Fibroblast attachment to Arg-Gly-Asp peptide-immobilized poly(gamma-methyl L-glutamate)

Current research progress of mammalian cell-based biosensors on the detection of foodborne pathogens and toxins

Foodborne diseases caused by pathogens and toxins are a serious threat to food safety and human health; thus, they are major concern to society. Existing conventional foodborne pathogen or toxin detection methods, including microbiological assay, nucleic acid-based assays, immunological assays, and instrumental analytical method, are time-consuming, labor-intensive and expensive. Because of the fast response and high sensitivity, cell-based biosensors are promising novel tools for food safety risk assessment and monitoring. This review focuses on the properties of mammalian cell-based biosensors and applications in the detection of foodborne pathogens (bacteria and viruses) and toxins (bacterial toxins, mycotoxins and marine toxins). We discuss mammalian cell adhesion and how it is involved in the establishment of 3D cell culture models for mammalian cell-based biosensors, as well as evaluate their limitations for commercialization and further development prospects.

High-yield activation of scaffold polymer surfaces to attach cell adhesion molecules

Zirconium tetra(tert-butoxide) reacts with surface amide groups of polyamide nylon 6/6 to give (eta(2)-amidate)zirconium complexes in high yield. These surface complexes react to bond the cell-adhesive peptide arginine-glycine-aspartic acid (RGD) to the polymer surface. A surface loading of 0.18 nmol/cm(2) of RGD is achieved, which is 20-1000 times higher than previously reported attainable on natural or synthetic polymers by other strategies. Approximately 40% of the nylon surface is covered by the RGD, which gives a surface that is both stable to hydrolysis and highly active for cell adhesion and spreading in vitro.

Self-assembly and applications of biomimetic and bioactive peptide-amphiphiles

Peptide-amphiphiles are amphiphilic structures with a hydrophilic peptide headgroup that incorporates a bioactive sequence and has the potential to form distinct structures, and a hydrophobic tail that serves to align the headgroup, drive self-assembly, and induce secondary and tertiary conformations. In this paper we review the different self-assembled structures of peptide-amphiphiles that range from micelles and nanofibers, to patterned membranes. We also describe several examples where peptide-amphiphiles have found applications as soft bioactive materials for model studies of bioadhesion and characterization of different cellular phenomena, as well as scaffolds for tissue engineering, regenerative medicine, and targeted drug delivery.

Biomimetic Peptide−Amphiphiles for Functional Biomaterials: The Role of GRGDSP and PHSRN

The study we present involves the use of a biomimetic system that allows us to study specific interactions in the alpha(5)beta(1) receptor-GRGDSP ligand system with an atomic force microscope (AFM). Bioartificial membranes that mimic the adhesion domain of the extracellular matrix protein fibronectin are constructed from peptide-amphiphiles. A novel peptide-amphiphile is designed that contains both GRGDSP (Gly-Arg-Gly-Asp-Ser-Pro, the primary recognition site for alpha(5)beta(1)) and PHSRN (Pro-His-Ser-Arg-Asn, the synergy binding site for alpha(5)beta(1)) sequences in a single peptide formulation, separated by a spacer. Two different antibodies are used to immobilize and activate isolated alpha(5)beta(1) integrins on the AFM tip. The interaction measured between immobilized alpha(5)beta(1) integrins and peptide-amphiphiles is specific for integrin-peptide binding and is affected by divalent cations in a way that accurately mimics the adhesion function of the alpha(5)beta(1) receptor. The strength of the PHSRN synergistic effect depends on the accessibility of this sequence to alpha(5)beta(1) integrins. An increase in adhesion is observed compared to surfaces displaying only GRGDSP peptides when the new biomimetic peptide-amphiphiles are diluted with lipidated poly(ethylene glycol), which provides more space for the peptide headgroups to bend and expose more of the PHSRN at the interface.

RGD modified polymers: biomaterials for stimulated cell adhesion and beyond

Since RGD peptides (R: arginine; G: glycine; D: aspartic acid) have been found to promote cell adhesion in 1984 (Cell attachment activity of fibronectin can be duplicated by small synthetic fragments of the molecule, Nature 309 (1984) 30), numerous materials have been RGD functionalized for academic studies or medical applications. This review gives an overview of RGD modified polymers, that have been used for cell adhesion, and provides information about technical aspects of RGD immobilization on polymers. The impacts of RGD peptide surface density, spatial arrangement as well as integrin affinity and selectivity on cell responses like adhesion and migration are discussed.

