Paulo J. Bártolo

Improved osteoblast cell affinity on plasma-modified 3-D extruded PCL scaffolds

Cellular adhesion and proliferation inside three-dimensional synthetic scaffolds represent a major challenge in tissue engineering. Besides the surface chemistry of the polymers, it is well recognized that scaffold internal architecture, namely pore size/shape and interconnectivity, has a strong effect on the biological response of cells. This study reports for the first time how polycaprolactone (PCL) scaffolds with controlled micro-architecture can be effectively produced via bioextrusion and used to enhance the penetration of plasma deposited species. Low-pressure nitrogen-based coatings were employed to augment cell adhesion and proliferation without altering the mechanical properties of the structures. X-ray photoelectron spectroscopy carried out on different sections of the scaffolds indicates a uniform distribution of nitrogen-containing groups throughout the entire porous structure. In vitro biological assays confirm that plasma deposition sensitively promotes the activity of Saos-2 osteoblast cells, leading to a homogeneous colonization of the PCL scaffolds.

The first systematic analysis of 3D rapid prototyped poly(ε-caprolactone) scaffolds manufactured through BioCell printing: the effect of pore size and geometry on compressive mechanical behaviour and in vitro hMSC viability

Novel additive manufacturing processes are increasingly 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. With regard to the mechanical and biological performances of 3D scaffolds, pore size and geometry play a crucial role. In this study, a novel integrated automated system for the production and inxa0vitro culture of 3D constructs, known as BioCell Printing, was used only to manufacture poly(ε-caprolactone) scaffolds for tissue engineering; the influence of pore size and shape on their mechanical and biological performances was investigated. Imposing a single lay-down pattern of 0°/90° and varying the filament distance, it was possible to produce scaffolds with square interconnected pores with channel sizes falling in the range of 245-433xa0µm, porosity 49-57% and a constant road width. Three different lay-down patterns were also adopted (0°/90°, 0°/60/120° and 0°/45°/90°/135°), thus resulting in scaffolds with quadrangular, triangular and complex internal geometries, respectively. Mechanical compression tests revealed a decrease of scaffold stiffness with the increasing porosity and number of deposition angles (from 0°/90° to 0°/45°/90°/135°). Results from biological analysis, carried out using human mesenchymal stem cells, suggest a strong influence of pore size and geometry on cell viability. On the other hand, after 21xa0days of inxa0vitro static culture, it was not possible to detect any significant variation in terms of cell morphology promoted by scaffold topology. As a first systematic analysis, the obtained results clearly demonstrate the potential of the BioCell Printing process to produce 3D scaffolds with reproducible well organized architectures and tailored mechanical properties.

Preparation and Characterization of Films Based on Alginate and Aloe Vera

Sodium alginate films with aloe vera extract were prepared by the casting/solvent evaporation technique. The resulting films were characterized by differential scanning calorimetry, Fourier transform-infrared spectroscopy, scanning electron microscopy, and mechanical and water absorption tests. The in vitro degradation of the films was also investigated over 14 days. Results show that aloe vera contributes to both enhancing the thermal and mechanical properties of the films and decreasing the weight loss during in vitro degradation.

Evaluation of in vitro degradation of PCL scaffolds fabricated via BioExtrusion. Part 1: Influence of the degradation environment

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(ϵ-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.

Influence of Aloe vera on water absorption and enzymatic in vitro degradation of alginate hydrogel films.

This study investigates the influence of Aloe vera on water absorption and the in vitro degradation rate of Aloe vera-Ca-alginate hydrogel films, for wound healing and drug delivery applications. The influence of A. vera content (5%, 15% and 25%, v/v) on water absorption was evaluated by the incubation of the films into a 0.1 M HCl solution (pH 1.0), acetate buffer (pH 5.5) and simulated body fluid solution (pH 7.4) during 24h. Results show that the water absorption is significantly higher for films containing high A. vera contents (15% and 25%), while no significant differences are observed between the alginate neat film and the film with 5% of A. vera. The in vitro enzymatic degradation tests indicate that an increase in the A. vera content significantly enhances the degradation rate of the films. Control films, incubated in a simulated body fluid solution without enzymes, are resistant to the hydrolytic degradation, exhibiting reduced weight loss and maintaining its structural integrity. Results also show that the water absorption and the in vitro degradation rate of the films can be tailored by changing the A. vera content.

Design of tissue engineering scaffolds based on hyperbolic surfaces: structural numerical evaluation.

Tissue engineering represents a new field aiming at developing biological substitutes to restore, maintain, or improve tissue functions. In this approach, scaffolds provide a temporary mechanical and vascular support for tissue regeneration while tissue in-growth is being formed. These scaffolds must be biocompatible, biodegradable, with appropriate porosity, pore structure and distribution, and optimal vascularization with both surface and structural compatibility. The challenge is to establish a proper balance between porosity and mechanical performance of scaffolds. This work investigates the use of two different types of triple periodic minimal surfaces, Schwarz and Schoen, in order to design better biomimetic scaffolds with high surface-to-volume ratio, high porosity and good mechanical properties. The mechanical behaviour of these structures is assessed through the finite element method software Abaqus. The effect of two parametric parameters (thickness and surface radius) is also evaluated regarding its porosity and mechanical behaviour.

Laser micromachining for mould manufacturing: I. The influence of operating parameters

Purpose – Laser milling is a recent process in mould making, providing several advantages over traditional mould making technologies by reducing manufacturing time, shortening the number of machining operations and avoiding expensive electrodes. This paper investigates the influence of the operating conditions on both the surface quality and material removal for two types of materials commonly used in mould making.Design/methodology/approach – Laser scanning strategies and operating parameters like scanning speed and laser frequency and power were tested, regarding surface quality and material removal rate. The most representative parameter of the real surface quality, Rk, the core roughness parameter, is used to characterise the surface finishing on all cavities.Findings – The findings of this research work suggest that it is possible to significantly reduce processing time by increasing the hatch spacing up to a value close to the laser beam spot diameter, without compromising surface quality. Lower pul...

Evaluation of in vitro degradation of PCL scaffolds fabricated via BioExtrusion – Part 2: Influence of pore size and geometry

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.

Biofabrication Strategies for Tissue Engineering

The 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.

3D printing of new biobased unsaturated polyesters by microstereo-thermal- lithography

New micro three-dimensional (3D) scaffolds using biobased unsaturated polyesters (UPs) were prepared by microstereo-thermal-lithography (μSTLG). This advanced processing technique offers indubitable advantages over traditional printing methods. The accuracy and roughness of the 3D structures were evaluated by scanning electron microscopy and infinite focus microscopy, revealing a suitable roughness for cell attachment. UPs were synthesized by bulk polycondensation between biobased aliphatic diacids (succinic, adipic and sebacic acid) and two different glycols (propylene glycol and diethylene glycol) using fumaric acid as the source of double bonds. The chemical structures of the new oligomers were confirmed by proton nuclear magnetic resonance spectra, attenuated total reflectance Fourier transform infrared spectroscopy and matrix assisted laser desorption/ionization-time of flight mass spectrometry. The thermal and mechanical properties of the UPs were evaluated to determine the influence of the diacid/glycol ratio and the type of diacid in the polyesters properties. In addition an extensive thermal characterization of the polyesters is reported. The data presented in this work opens the possibility for the use of biobased polyesters in additive manufacturing technologies as a route to prepare biodegradable tailor made scaffolds that have potential applications in a tissue engineering area.