3D Printed Templating of Extrinsic Freeze-Casting for Macro–Microporous Biomaterials

Abstract

As with most biological materials, natural bone has hierarchical structure. The microstructural features of compact bone are of various length scales with its porosity consisting of larger osteons (∼100 μm diameter) and vascular channels, as well as smaller lacuna spaces (∼10 μm diameter). In this study, the freeze-casting process, which has been previously used to form biocompatible porous scaffolds (made with hydroxyapatite, HA) has been improved to mimic the intrinsic hierarchical structure of natural bone by implementing an extrinsic 3D printed template. The results of pore characterization showed that this novel combined method of 3D printing and freeze-casting is able to produce porosity at multiple length scales. Nonporous, microporous (created with freeze-casting alone), and macro-micro porous (created with freeze-casting and 3D printed templating) scaffolds were compared as substrates to evaluate cellular activities using osteoblast-like MG63 cell lines. The number of cells oriented parallel to the HA wall structures in the freeze-cast scaffold was found to increase on the microporous and macro-micro porous samples when compare to the nonporous samples, mimicking the natural alignment of the lamella of natural bone. Regarding the cell morphologies, cells on microporous and macro-micro porous samples showed narrowly aligned shapes, whereas those on nonporous samples had polygonal shapes with no discernible orientation. Proliferation and differentiation tests demonstrated that no toxicity or functional abnormalities were found in any of the substrates due to potential chemical and mechanical residues that may have been introduced by the freeze-casting process. Monitoring of the three-dimensional distribution of cells in the scaffolds through microcomputed tomography indicates that the cells were well distributed in the interior pore spaces via the interpenetrating macro-micro pore networks. In summary, we demonstrate this novel approach can create porosity at multiple length scales and is highly favorable in creating a biocompatible, osteoconductive, and structurally hierarchical HA scaffolds for biomedical applications.

Recent advances in ice templating: from biomimetic composites to cell culture scaffolds and tissue engineering

“…As mentioned earlier, achieving biomaterials whose morphology is inspired by bone's ultrastructure can be attempted using ice templating. Hap, 37,94,[103][104][105][106][107] one of the main components of bone, is consequently holding a dominant place in the fabrication of scaffolds for bone tissue engineering applications. Hap scaffolds were obtained through the use of electric field assisted ice templating.…”

Mechanical Optimization of Diatomite Monoliths from Freeze Casting for High-Throughput Applications

“…Recent research has also demonstrated the incorporation of three-dimensional (3D) printing sacrificial scaffolding in freeze-cast monoliths to yield macrostructural control. 31 This shows promise for future applications that look to have substantial control over several length scales. By combining the advents of structural control from the macro-to the microscale in the field of freeze casting, with the structural diversity of diatom frustules, and further nanostructural functionalizations (i.e., metal−organic frameworks, zeolites, nanoparticles, and shape-preserving chemical alterations), the future of diatomite freeze-cast monoliths will potentially produce a wide-reaching array of applications.…”

A New Era of Integrative Ice Frozen Assembly into Multiscale Architecturing of Energy Materials

“…The resulting hierarchical structure of functional materials with the controlled compositions is expected to improve the electrochemical performances owing to the abundant surface‐exposed active sites, the rapid charge transfer, the fast 3D electron/ion/mass transporting pathways, the large accessible areas, the open spaces for the redox sites, and the ability to form structures with free volumes which provides stress buffering during electrochemical reaction. [ 75–84,86,87 ]…”

“…Moreover, the types of functional materials include ceramic, [75,76] metal, [33][34][35]38] polymer, [77][78][79] carbon, [36,80,81] and even biological materials. [82][83][84] Another advantage is that various alterations to processing conditions lead to drastic changes and controls in the micro and macrostructures of as-obtained ice templated scaffolds. The resulting hierarchical structure of functional materials with the controlled compositions is expected to improve the electrochemical performances owing to the abundant surface-exposed active sites, the rapid charge transfer, the fast 3D electron/ion/mass transporting pathways, the large accessible areas, the open spaces for the redox sites, and the ability to form structures with free volumes which provides stress buffering during electrochemical reaction.…”

“…The resulting hierarchical structure of functional materials with the controlled compositions is expected to improve the electrochemical performances owing to the abundant surface-exposed active sites, the rapid charge transfer, the fast 3D electron/ion/mass transporting pathways, the large accessible areas, the open spaces for the redox sites, and the ability to form structures with free volumes which provides stress buffering during electrochemical reaction. [75][76][77][78][79][80][81][82][83][84]86,87] Many review articles have been so far reported for the materials' design via ice frozen assembly process and for their wide range of applications. [88][89][90][91][92][93][94][95] More importantly, this conventional freeze casting has been currently revisited combining with other materials' synthesis and processing methodologies (such as, spinning, spraying, filtration, hydrothermal, oxygenation, gelation, and 3D printing) [63,[96][97][98][99] and thus, more complicated and hierarchical structures could be constructed targeting energy conversion and storage applications.…”