Lucia Baldino

FEM modeling of the reinforcement mechanism of Hydroxyapatite in PLLA scaffolds produced by supercritical drying, for Tissue Engineering applications.

Scaffolds have been produced by supercritical CO2 drying of Poly-L-Lactid Acid (PLLA) gels loaded with micrometric fructose particles used as porogens. These structures show a microporous architecture generated by the voids left in the solid material by porogen leaching, while they maintain the nanostructure of the gel, consisting of a network of nanofilaments. These scaffolds have also been loaded with Hydroxyapatite (HA) nanoparticles, from 10 to 50% w/w with respect to the polymer, to improve the mechanical properties of the PLLA structure. Based on miscroscopic and mechanical considerations, we propose a parametric Finite Element Method (FEM) model of PLLA-HA composites that describes the microporous structure as a close-packing of equal spheres and the nanoscale structure as a space frame of isotropic curved fibers. The effect of HA on the mechanical properties of the scaffolds has been modeled on the basis of SEM images and by taking into consideration the formation of concentric cylinders of HA nanoparticles around PLLA nanofibers. Modeling analysis confirms that mechanical properties of these scaffolds depend on nanofibrous network connections and that bending is the major factor causing deformation of the network. The FEM model also takes into account the formation of HA multi-layer coating on some areas in the nanofiber network and its increase in thickness with HA percentage. The Young modulus tends to a plateau for HA percentages larger than 30% w/w and when the coverage of the nanofibers produced by HA nanoparticles reaches a loaded surface index of 0.14 in the FEM model.

Interpenetration of Natural Polymer Aerogels by Supercritical Drying

Natural polymers, such as alginate and gelatin, can be used to produce scaffolds for tissue engineering applications; but, their mechanical and biochemical performance should be improved. A possible solution to obtain this result, is the generation of multi-component scaffolds, by blending two or more polymers. One way to realize it, is the formation of an interpenetrating polymer network (IPN). In this work, the interpenetration of alginate and gelatin hydrogels has been successfully obtained and preserved by supercritical CO2 (SC-CO2) drying performed at 200 bar and 35 °C, using different blend compositions: from alginate/gelatin = 20:80 v/v to alginate/gelatin = 80:20 v/v. The process allowed modulation of morphology and mechanical properties of these blends. The overall result was made possible by the supercritical drying process that, working at zero surface tension, allows preserving the hydrogels nanostructure in the corresponding aerogels.

3D PLLA/Ibuprofen composite scaffolds obtained by a supercritical fluids assisted process

The emerging next generation of engineered tissues is based on the development of loaded scaffolds containing bioactive molecules in order to control the cellular function or to interact on the surrounding tissues. Indeed, implantation of engineered biomaterials might cause local inflammation because of the host’s immune response; thereby, the use of anti-inflammatory agents, whether steroidal or nonsteroidal is required. One of the most important stages of tissue engineering is the design and the generation of a porous 3D structure, with high porosity, high interconnectivity and homogenous morphology. Various techniques have been reported in the literature for the fabrication of biodegradable scaffolds, but they suffer several limitations. In this study, for the first time, the possibility of generating 3D polymeric scaffolds loaded with an active compound by supercritical freeze extraction process is evaluated; this innovative process combines the advantages of the thermally induced phase separation process and of the supercritical carbon dioxide drying. Poly-l-lactid acid/ibuprofen composite scaffolds characterized by a 3D geometry, micrometric cellular structures and wrinkled pores walls have been obtained; moreover, homogeneous drug distribution and controlled release of the active principle have been assured.

SC-CO2-assisted process for a high energy density aerogel supercapacitor: The effect of GO loading

Energy density, safety, and simple and environmentally friendly preparation methods are very significant aspects in the realization of a compact supercapacitor. Herein we report the use of a supercritical CO2-assisted gel drying process (SC-CO2) for the preparation of porous electrodes containing dispersed graphene in a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) binder membrane to sandwich in a new portable supercapacitor based on graphene oxide (GO). A GO loading of 60 wt.% was found to give the best combination of factors (porosity, wettability, mechanical and electrochemical properties). Cycling voltammetry and charge/discharge studies showed an excellent capacitance behaviour and stability in an ionic liquid electrolyte, suggesting SC-CO2 processing as a promising platform to produce highly bulky and porous films for supercapacitors. The supercapacitor device delivers a very high energy density of 79.2 Wh kg-1 at a power density of 0.23 KW kg-1 (current density 0.5 A g-1, specific capacitance 36.2 F g-1) while that of steel remains at 50.3 Wh kg-1 at a power density of 2.8 KW kg-1 (current density 6 A g-1, specific capacitance 23.5 F g-1).

14 – Bone–tendon interface

Works in this area can be divided on whether the objective is to build an entire composite tissue unit or whether the objective is to assist the recreation of individual interfaces, such as improving integration of autografts with surrounding bone. The administration of active compounds to promote the anchoring of the interface lies on the hypothesis that it is possible to induce local restructuration of the specific tissue in the highly organized manner of the original junction. Its application requires complex procedures and relatively long times to produce interface reorganization. Techniques involving electrospinning have been applied to bone-to-tendon junction (BTJ) regeneration. Nevertheless, electrospun constructs are inherently discontinuous. Another approach potentially successful in BTJ regeneration is gel drying. The limit of this technique is the elimination of the organic solvents from the gel, avoiding the collapse of its nanostructure. Gel drying assisted by supercritical fluids has been recently proposed to eliminate the organic solvents in a simple and effective step, avoiding the structure collapse.

