially minimally invasive interventional ones, such as vascular stents, artificial heart valves, bioprosthetic cardiac occluders, artificial graft cardiac patches, atrial shunts, and injectable hydrogels against heart failure, have become the most effective means in the treatment of cardiovascular diseases. Herein, an overview of the challenges and research frontier of innovative biomaterials and devices for the treatment of cardiovascular diseases is provided, and their future development directions are discussed.

Pre-clinical Evolution of a Novel Transcatheter Bioabsorbable ASD/PFO Occluder Device

To date, there has been limited investigation of bioabsorbable atrial septal defect (ASD) or patent foramen ovale (PFO) closure devices using clinically relevant large animal models. The purpose of this study is to explore the function and safety of a bioabsorbable ASD occluder (BAO) system for PFO and/or secundum ASD transcatheter closure. Using a sheep model, the intra-atrial septum was evaluated by intracardiac echo (ICE). If a PFO was not present, atrial communication was created via transseptal puncture. Device implantation across the intra-atrial communication was performed with fluoroscopic and ICE guidance. Our 1st generation device consisted of a main structure of thin Poly(L-lactide-co-epsilon-caprolactone) (PLCL) fibers, and an internal Poly glycolic acid (PGA) fabric. Four procedures validated procedure feasibility. Subsequently, device design was modified for improved transcatheter delivery. The 2nd generation device has a two-layered structure and was implanted in six sheep. Results showed procedural success in 9/10 (90%) animals. With deployment, the 1st generation device did not reform into its original disk shape and did not conform nicely along the atrial septum. The 2nd generation device was implanted in six animals, 3 out of 6 survived out to 1 year. At 1 year post implantation, ICE confirmed no residual shunting. By necropsy, biomaterials had partially degraded, and histology of explanted samples revealed significant device endothelialization and biomaterial replacement with a collagen layer. Our results demonstrate that our modified 2nd generation BAO can be deployed via minimally invasive percutaneous transcatheter techniques. The BAO partially degrades over 1 year and is replaced by host native tissues. Future studies are needed prior to clinical trials.

A Prospective, Single-Center, Phase I Clinical Trial to Evaluate the Value of Transesophageal Echocardiography in the Closure of Patent Foramen Ovale With a Novel Biodegradable Occluder

Objective

Traditional metal alloy occluders for the closure of patent foramen ovale (PFO) may be associated with some potential complications, and may restrict the trans-septal access to the left atrium for future treatment of left-sided heart disease. Increasing attention has been paid to novel biodegradable occluders (NBOs) to achieve PFO closure. We aimed to evaluate the role of transesophageal echocardiography (TEE) in the diagnostic and anatomical evaluation of PFO, as well as in the Post-procedural assessment after transcatheter closure with a NBO.

Methods

We conducted a prospective, single-center clinical study of 44 patients who were diagnosed with PFO by contrast transthoracic echocardiography (c-TTE) and TEE from June 2019 to June 2020. All patients underwent PFO occlusion with NBO under TTE guidance. Follow-up was performed at 2 days and 3 months after the procedure with TTE, and at 6 months and 1 year after the procedure with c-TTE, TTE, and TEE.

Results

Interventional treatment was successfully performed in all patients. The left and right sides of the occluder device disc were significantly reduced at 3, 6, and 12 months compared to 2 days after the procedure (all P < 0.01), and decreased gradually. The thickness was significantly reduced at 12 months compared to the first three time points (all P < 0.01). Thrombus was found on the surface of the occluder device in three patients (6.4%) at 3 and 6 months after occlusion. At 6 months after procedure, there were 3 (6.8%) cases of extensive residual right-to-left shunt (RLS), 2 (4.5%) cases of moderate shunt, and 7 (15.9%) cases of small shunts. One year after procedure, 2 (4.5%) cases had a extensive residual shunt, 6 (13.6%) cases of small shunts were confirmed to originate from pulmonary veins by TEE, and the PFO-RLS occlusion rate reached 95.5%.

