Estrogen release from metallic stent surface for the prevention of restenosis

Biodegradable Iron-Based Materials-What Was Done and What More Can Be Done?

Iron, while attracting less attention than magnesium and zinc, is still one of the best candidates for biodegradable metal stents thanks its biocompatibility, great elastic moduli and high strength. Due to the low corrosion rate, and thus slow biodegradation, iron stents have still not been put into use. While these problems have still not been fully resolved, many studies have been published that propose different approaches to the issues. This brief overview report summarises the latest developments in the field of biodegradable iron-based stents and presents some techniques that can accelerate their biocorrosion rate. Basic data related to iron metabolism and its biocompatibility, the mechanism of the corrosion process, as well as a critical look at the rate of degradation of iron-based systems obtained by several different methods are included. All this illustrates as the title says, what was done within the topic of biodegradable iron-based materials and what more can be done.

Polymeric prodrug-functionalized polypropylene films for sustained release of salicylic acid

Medical devices decorated with salicylic acid-based polymer chains (polymeric prodrug) that slowly release this anti-inflammatory and anti-biofilm drug at the implantation site were designed. A "grafting from" method was implemented to directly grow chains of a polymerizable derivative of salicylic acid (2-methacryloyloxy-benzoic acid, 2MBA) onto polypropylene (PP). PP was modified both at bulk and on the surface with poly(2MBA) by means of an oxidative pre-irradiation method ((60)Co source), in order to obtain a grafted polymer in which salicylic acid units were linked by means of labile ester bonds. The grafting percent depended on absorbed dose, reaction time, temperature and monomer concentration. The functionalized films were analyzed regarding structure (FTIR-ATR, SEM-EDX, fluorescence microscopy), temperature stability (TGA), interaction with aqueous medium (water contact angle and swelling), pH-responsive release and cytocompatibility (fibroblasts). In the obtained poly(2MBA)-grafted biomaterial, poly(2MBA) behaved as a polymeric prodrug that regulates salicylic acid release once in contact with aqueous medium, showing pH-dependent release rate.

Controlling drug delivery from coronary stents: are we aiming for the right targets?

In this review article, the currently employed or explored delivery concepts for local intravascular drug delivery with drug-eluting stents (DES) are discussed with a special emphasis on clinical evidence regarding the desired release profiles. Traditional concepts to control drug release from DES include diffusion through polymers, polymer degradation and erosion as well as dissolution of particulate drug. Published clinical studies do not always reveal fine mechanistic details. The long duration of release favored for DES and the short duration of release favored for drug-eluting balloons require further investigation in experimental studies and clinical trials.

Deposition of organic−inorganic hybrid coatings over 316L surgical stainless steel and evaluation on vascular cells

Surface coating of metallic materials using the sol-gel technique is a suitable approach to obtain hybrid materials with improved properties for biomedical applications. In this study, an AISI 316L stainless steel surface was coated with ormosils prepared from tetraethylsiloxane and 3-glycidoxypropyltrimethoxysilane or polydimethylsiloxane. The characterization of structural and surface properties was performed by several techniques. Surface microstructure, morphology, and energy are dependent on organosilane type and content. Chemical stability of coatings was investigated by static immersion tests in phosphate buffer solution at 37 °C, and silicon leaching after 21 days was found to be in the range of ∼200−300 μg L−1. Mechanical adhesion was found to be within 1.0 and 3.7 N cm−1. The interaction of the samples and materials in the cardiovascular environment was investigated through cellular behavior. Biological assays were performed with slides to avoid any cytotoxic effects on human endothelial cells (HUVEC) and rabbit arterial smooth muscle cells (RASM). No significant alterations were observed after 24 h in the viability of RASM and HUVEC cells exposed to different coatings. No increase of HUVEC or RASM migration was observed after 24 h as evaluated by transwell migration assay. The hybrid materials showed suitable properties for potential application as biomaterials in cardiovascular environment as well as for incorporation of bioactive species with the aim to prepare drug-eluting stents.

Drug/Medical Device Combination Products with Stimuli-responsive Eluting Surface

Drug-eluting medical devices are designed to improve the primary function of the device and at the same time offer local release of drugs which otherwise might find it difficult to reach the insertion/implantation site. The incorporation of the drug enables the tuning of the host/microbial responses to the device and the management of device-related complications. On the other hand, the medical device acts as platform for the delivery of the drug for a prolonged period of time just at the site where it is needed and, consequently, the efficacy and the safety of the treatment, as well as its cost-effectiveness are improved. This chapter begins with an introduction to the combination products and then focuses on the techniques available (compounding, impregnation, coating, grafting of the drug or of polymers that interact with it) to endow medical devices with the ability to host drugs/biological products and to regulate their release. Furthermore, the methods for surface modification with stimuli-responsive polymers or networks are analyzed in detail and the performance of the modified materials as drug-delivery systems is discussed. A wide range of chemical-, irradiation- and plasma-based techniques for grafting of brushes and networks that are sensitive to changes in temperature, pH, light, ionic strength or concentration of certain biomarkers, from a variety of substrate materials, is currently available. Although in vivo tests are still limited, such a surface functionalization of medical devices has already been shown useful for the release on-demand of drugs and biological products, being switchable on/off as a function of the progression of certain physiological or pathological events (e.g. healing, body integration, biofouling or biofilm formation). Improved knowledge of the interactions among the medical device, the functionalized surface, the drug and the body are expected to pave the way to the design of drug-eluting medical devices with optimized and novel performances.

Quantitative spatial distribution of sirolimus and polymers in drug-eluting stents using confocal Raman microscopy

Raman spectroscopy was used to differentiate each component found in the CYPHER Sirolimus-eluting Coronary Stent. The unique spectral features identified for each component were then used to develop three separate calibration curves to describe the solid phase distribution found on drug-polymer coated stents. The calibration curves were obtained by analyzing confocal Raman spectral depth profiles from a set of 16 unique formulations of drug-polymer coatings sprayed onto stents and planar substrates. The sirolimus model was linear from 0 to 100 wt % of drug. The individual polymer calibration curves for poly(ethylene-co-vinyl acetate) [PEVA] and poly(n-butyl methacrylate) [PBMA] were also linear from 0 to 100 wt %. The calibration curves were tested on three independent drug-polymer coated stents. The sirolimus calibration predicted the drug content within 1 wt % of the laboratory assay value. The polymer calibrations predicted the content within 7 wt % of the formulation solution content. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra from five formulations confirmed a linear response to changes in sirolimus and polymer content.

Study on Adhesion and Biocompatibility of Copolymer of MMA-BMA-MAA for Coronary Stents Coatings

Implantation of drug releasing coronary stents has been developed as an useful method for prevention of the restenosis in blood vessels. Copolymers of methyl methacrylate (MMA), butyl methacrylate (BMA) and methacrylic acid (MAA) were prepared as the coating polymer for drug releasing stent. The adhesion of the polymer with metal substrate and the biocompatibility were studied. Effect of the polymer composition on the adhesion between polymer coatings and metal substrate, as well as the effect of the polymer purification method on biocompatibility of the polymer, was studied. The results showed that the copolymer coating has good dry and wet adhesion properties, which can be improved by control of the polymer compositions. Biocompatibility of the prepared copolymer comes within the permission limit.