Anion-Specific Effects on the Assembly of Collagen Layers Mediated by Magnesium Ion on Mica Surface

Critical Roles of Acidic Residues in Loop Regions of the Structural Surface for the Salt Tolerance of a GH39 β-d-Xylosidase

Xylan is the main component of hemicellulose. Complete hydrolysis of xylan requires synergistically acting xylanases, such as β-d-xylosidases. Salt-tolerant β-d-xylosidases have significant application benefits, but few reports have explored the critical amino acids affecting the salt tolerance of xylosidases. Herein, the site-directed mutation was used to demonstrate that negative electrostatic potentials generated by 19 acidic residues in the loop regions of the structural surface positively correlated with the improved salt tolerance of GH39 β-d-xylosidase JB13GH39P28. These mutants showed reduced negative potentials on structural surfaces as well as a 13-43% decrease in stability in 3.0-30.0% (w/v) NaCl. Six key residue sites, D201, D259, D297, D377, D395, and D474, were confirmed to influence both the stability and activity of GH39 β-d-xylosidase. The activity of the GH39 β-d-xylosidase was found promoting by SO42- and inhibiting by NO3-. Values of Km and Kcat/Km decreased aggravatedly in 30.0% (w/v) NaCl when mutation operated on residues E179 and D182 in the loop regions of the catalytic domain. Taken together, mutation on acidic residues in loop regions from catalytic and noncatalytic domains may cause the deformation of catalytic pocket and aggregation of protein particles then decrease the stability, binding affinity, and catalytic efficiency of the β-d-xylosidase.

pH-dependent interactions of biologically important metal ions with hen egg white lysozyme based on its hydration properties: Thermodynamic and mechanistic insights

Importance of metal ion selectivity in biomolecules and their key role in proteins are widely explored. However, understanding the thermodynamics of how hydrated metal ions alter the protein hydration and their conformation is also important. In this study, the interaction of some biologically important Ca2+, Mn2+, Co2+, Cu2+, and Zn2+ ions with hen egg white lysozyme at pH 2.1, 3.0, 4.5 and 7.4 has been investigated. Intrinsic fluorescence studies have been employed for metal ion-induced protein conformational changes analysis. Thermostability based on protein hydration has been investigated using differential scanning calorimetry (DSC). Thermodynamic parameters emphasizing on metal ion-protein binding mechanistic insights have been well discussed using isothermal titration calorimetry (ITC). Overall, these experiments have reported that their interactions are pH-dependent and entropically driven. This research also reports the strongly hydrated metal ions as water structure breaker unlike osmolytes based on DSC studies. These experimental results have highlighted higher concentrations of different metal ions effect on the protein hydration and thermostability which might be helpful in understanding their interactions in aqueous solutions.

Curcumin-based nanoformulations alleviate wounds and related disorders: A comprehensive review

Despite numerous advantages, curcumin's (CUR) low solubility and low bioavailability limit its employment as a free drug. CUR-incorporated nanoformulation enhances the bioavailability and angiogenesis, collagen deposition, fibroblast proliferation, reepithelization, collagen synthesis, neovascularization, and granulation tissue formation in different wounds. Designing nanoformulations with controlled-release properties ensure the presence of CUR in the defective area during treatment. Different nanoformulations encompassing nanofibers, nanoparticles (NPs), nanospray, nanoemulsion, nanosuspension, nanoliposome, nanovesicle, and nanomicelle were described in the present study comprehensively. Moreover, for some other systems which contain nano-CUR or CUR nanoformulations, including some nanofibers, films, composites, scaffolds, gel, and hydrogels seems the CUR-loaded NPs incorporation has better control of the sustained release, and thereby, the presence of CUR until the final stages of wound healing is more possible. Incorporating CUR-loaded chitosan NPs into nanofiber increased the release time, while 80% of CUR was released during 240 h (10 days). Therefore, this system can guarantee the presence of CUR during the entire healing period. Furthermore, porous structures such as sponges, aerogels, some hydrogels, and scaffolds disclosed promising performance. These architectures with interconnected pores can mimic the native extracellular matrix, thereby facilitating attachment and infiltration of cells at the wound site, besides maintaining a free flow of nutrients and oxygen within the three-dimensional structure essential for rapid and proper wound healing, as well as enhancing mechanical strength.

