Karl R. Fath

Ellagic acid promoted biomimetic synthesis of shape-controlled silver nanochains

In this work, ellagic acid (EA), a naturally occurring plant polyphenol, was utilized for the biomimetic synthesis of silver (Ag) nanoparticles, which over a period of time formed extended branched nanochains of hexagonal-shaped silver nanoparticles. It was found that EA not only has the capability of reducing silver ions, resulting in the formation of Ag nanoparticles, due to its extended polyphenolic system, but also appears to recognize and affect the Ag nanocrystal growth on the (111) face, leading to the formation of hexagon-shaped Ag nanocrystals. Initially, various Ag nanocrystal shapes were observed; however, over a longer period of time, a majority of hexagonal-shaped nanocrystals were formed. Although the exact mechanism of formation of the nanocrystals is not known, it appears that EA attaches to the silver nuclei, leading to lower surface energy of the (111) face. Further, the nanocrystals fuse together, forming interfaces among the aggregates, and, with time, those interfaces become lesser, and the nanoparticles merge together and share the same single crystallographic orientation, which leads to the formation of long elongated chains of hexagonal nanoparticles. This biomimetic approach may be developed as a green synthetic method to prepare building blocks with tunable properties for the development of nanodevices. Further, we explored the antibacterial properties and found that the tandem of EA-Ag nanochains substantially enhanced the antibacterial properties of both gram-positive and gram-negative bacteria compared to silver nanoparticles or EA alone. Additionally, the materials were also utilized for imaging of mammalian NRK (normal rat kidney) cells.

Layer-by-layer assembly of peptide based bioorganic–inorganic hybrid scaffolds and their interactions with osteoblastic MC3T3-E1 cells

In this work we have developed a new family of biocomposite scaffolds for bone tissue regeneration by utilizing self-assembled fluorenylmethyloxycarbonyl protected Valyl-cetylamide (FVC) nanoassemblies as templates. To tailor the assemblies for enhanced osteoblast attachment and proliferation, we incorporated (a) Type I collagen, (b) a hydroxyapatite binding peptide sequence (EDPHNEVDGDK) derived from dentin sialophosphoprotein and (c) the osteoinductive bone morphogenetic protein-4 (BMP-4) to the templates by layer-by-layer assembly. The assemblies were then incubated with hydroxyapatite nanocrystals blended with varying mass percentages of TiO2 nanoparticles and coated with alginate to form three dimensional scaffolds for potential applications in bone tissue regeneration. The morphology was examined by TEM and SEM and the binding interactions were probed by FITR spectroscopy. The scaffolds were found to be non-cytotoxic, adhered to mouse preosteoblast MC3T3-E1 cells and promoted osteogenic differentiation as indicated by the results obtained by alkaline phosphatase assay. Furthermore, they were found to be biodegradable and possessed inherent antibacterial capability. Thus, we have developed a new family of tissue-engineered biocomposite scaffolds with potential applications in bone regeneration.

Self‐Assembly and Growth of Smart Cell‐Adhesive Mucin‐Bound Microtubes

Microtubular structures were self‐assembled in aqueous media from a newly synthesized bolaamphiphile, bis(N‐α‐amido‐threonine)‐1,3‐propane dicarboxylate. The self‐assembly process was examined at varying pH. The formed microtubes were then functionalized with the highly glycosylated protein mucin. In nature, the O‐linked saccharides of mucin are generally associated with Thr or Ser residues of protein scaffolds. In this work, peptide microtubes with threonine functionality were prepared synthetically in order to enhance the affinity of the microtubes toward mucin, thus mimicking natural proteins. After binding the mucin to the microtubes, we investigated the biocompatibility of those materials by conducting in vitro cell attachment, cell proliferation, and cytotoxicity studies using normal rat kidney (NRK) cells. The studies revealed that the biomaterials were nontoxic, biocompatible, and showed significant adhesion to the cells. It is well known that natural mucins may degrade into their motifs; however, upon binding to the surface of microtubes, their stability may be increased. Because mucin is one of the major components of mucoadhesion, and various types of mucins are ubiquitous in human tissues, such mucin‐bound microtubes may potentially be used as mucoadhesive materials for targeted drug delivery and improve the localization of drugs.

