Dissipative Quartz Crystal Microbalance Research Articles

The effect of typical seawater cations on the adhesion of mussel protein Mefp-1 based on dissipative quartz crystal microbalance

The effect of typical seawater cations on the adhesion of mussel protein Mefp-1 based on dissipative quartz crystal microbalance

Conjugation of coconut protein with ferulic acid promotes interfacial adsorption and mitigates lipid oxidation in O/W emulsion

The formation of small droplets in emulsion systems promotes lipid oxidation, affecting their shelf life. In this study, ferulic acid was covalently grafted onto coconut protein (CPI) through alkaline treatment method. The structural characteristics, interfacial properties, emulsifying properties, and oxidative stability of emulsions prepared by coconut protein-ferulic acid covalent complexes (CPF) were investigated. The results showed that covalent grafting of ferulic acid could change the physicochemical properties of coconut protein, including altering protein secondary and tertiary structures, enhancing the absolute value of zeta potential and antioxidant activity [2, 2-diphenyl-1-picrylhydrazyl (DPPH•) and 2, 2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS•+)]. Meanwhile, the interfacial behavior of CPI and CPF was characterized by dissipative quartz crystal microbalance and dilatational rheology analysis. Compared to CPI, CPF could diffuse to the oil-water interface quickly (from 0.084 ± 0.002 to 0.154 ± 0.003 mN/m/s1/2), and formed a thick interfacial layer dominated by elasticity, which enhanced the centrifugal stability of CPF-stabilized emulsions and effectively inhibited lipid oxidation within a 15-day storage period. Our results clearly demonstrated that coconut protein-ferulic acid conjugated complexes could improve emulsion stability and mitigate lipid oxidation, owing to the strong electrostatic repulsion interaction and high diffusion rate at interface. These findings may provide comprehensive insights for the further design and development of protein-polyphenol covalent complexes in the food industry.

Saccharin Sodium Coupling Fluorinated Solvent Enabled Stable Interface for High-Voltage Li-Metal Batteries.

Optimizing the electrode/electrolyte interface structure is the key to realizing high-voltage Li-metal batteries (LMBs). Herein, a functional electrolyte is introduced to synergetically regulate the interface layer structures on the high-voltage cathode and the Li-metal anode. Saccharin sodium (NaSH) as a multifunctional electrolyte additive is employed in fluorinated solvent-based electrolyte (FBE) for robust interphase layer construction. On the one hand, combining the results of ex-situ techniques and in-situ electrochemical dissipative quartz crystal microbalance (EQCM-D) technique, it can be seen that the solid electrolyte interface (SEI) layer constructed by NaSH-coupled fluoroethylene carbonate (FEC) on Li-metal anode significantly inhibits the growth of lithium dendrites and improves the cyclic stability of the anode. On the other hand, the experimental results also confirm that the cathode-electrolyte interface (CEI) layer induced by NaSH-coupled FEC effectively protects the active materials of LiCoO2 and improves their structural stability under high-voltage cycling, thus avoiding the material rupture. Moreover, theoretical calculation results show that the addition of NaSH alters the desolvation behavior of Li+ and enhances the transport kinetics of Li+ at the electrode/electrolyte interface. In this contribution, the LiCoO2ǁLi full cell containing FBE+NaSH results in a high capacity retention of 80% after 530 cycles with a coulombic efficiency of 99.8%.

Development of high internal phase emulsions using coconut protein isolates modified by pulsed light: Relationship of interfacial behavior and emulsifying stability

Protein-stabilized high internal phase emulsions (HIPEs) are attracting considerable attention in the food industry. Herein, we reported a simple method to fabricate HIPEs by modifying coconut protein isolates. Coconut protein isolates were extracted using isoelectric precipitation, and modified by low-intensity pulsed light (0.76 W/cm2/nm). The influence of protein concentration (1–4%, w/v) on interfacial adsorption behavior was analyzed by dissipative quartz crystal microbalance and interfacial dilatational rheology. The results indicated that the increase of concentration was beneficial to form a thick and more elastic interfacial layer at oil-water interface for modified coconut protein isolates by pulsed light (PCPI). At high concentration, the interfacial layer exhibited the better ability to resist the perturbation of amplitude and frequency sweep. In addition, HIPEs could be stabilized by PCPI solely, all emulsions were dispersed well. Apart from the emulsion stabilized by 1% PCPI, other HIPEs exhibited a gel-like behavior when the containers were inverted. Increasing protein concentration caused a decrease in emulsion particle size, and rheological analysis showed that the viscosity of HIPEs was positively correlated with the content of PCPI. Moreover, the HIPEs stabilized by PCPI exhibited better centrifugal stability. This study demonstrated that coconut protein isolates could be an efficient stabilizer to prepare HIPEs after simple modification, which was useful for developing applications of coconut protein.

