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- Flow-induced motions of flexible filaments hanging in cross-flowPublication . Silva-Leon, Jorge; Cioncolini, Andrea; Filippone, Antonio; Domingos, MarcoExperiments were carried out to study the dynamics of hanging cantilever flexible filaments in air cross-flow. Thirteen flexible filaments of 0.61 mm diameter and lengths from 20 mm to 60 mm were tested with wind speeds in the range of 1–15 m/s, corresponding to Reynolds numbers of 25 < Red < 610 and reduced velocities in the range of 5 < U∗ < 130. Two synchronized fast-imaging cameras were used to reconstruct the motion of the filaments in three dimensions, and a blend of linear and nonlinear time-series analysis techniques was used to analyze the observed dynamics. Long filaments show a rich dynamics as the wind speed is gradually increased, ranging from small amplitude vibration to large amplitude limit-cycle oscillation and to a more complex chaotic motion. However, short filaments only exhibit a small amplitude vibration-like motion throughout the range of wind speeds tested. Turbulent buffeting is identified as the main source of excitation responsible for the observed filaments dynamics. The results highlight the importance of the filament damping ratio, which is modulated by the filament length, as a controlling parameter for the dynamics of flexible filaments in cross flow, in addition to the flow velocity. The Scruton number for these tests correspond to 31 < Sc < 86.
- Evaluation of in vitro degradation of PCL scaffolds fabricated via BioExtrusion – Part 2: Influence of pore size and geometry: The present study is to accurately investigate the influence of design parameters, such as filament distance (FD) and lay-down pattern, on the degradation behaviour and kinetics of PCL scaffolds, obtained via BioExtrusionPublication . Domingos, Marco; Chiellini, F.; Cometa, S.; Giglio, E. De; Grillo-Fernandes, E.; Bartolo, Paulo; Chiellini, E.The in vivo degradation processes by which scaffolds degrade and are replaced by neo-tissue are complex and may be influenced by many factors, including environmental conditions, material properties, porosity and 3D architecture. The present study is focused on the influence of design parameters, filament distance (FD) and lay-down pattern, on the degradation kinetics of Polycaprolactone (PCL) scaffolds obtained via BioExtrusion. Through the variation of design parameters it was possible to obtain two groups of scaffolds with distinct pore geometry and size. The in vitro degradation was performed in simulated body fluid (SBF) and in phosphate buffer solution (PBS) for six months. Our results highlight a more complex degradation pattern of the scaffolds in SBF than in PBS, probably related to a mineral deposition. Significant statistical differences in weight loss values at month 6, allowed us to conclude that degradation kinetics of PCL scaffolds is strongly influenced by the pore size.
- PHEMA-based thin hydrogel films for biomedical applicationsPublication . De Giglio, E.; Cafagna, D.; Giangregorio, MM; Domingos, Marco; Mattioli-Belmonte, M.; Cometa, S.Poly(2-hydroxyethyl methacrylate) based thin coatings were electro-synthesized by cyclic voltammetry on Au-coated quartz crystal surfaces to study different solid—liquid interfacial processes. By varying the electrochemical parameters and the presence or not of a crosslinking agent, films were obtained with thicknesses ranging from 5 to 90 nm. Surface characterization was performed by X-ray photoelectron spectroscopy, atomic force microscopy, and static contact angle measurements. Using quartz crystal microbalance with dissipation monitoring to investigate the relationship between the film thickness and the swelling behavior, it was found that these characteristics can be modulated by varying either the number of voltammetric cycles or the presence of the crosslinker. Cell adhesion and biocompatibility tests indicate that these film coatings were suitable for biomedical applications.
- Evaluation of in vitro degradation of PCL scaffolds fabricated via BioExtrusion. Part 1: Influence of the degradation environmentPublication . Domingos, M.; Chiellini, F.; Cometa, S.; De Giglio, E.; Grillo-Fernandes, E.; Bártolo, P.; Chiellini, E.One of the most promising approaches in tissue engineering (TE) comprises the development of 3D porous scaffolds which are able to promote tissue regeneration. Biocompatible and biodegradable poly(e-caprolactone) (PCL) structures are increasingly used as temporary extra-cellular matrices for bone tissue engineering. To ensure an appropriate bone restoration over the long term, the selected material must have a degradation rate that match the in-growth of new bone. The in vivo process, by which the scaffold degrades and is resorbed transferring the load and function back to the host tissue, is complex. Consequently, an appropriate preliminary in vitro study is required. A novel extrusion-based technology called BioExtruder was used to produce PCL porous scaffolds made with layers of directionally aligned microfilaments. The in vitro degradation behaviour in both simulated body fluid (SBF) and phosphate buffer solution (PBS) were investigated over 6 months. The characterization of the degradation behaviour of the structures was performed at specific times by evaluating changes in the average molecular weight, the weight loss and its thermal properties. Morphological and surface chemical analyses were also performed using a Scanning Electron Microscopy (SEM) and an X-ray Photoelectron Spectroscopy (XPS), respectively.
- Biofabrication Strategies for Tissue EngineeringPublication . Bártolo, Paulo Jorge; Domingos, Marco; Patrício, Tatiana; Cometa, Stefania; Mironov, Vladimir; Bártolo, Paulo JorgeThe success of Tissue Engineering (TE) strongly relies on the capability of designing biomimetic scaffolds closely resembling the host tissue environment. Due to the functional multitude of the native tissues, the considerations are complex and include chemical, morphological, mechanical and biological factors and their mutability with time. Nonetheless, to trigger and/or assist the “natural healing mechanism’’ of the human body it seems essential to provide an appropriate biomechanical environment and biomolecular signalling to the cells. Novel biomanufacturing processes are increasingly being recognized as ideal techniques to produce 3D biodegradable structures with optimal pore size and spatial distribution, providing an adequate mechanical support for tissue regeneration while shaping in-growing tissues. In this chapter, we discuss in detail the most recent advances in the field of biofabrication, providing and updated overview of processes and materials employed in the production of tissue engineering constructs. Bioprinting or ‘’scaffold-less’’ strategies are also presented in this work. They are based on the precise deposition of high-density tissue spheroids or cell aggregates being advantageous alternatives to the current scaffold-based tissue engineering approach.