The interaction between mucin and poly(amino acid)s with controlled cationic group content in bulk phase and in thin layers.

The type and concentration of charged groups in polymers have a key role in mucoadhesive interactions. A series of cationic poly(amino acid)s with different charge densities was designed to unravel the correlation between chemical structure and mucin-polymer interactions. Colloidal interactions between the mucin protein and synthetic polyaspartamides were tested by dynamic light scattering, zeta potential measurements and turbidimetric titration as a function of polymer-to-mucin mass ratio. The mucoadhesive interactions displayed a strongly non-linear change with polymer composition. The attractive interactions between mucin and the polyaspartamides with at least 50 % cationic groups caused increased light scattering of dispersions due to the aggregation of mucin particles upon their charge reversal. Interactions were further analysed in a thin mucin layer to model life-like situations using a quartz crystal microbalance (QCM) in flow mode. Results pointed out that the fully cationic polyaspartamide is not necessarily superior to derivatives with lower cationic group content. The maximum of adsorbed mass of polymers on mucin was experienced at medium cationic group contents. This emphasizes the relevance of cationic polyaspartamides as mucoadhesive excipients due to their multiple functionalities and the possibility of fine-tuning their interactions with mucin via straightforward chemical steps.

A robust mucin-containing poly(vinyl alcohol) hydrogel model for the in vitro characterization of mucoadhesion of solid dosage forms.

Mucoadhesion testing at macroscopic scale needs a robust, convenient in vitro method as ex vivo methods suffer from poor reproducibility and ethical problems. Here we synthesized mucin-free poly(vinyl alcohol) (PVA) and mucin-containing PVA hydrogel substrates (Muc/PVA) to measure adhesion of polymer tablets. Freezing-thawing method was used for gelation to avoid chemical cross-linking and to preserve the functionality of mucin. The adhesion of first generation mucoadhesive polymers, poly(acrylic acid) (PAA) and hydroxypropylmethylcellulose (HPMC) was tested with outstanding reproducibility on individual batches of hydrogels and qualitative agreement with ex vivo literature data. Negatively charged PAA was less adhesive on Muc/PVA surface than on mucin-free PVA whereas HPMC as a neutral polymer displayed similar adhesion strength on both surfaces. Chitosan as a positively charged polymer showed enhanced adhesion on Muc/PVA substrate compared to mucin-free PVA. These results are corroborated by turbidimetric titration which indicated attractive electrostatic interactions between chitosan and mucin in contrast to the lack of attractive interactions for PAA and HPMC. These results prove the role of electronic theory in macroscopic mucoadhesion.

Biochar application in organics and ultra-violet quenching substances removal from sludge dewatering leachate for algae production.

Algae production in nutrient rich sludge dewatering leachate after biogas production is a promising option for wastewater treatment plants. However, the ultra-violet (UV) absorbing characteristic of UV-quenching substances (UVQS) existing in these waters can notably reduce the light transmission within the liquid body. The present work demonstrates a comparative adsorptive removal of UVQS, and other organic substances (expressed as COD and TOC) onto the "acid catalyst" functionalised adsorbent (PPhA) and commercial activated carbon (CAC) from leachate originating from leftover sludge dewatering after biogas production. Laboratory scale column studies were performed to investigate the adsorption performance of selected parameters. The PPhA increased the UV transmittance of leachate more than 4 times and outperformed CAC. Bed Depth Service Time and Yan models were used on the experimental data in order to estimate the maximum adsorption capacity and evaluate the characteristics of the fixed-bed. The PPhA equilibrium uptake of COD and TOC amounted to 5.7 mg/g and 0.9 mg/g, respectively. The postulated removal mechanism in environmentally relevant conditions (e.g., pH neutral) suggested a complex interaction between the biochar and organic macromolecules. Diluted phosphoric acid solution (0.01 mol/L) was successfully used for the column regeneration. Beside the UVQS, PPhA showed affinity towards toxic heavy metals (e.g., Pb, Ni, Co) pointing out the rich surface chemistry of the PPhA. Based on the obtained results and successfully implemented scale-up methodology, the low-cost PPhA adsorbent might effectively compete with the CAC as a highly efficient platform in wastewaters leachate processing.