Conclusion

This study demonstrates the feasibility, safety, and effectiveness of NBO for the closure of PFO in humans, with a high rate of complete shunt closure. Accurate TEE assessment of the PFO anatomy before closure with NBO is important to ensure that the procedure remains safe and effective. Furthermore, TEE plays a crucial role in the Post-procedure follow-up.

Surface modification to enhance cell migration on biomaterials and its combination with 3D structural design of occluders to improve interventional treatment of heart diseases

The dominant source of thromboembolism in heart comes from the left atrial appendage (LAA). An occluder can close LAA and significantly reduce the risk of strokes, particularly for those patients with atrial fibrillation. However, it is technically challenging to fabricate an LAA occluder that is appropriate for percutaneous implantation and can be rapidly endothelialized to accomplish complete closure and avoid severe complication. Hypothesizing that a fast migration rate of endothelial cells on the implant surface would lead to rapid endothelialization, we fabricated an LAA occlusion device for interventional treatment with a well-designed 3D architecture and a nanoscale 2D coating. Through screening of biomaterials surfaces with cellular studies in vitro including cell observations, qPCR, RNA sequencing, and implantation studies in vivo, we revealed that a titanium-nitrogen nanocoating on a NiTi alloy promoted high migration rate of endothelial cells on the surface. The effectiveness of this first nanocoating LAA occluder was validated in animal experiments and a patient case, both of which exhibited successful implantation, fast sealing and long-term safety of the device. The mechanistic insights gained in this study will be useful for the design of medical devices with appropriate surface modification, not necessarily for improved cell adhesion but sometimes for enhanced cell migration.

Recent developments in next-generation occlusion devices

Transcatheter closure has been widely accepted as a highly effective way to treat abnormal blood flows and/or embolization of thrombus in the heart. It allows the closure of four types of congenital heart defects (CHDs) and stroke-associated left atrial appendage (LAA). The four types of CHDs include atrial septal defect (ASD), patent foramen ovale (PFO), patent ductus arteriosus (PDA), and ventricular septal defect (VSD). Advancements in the materials and configurations of occlusion devices have spurred the transition from open-heart surgery with high complexity and morbidity, or lifelong medication with a high risk of bleeding, to minimally invasive deployment. A variety of occlusion devices have been developed over the past few decades, particularly novel ones represented by biodegradable and 3D-printed occlusion devices, which are considered as next-generation alternatives to conventional Nitinol-based occlusion devices due to biodegradability, customization, and improved biocompatibility. The aim here is to comprehensively review the next-generation occlusion devices in terms of materials, configurations, manufacturing methods, deployment strategies, and (if available) experimental results or clinical data. The current challenges and the direction of future work are also proposed. STATEMENT OF SIGNIFICANCE: Implantation of occlusion devices has become a widely accepted and highly effective treatment for occluding abnormal blood/thrombus flow within the heart. Due to the serious complications such as erosion and displacement of conventional Nitinol-based occluders, next-generation occluders with reduced risk of complications and improved biocompatibility has emerged. Here, we comprehensively review the next-generation occluders developed for atrial septal defect (ASD), patent foramen ovale (PFO), patent ductus arteriosus (PDA), ventricular septal defect (VSD), and left atrial appendage (LAA), with special emphasis on biodegradable occluders. Besides, intelligent materials (e.g., automatically deployable shape memory polymers) and rapid customized manufacturing methods (3D/4D printing) for the fabrication of occluders are also introduced. Lastly, the directions of future work are highlighted.

