Rapid prototyping has emerged as a very auspicious manufacturing method of fabricating tissue engineering scaffolds. Using a 3D CAD design, the 3D printer features the ability of producing the predetermined forms and structures with very high level of accuracy and repeatability. Additionally, the 3D-printed tissue scaffolds are meant to act as replaceable constructs in a very demanding environment. The challenging conditions of the human body set high criteria demands that the scaffold should be capable of fulfilling. One of the most crucial demands is the capability of the scaffold to exhibit the desired mechanical properties depending on the loading conditions that it must cope up against. A mechanical property investigation of different scaffold designs can provide crucial information concerning this key factor in the criteria profile of a functional scaffold design. The target of the present study is to compare the mechanical properties of different scaffold designs that, however, feature same porosity and similar dimensions. Compressive strength testing was conducted in three 3D-printed scaffold designs. Also, a finite element study was conducted, simulating the compressive strength testing. The results of the compression testing experiment were found to be in good agreement with the computational analysis results. Furthermore, a computational fluid dynamic (CFD) simulation was conducted in order to look into the fluid shear stress inside the scaffold. Finally, the properties of the biomaterial hydroxyapatite were used in order to investigate the compressive and shear mechanical behavior of the aforementioned designs by conducting a finite element study.

In Fused Deposition Modeling (FDM), which is a common thermoplastic Additive Manufacturing (AM) method, the polymer model material that is in the form of a flexible filament is heated above its glass transition temperature (Tg) to a semi-molten state in the head’s liquefier. The heated material is extruded in a rastering configuration onto the building platform where it rapidly cools and solidifies with the adjoining material. The heating and rapid cooling cycles of the work materials exhibited during the FDM process provoke non-uniform thermal gradients and cause stress build-up that consequently result in part distortions, dimensional inaccuracy and even possible part fabrication failure. Within the purpose of optimizing the FDM technique by eliminating the presence of such undesirable effects, real-time monitoring is essential for the evaluation and control of the final parts’ quality. The present work investigates the temperature distributions developed during the FDM building process of multilayered thin plates and on this basis a numerical study is also presented. The recordings of temperature changes were achieved by embedding temperature measuring sensors at various locations into the middle-plane of the printed structures. The experimental results, mapping the temperature variations within the samples, were compared to the corresponding ones obtained by finite element modeling, exhibiting good correlation.

Abstract:We report on the design, modeling and fabrication by multi-photon polymerization of a complex medical fluidic device. The physical dimensions of the built micro-valve prototype are compared to those of its computer-designed model. Important fabrication issues such as achieving high dimensional resolution and ability to control distortion due to shrinkage are presented and discussed. The operational performance of both multi-photon and CAD-created models under steady blood flow conditions was evaluated and compared through computational fluid dynamics analysis.

Printed and reproducible scaffolds with regular structures are receiving an increased interest in tissue engineering since they offer greater control of the scaffold porosity, and pore size, and better prediction of the fluid flow inside the scaffold. One of the most important factors that must be examined before the construction of a scaffold for experimental use is the shear stress, which depends strongly on the geometrical characteristics of the scaffold. In this work, computational fluid dynamics (CFD) simulations are carried out for four different scaffold architectures and various porosities and pore sizes. The calculated shear stresses are used for investigating the relation between the shear stress and the scaffold architecture, the scaffold design parameters and the Darcian permeability factor. It is found that for each scaffold model there is a critical porosity and a critical permeability factor below which the shear stress increases significantly, leading to the conclusion that such design parameters must be avoided for effective cultivation.