Adhesion of α5β1 receptors to biomimetic substrates constructed from peptide amphiphiles

Biomimetic membrane surfaces functionalized with fragments of the extracellular matrix protein, fibronectin, are constructed from mixtures of peptide and polyethylene glycol (PEG) amphiphiles. Peptides from the primary binding loop, GRGDSP, were used in conjunction with the synergy site peptide, PHSRN, in the III(9-10) sites of human fibronectin. These peptides were attached to dialkyl lipid tails to form peptide amphiphiles. PEG amphiphiles were mixed in the layer to minimize non-specific adhesion in the background. GRGDSP and PEG amphiphiles or GRGDSP, PHSRN, and PEG amphiphiles were mixed in various ratios and deposited on solid substrates from the air-water interface using Langmuir-Blodgett techniques. In this method, peptide composition, density, and presentation could be controlled accurately. The effectiveness of these substrates to mimic native fibronectin is evaluated by their ability to generate adhesive forces when they are in contact with purified activated alpha5beta1 integrin receptors that are immobilized on an opposing surface. Adhesion is measured using a contact mechanical approach (JKR experiment). The effects of membrane composition, density, temperature, and peptide conformation on adhesion to activated integrins in this simulated cell adhesion setup were determined. Addition of the synergy site, PHSRN, was found to increase adhesion of alpha5beta1, to biomimetic substrates markedly. Increased peptide mobility (due to increased experimental temperature) increased integrin adhesion markedly at low peptide concentrations. A balance between peptide density and steric accessibility of the receptor binding face to alpha5beta1 integrin was required for highest adhesion.

Biological evaluation of RGD peptidomimetics, designed for the covalent derivatization of cell culture substrata, as potential promotors of cellular adhesion

Our aim was to replace the proteins and peptides, generally used for the biocompatibilization of polymer substrata, with synthetic molecules mimicking the RGD (Arg-Gly-Asp) active sequence. Based on the (L)-tyrosine template, RGD peptidomimetics were constructed; one molecule 3 was equipped with an anchorage arm that allowed its covalent grafting on a culture substratum made from poly(ethylene terephthalate) (PET) microporous membrane. The amount of fixed molecules was readily determined by XPS, using a fluorine tag incorporated in the peptidomimetic structure. The binding of peptidomimetics 1-3 to the vitronectin (VN) and fibronectin (FN) receptors could not be revealed in a test of inhibition of MSC 80 cells adhesion, by the synthetic compounds in solution placed in competition with the adhesive proteins (VN and FN) coating polystyrene plates. However, the cell-attachment activity of peptidomimetic 3 was shown by culturing CaCo2 cells, in the absence of serum, on the PET substratum grafted with 3. The performance of this support was similar to that of PET grafted with the reference peptide RGDS (Arg-Gly-Asp-Ser), and only reduced by half comparatively to the PET grafted with FN.

Modification of glassy carbon surfaces with synthetic laminin-derived peptides for nerve cell attachment and neurite growth

Interactions between cultured nerve cells and surfaces are of importance for the implantation of biocompatible electrode materials such as glassy carbon (GC). Since implants serve as recording sensors in prosthetic neuroscience, we investigated whether coating electrodes with certain laminin derivatives containing the peptide sequences SIKVAV, CDPGYIGSR, PDSGR, YFQRYLI, and RNIAEIIKDA influences neuronal adhesion and neurite outgrowth in vitro. The coating of GC was performed by electrochemical polymerization and, for comparison, by adsorption or covalent coupling. Electrochemical polymerization is suitable for the coupling of peptides to GC, as shown by amino acid analysis and sequencing. Embryonic chicken retinal ganglion cells and brain cells (days E7 or E17) were used for both attachment and growth studies. Surfaces made by electrochemical polymerization of peptides were more efficient than those made by adsorption or covalent coupling of peptides. Synthetic cyclic peptide derivatives of CDPGYIGSR and 18-mer SIKVAV were found to be more efficient than the linear peptides. Competitive effects that resulted in a decreased cell attachment could be found upon application of soluble peptides. Nevertheless, irrespective of the method of coating, peptides were less efficient compared with the whole laminin molecule, as expected from its multiple adhesion sites. When small GC pins were implanted into the brain of E17 chicken after coating with the 18-mer SIKVAV peptide, nerve cell attachment was observed in vivo. The results suggest that chronically implantable materials may exert a higher neurocompatibility when coated with synthetic peptides.

