Pulsatile Flow-Induced Fatigue-Resistant Photopolymerizable Hydrogels for the Treatment of Intracranial Aneurysms

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.

Organocatalyzed Phospha-Michael Addition: A Highly Efficient Synthesis of Customized Bis(acyl)phosphane Oxide Photoinitiators

Addition of the P-H bond in bis(mesitoyl)phosphine, HP(COMes)₂ (BAPH), to a wide variety of activated carbon-carbon double bonds as acceptors was investigated. While this phospha-Michael addition does not proceed in the absence of an additive or catalyst, excellent results were obtained with stoichiometric basic potassium or caesium salts. Simple amine bases can be employed in catalytic amounts, and tetramethylguanidine (TMG) in particular is an outstanding catalyst that allows the preparation of bis(acyl)phosphines, R-P(COMes)₂ , under very mild conditions in excellent yields after only a short time. All phosphines RP(COMes)₂ can subsequently be oxidized to the corresponding bis(acyl)phosphane oxides, RPO(COMes)₂ , a substance class belonging to the most potent photoinitiators for radical polymerizations known to date. Thus, a simple and highly atom economic method has been found that allows the preparation of a broad range of photoinitiators adapted to their specific field of application even on a large scale.

Performance of a Hydrogel Coated Nitinol with Oligonucleotide-Modified Nanoparticles Within Turbulent Conditions of Blood-Contacting Devices

INTRODUCTION

Hydrogels offer a wide range of applications in the antithrombotic modification of biomedical devices. The functionalization of these hydrogels with potentially drug-laden nanoparticles in the context of deviceassociated turbulence is critically under-studied. Thus, the purpose of this study was to use a hydrogel-coating nitinol surface as a model to understand the functions of hydrogels and the capture of nanoparticles under clinically relevant flow conditions.

METHODS

Nitinol was coated by an oligonucleotide (ON) functionalized hydrogel. Nanoparticles were functionalized with complementary oligonucleotides (CONs). The capture of CONfunctionalized nanoparticles by the ON-functionalized hydrogel surfaces was studied under both static and dynamic attachment conditions. Fluorescent-labelling of nanoparticles was utilized to assess capture efficacy and resistance to removal by device-relevant flow conditions.

RESULTS

The specificity of the ON-CON bond was verified, exhibiting a dose-dependent attachment response. The hydrogel coating was resistant to stripping by flow, retaining >95% after exposure to one hour of turbulent flow. Attachment of nanoparticles to the hydrogel was higher in the static condition than under laminar flow (p < 0.01), but comparable to that of attachment under turbulent flow. Modified nitinol samples underwent one hour of flow treatment under both laminar and turbulent regimes and demonstrated decreased nanoparticle loss following static conjugation rather than turbulent conjugation (36.1% vs 53.8%, p < 0.05). There was no significant difference in nanoparticle functionalization by upstream injection between laminar and turbulent flow.

CONCLUSION

The results demonstrate promising potential of hydrogelfunctionalized nitinol for capturing nanoparticles using nucleic acid hybridization. The hydrogel structure and ONCON bond integrity both demonstrated a resistance to mechanical damage and loss of biomolecular functionalization by exposure to turbulence. Further investigation is warranted to highlight drug delivery and antithrombogenic modification applications of nanoparticle-functionalized hydrogels.

Photosensitive Hydrogel-Based Embolic Agent Treatment of Wide-Necked Aneurysms: Preliminary Animal Results

Background: The endovascular treatment of cerebral aneurysms has become widespread but may still be limited by recurrence rates or complications. The discovery of novel embolic strategies may help mitigate these concerns. Methods: We formulated a Photosensitive Hydrogel Polymer (PHP) embolic agent which is low-viscosity, shear-thinning, and radio-opaque. After the filling of an aneurysm with PHP with balloon assistance, we utilized photopolymerization to induce solidification. Different methods of light delivery for photopolymerization were assessed in silicone models of aneurysms and in four acute animal trials with venous anastomosis aneurysms in pigs. Then, balloon-assisted embolization with PHP and photopolymerization was performed in three aneurysms in pigs with a one-month follow-up. Filling volume, recurrence rates, and complications were recorded. Results: The PHP was found to be suitable for the intravascular delivery and treatment of cerebral aneurysms. It was found that light delivery through the balloon catheter, as opposed to light delivery through the injection microcatheter, led to higher rates of filling in the 3D model and acute animal model for cerebral aneurysms. Using the balloon-assisted embolization and light delivery strategy, three wide-necked aneurysms were treated without complication. One-month follow-up showed no recurrence or neck remnants. Conclusions: We demonstrated a novel method of balloon-assisted photosensitive hydrogel polymer embolization and photopolymerization, leading to complete aneurysm filling with no recurrence at 1 month in three wide-necked aneurysms in pigs. This promising methodology will be investigated further with longer-term comparative animal trials.

Shape Memory Polymer-Based Endovascular Devices: Design Criteria and Future Perspective

Devices for the endovascular embolization of intracranial aneurysms (ICAs) face limitations related to suboptimal rates of lasting complete occlusion. Incomplete occlusion frequently leads to residual flow within the aneurysm sac, which subsequently causes aneurysm recurrence needing surgical re-operation. An emerging method for improving the rates of complete occlusion both immediately after implant and in the longer run can be the fabrication of patient-specific materials for ICA embolization. Shape memory polymers (SMPs) are materials with great potential for this application, owing to their versatile and tunable shape memory properties that can be tailored to a patient’s aneurysm geometry and flow condition. In this review, we first present the state-of-the-art endovascular devices and their limitations in providing long-term complete occlusion. Then, we present methods for the fabrication of SMPs, the most prominent actuation methods for their shape recovery, and the potential of SMPs as endovascular devices for ICA embolization. Although SMPs are a promising alternative for the patient-specific treatment of ICAs, there are still limitations that need to be addressed for their application as an effective coil-free endovascular therapy.

A Hydrogen Bonds-Crosslinked Hydrogels With Self-Healing and Adhesive Properties for Hemostatic

Hydrogels with adhesive properties have the potential for rapid haemostasis and wound healing in uncontrolled non-pressurized surface bleeding. Herein, a typical hydrogen bond-crosslinked hydrogel with the above functions was constructed by directly mixing solutions of humic acid (HA) and polyvinylpyrrolidone (PVP), in which the HA worked as a crosslinking agent to form hydrogen bonds with the PVP. By altering the concentration of HA, a cluster of stable and uniform hydrogels were prepared within 10 s. The dynamic and reversible nature of the hydrogen bonds gave the HA/PVP complex (HPC) hydrogels injectability and good flexibility, as well as a self-healing ability. Moreover, the numerous functional groups in the hydrogels enhanced the cohesion strength and interaction on the interface between the hydrogel and the substrate, endowing them with good adhesion properties. The unique chemical composition and cross-linking mechanism gave the HPC hydrogel good biocompatibility. Taking advantage of all these features, the HPC hydrogels obtained in this work were broadly applied as haemostatic agents and showed a good therapeutic effect. This work might lead to an improvement in the development of multifunctional non-covalent hydrogels for application to biomaterials.