Role of interfacial flexibility in emulsifying ability of coconut protein isolate remodeled by pulsed light coupled with weak alkali cycling treatment

The interfacial flexibility of proteins is a crucial factor that affects their functional properties. In this study, we investigated the role of interfacial flexibility in the emulsifying ability of coconut protein isolate (CPI) treated by pulsed light coupled with weak alkali cycling (pH 7 → 9 → 7). After treatment, the structure of CPI was unfolded and re-folded, which resulted in the exposure of hydrophobic groups and the formation of smaller aggregates, with the change of secondary structure. Additionally, the S–S bond content increased while the free –SH content decreased. The interfacial flexibility of CPI-based samples at the oil-water interface was evaluated by dissipative quartz crystal microbalance and interfacial dilatational rheology. Compared to CPI, PCPI-9 (CPI treated by pulsed light coupled with pH 9 cycling) possessed a greater viscoelastic modulus and a smaller relaxation time. Meanwhile, the anti-perturbation ability was better than CPI. Then, microstructure, centrifugal stability and emulsifying properties of the O/W emulsions stabilized by CPI-based samples were measured. The results showed that emulsion stabilized by PCPI-9 had significant advantages in long-term stability. The emulsification stability (ESI) increased by 25.45 times compared to CPI. In conclusion, moderate pulsed light coupled with weak alkali cycling treatment could improve the emulsifying ability of CPI by remodeling its structure to change the interfacial flexibility. These results could provide an in-depth insight into the relationship between interfacial flexibility and emulsifying properties of coconut protein isolate.

Designed Multifunctional Isopeptide for Enhanced Annexin A1 Biosensing Based on Peptide-Protein Interactions in Human Blood.

Specific peptide-protein interactions play an important role in biosensing systems based on functional peptides; however, the non-specific interactions with unrelated biomolecules and poor proteolytic stability restrict the clinical application of natural peptides. Here, we leveraged a self-designed multifunctional isopeptide (MISP) to construct an electrochemical biosensing platform for annexin A1 (ANXA1) detection in human blood. The MISP was designed to contain two parts: an antifouling cyclotide cyclo-C(EK)4 and a d-amino acid-containing carbohydrate-mimetic recognizing peptide IF-7 (D-IF7) connected by the isopeptide bond. We have discussed the properties of the cyclotide and illustrated its unique advantage over the natural linear antifouling peptides by molecular dynamics simulations, and the results were further confirmed by dissipative quartz crystal microbalance (QCM-D). In addition, through electrochemical experiments and fluorescence imaging experiments, we demonstrated that the MISP-based biosensor possessed excellent antifouling ability and proteinase hydrolysis stability. Interestingly, the assaying results of the MISP-biosensor were consistent with those of the commercial ANXA1 kits in a variety of healthy and ANXA1-upregulated clinical blood samples, and, more importantly, for the analysis of blood samples with lower ANXA1 expressions, the sensing capability of the biosensor was greatly superior to that of the kits because of the lower detection limit of the MISP-biosensor. This biosensing platform based on the designed MISP offers enormous potential for achieving accurate biomarker detection with robust operation in complex biological samples.

The interfacial behavior and long-term stability of emulsions stabilized by gum arabic and sugar beet pectin

Gum arabic (GA) is the most widely used natural emulsifier in food industry. However, due to its high price and unstable market supply, the search for substitutes of gum arabic has attracted the attention of researchers. Recent studies have shown that sugar beet pectin (SBP) has great potential as a natural emulsifier. However, the mechanisms and differences of GA- and SBP-stabilized emulsions are still unclear. In this study, the interfacial behavior of GA and SBP on the oil-water interface was studied and compared through dissipative quartz crystal microbalance and interfacial dilatational rheology. Then, droplet size, zeta-potential and viscosity of the emulsion stabilized by GA and SBP were measured. Meanwhile, the long-term stability of GA- and SBP-stabilized emulsions was evaluated and compared through a LUMiSizer stability analyzer. The study showed that at the same concentration, SBP-stabilized emulsion had significant advantages of a smaller droplet size, a larger viscosity, a thicker and more elastic interfacial layer, and better long-term stability. A comparison of the long-term stability of SBP2.0%- and GA15.0%-stabilized emulsions, evidenced that the elasticity of the interfacial layer plays a crucial role in the long-term stability of emulsions. This research may provide useful information for finding alternatives to GA.

