Percorrer por autor "Almeida, Henrique A."
A mostrar 1 - 10 de 11
Resultados por página
Opções de ordenação
- Additive manufacturing techniques for scaffold-based cartilage tissue engineeringPublication . Caseiro, Ana Rita; Almeida, Henrique A.; Bártolo, Paulo J.Articular cartilage damage is of great concern as it creates chronic pain and reduction of joint movement, leading to osteoarthritis. In current treatments, the resulting healing tissues lack structural organisation of cartilage and consequently have inferior mechanical properties when compared to native cartilage, therefore being prone to failure. Tissue engineering has long worked on cartilage regeneration and several requirements have been identified for the engineered structures to meet the desired function, by combining biodegradable and biocompatible materials, cells and growth factors, aiming at the production of biological structures closely resembling the native tissue.Within the scaffold based techniques for cartilage tissue production, conventional methods have shown limitations, especially regarding the control over the microstructure and repeatability of the produced constructs. Therefore, additive manufacturing techniques grew popular, allowing for a high level of control over the internal scaffold architecture and external shape of the construct, as well as guaranteeing its reproducibility.
- Combined Elastic and Shear Stress Solicitations for Topological Optimisation of Micro-CT Based ScaffoldsPublication . Almeida, Henrique A.; Bártolo, Paulo J.Advanced additive manufacturing technologies, namely Biomanufacturing, are being used to fabricate scaffolds with controlled architecture for tissue engineering applications. These technologies combined with computer-aided design (CAD) enable to produce three-dimensional structures layer-by-layer in a multitude of biomaterials. Actual prediction of the effective mechanical properties of scaffolds produced by Biomanufacturing, is very important for tissue engineering applications. A novel computer based technique for scaffold design is topological optimisation. Topological optimisation is a form of "shape" optimisation, usually referred to as "layout" optimisation. The goal of topological optimisation is to find the best use of material for a body that is subjected to either a single load or a multiple load distribution. In this research work, a topological optimization strategy is presented to find out the best material use for a construct subject to either a single load or a multiple load distribution, maximising its mechanical behaviour under tensile and shear stress solicitations. The proposed topological optimization scheme enables the design of ideal topological architectures based on existing biologic Micro-CT data for the design of biomimetic scaffolds.
- Computer modelling and simulation of a bioreactor for tissue engineeringPublication . Pereira, Rúben F.; Freitas, Dino; Tojeira, Ana; Almeida, Henrique A.; Alves, Nuno; Bartolo, Paulo J.A conventional approach to tissue engineering involves the implantation of porous, biodegradable and biocompatible scaffolds seeded with cells into the defect site. In some strategies, tissue engineering requires the in vitro culture of tissueengineering constructs for implantation later. In this case, bioreactors are used to grow 3D tissues under controlled and monitored conditions. However, the quality of the resulting 3D tissue is highly dependent on the design and dimensions of the bioreactor, as well on the operating conditions. In this work, a computational fluid dynamic software package was used to investigate the influence of cylindrical bioreactor dimensions (length and diameter) on the fluid flow and scaffold shear stress. Computer simulations were performed using three different rotational movements (horizontal, vertical and biaxial rotation) and appropriate boundary conditions. Results show that the effect of the bioreactor length on the scaffold shear stress is more important than the diameter, while high length is associated to low scaffold shear stress. On the other hand, the fluid flows within the bioreactor and scaffold shear stresses are dependent on the rotational movement, being more uniform in the biaxial rotation due to the combination of rotational movements.
- Design of tissue engineering scaffolds based on hyperbolic surfaces: Structural numerical evaluationPublication . Almeida, Henrique A.; Bártolo, Paulo J.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.
- Layer Thickness Evaluation Between Medical Imaging and Additive ManufacturingPublication . Almeida, Henrique A.; Vasco, Joel; Correia, Mário Simões; Ruben, Rui; Ruben, RuiAdditive manufacturing (AM) applied to the orthopaedic and surgical domains provided access to newer solutions for customised implants, customised scaffolds or even organ printing. These solutions are based on imagological data, gathered from CT-scans and/or MRI-scans. The compromise between patient’s radiation exposition and resolution along the focus direction plays an important role for the successful production of biological products. Scan detail can be increased with a thinner scanning thickness to obtain the required biological features for replication. On the other hand, a thinner scan thickness requires more scanning slices and therefore, higher exposition time to radiation. Literature shows that a maximum amount of radiation is admissible for humans, requiring an optimized approach concerning the acquisition of internal details of the human body tissues. State-of-the-art scans offer focus resolution in the range of 100 to 200 µm, although such resolution is not used for the patient’s protection. In fact, in clinical practice distance between slices are in the range of 1 to 6 mm. Concerning the AM processes that are able to use biocompatible materials, different layer thicknesses are available upon the final application in spite of the digital layer thickness that was applied during the medical imaging exam. The layer thickness during production also details the mechanical properties of the implant, with an additional aspect that the geometric data is based on information of a different layer thickness. This study intends to discuss the layer thickness used in medical imaging, the layer thickness used in AM systems providing public awareness of the operating gap between medical imaging systems and AM systems. A brief description of the accumulated errors is also presented.
