Ingenieurwissenschaften und zugeordnete Tätigkeiten
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- 2017 (8) (entfernen)
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- Additive manufacturing (3)
- 3D printing (1)
- Additive Fertigung (1)
- Additive manufacturing, 3D printing (1)
- Bone tissue engineering (1)
- Calcium alkali orthophosphate (1)
- Ceramics (1)
- Dense alumina (1)
- Flowability (1)
- Glass-ceramic (1)
Up to now, there exists a lack of methods for the additive manufacturing of voluminous ceramic parts with properties comparable to those of conventionally manufactured ones. A high density after sintering is needed to reach the superior properties of ceramic materials. We have developed a new additive manufacturing method, Laser-Induced Slip casting (LIS), to generate ceramic green bodies with high particle packing density and with virtually no restriction in the particle size of the feedstock, especially in terms of small particles. This is achieved by laser-induced local drying of slurries, with the process resembling many features of the well-established stereolithography, but without the excessive use of polymeric material. Thus, unlike the stereolithography process, the resulting green bodies can be processed like traditionally produced ceramic parts. This method allows large and dense additive-manufactured parts to be obtained from conventional water-based ceramic slurries. As an example, we will demonstrate the application of this novel technique with Si3N4.
Over the last decade there have been increasing efforts to develop three-dimensional (3D) scaffolds for bone tissue Engineering from bioactive ceramics with 3D printing emerging as a promising technology. The overall objective of the present study was to generate a tissue engineered synthetic bone graft with homogenously distributed osteoblasts and mineralizing bone Matrix in vitro, thereby mimicking the advantageous properties of autogenous bone grafts and facilitating usage for reconstructing segmental discontinuity defects in vivo . To this end, 3D scaffolds were developed from a silica-containing calcium alkali orthophosphate, using, fi rst, a replica technique – the Schwartzwalder – Somers method – and, second, 3D printing, (i.e. rapid prototyping). The mechanical and physical scaffold properties and their potential to facilitate homogenous colonization by osteogenic cells and extracellular bone matrix formation throughout the porous scaffold architecture were examined.
Osteoblastic cells were dynamically cultured for 7 days on both scaffold types with two different concentrations of 1.5 and 3 × 10⁹ cells/l. The amount of cells and bone matrix formed and osteogenic marker expression were evaluated using hard tissue histology, immunohistochemical and histomorphometric analysis. 3D-printed scaffolds (RPS) exhibited more micropores, greater compressive strength and silica release. RPS seeded with 3 × 10⁹ cells/l displayed greatest cell and extracellular Matrix formation, mineralization and osteocalcin expression. In conclusion, RPS displayed superior mechanical and biological properties and facilitated generating a tissue engineered synthetic bone graft in vitro, which mimics the advantageous properties of autogenous bone grafts, by containing homogenously distributed terminally differentiated osteoblasts and mineralizing bone matrix and therefore is suitable for subsequent in vivo implantation for regenerating segmental discontinuity bone defects.
Adapting trabecular structures for 3D printing: an image processing approach based on μCT data
(2017)
Materials with a trabecular structure notably Combine advantages such as lightweight, reasonable strength, and permeability for fl uids. This combination of advantages is especially interesting for tissue engineering in trauma surgery and orthopedics. Bone-substituting scaffolds for instance are designed with a trabecular structure in order to allow cell migration for bone ingrowth and vascularization. An emerging and recently very popular technology to produce such complex, porous structures is 3D printing. However, several technological aspects regarding the scaffold architecture, the printable resolution, and the feature size have to be considered when fabricating scaffolds for bone tissue replacement and regeneration. Here, we present a strategy to assess and prepare realistic trabecular structures for 3D printing using image analysis with the aim of preserving the structural elements. We discuss critical conditions of the printing system and present a 3-stage approach to adapt a trabecular structure from μ CT data while incorporating knowledge about the printing system. In the first stage, an image-based extraction of solid and void structures is performed, which results in voxel- and graph-based representations of the extracted structures. These representations not only allow us to quantify geometrical properties such as pore size or strut geometry and length. But, since the graph represents the geometry and the topology of the initial structure, it can be used in the second stage to modify and adjust feature size, volume and sample size in an easy and consistent way. In the final reconstruction stage, the graph is then converted into a voxel representation preserving the topology of the initial structure. This stage generates a model with respect to the printing conditions to ensure a stable and controlled voxel placement during the printing process.
Capsule summary
THE MATERIALS
Manufacturers can use preceramic polymers to produce ceramic components in a range of compositions using a variety of additive manufacturing technologies. Preceramic polymers even can overcome some of the problems that are intrinsic to additive manufacturing in general.
THE APPLICATION
Modifying the composition, molecular architecture, and molecular weight of preceramic polymers allows adaptation of these materials to specific processing requirements of individual additive manufacturing technologies.
THE OPPORTUNITY
Further development of new additive manufacturing technologies, in addition to improvement of existing technologies, will enable manufacturing of advanced ceramic components with enhanced mechanical characteristics and new functional properties.
Injectable, brushite-forming calcium phosphate cements (CPC) show potential for bone replacement, but they exhibit low mechanical strength. This study tested a CPC reinforced with poly(l-lactide-co-glycolide) acid (PLGA) fibers in a minimally invasive, sheep lumbar vertebroplasty model.
The study aimed to test the in vivo biocompatibility and osteogenic potential of a PLGA fiber-reinforced, brushite-forming CPC in a sheep large animal model.
Particle size gradation is regarded as an effective method for overcoming the contradicting requirements in three-dimensional printing (3DP). In present work, particle size gradation was optimized to obtain both acceptable flowability of the powder material and high-strength 3D-printed glass-ceramic products. The effect of gradation on the printing process, sintering process and performance of the 3D-printed glass-ceramic products was investigated comprehensively. The glass-ceramic powders with three size ranges were mixed in certain proportions and applied to print parts. The result showed parts printed with powder mixed by 60 wt% 45–100 µm and 40 wt% 0–25 µm particles had satisfactory density of 1.60 g/cm³ and bending strength of 13.8 MPa. The flowability decreased with an increasing proportion of fine particles. Part density was determined by the powder bulk density in the powder bed as well as the shrinkage during sintering while strength of part was found to be dependent on the sintering degree.
An improved method of powder 3D printing leading to dense ceramic parts is presented. The application of powder-based binder jetting 3D printing technologies to technical ceramics is generally limited by the low packing density of the powder and by the need to use a flowable powder. With layer-wise slurry deposition, it is, however, possible to deposit powder beds with high particle packing and furthermore using submicron powders. This method was combined with the binder jetting technology to develop a novel process, named LSD-print. By means of LSD-print, a submicron Al2O3 powder could be processed to produce samples with a density comparable with that of standard pressed samples, both in the green state and after sintering.