Microarchitectured Carbon Structures as Innovative Tissue‐Engineering Scaffolds

Abstract

Additive manufacturing technologies have enabled some of the most relevant advances in the fields of tissue engineering and biofabrication, [1,2] thanks to the solid freeform fabrication opportunities they provide, which prove very adequate for achieving complex geometries capable of interacting in personalized ways with the human body. From pioneering studies dealing with the fused deposition modeling of tissue scaffolds as extracellular matrixes for cells, [3,4] to more recent bioprinting approaches, [5-7] which typically use layer-by-layer fabrication techniques with living organisms and biomaterials to produce complex tissues in vitro [8] (or use computer-aided transfer processes for patterning and assembling living and nonliving materials with a prescribed 2D or 3D organization to produce bio-engineered structures), [9] the possibility of manipulating matter in an additive way has proven transformative. However, additional progress is needed, as there is not yet a single additive manufacturing technique (AMT) that provides the perfect compromise between achievable part size, printing resolution, dimensional operative range, structural stability, and overall biocompatibility. For instance, syringe-based bioprinting techniques are still less precise than the more traditional AMTs working with synthetic materials, which are already a mainstream trend in biomedical engineering, medical practice, and biotechnology fields (i.e., selective laser sintering or melting of metallic powders, laser stereolithography with biophotopolymers or lithography-based ceramic manufacturing, among others). [10-12] Other biomanufacturing techniques, such as laser-assisted bioprinting has led to an improved precision level for manipulating living organisms and biomaterials, [13] and could possibly synergize with 3D lattices, used as boundaries or structural supports. This would help to minimize hydrogel creep and to achieve multi-scale and multi-material scaffolding structures with biomimetic functional gradients of mechanical properties. In contrast, the most precise additive manufacturing technologies, especially two-photon polymerization, which enables interactions even at single cellular level, [14] are not still adequate in terms of throughput and the overall building volume is normally limited to less than 1 mm 3. Furthermore, the materials used by most industrial AMTs, especially those relying on photopolymerization, are normally inadequate for implantation and, consequently, the achieved cell culture systems are limited to performing in vitro studies. In some cases, the use of carbon coatings (i.e., diamond-like carbon) upon laser stereolithography microsystems [15] or the use of carbon fibers knitted to 3D-printed

Microarchitected Compliant Scaffolds of Pyrolytic Carbon for 3D Muscle Cell Growth

“…As expected and previously reported for PyC structures, [20,23,25] the pyrolysis process resulted in significant geometrical shrinkage due to the release of gaseous compounds during the thermochemical decomposition of the precursor resin. This shrinkage allowed for the PyC lattice thickness to be significantly smaller than the fabrication capabilities, as shown in Figure 1f.…”

“…A few studies have shown promising results in using architected 3D PyC structures in bone tissue engineering. [ 23,24 ] However, the pore sizes between lattice elements in these studies were significantly larger (>300 µm), restricting from achieving 3D cell colonization.…”

Graph Theory Design of 3D Printed Conductive Lattice Electrodes

“…The carbonization process makes the structures conductive while enhancing the resolution, preserving the microstructure of the 3D printed polymers while shrinking them to roughly 38% of their original printed size (see additional images in Figure S1, Supporting Information). Similar processes have been reported for carbonizing 3D printed resins printed by stereolithography using higher temperature anneals (900 °C) in nitrogen or argon, [21,28,29] however, our work achieves up to 7× smaller features while retaining fully solid struts (Figure S2, Supporting Information) and minimizing defects. Even the layers formed during printing, due to the layer-by-layer nature of the μSLA process, are maintained during carbonization, appearing as lines on the structures in Figure 3.…”

Comparing Carbon Origami from Polyaramid and Cellulose Sheets

“…The carbon materials were further characterized by XRD and Raman spectroscopy. The XRD pattern of the NC (Figure 3a) featured two broad peaks centering around 2θ = 24 • and 2θ = 44 • , which are characteristics of (002), (100) and (101) reflections of turbostratic carbon material (ICDD PDF number: 75-1621) [4,46]. The XRD diffractogram of CC also featured broad peaks of carbon.…”