50 research outputs found

    Influence of ECAP process on mechanical, corrosion and bacterial properties of Zn-2Ag alloy for wound closure devices

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    Actual polymeric wound closure devices are not optimal for load-bearing applications due to the low mechanical properties and the risk of inflammation and bacterial infection mainly produced by multifilament and braided configurations. Biodegradable metallic Zn alloys are promising materials candidates; however, mechanical performance, corrosion behaviour, and biological response should be controlled in order to inhibit the risk of inflammation and bacterial infection. To this end, a Zn-2Ag (2 wt% Ag) alloy was processed by ECAP to evaluate the concurrent combined effect of grain refinement and Ag alloying on biodegradation and antibacterial activity. Two ECAP cycles were successfully applied to a Zn-2Ag alloy obtaining a homogeneous ultra-fine-grained structure in which nanoindentation maps suggested isotropic mechanical properties. Lower UTS and YS with higher elongation was reported after ECAP with similar corrosion rates as before processing. ECAP processed samples showed a homogeneous Ag+ release below the minimum inhibitory concentration for S. Aureus and no antibacterial effect was observed by diffusion. As expected, the presence of Ag in Zn-Ag alloys reduced bacterial attachment. Nevertheless, ECAP processed Zn-2Ag provided an excellent antibacterial activity after 3 h probably caused by the uniformly degraded and thus, non‚Äď stable, surface observed after bacterial adhesion.Peer ReviewedPostprint (published version

    Solvent-cast direct-writing and electrospinning as a dual fabrication strategy for drug-eluting polymeric bioresorbable stents

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    Bioresorbable stents (BRS) are conceived to retain sufficient radial strength after implantation while releasing an antiproliferative drug in order to prevent vessel restenosis until complete resorption. Ongoing research trends involve the use of innovative manufacturing techniques to achieve thinner struts combined with optimized local drug delivery. This work presents a combination of solvent-cast direct-writing (SC-DW) and electrospinning (ES) using poly-l-lactic acid (PLLA) and poly(l-lactic-co-¬Ņ-caprolactone) (PLCL) as a new approach to generate everolimus-eluting BRS for cardiovascular applications. A Design of Experiment (DoE) was conducted to determine the optimal parameters to obtain a homogeneous coating with high specific surface. Manufactured stents were characterized by means of mechanical tests and scanning electron microscopy (SEM), with everolimus release in accelerated conditions quantified through High Performance Liquid Chromatography (HPLC). Drug loading was achieved either encapsulated in the struts of the stent or in an electrospun PLCL membrane covering the stent. In the former case, everolimus release was found to be insufficient, less than 3% of total drug loading after 8 weeks. In the latter, everolimus release considerably increased with respect to drug-loaded 3D-printed stents, with over 50% release in the first 6 hours of the test. In conclusion, everolimus release from PLCL-coated 3D-printed stents would match the dose and timeframe required for in vivo applications, while providing thinner struts than SC-DW drug-loaded stents.Peer ReviewedPostprint (published version

    Biodegradable metallic zinc alloys for biomedical applications

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    Biodegradable metals, such as zinc (Zn) appear to overcome some of the drawbacks of permanent metallic implants. However, the uncontrolled biodegradation of Zn-alloyed materials is still a concern for biomedical applications compromising biocompatibility and mechanical properties. In this work, two strategies based on severe plastic deformation or polymeric coatings are evaluated to overcome degradation drawbacks. Cold-rolled Zn-0.5Mg and Zn-2Ag bars (Goodfellow, UK) were modified as follows: (1) ECAP was performed to the bars, supplying an equivalent strain of 0.76 each pass; (2) PCL was dissolved in chloroform and spin-coated onto the surfaces. The microstructure was observed by SEM/EDS and EBSD. Tensile and nanoindentation tests were performed. The corrosion was studied by PDP and EIS. Fig. 1 shows the microstructure of the as-received alloys. Ultra-fine grain structure was achieved after ECAP (Fig. 2), providing superplastic behavior to the Zn-2Ag alloy (elongation over 200 %). Nanoindentation maps showed similar hardness distribution after ECAP. PCL-coated samples presented a noteworthy decrease in current density (from 15 A/cm2 down to 0.5 A/cm2), and EIS confirmed the effect of the PCL layer with a higher impedance modulus. The influence of the secondary phases on the mechanical reinforcement of Zn was previously studied [1]. However, their presence also forms galvanic pairs and favors localized corrosion, which could provoke the future cracking of the implant. Regarding this, our study showed that PCL coating delays early degradation, while the refined microstructure obtained after ECAP homogenizes further corrosion. Both approaches can be used to control corrosion at different degradation timepoints, fundamental for the proper biointegration of the Zn-based implants

