Polypeptide multilayer films

Enhanced Resistance of Polyelectrolyte Multilayer Microcapsules to Pepsin Erosion and Release Properties of Encapsulated Indomethacin

Polyelectrolyte multilayer films were prepared through layer-by-layer (LbL) self-assembly using polysaccharide sodium alginate (ALG) and chitosan (CHI). After incubation in an enzyme pepsin solution, the multilayer film was partially destroyed as detected by the decrease in fluorescent intensity because of the enzymatic degradation of CHI. The enzymatic desorption was also observed from the microcapsule wall made of the ALG/CHI multilayer film directly deposited on indomethacin (IDM) microcrystals through LbL self-assembly. After pepsin erosion, the IDM release from the microcapsules monitored by UV absorbance was obviously accelerated because of desorption. To enhance the stability of the ALG/CHI multilayer film to the enzymatic erosion, some physical and chemical methods were established to increase film thickness or to cross-link the polysaccharides within the film. Increasing the layer number and raising the deposition temperature effectively slowed down the enzymatic desorption and release rate. Especially, increasing deposition temperature was more effective because of producing a more perfect structure in the ALG/CHI multilayer film. Cross-linking the neighboring layers of ALG and CHI with 1-ethyl-3-(3-dimethylamino-propyl)carbodiimide in the ALG/CHI multilayer film significantly reduced the enzymatic desorption and release rate. Therefore, increasing deposition temperature and cross-linking neighboring layers are effective methods to protect the multilayer film fabricated using LbL assembly from the enzymatic erosion and to prolong the release of the encapsulated drug.

Salt concentration and pH-dependent adsorption of two polypeptides on planar and divided alumina surfaces. In situ IR investigations

The adsorption of proteins is the first process to take place when a solid is immersed in a biological fluid; though not yet thoroughly understood at a molecular level, this process is also known to be strongly influenced by the presence of salt in solution or by pH changes. In the present work, poly-L-glutamic acid (PG) and poly-L-lysine (PL) were selected to mimic the behavior of some protein fragments. Their adsorption was investigated by infrared spectroscopy in various modes, both on planar and on divided (powder) surfaces of aluminum oxide. These two peptides were shown to have different behaviors when adsorbed from solutions with or without CaCl2 and at various pH values. Polarization modulation-reflection absorption infrared spectroscopy, applied in a special cell designed to characterize the solid surface in contact with the liquid, enabled the observation of the influence of pH and salts upon polypeptide adsorption. At pH values higher than 5 and in the presence of CaCl2 in solution, a net increase of the PG adsorbed amount is observed, whereas no such effect could be detected for PL. Specific interactions between the COO- groups on the side chains and the surface, or between those of two different molecules, was inferred. Interestingly, similar conclusions could be drawn for the surface of alumina powders contacted with solutions of PG and PL and characterized by attenuated total reflectance IR. This work demonstrates the potential for IR investigations of solid oxide-liquid interfaces combining the study of planar and finely divided surfaces.

Antimicrobial polypeptide multilayer nanocoatings

A multilayer coating (or film) of nanometer-thick layers can be made by sequential adsorption of oppositely charged polyelectrolytes on a solid support. The method is known as layer-by-layer assembly (LBL). No special apparatus is required for LBL and nanofilms can be prepared under mild, physiological conditions. A multilayer nanofilm in which at least one of the constituent species is a polypeptide is a polypeptide multilayer nanofilm. The present work was aimed at assessing whether polypeptide multilayer nanofilms with specific antimicrobial properties could be prepared by incorporation of a known antimicrobial agent in the film structure, in this case the edible protein hen egg white lysozyme (HEWL). The chicken enzyme is widely employed as a human food preservative. An advantage of LBL in this context is that the nanofilm is fabricated directly on the surface of interest, eliminating the need to incorporate the antimicrobial in other packaging materials. Here, nanofilms were made of poly(L-glutamic acid) (PLGA), which is highly negatively charged in the mildly acidic pH range, and HEWL, which has a high net positive charge at acidic pH. We show that PLGA/HEWL nanofilms inhibit growth of the model microbe Microccocus luteus in the surrounding liquid medium. The amount of HEWL released from PLGA/HEWL films depends on the number of HEWL layers and therefore on the total quantity of HEWL in the films. This initial study provides a sketch of the scope for further development of LBL in the area of antimicrobial polypeptide multilayer films. Potential applications of such films include strategies for food preservation and coatings for implant devices.