4D Printing of Bioinspired Absorbable Left Atrial Appendage Occluders: A Proof-of-Concept Study

The significant mismatch of mechanical properties between the implanted medical device and biological tissue is prone to cause wear and even perforation. In addition, the limited biocompatibility and nondegradability of commercial Nitinol-based occlusion devices can easily lead to other serious complications, such as allergy and corrosion. The present study aims to develop a 4D printed patient-specific absorbable left atrial appendage occluder (LAAO) that can match the deformation of left atrial appendage (LAA) tissue to reduce complications. The desirable bioinspired network is explored by iterative optimization to mimic the stress-strain curve of LAA tissue and LAAOs are designed based on the optimal network. In vitro degradation tests are carried out to evaluate the effects of degradation on mechanical properties. In addition, 48 weeks of long-term subcutaneous implantation of the occluder shows favorable biocompatibility, and the 20-cycle compression test demonstrates outstanding durability of LAAO. Besides, a rapid, complete, and remote-controlled 4D transformation process of LAAO is achieved under the trigger of the magnetic field. The deployment of the LAAO in an isolated swine heart initially exhibits its feasibility for transcatheter LAA occlusion. To the best of our knowledge, this is the first demonstration of the 4D printed LAA occlusion device. It is worth noting that the bioinspired design concept is not only applicable to occlusion devices, but also to many other implantable medical devices, which is conducive to reducing complications, and a broad range of appealing application prospects can be foreseen.

Biodegradable atrial septal defect occluders: A current review

Atrial septal defect (ASD) is a common structural congenital heart disease. With the development of interventional closure devices and transcatheter techniques, interventional closure therapy has become the most well-accepted therapeutic alternative worldwide, as it offers a number of advantages over conventional therapies such as improved safety, easier operation, lower complication rates and invasiveness, and shorter anesthetic time and hospitalizations. During the past decades, various types of occluders based on nondegradable shape memory alloys have been used in clinical applications. Considering that the permanent existence of foreign nondegradable materials in vivo can cause many potential complications in the long term, the research and development of biodegradable occluders has emerged as a crucial issue for interventional treatment of ASD. This review aims to summarize partially or fully biodegradable occlusion devices currently reported in the literature from the aspects of design, construction, and evaluation of animal experiments. Furthermore, a comparison is made on the advantages and disadvantages of the materials used in biodegradable ASD occlusion devices, followed by an analysis of the problems and limitations of the occlusion devices. Finally, several strategies are proposed for future development of biodegradable cardiac septal defect occlusion devices. STATEMENT OF SIGNIFICANCE: Although occlusion devices based on nondegradable alloys have been widely used in clinical applications and saved numerouspatients, biodegradable occlusion devices may offer some advantages such as fewer complications, acceptable biocompatibility, and particularly temporary existence, thereby leaving "native" tissue behind, which will certainly become the development trend in the long term. This review summarizes almost all partially or fully biodegradable occlusion devices currently reported in the literature from the aspects of design, construction, and evaluation of animal experiments. Furthermore, a comparison is made on the advantages and disadvantages of the materials used in biodegradable ASD occlusion devices, followed by an analysis of the problems and limitations of the occlusion devices. Finally, several strategies are proposed for future development of biodegradable cardiac septal defect occlusion devices.

Atrial septal defect closure with the new Cardia Ultrasept II™ device with interposed Goretex patch: Mexican experience - has the perforation of Ivalon's membrane been solved?

OBJECTIVES

The objective of this study was to demonstrate the safety and feasibility of using the new Cardia Ultrasept II™ device with interposed Goretex patch referring to the perforation of polyvinyl alcohol membrane.

BACKGROUND

Great advances have been made in the development of devices for closure of atrial septal defect. The Cardia Ultrasept II™ with interposed Goretex patch is the modified last generation of Cardia devices, having the advantage of a super-low profile within the atria and an integral locking delivery-retrieval mechanism that ensures safe deployment. In addition, with the interposition of the Goretex, it has been possible to abolish perforation of Ivalon's membrane as a complication.Methods and resultsPatients with ostium secundum atrial septal defect with surrounding rims with a minimum length of 5 mm and who underwent atrial septal defect closure with the new Ultrasept II™ with Goretex patch were included from two paediatric cardiac centres. Primary end point was to determine perforation of the Goretex membrane at follow-up; secondary end point included right ventricular diastolic diameter. In total, 30 patients underwent atrial septal defect closure at a median age of 6 (1-29) years. At follow-up for 6 (range, 1-15) months, freedom from perforations was 100%. A continuous decrease in right ventricular diastolic diameter was found with an initial median of 30 (25-49) mm and after catheterisation of 27.5 (18-33) mm, p=0.01, and Z-score of 2.6 (1.7-3.6) versus 1.9 (1-2.9) after procedure, p=0.01.