Fabrication of ellagic acid incorporated self-assembled peptide microtubes and their applications

Ellagic acid (EA), a plant polyphenol known for its wide-range of health benefits was encapsulated within self-assembled threonine based peptide microtubes. The microtubes were assembled using the synthesized precursor bolaamphiphile bis(N-α-amido threonine)-1,5-pentane dicarboxylate. The self-assembly of the microstructures was probed at varying pH. In general, tubular formations were observed at a pH range of 4-6. The formed microtubes were then utilized for fabrication with EA. We probed the ability of the microtubes as drug release vehicles for EA as well as for antibacterial applications. It was found that the release of EA was both pH and concentration dependent. The biocompatibility as well as cytotoxicity of the EA-fabricated microtubes was examined in the presence of mammalian normal rat kidney (NRK) cells. Finally the antibacterial effects of the EA incorporated peptide microtubes was examined against Escherichia coli and Staphylococcus aureus.

Growth of Se Nanoparticles on Kinetin Assemblies and their Biocompatibility Studies

In this work we examined the growth and self-assembly of kinetin nano and microstructures under varying conditions followed by the utilization of the formed structures as templates for the growth of selenium nanoparticles. It was found that the self-assembly of kinetin nanostructures is pH and concentration dependant. The optimal pH for self-assembly was found to be between pH 5–7. The self-assembly of the nanostructures was aided by aromatic π–π stacking, solvophobic interactions, as well as hydrogen bonding interactions. The sizes of the nanostructures ranged from 200 nm–500 nm in diameter, which grew into microstructures over a longer period of time. The assemblies were then used as templates for the growth of selenium nanoparticles. The formation of the nanoconjugates was confirmed by spectroscopic and electron microscopic analysis. The utility of the nanoconjugates as anti-oxidants was examined by conducting the 2,2-diphenyl-1-picrylhydrazyl (DPPH·) assay, where in selenium nanoparticles bound kinetin nanofibers showed the ability to scavenge free radicals. Further, the biocompatibility of the materials was examined in the presence of normal rat kidney cells (NRK). Thus, such nanomaterials may potentially be useful as a new family of antioxidants for biological applications and for nanodevice fabrications.

Self-assembling peptide assemblies bound to ZnS nanoparticles and their interactions with mammalian cells.

Self-assembling peptide sequences (both synthetic and natural) have emerged as a new group of building blocks for diverse applications. In this work we investigated the formation of assemblies of three diverse peptide sequences derived from the crustacean cardioactive peptide CCAP (1-9), a cardioaccelerator and neuropeptide transmitter in crustaceans, atrial natriuretic hormone ANP (1-28), a powerful vasodilator secreted by heart muscle cells of mammals, as well as adamstsostatin peptide ADS (1-17), which functions as an inhibitor of angiogenesis. The formation of assemblies was found to be dependent upon the sequences as well as the pH in which the assemblies were grown. The secondary structural transformation of the peptides was studied by circular dichroism as well as FTIR spectroscopy. In order to render the sequences luminescent, we conjugated the assemblies with ZnS nanoparticles. Finally the interactions of the peptide bound ZnS nanoparticles with mammalian normal rat kidney cells were explored. In some cases the nanoconjugates were found to adhere not only to the cellular membranes but also extend into the cytoplasm. Thus, such nanocomposites may be utilized for cell penetration and have the potential to serve as coercive multifunctional vectors for bioimaging and cellular delivery.