Disassembly of layer-by-layer films of plasmid DNA and reducible TAT polypeptide

This paper reports the disassembly of layer-by-layer (LbL) films of plasmid DNA and a reducible cationic polypeptide. To utilize a reducing microenvironment of cellular plasma membrane as a potential trigger, LbL films are assembled to contain both DNA and the TAT-based polypeptide (PTAT) with reducible disulfide bonds in the backbone. The assembly and disassembly processes are monitored by goniometry, ellipsometry, and atomic force microscopy (AFM). The structure of the PTAT films is compared with that of non-reducible poly(L-lysine) (PLL) films. Both PTAT and PLL films exhibit exponential growth but with the contact angle alternating between characteristic values. Ellipsometry and AFM show a gradual and complete disassembly of the PTAT but not the PLL films in a 24h period in the reducing environment in vitro. This study suggests a potential of using reducible LbL films for controlled DNA delivery.

Nanostructured materials for applications in drug delivery and tissue engineering

Research in the areas of drug delivery and tissue engineering has witnessed tremendous progress in recent years due to their unlimited potential to improve human health. Meanwhile, the development of nanotechnology provides opportunities to characterize, manipulate and organize matter systematically at the nanometer scale. Biomaterials with nano-scale organizations have been used as controlled release reservoirs for drug delivery and artificial matrices for tissue engineering. Drug-delivery systems can be synthesized with controlled composition, shape, size and morphology. Their surface properties can be manipulated to increase solubility, immunocompatibility and cellular uptake. The limitations of current drug delivery systems include suboptimal bioavailability, limited effective targeting and potential cytotoxicity. Promising and versatile nano-scale drug-delivery systems include nanoparticles, nanocapsules, nanotubes, nanogels and dendrimers. They can be used to deliver both small-molecule drugs and various classes of biomacromolecules, such as peptides, proteins, plasmid DNA and synthetic oligodeoxynucleotides. Whereas traditional tissue-engineering scaffolds were based on hydrolytically degradable macroporous materials, current approaches emphasize the control over cell behaviors and tissue formation by nano-scale topography that closely mimics the natural extracellular matrix (ECM). The understanding that the natural ECM is a multifunctional nanocomposite motivated researchers to develop nanofibrous scaffolds through electrospinning or self-assembly. Nanocomposites containing nanocrystals have been shown to elicit active bone growth. Drug delivery and tissue engineering are closely related fields. In fact, tissue engineering can be viewed as a special case of drug delivery where the goal is to accomplish controlled delivery of mammalian cells. Controlled release of therapeutic factors in turn will enhance the efficacy of tissue engineering. From a materials point of view, both the drug-delivery vehicles and tissue-engineering scaffolds need to be biocompatible and biodegradable. The biological functions of encapsulated drugs and cells can be dramatically enhanced by designing biomaterials with controlled organizations at the nanometer scale. This review summarizes the most recent development in utilizing nanostructured materials for applications in drug delivery and tissue engineering.

