Perivascular delivery of heparin for the reduction of smooth muscle cell proliferation after endothelial injury

Liquid Drug Delivery Approaches for the Treatment of Occlusive Arterial Disease: A Systematic Review

OBJECTIVE

Local Liquid drug (LLD) delivery devices have recently emerged as a novel approach to treat peripheral arterial disease. This systemic review aims to identify and evaluate the clinical utility of the most commonly used delivery devices.

METHODS

A systemic review was performed using the Medical Subjects Heading terms of "drug delivery," "liquid," "local," and "cardiovascular disease" in PubMed, Google Scholar, and Scopus.

RESULTS

Four commonly used delivery devices were identified, including (1) the Bullfrog Micro-Infusion Device, (2) the ClearWay RX Catheter, (3) the Occlusion Perfusion Catheter, and (4) the Targeted Adjustable Pharmaceutical Administration. All have shown to successfully deliver liquid therapeutic into the target lesion and have exhibited favorable safety and efficacy profiles in preclinical and clinical trials. The LLD devices have the ability to treat very long or multiple lesions with a single device, providing a more economical option. The safety profile in LLD clinical studies is also favorable in view of recent concerns regarding adverse events with crystalline-paclitaxel-coated devices.

CONCLUSION

There is clear clinical evidence to support the concept of local liquid delivery to treat occlusive arterial disease.

CLINICAL IMPACT

The 'leave nothing behind' strategy has been at the forefront of the most recent innovations in the field of interventional cardiology and vascular interventions. Although drug coated balloons have overcome limitations associated with plain old balloon angioplasty and peripheral stents, recent safety concerns and cost considerations have impacted their usage. In this review, various liquid drug delivery devices are presented, showcasing their capabilities and success in both preclinical and clinical settings. These innovative liquid delivery devices, capable of targeted delivery and their ability to be re-used for multiple treatment sites, may provide solutions for current unmet clinical needs.

Perivascular patch using biodegradable polymers: Investigation of mechanical and drug elution characteristics

Intimal hyperplasia (IH) is the primary cause for the vascular graft stenosis. Perivascular devices offer a potential treatment option to reduce the impact of intimal hyperplasia by providing mechanical support and local administration of therapeutic agents to control cellular overgrowth. In the present study, a perivascular patch primarily made up of biodegradable polymer, Poly L-Lactide, has been designed with adequate mechanical strength and ability for sustained drug elution of anti-proliferative drug (Paclitaxel). The elastic modulus of the polymeric film has been optimized by blending the base polymer with different grades of biocompatible polyethylene glycols. Using design of experiments, the optimized parameters were obtained as PLLA with 2.5% PEG-6000 and have shown 3.14 MPa elastic modulus. The film prepared based on optimum conditions has been employed for prolonged drug delivery (about four months) under simulated physiological conditions. The addition of drug release rate enhancer (polyvinyl pyrrolidone K90F) has improved the drug elution rate and ∼83% drug was released over entire study period. The molecular weight of the base biodegradable polymer was estimated by gel permeation chromatography (GPC) which remained unchanged during the drug release study duration. Evidences of Paclitaxel drug crystallization were found to contribute to the sustained drug elution. The SEM examination of the surface morphology post-incubation revealed micropores on the surface, contributing to the overall drug release rate. The study concluded that perivascular biodegradable films could be tailored for their mechanical properties, and sustained drug elution could also be formulated with reasonable choices of biodegradable polymer and biocompatible additives.

Polyanhydride Chemistry

Polyanhydrides (PAs) are a class of synthetic biodegradable polymers employed as controlled drug delivery vehicles. They can be synthesized and scaled up from low-cost starting materials. The structure of PAs can be manipulated synthetically to meet desirable characteristics. PAs are biocompatible, biodegradable, and generate nontoxic metabolites upon degradation, which are easily eliminated from the body. The rate of water penetrating into the polyanhydride (PA) matrix is slower than the anhydride bond cleavage. This phenomenon sets PAs as "surface-eroding drug delivery carriers." Consequently, a variety of PA-based drug delivery carriers in the form of solid implants, pasty injectable formulations, microspheres, nanoparticles, etc. have been developed for the sustained release of small molecule drugs, and vaccines, peptide drugs, and nucleic acid-based active agents. The rate of drug delivery is often controlled by the polymer erosion rate, which is influenced by the polymer structure and composition, crystallinity, hydrophobicity, pH of the release medium, device size, configuration, etc. Owing to the above-mentioned interesting physicochemical and mechanical properties of PAs, the present review focuses on the advancements made in the domain of synthetic biodegradable biomedical PAs for therapeutic delivery applications. Various classes of PAs, their structures, their unique characteristics, their physicochemical and mechanical properties, and factors influencing surface erosion are discussed in detail. The review also summarizes various methods involved in the synthesis of PAs and their utility in the biomedical domain as drug, vaccine, and peptide delivery carriers in different formulations are reviewed.

