Small-Diameter Stents in Cardiovascular Applications

Small-diameter stents play a crucial role in treating congenital heart diseases and variety of vascular conditions that have application from paediatrics to geriatric conditions, and a comprehensive review in this direction is lacking. This review explores historical development, design innovations, material compositions and mechanistic insights into functions of small-diameter stents, with a specific emphasis on biodegradable options. The necessity for stents that can adapt to growth of paediatric patients is discussed, highlighting the transition from durable polymers to bioresorbable materials such as polylactic acid (PLA) and magnesium alloys. While acknowledging the advancements made in reducing complications like restenosis and thrombosis, the review addresses the challenges that persist, including the need for improved biocompatibility and minimization of late adverse cardiac events associated with certain stent technologies. A detailed examination of various stent generations emphasizes the importance of drug release kinetics, structural integrity and potential for personalized interventions based on patient-specific factors. The exploration of novel therapeutic compounds, including nanoparticles and interfering RNA, illustrates the ongoing research aimed at enhancing stent efficacy. Ultimately, the review seeks to provide a comprehensive understanding of current landscape while identifying the gaps that future research must address to develop the ideal stent for diverse patient populations.

Enhancing Stent Effectiveness with Nanofeatures

Drug-eluting stents are an effective therapy for symptomatic arterial obstructions, substantially reducing the incidence of restenosis by suppressing the migration and proliferation of vascular smooth muscle cells into the intima. However, current drug-eluting stents also inhibit the growth of endothelial cells, which are required to cover the vascular stent to reduce an excessive inflammatory response. As a result, the endothelial lining of the lumen is not regenerated. Since the loss of this homeostatic monolayer increases the risk of thrombosis, patients with drug-eluting stents require long-term antithrombotic therapy. Thus, there is a need for improved devices with enhanced effectiveness and physiological compatibility towards endothelial cells. Current developments in nanomaterials may enhance the function of commercially available vascular devices. In particular, modified design schemes might incorporate nanopatterns or nanoparticle-eluting features that reduce restenosis and enhance re-endothelialization. The intent of this review is to discuss emerging nanotechnologies that will improve the performance of vascular stents.

Perspectives On: Polymeric Drugs and Drug Delivery Systems

Therapeutic uses of a variety of drug carrier systems have significant impact on the treatment and potential cure of many chronic diseases, including cancer, diabetes, mellitus, rheumatoid arthritis, HIV infection, and drug addiction. Drug delivery technology is a multidisciplinary science involving the physical, biological, medicinal, pharmaceutical, biomedical engineering and biomaterial fields. Polymeric systems can deliver drugs directly to the intended site of action and can also improve efficacy while minimizing unwanted side effects elsewhere in the body, which often limit the long-term use of many drugs. In this article, some recent publications on several polymeric drug conjugates, gene delivery systems and polymer implants are addressed.

Synthesis and Modifications of Polyurethanes for Biomedical Purposes

Polyurethanes are known as a class of polymers with very high ‘hemocompatible‘ properties. In this study polyurethanes were prepared in various compositions and in medical purity without using any solvent, catalyst or additives. For the synthesis of polyurethanes, toluene diisocynate, diphenylmethane diisocynate or hexamethylene diisocynate were used as diisocyanate compounds and polypropylene-ethylene glycol or polypropylene glycol were used as polyol compounds. The surfaces were modified with plasma glow-discharge by using various gas atmospheres and by applying different powers. Some samples were also modified by heparin immobilization to increase the blood compatibility. Chemical structure, mechanical strength, thermal behavior, oxygen permeability, water contact angle values, as well as protein and cell attachment capabilities of the prepared and modified polyurethanes were examined as possible candidates for biomedical applications. Plasma altered the chemistry of the surface, increased hydrophilic character, and caused a decrease in protein adsorption as the applied power was increased. On the other hand, an optimum power value which caused maximum attachment for Vero cells was observed. In-vitro experiments carried out with blood cells, plasma modification caused an increase on cell adhesion while further heparin immobilization resulted with a significant decrease.

On imparting radiopacity to a poly(urethane urea)

A poly(urethane urea) (PUU) synthesized from 2,4-toluene diisocyanate (TDI) and polyethylene glycol (PEG) with ethylenediamine (ED) as the chain extender was rendered radiopaque by attaching 3,4,5-triiodobenzoic acid (TIB) onto the polymer backbone. The radiopaque polyurethane obtained was characterized by infra red (IR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-radiography. By optimizing the reaction conditions, it was possible to carry out the modification without adversely affecting the properties of the starting polymer significantly. IR spectral evidence suggested that the hydrogen bonded structure of PUU remained undisrupted even after modification. However, the product exhibited altered thermal characteristics when compared to the parent polymer. Degradation characteristics as observed from the TGA remained unchanged, while one of the glass transitions got shifted to a lower temperature. The observed changes in thermal characteristics were explained on the basis of possible inter-phase mixing and the changes in the close packing of the polymer chains by the introduction of bulky iodine atoms.