The purpose of this study was to synthesize S-protected thiolated hyaluronic acid (HA) and to evaluate its potential for 3D cell culture scaffold. S-protected thiolated HA was synthesized by the covalent attachment of N-acetyl-S-((3-((2,5-dioxopyrrolidin-1-yl)oxy)-3-oxopropyl)thio)cysteine hydrazide ligand to the HA. Hydrogels were characterized for texture, swelling behavior and rheological properties. Furthermore, the potential of S-protected thiolated HA hydrogels as a scaffold for tissue engineering was evaluated by cell proliferation studies with Caco-2 and NIH 3T3 cells. It showed enhanced cohesion upon addition of N-acetyl cysteine (NAC). Dynamic viscosity of S-protected thiolated HA hydrogel was increased up to 19.5-fold by addition of NAC and 10.1-fold after mixing with mucus. Furthermore, Caco-2 and NIH 3T3 cells encapsulated into hydrogels proliferated in-vitro. As this novel S-protected thiolated HA is stable towards oxidation and forms highly cohesive gels when getting into contact with endogenous thiols due to disulfide-crosslinking, it is a promising tool for 3D cell culture scaffold.

The purpose of the study was to develop a per-6-thiolated α-cyclodextrin (α-CD) by substituting all primary hydroxyl groups of α-CD with thiol groups and to assess its solubility improving and permeation enhancing properties for a BCS Class IV drug in-vitro as well as in-vivo. Primary hydroxyl groups of α-CD were replaced by iodine followed by substitution with –SH groups. The structure of per-6-thiolated α-CD was approved by FT-IR and 1H NMR spectroscopy. The per-6-thiolated was characterized for thiol content, –SH stability, cytotoxicity and solubility improving properties by using the model BCS Class IV drug furosemide (FUR). Mucoadhesive properties of the thiolated oligomer were investigated via viscoelastic measurements with porcine mucus, whereas permeation enhancing features were evaluated on Caco-2 cell monolayer and rat gut mucosa. Furthermore, oral bioavailability studies were performed in rats. Per-6-thiolated α-CD oligomer displayed 4244 ± 402 µmol/g thiol groups. These –SH groups were stable at pH ≤ 4 exhibiting a pKa value of 8.1 but subject to oxidation at higher pH > 5. Per-6-thiolated α-CD was not cytotoxic to Caco-2 cells in 0.5% (m/v) concentration within 24 hour. It improved the solubility of FUR in the same manner as unmodified α-CD. Addition of per-6-thiolated α-CD (0.5% m/v) increased the mucus viscosity up to 5.8-fold at 37 °C within 4 hours. Due to incorporation in per-6-thiolated α-CD, the apparent permeability coefficient (Papp) of FUR was 6.87-fold improved on Caco-2 cell monolayer and 6.55-fold on the intestinal mucosa. Moreover, in-vivo studies showed a 4.9-fold improved oral bioavailability of FUR due to incorporation in per-6-thiolated α-CD. These results indicate that per-6-thiolated α-CD would be a promising auxiliary agent for mucosal delivery of in particular BCS Class IV drugs.

The aim of this study was to develop hydrophobic ionic drug polymer complexes in order to provide sustained drug release from self-emulsifying drug delivery systems (SEDDS). Captopril (CTL) was used as an anionic model drug to form ionic complexes with the cationic polymers Eudragit® RS, RL and E. Complexes of polymer to CTL charge ratio 1:1, 2:1 and 4:1 were incorporated in two SEDDS, namely FA which was 40% Kolliphor RH 40, 20% Kolliphor EL and 40% castor oil and FB, which was 40% Kolliphor RH 40, 30% glycerol, 15% Kolliphor EL and 15% castor oil. Blank and complex loaded SEDDS were characterized regarding their droplet size, poly dispersity index (PDI) and zeta potential. Resazurin assay was performed on Caco-2 cells to evaluate the biocompatibility of SEDDS. Release of CTL from SEDDS was determined in release medium containing 0.2 mg/mL of 5,5’-dithiobis-(2-nitrobenzoic acid) (DNTB) allowing quantification of free drug released into solution via a thiol/disulfide exchange reaction between CTL and DNTB forming a yellow dye. The droplet size of SEDDS FA and SEDDS FB were in the range of 100 ± 20 nm and 40 ± 10 nm, respectively with a PDI < 0.5. Zeta potential of SEDDS FA and SEDDS FB increased after the incorporation of complexes. Cell viability remained above 80% after incubation with SEDDS FA and SEDDS FB in a concentration of 1% and 3% for 4 h. Without any polymer, CTL was entirely released from both SEDDS within seconds. In contrast, the higher the cationic lipophilic polymer to CTL ratio in SEDDS, the more sustained was the release of CTL. Among the polymers which were evaluated, Eudragit® RL provided the most sustained release. SEDDS FA containing Eudragit® RL and CTL in a ratio of 1:1, released 64.78 ± 8.28% of CTL whereas SEDDS FB containing the same complex showed a release of 91.85 ± 1.17% within one hour. Due to the formation of lipophilic ionic polymer complexes a sustained drug release from oily droplets formed by SEDDS can be achieved. Taking into account that drugs are otherwise instantly released from SEDDS, results of this study might open the door for numerous additional applications of SEDDS for that a sustained drug release is essential. Keywords: Hydrophobic polymer complexes; self-emulsifying drug delivery systems; captopril; log SRSEDDS/release medium; sustained release; nanoemulsions.