Tubular TPU/SF nanofibers covered with chitosan-based hydrogels as small-diameter vascular grafts with enhanced mechanical properties

Native grafts such as internal mammary artery and saphenous vein are the main choice for coronary artery bypass graft. However, due to the limitations associated with their availability and rapid failure caused by hyperplasia, small diameter tissue-engineered vascular grafts (TEVGs) with sufficient post-implantation patency are urgently demanded as artificial alternatives. In our previous work, we innovatively fabricated a bilayer vascular graft providing appropriate structural and biological properties using electrospinning and freeze-drying methods. It was proved that the mechanical properties of the proposed graft enhanced in comparison with using either of methods individually. Here, we adopted the same methods and incorporated an anticoagulant internal layer (inner diameter 4 mm), comprised of co-electrospun fibers of silk fibroin (SF) and heparinized thermoplastic polyurethane (TPU), and an external highly porous hydrogel fabricated by freeze-drying method. The electrospun layer exhibited strong mechanical properties including superior elastic modulus (4.92 ± 0.11 MPa), suture retention force (6.73 ± 0.83 N), elongation at break (196 ± 4%), and comparable burst pressure (1140 ± 12 mmHg) while the external hydrogel provided SMCs viability. The heparin was released in a sustain manner over 40 days, and the cytocompatibility and blood compatibility of scaffold were approved using MTT assay and platelet adhesion test. Thus, the proposed graft has a potential to be used as an artificial blood vessel scaffold for later in-vivo transplantation.

Drug Delivery and Drug Efficacy from Amorphous Poly(thioether anhydrides)

The correlation between erosion and drug (lidocaine and 6-mercaptopurine, 6-MP) release from amorphous poly(thioether anhydrides), which are synthesized using radical-mediated thiol-ene polymerization, is reported. Cytotoxicity studies of the polymer toward human fibroblast human dermal fibroblasts adult, melanoma A-375, and breast cancer MCF-7 cells are conducted, and drug efficacy of a cancer and autoimmune disease drug (6-MP) when released from the poly(thioether anhydrides) is examined against two cancerous cell types (A-375 and MCF-7). Erosion and drug release studies reveal that lidocaine release is governed by network erosion whereas 6-MP is released by a combination of erosion and diffusion. The cytotoxicity studies show that all three cell types demonstrate high viability, thus cytocompatibility, to poly(thioether anhydrides). Toxicity to the material is dose dependent and comparable to other polyanhydride systems. The 6-MP cancer drug is shown to remain bioactive after encapsulation in the poly(thioether anhydride) matrix and the polymer does not appear to modify the efficacy of the drug.

Recent Advances in Polyanhydride Based Biomaterials

This review focusses on recent developments of polyanhydrides, a class of degradable synthetic biopolymers. Polyanhydrides have been used as carriers for controlled delivery of drugs. A polyanhydride copolymer of carboxyphenoxy propane and sebacic acid has been used in Gliadel brain tumor implants for the controlled delivery of carmustine or bis-chloroethylnitrosourea. They are easy and inexpensive to synthesize (especially scale up). However, polyanhydrides possess a short shelf-life. Hydrolytic cleavage and anhydride interchanges lower their molecular weights during storage. One of the highlights in recent developments of polyanhydride chemistry is the discovery of alternating copolymers having extended shelf-life. Other highlights include their applications in biomedical electronics, vaccine delivery, and nano/micro particulate delivery systems. This review examines approaches for polyanhydride synthesis followed by their recent developments in biomedical applications.

Perivascular medical devices and drug delivery systems: Making the right choices

Perivascular medical devices and perivascular drug delivery systems are conceived for local application around a blood vessel during open vascular surgery. These systems provide mechanical support and/or pharmacological activity for the prevention of intimal hyperplasia following vessel injury. Despite abundant reports in the literature and numerous clinical trials, no efficient perivascular treatment is available. In this review, the existing perivascular medical devices and perivascular drug delivery systems, such as polymeric gels, meshes, sheaths, wraps, matrices, and metal meshes, are jointly evaluated. The key criteria for the design of an ideal perivascular system are identified. Perivascular treatments should have mechanical specifications that ensure system localization, prolonged retention and adequate vascular constriction. From the data gathered, it appears that a drug is necessary to increase the efficacy of these systems. As such, the release kinetics of pharmacological agents should match the development of the pathology. A successful perivascular system must combine these optimized pharmacological and mechanical properties to be efficient.