LL37 and collagen-binding domain-mediated LL37 binding with type I collagen: Quantification via QCM-D

Antimicrobial peptide (AMP)-loaded biomaterials may represent a viable alternative for stimulating wound healing while protecting against infections. Previously, to develop an efficient delivery system for the cathelicidin antimicrobial peptide, LL37, our lab modified LL37 with a collagen-binding domain derived from collagenase (cCBD) as an anchoring unit to collagen-based wound dressings. However, a direct quantification of unmodified LL37 and cCBD-LL37 binding with collagen has not been performed. In this study, we used quartz crystal microbalance with dissipation monitoring (QCM-D), immunohistochemistry (IHC), and atomic force microscopy (AFM) to establish and characterize an adsorbed layer of type I collagen on the QCM-D sensor and quantify peptide-collagen binding. A collagen deposition protocol was successfully established by measuring concentration-dependent deposition of collagen in QCM-D, and collagen self-assembly was observed by IHC and AFM. Hydrophobicity is known to affect the behavior of collagen adsorption. Therefore, we compared the deposition of collagen on hydrophilic SiO₂-coated sensors vs. hydrophobic polystyrene (PS)-coated sensors via QCM-D, and found that the hydrophobic surface yielded more collagen adsorption, which suggested that hydrophobic surfaces are preferable for collagen layer establishment. There was no significant difference between LL37 and cCBD-LL37 binding with collagen, but the cCBD-LL37 showed better retention on the collagen after washing with PBS, indicating that there is an advantage to using cCBD as an anchoring unit to collagen. Collectively, these results provide important information on cCBD-mediated AMP-binding mechanisms and establish an effective method for quantifying peptide-collagen binding.

The chaotropic effect of ions on the self-aggregating propensity of Whitlock's molecular tweezers

Molecular tweezers feature the first class of artificial receptors to pique the interest of researchers and emerge as an effective therapeutic candidate. The exceptional structure and exquisite binding specificity of tweezers establish this overall class of receptors as a promising tool, with abundant applications. However, their inclination to self-aggregate by mutual π-π stacking interactions of their aromatic arms diminishes their efficacy as a therapeutic candidate. Therefore, following up on sporadic studies, since the discovery of the Hofmeister series, on the ability of ions to either solvate (salting-in) or induce aggregation (salting-out) of hydrophobic solutes, the notions of ion-specificity effects are utilized on tweezer moieties. The impacts of three different aluminum salts bearing anions Cl^-, ClO₄^- and SCN^- on the self-association propensity of Whitlock's caffeine-pincered molecular tweezers are investigated, with a specific emphasis placed on elucidating the varied behavior of the ions on the hydration ability of tweezers. The comparative investigation is conducted employing a series of all-atom molecular dynamics simulations of five tweezer molecules in pure water and three salt solutions, at two different concentrations each, maintaining a temperature of 300 K and a pressure of 1 atm, respectively. Radial distribution functions, coordination numbers, and SASA calculations display a steady reduction in the aggregation proclivity of the receptor molecules with an increase in salt concentration, as progressed along the Hofmeister series. Orientational preferences between the tweezer arms reveal a disruptive effect in the regular π-π stacking interactions, in the presence of high concentrations of ClO₄^- and SCN^- ions, while preferential interactions and tetrahedral order parameters unveil the underlying mechanism, by which the anions alter the solubility of the hydrophobic molecules. Overall, it is observed that SCN^- exhibits the highest salting-in effect, followed by ClO₄^-, with both anions inhibiting tweezer aggregation through different mechanisms. ClO₄^- ions impart an effect by moderately interacting with the solute molecules as well as modifying the water structure of the bulk solution promoting solvation, whereas, SCN^- ions engage entirely in interaction with specific tweezer sites. Cl^- being the most charge-dense of the three anionic species experiences stronger hydration and therefore, imparts a very negligible salting-in effect.

Hofmeister Effect Mediated Strong PHEMA-Gelatin Hydrogel Actuator

Hydrogels have become popular in biomedical applications, but their applications in muscle and tendon-like bioactuators have been hindered by low toughness and elastic modulus. Recently, a significant toughness enhancement of a single hydrogel network has been successfully achieved by the Hofmeister effect. However, little has been conducted for the Hofmeister effect on the hybrid hydrogels, although they have a special network structure consisting of two types of polymer components. Herein we fabricated hybrid poly(2-hydroxyethyl methacrylate) (PHEMA)-gelatin hydrogels with high mechanical performance and stimuli response. An ideal bicontinuous phase separation structure of the PHEMA (rigid) and gelatin (ductile) was observed with embedded microdisc-like gelatin in the three-dimensional polymeric network of PHEMA. A significant enhancement of mechanical performance by the Hofmeister effect was attributed to the salting-out-induced stronger and closer interphase interaction between PHEMA and gelatin. A superior comprehensive mechanical performance with fracture elongation over 650%, tensile strength of 5.2 MPa, toughness of 13.5 MJ/m3, and modulus of 45.6 MPa was achieved with the salting-out effect. More specifically, the synergy of phase separation and Hofmeister effect enable the hydrogel to contract with an enhanced modulus in high-concentration salt solutions, while the same hydrogel swells and relaxes in dilute solutions, exhibiting an ionic stimulus response and excellent shape-memory properties like those of most artificial muscle. This is manifested in highly stretched, twisted, and knotted hydrogel strips that can rapidly recover their original shape in a dilute salt solution. The high strength and modulus, ionic stimuli response, and shape memory property make the hybrid hydrogel a promising material for bioactuators in various biomedical applications.