    Micropatterned 3D-printed PLLA/PLCL bioresorsable stents: degradation and influence of sterilization

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    Bioresorbable stents (BRS) are cylindrical scaffolds designed to provide a temporary support to the vessel wall while the structure slowly degrades until completely resorbed [1]. Current stent fabrication technology hinders local modification of the surface topography. This work presents a novel solvent-cast direct-write (SC-DW) 3D printing system to manufacture inner patterned BRS. Poly-L-lactic acid (PLLA) and poly(lactic-co-caprolactone) (PLCL) stents were obtained by cylindrical printing onto a √ė 3 mm rotating mandrel (Figure 1a) [2]. The ink consisted in a solution of high Mw PLLA or PLCL copolymer (95:5) in chloroform at 10% w/v and 12.5% w/v, respectively. Steel mandrels were modified by direct laser interference patterning with a femtosecond laser to obtain a linear micropatterning with a periodicity of 10 őľm, which was transferred onto stents' luminal surface (Figure 1b). Stents biodegradation was characterized by an accelerated degradation assay in PBS at 50oC over 4 months and characterized in terms of mass loss, SEM, DSC, mechanical tests, GPC and 1 H-NMR. PLLA and PLCL stents underwent bulk degradation, with a sustained decrease in molecular weight and an increase in crystallinity as degradation proceeded. PLCL stents degraded 1.5 times faster than PLLA stents due to higher water penetration in amorphous regions. Finally, two sterilization methods were evaluated: ő≥-irradiation (8 kGy) and ethylene oxide (EtO). Whereas ő≥- irradiation induced chain scission and a marked decrease in molecular weight, no structural or chemical alterations were found after EtO sterilization (Figure 1c). In conclusion, customizable PLLA and PLCL BRS were successfully fabricated through SC-DW technique, showing luminal micropatterning for enhanced endothelialization and adequate degradation timeframe for resorption

    Numerical simulation of the micro-extrusion process of printable biomaterials

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    This work aims to gain a better understanding of how the rheological properties of printable materials affect their processability, as well as the quality of the final product, which at the end can lead to reducing time and costs of the process and increase product development. As the first step, the proper rheological non-Newtonian models are extracted from experimental studies. Later, three-dimensional numerical simulation of extrusion process is performed in the context of Direct Numerical Simulation (DNS) of governing equations, where the whole physics of fluid motion is taken into account. A finite-volume fractional step approach is used to solve the Navier-Stocks equations on collocated arbitrary meshes. Geometrical volume-of-fluid (GVOF) interface capturing approach is used to resolve the topological changes of the moving interface. The governing equations are solved using High-Performance Computing (HPC) parallel approaches. Besides the contribution of this work to the advancement of numerical techniques applied to multiphase complex flows, obtained results will shed light on the nature of non-Newtonian extrusion process with vast applications in the 3D printer industrial sectors.This work was developed in the context of a research project (BASE3D 001-P-001646) co-financed by the European Union Regional Development Fund within the framework of the ERDF Operational Program of Catalonia 2014-2020 with a grant of 50% of total cost eligible.Postprint (published version

    Binder jetting additive manufacturing of biodegradable Zn

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    Biodegradable materials avoid second surgeries and long-term associated risks of conventional inert implants. Zn arose as a potential candidate for bioresorbable implants due to its proper degradation behaviour and biocompatibility [1]. However, its low melting point induces uncontrolled porosity in LPBF, promoting the future cracking of the implant. Therefore, new fabrication techniques need to be explored. In this work, binder jetting 3d printing (BJ3P) was studied for Zn powders. The samples were printed and sintered under different conditions. It is concluded that, the increase the temperature almost up to melting point leads to higher densification, at the same time, the rise of temperature provokes the formation and growth of oxidized layer on the surface of the powders

