An Investigation into Patient-Specific 3D Printed Titanium Stents and the use of Etching to Overcome Selective Laser Melting Design Constraints

There is currently a clear clinical need in the area of stenting for paediatric patients, whereby currently commercially available adult stents are often required to be used off-label for paediatric patients resulting in less than optimal outcomes. The increasingly widespread use of CT and/or MR imaging for pre-surgical assessment, and the emergence of additive manufacturing processes such as 3D printing, could enable bespoke devices to be produced efficiently and cost-effectively. However, 3D printed metallic stents need to be self-supporting leading to limitations in the design of stents available through additive manufacturing. In this study we investigate the use of etching to overcome these design constraints and improve stent surface finish. Furthermore, using a combination of experimental bench testing and finite element methods we investigate how etching influences stent performance and using an inverse finite element approach the material properties of the printed and etched stents were calibrated and compared. Finally, using patient-specific finite element models the stent performance was tested to assess patient outcomes. Within this study, etching is confirmed as a means to create open-cell stent designs whilst conforming to additive manufacturing ‘rules’ and concomitantly improving stent surface finish. Additionally, the feasibility of using an in-vivo imaging to product development pipeline is demonstrated that enables patient-specific stents to be produced for varying anatomies to achieve optimum device performance. Figure 1. Graphical abstract.

Investigation of the Finishing Technology of SLM Implants

In this research, the use of plasma electrolytic polishing (PEP) as a finishing treatment of materials obtained by the SLM method from CoCr30 cobalt-chromium powder is proposed. To assess the possibility of using this method, a simulator sample was used. The imitation sample was polished for 60 seconds. The roughness and the size of the removal material were measured. Based on the results obtained for the simulator sample, a conclusion was made about the possibility of using PEP technology for finishing the treatment stent. The stent simulator was also polished. The processing time was 30s and 60s. The geometric parameters were measured, and the removal material was calculated. Images of the stent surface were taken before and after PEP. It was found that with an increase in the processing time from 30 to 60 seconds, the allowance removed from all surfaces increases almost twice. The possibility of using the PEP technology as a finishing operation for the manufacture of stents from cobalt-chromium alloys is shown.

Determination of the Entire Stent Surface Area by a New Analytical Method

Stenting is a widely used treatment procedure for coronary artery disease around the world. Stents have a complex geometry, which makes the characterization of their corrosion difficult due to the absence of a mathematical model to calculate the entire stent surface area (ESSA). Therefore, corrosion experiments with stents are mostly based on qualitative analysis. Additionally, the quantitative analysis of corrosion is conducted with simpler samples made of stent material instead of stents, in most cases. At present, several methods are available to calculate the stent outer surface area (SOSA), whereas no model exists for the calculation of the ESSA. This paper presents a novel mathematical model for the calculation of the ESSA using the SOSA as one of the main parameters. The ESSA of seven magnesium alloy stents (MeKo Laser Material Processing GmbH, Sarstedt, Germany) were calculated using the developed model. The calculated SOSA and ESSA for all stents are 33.34%(±0.26%) and 111.86 mm (±0.85 mm), respectively. The model is validated by micro-computed tomography (micro-CT), with a difference of 12.34% (±0.46%). The value of corrosion rates calculated using the ESSA computed with the developed model will be 12.34% (±0.46%) less than that of using ESSA obtained by micro-CT.

Uropathogens Preferrentially Interact with Conditioning Film Components on the Surface of Indwelling Ureteral Stents Rather than Stent Material

Despite routine implementation in urology, indwelling ureteral stents pose as a nidus for infection. Conditioning film accumulates on stents, which prime pathogen adhesion, promoting infectious biofilm formation. However, the extent to which conditioning film components play a role in facilitating bacterial adhesion and biofilm formation remains largely unknown. Here, we examined the interaction of previously identified stent-bound conditioning film components (fibrinogen, uromodulin, and albumin) with bacterial uropathogens. Cytoscopically removed stents were incubated with common uropathogens (Escherichia coli, Enterococcus faecalis, and Staphylococcus aureus). Immunofluorescent double staining was performed to study the localization of uropathogens relative to stent-bound conditioning film proteins. Conditioning film components were identified on the external stent surface with some deposition in the inner lumen. Bacteria co-localized with fibrinogen, uromodulin, and albumin, suggesting a potential mechanism for stent-associated infections. Here, we determine strong co-localization between common uropathogenic bacterial species with prominent conditioning film components on ureteral stents. Further functional validation of interactions amongst these uropathogens and conditioning film proteins may enhance clinical management for stent-associated infections and development of improved stent technologies.

Preliminary study of thrombogenicity induced by the nanoparticle surface coating of intracranial stents

Endovascular treatment of intracranial aneurysms with intracranial stents was proven to be clinically safe and effective, but is still associated with a risk of thromboembolic complications. Stent thrombosis could be a sever complication associated with specific stent surface coatings and designs. Standardized in vitro tests for investigation of thrombogenicity induced by different nanomaterials were used as the basic method in carrying out the present study. Therefore, the aim of this study was to evaluate the thrombogenicity of three different nanomaterials (ZnO, TiO2 si Fe3O4) possible used as surface coating for intracranial stents. This study is based on a procedure for in vitro analyses of plasma coagulation time. To measure the plasma coagulation time, platelet-poor plasma from human whole blood was in vitro exposed to nanoparticles and analysed in prothrombin (PT) and activated partial thromboplastin (APTT).

Capturing Endothelial Cells by Coronary Stents - From Histology to Clinical Outcomes

Introduction of drug-eluting stents (DES) in the therapy of patients with coronary artery disease resulted in the significant reduction of in-stent restenosis compared to bare-metal stent (BMS) treatment. However, the high incidence of late stent thrombosis with DES emerged as one of the safety concerns after their implantation. Enhancing stent endothelization by improved early healing and neointimal strut coverage emerged as possible solution for this late complication. Endothelial progenitor cells (EPC) capturing stents are designed to promote in situ endothelization with immobilized, antihuman, anti-CD34 antibodies attached to the luminal stent surface. Anti-CD34 antibodies target and capture EPC from circulation, which further differentiate into vascular endothelial cells and form functional endothelial layer on the stent surface. These cells are also capable of secreting pro-angiogenic factors that stimulate local endothelial cells to proliferate and migrate. Preclinical and clinical studies proved feasibility, efficacy and safety of EPC capturing stents in stable and high-risk patients with coronary artery disease. Rapid and extensive endothelization of EPC capturing stents translated into favorable profile of clinical outcomes, comparable to efficacy of BMSs and DESs. Therefore, we here present the most important results from the experimental and clinical studies that explored ECP capturing strategy to enhance endothelization, reduce the incidence of instent thrombosis and improve outcomes of patients with coronary artery disease, along with the future perspectives in this promising therapeutic approach.