A Single-Connector Stent Antenna for Intravascular Monitoring Applications

Recently, smart stents have been developed by integrating various sensors with intravascular stents for detecting vascular restenosis or monitoring intravascular biomedical conditions such as blood pressure or blood flow velocity. The information on biomedical signals is then transmitted to external monitoring systems via wireless communications. Due to the limited volumes of blood vessels and limited influence of blood flow, antennas with good radiation performance are required for intravascular applications. In this paper, we propose a stent antenna composed of multiple rings containing crowns and struts, where each ring is connected with one connector. Unlike a conventional stent, wherein each ring is connected with several connectors, the single connector prevents the random distribution of electrical current and thus achieves good radiation performance. The implantable stent antenna is designed for the frequency range of 2 to 3 GHz for minimum penetration loss in the human body and tissues. Mechanical FEM simulations were conducted to ensure that the mechanical deformation was within specific limits during balloon expansions. A prototype was fabricated with laser cutting techniques and its radiation performance experimentally characterized. It was demonstrated that the fabricated stent antenna had an omnidirectional radiation pattern for arbitrary receiving angles, a gain of 1.38 dBi, and a radiation efficiency of 74.5% at a resonant frequency of 2.07 GHz. The main contribution of this work was the manipulation of the current distributions of the stent for good EM radiation performances which needed to be further examined while inserted inside human bodies. These research results should contribute to the further development of implantable wireless communications and intravascular monitoring of biomedical signals such as blood pressure and blood flow velocity.

Mechanical Design of Antichiral-Reentrant Hybrid Intravascular Stent

Chiral and reentrant metastructures with auxetic deformation abilities can serve as the building blocks in many industrial applications because of their light weight, high specific strength, energy absorption properties. In this paper, we report an innovative tubular-like structure by a combined mechanical effect of antichiral and reentrant. 2D antichiral-reentrant hybrid structures consisting of circular nodes and tangentially-connected ligaments are predesigned and fabricated using laser cutting technology with high-resolution. The elastic properties and auxeticity of the plane structure are analyzed and compared based on finite element analysis (FEA) and experimental results. For the first time, the antichiral-reentrant hybrid intravascular stents with the auxetic feature are proposed and parametric models are devised with good geometrical structure demonstrated. A series of large-scale stents are manufactured with stereolithography apparatus (SLA) additive manufacturing technique, and their mechanical behaviors are investigated in both experimental tests and FEA. As the selected antichiral-reentrant hybrid stents with tailored expansion ability are subjected to radial loading by the dilation of the balloon, stents undergo identifiable deformation mechanism due to the beam-like ligaments and circular node elements in the varied geometrical design, resulting in the distinct stress outcomes in plaque. It is also demonstrated that the antichiral-reentrant hybrid stents with tunable auxeticity possess robust mechanical properties through implantation inside the obstructed lesion.

Fibrosing Mediastinitis

Fibrosing mediastinitis is an uncommon thoracic disorder characterized by the extensiveproliferation of fibrous tissue in the mediastinum. This disorder frequently develops followingHistoplasma capsulatum infection with involvement of mediastinal lymph nodes. The fibroustissue can invade and compress mediastinal structures, including vessels, large airways, andthe esophagus. These patients may present with cough, sputum production, and dyspneadepending on location and extent of fibrosis. The radiographic presentation depends on thetype and extent of obstruction. Diagnosis requires computed tomography with angiography,ventilation-perfusion scans, and pulmonary function tests. Management depends on thestructures involved and the extent of infiltration and/or compression. Possible approachesinclude the use of endobronchial stents, intravascular stents, vascular bypass grafts, andthe resection of nonfunctional pulmonary tissue. Extensive surgical procedures are usuallynot warranted. These patients usually do not respond to antifungal or anti-inflammatorymedications. Several patients have responded to rituximab, and this drug is a possibleconsideration in patients with ongoing inflammation in the mediastinum.

Design and characterization of PDO biodegradable intravascular stents

Two novel biodegradable intravascular stents (BIS) with different structures are introduced. Braiding-structural BIS and Z-structural BIS were fabricated from polydioxanone (PDO) monofilament by a hand-braiding method with a perforated mold, imitating commercial stents that have been used clinically. The fabrication process of these two BIS is described and stent parameters, mechanical properties, and degradation properties are reported. The findings reveal that Z-structural BIS have higher porosity, smaller longitudinal shortening rate, and higher radial force and recovery rate compared with the braiding-structural stent. During the degradation process, braiding-structural BIS maintained their mechanical properties higher than international standards for 12 weeks, while Z-structural stents maintained them for 16 weeks.

In Vitro Degradation Behaviours of PDO Monofilament and Its Intravascular Stents with Braided Structure

Biodegradable intravascular stent has attracted more and more focus in recent years as an effective solution for angiostenosis. Ideal stents were expected to exhibit sufficient radial force to support the vascular wall, while suitable flexibility for the angioplasty. After vascular remodeling, stents should be degraded into small molecular and be eliminated from human body, causing no potential risk. In this paper, poly-p-dioxanone (PDO) monofilament was braided into net structure with four different braiding density, two of which exhibited sufficient radial force larger than 30 kPa, and three of which showed the bending rigidity within 11.7–88.1 N•mm2. The degradation behaviors of monofilaments and stents have been observed for 16 weeks. The findings obtained indicate that degradation first occurred in morphology region, which induced temporary increase of crystallinity, monofilament bending rigidity and stent mechanical properties. During this period, monofilament tends to be hard and brittle and lost its tensile properties. Then the crystalline region was degraded and stent mechanical properties decreased. All the results reveal that the PDO intravascular stents with braided structure were able to afford at least 10 weeks of sufficient support to the vascular wall.