Interlinked Macroporous 3D Scaffolds from Microgel Rods

Summary

Microgel rods with complementary reactive groups are produced via microfluidics with the ability to interlink in aqueous solution. The anisometric microgels jam and interlink into stable constructs with larger pores compared to spherical-based systems. Microgels modified with GRGDS-PC form macroporous 3D constructs that can be used for cell culture.

Abstract

A two-component system of functionalized microgels from microfluidics allows for fast interlinking into 3D macroporous constructs in aqueous solutions without further additives. Continuous photoinitiated on-chip gelation enables variation of the microgel aspect ratio, which determines the building block properties for the obtained constructs. Glycidyl methacrylate (GMA) or 2-aminoethyl methacrylate (AMA) monomers are copolymerized into the microgel network based on polyethylene glycol (PEG) star-polymers to achieve either epoxy or amine functionality. A focusing oil flow is introduced into the microfluidic outlet structure to ensure continuous collection of the functionalized microgel rods. Based on a recent publication, microgel rod-based constructs result in larger pores of several hundred micrometers and, at the same time, lead to overall higher scaffold stability in comparison to a spherical-based model. In this way, it is possible to produce higher-volume constructs with more free volume while reducing the amount of material required. The interlinked macroporous scaffolds can be picked up and transported without damage or disintegration. Amine and epoxy groups not involved in interlinking remain active and can be used independently for post-modification. This protocol describes an optimized method for the fabrication of microgel rods to form macroporous interlinked scaffolds that can be utilized for subsequent cell experiments.

Introduction

To study complex cooperative cell behavior in 3D constructs, scaffold platforms need to show consistent performance in reproducibility, have suitable geometry for cell migration, and, at the same time, allow certain flexibility in terms of parameter alteration to investigate their influence on the living tissue¹. In recent years, the concept of macroporous annealed particles (MAP), first described by Segura et al., developed into an efficient and versatile platform for 3D scaffold production². The tailored composition of the microgels, which are the building blocks of the final 3D scaffold, predefines properties such as ....

Protocol

1. Required material and preparations for microfluidics

1. For the described microfluidic procedure, use 1 mL and 5 mL glass syringes and syringe pumps. On-chip droplet formation is observed via an inverted microscope equipped with a high-speed camera.
2. Create the microfluidic chip design (Figure 1B) using a computer-aided design software and produce a master template as already reported¹².
3. Achieve controlled UV-irradiation using a self-constructed UV-LED (λ = 365 nm, spot diameter ~4.7 mm) providing irradiance at 957 mW/cm² through a 0.13 mm thi....

Results

Figure 2: Macroporous crosslinked scaffold structure. (A) 3D projection of a 500 µm confocal microscopy Z-stack of the interlinked macroporous scaffold. Scale bar represents 500 µm. (B) Interlinked scaffold composed of ~10,000 microgel rods on a cover glass taken directly out of water. Scale bar repre.......

Discussion

One of the critical steps in this protocol is the quality of the 2-aminoethyl methacrylate (AMA) used as the comonomer for primary amine functionalization. The AMA should be a fine-grained and preferably colorless powder delivered in a gas-tight brown glass container. One should avoid using greenish and lumpy material, as it significantly impairs the gelation reaction and negatively affects the reproducibility of the results. In case of poor gelation and unstable microgel rods, one can consider changing the supplier.

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Materials

Name	Company	Catalog Number	Comments
ABIL EM 90	Evonik	144243-53-8	non-ionic surfactant
2-Aminoethyl methacrylate hydrochloride	TCI Chemicals	A3413	>98.0%(T)(HPLC)
8-Arm PEG-acrylate 20 kDa	Biochempeg Scientific Inc.	A88009-20K	≥ 95 %
AutoCAD 2019	Autodesk		computer-aided design (CAD) software; modeling of microfluidic designs
CHROMAFIL MV A-20/25 syringe filter	CHROMAFILCarl Roth GmbH+Co.KG	XH49.1	pore size 0.20 µm; Cellulose Mixed Esters (MV)
Cover glass	Marienfeld-Superior		type No. 1
EMS Swiss line core sampling tool 0.75 mm	Electron Microscopy Sciences		0.77 mm inner diameter, 1.07 mm outer diameter
Ethanol absolut	VWR Chemicals
FL3-U3-13Y3M 150 FPS series high-speed camera	FLIR Systems
Fluoresceinamine isomer I	Sigma-Aldrich	201626
Fluorescein isothiocyanate	Thermo Fisher Scientific	46424
25G x 5/8’’ 0,50 x 16 mm needles	BD Microlance 3
Glycidyl methacrylate	Sigma-Aldrich	779342	≥97.0% (GC)
GRGDS-PC	CPC Scientific	FIBN-015A
Hamilton 1000 Series Gastight syringes	Thermo Fisher Scientific	10772361/10500052	PFTE Luer-Lock
Hexane	Sigma-Aldrich	1,04,367
Lithium phenyl-2,4,6-trimethylbenzoylphosphinate	Sigma-Aldrich	900889	≥95 %
Motic AE2000 trinocular microscope	Ted Pella, Inc.	22443-12
Novec 7100	Sigma-Aldrich	SHH0002
Oil Red O	Sigma-Aldrich	O9755
Paraffin	VWR Chemicals	24679320
Pavone Nanoindenter Platform	Optics11Life
Phosphate buffered saline	Thermo Fisher Scientific	AM9624
Polyethylene Tubing 0.38×1.09mm medical grade	dropletex		ID 0.38 mm OD 1.09 mm
2-Propanol	Sigma-Aldrich	190764	ACS reagent, ≥99.5%
Protein LoBind Tubes	Eppendorf	30108132
Pump 11 Pico Plus Elite Programmable Syringe Pump	Harvard Apparatus
RPMI 1640 medium	Gibco	11530586
SYLGARD 184 silicone elastomer kit	Dow SYLGARD	634165S
Trichloro-(1H,1H,2H,2H-perfluoroctyl)-silane	Sigma-Aldrich	448931
UVC LED sterilizing box	UVLED Optical Technology Co., Ltd.	9S SZH8-S2