Enhancing the Activity of Surface Immobilized Antimicrobial Peptides Using Thiol-Mediated Tethering to Poly(ethylene glycol).

Considering the need for versatile surface coatings that can display multiple bioactive signals and chemistries, the use of more novel surface modification methods is starting to emerge. Thiol-mediated conjugation of biomolecules is shown to be quite advantageous for such purposes due to the reactivity and chemoselectivity of thiol functional groups. Herein, the immobilization of poly(ethylene glycol) (PEG) and antimicrobial peptides (AMPs) to silica colloidal particles based on thiol-mediated conjugation techniques, along with an assessment of the antimicrobial potential of the functionalized particles against Pseudomonas aeruginosa and Staphylococcus aureus is investigated. Immobilization of PEG to thiolated Si particles is performed by either a two-step thiol-ene "photo-click" reaction or a "one-pot" thiol-maleimide type conjugation using terminal acrylate or maleimide functional groups, respectively. It is demonstrated that both immobilization methods result in a significant reduction in the number of viable bacterial cells compared to unmodified samples after the designated incubation periods with the PEG-AMP-modified colloidal suspensions. These findings provide a promising outlook for the fabrication of multifunctional surfaces based upon the tethering of PEG and AMPs to colloidal particles through thiol-mediated biocompatible chemistry, which has potential for use as implant coatings or as antibacterial formulations that can be incorporated into wound dressings to prevent or control bacterial infections.

Galactose Tethered Decellularized Liver Matrix: Toward a Biomimetic and Biofunctional Matrix for Liver Tissue Engineering.

The major challenge in liver tissue engineering is the replication of the microenvironment and microarchitecture of the liver tissue at the nanoscale. Decellularized liver matrix (DLM) provides an ideal material for scaffold preparation, as it retains the relevant structural and biochemical composition. However, the loss of bioactive factors during decellularization needs to be taken into account when using DLM and should be supplemented accordingly for an expected outcome. This study reports on the modification of DLM by the addition of galactose residues using a two-step thiol-ene-mediated photoclick chemistry for the coupling of galactose moieties to the DLM. Modification with galactose enhanced the function of hepatocytes and provides many advantages over currently used DLM and DLM-based materials. The galactose modified DLM enhanced the initial HepG2 cell adhesion to the substrate with changes in dynamics over time such as spheroid formation and further migration on the matrix. Our observation is that the galactose ligand decoration can also enhance the liver-specific metabolism of HepG2 compared to unmodified DLM. Galactosylated DLM also showed a better establishment of cellular polarity which also contributes to the function of HepG2 cells. Together our results demonstrate the advantages of adding galactose residues to currently available biomaterials, which makes this approach an attractive method for ECM-based liver tissue engineering.

Binary colloidal crystals (BCCs): Interactions, fabrication, and applications.

The organization of matter into hierarchical structures is a fundamental characteristic of functional materials and living organisms. Binary colloidal crystal (BCC) systems present a diversified range of nanotopographic structures where large and small colloidal particles simultaneously self-assemble into either 2D monolayer or 3D hierarchical crystal lattices. More importantly, understanding how BCCs form opens up the possibility to fabricate more complex systems such as ternary or quaternary colloidal crystals. Monolayer BCCs can also offer the possibility to achieve surface micro- and nano-topographies with heterogeneous chemistries, which can be challenging to achieve with other traditional fabrication tools. A number of fabrication methods have been reported that enable generation of BCC structures offering high accuracy in growth with controllable stoichiometries; however, it is still a challenge to make uniform BCC structures over large surface areas. Therefore, fully understand the mechanism of binary colloidal self-assembly is crucial and new/combinational methods are needed. In this review, we summarize the recent advances in BCC fabrication using particles made of different materials, shapes, and dispersion medium. Depending on the potential application, the degree of order and efficiency of crystal formation has to be determined in order to induce variability in the intended lattice structures. The mechanisms involved in the formation of highly ordered lattice structures from binary colloidal suspensions and applications are discussed. The generation of BCCs can be controlled by manipulation of their extensive phase behavior, which facilitates a wide range potential applications in the fields of both material and biointerfacial sciences including photonics, biosensors, chromatography, antifouling surfaces, biomedical devices, and cell culture tools.

