Transcatheter embolization using degradable crosslinked hydrogels

Embolization therapy with microspheres for the treatment of liver cancer: State-of-the-art of clinical translation

Embolization with microspheres is a therapeutic strategy based on the selective occlusion of the blood vessels feeding a tumor. This procedure is intraarterially performed in the clinical setting for the treatment of liver cancer. The practice has evolved over the last decade through the incorporation of drug loading ability, biodegradability and imageability with the subsequent added functionality for the physicians and improved clinical outcomes for the patients. This review highlights the evolution of the embolization systems developed through the analysis of the marketed embolic microspheres for the treatment of malignant hepatocellular carcinoma, namely the most predominant form of liver cancer. Embolic microspheres for the distinct modalities of embolization (i.e., bland embolization, chemoembolization and radioembolization) are here comprehensively compiled with emphasis on material characteristics and their impact on microsphere performance. Moreover, the future application of the embolics under clinical investigation is discussed along with the scientific and regulatory challenges ahead in the field. STATEMENT OF SIGNIFICANCE: Embolization therapy with microspheres is currently used in the clinical setting for the treatment of most liver cancer conditions. The progressive development of added functionalities on embolic microspheres (such as biodegradability, imageability or drug and radiopharmaceutical loading capability) provides further benefit to patients and widens the therapeutic armamentarium for physicians towards truly personalized therapies. Therefore, it is important to analyze the possibilities that advanced biomaterials offer in the field from a clinical translational perspective to outline the future trends in therapeutic embolization.

One-step preparation of photoclick method for embolic microsphere synthesis and assessment for transcatheter arterial embolization

Vascular embolization is a well-known therapeutic treatment against hepatocellular carcinoma. However, existing embolic agents require complex synthesis, toxic organic solvents and sometimes produce only low yields. In this study, a novel photopolymerization technique, which addresses these issues, was used to prepare embolic microspheres successfully from the sucrose multi-allyl ether monomer in one step. Compared to the preparation of such microspheres always involved in multiple steps or complicated conditions, we obtained the microspheres used photoclick method in a soft template with simple, economic and feasible procedure. This work focuses on the synthesis of new materials by conducting a photopolymerzation in the presence of the sucrose monomer and the photoinitiator. Then, the embolic microspheres obtained were characterized by morphology assay, degradation, and swelling test. Cell experiments showed that the microspheres had good biocompatibility. Rabbit embolizations showed that the microspheres had long-term embolic effects. It is manifested that one-step preparation of photoclick method hold great potential and competitiveness of being used in preparation embolic microspheres in clinic.

Preparation and evaluation of phytantriol liquid crystal as a liquid embolic agent

Transcatheter arterial chemoembolization (TACE) is the preferred treatment for patients with advanced hepatocellular carcinoma (HCC), but it lacks safe and effective embolic agents. 5-Fluorouracil (5-FU) is a broad-spectrum anticancer drug, but its clinical application is limited due to drug resistance and toxic side effects. Therefore, in this study, we developed a new liquid embolic agent with 5-FU as the model drug. We found that this liquid embolic agent possesses good gelling properties and embolic effects. An in vitro drug release model of the agent conformed to the Weibull model. Cumulative release of the drug over 7 d was ∼90%, consisting of an initial burst followed by sustained release. Cytotoxicity testing showed that each liquid embolic composition is cytocompatible and only mildly cytotoxic. Pharmacokinetic experiments showed that the formulation significantly prolongs the t_1/2 of 5-FU (approximately five times that of 5-FU solution) and 5-FU residence time in the body (approximately three times that of 5-FU solution). These results indicate that the liquid embolic agent has embolic capacity and could be used as a potential therapeutic method for TACE.

Advances in Biomaterials and Technologies for Vascular Embolization

Minimally invasive transcatheter embolization is a common nonsurgical procedure in interventional radiology used for the deliberate occlusion of blood vessels for the treatment of diseased or injured vasculature. A wide variety of embolic agents including metallic coils, calibrated microspheres, and liquids are available for clinical practice. Additionally, advances in biomaterials, such as shape-memory foams, biodegradable polymers, and in situ gelling solutions have led to the development of novel preclinical embolic agents. The aim here is to provide a comprehensive overview of current and emerging technologies in endovascular embolization with respect to devices, materials, mechanisms, and design guidelines. Limitations and challenges in embolic materials are also discussed to promote advancement in the field.

