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BIORESORBABLE STENT A FUTURE OF STENT BUSINESS

BIORESORBABLE STENT

Over the past several years at TCT, there has been a focus away from traditional metallic drug-eluting stents (DES) to these bioresorbable scaffold technologies as the next step in stent evolution. However, recent trial data, especially from the ABSORB III Trial, and the first commercial bioresorbable stent being pulled off the market on Sept. 14, 2017, has dampened that view.

The latest round of trial data for the Abbott Absorb everolimus-eluting bioresorbable vascular scaffold (BVS) at TCT shed light on why the company announced last September it was pulling the stent off the market. Data from several ABSORB trials statistically showed good performance compared to the market-leading Xience everolimus-eluting metallic stent. However, there was signal in the data for slightly poorer outcomes, negating any long-term benefits the stent might offer. Experts involved in the trials said Absorb saw a very low usage rate, with estimates of U.S, usage of less than 5 percent.

A key prediction for interventional cardiology coming out of recent Transcatheter Cardiovascular Therapeutics (TCT) and American College of Cardiology (ACC) meetings is that bioresorbable stents will eventually replace conventional metallic stents in the coming years. Experts say dissolving stents have their drawbacks compared to metallic stents, but as the technology continues to advance, these issues may be resolved. Even if they are not, experts say growing clinical data shows the benefits of bioresorbable stents may outweigh any drawbacks.

Most bioresorbable stents are made of polylactic acid, a naturally dissolvable material that is used in medical implants such as dissolving sutures. The drawbacks of using polymer include recoil after expansion, stent thickness causing maneuverability and crossing issues, difficulty visualizing a non-metallic stent on fluoroscopy and stents not crimping firmly on delivery balloons. 

However, the advantage is not implanting a permanent metal prosthesis. Since the stent disappears, it eliminates the cause of potential inflammation that can lead to late-stent thrombosis and restenosis. Once the stent dissolves after about two years, it restores the vessel to a natural state of vasoconstriction and vasodilatation. The disappearance of the device also leaves open all options if future interventions are needed.

Coronary stents are used in percutaneous coronary intervention (PCI) procedures for the treatment of coronary heart disease. Stents are tube-like devices that are used to open and widen clogged heart arteries. Bioresorbable stent (BRS) devices, also known as bioabsorbable or biodegradable stents, refer to coronary stents that can fully dissolve in the body. The main advantage and promise of using a BRS is that it will clear out of the body within a few years, thereby theoretically reducing the long-term adverse effects normally seen with conventional stents.

Percutaneous coronary intervention (PCI) with bioabsorbable stents has created interest because the need for mechanical support for the healing artery is temporary, and beyond the first few months there are potential disadvantages of a permanent metallic prosthesis. Stents improve immediate outcomes, including profoundly reducing acute vessel occlusion after PCI by scaffolding intimal tissue flaps that have separated from deeper layers and by optimizing vessel caliber. They limit restenosis by preventing negative remodeling. The intimal hyperplastic healing response to PCI that contributes to restenosis, especially after bare metal stenting, can be limited by coating stents with antiproliferative medications.

Potential advantages of having the stent disappear from the treated site include reduced or abolished late stent thrombosis, improved lesion imaging with computed tomography or magnetic resonance, facilitation of repeat treatments (surgical or percutaneous) to the same site, restoration of vasomotion, and freedom from side-branch obstruction by struts and from strut fracture-induced restenosis. Bioabsorbable stents have a potential pediatric role because they allow vessel growth and do not need eventual surgical removal. The progression of stenosis seen within stents 7 to 10 years after stenting has been attributed, at least in part, to inflammation around metallic struts, which might argue for an absorbable stent. Progression is also observed late after balloon angioplasty. Some patients say they prefer an effective temporary implant rather than a permanent prosthesis.

DIAMOND LIKE CARBON (DLC) COATING IN MEDICAL APPLICATION

DIAMOND LIKE CARBON (DLC) COATING IN MEDICAL APPLICATION

Diamond Like Carbon(DLC) coatings exist in several different forms of amorphous carbon materials that display some of the unique properties of diamond. DLC coatings can be amorphous, more or less flexible, hard, strong, and slick according to the composition and processing method. Film formation can be obtained by plasma-assisted chemical vapor deposition, ion beam deposition, sputter deposition, and RF plasma deposition.

