Chemico-physical characterisation and in vivo biocompatibility assessment of DLC-coated coronary stents

Application of PVD coatings in medical implantology for enhanced performance, biocompatibility, and quality of life

Physical vapor deposition (PVD) coating is a versatile and well-liked method for depositing thin films of materials onto surfaces in a range of industries. Due to their numerous functional and aesthetic benefits, PVD coatings are beneficial in several applications, from electronics and optics to automotive and medical equipment. PVD coating technology dramatically improves the effectiveness and quality of medical implants. PVD-coated medical implants improve osseointegration, lower wear and friction, increase corrosion resistance, and have antibacterial properties, which lead to better patient outcomes, fewer complications, and overall higher quality of life for people who need implantable medical devices. The essential concepts of PVD coating and the numerous deposition techniques and materials used are covered at the study's outset. The specific uses of PVD-coated medical implants are then highlighted, including those for orthopedic and dental implants and cardiovascular and neurosurgical devices. The review also emphasizes the critical contribution of PVD coatings to reducing wear and friction, improving corrosion resistance, augmenting biocompatibility, enhancing osseointegration, and aesthetic appeal. The challenges and prospects of PVD coating technologies were further addressed in this article. This review is invaluable for academics, doctors, and businesspeople interested in the beneficial combination of PVD coating and medical implantology.

Development of Antimicrobial Surfaces Using Diamond-like Carbon or Diamond-like Carbon-Based Coatings

The medical device market is a high-growth sector expected to sustain an annual growth rate of over 5%, even in developed countries. Daily, numerous patients have medical devices implanted or inserted within their bodies. While medical devices have significantly improved patient outcomes, as foreign objects, their wider use can lead to an increase in device-related infections, thereby imposing a burden on healthcare systems. Multiple materials with significant societal impact have evolved over time: the 19th century was the age of iron, the 20th century was dominated by silicon, and the 21st century is often referred to as the era of carbon. In particular, the development of nanocarbon materials and their potential applications in medicine are being explored, although the scope of these applications remains limited. Technological innovations in carbon materials are remarkable, and their application in medicine is expected to advance greatly. For example, diamond-like carbon (DLC) has garnered considerable attention for the development of antimicrobial surfaces. Both DLC itself and its derivatives have been reported to exhibit anti-microbial properties. This review discusses the current state of DLC-based antimicrobial surface development.

Nanotechnology in development of next generation of stent and related medical devices: Current and future aspects

Coronary stents have saved millions of lives in the last three decades by treating atherosclerosis especially, by preventing plaque protrusion and subsequent aneurysms. They attenuate the vascular SMC proliferation and promote reconstruction of the endothelial bed to ensure superior revascularization. With the evolution of modern stent types, nanotechnology has become an integral part of stent technology. Nanocoating and nanosurface fabrication on metallic and polymeric stents have improved their drug loading capacity as well as other mechanical, physico-chemical, and biological properties. Nanofeatures can mimic the natural nanofeatures of vascular tissue and control drug-delivery. This review will highlight the role of nanotechnology in addressing the challenges of coronary stents and the recent advancements in the field of related medical devices. Different generations of stents carrying nanoparticle-based formulations like liposomes, lipid-polymer hybrid NPs, polymeric micelles, and dendrimers are discussed highlighting their roles in local drug delivery and anti-restenotic properties. Drug nanoparticles like Paclitaxel embedded in metal stents are discussed as a feature of first-generation drug-eluting stents. Customized precision stents ensure safe delivery of nanoparticle-mediated genes or concerted transfer of gene, drug, and/or bioactive molecules like antibodies, gene mimics via nanofabricated stents. Nanotechnology can aid such therapies for drug delivery successfully due to its easy scale-up possibilities. However, limitations of this technology such as their potential cytotoxic effects associated with nanoparticle delivery that can trigger hypersensitivity reactions have also been discussed in this review. This article is categorized under: Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement Therapeutic Approaches and Drug Discovery > Nanomedicine for Cardiovascular Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Preparation and Characterization of Diamond-like Carbon Coatings for Biomedical Applications-A Review