Polyanhydrides: Synthesis, Properties, and Applications

This review focusses on polyanhydrides, a fascinating class of degradable polymers that have been used in and investigated for many bio-related applications because of their degradability and capacity to undergo surface erosion. This latter phenomenon is driven by hydrolysis of the anhydride moieties at the surface and high hydrophobicity of the polymer such that degradation and mass loss (erosion) occur before water can penetrate deep within the bulk of the polymer. As such, when surface-eroding polymers are used as therapeutic delivery vehicles, the rate of delivery is often controlled by the rate of polymer erosion, providing predictable and controlled release rates that are often zero-order. These desirable attributes are heavily influenced by polymer composition and morphology, and therefore also monomer structure and polymerization method. This review examines approaches for polyanhydride synthesis, discusses their general thermomechanical properties, surveys their hydrolysis and degradation processes along with their biocompatibility, and looks at recent developments and uses of polyanhydrides in drug delivery, stimuli-responsive materials, and novel nanotechnologies.

Drug-eluting metallic stents in urology

Drugeluting metal stents (DESs) have been extensively used in coronary and vascular disease. This type of stents has been proven to provide significantly lower restenosis rates due to the reduction of neo-intimal hyperplasia in comparison to the traditionally used bare metal stents (BMSs). The latter stents have been evaluated for more than a decade in urological practice in an attempt to provide permanent relief of urethral or ureteral obstruction. Although the initial results were promising, long-term experience revealed significant complications, which are mainly attributed to stent-related hyperplastic reaction compromising stent patency. The favorable experience of vascular DESs led to the application of DESs in both the urethra and ureter of animal models. These experimental results demonstrated a reduction of hyperplastic reaction of DESs in comparison to BMSs. Nevertheless, clinical data are currently not available. Considering the fact that DESs are under continuous development, the use of DESs in urology holds promise for the future and seems to be an intriguing field.

Nasal administration of heparin-loaded microspheres based on poly(lactic acid)

In this study, heparin-loaded microspheres having smooth surface and small particle size were designed in order to provide the absorption of heparin through nasal mucosa. For this purpose, microspheres at different polymer/drug ratios (1:10, 1:2.5 and 1:1) and at different concentrations of polyvinyl alcohol, emulsifying agent (1.5% and 2.5% w/v) were prepared by solvent evaporation method with poly(lactic acid). The microspheres were for evaluated shape and surface properties, particle size, production yield, encapsulation efficiency and in vitro drug release. Based on the in vitro data, selected microspheres were applied by nasal route to Wistar albino rats. According to in vivo studies, heparin-loaded microspheres may be used by nasal route as an alternative to parenteral route.

Vascular Access in Hemodialysis: Issues, Management, and Emerging Concepts

This article (1) identifies the types of hemodialysis access, (2) summarizes the clinical standard of care for dialysis access grafts and fistulae, (3) describes the pathology and pathogenesis of venous stenosis in dialysis access grafts and fistulae, (4) tabulates avail-able therapies for hemodialysis vascular access dysfunction and speculates on the rea-sons for the lack of effective therapies, and (5) discusses the development and application of novel therapeutic interventions for this difficult clinical problem. The possibility that dialysis access grafts and fistulae could be the ideal clinical model for testing novel local therapies to block neointimal hyperplasia is discussed.

Novel therapies for hemodialysis vascular access dysfunction: fact or fiction!

Hemodialysis vascular access dysfunction is a major cause of morbidity in the hemodialysis population and contributes significantly to the overall cost of end-stage renal disease programs. At a histological level, most hemodialysis vascular access dysfunction (in both native arteriovenous fistulae and PTFE dialysis access grafts) is due to venous stenosis and thrombosis, secondary to venous neointimal hyperplasia. However, despite a wealth of experimental and clinical data on the use of novel therapeutic interventions that target neointimal hyperplasia in the setting of coronary artery disease, there are unfortunately no effective therapeutic interventions for hemodialysis vascular access dysfunction at the present time. This is particularly unfortunate, since neointimal hyperplasia in the setting of hemodialysis vascular access fistulae and grafts could be the ideal clinical model to test novel therapeutic interventions for neointimal hyperplasia.