Study on the mechanism of rapid formation of ultra-thick tribofilm by CeO2 nano additive and ZDDP

CeO2 nanoparticles are potential anti-wear additives because of their outstanding anti-wear and load-bearing capacity. However, the shear-sintering tribo-film formation mechanism of oxide nanoparticles limits the tribo-film formation rate and thickness greatly. In this study, by compounding with zinc dioctyl dithiophosphate (ZDDP), ultra-fine CeO2 nanoparticles modified with oleylamine (OM) can quickly form 2 µm ultra-thick tribo-film, which is 10–15 times thicker than that of ZDDP and CeO2, respectively. The ultra-thick tribo-film presents a nanocomposite structure with amorphous phosphate as binder and nano-CeO2 as filling phase, which leads to the highest loading capacity of composite additives. The results of adsorption experiments tested by dissipative quartz crystal microbalance (QCM-D) showed that the PB value of additive has nothing to do with its equilibrium adsorption mass, but is directly proportional to its adsorption rate in 10 s. The compound additive of CeO2 and ZDDP presented the co-deposition mode of ZDDP monolayer rigid adsorption and CeO2 viscoelastic adsorption on the metal surface, which showed the highest adsorption rate in 10 s. It is found that the tribo-film must have high film forming rate and wear resistance at the same time in order to achieve super thickness. Cerium phosphate was formed from ZDDP and CeO2 through tribochemistry reaction, which promotes the formation of an ultra-thick tribo-film with nanocomposite structure, which not only maintains the low friction characteristics of CeO2, but also realizes high PB and high load-carrying capacity.

Relationships between the behavior of three different sources of pectin at the oil-water interface and the stability of the emulsion

In this study, structural characterization and chemical compositions of three pectins from different sources were studied, which showed that compared with apple pectin (AP) and citrus peel pectin (CPP), sugar beet pectin (SBP) has higher protein contents, feruloylated groups, acetyl groups and more hairy regions. Molecular dynamics simulations showed that HG domain was tiled on the oil-water interface, while RG-Ⅰ and RG-Ⅱ domains were adsorbed on the oil-water interface in a folded form, resulting in a thick viscoelastic film. Dissipative quartz crystal microbalance (QCM-D) and dilatational rheology studies showed that under high-concentration and acidic conditions, pectin molecules were adsorbed in multiple layers at the oil-water interface, forming a thicker viscoelastic film, which was crucial for the long-term stability of pectin-stabilized emulsions.

Protein–Ligand interactions for hydrophobic charge-induction chromatography: A QCM-D study

Hydrophobic charge-induction chromatography (HCIC) is a novel technology for antibody purification. The interaction between immunoglobulin G (IgG) and HCIC ligands was investigated by dissipative quartz crystal microbalance (QCM-D). HCIC ligands 2-mercapto-1-methylimidazole (MMI), 2-mercaptobenzimidazole (MBI) and 2-mercapto-4-methylpyrimidine hydrochloride (MMp) were coupled to the surface of a self-assembled monolayer (SAM) terminated by epoxy groups. The ellipsometric ligand densities of MMI, MBI and MMp on the SAMs were 1.54, 1.64 and 1.47 chain/nm2, respectively. QCM results indicated the Au–MBI sensor to exhibit excellent performance in IgG adsorption compared with other sensors, with a maximum adsorption capacity of 1601 ng/nm2 and a dissociation constant of 2.84 × 10−6 M. The structure of the adsorbed IgG layer changed as a result of changes in the pH of the protein buffer and the addition of free and stable salts, probably due to changes in IgG conformation. According to Au–MBI surface regeneration experiments, the degree of regeneration afforded by NaOH 0.1 M was 99.7%. The QCM-D platform based on SAMs proved to be a powerful tool for studying ligand–protein interactions and the structures of protein adsorption layers. This study provides accurate theoretical guidance for the practical application of protein adsorption and antibody purification procedures.

