DNA hydrogel microparticles as phantom cells for tissue engineering

While the bottom-up creation of living synthetic cells remains unattained, current cell-mimics have found ample application in tissue engineering and biomedical sciences. In this context, they have been integrated into 3D cell culture systems where they aid cellular development and allow functional readouts based on chemical and physical interactions with living cells. These interactions can be tailored to emulate the properties of specific tissues and cells. We can call these cell mimics “phantom cells”, as they are not alive themselves, but reconstitute functional interfaces with living cells by emulating their specific properties. Hydrogel microparticles, in particular, are the most common type of phantom cells as they allow for the formation of cell-sized particles with tunable mechanical properties, high stability and response to external triggers. Many currently used hydrogel systems, however, lack versatile chemical addressability in combination with tunable mechanical properties; attributes inherent to DNA-based hydrogels. In this PhD thesis, I thus develop fully DNA-based hydrogel microparticles (DNA-HMPs) as phantom cells for tissue engineering. In the first part of the thesis, I create DNA-HMPs in a droplet-templated manner based on five distinct DNA hydrogel designs with adjustable valency. These exhibit type-specific viscoelastic properties, which are tunable by DNA sequence design. They further allow for mechanical sensing in a 3D cellular system based on designed cell-HMP interactions using the ECM-derived peptide sequence cRGD. In the second part of the thesis, I show that DNA-HMP mechanical properties can be tailored to mimic those of medaka retinal stem cells. Microinjected into retinal organoids, the DNA-HMPs then enable the formation of spatio-temporally controlled morphogen gradients. For this, the HMPs are equipped with light-responsive DNA structures allowing for external control over morphogen release. Internal morphogen gradients then result in higher cell type diversity of the final organoids. In the last part, I further develop DNA-HMPs towards quantitative mechanical readouts in cellular systems, adding fluorescent markers and lipid layers onto the DNA-HMPs. Lastly, they are formed into phantom-tissues as microporous annealed particle gels for future applications in tissue engineering. Combining tunable mechanical properties with straightforward chemical addressability and stimuli-response, DNA-HMPs thus present a new generation of multifunctional phantom cells for tissue engineering applications.