Synthesis and assessment of drug-eluting microspheres for transcatheter arterial chemoembolization

Transcatheter arterial chemoembolization (TACE) is well known as an effective treatment for inoperable hepatocellular carcinoma (HCC). In this study, a novel embolic agent of ion-exchange poly(hydroxyethyl methacrylate-acrylic acid) microspheres (HAMs) was successfully synthesized by the inverse suspension polymerization method. Then, HAMs were assessed for their activity as an embolic agent by investigating morphology, particle size, water retention capability, elasticity and viscoelasticity, microcatheter/catheter deliverability, cytotoxicity, renal arterial embolization to rabbits and histopathological examinations. The ability of drug loading and drug eluting of HAMs was also investigated by using doxorubicin (Dox) as the model drug. HAMs showed to be feasible and effective for vascular embolization and to be as a drug vehicle for loading positively charged molecules and potential use in the clinical interventional chemoembolization therapy. STATEMENT OF SIGNIFICANCE: A novel embolic agent of ion-exchange poly(hydroxyethyl methacrylate-acrylic acid) microspheres (HAMs) was successfully synthesized by the inverse suspension polymerization method and was used as a drug vehicle to load positively charged molecules by ion absorption. Then, a series of assessments including physicochemical properties, mechanical properties, drug-loading capability, and embolic efficacy were performed. Surface and cross-section morphology and pore size of fully hydrated HAMs were first investigated by Phenom ProX SEM, which intuitively disclosed the "honeycomb" network morphology. HAMs also showed to be feasible and effective for vascular occlusion and have potential use in clinical interventional embolization therapy.

Semi-interpenetrating network hyaluronic acid microgel delivery systems in micro-flow

Macroscopic hydrogels are commonly used as injectable scaffolds or fillers, however they may easily obstruct blood vessels, which poses risks and limits their clinical use. In the present study, three types of hyaluronic acid (HA)-based hydrogel micro-particles with non-covalent, covalent semi-interpenetrating and conventional 3D molecular networks, have been designed, fabricated and characterized. The micro-particles are spherical, biconcave or irregular in shape and their diameter ranged between 2.5 and 3.5 µm; their suspensions exhibit a tuneable viscosity, shear-thinning behaviour, dynamic stability and dispersity in microfluidic flow as a result of their specific particulate nature, providing thus a well-controlled injectable platform. Hydrogel particle suspensions also demonstrate an enhanced safety profile, in terms of the dispersity, cell safety, and hemocompatibility. In addition, Rhodamine 6G has successfully been loaded and released from the particles as a model for drug delivery. Functionalisation of hydrogel microparticles using synthetic polymers has been proven to be a cost-effective way to achieve desirable rheological properties and flow dynamic stability with improved physicochemical properties and biocompatibility in vitro, showing promise as a multifunctional biomedical material for various advanced surgical devices and therapies.

Advances in Degradable Embolic Microspheres: A State of the Art Review

Considerable efforts have been placed on the development of degradable microspheres for use in transarterial embolization indications. Using the guidance of the U.S. Food and Drug Administration (FDA) special controls document for the preclinical evaluation of vascular embolization devices, this review consolidates all relevant data pertaining to novel degradable microsphere technologies for bland embolization into a single reference. This review emphasizes intended use, chemical composition, degradative mechanisms, and pre-clinical safety, efficacy, and performance, while summarizing the key advantages and disadvantages for each degradable technology that is currently under development for transarterial embolization. This review is intended to provide an inclusive reference for clinicians that may facilitate an understanding of clinical and technical concepts related to this field of interventional radiology. For materials scientists, this review highlights innovative devices and current evaluation methodologies (i.e., preclinical models), and is designed to be instructive in the development of innovative/new technologies and evaluation methodologies.

Drug-eluting embolic microspheres for local drug delivery - State of the art

Embolic microspheres or beads used in transarterial chemoembolization are an established treatment method for hepatocellular carcinoma patients. The occlusion of the tumor-feeding vessels by intra-arterial injection of the beads results in tumor necrosis and shrinkage. In this short review, we describe the utility of using these beads as devices for local drug delivery. We review the latest advances in the development of non-biodegradable and biodegradable drug-eluting beads for transarterial chemoembolization. Their capability to load different drugs, such as chemotherapeutics and anti-angiogenic compounds with different physicochemical properties, like charge and hydrophilicity/hydrophobicity, are discussed. We specifically address controlled and sustained drug release from the microspheres, and the resulting in vivo pharmacokinetics in the plasma vs. drug distribution in the targeted tissue.