Diamond-like carbon (DLC) films are generally used in biomedical applications, mainly because of their tribological and chemical properties that prevent the release of substrate ions, extend the life cycle of the material, and promote cell growth. The unique properties of the coating depend on the ratio of the sp³/sp² phases, where the sp² phase provides coatings with a low coefficient of friction and good electrical conductivity, while the share of the sp³ phase determines the chemical inertness, high hardness, and resistance to tribological wear. DLC coatings are characterized by high hardness, low coefficient of friction, high corrosion resistance, and biocompatibility. These properties make them attractive as potential wear-resistant coatings in many compelling applications, including optical, mechanical, microelectronic, and biomedical applications. Another great advantage of DLC coatings is that they can be deposited at low temperatures on a variety of substrates and can thus be used to coat heat-sensitive materials, such as polymers. Coating deposition techniques are constantly being improved; techniques based on vacuum environment reactions are mainly used, such as physical vapor deposition (PVD) and chemical vapor deposition (CVD). This review summarizes the current knowledge and research regarding diamond-like carbon coatings.

OCT Emerging Technologies: Coronary Micro-optical Coherence Tomography

Optical coherence tomography (OCT) is an imaging modality that is used in a significant number of interventional cardiology procedures. Key structural changes occurring within the vessel wall, including presence of neutrophils, macrophages, monocytes, and vascular smooth muscle cells, are below the resolution of clinical intracoronary OCT. To address this challenge, a new form of OCT with 1 to 2 μm resolution, termed micro-OCT (μOCT), has been developed. This review article summarizes the ability of μOCT technology to visualize coronary microstructures and discusses its clinical implications.

Surface engineering at the nanoscale: A way forward to improve coronary stent efficacy

Coronary in-stent restenosis and late stent thrombosis are the two major inadequacies of vascular stents that limit its long-term efficacy. Although restenosis has been successfully inhibited through the use of the current clinical drug-eluting stent which releases antiproliferative drugs, problems of late-stent thrombosis remain a concern due to polymer hypersensitivity and delayed re-endothelialization. Thus, the field of coronary stenting demands devices having enhanced compatibility and effectiveness to endothelial cells. Nanotechnology allows for efficient modulation of surface roughness, chemistry, feature size, and drug/biologics loading, to attain the desired biological response. Hence, surface topographical modification at the nanoscale is a plausible strategy to improve stent performance by utilizing novel design schemes that incorporate nanofeatures via the use of nanostructures, particles, or fibers, with or without the use of drugs/biologics. The main intent of this review is to deliberate on the impact of nanotechnology approaches for stent design and development and the recent advancements in this field on vascular stent performance.

Argon and oxygen plasma treatment increases hydrophilicity and reduces adhesion of silicon-incorporated diamond-like coatings

In this study, the structure, adhesion, and cell viability characteristics of silicon-incorporated diamond-like carbon (Si-DLC) coatings on fused silica substrates were investigated. The effects of argon and oxygen postprocessing plasma treatments on the Si-DLC coatings were also studied. The contact angle results showed that the Si-DLC coatings were more hydrophilic than the uncoated surfaces, and postprocessing plasma treatment increased the hydrophilicity of the Si-DLC coatings. Atomic force microscopy and profilometry confirmed that postprocessing plasma treatment increased the thickness and roughness of the Si-DLC coatings. The results of microscratch testing indicated that the plasma treatments reduced the adhesion of the coatings. The x-ray photoelectron spectroscopy (XPS) showed the presence of carbon, oxygen, and silicon in the Si-DLC coatings before and after the plasma treatments. These results show that the postprocessing plasma treatment significantly reduced the atomic percentage of the carbon in the Si-DLC coatings. XPS also confirmed the presence of carbon in the form of sp³(C-C), sp²(C=C), C-O, and C=O bonds in the Si-DLC coatings; it showed that postprocessing treatments significantly increased the percentage of oxygen in the Si-DLC coatings. Fourier transform infrared spectroscopy (FTIR) analysis showed features associated with C-OH stretching, C-H bending, as well as Si-CH₂ and C-H bending in the Si-DLC coating. The XPS and FTIR results confirmed that the plasma treatment caused dissociation of the sp² and sp³ bonds and formation of C-OH bonds. The contact angle data indicated that postprocessing treatment increased the hydrophilicity of the Si-DLC coating. Similar to the uncoated substrates, L929 cells showed no change in cell viability when cultured on Si-DLC coatings. These results of the study indicate the suitability of Si-DLC coatings as inert coatings for medical and biotechnology applications.