Implantable bioelectric interfaces for lost nerve functions

Neuronal cells are unique within the organism. In addition to forming long-distance connections with other nerve cells and non-neuronal targets, they lose the ability to regenerate their neurites and to divide during maturation. Consequently, external violations like trauma or disease frequently lead to their disappearance and replacement by non-neuronal, and thus not properly functioning cells. The advent of microtechnology and construction of artificial implants prompted to create particular devices for specialised regions of the nervous system, in order to compensate for the loss of function. The scope of the present work is to review the current devices in connection with their applicability and functional perspectives. (1) Successful implants like the cochlea implant and peripherally implantable stimulators are discussed. (2) Less developed and not yet applicable devices like retinal or cortical implants are introduced, with particular emphasis given to the reasons for their failure to replace very complex functions like vision. (3) Material research is presented both from the technological aspect and from their biocompatibility as prerequisite of any implantation. (4) Finally, basic studies are presented, which deal with methods of shaping the implants, procedures of testing biocompatibility and modification of improving the interfaces between a technical device and the biological environment. The review ends by pointing to future perspectives in neuroimplantation and restoration of interrupted neuronal pathways.

Incorporation of adhesion peptides into nonadhesive hydrogels useful for tissue resurfacing

Photopolymerized crosslinked networks of poly(ethylene glycol; PEG) diacrylate (MW 8000) were derivitized throughout their bulk with Arg-Gly-Asp (RGD)-containing peptide sequences. Incorporation was achieved by functionalizing the amine terminus of the peptide with an acrylate moiety, thereby enabling the adhesion peptide to copolymerize rapidly with the PEG diacrylate upon photoinitiation. PEG diacrylate hydrogels derivitized with RGD peptide at surface concentrations ranging from 0.001 to 1 pmol/cm2 were studied in vitro for their ability to promote spreading of human foreskin fibroblasts over 24 h. Hydrogels not derivitized with peptides were poor substrates for adhesion, permitting spreading of only 5% of the seeded cells. When immobilized with no spacer arm, both RGD and RDG (inactive control) supported spreading of approximately 50% and approximately 15% of cells at 1 and 0.1 pmol/cm2 surface concentrations respectively; lower concentrations did not promote spreading. When a MW 3400 PEG spacer arm was incorporated between the hydrogel and the peptide linkage, incorporation of 1 pmol/cm2 RGD promoted 70% spreading whereas RDG at the same concentration did not promote spreading. In addition, when cells were seeded in serum-free medium, only RGD peptides incorporated with a spacer arm were able to promote spreading. Thus peptide incorporated into PEG 8000 diacrylate hydrogels without a spacer arm nonspecifically mediated cell spreading whereas incorporation via a MW 3400 PEG spacer arm was required to permit cell spreading to be specifically mediated.

Randomness and biospecificity: random copolymers are capable of biospecific molecular recognition in living systems

Biospecific molecular recognition in living systems is known to be based on the lock and key principle as proposed by Emil Fischer. Based on this concept, biospecific polymers have been produced synthetically by attaching biospecific 'keys' to the polymer chain. We postulate that biospecificity can be achieved by alternative means, namely random substitution of a preformed polymer with suitable chemical groups or random copolymerization of suitable functional monomers. Such polymers, we suggest, will contain arrangements of the chemical functions which mimic natural biospecific sites and the probability of occurrence of such arrangements will depend on the average composition of the polymer. In support of this principle, we have developed several functional random copolymer systems which possess a variety of biological properties depending on the type of chemical function. Examples are: polymers possessing anticoagulant properties similar to those of heparin; polymers which interact specifically with components of the immune system; and polymers which, in contact with cells, affect their growth and metabolism. In the case of statistical copolymers possessing 'DNA-like' properties obtained by phosphorylation of hydroxylated polystyrene derivatives, Monte Carlo simulations were used to determine the distribution of phosphodiester (PDE) groups along the chains and to compute the probabilities of occurrence of particular arrangements of PDE found in the 'DNA-like' sites. The results showed that these sites are made up of PDE groups separated by distances that closely match those between the same groups along a generatrix of the DNA double-helix cylinder. These findings offer the prospect of manufacturing polymeric biomaterials endowed with biomimetic character. Moreover, they provide the basis for a hypothesis regarding the appearance of biospecificity at the origin of life, suggesting that biospecific structures may have evolved by natural selection from purely random copolymers. It is likely therefore that biospecificity is a continuous function of randomness, arising from purely statistical distributions of reactivity and evolving into precisely defined structures such as those involved in ligand-receptor interactions.