Polypeptide multilayer nanofilm artificial red blood cells

Reliable encapsulation of hemoglobin (Hb) within polypeptide multilayer nanofilms has been achieved by a template-based approach, and protein functionality has been demonstrated postencapsulation. The method is general in scope and could be useful for many other encapsulants. Met-Hb was adsorbed onto 5 microm-diameter CaCO3 microparticles, and the Hb-coated particles were encapsulated within a multilayer nanofilm of poly(L-glutamic acid) (PLGA) and poly(L-lysine) (PLL) by layer-by-layer assembly. The CaCO3 templates were then dissolved within the PLGA/PLL nanofilms by addition of ethylenediaminetetraacetic acid. Encapsulation of Hb was proved by fluorescence microscopy, the pH-dependence of retention of Hb was determined by visible wavelength absorbance, and conversion of the encapsulated met-Hb to deoxy-Hb and oxy-Hb was demonstrated by spectroscopic analysis of the Soret absorption peak under various conditions. It thus has been shown that control of Hb oxygenation within polypeptide multilayer nanofilm artificial cells is possible, and that Hb thus encapsulated can bind, release, and subsequently rebind molecular oxygen. This work therefore represents an advance in the development of polypeptide multilayer film artificial red blood cells.

Stimulated release of small molecules from polyelectrolyte multilayer nanocoatings

Free thiol-containing polyelectrolytes serve simultaneously as a material for self-assembly of a multilayer nanocoating and as a carrier of small molecules for release from the coating in response to an environmental cue.

Electrochemically Induced Disintegration of Layer-by-Layer-Assembled Thin Films Composed of 2-Iminobiotin-Labeled Poly(ethyleneimine) and Avidin

A layer-by-layer assembly composed of avidin and 2-iminobiotin-labeled poly(ethyleneimine) (ib-PEI) was prepared on the surface of a platinum (Pt) film-coated quartz resonator, and an electrochemically induced disintegration of the avidin-ib-PEI assembly was studied using a quartz crystal microbalance. The resonance frequency of a five-bilayer (avidin-ib-PEI)5 film-coated quartz resonator was increased upon application of an electric potential to the Pt layer of the quartz resonator, suggesting that the mass on the quartz resonator was decreased as a result of disintegration of the (avidin-ib-PEI)5 film, due to a pH change in the vicinity of the surface of the Pt-coated quartz resonator. It may be that the (avidin-ib-PEI)5 film assembly was decomposed by acidification of the local pH on the surface of the Pt layer, which in turn was induced through electrolysis of water on Pt, because ib-PEI forms complexes with avidin only in basic media. In pH 9 solution, the (avidin-ib-PEI)5 film was decomposed under the influence of an applied potential of 0.6-1.0 V versus Ag/AgCl. The (avidin-ib-PEI)5 film was decomposed almost completely within a minute in a low concentration buffer (1 mM, pH 9), while the decomposition was slower in 10 and 100 mM buffer solutions at the same pH. The decomposition of the assembly was rapid when the electrode potential was applied in pH 9 solutions, while the response was relatively slow in pH 10 and 11 solutions. All the results are rationalized on the basis of an electrochemically induced acidification of the local environment around the (avidin-ib-PEI)5 film on the Pt layer.

Complex buckling instability patterns of nanomembranes with encapsulated gold nanoparticle arrays

The nanomechanical properties of micropatterned nanomembranes containing gold nanoparticle microarrays were investigated with the buckling instability method. An unusual, complex pattern of buckling instability was observed for the nanoscale polymeric films under compressive stresses. An intriguing two-stage wrinkling was observed for these nanoscale films with spatially correlated instabilities. Two concurrent strain-dependent buckling modes were observed above a certain critical strain. Transformation from conventional transversal buckling mode to zigzag buckling is attributed to the development of the biaxial stress along the boundary lines for micropatterned areas. The binary buckling pattern observed here allowed the "one-shot" evaluation of the elastic moduli of two compositionally different regions (with and without gold nanoparticles).

Physics of polypeptide multilayer films

Polypeptide multilayer films are promising for the development of coatings for implant devices, biosensors, and artificial cells. This paper discusses aspects of the physics of these films. Three sub-topics in the physics of peptide adsorption in multilayer film assembly covered here are peptide structure at the film/solid support interface, adsorbed layer thickness, and dynamics of peptide adsorption. A synopsis of work in these areas is preceded by an introduction to the subject and a review of some aspects of polymer theory.