CONCLUSIONS

The new modified generation of the Ultrasept II™ device with interposed Goretex patch is a good alternative to achieve atrial septal defect closure safely and feasibly with no membrane perforation at follow-up.

A comparison of the in vivo neoendothelialization and wound healing processes of three atrial septal defect occluders used during childhood in a nonrandomized prospective trial

Objective:

We prospectively investigated the neoendothelialization of transcatheter secundum atrial septal defect (ASD) closure in children receiving one of three different occluders.

Methods:

Transcatheter ASD closure was performed for 44 children. The patients were divided into three groups: group I: Amplatzer, group II: Lifetech CeraFlex, and group III: Occlutech Figulla Flex II septal occluder. The data were prospectively analyzed. Markers of the three phases of wound healing were studied in all patients before and on the 1^st and 10^th days and 1^st month post intervention.

Results:

The mean age of children was 7.08±3.51 years, and the mean weight was 26.07±15.07 kg. The mean ASD diameter was 12.65±3.50 mm. Groups I, II, and III comprised 34.1%, 31.8%, and 34.1% patients, respectively. No significant differences were observed between the groups regarding patient number, age, defect size, device diameter, or total septum/device ratio (p>0.05). Inflammatory and proliferative phase marker levels increased following the procedure (p<0.05). However, scar formation markers did not change after 1 month. No significant differences in neoendothelializaton were observed among the different occluders (p>0.05).

Conclusion:

All three devices were composed of nitinol with different surface coating techniques. Although the different manufacturing features were claimed to facilitate of neoendothelialization, no differences were observed among the three devices 1 month following the procedure.

Translation in cardiovascular stents and occluders: From biostable to fully degradable

Cardiovascular disease is a major cause of morbidity and mortality, especially in developed countries. Most academic research efforts in cardiovascular disease management focus on pharmacological interventions, or are concerned with discovering new disease markers for diagnosis and monitoring. Nonpharmacological interventions with therapeutic devices, conversely, are driven largely by novel materials and device design. Examples of such devices include coronary stents, heart valves, ventricular assist devices, and occluders for septal defects. Until recently, development of such devices remained largely with medical device companies. We trace the materials evolution story in two of these devices (stents and occluders), while also highlighting academic contributions, including our own, to the evolution story. Specifically, it addresses not only our successes, but also the challenges facing the translatability of concepts generated via academic research.

Migraine Modulation and Debut after Percutaneous Atrial Septal Defect Closure: A Review

INTRODUCTION

Change in migraine headache (MH)-preexisting MH change or development of de novo MH-are known potential complications following percutaneous closure of atrial septal defect (ASD), but consensus on a causal trigger remains elusive.

OBJECTIVES

To expose potential MH triggers linked, mainly by timing and occurrence, to the emergence of de novo MH or change in preexisting MH subsequent to percutaneous ASD closure (pASDC).

METHODS

The literature was systematically searched for studies available in English reporting MH status after pASDC published between January 1, 1990 and November 15, 2015. We determined the number and percentage of patients experiencing MH status change within 7 days post procedure and the cumulative total by final follow-up (Mdn = 12 months).

