Papers by Author: Diego Mantovani

Abstract: Titanium and its alloys are considered the gold standard for bone contact implants due to their suitable mechanical properties and biological performances. However, their long-term performance remains impaired, mainly due to insufficient integration with surrounding tissues and infections. To overcome these problems, several strategies, particularly coatings, are explored. However, certain drawbacks remain such as lack of adhesion or low mechanical resistance. Among these coatings, diamond-like carbon (DLC) has emerged as a promising material due to its superior mechanical and tribological properties, chemical inertness and stability. In addition, the microstructure of DLC allows the incorporation of other species such as antibacterial agents (Ag, ZnO, etc.), leading to multifunctional protective coating. However, due to the high intrinsic stresses of DLC compared to the native oxide layer, the adhesion of DLC to metallic surfaces remains rather low. Therefore, in order to overcome adhesion issues, this work investigates the impact of different pretreatments, namely etching, carburization or both, on the adhesion of DLC deposited by plasma-assisted chemical vapor deposition, on titanium substrates. The results showed that carburizing 10 min was the most promising pretreatment for improving the DLC adhesion on Ti surfaces. Furthermore, the DLC coating appeared stable even after 7 days of aging in pseudo-physiological conditions, making the process promising for improving Ti implants.

Abstract: Current research on biodegradable iron-based alloys mainly focuses at regulating the material degradation rate, as well as its biological behavior, especially from the point of view of the hemocompatibility and cytocompatibility. In fact, fine-tuning of the surface roughness, morphology and chemical composition can improve the functional response of the material. For that purpose, a surface modification strategy, namely plasma immersion ion implantation (PIII), is proposed to perform the selective modification of surface properties without affecting the bulk ones. In this work, the influence of treatment time (t_imp = 15, 60 and 120 min.) and implanted species (O, N or C) on the surface properties of a Fe-13Mn-1.2C resorbable alloy was investigated. The findings demonstrated that varying the process gas and the exposition time led to a variety of topographies, surface energies and chemical compositions. XPS analyses and depth profiles clearly showed the impact of the process parameters on the surface features and element distribution, due to implanted species penetration into the alloy. The implanted samples showed a delayed clotting time, thus a better hemocompatibility. In contrast, nitrogen-treated surfaces displayed a more pronounced hemolytic behavior, whereas oxygen and methane did not. PIII implantation appears to be a versatile solution for fine-tuning surface topography, composition and biological properties, making the process promising for the improvement of metallic biodegradable vascular implants.

Abstract: Open-air aerosol-assisted plasma deposition has emerged as an efficient process to deposit innovative composite coatings. In this work, it was used to investigate biodegradable polymeric coatings loaded with carbon dots (CDs) for bioengineering and biomedical applications. The structure, composition, wettability, and biodegradation of these coatings depend on the precursors used, here methacrylic anhydride and ethylene glycol di-methacrylate. The effectiveness of the deposition was confirmed by X-ray photoelectron and Fourier-transformed infrared spectroscopies, i.e., polymerization of vinyl groups and integrity of hydrolysable functions. The latter allow control the CDs release over time, which were homogenously distributed in the coating, as confirmed by electronic and confocal microscopies. Both coatings were found to be non-cytotoxic to human dermal fibroblasts. This one-step open-air acrylate-based plasma deposition strategy has enabled the tuning of the coating release profile and offers new perspectives for drug delivery applications.

Abstract: Surgical implantation of metallic stents is today a common procedure for restoring narrowed arteries. However, main complications as in-stent restenosis, partial or total thrombosis, inflammation and devices degradation are still a serious clinical concern. The coating of stents with fluorocarbon (CF_x) ultrathin films represents a valuable strategy to limit these complications. Moreover, an additional step for the modification of some key surface properties of CF_x coatings could further enhance their blood compatibility. Therefore, the objective of this work was to develop an oxidation process specific to ultrathin CF_x coatings based on a methanol plasma treatment to modulate their biological response. Oxidized and non-oxidized coatings were investigated by XPS, ToF-SIMS, water contact angle, SEM and AFM. Tunable oxidation of the surface of CF_x coatings was obtained by methanol plasma treatment, thus producing an increase of surface wettability, without affecting morphology, roughness and adhesion of the coatings. Blood test results showed an increased hemocompatibility of the oxidized samples, confirming the hypothesis that such treatment can succeed in modulating the blood contact behavior of the CF_x oxidized coatings.

Abstract: Environmental surfaces have been widely recognized as an important source of hospital-associated transmissions. A number of silver-based antibacterial coatings have been reported in the literature. However, the success of any antibacterial strategy depends on the ability to control the kinetics of the silver ions released from the coating. The novel strategy proposed in this work is based on plasma surface engineering for a controlled-release of silver ions. Plasma-based nanocoatings, plasma oxidation processes and surface patterning of silver coatings were designed and optimized. Surface analyses such as XPS and AFM, as well as silver ion release over 168 h, was evaluated by MIP-AES. Results showed that surface plasma engineering successfully allow tuning the silver release and bioactivity in Ag-containing antibacterial coatings.

