RESUMO
Triply Periodic Minimal Surfaces (TPMS), such as Gyroid, are widely accepted for bone tissue engineering due to their interconnected porous structures with tunable properties that enable high surface area to volume ratios, energy absorption, and relative strength. Among these topologies, the Fischer-Koch-S (FKS) has also been suggested for compact bone scaffolds, but few studies have investigated these structures beyond computer simulations. FKS scaffolds have been fabricated in metal and polymer, but to date none have been fabricated in a ceramic used in bone tissue engineering (BTE) scaffolds. This study is the first to fabricate ceramic FKS scaffolds and compare them with the more common Gyroid topology. Results showed that FKS scaffolds were 32% stronger, absorbed 49% more energy, and had only 11% lower permeability than Gyroid scaffolds when manufactured at high porosity (70%). Both FKS and Gyroid scaffolds displayed strength and permeability in the low range of trabecular long bones with high reliability (Weibull failure probability) in the normal direction. Fracture modes were further investigated to explicate the quasi-brittle failure exhibited by both scaffold topologies, exploring stress-strain relationships along with scanning electron microscopy for failure analysis. Considering the physical aspects of successful bone tissue engineering scaffolds, FKS scaffolds appear to be more promising for further study as bone regeneration scaffolds than Gyroid due to their higher compressive strength and reliability, at only a small penalty to permeability. In the context of BTE, FKS scaffolds may be better suited than Gyroids to applications where denser bone and strength is prioritized over permeability, as suggested by earlier simulation studies.
RESUMO
PURPOSE: Bioprinting is an additive manufacturing technology analogous to 3D printing. Instead of plastic or resin, cell-laden hydrogels are used to produce a construct of the intended biological structure. Over time, cells transform this construct into a functioning tissue or organ. The process of printing followed by tissue maturation is referred to as 4D bioprinting. The fourth dimension is temporal. Failure to provide living cells with sufficient amounts of oxygen at any point along the developmental timeline may jeopardize the bioprinting goals. Even transient hypoxia may alter cells' differentiation and proliferation or trigger apoptosis. Electron paramagnetic resonance (EPR) imaging modality is proposed to permit 4D monitoring of oxygen within bioprinted structures. PROCEDURES: Lithium octa-n-butoxy-phthalocyanine (LiNc-BuO) probes have been introduced into gelatin methacrylate (GelMA) bioink. GelMA is a cross-linkable hydrogel, and LiNc-BuO is an oxygen-sensitive compound that permits longitudinal oximetric measurements. The effects of the oxygen probe on printability have been evaluated. A digital light processing (DLP) bioprinter was built in the laboratory. Bioprinting protocols have been developed that consider the optical properties of the GelMA/LiNc-BuO composites. Acellular and cell-laden constructs have been printed and imaged. The post-printing effect of residual photoinitiator on oxygen depletion has been investigated. RESULTS: Models have been successfully printed using a lab-built bioprinter. Rapid scan EPR images reflective of the expected oxygen concentration levels have been acquired. An unreported problem of oxygen depletion in bioprinted constructs by the residual photoinitiator has been documented. EPR imaging is proposed as a control method for its removal. The oxygen consumption rates by HEK293T cells within a bioprinted cylinder have been imaged and quantified. CONCLUSIONS: The feasibility of the cointegration of 4D EPR imaging and 4D bioprinting has been demonstrated. The proof-of-concept experiments, which were conducted using oxygen probes loaded into GelMA, lay the foundation for a broad range of applications, such as bioprinting with many types of bioinks loaded with diverse varieties of molecular spin probes.