A molecular dynamics study of the physical basis of stability of polypeptide multilayer nanofilms

Electrostatic layer-by-layer assembly (LBL) is a versatile method of fabricating ultrathin multilayer films, coatings, and microcapsules from materials in solution, notably, oppositely charged polyelectrolytes in water. Polypeptides, a special type of polyelectrolyte, have recently shown promise for a range of applications in biotechnology and medicine, for example, artificial cells, drug delivery systems, cell/tissue scaffolds, artificial viruses, and implantable device coatings. Poly(L-lysine) (PLL) and poly(L-glutamic acid) (PLGA) at neutral pH are model oppositely charged polypeptides. Experimental studies have shown that PLL/PLGA multilayer films contain a substantial amount of beta-sheets. Here, we present findings of a molecular dynamics (MD) study of the physical basis of interaction between PLL and PLGA in multilayer film models. Simulations have been carried out to study structural and dynamical properties of PLL/PLGA aggregates in beta-sheet conformation. The results suggest that hydrophobic interactions, in addition to electrostatics interactions, play a significant role in PLL/PLGA multilayers. The preferred orientation of peptides in the beta-sheet structures is antiparallel within sheets and parallel between sheets. Intersheet hydrogen-bond formation is more likely the result of peptide association than the cause. The approach provides a general means to understand better how various types of noncovalent interactions contribute to the structure and stability of polypeptide multilayer films.

Quantal Self-Assembly of Polymer Layers in Polypeptide Multilayer Nanofilms

Simple molecular models predict key aspects of the "microscopic" assembly behavior of various peptide systems in the fabrication of multilayer films. Such films show substantial differences in density for different peptide systems. The data suggest that exponential film growth is possible in the absence of polymer diffusion and that "macroscopic" assembly behavior is more a function of peptide-peptide interactions than peptide sequence alone.

Visualizing the interaction between poly-L-lysine and poly(acrylic acid) microgels using microscopy techniques: effect of electrostatics and peptide size

The interaction between lightly cross-linked poly(acrylic acid) (pAA) microgels (50-150 microm in diameter) and poly-L-lysine (pLys) was studied as a function of pH, ionic strength, peptide size, and concentration. The swelling response and distribution of polypeptides within microgel particles was monitored by micromanipulator-assisted light microscopy and confocal laser scanning microscopy, while binding isotherms of pLys in the microgels were determined spectrophotometrically. Conformational changes of pLys were investigated by circular dichroism. The molecular weight of pLys was found to influence the degree of peptide-induced microgel deswelling, largely due to limitation of peptides larger than the effective network mesh size to penetrate the entire gel. Large peptides were concentrated within a surface layer of the gel particles, and at low ionic strength this dense surface layer was shown to act as a largely steric barrier for further penetration of compounds into the gel core. Small peptides, however, distributed evenly throughout the microgel particles and were able to create large microgel volume reductions. The deswelling of microgels increased with decreasing pH, while the uptake of pLys was significantly reduced at low pH. The effect of ionic strength on the interactions of pLys and oppositely charged pAA microgels was moderate and only pronounced for deswelling of gels at high pH. A significant increase in the alpha-helix content of pLys interacting with the oppositely charged microgels was observed for high molecular weight peptides, and the extent of alpha-helix formation was as expected more pronounced at high pH, i.e., at high charge density of the microgels but reduced charge density of the peptides.

Polyelectrolyte Films Based on Polysaccharides of Different Conformations: Effects on Multilayer Structure and Mechanical Properties

Ultrathin films were prepared with cationic poly(allylamine hydrochloride) (PAH) and two anionic polysaccharides, iota- and lambda-carrageenan, of similar chemical composition but different conformations using the layer-by-layer (LbL) technique. The study of aqueous solutions of carrageenans confirms that iota-carrageenan is at room temperature in helical conformation while lambda-carrageenan is in random coil conformation. Characterization of the multilayers by ellipsometry, circular dichroism, and AFM revealed that iota-carrageenan keeps its helical conformation within the films while lambda-carrageenan chains are in random coil conformation. Investigation of the mechanical properties of the films by performing nanoindentation experiments using force spectroscopy showed clear differences between the two films based on carrageenans of different conformations.