Self-assembly of collagen fibrils on graphene oxide and their hybrid nanocomposite films

In order to explore the distribution, conformation and interaction of collagen on GO nanosheet surfaces, the mechanism of self-assembly of collagen was investigated in the presence of GO nanosheets. Atomic force microscopy (AFM) was employed to observe the conformation of self-assembled collagen fibrils on the GO nanosheets surfaces. The collagen concentration and incubation time mainly affect the size of the collagen fibrils while the pH of the dispersion determines the self-assembly sites of collagen fibrils on the GO nanosheets surfaces. This pH-dependent adsorption is attributed to the interfacial interactions between the tunable ionization of the collagen molecules and the amphiphilic GO nanosheets. Vacuum-assisted self-assembly technology confirmed that GO nanosheets can direct the self-assembly of collagen molecules and form nacre-like nanocomposites. The GO/collagen nanocomposite films combine the remarkable properties of GO nanosheets and collagen to form functional nanocomposites with well-ordered hierarchical structures. Further, strong interfacial interactions between GO nanosheets with collagen fibrils result in enhanced mechanical properties and biocompatibility of nanocomposite films, which is conducive to enhance the neuronal differentiation of SH-SY5Y cells. Overall, this work provides fresh insight into the interactions between GO and collagen, which is essential for the design and manufacture of bioinspired nanocomposites with tailored mechanical properties.

Uncovering a Universal Molecular Mechanism of Salt Ion Adsorption at Solid/Water Interfaces

Solid/water interfaces, in which salt ions come in close proximity to solids, are ubiquitous in nature. Because water is a polar solvent and salt ions are charged, a long-standing puzzle involving solid/water interfaces is how do the electric fields exerted by the salt ions and the interfacial water molecules polarize the charge distribution in the solid and how does this polarization, in turn, influence ion adsorption at any solid/water interface. Here, using state-of-the-art polarizable force fields derived from quantum chemical simulations, we perform all-atomistic molecular dynamics simulations to investigate the adsorption of various ions comprising the well-known Hofmeister series at the graphene/water interface, including comparing with available experimental data. Our findings reveal that, in vacuum, the ionic electric field-induced polarization of graphene results in a significantly large graphene-ion polarization energy, which drives all salt ions to adsorb to graphene. On the contrary, in the presence of water molecules, we show that the ions and the water molecules exert waves of molecular electric fields on graphene which destructively interfere with each other. This remarkable phenomenon is shown to cause a water-mediated screening of more than 85% of the graphene-ion polarization energy. Finally, by investigating superhydrophilic and superhydrophobic model surfaces, we demonstrate that this phenomenon occurs universally at all solid/water interfaces and results in a significant weakening of the ion-solid interactions, such that ion specific effects are governed primarily by a competition between the ion-water and water-water interactions, irrespective of the nature of the solid/water interface.

Hofmeister Series: Insights of Ion Specificity from Amphiphilic Assembly and Interface Property

Hofmeister series (HS), ion specific effect, or lyotropic sequence acts as a pivotal part in a number of biological and physicochemical phenomena, e.g., changing the solubility of hydrophobic solutes, the cloud points of polymers and nonionic surfactants, the activities of various enzymes, the action of ions on an ion-channel, and the surface tension of electrolyte solutions, etc. This review focused on how ion specificity influences the critical micelle concentration (CMC) and how the thermoresponsive behavior of surfactants, and the dynamic transition of the aggregate, controls the aggregate transition and gel formation and tunes the properties of air/water interfaces (Langmuir monolayer and interfacial free energy). Recent progress of the ion specific effect in bulk phase and at interfaces in amphiphilic systems and gels is summarized. Applications and a molecular level theoretical explanation of HS are discussed comprehensively. This review is aimed to supply a fresh and comprehensive understanding of Hofmiester phenomena in surfactants, polymers, colloids, and interface science and to provide a guideline to design the microstructures and templates for preparation of nanomaterials.

