Evaluation of the methylene blue addition in binary polymeric systems composed by poloxamer 407 and Carbopol 934P using quality by design: rheological, textural, and mucoadhesive analysis

<p>This study describes the investigation about the physicochemical behavior of methylene blue (Mb) addition to systems containing poloxamer 407 (Polox), Carbopol 934P (Carb), intended to be locally used by photodynamic therapy. A factorial design 2³ (plus center point) was used to analyze the rheological, mucoadhesive and textural properties of the preparations. Systems containing the lower concentrations of Polox (15 and 17.5%, w/w) exhibited pseudoplastic flow and low degrees of rheopexy. On the other hand, at higher Polox concentration (20%, w/w) the systems display plastic flow and thixotropy. Carb and Mb exhibited a negative influence for the consistency and flow behavior index, due to the interaction between them. For most of the formulations, the increase of Polox and Mb content significantly increased storage modulus, loss modulus and dynamic viscosity. The systems display a sol–gel transition temperature, existing as a liquid at room temperature and gel at 29–37 °C. Increasing the temperature and the polymer concentration, the compressional properties of systems significantly increased. The mucoadhesion was noted to all formulations, except to systems composed by 15% (w/w) of Polox. The analyses enabled to understand and predict the performance of formulations and the polymer–Mb interactions, tailoring to the suit systems (Polox/Carb/Mb): 17.5/0.50/0.20 and 20/0.15/0.25.</p

Scanning electron microscopy of: commercial curdlan—(A) 40x and (B) 1000x magnification; pre-gelled commercial curdlan—(C) 40x and (D) 1000x magnification; curdlan produced by <i>Agrobacterium</i> sp. IFO 13140 (pre-gelation method)—(E) 40x and (F) 1000x magnification; curdlan produced by <i>Agrobacterium</i> sp. IFO 13140 (precipitation method)—(G) 40x and (H) 1000x magnification.

<p>Scanning electron microscopy of: commercial curdlan—(A) 40x and (B) 1000x magnification; pre-gelled commercial curdlan—(C) 40x and (D) 1000x magnification; curdlan produced by <i>Agrobacterium</i> sp. IFO 13140 (pre-gelation method)—(E) 40x and (F) 1000x magnification; curdlan produced by <i>Agrobacterium</i> sp. IFO 13140 (precipitation method)—(G) 40x and (H) 1000x magnification.</p

Water Holding Capacity (WHC), Oil Holding Capacity (OHC) and Water Solubility Index (WSI) (g g^-1) of the commercial, pre-gelled commercial curdlans and those produced by <i>Agrobacterium</i> sp. IFO 13140 (pre-gelation method).

<p>Values indicate mean ± standard-deviation.</p

FT-Raman spectra of: (A) commercial curdlan, (B) pre-gelled commercial curdlan, (C) curdlan produced by <i>Agrobacterium</i> sp. IFO 13140 (pre-gellation method), (D) curdlan produced by <i>Agrobacterium</i> sp. IFO 13140 (precipitation method).

<p>The dotted lines show the characteristic peaks of the samples.</p

Carbohydrate, moisture and sodium content (%) of different samples of curdlan.

<p>Values indicate mean ± standard-deviation.</p

Temperature dependency of: (A) apparent viscosity and (B) G' (continuous line) and G" (dotted line) modulus of the aqueous dispersions of curdlan.

<p>Pre-gelled commercial curdlan (empty symbol) and curdlan produced by <i>Agrobacterium</i> sp. IFO 13140 recovered by the pre-gelation method (full symbol) at (■) 20, (●) 40 and (▲) 80 g L^-1.</p

Flow curves of yogurt samples without heat treatment (A) with heat treatment (B); viscosity curves of yogurt samples without heat treatment (C) and with heat treatment (D).

<p>Yogurt without curdlan (–), with commercial curdlan (Δ), with pre-gelled commercial curdlan (○) and with curdlan produced by <i>Agrobacterium</i> sp. IFO 13140 (pre-gelation method) (■). The direction of the gray arrows indicates the ascendant and descendant curves.</p

Strength (×10⁻³ N) of pre-gelled commercial curdlan and the curdlan produced by <i>Agrobacterium</i> sp. IFO 13140 (pre-gelation method) samples after undergoing different heat treatments.

<p>Values indicate mean ± standard-deviation.</p