Tiopronin (N-(2-Mercaptopropionyl)glycine) protected gold nanoparticles (TPAu) were crosslinked to collagen via EDC (1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide) coupling. On average, each TPAu forms 8 amide bonds with collagen lysine moieties. The resulting gels were studied with Environmental-SEM, TEM, micro-DSC, and TNBS assay. The porous structure of collagen was significantly altered by crosslinking, resulting in the reduction of the pore size from ca. 140 μm to less than 1μm depending upon the concentration of nanoparticles. The collagenase biodegradation assay showed improved stability of crosslinked material. The cell viability assay, CellTiter 96®, indicates that the gold nanoparticles are not toxic at the concentrations used in gel synthesis. This new material has potential for the delivery of small molecule drugs, as well as Au nanoparticles for photothermal therapies, imaging, and cell targeting.

Iron-based metal–organic frameworks (Fe-MOFs) have emerged as promising candidates for drug delivery applications due to their low toxicity, structural flexibility, and safe biodegradation in a physiological environment. Here, we studied two types of Fe-MOFs: MIL-53 and MIL-88B, for in vitro drug loading and releasing of ibuprofen as a model drug. Both Fe-MOFs are based on the same iron clusters and organic ligands but form different crystal structures as a result of two different nucleation pathways. The MIL-53 structure demonstrates one-dimensional channels, while MIL-88B exhibits a three-dimensional cage structure. Our studies show that MIL-53 adsorbs more ibuprofen (37.0 wt %) compared to MIL-88B (19.5 wt %). A controlled drug release was observed in both materials with a slower elution pattern in the case of the ibuprofen-encapsulated MIL-88B. This indicates that a complex cage structure of MIL-88 is beneficial to control the rate of drug release. A linear correlation was found between cumulative drug release and the degree of material degradation, suggesting the biodegradation of Fe-MILs as the main drug elution mechanism. The cytotoxicity of MIL-88B was evaluated in vitro with NIH-3T3 Swiss mouse fibroblasts, and it shows that MIL-88B has no adverse effects on cell viability up to 0.1 mg/mL. This low toxicity was attributed to the morphology of MIL-88B nanocrystals. The very low toxicity and controlled drug release behavior of Fe-MIL-88B suggest that better materials for drug-delivery applications can be created by controlling not only the composition but also the crystal structure and nanoparticle morphology of the material.

Cell-Penetrating Peptides (CPPs) are known as efficient transporters of molecular cargo across cellular membranes. Their properties make them ideal candidates for in vivo applications. However, challenges in development of effective CPPs still exist: CPPs are often fast degraded by proteases and large concentration of CPPs required for cargo transporting can cause cytotoxicity. It was previously shown that restricting peptide flexibility can improve peptide stability against enzymatic degradation and limiting length of CPP peptide can lower cytotoxic effects. Here we present peptides (30-mers) that efficiently penetrate cellular membranes by combining very short CPP sequences and collagen-like folding domains. The CPP domains are hexa-arginine (R6) or arginine/glycine (RRGRRG). Folding is achieved through multiple proline-hydroxyproline-glycine (POG)n repeats that form a collagen-like triple helical conformation. The folded peptides with CPP domains are efficiently internalized, show stability against enzymatic degradation in human serum, and have minimal toxicity. Peptides lacking correct folding (random coil) or CPP domains are unable to cross cellular membranes. These features make triple helical cell penetrating peptides promising candidates for efficient transporters of molecular cargo across cellular membranes.

Scanning electron microscopy, transmission electron micrsocopy, rheomerty, and electrochemistry were used to provide insight into the microstructure of collagen type I gel (1% w/v) modified with the tiopronin-protected (N-(2-mercaptopropionyl)glycine) gold nanoparticles (TPAu), a multivalent crosslinker. The cross-linking reaction, performed via EDC (1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide) coupling, results in compliant, mechanically stable and continuous gels. The gels contain unusual interconnected collagen-TPAu particles. Electrochemical measurements of 4-hydroxy-(2,2,6,6-tetramethylpiperidine-1-oxyl) (4HT) diffusion within the gel reveal that the gel hindrance is nearly independent of the TPAu concentration. The properties of the collagen-TPAu gel make it suitable for potential biomedical applications, such as delivery of small molecule drugs.

Oxidative mercury-thiolate bond formation accounts for the assembly of densely packed monolayers of per-2,3-methylated per-6-thiolated R-, β-, and γ-cyclodextrins on the hanging mercury drop electrode. Inclusion of inorganic ions and uncharged hydrophobic guests into these monolayers was investigated by capacitance measurements. In the range of potentials where the electrode is positively charged, the interfacial capacitance depends on the type of electrolyte anions and on the applied potential. This can be explained with electrostatic double-layer forces. Whereas the smaller and less well solvated anions Cl -, NO3 -, and ClO4are included in the cyclodextrin cavities of these monolayers, the larger and more strongly solvated anions F -, SO4 2-, and H2PO4are excluded. Anion inclusion constants can be obtained from the dependence of the interfacial capacitance on the anion concentration. The potential dependence of these inclusion constants shows that the nonelectrostatic contribution to the driving force for NO3inclusion is negligibly small. Competitive binding of hydrophobic guest molecules decreases the interfacial capacitance. Fitting Langmuir isotherms to the plots of the interfacial capacitance as a function of adamantanol concentration yielded the binding constants 1.0 × 10 4 and 2.6 × 10 4 M -1 for the β-and γ-cyclodextrin monolayers, respectively. Binding of adamantanol to R-cyclodextrin monolayers could not be observed, apparently because this guest is too large for the internal cavity of the R-cyclodextrin receptor. In contrast, 1-hexanol binds to R-cyclodextrin monolayers with the binding constant 8.9 × 10 4 M -1 . This shows that changes in the capacitance can serve as a general signal transduction mode to monitor interactions between cyclodextrin monolayers and charged or neutral guests. Also, the extension of these types of measurements into solid electrodes and the application to other guest-selective host monolayers open the possibility of designing a novel type of electrochemical sensors for electroinactive analytes.