Developing an in situ forming polyphosphate coacervate as a new liquid embolic agent: From experimental design to pilot animal study

A radiopaque temporary liquid embolic agent was synthesized from polyphosphate (PP) coacervates and optimized using a design of experiments approach. Variables studied were: strontium substitution (0-15 mol%), barium substitution (0-15 mol%), PP concentration and degree of polymerization of the polyphosphate (Dp). The viscosity, radiopacity and cell viability of the resulting coacervates were measured for 60 formulations and response surface modeling was used to determine the optimum coacervate that maximized radiopacity and cell viability. The optimum coacervate made from PP with a large Dp (9.5 g NaPP/100mL, 2.2 mol% Sr, 9 mol% Ba and 3.8 mol% Ca) was taken forward to a pilot animal trial. In this rabbit model, PP embolic agent successfully occluded the central auricular artery with promising biocompatibility. Further study is required to optimize the cohesiveness and clinical effectiveness of PP as an in situ setting temporary embolic agent.

STATEMENT OF SIGNIFICANCE

This article describes the development of a new radiopaque temporary liquid embolic agent from the optimization using design of experiments to a pilot animal study. Embolization is a minimally invasive interventional radiology procedure used to block blood flow in a targeted blood vessel. This procedure is used to treat many conditions including: tumors, aneurysms and arteriovenous malformations. Currently, no inherent radiopaque embolic agents are available in the clinic, which would allow for direct imaging of the material during the procedure and follow up treatment.

Arming embolic beads with anti-VEGF antibodies and controlling their release using LbL technology

Transarterial chemoembolization (TACE) is used to treat various types of hypervascular tumors such as hepatocellular carcinoma and renal cancer. However, embolization and blocking of blood vessels nourishing a tumor mass evokes an angiogenic response due to the secretion of vascular endothelial growth factor (VEGF), which results in the formation of new blood vessels and eventually limitation in therapeutic efficacy. The presented work investigates the feasibility of loading the clinically used embolic beads (DC Bead®) with Bevacizumab (BEV), an anti-VEGF antibody, and control its release kinetics via Layer-by-Layer (LbL) coating. This strategy has the aim to achieve high, localized and sustained concentrations of BEV at the tumor site and reduce drug exposure in the systemic circulation. High loading of BEV on lyophilized beads of about 76mg BEV/bead vial was achieved. LbL coating was carried out by depositing alternating layers of the biocompatible polymers alginate and poly-L-lysine. Coating was proven successful by monitoring the reversal of zeta potential after addition of each layer. Morphological changes of the bead surface before and after coating were illustrated using SEM imaging. Moreover, release profiles from different formulations were studied and results showed that optimizing the number of deposited layers effectively slows the release of BEV for three days. Activity of released BEV was studied in different 2D and 3D cell based assays. Released BEV fractions showed comparable activity to fresh BEV solution used as control after 3days. In conclusion, our results suggest the opportunity for loading anti-VEGF antibodies on commercially available embolic beads to increase the efficacy of TACE of hypervascular tumors.

pH-Sensitive sulfamethazine-based hydrogels as potential embolic agents for transcatheter vascular embolization

After delivery through a catheter, a three-dimensional hydrogel network was formed upon the change of environmental pH, and thus block the targeted blood vessels, as presented in white color under the fluoroscopic angiogram.

Arrested Phase Separation of Elastin-like Polypeptide Solutions Yields Stiff, Thermoresponsive Gels

The preparation of new responsive hydrogels is crucial for the development of soft materials for various applications, including additive manufacturing and biomedical implants. Here, we report the discovery of a new mechanism for forming physical hydrogels by the arrested phase separation of a subclass of responsively hydrophobic elastin-like polypeptides (ELPs). When moderately concentrated solutions of ELPs with the pentapeptide repeat (XPAVG)n (where X is either 20% or 60% valine with the remainder isoleucine) are warmed above their inverse transition temperature, phase separation becomes arrested, and hydrogels can be formed with shear moduli on the order of 0.1-1 MPa at 20 wt % in water. The longest stress relaxation times are well beyond 10(3) s. This result is surprising because ELPs are classically known for thermoresponsive coacervation that leads to macrophase separation, and solids are typically formed in the bulk or by supplemental cross-linking strategies. This new mechanism can form gels with remarkable mechanical behavior based on simple macromolecules that can be easily engineered. Small angle scattering experiments indicate that phase separation arrests to form a network of nanoscale domains, exhibiting rheological and structural features consistent with an arrested spinodal decomposition mechanism. Gel nanostructure can be modeled as a disordered bicontinuous network with interdomain, intradomain, and curvature length scales that can be controlled by sequence design and assembly conditions. These studies introduce a new class of reversible, responsive materials based on a classic artificial biopolymer that is a versatile platform to address critical challenges in industrial and medical applications.

