Ignacio Rintoul

SURFACE CONDITIONING OF CARDIOVASCULAR 316L STAINLESS STEEL STENTS: A REVIEW

Cardiovascular disease is the leading cause of death worldwide and 90% of coronary interventions consists in stenting procedures. Most of the implanted stents are made of AISI 316L stainless steel (SS). Excellent mechanical properties, biocompatibility, corrosion resistance, workability and statistically demonstrated medical efficiency are the reasons for the preference of 316L SS over any other material for stent manufacture. However, patients receiving 316L SS bare stents are reported with 15–20% of restenosis probability. The decrease of the restenosis probability is the driving force for a number of strategies for surface conditioning of 316L SS stents. This review reports the latest advances in coating, passivation and the generation of controlled topographies as strategies for increasing the corrosion resistance and reducing the ion release and restenosis probability on 316L SS stents. Undoubtedly, the future of technique is related to the elimination of interfaces with abrupt change of properties, the elimination of molecules and any other phase somehow linked to the metal substrate. And leaving the physical, chemical and topographical smart modification of the outer part of the 316L SS stent for enhancing the biocompatiblization with endothelial tissues.

Novel Poly(Diol Sebacate)s as Additives to Modify Paclitaxel Release From Poly(Lactic-co-Glycolic Acid) Thin Films

Paclitaxel (PTX) incorporation in poly(lactic-co-glycolic acid) (PLGA) matrices produce films with high tensile rigidity and slow release that fail to deliver the required release rate for most biomedical applications such as in drug eluting stents and cancer treatments. To modify and improve this behavior, a set of poly(diol sebacate)s were synthesized and fully characterized as possible additives. The tensile properties of PLGA blends were evaluated as these materials could be used as coatings in drug eluting stent applications. A significant improvement in mechanical flexibility was observed with 20% additive content, as it reduced the Youngs modulus value and increased the maximum deformation at break. PTX release was studied and correlated with the release of additive from PLGA films. An increase in the initial burst release phase was observed on all blends when compared to the control films of PLGA. Modulation of PTX release was achieved by altering the hydrophilicity degree of the additive or its percentage content on the blend. This supports the possibility that PTX was partitioned into the additive phase. Cytotoxicity analyses of novel additives were performed on mouse embryonic fibroblasts NIH/3T3.

Poly(polyol sebacate) elastomers as coatings for metallic coronary stents

Biocompatible polymeric coatings for metallic stents are desired, as currently used materials present limitations such as deformation during degradation and exponential loss of mechanical properties after implantation. These concerns, together with the present risks of the drug-eluting stents, namely, thrombosis and restenosis, require new materials to be studied. For this purpose, novel poly(polyol sebacate)-derived polymers are investigated as coatings for metallic stents. All pre-polymers reveal a low molecular weight between 3000 and 18 000 g mol-1 . The cured polymers range from flexible to more rigid, with E-modulus between 0.6 and 3.8 MPa. Their advantages include straightforward synthesis, biodegradability, easy processing through different scaffolding techniques, and easy transfer to industrial production. Furthermore, electrospraying and dip-coating procedures are used as proof-of-concept to create coatings on metallic stents. Biocompatibility tests using adipose stem cells lead to promising results for the use of these materials as coatings for metallic coronary stents.

Absolute determination of the gelling point of gelatin under quasi-thermodynamic equilibrium.

Thermodynamic studies on phase transformation of biopolymers in solution are useful to understand their nature and to evaluate their technological potentials. Thermodynamic studies should be conducted avoiding time-related phenomena. This condition is not easily achieved in hydrophilic biopolymers. In this contribution, the simultaneous effects of pH, salt concentration, and cooling rate (Cr) on the folding from random coil to triple helical collagen-like structures of gelatin were systematically studied. The phase transformation temperature at the absolute invariant condition of Cr = 0 °C/min (T(T)Cr=0) ) is introduced as a conceptual parameter to study phase transformations in biopolymers under quasi-thermodynamic equilibrium and avoiding interferences coming from time-related phenomena. Experimental phase diagrams obtained at different Cr are presented. The T(T)(Cr=0) compared with pH and TT(Cr=0) compared with [NaCl] diagram allowed to explore the transformation process at Cr = 0 °C/min. The results were explained by electrostatic interactions between the biopolymers and its solvation milieu.

Accurate prediction of shape and size of polyvinyl alcohol beads produced by extrusion dripping

Beads are one of the particulate delivery systems used to achieve protection and/or controlled delivery of different active ingredients or microorganisms. Polyvinyl alcohol is a non-toxic and biodegradable polymer and possesses extensive applications as a biomaterial. In the present work, two different strategies were applied for the prediction of shape and size of polyvinyl alcohol beads. These beads were obtained by extrusion dripping of a boric acid–polyvinyl alcohol aqueous solution into a basic aqueous gelling bath. The shapes and sizes of immature, mature and dry beads were determined using optical microscopy. Two different strategies included statistical and fluid dynamical (mechanistic) models to fit the experimental data. The shape of immature and mature beads was found to be dependent on the viscosity of the dripping solution for the former and the maturation time for the latter. The shape of dry beads was found to be mainly dependent on the particle contraction in the drying process. The size of mature and dried beads was correctly predicted from the operating conditions by means of a statistically developed model and from the dripping solution properties by means of a fluid dynamical approach. The optimal conditions for minimal dried bead size were calculated. The obtained mathematical models allow reduction in the amount of resources and time taken in the initial stages of the development of a novel encapsulated formulation. The mechanistic model may be applied to other polymeric systems once the corresponding parameters have been determined during proof-of-concept experiments.