Experimental Investigation of Different Cellular Lattice Structures Manufactured by Fused Deposition Modeling

Experimental tests were conducted to evaluate the compressive properties (yield strength and compressive modulus) and build time for five different cellular lattice structures fabricated by the Fused Deposition Modeling (FDM) process. The lattice structures had repeating unit cells, and the shapes of the unit cell under study included honeycomb, square, diamond, triangle, and circle. Test specimens were manufactured by a Stratasys Fortus 400mc machine using ABS (Acrylonitrile Butadiene Styrene) as the part material. The five different lattice structures were compared with each other and also with the sparse and sparse-double dense build styles that are directly available from the Fortus machine. Honeycomb structure was found to have the best compression properties for the same porosity, although the differences among the different lattice structures were small ( \u3c 7%). All of these lattice structures were found to have much higher strength than the specimens with the same porosity built using the sparse and sparse-double dense styles. However, the various lattice structures required significantly longer build times than the sparse and sparse-double dense builds. For the honeycomb structure, our investigation also included the effects of porosity and cell size. Higher porosity led to lower compression strength but shorted build time. For the same porosity, the yield strength could be increased and the build time shortened simultaneously by having a certain cell size

Computed tomography-based tissue-engineered scaffolds in craniomaxillofacial surgery

Introduction Tissue engineering provides an alternative modality allowing for decreased morbidity of donor site grafting and decreased rejection of less compatible alloplastic tissues. Methods Using image-based design and computer software, a precisely sized and shaped scaffold for osseous tissue regeneration can be created via selective laser sintering. Polycaprolactone has been used to create a condylar ramus unit (CRU) scaffold for application in temporomandibular joint reconstruction in a Yucatan minipig animal model. Following sacrifice, micro-computed tomography and histology was used to demonstrate the efficacy of this particular scaffold design. Results A proof-of-concept surgery has demonstrated cartilaginous tissue regeneration along the articulating surface with exuberant osseous tissue formation. Bone volumes and tissue mineral density at both the 1 and 3 month time points demonstrated significant new bone growth interior and exterior to the scaffold. Conclusion Computationally designed scaffolds can support masticatory function in a large animal model as well as both osseous and cartilage regeneration. Our group is continuing to evaluate multiple implant designs in both young and mature Yucatan minipig animals. Copyright © 2007 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/57391/1/143_ftp.pd

Numerical prediction of the printable density range of lattice structures for additive manufacturing

Structured cellular structures are nowadays printed using additive manufacturing methods like powder bed fusion. The relative density of the cellular structures has a big role in the suitability of a lattice for printing due to the minimum printable radius constraint and powder being trapped inside an inclusion. In this work, the theoretical limits of the printable range of relative density of different lattice types are found based on the cell size using computer methods by leaving other process parameters for further research as the current parameters are the most basic ones. The results are approximated using simple polynomials to enable practical usage. (C) 2017 Elsevier Ltd. All rights reserved

A simple and effective geometric representation for irregular porous structure modeling

Computer-aided design of porous structures is a challenging task because of the high degree of irregularity and intricacy associated with the geometries. Most of the existing design approaches either target designing artifacts with regular-shaped pores or reconstructing geometric models from existing porous objects. For regular porous structures, it is difficult to control the pore shapes and distributions locally; for reconstructed models, a design is attainable only if there are some existing objects to reconstruct from. This paper is motivated to present an alternative approach to design irregular porous artifacts with controllable pore shapes and distributions, yet without requiring any existing objects as prerequisites. Inspired by the random colloid-aggregation model which explains the formation mechanism of random porous media, Voronoi tessellation is first generated to partition the space into a collection of compartments. Selective compartments are then merged together to imitate the random colloid aggregations. Through this Voronoi cell merging, irregular convex and concave polygons are obtained and the vertices of which are modeled as control points of closed B-Spline curves. The fitted B-Spline curves are then employed to represent the boundaries of the irregular-shaped pores. The proposed approach drastically improved the ease of irregular porous structure modeling while at the same time properly maintained the irregularity that is widely found in natural objects. Compared with other existing CAD approaches, the proposed approach can easily construct irregular porous structures which appear more natural and realistic. © 2010 Elsevier Ltd. All rights reserved.postprin

