Indirect Solid Freeform Fabrication Research Articles

Controlling the processing of collagen-hydroxyapatite scaffolds for bone tissue engineering

Scaffolds are an important aspect of the tissue engineering approach to tissue regeneration. This study shows that it is possible to manufacture scaffolds from type I collagen with or without hydroxyapatite (HA) by critical point drying. The mean pore sizes of the scaffolds can be altered from 44 to 135 microm depending on the precise processing conditions. Such pore sizes span the range that is likely to be required for specific cells. The mechanical properties of the scaffolds have been measured and behave as expected of foam structures. The degradation rate of the scaffolds by collagenase is independent of pore size. Dehydrothermal treatment (DHT), a common method of physically crosslinking collagen, was found to denature the collagen at a temperature of 120 degrees C resulting in a decrease in the scaffold's resistance to collagenase. Hybrid scaffold structures have also been manufactured, which have the potential to be used in the generation of multi-tissue interfaces. Microchannels are neatly incorporated via an indirect solid freeform fabrication (SFF) process, which could aid in reducing the different constraints commonly observed with other scaffolds.

Internal Structure Evaluation of Three-Dimensional Calcium Phosphate Bone Scaffolds: A Micro-Computed Tomographic Study

Micro-computed tomography (μ-CT) was used to examine the fidelity of three-dimensional (3D) bioceramic scaffolds made from dicalcium phosphate dihydrate (DCPD) cement. The scaffolds were produced with a multi-step indirect solid freeform fabrication method. Accuracy and fidelity were examined after each step. The pre-tracing of the perimeter of a layer in the mold fabrication step caused the round-off of the square channels from the design. However, the overall shape of the scaffold was not significantly different from the wax mold. There is relatively no change in the strut and the channel-size measurements between the computer-generated model and the molds fabricated by 3D printing. The change in volume fraction of DCPD cement scaffolds is higher than biphasic scaffolds due to the internal pores. These results demonstrated that μ-CT is a very useful tool to analyze and evaluate the internal architectural of the complicated 3D scaffold-fabrication process.

Mechanical Behavior of Complex 3D Calcium Phosphate Cement Scaffolds Fabricated by Indirect Solid Freeform Fabrication In Vivo

Calcium phosphate cement is a bioceramic with potential applications for bone-tissue engineering. In this work, controlled porous calcium phosphate scaffolds with interconnected pores were computationally designed by an image-based approach and fabricated by indirect solid freeform fabrication (ISFF) or ‘lost mold’ technique. Voxel finite-element analysis (FEA) showed that mechanical properties of design and fabricated scaffold can be predicted computationally. Scaffolds were then implanted subcutaneously to demonstrate tissue in-growth. Previously, we showed the ability of porous calcium phosphate cement scaffolds to have sufficiently strong mechanical properties for bone tissue engineering applications. This work shows the image-based FEAs from micro-CT scans in vivo (four- and eight weeks). Extensive new bone apposition was noted with micro-CT technique after four- and eight weeks. FEA models of the original design and scaffolds with newly bone formed were compared.

Design and fabrication of CAP scaffolds by indirect solid free form fabrication

PurposeTo fabricate the self‐hardening calcium phosphate composite scaffolds with controlled internal pore architectures using rapid prototyping (RP) techniques and investigate their in vitro bone tissue engineering responses.Design/methodology/approachThe three‐dimensionally interconnected pores in scaffolds can facilitate sufficient supply of blood, oxygen and nutrients for the ingrowth of bone cells, tissue regeneration, and vascularization. It is essential for bone tissue engineering to provide an accurate control over the scaffolds material, porosity, and internal pore architectures. Negative image of scaffold was designed and epoxy resin molds were fabricated on sterolithography apparatus. Calcium phosphate cement slurry was cast in these molds. After self‐hardening, the molds were removed by pyrolysis and the resulting scaffolds were obtained.FindingsEight scaffolds with 54.45 percent porosity were tested on an Instron machine. The average compressive strength measured was 5.8±0.8 Mpa. Cytotoxicity and cell proliferation studies were conducted with rabbit osteoblast. Results showed that these scaffolds were non‐toxic and displayed excellent cell growth during the 2 weeks of in vitro culture.Research limitations/implicationsThe resulting scaffolds inherited errors and defects from the molds, such as cracks and dimensional changes.Originality/valueThe present method enhances the versatility of scaffold fabrication by RP. It is capable of reproducibly fabricating scaffolds from a variety of biomaterials.

Indirect solid freeform fabrication by binder assisted slip casting

A method has been developed for the consolidation of ceramic bodies in molds prepared by solid freeform fabrication. The method is based on slip casting with an added latex binder. The latex binder makes it possible to create internal structures, such as pore channels, without the cracking that usually takes place when shrinkage is obstructed by internal mold structures. The latex binder adds plasticity to the consolidating body in the wet state. This was observed by rheological measurements during slip casting. Measurements of mechanical properties showed that the latex binder also adds plasticity and strength in the dry state.

High‐Frequency Electromagnetic Bandgap Structures via Indirect Solid Freeform Fabrication

The indirect solid freeform fabrication process is used to fabricate low‐loss complex geometry periodic dielectrics for use in the microwave range. Relevant processing details, such as mold fabrication, slurry rheology, curing, and binder burnout, are discussed. Woodpile electromagnetic bandgap structures exhibiting a −40 dB well were shown to be operational at frequencies >110 GHz. Novel designs of planar periodic dielectric resonators with Q= 965 at 33 GHz (Q= ratio of the power stored to power lost in the resonator) were realized in alumina. Metallo‐dielectric filters with low‐insertion loss were also created via ISFF; modeling of these structures using resistor‐inductor‐capacitor‐equivalent circuit analysis was performed to calculate a Q of 645.

Indirect solid free form fabrication of local and global porous, biomimetic and composite 3D polymer-ceramic scaffolds

Precise control over scaffold material, porosity, and internal pore architecture is essential for tissue engineering. By coupling solid free form (SFF) manufacturing with conventional sponge scaffold fabrication procedures, we have developed methods for casting scaffolds that contain designed and controlled locally porous and globally porous internal architectures. These methods are compatible with numerous bioresorbable and non-resorbable polymers, ceramics, and biologic materials. Phase separation, emulsion-solvent diffusion, and porogen leaching were used to create poly( l)lactide (PLA) scaffolds containing both computationally designed global pores (500, 600, or 800 μm wide channels) and solvent fashioned local pores (50–100 μm wide voids or 5–10 μm length plates). Globally porous PLA and polyglycolide/PLA discrete composites were made using melt processing. Biphasic scaffolds with mechanically interdigitated PLA and sintered hydroxyapatite regions were fabricated with 500 and 600 μm wide global pores. PLA scaffolds with complex internal architectures that mimicked human trabecular bone were produced. Our indirect fabrication using casting in SFF molds provided enhanced control over scaffold shape, material, porosity and pore architecture, including size, geometry, orientation, branching, and interconnectivity. These scaffolds that contain concurrent local and global pores, discrete material regions, and biomimetic internal architectures may prove valuable for multi-tissue and structural tissue interface engineering.