Cholesterol Hinders the Passive Uptake of Amphiphilic Nanoparticles into Fluid Lipid Membranes.

Plasma membranes represent pharmacokinetic barriers for the passive transport of site-specific drugs within cells. When engineered nanoparticles (NPs) are considered as transmembrane drug carriers, the plasma membrane composition can affect passive NP internalization in many ways. Among these, cholesterol-regulated membrane fluidity is probably one of the most biologically relevant. Herein, we consider small (2–5 nm in core diameter) amphiphilic gold NPs capable of spontaneously and nondisruptively entering the lipid bilayer of plasma membranes. We study their incorporation into model 1,2-dioleoyl-sn-glycero-3-phosphocholine membranes with increasing cholesterol content. We combine dissipative quartz crystal microbalance experiments, atomic force microscopy, and molecular dynamics simulations to show that membrane cholesterol, at biologically relevant concentrations, hinders the molecular mechanism for passive NP penetration within fluid bilayers, resulting in a dramatic reduction in the amount of NP incorporated.

Investigating Adsorption of Naphthalene to Organo-Modified Montmorillonites and Influencing Factors

There are many sites contaminated by polycyclic aromatic hydrocarbons (PAHs) or combined PAHs-heavy metal in China, which pose serious health-risks to local people and environments. Dissipative quartz crystal microbalance (QCM-D) was applied to investigate the adsorption of naphthalene to two organic-modified smectite clays (cetyltrimethyl ammonium bromide modified montmorillonite, CTAB-SMF, and 3-mercapto propyl trimethoxy silane modified montmorillonite, TMSP-SMF) and original SMF, together with batch adsorption experiments. The results, based on in-situ online QCM-D experiments, showed that the adsorption sites of CTAB-SMF on naphthalene were mainly CTAB grouped between the interlayers of clay particles, while TMSP-SMF's were TMSP grouped on the surfaces of clay particles. The isotherms of naphthalene adsorption to CTAB-SMF fitted well (R2>0.92) with the Freundlich model, while the adsorption isotherms to TMSP-SMF and SMF fitted well with the Langmuir model (R2>0.96). The parameters of CTAB-SMF (n>1) indicated that the adsorption sites of naphthalene to CTAB-SMF were heterogeneous and the adsorption increases at higher equilibrium concentration. The adsorption capacity qmax of TMSP-SMF is significantly greater than that of SMF (P<0.05). Based on the calculation, the value of ΔHobs for these three clays (CTAB-SMF, TMSP-SMF, and SMF) were within the range of -30 to -10 kJ·mol-1, which indicated that it was a spontaneous exothermic physical process. The solution ionic strength could decrease the adsorption of naphthalene to SMF, but had limited effects on naphthalene adsorption to the two organo-modified clay particles. The existence of Cu2+ in the solution could enhance naphthalene adsorption to the three particles, and naphthalene could improve Cu2+ adsorption to these two modified clays. The results of this study show that QCM-D is a useful technique to indicate the changes of clay film during the process of adsorption, and the two organo-modified clay particles have the potential to be remediation materials to remediate PAHs or PAHs-heavy metal-contaminated sites.

Effect of electrolytes on interactions between a novel organic-inorganic hybrid polymer flocculant and kaolinite particles

A novel copolymer, Al(OH)3-poly[N-isopropylacrylamide-co-N-[3-(Dimethylamino)propyl]methacrylamide] polyacrylamide (Al(OH)3-p[NIPAM-co-PMADMA]) was synthesized and characterized. The flocculation behavior of fine kaolinite by the temperature-responsive copolymer in different electrolyte solutions was studied by settling tests, measurements of lower critical solution temperature (LCST) and dissipative quartz crystal microbalance (QCM-D). The solution salinity and the type of electrolytes were shown to play a critical role in controlling the interactions between the synthesized flocculants and kaolinite particles. The initial settling rate (ISR) of kaolinite suspension increased initially and then decreased with further increasing the electrolyte concentration of NaCl, CaCl2, NaH2PO4 or Na2CO3. At low electrolyte concentrations, the electrolyte addition increased the adsorption of polymer on kaolinite particles. The effect of electrolyte addition on kaolinite flocculation followed the trend of Na2CO3＞CaCl2＞NaH2PO4＞NaCl, which can be described by the classical DLVO theory. However, the higher concentration of electrolytes led to a weaker adsorption and more compressed conformations of Al(OH)3-p[NIPAM-co-PMADMA] chains on both silica and alumina surfaces which mimic two types of kaolinite basal planes. The salting-out effect was found to be an important reason for polymer phase transfer, which inhibited the flocculation performance at higher electrolyte concentrations.

