Isogeometric Analysis of Electrophysiological Models on Surfaces

In this project we numerically simulate electrophysiological models for cardiac applications by means of Isogeometric Analysis. Specifically, we aim at understanding the advantages of using high order continuous NURBS (Non-UniformRational B-Splines) basis functions in the approximation of the traveling waves of the action potential. As application, we consider the numerical simulations on the human left atrium modeled as a surface. Firstly in our analysis, we consider a benchmark time dependent diffusion-reaction problem describing a traveling front in a two dimensional domain, for which we aim at understanding the role of NURBS basis functions in the approximation of the conduction velocity. Then, we extend the analysis to more complex electrophysiological models, in particular to the numerical approximation of the monodomain equation. The latter is a Partial Differential Equation and a system of Ordinary Differential Equations. We consider the Aliev-Panfilov model and we analyze the different aspects related to its numerical approximation, including the role of high order continuous NURBS basis functions in the simulation of cardiac excitation models. Then, we consider realistic simulations of the Mitchell-Schaeffer model on the human left atrium represented as a surface for which the strong anisotropic behavior of the action potential, due to the fiber orientation of the cardiac tissue, is taken into accoun

Nanoroughness, Surface Chemistry and Drug Delivery Control by Atmospheric Plasma Jet on Implantable Devices

Implantable devices need specific tailored surface morphologies and chemistries to interact with the living systems or to actively induce a biological response also by the release of drugs or proteins. These customised requirements foster technologies that can be implemented in additive manufacturing systems. Here we present a novel approach based on spraying processes that allows to control separately topographic features in the submicron range ( 3d 60 nm - 2 \ub5m), ammine or carboxylic chemistry and fluorophore release even on temperature sensitive biodegradable polymers such as polycaprolactone (PCL). We developed a two-steps process with a first deposition of 220 nm silica and poly(lactic-co-glycolide) (PLGA) fluorescent nanoparticles by aerosol followed by the deposition of a fixing layer by atmospheric pressure plasma jet (APPJ). The nanoparticles can be used to create the nano-roughness and to include active molecule release, while the capping layer ensures stability and the chemical functionalities. The process is enabled by a novel APPJ which allows deposition rates of 10 - 20 nm\ub7s-1 at temperatures lower than 50 \ub0C using argon as process gas. This approach was assessed on titanium alloys for dental implants and on PCL films. The surfaces were characterized by FT-IR, AFM and SEM. Titanium alloys were tested with pre-osteoblasts murine cells line, while PCL film with fibroblasts. Cell behaviour was evaluated by viability and adhesion assays, protein adsorption, cell proliferation, focal adhesion formation and SEM. The release of a fluorophore molecule was assessed in the cell growing media, simulating a drug release. Osteoblast adhesion on the plasma treated materials increased by 20% with respect to commercial titanium alloys implants. Fibroblast adhesion increased by a 100% compared to smooth PCL substrate. The release of the fluorophore by the dissolution of the PLGA nanoparticles was verified and the integrity of the encapsulated drug model confirmed

Safe-by-design strategies applied to scaffold hybrid manufacturing

The EU-project FAST (GA 685825) has developed a 3D printer machine prototype for the manufacture of bone implants (scaffolds), by merging masterbatches of biodegradable polymer poly(ethylene oxide)terephthalate/poly(butylene terephthalate) [PEOT/PBT] doped with nanofillers [reduced graphene oxide (rGO), hydroxyapatite (HA) and magnesium aluminium hydroxide ciprofloxacin hydrotalcite (LDH-CFX)], and atmospheric plasma technology. This paper focus on the safe design strategies identified by FAST to address the risk to health resulting from the potential airborne emission of nano-objects and their aggregates and agglomerates (NOAAs) by the 3D printer prototype, which might result in occupational exposures by inhalation. The work also includes measurements of airborne emissions and occupational exposures carried out during the verification stage of the prototype design. Nanofillers particles (rGO, n-HA, LDH-CFX) were not observed, neither at source nor in the working area, suggesting no release of free nanofillers to the air one they have been embedded in the polymer masterbatch. Additionally, the exposure in the workplace was far below the selected Occupational Exposure Levels (OELs), for total particle number concentration (PNC), dust, elemental carbon (EC) and volatile organic compounds (VOCs). The results showed that, when working with the current prototype in normal operation (for its intended use) and with controls enabled [enclosure with the doors closed and Local Exhaust Ventilation (LEV) activated], the emission from the machine and the worker's exposure to NOAAs are well controlled.The project FAST received funding from the European Union’s Horizon 2020 research and innovation programme, under grant agreement Nº 685825. This paper reflects only the authors’ views, and the Commission is not responsible for any use that may be made of the information contained therein

Influence of the substrate temperature on the layer properties made by an atmospheric plasma jet using different precursors

In this work the surface temperature of porous polymer scaffolds treated with an atmospheric plasma jet was determined by theoretical estimations and infrared was measurements. Based on these results the scaffolds were coated with functional plasma polymer layers using this plasma jet and different precursors. The influence of the substrate temperature on the plasma polymer layer properties like thickness and chemical reactivity was investigated

Effect of high content nanohydroxyapatite composite scaffolds prepared via melt extrusion additive manufacturing on the osteogenic differentiation of human mesenchymal stromal cells