Abstract: Powders of Mg_0.4Ca_0.6Fe₂O₄ were prepared by sol-gel using ethylene glycol and Mg, Ca and Fe nitrates as starting materials. Those powders were heat treated at different temperatures (300, 400, 500 and 600 °C) for 30 min. The materials obtained were characterized by X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). The Ca-Mg ferrite with the most appropriate magnetic properties was further analyzed by transmission electron microscopy (TEM). The heating capability of the nanoferrites was also tested via magnetic induction. The XRD patterns of these Ca-Mg ferrites showed a cubic inverse spinel structure. Furthermore, neither traces of hematite nor orthorhombic Ca ferrite phases were detected. Moreover, all the Ca-Mg ferrites are superparamagnetic and the particle size distribution of these Ca-Mg magnetic nanoparticles exhibits an average diameter within the range of 10-14 nm. The needed temperature for hyperthermia treatment was achieved at around 12 min.

Abstract: L605 (ASTM F90), a cobalt-chromium-tungsten alloy with excellent mechanical properties and high radiopacity, has been widely accepted as a suitable alloy for stent applications. The presence of carbides in this alloy, primary carbides and secondary carbides, leads to difficulties in controlling mechanical performances and therefore in optimizing stent size and performances. This work is thus to investigate the carbides and their role in advanced mechanical properties of L605 alloy for stent fabrication. Herein, the nature, nucleation, distribution and dissolution of the carbides were investigated in a series of recrystallized L605 tubes from hard-drawn (HD) state. The mechanical properties corresponding to each carbide state were examined by tensile tests and microhardness measurements. The results indicate important relationships among carbide precipitation, grain size and mechanical behaviors, as a function of annealing temperature and duration. The intergranular secondary carbides, induced at the onset of the recrystallization of L605 matrix, were preferentially precipitated at grain boundaries. The nucleation of such particulate phase leads to a pinning effect on grain coarsening, resulting in a strengthening effect of the material. However, the further growth of the secondary carbides brings about considerable reduction of ductility, which is inacceptable for stent application. Therefore, an optimization protocol on carbides controlling was developed to maintain the strengthening effect without losing ductility and small grain size.

Abstract: Biodegradable metals have been proposed for temporary implants such as coronary artery stent and internal bone fixators. During implantation, a stent is inserted and expanded by using a catheter into a narrowed coronary artery and is subjected to mechanical stress in a corrosive body fluid environment, a condition where stress corrosion cracking may occur. This letter reports an experimental work to verify the susceptibility of Fe-35Mn alloy, a proposed alloy for biodegradable coronary stent, to stress corrosion cracking under a pseudo-physiological condition.

Abstract: During the last few decades, titanium alloys are more and more popular and developed as biomedical devices because of their excellent biocompatibility, very good combination of mechanical properties and prominent corrosion resistance [1-3]. Recently, a new generation of beta titanium alloys dedicated to biomedical applications has been developed. Based on biocompatible alloying elements such as Ta, Nb, Zr and Mo, these alloys were designed as low modulus alloys [4] or nickel-free superelastic materials [5, 6] mainly for orthopedic or dental applications as osseointegrated implants. Beta type titanium alloys take great advantages from their capacity to display several deformation mechanisms as a function of beta phase stability. Therefore, from low to high beta stability, stress assisted martensitic phase transformation (β-α’’), mechanical twinning or simple dislocation slip can alternatively be observed [7]. As a consequence, a very large range of mechanical properties can be reached, including low apparent modulus, large reversible elastic deformation or high yield stress. Although titanium alloys display now a long history of successful applications in orthopedic and dental devices, none of them have been commercially exploited in the area of coronary stents, despite their superior long term haemocopatibility compared to the 316L stainless steel. However, according to previous researches on the biocompatibility of various metals, the corrosion behavior of stainless steel is dominated by its nickel and chromium components, which may induce redox reaction, hydrolysis and complex metal ion–organic molecule binding reactions, whereas none are observed with titanium [8, 9].

Abstract: Small caliber vascular replacement (<4 mm) still remains a challenge for medical and research teams, as no available vascular substitutes (VS) are suitable for small diameter bypass. Vascular engineering proposes new models of small diameter VS but rare are those that meet the biocompatibility and mechanical criteria. In this study, we developed a new scaffold made by the combination of two natural biomacromolecules: collagen and silk fibroin. The scaffold was further cellularised with porcine smooth muscle cells. First, the behavior of cells in the collagen-fibroin constructs was verified in order to evaluate the biocompatibility of the scaffold with the cells. Then, gel mass loss and cellular attachment, morphology, spreading and viability were analysed. The results showed an excellent interaction and biocompatibility between collagen, silk fibroin fibers and cells. Thus, the collagen-fibroin construct appears to be a very attractive material for vascular tissue engineering.