3D Patterning within Hydrogels for the Recreation of Functional Biological Environments

Abstract

Biological structures are inherently complex in nature. Structural hierarchy, chemical anisotropy, and compositional heterogeneity are ubiquitous in biological systems and play a key role in the functionality of living systems. For decades, methods such as soft lithography have enabled recreation of such arrangements through precise spatial control of molecular patterns in 2D. With technological advances and increasing understanding of molecular and structural biology, there has been an increasing interest in recreating such spatial organizations in 3D. In this review, a comprehensive summary of the latest technologies being used to create 3D patterns of functional molecules within hydrogels for tissue engineering applications is presented. The review is divided into five groups of technologies defined according to the main driving force used to fabricate the patterns including light, precise chemical design, microfluidics, 3D printing, and non‐contact forces (i.e. electric, magnetic, or acoustic fields and self‐assembly).

Multiphoton Laser Fabrication of Hybrid Photo-Activable Biomaterials

“…They used single-photon lithography, discussing the possibility to implement a MPL fabrication. Other efforts in this direction, made with methods complementary to laser fabrication, including precise chemical design, microfluidics, 3D printing, and non-contact forces, have been recently reviewed by Primo and Mata [ 86 ]. Stiffness is always related to the degree of cross-linking that can occur via photo-activation, thermally or chemically.…”

Modelling the central nervous system: tissue engineering of the cellular microenvironment

“…Light-based approaches, such as two-photon polymerisation, allow better resolution on the micro to nanoscale; however often require transparent materials [105][106][107]. Photopatterning is also a well-established method of patterning biologically active growth factors, proteins and peptides into hydrogel scaffolds [99,108]. Microfluidics enable creation of devices with microchannels and segregated compartments [54,61]; as well as enabling tight control over microscale features via precise biochemical patterning of organoids and hydrogel scaffolds [48,99].…”

“…Fluid gels show particular promise as bioinks, protecting cells from shear forces during the printing process that would otherwise reduce viability [ 69 , 93 , 97 ]. 3D bioprinting of hydrogels allows reliable production of spatially defined macrostructures, including vascular components, with the use of sacrificial inks suggested as a means to create complex vascular networks [ 70 , 98 , 99 ]. Microfluidics present an alternative for creation of perfusable culture systems to mimic vasculature within 3D in vitro models of the CNS [ 52 ].…”

“…Photopatterning is also a well-established method of patterning biologically active growth factors, proteins and peptides into hydrogel scaffolds [ 99 , 108 ]. Microfluidics enable creation of devices with microchannels and segregated compartments [ 54 , 61 ]; as well as enabling tight control over microscale features via precise biochemical patterning of organoids and hydrogel scaffolds [ 48 , 99 ]. Lithographic patterning and chemical modification has been used to support formation of segregated cell populations and microchannels within a microfluidic device to study network connectivity [ 109 ], whilst fabrication techniques such as electrospinning of fibrous scaffolds or structural patterning of parallel grooves has shown to mimic in vivo ECM topographies to induce axis alignment [ 32 , 68 , 110 ].…”

“…It is extremely difficult to achieve all of the architectural, compositional and biological features necessary for valid and biologically relevant in vitro culture. A tissue engineering approach, utilising innovative techniques for structural patterning of hydrogels alongside bioconjugation and controlled delivery systems, holds the most promise for producing advanced biomaterials with the capability for dynamic spatiotemporal guidance of tissue formation [ 65 , 73 , 81 , 99 ]. However, it is vital to carefully consider the fabrication approach to find a balance between heterogeneity, functionality and practicality of the model.…”