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Browsing by Author "Kim, Min Hee"
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ItemAssessing monocyte phenotype in poly(γ-glutamic acid) hydrogels formed by orthogonal thiol–norbornene chemistry(IOP, 2021-07) Kim, Min Hee; Lin, Chien-Chi; Biomedical Engineering, School of Engineering and TechnologyHydrogels with tunable properties are highly desirable in tissue engineering applications as they can serve as artificial extracellular matrix to control cellular fate processes, including adhesion, migration, differentiation, and other phenotypic changes via matrix induced mechanotransduction. Poly(γ-glutamic acid) (PGA) is an natural anionic polypeptide that has excellent biocompatibility, biodegradability, and water solubility. Moreover, the abundant carboxylic acids on PGA can be readily modified to introduce additional functionality or facilitate chemical crosslinking. PGA and its derivatives have been widely used in tissue engineering applications. However, no prior work has explored orthogonal crosslinking of PGA hydrogels by thiol-norbornene (NB) chemistry. In this study, we report the synthesis and orthogonal crosslinking of PGA-norbornene (PGANB) hydrogels. PGANB was synthesized by standard carbodiimide chemistry and crosslinked into hydrogels via either photopolymerization or enzymatic reaction. Moduli of PGA hydrogels were readily tuned by controlling thiol-NB crosslinking conditions or stoichiometric ratio of functional groups. Orthogonally crosslinked PGA hydrogels were used to evaluate the influence of mechanical cues of hydrogel substrate on the phenotype of naïve human monocytes and M0 macrophages in 3D culture. ItemDual Functionalization of Gelatin for Orthogonal and Dynamic Hydrogel Cross-Linking(American Chemical Society, 2021) Kim, Min Hee; Nguyen, Han; Chang, Chun-Yi; Lin, Chien-Chi; Biomedical Engineering, School of Engineering and TechnologyGelatin based hydrogels are widely used in biomedical fields owing to its abundance of bioactive motifs that support cell adhesion and matrix remodeling. While inherently bioactive, unmodified gelatin exhibits temperature-dependent rheology and solubilizes at body temperature, making it unstable for three-dimensional (3D) cell culture. Therefore, the addition of chemically reactive motifs is required to render gelatin-based hydrogels with highly controllable crosslinking kinetics and tunable mechanical properties that are critical for 3D cell culture. This article provides a series of methods toward establishing orthogonally crosslinked gelatin-based hydrogels for dynamic 3D cell culture. In particular, we prepared dually functionalized gelatin macromers amenable for sequential, orthogonal covalent crosslinking. Central to this material platform is the synthesis of norbornene-functionalized gelatin (GelNB), which forms covalently crosslinked hydrogels via orthogonal thiol-norbornene click crosslinking. Using GelNB as the starting material, we further detail the methods for synthesizing gelatin macromers susceptible to hydroxyphenylacetic acid (HPA) dimerization (i.e., GelNB-HPA) and hydrazone bonding (i.e., GelNB-CH) for on-demand matrix stiffening. Finally, we outline the protocol for synthesizing a gelatin macromer capable of adjusting hydrogel stress-relaxation via boronate ester bonding (i.e., GelNB-BA). The combinations of these orthogonal chemistries affords a wide range of gelatin based hydrogels as biomimetic matrices in tissue engineering and regenerative medicine applications. ItemEngineering Tools for Regulating Hypoxia in Tumour Models(Wiley, 2021) Kim, Min Hee; Green, Steven D.; Lin, Chien-Chi; Konig, Heiko; Biomedical Engineering, School of Engineering and TechnologyMajor advances in the field of genomic technologies have led to an improvement in cancer diagnosis, classification and prognostication. However, many cancers remain incurable due to the development of drug resistance, minimal residual disease (MRD) and disease relapse, highlighting an incomplete understanding of the mechanisms underlying these processes. In recent years, the impact of non-genetic factors on neoplastic transformations has increasingly been acknowledged, and growing evidence suggests that low oxygen (O2) levels (ie hypoxia) in the tumour microenvironment play a critical role in the development and treatment of cancer. As a result, there is a growing need to develop research tools capable of reproducing physiologically relevant O2 conditions encountered by cancer cells in their natural environments in order to gain in-depth insight into tumour cell metabolism and function. In this review, the authors highlight the importance of hypoxia in the pathogenesis of malignant diseases and provide an overview of novel engineering tools that have the potential to further drive this evolving, yet technically challenging, field of cancer research. ItemNorbornene-functionalized methylcellulose as a thermo- and photo-responsive bioink(IOP, 2021-09-21) Kim, Min Hee; Lin, Chien-Chi; Biomedical Engineering, School of Engineering and Technology3D bioprinting has emerged as an important tool to fabricate scaffolds with complex structures for tissue engineering and regenerative medicine applications. For extrusion-based 3D bioprinting, the success of printing complex structures relies largely on the properties of bioink. Methylcellulose (MC) has been exploited as a potential bioink for 3D bioprinting due to its temperature-dependent rheological properties. However, MC is highly soluble and has low structural stability at room temperature, making it suboptimal for 3D bioprinting applications. In this study, we report a one-step synthesis protocol for modifying MC with norbornene (MCNB), which serves as a new bioink for 3D bioprinting. MCNB preserves the temperature-dependent reversible sol-gel transition and readily reacts with thiol-bearing linkers through light-mediated step-growth thiol-norbornene photopolymerization. Furthermore, we rendered the otherwise inert MC network bioactive through facile conjugation of integrin-binding ligands (e.g., CRGDS) or via incorporating cell-adhesive and protease-sensitive gelatin-based macromer (e.g., GelNB). The adaptability of the new MCNB-based bioink offers an attractive option for diverse 3D bioprinting applications. ItemPoly(ethylene glycol)-Norbornene as a Photo-Click Bioink for Digital Light Processing 3D Bioprinting(American Chemical Society, 2023) Kim, Min Hee; Lin, Chien-Chi; Biomedical Engineering, School of Engineering and TechnologyDigital light processing (DLP) bioprinting is an emerging technology for 3D bioprinting (3DBP) owing to its high printing fidelity, fast fabrication speed, and higher printing resolution. Low viscosity bioink such as poly(ethylene glycol) diacrylate (PEGDA) is commonly used for DLP-based bioprinting. However, the crosslinking of PEGDA proceeds via chain-growth photopolymerization that displays significant heterogeneity in crosslinking density. In contrast, step-growth thiol-norbornene photopolymerization is not oxygen inhibited and produces hydrogels with an ideal network structure. The high cytocompatibility and rapid gelation of thiol-norbornene photopolymerization has lend itself to the crosslinking of cell-laden hydrogels but has not been extensively used for DLP bioprinting. In this study, we explored 8-arm PEG-norbornene (PEG8NB) as a bioink/resin for visible light initiated DLP-based 3DBP. PEG8NB-based DLP resin showed high printing fidelity and cytocompatibility even without the use of any bioactive motifs and high initial stiffness. In addition, we demonstrated the versatility of PEGNB resin by printing solid structures as cell culture devices, hollow channels for endothelialization, and microwells for generating cell spheroids. This work not only expands the selection of bioinks for DLP-based 3DBP, but also provides a platform for dynamic modification of the bioprinted constructs.