Viscoelastic Properties of Polyelectrolyte Multilayers Swollen with Ionic Liquid Solutions.

Polyelectrolyte multilayers (PEM) obtained by layer-by-layer assembly can be doped with ionic liquid (IL) via the swelling of the films with IL solutions. In order to examine the mechanical properties of IL-containing PEM, we implement a Kelvin-Voigt model to obtain thickness, viscosity and elastic modulus from the frequency and dissipation shifts determined by a dissipative quartz crystal microbalance (QCM-D). We analyze the changes in the modeled thickness and viscoelasticity of PEI(PSS/PADMAC)4PSS and PEI(PSS/PAH)4PSS multilayers upon swelling by increasing the concentration of either 1-Ethyl-3-methylimidazolium chloride or 1-Hexyl-3-methylimidazolium chloride, which are water soluble ILs. The results show that the thickness of the multilayers changes monotonically up to a certain IL concentration, whereas the viscosity and elasticity change in a non-monotonic fashion with an increasing IL concentration. The changes in the modeled parameters can be divided into three concentration regimes of IL, a behavior specific to ILs (organic salts), which does not occur with swelling by simple inorganic salts such as NaCl. The existence of the regimes is attributed to a competition of the hydrophobic interactions of large hydrophobic ions, which enhance the layer stability at a low salt content, with the electrostatic screening, which dominates at a higher salt content and causes a film softening.

Research progress in the characterization of protein adsorption on biomaterial surface

The characterization methods in the field of protein adsorption on biological materials in recent years were reviewed from the aspects of protein adsorption amount, adsorption layer thickness, molecular conformational change after protein adsorption, molecular morphology after protein adsorption, and protein molecule adsorption process simulation. These methods include biochemical analysis, surface plasmon resonance (SPR), dissipative quartz crystal microbalance (QCM-D), ellipsometry (ELM), optical interference reflection (RIFS), attenuated total reflection Fourier transformed infrared spectroscopy (ATR-FTIR), circular dichroism (CD), atomic force microscopy (AFM) and computer molecular simulation techniques. In this paper, the basic principles, the advantages and disadvantages of the above characterization methods and related researches were reviewed. This paper provides a comprehensive and reliable basis for the selection of protein experimental characterization methods in protein adsorption, biomaterial design and other research, and provides new ideas for research in the field of protein. Key words: Protein; Adsorption; Biomaterial; Characterization

Dissipative Microgravimetry to Study the Binding Dynamics of the Phospholipid Binding Protein Annexin A2 to Solid-supported Lipid Bilayers Using a Quartz Resonator.

The dissipative quartz crystal microbalance technique is a simple and label-free approach to measure simultaneously the mass uptake and viscoelastic properties of the absorbed/immobilized mass on sensor surfaces, allowing the measurements of the interaction of proteins with solid-supported surfaces, such as lipid bilayers, in real-time and with a high sensitivity. Annexins are a highly conserved group of phospholipid-binding proteins that interact reversibly with the negatively charged headgroups via the coordination of calcium ions. Here, we describe a protocol that was employed to quantitatively analyze the binding of annexin A2 (AnxA2) to planar lipid bilayers prepared on the surface of a quartz sensor. This protocol is optimized to obtain robust and reproducible data and includes a detailed step-by-step description. The method can be applied to other membrane-binding proteins and bilayer compositions.