Fabrication of Collagen–Elastin-Bound Peptide Microtubes for Mammalian Cell Attachment

Abstract In this work we have designed self-assembled peptide-based microconstructs and examined their interactions with elastin and collagen for potential application as scaffolds for chondrocyte cell attachment. Being biological in nature, peptide-based nano- and microstructures have intrinsic molecular recognition properties which allow extensive chemical, conformational and functional diversity. We have synthesized a new peptide bolaamphiphile, bis(N-α-amido-val)-1,5-pentane dicarboxylate, and examined its self-assembly at varying pH values. The formation of high-density networks of nano- and microtubular structures was found to be in the range of pH 4–6. The formed microtubes were then covalently bound to varying concentrations of the extracellular matrix protein elastin, a versatile protein that allows for an extensive array of physical and chemical modifications to attune properties towards diverse necessities of biomedical applications. We found that binding to microtubes was concentration dependent. The morphological and chemical changes complementing the processes of self-assembly and binding to elastin were examined by electron microscopic and spectroscopic methods. Furthermore, we also incorporated the extracellular matrix protein type-I collagen, a critical constituent for designing biocompatible scaffolds, into the elastin functionalized micro-tubes. Since the main goal is to develop highly biocompatible protein functionalized microstructures that support cellular interactions, we examined the interactions of the microcomposites with chondrocyte cell line, in order to assess the biocompatibility and interaction between the microconstructs and the cells. The designed elastin and collagen-bound peptide microtubes may potentially serve as a new class of biomaterials by promoting cell growth and proliferation.

Biomimetic growth of gallic acid–ZnO hybrid assemblies and their applications

In this study, we probed the biomimetic formation of gallic acid (GA)–ZnO nanoparticle hybrids. It was found that the morphologies formed were dependent upon pH values, resulting in GA–ZnO hybrids of varying shapes such as micro or nanoplates or fibers. The formed supramolecular GA–ZnO hybrids were found to be luminescent as indicated by confocal microscopy and were utilized for the photocatalytic degradation of the organic dye methylene blue. We also explored the bactericidal effects of the hybrids on Staphylococcus aureus (S. aureus) as well as Escherichia Coli (E. Coli). Thus, we have developed a new class of shape-controlled nanohybrid assemblies via mild, green synthetic methods that may be utilized for photocatalytic degradation for environmental remediation as well as for antibacterial applications.

Roles of the Actin Cytoskeleton and Myosins in the Endomembrane System

The positioning of the endomembrane system (biosynthetic/secretory and endocytic pathways) and the constant movement of constituents between these compartments requires the involvement of the cytoskeleton and cytoskeletal‐based motors. Whereas much is known about the roles of the microtubule (MT) cytoskeleton in these events, considerably less is known about the roles of the actin cytoskeleton. Recent work has shown that the Golgi complex is linked to an actin‐based network that is important for Golgi morphology and the trafficking of Golgi‐derived membranes. Moreover, many of the cellular players used to transport cargo near the actin‐rich network subjacent to the plasma membrane (PM) may function near the Golgi.

Formation of Calcium Phosphate-Ellagic Acid Composites by Layer by Layer Assembly for Cellular Attachment to Osteoblasts

The quest for new biomaterials to serve as cell scaffolds for applications in tissue engineering is of prime importance. In this work, we investigated microfiber assemblies of Ellagic Acid (EA), a plant polyphenol to serve as scaffolds for attachment and proliferation of osteoblasts. The advantage of Ellagic Acid self-assembling system is its intrinsic ability to order into multiple layers due to its capability to form liquid crystalline assemblies. We prepared ellagic acid-microfiber composites by the layer-by-layer (LBL) assembly method, where collagen (COL), poly-Arginine (poly-R), and calcium phosphate nanocrystals were coated on the surface of ellagic acid microfibers. The attachment of the various layers was confirmed by various spectroscopic and microscopic methods. The samples were found to be porous with an average pore size of 600 nm. The formed microconjugates were biodegradable and supported the growth of human fetal osteoblast (hFOB) cells in vitro. Our findings suggest that this system not only promotes initial cell adhesion but also can be utilized to deliver the vital biological molecule ellagic acid to cells at the scaffold interface and displays a new strategy for the design of biomaterials.