Development of a novel 3D hydrogel for tissue engineering and microfluidics applications

Millions of patients suffer from end-stage organ failure and tissue loss each year. The most practical approach to this problem is the use of standard therapies such as tissue and organ transplantation, with the consequence of limited organ and tissue donors. To address this growing issued, a new method combining cells and biomaterials has been introduced—namely tissue engineering (TE). TE is an interdisciplinary field that applies the ideology of engineering and life sciences toward the development of biological substitutes that maintain, improve or restore the function of organs or tissue. For the regeneration of tissue to be successful, the fabrication of a porous, 3D, biodegradable, biocompatible scaffold with interconnecting pores and appropriate mechanical strength is required. There have been extensive studies on the efficacy of biocompatible polymeric material hydrogels as 3D tissue scaffolds, ranging from natural to synthetic polymers with the ability to degrade and function as “smart” hydrogels, as well as in the microfluidics field. However, the use of modified cellulose as a 3D tissue scaffold has yet to be fully exploited. In this study, a novel biodegradable and macroporous scaffold—a modified cellulose, called hydroxypropyl cellulose (HPC)—has been synthesized with methacrylate anhydride (MA), resulting in bifunctional hydroxypropyl cellulose methacrylate (HPC-MA). HPC-MA hydrogel scaffolds with open biphasic feature were prepared by exploiting the thermal responsive phase behavior of HPC and temperature mediated phase separation of HPC-MA. The resulting scaffolds exhibited pore size ranging from 30 to 300 μm and interconnected porosity of ~90 %. The swelling ratio (SR) and storage modulus of HPC-MA scaffolds were in the range of 12.94 to 35.83 and 0.75 to 4.28 kPa respectively. The swelling ratio and storage modulus suggested that the scaffold exhibits high water retention, allowing medium exchange during cell culturing and making it suitable for adipose tissue regeneration. The HPC-MA scaffolds were found to be biocompatible to human adipose-derived stem cells (ASCs). ASCs were successfully differentiated into adipocytes inside the scaffolds. Success in the fabrication of the HPC-MA scaffold led to the development of a thermo-sensitive cellulosic membrane for cell grafting through the use of the temperature responsive properties of HPC. The resultant macromonomer retains the characteristic thermo-responsive phase behavior of HPC, with an onset temperature of 36 C and a lower critical solution temperature (LCST) of 37~38 oC (as determined by turbidity measurement). The hydrogels exhibited temperature-dependent surface hydrophilicity/hydrophobicity, equilibrium water content and mechanical properties. Cell-releasing characteristics were demonstrated using African green monkey kidney cell line (COS-7 cells) and Murine-derived embryonic stem (Oct4b2) cell line. When the temperature was dropped to 4 oC, the cultivated cells spontaneously detached from the hydrogels without trypsin treatment. These unique properties make the HPC-MA membrane a potential substrate for cell sheet engineering. Another application of the HPC-MA is the fabrication of a freestanding and degradable hybrid paper microfluidic device for bioengineering applications. Paper-based microfluidic devices are emerging as a promising point-of-care diagnostic technology due to their fabrication simplicity, cost effectiveness and versatility. In this study, a method was developed to prepare hybrid paper microfluidic devices where modified cellulose is crosslinked to form a freestanding, paper-like construct that provides a stable structure in an aqueous environment. The resulting HPC construct is a hybrid that possesses the properties of both paper and hydrogel. The hybrid construct has good mechanical properties and can provide structural support for cell anchorage. The feasibility of functionalising these HPC structures with biochemical cues was verified post fabrication, and they were shown to facilitate the adhesion of mesenchymal progenitor cells. The usefulness of this hybrid paper device for a protein assay has also been demonstrated. The HPC structures were found to be biocompatible and hydrolytically degradable, thus enabling cell proliferation and cell migration and thereby constituting an ideal candidate for long-term cell culture and tissue scaffold applications.