Hydrogel Microwell Arrays Fabrication

To bond the hydrogels onto the glass surface, the following procedure was carried out. The microscopic glass slide was soaked in 0.4% v/v 3-(trimethoxysilyl) propyl methacrylate (TMS-PMA) (Sigma Aldrich, Singapore) for 12 h to provide bonding sites on the glass surface [54 (link)]. The glass side was then rinsed with water and dried at 70 °C for 2 h. Two coverslips were stacked up as spacers on the glass slide. Then the PDMS stamp was placed on top of the two coverslips (Figure 7B). To make the PDMS surface wettable, the PDMS stamp was treated using an oxygen plasma cleaner (Harrick Plasma, Ithaca, NY, USA) for 3 min. Afterwards, 50 μL of 5.0% w/v MeHA prepolymer solution was carefully added into the gap between the PDMS stamp and glass slide using a micropipette. The prepolymer solution was then exposed to ultraviolet (UV) radiation of 4.3 W/cm² for 40 s at 4 cm to the light source OmniCure s2000 (Excelitas Technologies, Waltham, MA, USA). After exposure, the PDMS stamp was peeled off from the surface, coverslip spacers were removed, and the formed hydrogel microwell array was placed in 10 mL of PBS solution.
The fabrication of hydrogel microwell arrays containing DPSCs is presented separately in Section 2.6.