Recent Advances in Manufacturing Innovative Stents

Cardiovascular diseases are the most distributed cause of death worldwide. Stenting of arteries as a percutaneous transluminal angioplasty procedure became a promising minimally invasive therapy based on re-opening narrowed arteries by stent insertion. In order to improve and optimize this method, many research groups are focusing on designing new or improving existent stents. Since the beginning of the stent development in 1986, starting with bare-metal stents (BMS), these devices have been continuously enhanced by applying new materials, developing stent coatings based on inorganic and organic compounds including drugs, nanoparticles or biological components such as genes and cells, as well as adapting stent designs with different fabrication technologies. Drug eluting stents (DES) have been developed to overcome the main shortcomings of BMS or coated stents. Coatings are mainly applied to control biocompatibility, degradation rate, protein adsorption, and allow adequate endothelialization in order to ensure better clinical outcome of BMS, reducing restenosis and thrombosis. As coating materials (i) organic polymers: polyurethanes, poly(ε-caprolactone), styrene-b-isobutylene-b-styrene, polyhydroxybutyrates, poly(lactide-co-glycolide), and phosphoryl choline; (ii) biological components: vascular endothelial growth factor (VEGF) and anti-CD34 antibody and (iii) inorganic coatings: noble metals, wide class of oxides, nitrides, silicide and carbide, hydroxyapatite, diamond-like carbon, and others are used. DES were developed to reduce the tissue hyperplasia and in-stent restenosis utilizing antiproliferative substances like paclitaxel, limus (siro-, zotaro-, evero-, bio-, amphi-, tacro-limus), ABT-578, tyrphostin AGL-2043, genes, etc. The innovative solutions aim at overcoming the main limitations of the stent technology, such as in-stent restenosis and stent thrombosis, while maintaining the prime requirements on biocompatibility, biodegradability, and mechanical behavior. This paper provides an overview of the existing stent types, their functionality, materials, and manufacturing conditions demonstrating the still huge potential for the development of promising stent solutions.

Carbon-Coated Stent and the Role of the Kallikrein-Kinin System in Peripheral Angioplasty

OBJECTIVE

The purpose of this study was to investigate the clinical evolution of patients treated with carbon-coated stent, as well as its patency and the inflammatory response triggered by this process through the quantification of serum elements of the kallikrein-kinin system (KKS).

METHODS

This was a single-center prospective study with 27 patients with peripheral artery disease (PAD) who required percutaneous transluminal angioplasty and stenting of the iliacofemoropopliteal segment using carbon-coated stent grafts (carbostents). The blood concentrations of the total and kininogen fractions were evaluated using immunoenzymatic methods. Plasma kallikrein levels were assessed by the colorimetric method and tissue kallikrein levels were evaluated by the spectrophotometric method. The activity of kininase II was measured by -fluorometric analysis.

RESULTS

Of the 27 patients who completed the 6 months of the study (11 iliac territory, 16 femoropopliteal territory), only one experienced restenosis (3.7%) (femoropopliteal segment) and no patient had occlusion (96.3% of patency). In 1 year, four patients were lost to follow-up and all 23 patients evaluated maintained stent patency, except for the patient who had restenosis throughout the first 6 months. We report complete (100%) member salvage in 12 months of follow-up. The activity levels of high- and low-molecular-weight kininogens decreased significantly over time (before vs. 24 h, p < 0.01; before vs. 6 months, p < 0.001, and before vs. 24 h, p < 0.01; before vs. 6 months, p < 0.001; 24 h vs. 6 months, p < 0.001, respectively). Patients also had significantly lower levels of plasma and tissue kallikrein (before vs. 24 h, p < 0.001; before vs. 6 months, p < 0.001, and before vs. 24 h, p < 0.01; before vs. 6 months, p < 0.05, respectively). There was a significant increase in the enzymatic activity of kininase II at 24 h and after 6 months compared to the pre-treatment control (p < 0.001).

CONCLUSION

Our early experience shows that the use of carbon-coated stents in PAD appears to be safe, with low rates of early restenosis (3.7% in the first 6 months and 5% in the 12 months of follow-up). We concluded that KKS was involved in the inflammatory response caused by the placement of carbon-coated stents.

