Embedded 3D Printing of Cryogel-Based Scaffolds

Cryogel-based scaffolds have attracted great attention in tissue engineering due to their interconnected macroporous structures. However, three-dimensional (3D) printing of cryogels with a high degree of precision and complexity is a challenge, since the synthesis of cryogels occurs under cryogenic conditions. In this study, we demonstrated the fabrication of cryogel-based scaffolds for the first time by using an embedded printing technique. A photo-cross-linkable gelatin methacryloyl (GelMA)-based ink composition, including alginate and photoinitiator, was printed into a nanoclay-based support bath. The layer-by-layer extruded ink was held in complex and overhanging structures with the help of pre-cross-linking of alginate with Ca2+ present in the support bath. The printed 3D structures in the support bath were frozen, and then GelMA was cross-linked at a subzero temperature under UV light. The printed and cross-linked structures were successfully recovered from the support bath with an integrated shape complexity. SEM images showed the formation of a 3D printed scaffold where porous GelMA cryogel was integrated between the cross-linked alginate hydrogels. In addition, they showed excellent shape recovery under uniaxial compression cycles of up to 80% strain. In vitro studies showed that the human fibroblast cells attached to the 3D printed scaffold and displayed spread morphology with a high proliferation rate. The results revealed that the embedded 3D printing technique enables the fabrication of cytocompatible cryogel based scaffolds with desired morphology and mechanical behavior using photo-cross-linkable bioink composition. The properties of the cryogels can be modified by varying the GelMA concentration, whereby various shapes of scaffolds can be fabricated to meet the specific requirements of tissue engineering applications.

[Embedded 3D printing of porous silicon orbital implants and its surface modification]

OBJECTIVE

To prepare customized porous silicone orbital implants using embedded 3D printing and assess the effect of surface modification on the properties of the implants.

METHODS

The transparency, fluidity and rheological properties of the supporting media were tested to determine the optimal printing parameters of silicone. The morphological changes of silicone after modification were analyzed by scanning electron microscopy, and the hydrophilicity and hydrophobicity of silicone surface were evaluated by measuring the water contact angle. The compression modulus of porous silicone was measured using compression test. Porcine aortic endothelial cells (PAOECs) were co-cultured with porous silicone scaffolds for 1, 3 and 5 days to test the biocompatibility of silicone. The local inflammatory response to subcutaneous porous silicone implants was evaluated in rats.

RESULTS

The optimal printing parameters of silicone orbital implants were determined as the following: supporting medium 4% (mass ratio), printing pressure 1.0 bar and printing speed 6 mm/s. Scanning electron microscopy showed that the silicone surface was successfully modified with polydopamine and collagen, which significantly improved hydrophilicity of the silicone surface (P < 0.05) without causing significant changes in the compression modulus (P > 0.05). The modified porous silicone scaffold had no obvious cytotoxicity and obviously promoted adhesion and proliferation of PAOECs (P < 0.05). In rats bearing the subcutaneous implants, no obvious inflammation was observed in the local tissue.

CONCLUSION

Poprous silicone orbital implants with uniform pores can be prepared using embedded 3D printing technology, and surface modification obviously improves hydrophilicity and biocompatibility of the silicone implants for potential clinical application.

Embedded 3D Printing of Architected Ceramics via Microwave-Activated Polymerization

Light- and ink-based 3D printing methods have vastly expanded the design space and geometric complexity of architected ceramics. However, light-based methods are typically confined to a relatively narrow range of preceramic and particle-laden resins, while ink-based methods are limited in geometric complexity due to layerwise assembly. Here, embedded 3D printing is combined with microwave-activated curing to generate architected ceramics with spatially controlled composition in freeform shapes. Aqueous colloidal inks are printed within a support matrix, rapidly cured via microwave-activated polymerization, and subsequently dried and sintered into dense architectures composed of one or more oxide materials. This integrated manufacturing method opens new avenues for the design and fabrication of complex ceramic architectures with programmed composition, density, and form for myriad applications.

Embedded 3D Printing of Multimaterial Polymer Lattices via Graph-Based Print Path Planning

Recent advances in computational design and 3D printing enable the fabrication of polymer lattices with high strength-to-weight ratio and tailored mechanics. To date, 3D lattices composed of monolithic materials have primarily been constructed due to limitations associated with most commercial 3D printing platforms. Here, freeform fabrication of multi-material polymer lattices via embedded three-dimensional (EMB3D) printing is demonstrated. An algorithm is developed first that generates print paths for each target lattice based on graph theory. The effects of ink rheology on filamentary printing and the effects of the print path on resultant mechanical properties are then investigated. By co-printing multiple materials with different mechanical properties, a broad range of periodic and stochastic lattices with tailored mechanical responses can be realized opening new avenues for constructing architected matter.