RESULTS

Twenty-five studies met the inclusion criteria, which accounted for a total of 1,646 pASDC patients. Pre-procedure MH prevalence was 8% (126/1,646). Change in preexisting MH occurred in a total of 72% (91/126), 12% (11/91) within 7-days after pASDC; within follow-up MH improved in 14% (18/126), resolved in 37% (47/126), but persisted in 63% (79/126). De novo MH incidence ranged between 10 (153/1,520) and 18.3% (153/836); 34% incipience (52/153) was within 7-days of pASDC; females accounted for 80% (63/79) of gender differentiated cases; of type distinguished cases, 42% (51/122) were MH without aura (MO) and 58% (71/122) were MH with aura (MA); MH improved in 10% (16/153), resolved in 24% (37/153) but persisted beyond final follow-up in 76% (116/153). Antiplatelet agents were effective modulators of MH in 44% (11/25) studies. Possible adverse MH-predisposing traits were scarce: larger ASD size reported in ~2% (39/1,646) of patients experiencing de novo MH or preexisting MH exacerbation; short aortic rim reported in three de novo MH patients; allergic response to occluder nickel alloy in four patients with MH status change from baseline (de novo or preexisting MH change not specified).

INTERPRETATION

Early intensification of MH status change but later amelioration (virtually paralleling stages of endothelialization), relatively high efficacy of antiplatelet agents, and the emergence of MA as the dominant de novo MH type favor proinflammatory triggers of MH status change after pASDC.

Device-in-device: A transcatheter alternative to surgical explantation of a failing atrial septal defect intracardiac prosthesis

A failing intracardiac device is traditionally addressed by open-heart surgery. Surgical explantation of the device, although a simple procedure, carries risks that some patients are not able or willing to cope with. Thus, a nonsurgical option seems desirable in selected cases. We report on four cases of early malfunction of the Polyvinyl Alcohol membrane of Ultrasept II™ CARDIA ASD devices. In all cases, transthoracic echo (TTE) surveillance 4-6 months after the index procedure, depicted significant left-to-right atrial shunts through the center portion of the devices. A second nitinol double disk device with a connecting pin (Lifetech CERA™ Multifenestrated ASD device) was implanted over the CARDIA devices, with excellent results. All procedures were uneventful and all patients are asymptomatic with no residual shunts, in short-term follow-up. This device-in-device technique prevents surgical explantation of failing ASD devices, and may become a less invasive option in selected patients. © 2016 Wiley Periodicals, Inc.

The mechanical behavior and biocompatibility of polymer blends for Patent Ductus Arteriosus (PDA) occlusion device

Patent Ductus Arteriosus (PDA) is a cardiovascular defect that occurs in 1 out of every 2000 births, and if left untreated, may lead to severe cardiovascular problems. Current options for occluding utilize meta scaffolds with polymer fabric, and are permanent. The purpose of this study was to develop a fully degradable occluder for the closure of PDA, that can be deployed percutaneously without open-heart surgery. For percutaneous deployment, both elasticity and sufficient mechanical strength are required of the device components. As this combination of properties is not achievable with currently-available homo- or copolymers, blends of biodegradable poly(ε-caprolactone) (PCL) and poly(L-lactide-co-ε-caprolactone) (PLC) with various compositions were studied as the potential material for the PDA occlusion device. Microstructures of this blend were characterized by differential scanning calorimetry (DSC) and tensile tests. DSC results demonstrated the immiscibility between PCL and its copolymer PLC. Furthermore, the mechanical properties, i.e. elastic modulus and strain recovery, of the blends could be largely tailored by changing the continuous phase component. Based on the thermo-mechanical tests, suitable blends were selected to fabricate a prototype of PDA occluder and its in vitro performance, in term of device recovery (from its sheathed configuration), biodegradation rate and blood compatibility, was evaluated. The current results indicate that the device is able to recover elastically from a sheath within 2-3min for deployment; the device starts to disintegrate within 5-6 months, and the materials have no adverse effects on the platelet and leucocyte components of the blood. Biocompatibility implantation studies of the device showed acceptable tissue response. Finally, an artificial PDA conduit was created in a pig model, and the device deployment was tested from a sheath: the device recovered within 2-3min of unsheathing and fully sealed the conduit, the device remains stable and is completely covered by tissue at 1 month follow up. Thus, a novel prototype for PDA occlusion that is fully degradable has been developed to overcome the limitations of the currently used metal/fabric devices.