pH measurements of PLM
The pH of the PLM was measured against external standards with pH: 4.01, 7.0, 10.01 using a pH electrode (Orion, Thermo Scientific, UK, NE) attached to a benchtop potentiometer (Oakton Ion 2700, OAKTON Instruments, IL., USA). Initially, the baseline pH of the PLM was measured without any intervention. Then, the Perspex® blocks were coated with respective varnishes and introduced in Sterilin™ tubes (Bijou, Thermo Scientific, Newport, UK) with PLM to measure pH at 0 min, 30 min, 1 h and 4 h. In between measurements, the tubes were left static on the laboratory bench at room temperature.