    Functionalization strategies and fabrication of solvent-cast PLLA for bioresorbable stents

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    Actual polymer bioresorbable stents (BRS) generate a risk of device thrombosis as a consequence of the incomplete endothelialization after stent implantation. The material-tissue interactions are not fully controlled and stent fabrication techniques do not allow personalized medical solutions. This work investigates the effect of different functionalization strategies onto solvent-cast poly(l-lactic acid) (PLLA) surfaces with the capacity to enhance surface endothelial adhesion and the fabrication of 3D printed BRS. PLLA films were obtained by solvent casting and treated thermally to increase mechanical properties. Surface functionalization was performed by oxygen plasma (OP), sodium hydroxide (SH) etching, or cutinase enzyme (ET) hydrolysis, generating hydroxyl and carboxyl groups. A higher amount of carboxyl and hydroxyl groups was determined on OP and ET compared to the SH surfaces, as determined by contact angle and X-ray photoelectron spectroscopy (XPS). Endothelial cells (ECs) adhesion and spreading was higher on OP and ET functionalized surfaces correlated with the increase of functional groups without affecting the degradation. To verify the feasibility of the approach proposed, 3D printed PLLA BRS stents were produced by the solvent-cast direct writing techniquePeer ReviewedPostprint (published version

    Solvent-cast direct-writing as a fabrication strategy for radiopaque stents

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    Bioresorbable stents (BRS) potential in treating coronary heart disease is still to be further developed. Current trends include research with new polymeric materials, the need for thinner struts combined with appropriate mechanical properties, radiopacity and optimized local drug delivery. This work presents a novel solvent-cast direct-write (SC-DW) printing system to manufacture BRS onto a rotating cylinder with poly-l-lactic acid (PLLA) and poly(l-lactic-co- ¬Ņ -caprolactone) (PLCL) inks. Printed stents were characterized in terms of mechanical, thermal and biological properties with human umbilical vein endothelial cells (HUVECs). Expansion assays showed that stents withstood pressures of at least 16 atm and the indirect cytotoxicity test indicated that stents were biocompatible. Polymeric inks were further modified with the addition of 3 radiopaque agents, namely iodine, triiodobenzoic acid (TIBA) and barium sulfate (BaSO) to render stents radiopaque. Subsequent characterization showed a general increase in strut thickness with respect to control PLLA or PLCL stents, which in turn resulted in higher resistance to compression. Microcomputed tomography was used to assess stents‚Äô radiopacity, showing that TIBA and BaSO-containing stents presented high X-ray attenuation values and maintained their radiopacity after 3 months incubation time.Peer ReviewedPostprint (published version

    Enhanced osteoconductivity on electrically charged titanium implants treated by physicochemical surface modifications methods

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    Biomimetic design is a key tenet of orthopedic device technology, and in particular the development of responsive surfaces that promote ion exchange with interfacing tissues, facilitating the ionic events that occur naturally during bone repair, hold promise in orthopedic fixation strategies. Non-bioactive nanostructured titanium implants treated by shot-blasting and acid-etching (AE) induced higher bone implant contact (BIC=52% and 65%) compared to shot-blasted treated (SB) implants (BIC=46% and 47%) at weeks 4 and 8, respectively. However, bioactive charged implants produced by plasma (PL) or thermochemical (BIO) processes exhibited enhanced osteoconductivity through specific ionic surface-tissue exchange (PL, BIC= 69% and 77% and BIO, BIC= 85% and 87% at weeks 4 and 8 respectively). Furthermore, bioactive surfaces (PL and BIO) showed functional mechanical stability (resonance frequency analyses) as early as 4 weeks post implantation via increased total bone area (BAT=56% and 59%) ingrowth compared to SB (BAT=35%) and AE (BAT=35%) surfaces.Peer ReviewedPostprint (author's final draft
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