Characteristics of different cathodic arc deposition coatings on CoCrMo for biomedical applications

Coatings of endoprostheses are used to improve the tribological performance of arthroplasties. A major challenge for the successful use of these coatings, however, is a stable layer adhesion, a smooth surface, as well as a reduction in droplet formation during the coating process. Explants with commercially available coatings were investigated to assess surface/layer defects and adhesion properties. For the investigation of new coatings, we used cathodic arc deposition (Arc-PVD) to generate TiN, ZrN similar to the currently commercially available coatings and three different diamond like carbon (DLC) coatings on CoCrMo substrate. All surface coatings were mechanically specified by measuring roughness, coating thickness, abrasive wear and critical loads. A friction wear test was modified using an UHMWPE counterpart with a contact pressure of 10 MPa to compare different coatings in one tribological test setup. Calf serum was used as lubricant. The commercially used coatings on the retrieved explants show several defects and the critical load for coating failure varied widely. All produced surface coatings showed an increased surface roughness after coating compared to uncoated samples, which was due to droplet formation, especially in the DLC coatings. A diamond post-polishing process was performed to reduce the surface roughness and reach the ISO standard of R_a < 50 nm. The ZrN and TiN coatings exhibited a decreased friction after removing of the droplets in comparison to uncoated CoCrMo samples, indicating that the post-polishing process might be a useful tool to ameliorate the tribological performance. The friction coefficient for all tested DLC layers was more than two times increased compared to the CoCrMo samples. The use of hard/soft bearings with DLC coated endoprostheses seems to be not advantageous.

Nanomaterial coatings applied on stent surfaces

The advent of percutaneous coronary intervention and intravascular stents has revolutionized the field of interventional cardiology. Nonetheless, in-stent restenosis, inflammation and late-stent thrombosis are the major obstacles with currently available stents. In order to enhance the hemocompatibility of stents, advances in the field of nanotechnology allow novel designs of nanoparticles and biomaterials toward localized drug/gene carriers or stent scaffolds. The current review focuses on promising polymers used in the fabrication of newer generations of stents with a short synopsis on atherosclerosis and current commercialized stents, nanotechnology's impact on stent development and recent advancements in stent biomaterials is discussed in context.

Diamond thin films: giving biomedical applications a new shine

Progress made in the last two decades in chemical vapour deposition technology has enabled the production of inexpensive, high-quality coatings made from diamond to become a scientific and commercial reality. Two properties of diamond make it a highly desirable candidate material for biomedical applications: first, it is bioinert, meaning that there is minimal immune response when diamond is implanted into the body, and second, its electrical conductivity can be altered in a controlled manner, from insulating to near-metallic. In vitro, diamond can be used as a substrate upon which a range of biological cells can be cultured. In vivo, diamond thin films have been proposed as coatings for implants and prostheses. Here, we review a large body of data regarding the use of diamond substrates for in vitro cell culture. We also detail more recent work exploring diamond-coated implants with the main targets being bone and neural tissue. We conclude that diamond emerges as one of the major new biomaterials of the twenty-first century that could shape the way medical treatment will be performed, especially when invasive procedures are required.

A chemical stability study of trimethylsilane plasma nanocoatings for coronary stents

Trimethylsilane (TMS) plasma nanocoatings were deposited onto stainless steel coupons in direct current (DC) and radio frequency (RF) glow discharges and additional NH₃/O₂ plasma treatment to tailor the coating surface properties. The chemical stability of the nanocoatings were evaluated after 12 week storage under dry condition (25 °C) and immersion in simulated body fluid (SBF) at 37 °C. It was found that nanocoatings did not impact surface roughness of underlying stainless steel substrates. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to characterize surface chemistry and compositions. Both DC and RF nanocoatings had Si- and C-rich composition; and the O- and N-contents on the surfaces were substantially increased after NH₃/O₂ plasma treatment. Contact angle measurements showed that DC-TMS nanocoating with NH₃/O₂ treatment generated very hydrophilic surfaces. DC-TMS nanocoatings with NH₃/O₂ treatment showed minimal surface chemistry change after 12 week immersion in SBF. However, nitrogen functionalities on RF-TMS coating with NH₃/O₂ post treatment were not as stable as in DC case. Cell culture studies revealed that the surfaces with DC coating and NH₃/O₂ post treatment demonstrated substantially improved proliferation of endothelial cells over the 12 week storage period at both dry and wet conditions, as compared to other coated surfaces. Therefore, DC nanocoatings with NH₃/O₂ post treatment may be chemically stable for long-term properties, including shelf-life storage and exposure to the bloodstream for coronary stent applications.

