Biocompatibility and Biostability of Metallic Endovascular Implants: State of the Art and Perspectives

Corrosion induced fracture of NiTi wires in simulated oral environments

This work aims to assess the influence of corrosion on fracture of nickel titanium (NiTi) superelastic wires in physiological solutions (9 g/l NaCl) with and without addition of 1 g/l NaF. The electrochemical cell was coupled to a Hounsfield Tensiometer tensile machine commonly used for corrosion investigation of alloys under stress and strain. Corrosion tests were performed on unstrained and strained conditions up to 4% total strain. This strain limit corresponds to 50% of the total elongation achieved into the superelastic stress plateau of the alloy. All wire specimens were analyzed after testing by scanning electron microscopy (SEM). The results showed that localized corrosion occurred for NiTi wires in solution containing fluoride, while no corrosion attack was detected in NaCl 9 g/l solution. There was no significant difference between the corrosion resistance of unstrained and strained wires. However, brittle like fracture occurred in NaCl + NaF solution within the superelastic domain of the material. The most relevant conclusion achieved is that the use of superelastically strained NiTi in oral environments in the presence of fluoride is followed by significant risk of corrosion induced fracture.

Implantable chemothermal brachytherapy seeds: A synergistic approach to brachytherapy using polymeric dual drug delivery and hyperthermia for malignant solid tumor ablation

Chemothermal brachytherapy seeds have been developed using a combination of polymeric dual drug chemotherapy and alternating magnetic field induced hyperthermia. The synergistic effect of chemotherapy and hyperthermia brachytherapy has been investigated in a way that has never been performed before, with an in-depth analysis of the cancer cell inhibition property of the new system. A comprehensive in vivo study on athymic mice model with SCC7 tumor has been conducted to determine optimal arrays and specifications of the chemothermal seeds. Dual drug chemotherapy has been achieved via surface deposition of polydopamine that carries bortezomib, and also via loading an acidic pH soluble hydrogel that contains 5-Fluorouracil inside the chemothermal seed; this increases the drug loading capacity of the chemothermal seed, and creates dual drug synergism. An external alternating magnetic field has been utilized to induce hyperthermia conditions, using the inherent ferromagnetic property of the nitinol alloy used as the seed casing. The materials used in this study were fully characterized using FESEM, H¹ NMR, FT-IR, and XPS to validate their properties. This new approach to experimental cancer treatment is a pilot study that exhibits the potential of thermal brachytherapy and chemotherapy as a combined treatment modality.

Development of implantable medical devices: from an engineering perspective

From the first pacemaker implant in 1958, numerous engineering and medical activities for implantable medical device development have faced challenges in materials, battery power, functionality, electrical power consumption, size shrinkage, system delivery, and wireless communication. With explosive advances in scientific and engineering technology, many implantable medical devices such as the pacemaker, cochlear implant, and real-time blood pressure sensors have been developed and improved. This trend of progress in medical devices will continue because of the coming super-aged society, which will result in more consumers for the devices. The inner body is a special space filled with electrical, chemical, mechanical, and marine-salted reactions. Therefore, electrical connectivity and communication, corrosion, robustness, and hermeticity are key factors to be considered during the development stage. The main participants in the development stage are the user, the medical staff, and the engineer or technician. Thus, there are three different viewpoints in the development of implantable devices. In this review paper, considerations in the development of implantable medical devices will be presented from the viewpoint of an engineering mind.

Thermally cross-linked PNVP films as antifouling coatings for biomedical applications

Protein repellent coatings are widely applied to biomedical devices in order to reduce the nonspecific adhesion of plasma proteins, which can lead to failure of the device. Poly(N-vinylpyrrolidone) (PNVP) is a neutral, hydrophilic polymer with outstanding antifouling properties often used in these applications. In this paper, we characterize for the first time a cross-linking mechanism that spontaneously occurs in PNVP films upon thermal annealing. The degree of cross-linking of PNVP films and their solubility in water can be tailored by controlling the annealing, with no need for additional chemical treatment or irradiation. The physicochemical properties of the cross-linked films were investigated by X-ray photoelectron spectroscopy, infrared spectroscopy, neutron and X-ray reflectometry, ellipsometry, and atomic force microscopy, and a mechanism for the thermally induced cross-linking based on radical formation was proposed. The treated films are insoluble in water and robust upon immersion in harsh acid environment, and maintain the excellent protein-repellent properties of unmodified PNVP, as demonstrated by testing fibrinogen and immunoglobulin G adsorption with a quartz crystal microbalance. Thermal cross-linking of PNVP films could be exploited in a wide range of biotechnological applications to give antifouling properties to objects of any size, essentially making this an alternative to high-tech surface modification techniques.

Early Surgical Outcome After Failed Primary Stenting for Lower Limb Occlusive Disease

PURPOSE

To evaluate the early results of revascularization after failed primary stent placement for lower limb occlusive disease.

METHODS

A retrospective review was conducted of 25 consecutive patients (16 men; mean age 65 years, range 32-89) treated between January 2001 to October 2003 for infrainguinal stent failure at a median 6.6 months (range 3-60) after primary stent implantation (27 femoropopliteal and 20 popliteal-crural) at referring hospitals. All surgical procedures for stent failure were performed at tertiary centers. The results of bypass grafting for failed stenting were compared to a contemporaneous cohort of patients undergoing primary bypass surgery performed by the same surgeons.

RESULTS

At the time of admission, 22 stents were thrombosed, and 3 patent stents presented with >50% in-stent stenosis. Twenty patients had 7 femoropopliteal or 9 femorodistal vein bypasses and 4 reconstructions of the common femoral or profunda femoris artery. Four patients had 3 primary amputations and 1 lumbar sympathectomy. One patient with claudication was treated conservatively. Procedure-related complications were observed in 40%; 30-day mortality was 4% (1/25). Early (30-day) graft thrombosis occurred in 6 (30%) of 20 arterial reconstructions, necessitating 8 secondary amputations (44% [11/ 25] overall amputation rate). A total of 47 surgical procedures were performed in the 24 surviving patients (median 2 operations per patient, range 1-9) over an 11-month period (range 1-57). Primary patency rates at 30 days and at 6 and 12 months were 67%, 44%, and 33%, respectively, in the poststent bypass cohort versus 98%, 96%, and 88%, respectively, in a contemporaneous group of patients treated with primary bypass grafting.

CONCLUSIONS

Failed stents in lower limb arteries often require distal reconstructive bypass surgery, which is associated with high complication rates and poor outcome, including major amputations. There is no scientific evidence to support stenting below the inguinal ligament.