Binary Colloidal Crystal Layers as Platforms for Surface Patterning of Puroindoline-Based Antimicrobial Peptides.

The ability of bacteria to form biofilms and the emergence of antibiotic-resistant strains have prompted the need to develop the next generation of antibacterial coatings. Antimicrobial peptides (AMPs) are showing promise as molecules that can address these issues, especially if used when immobilized as a surface coating. We present a method that explores how surface patterns together with the selective immobilization of an AMP called PuroA (FPVTWRWWKWWKG-NH2) can be used to both kill bacteria and also as a tool to study bacterial attachment mechanisms. Surface patterning is achieved using stabilized self-assembled binary colloidal crystal (BCC) layers, allowing selective PuroA immobilization to carboxylated particles using N-(3-dimethylaminopropyl)-N'-ethyl carbodiimide (EDC) hydrochloride/N-hydroxysuccinimide (NHS) coupling chemistry. Covalent immobilization of PuroA was compared with physical adsorption (i.e., without the addition of EDC/NHS). The AMP-functionalized colloids and BCC layers were characterized by X-ray photoelectron spectroscopy, ζ potentials, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Surface antimicrobial activity was assessed by viability assays using Escherichia coli. MALDI-TOF MS analysis revealed that although not all of PuroA was successfully covalently immobilized, a relatively low density of PuroA (1.93 × 1013 molecules/cm2 and 7.14 × 1012 molecules/cm2 for covalent and physical immobilization, respectively) was found to be sufficient at significantly decreasing the viability of E. coli by 70% when compared to that of control samples. The findings provide a proof of concept that BCC layers are a suitable platform for the patterned immobilization of AMPs and the importance of ascertaining the success of small-molecule grafting reactions using surface-MALDI, something that is often assumed to be successful in the field.

Long range charge transfer in trimetallic mixed-valence iron complexes mediated by redox non-innocent cyanoacetylide ligands.

The reaction of Fe(C≡CC≡N)(dppe)Cp (1) with one-half equivalent of [trans-Fe(N≡CMe)2(dppx)2][BF4]2 (dppx = dppe ([2][BF4]2) or dppm ([3][BF4]2)) affords trimetallic [trans-Fe{N≡CC≡CFe(dppe)Cp}2(dppx)2][BF4]2 (dppx = dppe [4][BF4]2; dppx = dppm [5][BF4]2). Both [4][BF4]2 and [5][BF4]2 undergo three, one-electron oxidation processes, arising from sequential oxidation of the two terminal Fe(C≡CR)(dppe)Cp moieties and finally the central Fe(N≡CR)2(dppx)2 fragment. The redox products [4](n+) and [5](n+) (n = 3, 4) have been characterised by UV-vis-NIR and IR spectroelectrochemistry. The shifts in the characteristic ν(C≡CC≡N) bands upon oxidation demonstrate not only the localised electronic structure of the trications, but also the redox non-innocence of the cyanoacetylide ligands. The trimetallic [formally Fe(II/II/III) mixed-valence] complexes [4](3+) and [5](3+) feature two distinct IVCT transitions, one associated with charge transfer from the central 18-electron {Fe(N≡CR)2(dppx)2}(2+) to terminal {Fe(C≡CR)(dppe)Cp}(+) moiety, and a lower energy transition involving charge transfer between the terminal Fe fragments which are separated by the redox active 9-atom, 10-bond -C≡C-C≡N{Fe(dppx)2}N≡C-C≡C- bridge. The tetracationic complexes [4](4+) and [5](4+) generated by a further stepwise oxidation exhibit a single {Fe(N≡CR)2(dppx)2}(2+)→{Fe(C≡CR)(dppe)Cp}(+) IVCT transition.