Raman imaging of drug delivery systems

This review article includes an introduction to the principals of Raman spectroscopy, an outline of the experimental systems used for Raman imaging and the associated important considerations and limitations of this method. Common spectral analysis methods are briefly described and examples of interesting published studies which utilised Raman imaging of pharmaceutical and biomedical devices are discussed, along with summary tables of the literature at this point in time.

Methanol tolerant, high performance, noble metal free electrocatalyst developed from polyaniline and ferric chloride for the oxygen reduction reaction

Here, we report a low-cost, noble metal free Fe–N–C catalyst prepared using carbonized polyaniline (PANI) and ferric chloride as precursors in an inert atmosphere for oxygen reduction reaction.

Biliary endoprosthesis: a prospective analysis of bacterial colonization and risk factors for sludge formation

Bacterial colonization of biliary stents is one of the driving forces behind sludge formation which may result in stent occlusion. Major focus of the study was to analyze the spectrum and number of microorganisms in relation to the indwelling time of stents and the risk factors for sludge formation. 343 stents were sonicated to optimize the bacterial release from the biofilm and identified by matrix-associated laser desorption/ionization-time of flight mass spectrometer (MALDI-TOF). 2283 bacteria were analyzed in total. The most prevalent microorganisms were Enterococcus species (spp.) (504;22%), followed by Klebsiella spp. (218;10%) and Candida spp. (188;8%). Colonization of the stents mainly began with aerobic gram-positive bacteria (43/49;88%) and Candida spp. (25/49;51%), whereas stents with an indwelling time>60 days(d) showed an almost equal colonization rate by aerobic gram-negative (176/184;96%) and aerobic gram-positive bacteria (183/184;99%) and a high proportion of anaerobes (127/184;69%). Compared to stents without sludge, more Clostridium spp. [(P = 0.02; Odds Ratio (OR): 2.4; 95% confidence interval (95%CI): (1.1-4.9)]) and Staphylococcus spp. [(P = 0.03; OR (95%CI): 4.3 (1.1-16.5)] were cultured from stents with sludge. Multivariate analysis revealed a significant relationship between the number of microorganisms [P<0.01; OR (95%CI): 1.3(1.1-1.5)], the indwelling time [P<0.01; 1-15 d vs. 20-59 d: OR (95%CI): 5.6(1.4-22), 1-15 d vs. 60-3087 d: OR (95% CI): 9.5(2.5-35.7)], the presence of sideholes [P<0.01; OR (95%CI): 3.5(1.6-7.9)] and the occurrence of sludge. Stent occlusion was found in 70/343(20%) stents. In 35% of cases, stent occlusion resulted in a cholangitis or cholestasis. In conclusion, microbial colonization of the stents changed with the indwelling time. Sludge was associated with an altered spectrum and an increasing number of microorganisms, a long indwelling time and the presence of sideholes. Interestingly, stent occlusion did not necessarily lead to a symptomatic biliary obstruction.

Surface modification of coronary stents with SiCOH plasma nanocoatings for improving endothelialization and anticoagulation

The surface properties of intravascular stent play a crucial role in preventing in-stent restenosis (ISR). In this study, SiCOH plasma nanocoatings were used to modify the surfaces of intravascular stents to improve their endothelialization and anticoagulation properties. SiCOH plasma nanocoatings with thickness of 30-40 nm were deposited by low-temperature plasmas from a gas mixture of trimethysilane (TMS) and oxygen at different TMS:O2 ratios. Water contact angle measurements showed that the SiCOH plasma nanocoating surfaces prepared from TMS:O2  = 1:4 are hydrophilic with contact angle of 29.5 ± 1.9°. The SiCOH plasma nanocoated 316L stainless steel (316L SS) wafers were first characterized by in vitro adhesion tests for blood platelets and human umbilical vein endothelial cells. The in vitro test results showed that the SiCOH plasma nanocoatings prepared from TMS:O2  = 1:4 had excellent hemo- and cytocompatibility. With uncoated 316L SS stents as the control, the SiCOH plasma nanocoated 316L SS stents were implanted into rabbit abdominal artery model for in vivo evaluation of re-endothelialization and ISR inhibition. After implantation for 12 weeks, the animals testing results showed that the SiCOH plasma nanocoatings accelerated re-endothelialization and inhibited ISR with lumen reduction of 26.3 ± 10.1%, which were considerably less than the 41.9 ± 11.6% lumen reduction from the uncoated control group.