An investigation into patient-specific 3D printed titanium stents and the use of etching to overcome Selective Laser Melting design constraints.

Due to limitations in available paediatric stents for treatment of aortic coarctation, adult stents are often used off-label 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 their design. 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 (FE) methods we investigate how etching influences stent performance. Then using an inverse finite element approach the material properties of the printed and etched stents were calibrated and compared. We show that without etching the titanium stents, the inverse FE approach underestimates the stiffness of the as-built stent (E = 33.89 GPa) when compared to an average of 76.84 GPa for the etched stent designs. Finally, using patient-specific finite element models the different stents' performance were tested to assess patient outcomes and lumen gain and vessel stresses were found to be strongly influenced by the stent design and postprocessing. Within this study, etching is confirmed as a means to create open-cell stent designs whilst still 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.

Screening for primary aldosteronism: How to adjust existing antihypertensive medications to avoid diagnostic errors.

BACKGROUND: Screening for primary aldosteronism is infrequently performed in primary care. This is partly because screening is complicated by the need to adjust existing antihypertensive medications. This article provides an approach to screening patients who are already taking antihypertensive medication. OBJECTIVE: The objective of this article is to describe how to alter antihypertensive medications to allow accurate screening for primary aldosteronism. DISCUSSION: The ideal time to screen for primary aldosteronism is prior to initiating antihypertensive medications. If the patient is already undergoing treatment, replacing commonly used medications with sustained-release verapamil, prazosin, moxonidine and/or hydralazine results in fewer false positives and false negatives. Accuracy is also improved by ensuring normokalaemia. Screening should be performed six weeks after these conditions are met. A positive result should trigger a referral to an endocrine hypertension unit for further evaluation.