Dissipative Microgravimetry to Study the Binding Dynamics of the Phospholipid Binding Protein Annexin A2 to Solid-supported Lipid Bilayers Using a Quartz Resonator

The dissipative quartz crystal microbalance technique is a simple and label-free approach to measure simultaneously the mass uptake and viscoelastic properties of the absorbed/immobilized mass on sensor surfaces, allowing the measurements of the interaction of proteins with solid-supported surfaces, such as lipid bilayers, in real-time and with a high sensitivity. Annexins are a highly conserved group of phospholipid-binding proteins that interact reversibly with the negatively charged headgroups via the coordination of calcium ions. Here, we describe a protocol that was employed to quantitatively analyze the binding of annexin A2 (AnxA2) to planar lipid bilayers prepared on the surface of a quartz sensor. This protocol is optimized to obtain robust and reproducible data and includes a detailed step-by-step description. The method can be applied to other membrane-binding proteins and bilayer compositions.

PH-Responsive Host⁻Guest Complexation in Pillar[6]arene-Containing Polyelectrolyte Multilayer Films.

A water-soluble, anionic pillar[6]arene derivative (WP6) is applied as monomeric building block for the layer-by-layer self-assembly of thin polyelectrolyte multilayer films, and its pH-dependent host–guest properties are employed for the reversible binding and release of a methylviologen guest molecule. The alternating assembly of anionic WP6 and cationic diazo resin (DAR) is monitored in-situ by a dissipative quartz crystal microbalance (QCM-D). In solution, the formation of a stoichiometric inclusion complex of WP6 and cationic methylviologen (MV) as guest molecule is investigated by isothermal titration calorimetry and UV-vis spectroscopy, respectively, and attributed to electrostatic interactions as primary driving force of the host–guest complexation. Exposure of WP6-containing multilayers to MV solution reveals a significant decrease of the resonance frequency, confirming MV binding. Subsequent release is achieved by pH lowering, decreasing the host–guest interactions. The dissociation of the host–guest complex, release of the guest from the film, as well as full reversibility of the binding event are identified by QCM-D. In addition, UV-vis data quantify the surface coverage of the guest molecule in the film after loading and release, respectively. These findings establish the pH-responsiveness of WP6 as a novel external stimulus for the reversible guest molecule recognition in thin films.

Interactions of Aqueous Imidazolium-Based Ionic Liquid Mixtures with Solid-Supported Phospholipid Vesicles.

Despite the environmentally friendly reputation of ionic liquids (ILs), their safety has been recently questioned given their potential as cytotoxic agents. The fundamental mechanisms underlying the interactions between ILs and cells are less studied and by far not completely understood. Biomimetic films are here important biophysical model systems to elucidate fundamental aspects and mechanisms relevant for a large range of biological interaction ranging from signaling to drug reception or toxicity. Here we use dissipative quartz crystal microbalance QCM-D to examine the effect of aqueous imidazolium-based ionic liquid mixtures on solid-supported biomimetic membranes. Specifically, we assess in real time the effect of the cation chain length and the anion nature on a supported vesicle layer of the model phospholipid DMPC. Results indicate that interactions are mainly driven by the hydrophobic components of the IL, which significantly distort the layer and promote vesicle rupture. Our analyses evidence the gradual decrease of the main phase transition temperature upon increasing IL concentration, reflecting increased disorder by weakening of lipid chain interactions. The degree of rupture is significant for ILs with long hydrophobic cation chains and large hydrophobic anions whose behavior is reminiscent of that of antimicrobial peptides.

Adsorption of poly(diallyldimethylammonium chloride)—sodium methyl-cocoyl-taurate complexes onto solid surfaces

The study of the adsorption of supramolecular complexes formed by a highly charged cationic homopolymer (poly(diallyldimethylammonium chloride), PDADMAC), and a sulfate-free anionic surfactant, sodium methyl cocoyl taurate (SMCT), on liquid/solid interfaces was performed by dissipative quartz crystal microbalance, ellipsometry and atomic force microscopy. Moreover, turbidimetry, dynamic light scattering and ζ-potential measurements were carried out to characterize the bulk solutions. The complexes adsorb onto the solid surfaces, leading to inhomogeneous films formed by isolated aggregates randomly distributed through the surface. Additionally, the adsorption kinetics of the bulk complexes onto the negatively charged surface was studied. This work aims to understand the physico—chemical mechanisms involved in the adsorption of polycation—negatively charged surfactant mixtures, interesting for the design of conditioner cosmetic formulations, onto negatively charged surfaces. It is expected that the results here obtained may provide a better understanding of the conditioning effect of cosmetic products on keratinic (hair) substrates.