Tailoring Bioengineered Scaffolds for Regenerative Medicine

The vision to unravel and develop biological healing mechanisms based on evolving molecular and cellular technologies has led to a worldwide scientific endeavor to establish regenerative medicine. This is a multidisciplinary field that involves basic and preclinical research and development on the repair, replacement, and regrowth or regeneration of cells, tissues, or organs in both diseases (congenital or acquired) and traumas. A total of over 63,000 patients were officially placed on organs’ waiting lists on 31 December 2013 in the European Union (European Commission, 2014). Tissue engineering and regenerative medicine have emerged as promising fields to achieve proper solutions for these concerns. However, we are far from having patient-specific tissue engineering scaffolds that mimic the native tissue regarding both structure and function. The proposed chapter is a qualitative review over the biomaterials, processes, and scaffold designs for tailored bioprinting. Relevant literature on bioengineered scaffolds for regenerative medicine will be updated. It is well known that mechanical properties play significant effects on biologic behavior which highlight the importance of an extensively discussion on tailoring biomechanical properties for bioengineered scaffolds. The following topics will be discussed: scaffold design, biomaterials and scaffolds bioactivity, biofabrication processes, scaffolds biodegradability, and cell viability. Moreover, new insights will be pointed out

Fabrication and Compressive Yield Strength of Open Cell Corrugated Cellular Solids

This thesis studied the fabrication and compressive yield strength of open cell corrugated cellular solids made from type 304 stainless steel. Test samples were made by corrugating woven wire meshes, then laminating these in a high temperature argon environment. Mesh sizes ranging from 9.5 pore/cm (24 pore/in) to 31.5 pore/cm (80 pore/in) with wire diameters ranging from 0.178 mm (0.007 in) to 0.3556 mm (0.014 in) were bonded using lithobraze 925 (Ag-7.5Cu-0.2Li) to create cellular solids having relative densities ranging from 0.0384 to 0.0920. Test samples were then quasistatically compressed to measure the stress-strain response. The stress level at 25% strain (compressive yield strength) was plotted as a function of relative density and then compared to predicted behavior. It was found that the relative compressive yield strength variation with relative density could be accurately modeled using the Gibson-Ashby open cell model

Análisis de esfuerzos en geometrías de andamios óseos bajo cargas de compresión con las propiedades mecánicas de un material de Hidroxiapatita/ácido láctico

La relación entre la resistencia del material y la geometría de los andamios óseos asegura que los poros del andamio se mantengan íntegros mientras las células de los huesos se desarrollan a través de ellos. En este estudio se presentan las simulaciones mecánicas de dos geometrías de andamios óseos usando las propiedades mecánicas de la Hidroxiapatita (HAp) mezclado con ácido láctico. Se realizaron ensayos de compresión en la HAp para conocer sus propiedades mecánicas, después se modelaron dos geometrías de andamios óseos en base a la porosidad y tamaño adecuados para la regeneración celular según lo reportado en la literatura y se usaron los valores de las propiedades mecánicas para las simulaciones MEF.  Se encontró un módulo elástico de 253.4 MPa, el esfuerzo de cedencia de 7.53 MPa y el módulo de Poisson de 0.33. Las porosidades calculadas para los modelos CAD cúbico y cilíndrico son de 43.83% y de 50.51% respectivamente.  Se encontró que el modelo cúbico soportó una fuerza de 21 N en contraste con el modelo cilíndrico que soportó una fuerza de 19 N, estas fuerzas se aplicaron en las simulaciones con la finalidad de no superar el esfuerzo máximo permisible de 4.5 MPa de la HAp

Evaluation on performance of square finned conformal cooling channel (sfccc) fabricated by selective laser melting (slm) on plastic moulded part

In plastic injection moulding (PIM) process, the cooling stage is the most important phase because it significantly affects the productivity and quality of the molded part. Thus, the cooling system need to be emphasized in designing the injection mould system. The application of conformal cooling channels which only can be fabricated by additive manufacturing technology (AM) are proven to increase the injection moulding performance and able to reduce the quality issues. This research introduced the Square Finned Conformal Cooling Channel (SFCCC) in the PIM as a way to enhance the performance of square shape conformal cooling channel (SSCCC) in PIM. The mould insert with SFCCC has been designed, simulated via finite element analysis software, fabricated (by combination of High Speed Machining and Selective Laser Melting (SLM)), and tested using a front panel housing as the injected part for the case study. Eight types of variate SFCCC design (SFCCC 1 to SFCCC 8) employing finned and sub groove concept were analysed via simulation work to determine the best design in terms of shortest cooling time. The results showed that the shortest cooling time recorded by SFCCC 8 was at 7.621 sec, an improvement of 16.44% compared with SSCCC. In terms of cycle time, the SFCCC is able to improve the SSCCC by 8.33% to 10.26%. Meanwhile, in comparison with industrial mould using Milled Groove Conformal Cooling Channel (MGCCC), the SFCCC showed an improvement of 19.60% to 39.36% based on the coolant temperature. The experimental results showed the greatest shrinkage in the X-direction at 0.93% and the smallest shrinkage at 0.6%. For the Y-direction, the greatest shrinkage is 0.97% and the smallest shrinkage is 0.39%. In comparison with the injected part via MGCCC, the SFCCC had a slightly greater overall shrinkage in relation to the shrinkage and warpage at points X and Y direction. Most front panel housing shrinkage and warpage values in the experimental study were smaller than those of the simulative study. However, the experimental results were in line with the simulative results, proving that the SFCCC design had better cycle times and acceptable quality for an industrial mould

