Figure 2. Characterization of capillary pinning features used in STOMP to generate multi-region suspended tissues.

Geometric considerations of a) vampire and b) cavity pinning feature designs. Graphs of maximum Laplace pinning pressure plotted against c) $\alpha$, pin angle of the vampire feature and d) $\beta$, pin angle of the cavity feature. Solid lines represent a Laplace pinning pressure ($\mathrm{\Delta }{\mathrm{P}}_{\text{vampire}}$ or $\mathrm{\Delta }{\mathrm{P}}_{\text{cavity}}$) for a contact angle of $\theta =30°$, which is the average contact angle for 5 mg/mL collagen on 3D-printed resin treated with 1% BSA at room temperature for one hour. Upper and lower bounds of the Laplace pinning pressure is calculated based on the largest measured contact angle ($\theta =48$°) and the smallest measured contact angle ($\theta =15°$) on 1% BSA-treated 3D-printed resin. If the Laplace pinning pressure is greater than that of the hydrostatic pressure ($\mathrm{\Delta }{\mathrm{P}}_{\text{hydrostatic}}=33.5\mathrm{P}\mathrm{a}$) then pinning is predicted to occur (shaded in green). If the Laplace pinning pressure is less than $\mathrm{\Delta }{\mathrm{P}}_{\text{hydrostatic}}$, then pinning will not occur (shaded in magenta). e) Representative video still images of 23 μL of a 5 mg/mL precursor collagen solution pipetted into two different 1% BSA treated STOMP devices containing the vampire pinning features; left four images use devices with $\alpha ={20}^{\circ }$ and right four images use devices $\alpha =45°$. f) Representative video still images of 23 μL of a 5 mg/mL precursor collagen solution pipetted into two different 1% BSA treated STOMP devices containing the cavity pinning features; left four images uses devices with $\beta =40°$ and right four images use devices with $\beta =100°$. Scale bars on insets are 1 mm. All other scale bars are 3 mm. g) Visualization for the loss of pinning mechanism, where a pink arrow indicates the direction of flow of the purple hydrogel, with pinning first lost at the bottom of the channel.