The field of bone tissue engineering seeks to mimic the bone extracellular matrix composition, balancing the organic and inorganic components. In this regard, additive manufacturing (AM) of high content calcium phosphate (CaP)-polymer composites holds great promise towards the design of bioactive scaffolds. Yet, the biological performance of such scaffolds is still poorly characterized. In this study, melt extrusion AM (ME-AM) was used to fabricate poly(ethylene oxide terephthalate)/poly(butylene terephthalate) (PEOT/PBT)-nanohydroxyapatite (nHA) scaffolds with up to 45 wt% nHA, which presented significantly enhanced compressive mechanical properties, to evaluate their in vitro osteogenic potential as a function of nHA content. While osteogenic gene upregulation and matrix mineralization were observed on all scaffold types when cultured in osteogenic media, human mesenchymal stromal cells did not present an explicitly clear osteogenic phenotype, within the evaluated timeframe, in basic media cultures (i.e. without osteogenic factors). Yet, due to the adsorption of calcium and inorganic phosphate ions from cell culture media and simulated body fluid, the formation of a CaP layer was observed on PEOT/PBT-nHA 45 wt% scaffolds, which is hypothesized to account for their bone forming ability in the long term in vitro, and osteoconductivity in vivo.We are grateful to H2020-NMP-PILOTS-2015 (GA n. 685825) for financial support. PH gratefully acknowledges the Gravitation Program ‘Materials-Driven Regeneration’, funded by the Netherlands Organization for Scientific Research (NWO) (024.003.013). Some of the materials used in this work were provided by the Texas A&M Health Science Center College of Medicine Institute for Regenerative Medicine at Scott & White through a grant from NCRR of the NIH (Grant #P40RR017447). We would also like to thank Eva Gubbins from MERLN Institute for performing the ICP-MS measurements

A novel plasma jet with RF and HF coupled electrodes

In order to achieve low processing temperature and efficient coatings deposition for manufacturing applications, a novel torch has been developed that couples in a double DBD design high frequency (HF ~17 kHz) and radio frequency (RF ~27 MHz) excitations. The design allows to obtain a stable RF plasma also in reactive processes and with the possibility to control on the treated substrates ions flux and surface charging, avoiding the micro-discharges. The plasma has been electrically and optically characterized by emission spectroscopy

3D additive manufactured composite scaffolds with antibiotic-loaded lamellar fillers for bone infection prevention and tissue regeneration

Bone infections following open bone fracture or implant surgery remain a challenge in the orthopedics field. In order to avoid high doses of systemic drug administration, optimized local antibiotic release from scaffolds is required. 3D additive manufactured (AM) scaffolds made with biodegradable polymers are ideal to support bone healing in non-union scenarios and can be given antimicrobial properties by the incorporation of antibiotics. In this study, ciprofloxacin and gentamicin intercalated in the interlamellar spaces of magnesium aluminum layered double hydroxides (MgAl) and α-zirconium phosphates (ZrP), respectively, are dispersed within a thermoplastic polymer by melt compounding and subsequently processed via high temperature melt extrusion AM (~190 °C) into 3D scaffolds. The inorganic fillers enable a sustained antibiotics release through the polymer matrix, controlled by antibiotics counterions exchange or pH conditions. Importantly, both antibiotics retain their functionality after the manufacturing process at high temperatures, as verified by their activity against both Gram + and Gram - bacterial strains. Moreover, scaffolds loaded with filler-antibiotic do not impair human mesenchymal stromal cells osteogenic differentiation, allowing matrix mineralization and the expression of relevant osteogenic markers. Overall, these results suggest the possibility of fabricating dual functionality 3D scaffolds via high temperature melt extrusion for bone regeneration and infection prevention.We are grateful to the FAST project funded under the H2020-NMP- PILOTS-2015 scheme (GA n. 685825) for financial support. Some of the materials used in this work were provided by the Texas A&M Health Science Center College of Medicine Institute for Regenerative Medicine at Scott & White through a grant from NCRR of the NIH (Grant #P40RR017447)

Size effects in finite element modelling of 3D printed bone scaffolds using hydroxyapatite PEOT/PBT composites

Additive manufacturing (AM) of scaffolds enables the fabrication of customized patient-specific implants for tissue regeneration. Scaffold customization does not involve only the mac-roscale shape of the final implant, but also their microscopic pore geometry and material properties, which are dependent on optimizable topology. A good match between the experimental data of AM scaffolds and the models is obtained when there is just a few millimetres at least in one direction. Here, we describe a methodology to perform finite element modelling on AM scaffolds for bone tissue regeneration with clinically relevant dimensions (i.e., volume > 1 cm3). The simulation used an equivalent cubic eight node finite elements mesh, and the materials properties were derived both empirically and numerically, from bulk material direct testing and simulated tests on scaffolds. The experimental validation was performed using poly(ethylene oxide terephthalate)-poly(butylene ter-ephthalate) (PEOT/PBT) copolymers and 45 wt% nano hydroxyapatite fillers composites. By applying this methodology on three separate scaffold architectures with volumes larger than 1 cm3, the simulations overestimated the scaffold performance, resulting in 150–290% stiffer than average values obtained in the validation tests. The results mismatch highlighted the relevance of the lack of printing accuracy that is characteristic of the additive manufacturing process. Accordingly, a sensi-tivity analysis was performed on nine detected uncertainty sources, studying their influence. After the definition of acceptable execution tolerances and reliability levels, a design factor was defined to calibrate the methodology under expectable and conservative scenarios.This research was funded by the European Union, represented by the European Commission, grant number 685825-FAST-H2020-NMP-2014-2015/H2020-NMP-PILOTS-2015