Dissipative Particle Dynamics Study of Alginate/Gelatin Aerogels Obtained by Supercritical Drying

The properties of alginate/gelatin (A/G) interpenetrated polymer networks have been studied by dissipative particle dynamics (DPD) simulations. The simulation predicted some mechanical properties of A/G blends with different A/G ratios in water. Results from new synthesized aerogels have been used to validate the range of exploitation of the DPD simulations. Good mechanical and morphological properties of the aerogels have been achieved from aerogels derived from hydrogels with water content higher than 95%. DPD simulation results indicated that an optimal shear viscosity is reached for a composition of 95% water, 3% alginate and 2% gelatin. Furthermore, this approach can be of great interest in designing novel materials.

Sensibility Analyses on Morphological Parameters of Cellulose Acetate - Graphene Oxide Nanocomposites Using a Periodic 3d-fem Model

This article focused on the study of the influence of morphological parameters on the mechanical performance (Young’s modulus) of Cellulose Acetate-Graphene Oxide nanocomposites produced by Supercritical CO2 assisted phase inversion, by means of an algorithm managing two parametric variational 3D finite element (FE) models simulating microand nano-level of the nanocomposite. Micro-level showed interconnected spherical pores, while nano-level showed a dispersion of not fully exfoliated graphene sheets. 3D FE model exploited the periodic representative volume element (PRVE) concept and accounted for the nanocomposite morphology as determined from Field Emission Scanning Electron Microscopy (FESEM) experiments. Model predictions were compared with experimental results obtained by compression tests at different weight percentages of graphene oxide with respect to the polymer. Once validated, such a FE simulation procedure allows to know in advance which and how to vary the geometrical parameters during the nanocomposite production to improve its final mechanical performance.

Smart membranes production by supercritical phase inversion to increase food shelf-life

The freshness of minimally processed foods is also determined by their appearance; browning due to oxidative phenomena is one of the main reasons of discarded by consumers. To overcame this problem, the development of antioxidant active packaging has gained increasing interest in the food industry. In this work, a supercritical phase inversion process was tested to produce Curcumin (Cu) loaded Cellulose Acetate (CA) membranes, to be inserted in food packaging as antioxidant devices. Active membranes were produced at different process conditions (pressures ranging between 150-250 bar and temperatures ranging between 35-55 °C), polymer amount (12, 18, 24% w/w) and at constant ratio Cu/CA (10% w/w). Cu-loaded membranes showed an homogeneous cellular morphology with a mean pore size lower than 12 μm. Cu release was measured and a maximum release time of about 2 days was obtained; moreover, antioxidant tests were also performed on the loaded membranes, showing an activity up to 90%.

Optimization of Hyaff Membranes Morphology Produced by Supercritical Phase Separation for Biomedical Applications

In this study, it was evaluated the capability to generate HYAFF membranes by phase inversion assisted by supercritical fluids. HYAFF is a biopolymer, hyaluronic acid ester, much used in the pharmaceutical and biomedical applications. Several techniques have been tested to generate structures (membranes and scaffolds) for biomedical applications; but, all of them present several limitations. For these reasons, supercritical fluids assisted processes have been implemented for biomedical applications. Using SC-CO2 phase inversion process, we obtained HYAFF membranes with different morphological characteristics, depending on the process conditions adopted, such as polymer starting concentrations, pressure (ranging from 90 to 200 bar) and temperature (ranging from 35 to 55°C). The behavior of membranes structure has been studied and has been related to the ternary diagram HYAFF-DMSO-SC-CO2 analyzing the thermodynamic and kinetic aspect of the process.

Antimicrobial membranes produced by supercritical assisted phase inversion

In this study, antimicrobial membranes of cellulose acetate (CA) loaded with potassium sorbate (Psb) were generated by supercritical assisted phase inversion for active packaging applications. To achieve appropriate membranes morphology, the starting solutions were prepared by dissolving Psb in water, and then, adding it to CA-Acetone solution and were processed at different pressures and temperatures. The loaded membranes were analyzed by FESEM, EDX and UV/VIS spectrophotometer, to determine: membrane morphology, distribution of the active compound inside the polymeric matrix and Psb release rate, respectively. The results indicate that, by changing the operative conditions (ranging from 150 to 250 bar, and 35 to 55 °C), cellular structures characterized by different pore size were obtained. EDX analyses showed as the active compound was uniformly distributed in the polymeric matrix at all process conditions tested. Moreover, Psb release time was influenced by membranes morphology, since the active compound diffusion was slowered when the polymer matrix was denser. These results suggest that the antimicrobial membranes, prepared in this study, could be used as food packaging material achieving a controlled release of the active compound, improving the food quality and safety.