For example, Morgan Technical Ceramics proposes Diamonex DLC coatings deposited at temperatures below 150 °C by ion beam direct deposition or RF Plasma CVD and offering a wear-resistant chemical barrier for plastics. Benefits include wear and abrasion resistance, low Friction, high hardness, antireflective properties, corrosion resistance, gas barrier effect.

The results of experimental studies on amorphous diamond carbon layers obtained by a new method of r.f. dense plasma chemical vapour deposition onto orthopaedic pins and screws are presented. Research on this subject which has been carried out over many years allows us to draw optimistic conclusions concerning the biomedical applications of diamond-like carbon (DLC). In particular, preliminary medical research on a new DLC-steel substrate system developed in 1992, which has just been concluded, is extremely promising.

Elements-added diamond-like carbon films for biomedical applications were investigated. The aim of this work was to study the effects of the elemental contents (silicon and silicon-nitrogen) in a DLC film on its properties for biomedical applications. Pure DLC, Si-DLC, and Si-N-DLC films were prepared from C₂H₂, C₂H₂ : TMS, and C₂H₂ : TMS : N₂ gaseous mixtures, deposited on an AISI 316L substrate using the plasma-based ion implantation (PBII) technique. The structure of films was analyzed using Raman spectroscopy. The chemical composition of films was measured using energy dispersive X-ray spectroscopy (EDS). The average surface roughness of films was measured by using a surface roughness tester. The hardness and elastic modulus of films were measured by using a nanoindentation hardness tester. The friction coefficient of films was determined using a ball-on-disk tribometer. The surface contact angle was measured by a contact angle measurement. The corrosion performance of each specimen was measured using potentiodynamic polarization. The biocompatibility property of films was conducted using the MTT assay cytotoxicity test. The results indicate that the Si-N-DLC film shows the best hardness and friction coefficient (34.05 GPa and 0.13, respectively) with a nitrogen content of 0.5 at.%N, while the Si-DLC film with silicon content of 14.2 at.%Si reports the best contact angle and corrosion potential (92.47  and 0.398 V, respectively). The Si-N-DLC film shows the highest cell viability percentage of 81.96%, which is lower than the uncoated AISI 316L; this is a considerable improvement. All specimens do not demonstrate any cytotoxicity with approximate viabilities between 74% and 107%, indicating good biocompatibilities.

Implantable biomedical devices are one of the most popular methods of medical field to treat human illnesses. There are many kinds of biomedical devices, such as vascular stents, artificial joints, artificial knees, and bone plates. Most biomedical devices are made from stainless steel and titanium alloys because of the favorable mechanical and biocompatibility properties of these materials.

However, problems arising from material deterioration are often detected after long-term use. Corrosion is unavoidable due to various ions in the body reacting electrochemically with the surface of these metallic materials. A metal device may release metal into the body, causing allergic reactions as thrombogenicity of the blood in complicated and aggressive physiological environments. Thus, ideal biomedical devices provide biocompatibility that prevents metallic ion release. Surface coatings can improve both the mechanical properties and biocompatibility of biomedical devices that are in direct contact with blood and tissue.

Coating film technology has been studied for biomedical applications and includes diamond-like carbon (DLC) film. DLC films have many excellent properties including high hardness, low friction coefficient, good corrosion resistance, and good biocompatibility properties. Additionally, DLC films can be doped with certain elements, such as hydrogen (H-DLC), fluorine (F-DLC), and sulfur (S-DLC), to improve performance. Previous studies have shown that DLC films doped with silicon (Si-DLC) are significantly improved corrosion properties due to the formation of a passive film on their surfaces. Moreover, silicon-doped DLC films deposited by the sputtering method with the Si concentration varied from 4 to 16 at.% can reduce platelet adhesion on the material surface by modifying the hydrophobicity of the material [17]. Additionally, the corrosion resistance of a pure DLC film can be increased via silicon and nitrogen doping by increasing the number of sp³ sites in the film .

Plasma-based ion implantation (PBII) has been developed to improve DLC film properties and fabricate three-dimensional (3D) materials with complex shapes. In this technique, low working temperature avoids film quality degradation, such as loose and rough surface structure, and avoids DLC graphitization caused by normal CVD technique which is performed at higher working temperature.

Currently, there is no report on the deposition of Si- and Si-N-added DLC films on the AISI 316L substrates by the PBII method aimed at comparing the mechanical, tribological, and corrosion performance, especially to compare the cell viability percentage.