Fig 1.
Microwave reflection measurement.
(A) A patch antenna, optimized at f = 7.9 GHz, was connected to a network analyzer (NWA) and microwaves were introduced to a substance under test (SUT). Following microwave emission, the reflected signal was detected. (B) Each SUT exhibited a specific return loss (RL) and frequency at the local minimum (fmin), exemplarily shown for purified water (aq. dest.) and air. Measurements were compared to a mathematical electromagnetic antenna model. The reflection minimum and frequency for air shifted in a range between 7000–9000 MHz for simulation and measurements.
Fig 2.
Retun loss (RL) and fmin of fluids exhibiting different polarities and osmolalities in comparison to purified water (aq. dest.) and phosphate buffered saline (PBS).
(A) fmin decreased with lower polarity. Water; exhibiting the highest polarity showed the highest fmin compared to methanol (MeOH), ethanol (EtOH) and propanol (PrOH) with decreasing polarities. (B) RL decreased with lower polarity from aq. dest. to PrOH. (C) fmin decreased with higher osmolality from aq. dest. to sodium chloride (NaCl) solutions at concentrations ranging from 0.1 to 20%. (D) RL decreased with a higher osmolality. Bar diagrams show mean values and error bars depict standard deviation. Asterisks indicate statistical relevant differences (p-value ≤ 0.5). Each group comprised three individual samples that were measured in triplicate.
Fig 3.
Measurement of cell-free dermal equivalents at different collagen concentrations.
(A) A plastic compression system allowed generating dermal equivalents exhibiting collagen concentrations ranging from c = 6.67 mg/ml to c = 26.67 mg/ml. During processing, hydrogels were compressed to a defined volume of V = 3.6 cm2 employing a linear motion engine. The squeezer (1) compressed the hydrogel (2) in the bioreactor (3). Pried water was aspirated via the port near the bottom of the chamber (4). (B) Comparison of dry to wet weight showed an increase in weight with a higher collagen concentration, whereas (C) fmin at the detected minimum declined with a higher collagen concentration, and (D) RL decreased at higher collagen concentration. Plots show mean values, error bars depict standard deviation. Each group comprised 3 individual samples that were measured in triplicate.
Fig 4.
Microwave reflection signal of dermal equivalents at different osmolalities and cell concentrations.
(A) Comparison of dry to wet weight ratio demonstrated that the weight of the dry component increased with a higher osmolality and cell concentration of the remaining substances. (B) fmin declined at higher cell concentrations (from 4.5x105 to 9x105 cells) and osmolalities, mimicking hypo-, iso- and hypernatraemia. (C) In analogy to fmin, RL dropped with a higher osmolality. Bar diagrams show mean values, error bars depict standard deviation. Asterisks indicate statistical relevant differences (p-value ≤ 0.5). Each group comprised 3 individual samples that were measured in triplicate.
Fig 5.
Microwave signals of 3D skin models at different osmolalities.
(A) H&E-staining of full-thickness 3D skin models (FT 3D skin) with intact and removed epidermal layer following treatment with PBS. (B) The dry to wet weight ratio increased with higher osmolality (from aq. dest. to NaCl), whereas (C) fmin decreased with a higher osmolality. (D) RL increased with a higher osmolality and was highest where no epidermal layer was present (PBS w/o rHE). All scale bars indicate 50 μm. Bar diagrams show mean values, error bars depict standard deviation. Asterisks indicate statistical relevant differences (p-value ≤ 0.5). Each group comprised 3 individual samples that were measured in triplicate.
Fig 6.
Microwave signal of fluids and in vitro test models measurements at 8.2 GHz.
(A) Microwave measurements with fluids. Compared to Control, RL showed increased values for polarity measurements (Polarity) at a constant frequency of 8.2 GHz with a lower polarity from aq. dest. to PrOH. Osmolality measurements displayed a decreasing RL with the highest osmolality at NaCl 20%. (B) Microwave measurements with in vitro models. RL displayed increasing values at a constant frequency of 8.2 GHz for measurements with cell-free collagen hydrogels (Collagen). RL dropped with higher osmolalities for both dermal (Dermis) and full-thickness 3D skin models (FT 3D skin). Bar diagrams depict mean values, error bars depict standard deviations. Asterisks indicate statistical relevant differences (p-value ≤ 0.5). Each group comprised 3 individual samples that were measured in triplicate.