Performance evaluation of alsi10mg mould insert material fabricated by selective laser melting process

In this thesis the physical properties, mechanical properties, different profile building feasibility and dimension accuracy of AlSi10Mg samples fabricated by selective laser melting (SLM) technique, as well as novel fabrication strategies as an alternative to conventional methods in order to produce of plastic injection mould (PIM) tools was investigated. Response surface method (RSM) and variance analysis (ANOVA) are utilized to optimize the SLM parameters and develop the mathematical models. The optimum values input parameters for laser power, scan speed and hatch distance recommended to achieve optimum value of relative density and ultimate tensile strength (UTS) were 348.14 Watt, 1483.25 mm/s and 0.1207 mm, respectively. Other than almost full density achievement with the value of 99.3547% from the experiment, the experimental value of UTS (411.881MPa) was higher compared to A360F and A360T6 HDPC alloys. The feasibility and accuracy results indicate that the benchmark model fabricated by SLM technique revealed the potential of producing near net shape parts. Only 0.5mm offset was added in the normal direction during the fabrication of PIM tool inserts for post-processing purpose. The total time reduction in fabricating the PIM tool inserts using the combination of SLM and high speed machining (HSM) strategy was 34 hours. By introducing square fin conformal cooling channel (SFCCC) in PIM tool inserts has shorten the cycle time and improved the injected product quality due to uniform and faster heat dissipation during the moulding cycle. Whereas the total impact of conformal cooling channel and AlSi10Mg as PIM tool insert materials led to almost 32% reduction on cycle time during the moulding cycle compared to the reference PIM tool. Although with the reduction of fabrication time and cycle time, still the cost modelling result highlights that, in order the SLM AlSi10Mg fabricated PIM with square fin conformal cooling to be cheaper than the reference PIM, an endurance of at least 40 000 cycles is required

FABRICATION AND OPTIMAL-DESIGN OF BIODEGRADABLE STENTS FOR THE TREATMENT OF ANEURYSMS

An aneurysm is a balloon-like bulge in the wall of blood vessels, occurring in major arteries from the heart and brain. Biodegradable stent-assisted coiling is expected to be the ideal treatment of wide-neck complex aneurysms. A number of biodegradable stents are promising, but also with issues and/or several limitations to be addressed. From the design point of view, biodegradable stents are typically designed without structure optimization. The drawbacks of these stents often cause weaker mechanical properties than native arterial vessels. From the fabrication point of view, the conventional methods of the fabricating stent are time-consuming and expensive, and also lack precise control over the stent microstructure. As an emerging fabrication technique, dispensing-based rapid prototyping (DBRP) allows for more accurate control over the scaffold microstructure, thus facilitating the fabrication of stents as designed. This thesis is aimed at developing methods for fabrication and optimal design of biodegradable stents for treating aneurysms. Firstly, a method was developed to fabricate biodegradable stents by using the DBRP technique. Then, a compression test was carried out to characterize the radial deformation of the stents fabricated. The results illustrated the stent with a zigzag structure has a higher radial stiffness than the one with a coil structure. On this basis, the stent with a zigzag structure was chosen to develop a finite element model for simulating the real compression tests. The result showed the finite element model of biodegradable stents is acceptable within a range of radial deformation around 20%. Furthermore, an optimization of the zigzag structure was performed with ANSYS DesignXplorer, and the results indicated that the total deformation could be decreased by 35% by optimizing the structure parameters, which would represent a significant advance of the radial stiffness of biodegradable stents. Finally, the optimized stent was used to investigate its deformation in a blood vessel. The deformation is found to be 0.25 mm in the simulation, and the rigidity of biodegradable stents is 7.22%, which is able to support the blood vessel all. It is illustrated that the finite element analysis indeed helps in designing stents with new structures and therefore improved mechanical properties