skip to main content

This content will become publicly available on November 21, 2024

Title: 3D printing microporous scaffolds from modular bioinks containing sacrificial, cell-encapsulating microgels

Blending sacrificial, cell-laden microgels with structural, UV-crosslinkable microgels produces a family of modular bioinks with tunable void fractions that influence cellular morphology while maintaining a depth-independent cell distribution.

more » « less
Award ID(s):
Author(s) / Creator(s):
; ; ; ;
Publisher / Repository:
Royal Society of Chemistry
Date Published:
Journal Name:
Biomaterials Science
Page Range / eLocation ID:
7598 to 7615
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Microgels have recently received widespread attention for their applications in a wide array of domains such as tissue engineering, regenerative medicine, and cell and tissue transplantation because of their properties like injectability, modularity, porosity, and the ability to be customized in terms of size, form, and mechanical properties. However, it is still challenging to mass (high-throughput) produce microgels with diverse sizes and tunable properties. Herein, we utilized an air-assisted co-axial device (ACAD) for continuous production of microgels in a high-throughput manner. To test its robustness, microgels of multiple hydrogels and their combination, including alginate (Alg), gelatin methacrylate (GelMA) and Alg–GelMA, were formed at a maximum production rate of ∼65 000 microgels s−1while retaining circularity and a size range of 50–500µm based on varying air pressure levels. The ACAD platform allowed single and multiple cell encapsulation with 74 ± 6% efficiency. These microgels illustrated appealing rheological properties such as yield stress, viscosity, and shear modulus for bioprinting applications. Specifically, Alg microgels have the potential to be used as a sacrificial support bath while GelMA microgels have potential for direct extrusion both on their own or when loaded in a bulk GelMA hydrogel. Generated microgels showed high cell viability (>90%) and proliferation of MDA-MB-231 and human dermal fibroblasts over seven days in both encapsulation and scaffolding applications, particularly for GelMA microgels. The developed strategy provides a facile and rapid approach without any complex or expensive consumables and accessories for scalable high-throughput microgel production for cell therapy, tissue regeneration and 3D bioprinting applications.

    more » « less
  2. Abstract

    Poor oxygen transport is a major obstacle currently for 3D microtissue culture platforms, which at this time cannot be grown large enough to be truly physiologically relevant and replicate adult human organ functions. To overcome internal oxygen transport deficiencies, oxygenating microgels are formed utilizing perfluorocarbon (PFC) modified chitosan and a highly scalable water‐in‐oil miniemulsion method. Microgels that are on the order of a cell diameter (≈10 µm) are formed allowing them to directly associate with cells when included in 3D spheroid culture, while not being internalized. The presence of immobilized PFCs in these microgels allows for enhancement and tuning of oxygen transport when incorporated into cultured microtissues. As such, it is demonstrated that incorporating oxygenating microgels at ratios ranging from 50:1 to 400:1 (# of cells:# of microgels) into dense human fibroblast‐based spheroids facilitated the growth of larger human cell‐based spheroids, especially at the highest incorporation percentages (50:1), which lacked defined hypoxic cores. Quantification of total double‐stranded (ds)‐DNA, a measure of number of live cells, demonstrated similar results to hypoxia quantification, showing more ds‐DNA due incorporation of oxygenating microgels. Finally, oxygen concentrations are measured at different depths within spheroids directly and confirmed higher oxygen partial pressures due to chitosan‐PFC microspheres.

    more » « less
  3. Abstract

    Micrometer‐sized hydrogels, termed microgels, are emerging as multifunctional platforms that can recapitulate tissue heterogeneity in engineered cell microenvironments. The microgels can function as either individual cell culture units or can be assembled into larger scaffolds. In this manner, individual microgels can be customized for single or multicell coculture applications, or heterogeneous populations can be used as building blocks to create microporous assembled scaffolds that more closely mimic tissue heterogeneities. The inherent versatility of these materials allows user‐defined control of the microenvironments, from the order of singly encapsulated cells to entire 3D cell scaffolds. These hydrogel scaffolds are promising for moving towards personalized medicine approaches and recapitulating the multifaceted microenvironments that exist in vivo.

    more » « less
  4. Abstract

    Granular, microgel‐based materials have garnered interest as promising tissue engineering scaffolds due to their inherent porosity, which can promote cell infiltration. Adapting these materials for 3D bioprinting, while maintaining sufficient void space to enable cell migration, can be challenging, since the rheological properties that determine printability are strongly influenced by microgel packing and void fraction. In this work, a strategy is proposed to decouple printability and void fraction by blending UV‐crosslinkable gelatin methacryloyl (GelMA) microgels with sacrificial gelatin microgels to form composite inks. It is observed that inks with an apparent viscosity greater than ≈100 Pa s (corresponding to microgel concentrations ≥5 wt%) have rheological properties that enable extrusion‐based printing of multilayered structures in air. By altering the ratio of GelMA to sacrificial gelatin microgels, while holding total concentration constant at 6 wt%, a family of GelMA:gelatin microgel inks is created that allows for tuning of void fraction from 0.20 to 0.57. Furthermore, human umbilical vein endothelial cells (HUVEC) seeded onto printed constructs are observed to migrate into granular inks in a void fraction‐dependent manner. Thus, the family of microgel inks holds promise for use in 3D printing and tissue engineering applications that rely upon cell infiltration.

    more » « less
  5. Abstract

    Many cell types require direct cell–cell interactions for differentiation and function; yet, this can be challenging to incorporate into 3‐dimensional (3D) structures for the engineering of tissues. Here, a new approach is introduced that combines aggregates of cells (spheroids) with similarly‐sized hydrogel particles (microgels) to form granular composites that are injectable, undergo interparticle crosslinking via light for initial stabilization, permit cell–cell contacts for cell signaling, and allow spheroid fusion and growth. One area where this is important is in cartilage tissue engineering, as cell–cell contacts are crucial to chondrogenesis and are missing in many tissue engineering approaches. To address this, granular composites are developed from adult porcine mesenchymal stromal cell (MSC) spheroids and hyaluronic acid microgels and simulations and experimental analyses are used to establish the importance of initial MSC spheroid to microgel volume ratios to balance mechanical support with tissue growth. Long‐term chondrogenic cultures of granular composites produce engineered cartilage tissue with extensive matrix deposition and mechanical properties within the range of cartilage, as well as integration with native tissue. Altogether, a new strategy of injectable granular composites is developed that leverages the benefits of cell–cell interactions through spheroids with the mechanical stabilization afforded with engineered hydrogels.

    more » « less