Calibrated Bioresorbable Microspheres as an Embolic Agent: An Experimental Study in a Rabbit Renal Model

PURPOSE

To evaluate the time frame of resorption and tissue response of newly developed bioresorbable microspheres (BRMS) and vessel recanalization after renal embolization.

MATERIALS AND METHODS

Embolization of lower poles of kidneys of 20 adult rabbits was performed with BRMS (300-500 µm). Two rabbits were sacrificed immediately after embolization (day 0). Three rabbits were sacrificed after follow-up angiography at 3, 7, 10, 14, 21, and 30 days. The pathologic changes in the renal parenchyma, BRMS degradation, and vessel recanalization were evaluated histologically and angiographically.

RESULTS

Embolization procedures were successfully performed, and all animals survived without complication. Infarcts were observed in all kidneys that received embolization harvested after day 0. Moderate degradation of BRMS (score = 1.07 ± 0.06) was observed by day 3. Of BRMS, 95% were resorbed before day 10 with scant BRMS materials remaining in the arteries at later time points. Partial vessel recanalization was observed by angiography starting on day 3, whereas new capillary formation was first identified histologically on day 7. Vascular inflammation associated with BRMS consisted of acute, heterophilic infiltrate at earlier time points (day 3 to day 10); this was resolved with the resorption of BRMS. Inflammation and fibrosis within infarcted regions were consistent with progression of infarction.

CONCLUSIONS

BRMS were bioresorbable in vivo, and most BRMS were resorbed before day 10 with a mild tissue reaction. Vessel recanalization occurred secondary to the resorption of BRMS.

In vitro and in vivo evaluation of chitosan microspheres with different deacetylation degree as potential embolic agent

To evaluate the potential of N-acetylated chitosan microspheres used as a chemoembolic agent in vivo and in vitro. Calibrated spherical chitosan microspheres (CMs) were prepared via Water-in-Oil emulsification method and CMs were acetylated (ACMs). The swelling rate of CMs was greatly affected by pH than that of ACMs and both of them affected by temperature. Microspheres with excellent thermal stability demonstrated controllable degradation in lysozyme solution. Doxorubicin was released from microspheres in vitro and exhibited excellent control release profile. ACMs caused hemolysis less than CMs (<5% of the time). Co-culture with mouse embryo fibroblasts revealed that microspheres have non-cytotoxic nature. Microspheres planted in a rat gluteal muscle demonstrated that it were biodegradable and biocompatible. ACMs were performed in rabbit ear embolization model and ischemic necrosis on ear was visible due to the vascular occlusion after 15 days. Acetylated chitosan microspheres could be used as potential biocompatible and biodegradable embolic agents.

Microfluidic fabrication of 6-methoxyethylamino numonafide-eluting magnetic microspheres

Recently, 6-methoxyethylamino numonafide (MEAN) exhibited potent inhibition of hepatocellular carcinoma (HCC) cell growth and less systemic toxicity than amonafide. MEAN may serve as an ideal candidate for the treatment of HCC; however, liver-directed, selective infusion methods may be critical to maximize the MEAN dose delivered to the targeted tumors. This study describes the microfluidic fabrication of MEAN-eluting ultrasmall superparamagnetic iron oxide (USPIO) nanocluster-containing alginate microspheres (MEAN-magnetic microspheres) intended for selective transcatheter delivery to HCC. The resulting drug delivery platform was mono-disperse, microsphere sizes were readily controlled based on channel flow rates during synthesis procedures, and drug release rates from the microspheres could be readily controlled with the introduction of USPIO nanoclusters. The MR relaxivity properties of the microspheres suggest the feasibility of in vivo imaging after administration, and these microspheres exhibited potent therapeutic effects significantly inhibiting cell growth inducing apoptosis in hepatoma cells.