- PrefacePublication . Almeida, Henrique A.; Vasco, Joel C.The “Progress in Digital and Physical Manufacturing” book contains keynotes and papers presented at the first International Conference on Progress in Digital and Physical Manufacturing (ProDPM’19), organized by the School of Technology and Management (ESTG) of the Polytechnic Institute of Leiria (IPLeiria), from October 2 to 4, 2019. This international conference aims to provide a major international forum for the scientific exchange of multi-disciplinary and inter-organizational aspects performed by academics, researchers, and industrial partners in order to exchange ideas in the field of digital and physical manufacturing and related areas. It represents a significant contribution to the current advances in industrial digital and physical manufacturing issues as it contains topical research in this field.
- Production and Characterisation of PCL/ES Scaffolds for Bone Tissue EngineeringPublication . Biscaia, Sara I.; Viana, Tânia F.; Almeida, Henrique A.; Bártolo, Paulo J.The combination of bio-fillers with synthetic polymers has been an exciting route for developing tissue engineering scaffolds, in particular for bone tissue regeneration. In this study, poly(e{open}-caprolactone) (PCL) scaffolds were produced using an additive manufacturing technique and eggshell (ES) powder was used as a filler. The morphology of PCL and PCL/ES scaffolds were analysed and the effect of ES in the polymer matrix was characterized using techniques of Differential Scanning Calorimetry and Thermogravimetric Analysis, Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray Diffraction (XRD). Morphological observation revealed that the incorporation of ES in the polymer matrix modifies the flow behaviour of the material in spite of the same processing parameters, resulting in a decrease of scaffold pore size. Thermal analysis showed that the addition of the bio-filler improves the crystallization properties and thermal stability of the PCL. FT-IR spectra of ES powder showed characteristic bands of calcium carbonate and processed materials spectra indicated no changes on the functional groups compared to non-processed materials. Crystalline nature of ES was demonstrated through a characteristic broad peak in XRD pattern around 30o, which was also observed in the composites XRD spectra. The results indicate the potential of ES powder to be used as a filler for bio-based polymer scaffold composites.
- Progress in Digital and Physical ManufacturingPublication . Almeida, Henrique A.; Vasco, Joel C.This book contains selected papers from the First International Conference on Progress in Digital and Physical Manufacturing (ProDPM'19), organized by the School of Technology and Management (ESTG) of the Polytechnic Institute of Leiria (IPL). It presents a significant contribution to the current advances in digital and physical manufacturing issues as it contains topical research in this field. The book content is of interest to those working on digital and physical manufacturing, promoting better links between the academia and the industry. The conference papers cover a wide range of important topics like biomanufacturing, advanced rapid prototyping technologies, rapid tooling and manufacturing, micro-fabrication, 3D CAD and data acquisition, and collaborative design.
- Tensile and Shear Stress Evaluation of Schwartz Surfaces for Scaffold DesignPublication . Almeida, Henrique A.; Bartolo, J. PauloTissue engineering represents a new, emerging interdisciplinary field involving combined efforts of several scientific domains towards the development of biological substitutes to restore, maintain, or improve tissue functions. Scaffolds provide a temporary mechanical and vascular support for tissue regeneration while shaping the in-growth tissues. These scaffolds must be biocompatible, biodegradable, with appropriate porosity, pore structure and pore distribution and optimal structural and vascular performance, having both surface and structural compatibility. Surface compatibility means a chemical, biological and physical suitability to the host tissue. Structural compatibility corresponds to an optimal adaptation to the mechanical behaviour of the host tissue. The design of optimised scaffolds based on the fundamental knowledge of its macro microstructure is a relevant topic of research. This research proposes the use of geometric structures based on Triple Periodic Minimal Surfaces, namely, Schwartz geometries for tensile and shear stress applications. Geometries based on these surfaces enables the design of vary high surface-to-volume ratio structures with high porosity and mechanical/vascular properties. Numerical simulations on the Schwartz surfaces were performed considering two geometric variations: surface thickness and surface radius construction. The results demonstrate how the mechanical (Elastic and Shear) cell stimuli vary with the geometric variations of the Schwartz surfaces.
- Topological Shear Stress Optimisation of Micro-CT Based ScaffoldsPublication . Almeida, Henrique A.; Bártolo, Paulo J.Additive manufacturing technologies are being used to fabricate scaffolds with controlled architecture for tissue engineering applications. These technologies combined with computer-aided design systems enable to produce three-dimensional structures layer-by-layer in a multitude of materials. Actual prediction of the effective mechanical properties of scaffolds produced by Additive manufacturing systems, is very important for tissue engineering applications. One of the existing computer based techniques for scaffold design is topological optimisation. The goal of topological optimisation is to find the best use of material for a body that is subjected to either a single load or a multiple load distribution. This paper proposes a topological optimisation scheme based on existing micro-CT data in order to obtain the ideal topological architectures of scaffolds, maximising its mechanical behaviour under shear stress solicitations. This approach is based on micro-CT data of real biological tissues to create the loading (shear stress) and constraint surfaces of the scaffold during the topological optimisation process. This particular topological optimisation scheme uses the surface boundaries to produce novel models with different characteristics, which are different from the initial micro-CT models. This approach enables to produce valid biomimetic scaffold topologies for tissue engineering applications.