Controlled release of avermectin from porous hollow silica nanoparticles

Porous hollow silica nanoparticles (PHSNs) with a diameter of ca 100 nm and a pore size of ca 4.5 nm were synthesized via a sol-gel route using inorganic calcium carbonate nanoparticles as templates. The synthesized PHSNs were subsequently employed as pesticide carriers to study the controlled release behaviour of avermectin. The avermectin-loaded PHSN (Av-PHSN) samples were characterized by BET, thermogravimetric analysis and IR, showing that the amount of avermectin encapsulated in the PHSN carrier could reach 58.3% w/w by a simple immersion loading method, and that most of the adsorption of avermectin on the Av-PHSN carrier might be physical. Avermectin may be loaded on the external surface, the pore channels in the wall and the inner core of the PHSN carriers, thus leading to a multi-stage sustained-release pattern from the Av-PHSN samples. Increasing pH or temperature intensified the avermectin release.

Role of polyanhydrides as localized drug carriers

Many drugs that are administered in an unmodified form by conventional systemic routes fail to reach target organs in an effective concentration, or are not effective over a length of time due to a facile metabolism. Various types of targeting delivery systems and devices have been tried over a long period of time to overcome these problems. Targeted delivery or localized drug delivery offers an advantage of reduced body burden and systemic toxicity of the drugs, especially useful for highly toxic drugs like anticancer agents. Local drug delivery via polymer is a simple approach and hypothesized to avoid the above stated problems. Polyanhydrides are a unique class of polymer for drug delivery because some of them demonstrate a near zero order drug release and relatively rapid biodegradation in vivo. Further, the release rate of polyanhydride fabricated device can be altered over a thousand fold by simple changes in the polymer backbone. Hence, these are one of the best-suited polymers for drug delivery, with biodegradability and biocompatibility. The review focuses on the advantages of polyanhydride carriers in localized drug delivery along with their degradability behavior, toxicological profile and role in various disease conditions.

Fabrication of porous hollow silica nanoparticles and their applications in drug release control

Preparation and characterization of porous hollow silica nanoparticles (PHSN) for controlled release applications were investigated. Through orthogonally designed experiments, the optimal synthesis conditions for the preparation of PHSN were obtained and the produced PHSN were characterized by BET, SEM, TEM and IR. Scanning and transmission electron microscopy images revealed their hollow shell-core structure and also demonstrated that the size and shape of PHSN are determined by the templating CaCO3 nanoparticles. The produced PHSN were applied as a carrier to study the controlled release behaviors of Brilliant Blue F (BB), which was used as a model drug. Being loaded into the inner core and on the surfaces of the nanoparticles, BB was released slowly into a bulk solution for about 1140 min as compared to only 10 min for the normal SiO2 nanoparticles, thus exhibited a typical sustained release pattern without any burst effect. In addition, higher BET of the carriers, lower pH value and lower temperature prolonged BB release from PHSN, while stirring speed showed little influence on the release behavior. It showed that PHSN have a promising future in controlled drug delivery applications.

Controlled release of heparin from polypyrrole-poly(vinyl alcohol) assembly by electrical stimulation

A surface modification technique was developed for the covalent immobilization of poly(vinyl alcohol) (PVA)-heparin hydrogel onto electrically conductive polypyrrole (PPY) film with the objective of achieving controlled release of heparin. First, aldehyde groups were introduced onto PPY film through poly(ethylene glycol) monomethacrylate graft copolymerization and subsequent oxidation in acetic anhydride and dimethyl sulfoxide mixture. Then, the prepared PVA-heparin hydrogel was cast onto the PPY film and covalently immobilized to the film through the reaction between the aldehyde groups on the PPY film and the hydroxyl groups of PVA. X-ray photoelectron spectroscopy was used to characterize the surface-modified film after each stage. The strong attachment of the PVA-heparin layer on the PPY film was confirmed by peel test and scanning electron microscopy. The release behavior of heparin from the substrate with and without electrical stimulation was studied and the experimental results showed that the heparin release rate from the prepared substrate using an electric current of 3.5 mA is twofold higher than that without current.

Polymeric sustained local drug delivery system for the prevention of vascular intimal hyperplasia

Anastomotic intimal hyperplasia (IH) is a major cause of both autologous vein and synthetic vascular graft failure. We have previously published data suggesting that cyclosporin may reduce the development of IH in a canine model. However, systemic administration of cyclosporin could create serious adverse effects. Therefore, it is our long-term goal to test the hypothesis that the controlled local release of cyclosporin from a polymeric vascular wrap will prevent the development of IH. To test this hypothesis, we developed a controlled release vascular wrap (sheet/ring) using a poly(ethylene glycol) (PEG) hydrogel. Sterilization of the polymers was performed using the ethylene oxide and hydrogen peroxide sterilization methods. It was found that except for one combination (8000 molecular weight and 1:1 crosslinking ratio), the differences in the swelling ratios for the sterilized and unsterilized hydrogels were not statistically significant. Release studies from unsterilized and ethylene oxide-sterilized PEG hydrogels were conducted. It was found that release lasted for approximately 50 h for sterilized as well as unsterilized PEG hydrogels. Acute animal studies, to test the deployment of both the polymeric sheets and rings to the adventitial surface of native arteries and veins, were completed successfully.

