Tailoring and visualising pore openings in gelatin-based hydrogel foams

While tailoring the pore diameters in hydrogel foams has been demonstrated in numerous studies, fine control over the diameters of the pore openings is still a challenge. We hypothesise that this can be achieved by controlling the size of the thin films which separate the bubbles in the liquid foam template. If this is the case, systematic changes of the template's gas fraction ϕ (the higher ϕ, the larger are the thin films) will lead to corresponding changes of the pore opening diameter.

Since the size of the thin films depends on both bubble size 〈D_b〉 and gas fraction ϕ, we need to decouple both parameters to control the film size. Thus, we generated foams with constant bubble sizes via microfluidics and adjusted the gas fractions via two different techniques. The foams were solidified using UV light. Subsequently, they were analysed with confocal fluorescence microscopy.

We were able to change the pore opening diameter 〈d_p〉 at a constant pore diameter 〈D_p〉 by adjusting the gas fraction of the foam template. The obtained 〈d_p〉/〈D_p〉 ratios are between those obtained theoretically for disordered foams and FCC ordered foams, respectively.