Embedded 3D Printing in Self-Healing Annealable Composites for Precise Patterning of Functionally Mature Human Neural Constructs

Human in vitro models of neural tissue with tunable microenvironment and defined spatial arrangement are needed to facilitate studies of brain development and disease. Towards this end, embedded printing inside granular gels holds great promise as it allows precise patterning of extremely soft tissue constructs. However, granular printing support formulations are restricted to only a handful of materials. Therefore, there has been a need for novel materials that take advantage of versatile biomimicry of bulk hydrogels while providing high-fidelity support for embedded printing akin to granular gels. To address this need, Authors present a modular platform for bioengineering of neuronal networks via direct embedded 3D printing of human stem cells inside Self-Healing Annealable Particle-Extracellular matrix (SHAPE) composites. SHAPE composites consist of soft microgels immersed in viscous extracellular-matrix solution to enable precise and programmable patterning of human stem cells and consequent generation mature subtype-specific neurons that extend projections into the volume of the annealed support. The developed approach further allows multi-ink deposition, live spatial and temporal monitoring of oxygen levels, as well as creation of vascular-like channels. Due to its modularity and versatility, SHAPE biomanufacturing toolbox has potential to be used in applications beyond functional modeling of mechanically sensitive neural constructs.

Fluid Bath-Assisted 3D Printing for Biomedical Applications: From Pre- to Postprinting Stages

Fluid bath-assisted three-dimensional (3D) printing is an innovative 3D printing strategy that extrudes liquid ink materials into a fluid bath to form various 3D configurations. Since the support bath can provide in situ support, extruded filaments are able to freely construct complex 3D structures. Meanwhile, the supporting function of the fluid bath decreases the dependence of the ink material's cross-linkability, thus broadening the material selections for biomedical applications. Fluid bath-assisted 3D printing can be divided into two subcategories: embedded 3D printing and support bath-enabled 3D printing. This review will introduce and discuss three main manufacturing processes, or stages, for these two strategies. The stages that will be discussed include preprinting, printing, and postprinting. In the preprinting stage, representative fluid bath materials are introduced and the bath material preparation methods are also discussed. In addition, the design criteria of fluid bath materials including biocompatibility, rheological properties, physical/chemical stability, hydrophilicity/hydrophobicity, and other properties are proposed in order to guide the selection and design of future fluid bath materials. For the printing stage, some key technical issues discussed in this review include filament formation mechanisms in a fluid bath, effects of nozzle movement on printed structures, and design strategies for printing paths. In the postprinting stage, some commonly used postprinting processes are introduced. Finally, representative biomedical applications of fluid bath-assisted 3D printing, such as standalone organoids/tissues, biomedical microfluidic devices, and wearable and bionic devices, are summarized and presented.

UV-Resistant Self-Healing Emulsion Glass as a New Liquid-like Solid Material for 3D Printing

Directly writing 3D structures into supporting mediums is a relatively new developing technology in additive manufacturing. In this work, durable and recyclable liquid-like solid (LLS) materials are developed as supporting mediums that are stable for both UV and thermal solidification. Our LLS material is comprised of densely packed oil droplets in a continuous aqueous medium, known as emulsion glass. Its elastic nature emerges from the jammed structure of oil droplets, which offers this LLS material rapidly self-healing ability. Moreover, the yield stress of the glass is relatively low and can be tuned by the viscosity and weight percentage of oil. The capability of the emulsion glass as supporting mediums is successfully demonstrated by directly writing and then curing designed structures. The emulsion glass has been repeatedly used at least 6 times upon exposure to UV irradiation and heat, implying it can expand the applications of supporting medium to the writing process involving UV- and thermal-curable inks simultaneously.

Generation of Cost-Effective Paper-Based Tissue Models through Matrix-Assisted Sacrificial 3D Printing

Due to the combined advantages of cellulose and nanoscale (diameter 20-60 nm), bacterial cellulose possesses a series of attractive features including its natural origin, moderate biosynthesis process, good biocompatibility, and cost-effectiveness. Moreover, bacterial cellulose nanofibers can be conveniently processed into three-dimensional (3D) intertwined structures and form stable paper devices after simple drying. These advantages make it suitable as the material for construction of organ-on-a-chip devices using matrix-assisted sacrificial 3D printing. We successfully fabricated various microchannel structures embedded in the bulk bacterial cellulose hydrogels and retained their integrity after the drying process. Interestingly, these paper-based devices containing hollow microchannels could be rehydrated and populated with relevant cells to form vascularized tissue models. As a proof-of-concept demonstration, we seeded human umbilical vein endothelial cells (HUVECs) into the microchannels to obtain the vasculature and inoculated the MCF-7 cells onto the surrounding matrix of the paper device to build a 3D paper-based vascularized breast tumor model. The results showed that the microchannels were perfusable, and both HUVECs and MCF-7 cells exhibited favorable proliferation behaviors. This study may provide a new strategy for constructing simple and low-cost in vitro tissue models, which may find potential applications in drug screening and personalized medicine.

High-Performance and Lightweight Thermal Management Devices by 3D Printing and Assembly of Continuous Carbon Nanotube Sheets

Free-standing carbon nanotube films or buckypaper can provide a significant platform to develop practical applications of nanocarbon materials. For this research, buckypaper with high thermal conductivity (20 W/m K) and large surface area (350 m²/g) was mass produced in-house to investigate for use in lightweight thermal management devices. Floating catalyst chemical vapor deposition carbon nanotube sheets were also studied in this work. We introduced two manufacturing techniques to use the sheets for heat dissipation: (1) printing conductive composite ink on the sheets to make lightweight thermal devices, such as heat sinks and (2) assembling the sheets directly into 3D structures that were mounted on the back of heat-generating devices. These manufacturing techniques resulted in extremely lightweight, high-performance heat dissipation devices compared with other heat sink materials.