Characterization of perivascular poly(lactic-co-glycolic acid) films containing paclitaxel

The objectives of this study were to investigate the use of poly(lactic-co-glycolic acid) (PLGA) for the formulation of paclitaxel loaded films and to characterize these films for potential application as perivascular "wraps" to prevent restenosis. Films were manufactured from PLGA blended with either methoxypolyethylene glycol (MePEG) or a diblock copolymer composed of poly(D,L-lactic acid)-block-methoxypolyethylene glycol, PDLLA-MePEG (diblock) by solvent evaporation on teflon discs. Elasticity was determined by gravimetric stress/strain analysis. Thermal analysis was determined using differential scanning calorimetry (DSC). Changes in film composition and degradation in aqueous media were determined using gel permeation chromatography (GPC). Paclitaxel release from films was measured by incubation of the films in phosphate buffered saline (PBS) with drug analysis by HPLC methods. The addition of MePEG or diblock to PLGA caused a concentration dependent increase in the elasticity of films, due to plasticizing effects. DSC analysis showed that MePEG and diblock caused a concentration dependent decrease in the glass transition temperature (Tg) of PLGA indicating miscibility of the polymers. When placed in aqueous media, more than 75% of MePEG dissolved out of the PLGA films within 2 days, whereas diblock partitioned slowly and in a controlled manner out of the films. Paclitaxel release from PLGA/MePEG films was very slow with less than 5% of the encapsulated drug being released over 2 weeks. The addition of 30% diblock to paclitaxel loaded PLGA films caused a substantial increase (five- to eight-fold) in the release rate of paclitaxel. PLGA films containing 30% diblock and either 1% or 5% paclitaxel were partially or completely degraded following perivascular implantation in rats.

Nonlinear fatty acid terminated polyanhydrides

A systemic study on the synthesis, characterization, degradation, drug release, and stability of nonlinear fatty acid terminated poly(sebacic anhydride) (PSA) is reported. Ricinoleic acid was transformed into a nonlinear fatty acid by esterification with fatty acid chlorides of C8-C18 chain length in the presence of pyridine. Pure nonlinear fatty acids were obtained by purification of the reaction product using column chromatography. Poly(sebacic acid)s terminated with 30 wt % of various nonlinear fatty acids were synthesized by melt condensation to yield waxy off-white materials with molecular weights in the range of 5000-9000. The terminated polymers are soluble in common organic solvents and melt at temperatures between 70 and 79 degrees C, which allow their fabrication into microspheres and implants. These polymers degrade into their counterparts during a period of a few weeks while constantly releasing an incorporated drug. The incorporation of nonlinear fatty acid terminals to poly(sebacic anhydride) increased the polymer hydrophobicity and decreased polymer crystallinity when compared to PSA or to linear fatty acid terminated PSA. The hydrophobic nonlinear side chains retard water from penetrating into the polymer mass, which resulted in higher stability and surface erosion front mechanism of polymer degradation and drug release.

Polyanhydrides: an overview

Polyanhydrides have been considered to be useful biomaterials as carriers of drugs to various organs of the human body such as brain, bone, blood vessels, and eyes. They can be prepared easily from available, low cost resources and can be manipulated to meet desirable characteristics. Polyanhydrides are biocompatible and degrade in vivo into non-toxic diacid counterparts that are eliminated from the body as metabolites. Owing to their usefulness, this review focuses on the development, synthesis methods, structures and characterization of polyanhydrides, which will provide an overview for the researchers in the field. Their in vitro and in vivo degradability, toxicity, biocompatibility and applications are discussed in the subsequent chapters of this special issue on polyanhydrides and poly(ortho esters).

In vitro release of heparin from silica xerogels

Heparin, a powerful anticoagulant used for the prophylaxis of both surgical and medical thrombosis, was incorporated into a silica xerogel matrix during polycondensation of organic silicate. The influence of various chemical sol-gel parameters (the properties of reaction precursors, catalyst and final moisture content of the gel and heparin concentration) was studied. The release of heparin from the gel was according to zero order during the dissolution period and the release rate of heparin was proportional to the drug load in the concentration range between 6.8 and 13.6 wt%. It was found that the catalyst used for the preparation of the gel, the final moisture content and the chemical modification of silica xerogel network have an influence on the release rate of heparin. The released heparin from all the different xerogels studied retained about 90% of its biological activity.