Tuning the Mechanical Properties of Poly(Ethylene Glycol) Microgel‐Based Scaffolds to Increase 3D Schwann Cell Proliferation

Abstract

2D in vitro studies have demonstrated that Schwann cells prefer scaffolds with mechanical modulus approximately 10× higher than the modulus preferred by nerves, limiting the ability of many scaffolds to promote both neuron extension and Schwann cell proliferation. Therefore, the goals of this work are to develop and characterize microgel-based scaffolds that are tuned over the stiffness range relevant to neural tissue engineering and investigate Schwann cell morphology, viability, and proliferation within 3D scaffolds. Using thiol-ene reaction, microgels with surface thiols are produced and crosslinked into hydrogels using a multiarm vinylsulfone (VS). By varying the concentration of VS, scaffold stiffness ranges from 0.13 to 0.76 kPa. Cell morphology in all groups demonstrates that cells are able to spread and interact with the scaffold through day 5. Although the viability in all groups is high, proliferation of Schwann cells within the scaffold of G* = 0.53 kPa is significantly higher than other groups. This result is ≈ 5× lower than previously reported optimal stiffnesses on 2D surfaces, demonstrating the need for correlation of 3D cell response to mechanical modulus. As proliferation is the first step in Schwann cell integration into peripheral nerve conduits, these scaffolds demonstrate that the stiffness is a critical parameter to optimizing the regenerative process.

Tailoring 3D hydrogel systems for neuronal encapsulation in living electrodes

“…A similar phenomena has been observed in analogue PEG‐based biosynthetic hydrogels. Zhou et al showed that the degree of cellular associations across the hydrogel network decreases in hydrogels with low modulus (0.24 kPa) in comparison with stiffer hydrogels (0.53–0.76 kPa). In contrast, previous studies have shown that encapsulated SCs in collagen or fibrin hydrogels were not able to spread disregarding the presence of transforming growth factor (TGF‐β1), which is known to induce SCs morphological changes associated with SCs motility .…”

“…Tailoring hydrogels for 3D cell encapsulation requires precise control of many variables. These include the chemistry and mechanics of the hydrogel, physical parameters such as stiffness and the incorporation of biological signals such as adhesion molecules and growth factors . The conundrum is that altering any one of these variables can significantly impact on other variables and thus alter the final properties.…”

“…Hern and Hubbell have demonstrated that hydrogels such as PEG are inherently nonadhesive and cells fail to attach and grow unless modified with peptides. Modification of synthetic hydrogels through incorporation of bioactive molecules has been shown to enhance cellular interaction while maintaining the benefit of controlled mechanical properties . PVA and PEG, materials that resist cell adhesion, can be modified with gelatin or other cell adhesive peptides to form biosynthetic hydrogels that promote cell attachment …”

“…Photopolymerization for cellular encapsulation is a well‐established process to deliver cells for biomedical applications, as it provides fast curing times, low heat generation, and control over temporal and spatial polymerization . It has been shown that numerous initiating systems, ranging from UV to visible light, can be used to encapsulate a range of cell types . While UV mediated crosslinking is widespread in hydrogel fabrication and cell encapsulation, this type of radiation is known to damage cells and proteins .…”

Tissue engineering-based therapeutic strategies for vocal fold repair and regeneration

“…In attempts to overcome these limitations, biocompatible microgels with large surface-to-volume ratio and wide range of particle size distributions have been investigated for numerous biomedical applications including vocal fold tissue engineering. [117–119] Jia et al developed HA-based microgels and crosslinked microgel networks with tunable degradation and mechanical properties suitable for vocal fold regeneration. Hydrazide-modified HA (HAADH) and aldehyde-functionalized HA (HAALD) were crosslinked to form microgels through the inverse emulsion droplets yielding microspheres with an average diameter size of 10 μ m. The presence of residual functional groups allows subsequent cross-linking of the microgels with other polymers to generate doubly crosslinked networks (DXN)s. DXNs had tunable viscoelasticity similar to the range of canine vocal fold tissue when assessed via torsional wave experiments measured at human phonation frequencies.…”