In vitro and in vivo evaluation of biodegradable embolic microspheres with tunable anticancer drug release

Natural polymer-derived materials have attracted increasing interest in the biomedical field. Polysaccharides have obvious advantages over other polymers employed for biomedical applications due to their exceptional biocompatibility and biodegradability. None of the spherical embolic agents used clinically is biodegradable. In the current study, microspheres prepared from chitosan and carboxymethyl cellulose (CMC) were investigated as a biodegradable embolic agent for arterial embolization applications. Aside from the enzymatic degradability of chitosan units, the cross-linking bonds in the matrix, Schiff bases, are susceptible to hydrolytic cleavage in aqueous conditions, which would overcome the possible shortage of enzymes inside the arteries. The size distribution, morphology, water retention capacity and degradability of the microspheres were found to be affected by the modification degree of CMC. An anticancer drug, doxorubicin, was successfully incorporated into these microspheres for local release and thus for killing cancerous cells. These microspheres demonstrated controllable degradation time, variable swelling and tunable drug release profiles. Co-culture with human umbilical vein endothelial cells revealed non-cytotoxic nature of these microspheres compared to monolayer control (P>0.95). In addition, a preliminary study on the in vivo degradation of the microspheres (100-300μm) was performed in a rabbit renal embolization model, which demonstrated that the microspheres were compatible with microcatheters for delivery, capable of occluding the arteries, and biodegradable inside arteries. These microspheres with biodegradability would be promising for embolization therapies.

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.

Novel polymeric nanoparticles containing tanshinone IIA for the treatment of hepatoma

Novel polylactic acid nanoparticles containing tanshinone IIA (TS-PLA-NPs) were synthesized by a single oil-in-water emulsion/solvent evaporation method. In this study, the optimized nanoparticles were characterized for morphology, mean particle size, zeta potential, entrapment efficiency, drug-loading content, X-ray diffractometer measurement, and in vitro release. The obtained nanoparticles were spherical and intact. The mean particle size was 192.5 nm with polydispersity index being 0.029 and zeta potential - 26.27 mV. The mean entrapment efficiency and loading of tanshinone IIA (TSIIA) in TS-PLA-NPs were 86.35 and 1.61%, respectively. The in vitro release study was performed at pH 7.4 using a dialysis membrane. Without initial burst effect, the TSIIA sustained release from TS-PLA-NPs for more than 7 days. The mean in vitro cumulative release percentage of TSIIA from TS-PLA-NPs vs. time curve fitted well with the Higuchi Equation (Q = 2.0365 + 13.564 x t(1/2), r = 0.9950). In pharmacokinetics and tissue distribution studies, the concentrations of TSIIA are higher in hepatoma and lower in blood, heart, kidney, spleen, and lung at 2 h after TS-PLA-NPs was administered via caudal vein. TS-PLA-NPs were effective in destroying the human liver cancer cells by the Mono-nuclear cell direct cytotoxicity assay (MTT) assay, and the growth-inhibitory effect of TS-PLA-NPs on human liver cancer cells was concentration and time dependent. The effect of TS-PLA-NPs on hepatoma in mice was also performed. The results of TS-PLA-NPs were markedly more effective than both of TSIIA and blank PLA nanoparticles in preventing tumor growth and increasing survival time of mice with hepatoma. This study provided support for the new paradigm, the application of TSIIA for the treatment of hepatoma.

Poly(2-hydroxyethyl methacrylate) emboli with increased haemostatic effect for correction of haemorrhage of complex origin in endovascular surgery of children

Poly(2-hydroxyethyl methacrylate) (PHEMA) embolization particles with enhanced haemostatic properties were prepared by bulk or suspension polymerisation of 2-hydroxyethyl methacrylate (HEMA) followed by particle soaking in ethamsylate solution. The particles accelerated thrombus formation as evidenced by blood analysis of rabbits with implanted emboli. Usefulness of both spherical and cylindrical PHEMA particles with enhanced haemostatic effect was demonstrated on the embolization of arterial anastomosis, fistulas of the lower extremity and abdominal cavity, haemangioma and arteriovenous malformation of the head of several children.

Novel polymeric microspheres containing norcantharidin for chemoembolization

Chemoembolization has been found to be a potentially effective method of treating certain types of cancer. It involves arterial embolization of a tumor, in combination with simultaneous or subsequent local delivery of chemotherapeutic agents. In this study, PLGA-alginate microspheres were evaluated for their potential application in chemoembolization. Norcantharidin, which possesses anti-tumor properties, was used to investigate the application of drug-containing microspheres for chemoembolization. The release profiles of alginate, PLGA and PLGA-alginate microspheres were markedly different in phosphate buffered saline, with the composite microspheres showing the most appropriate release rate for chemoembolization. Burst effect decreased while particle size increased with increasing proportion of alginate in the PLGA-alginate microspheres. PLGA-alginate microspheres containing norcantharidin were effective in destroying the cancer cells used in this study. The growth inhibitory effect was concentration and time dependent. These microspheres also exhibited excellent embolization and therapeutic effects on rats with transplanted tumors.