Independent Tunability of Viscoelastic Properties in Additively Manufactured Polyacrylamide Hydrogels via Polyethylene Glycol Integration

Author

• Nicholas James Chambers, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2026

Degree Name

Master of Science

Department

Mechanical Engineering

First Advisor

Chowdhury, Farhan

Abstract

In the fields of tissue engineering and mechanobiology biomimetic gels are a commonly used substrate for the study of stem cell differentiation. Researchers have observed that stem cells seeded onto substrates with mechanical properties mimicking the body’ native tissues will differentiate into those respective tissue cells. Because native tissues are viscoelastic, these substrates must also be viscoelastic. However, conventional methods of substrate fabrication produce purely elastic gels. Recently, through the use of additive manufacturing in the form of vat photopolymerization, recent work from our laboratory have developed a system of fabricating viscoelastic substrates. When studying their mechanical properties, three factors are considered; the storage modulus (G’), which represents the elastic component, the loss modulus (G”), which represents the viscous component, and the ratio of G”/G’ known as the loss tangent or tan(δ). In order to better mimic a wide variety of native tissues these properties must be individually tunable. In order to achieve this, the makeup of these substrates can be changed both in composition, in terms of the ratio of elements, and printing parameters such as layer height and exposure time. The current resin composition consists of 40% acrylamide solution, 2% bis-acrylamide solution, a photo-initiator, and water. By simply changing the ratio of these ingredients, the G’ of the gel is highly tunable. However, this system is currently limited in its ability to independently tune the G” and tan(δ) of the gels. Rheological testing demonstrated that the incorporation of polyethylene glycol (PEG) of defined chain length provided an effective method of independent tunability of the G” and tan(δ) values. This was achieved through the incorporation of non-crosslinked linear PEG chains with a defined molecular length, such as linear PEG chains, thus creating a semi-interpenetrating polymer network capable of enhanced energy dissipation, which enabled the fabrication of hydrogels capable of reproducing a wider range of tissue-mimicking viscoelastic environments. Together, these findings provide a platform for future studies focused on the investigation of viscoelastic microenvironments and their impact on stem cell behavior and differentiation.