Hydration of Hofmeister ions

Water dissolves salt into ions and then hydrates the ions to form an aqueous solution. Hydration of ions deforms the hydrogen bonding network and triggers the solution with what the pure water never shows such as conductivity, molecular diffusivity, thermal stability, surface stress, solubility, and viscosity, having enormous impact to many branches in biochemistry, chemistry, physics, and energy and environmental industry sectors. However, regulations for the solute-solute-solvent interactions are still open for exploration. From the perspective of the screened ionic polarization and O:H-O bond relaxation, this treatise features the recent progress and a perspective in understanding the hydration dynamics of Hofmeister ions in the typical YI, NaX, ZX₂, and NaT salt solutions (Y = Li, Na, K, Rb, Cs; X = F, Cl, Br, I; Z = Mg, Ca, Ba, Sr; T = ClO₄, NO₃, HSO₄, SCN). Phonon spectrometric analysis turned out the f(C) number fraction of bonds transition from the mode of deionized water to the hydrating. The linear f(C) ∝ C form features the invariant hydration volume of small cations that are fully-screened by their hydration H₂O dipoles. The nonlinear f(C) ∝ 1 - exp.(-C/C₀) form describes that the number insufficiency of the ordered hydrating H₂O dipoles partially screens the anions. Molecular anions show stronger yet shorter electric field of dipoles. The screened ionic polarization, inter-solute interaction, and O:H-O bond transition unify the solution conductivity, surface stress, viscosity, and critical energies for phase transition.

Cation-Specific Effects on the Self-Assembly of Collagen Molecules Mediated by Acetate on Mica Surface Observed with Atomic Force Microscopy

The well-organized collagen layers on mica surface have drawn extensive attention for its essential applications and studies on the process of self-assembly as a model system. In this work, collagen extracted from fish scales by acid-base method was used to explore the self-assembly characters, and atomic force microscopy was applied to observe the collagen assembled on mica surface mediated by acetate with four different cations, including K+, Na+, Mg2+, and Ca2+. It showed that cations might influence the interaction between collagen fibrils and mica surface at high ionic concentration. And a similar network structure was acquired with uniform pore size for four kinds of acetates; nearly ranged collagen fibrils in the same direction were collected in Mg2+ solutions, while flat films with some fibrils were achieved in K+ solutions. The Hofmeister series and Collins’ model were adapted to explain the effects of cations and acetate on the self-assembly of collagen. These results and analysis would be helpful for directing the pattern of collagen assembly on a solid surface with a potential application in food science and engineering.

Accessing the biocompatibility of layered double hydroxide by intramuscular implantation: histological and microcirculation evaluation

Biocompatibility of layered double hydroxides (LDHs), also known as hydrotalcite-like materials or double metal hydroxides, was investigated by in vivo assays via intramuscular tablets implantation in rat abdominal wall. The tablets were composed by chloride ions intercalated into LDH of magnesium/aluminum (Mg2Al-Cl) and zinc/aluminum (Zn2Al-Cl). The antigenicity and tissue integration capacity of LDHs were assessed histologically after 7 and 28 days post-implantation. No fibrous capsule nearby the LDH was noticed for both materials as well any sign of inflammatory reactions. Sidestream Dark Field imaging, used to monitor in real time the microcirculation in tissues, revealed overall integrity of the microcirculatory network neighboring the tablets, with no blood flow obstruction, bleeding and/or increasing of leukocyte endothelial adhesion. After 28 days Mg2Al-Cl promoted multiple collagen invaginations (mostly collagen type-I) among its fragments while Zn2Al-Cl induced predominantly collagen type-III. This work supports previous results in the literature about LDHs compatibility with living matter, endorsing them as functional materials for biomedical applications.

Magnesium Modifies the Structural Features of Enzymatically Mineralized Collagen Gels Affecting the Retraction Capabilities of Human Dermal Fibroblasts Embedded within This 3D System

Mineralized collagen gels have been developed as in vitro models to better understand the mechanisms regulating the calcification process and the behavior of a variety of cell types. The vast majority of data are related to stem cells and to osteoblast-like cells, whereas little information is available for dermal fibroblasts, although these cells have been associated with ectopic calcification and consequently to a number of pathological conditions. Therefore, we developed and characterized an enzymatically mineralized collagen gel in which fibroblasts were encapsulated within the 3D structure. MgCl₂ was also added during gel polymerization, given its role as (i) modulator of ectopic calcification; (ii) component of biomaterials used for bone replacement; and (iii) constituent of pathological mineral deposits. Results demonstrate that, in a short time, an enzymatically mineralized collagen gel can be prepared in which mineral deposits and viable cells are homogeneously distributed. MgCl₂ is present in mineral deposits and significantly affects collagen fibril assembly and organization. Consequently, cell shape and the ability of fibroblasts to retract collagen gels were modified. The development of three-dimensional (3D) mineralized collagen matrices with both different structural features and mineral composition together with the use of fibroblasts, as a prototype of soft connective tissue mesenchymal cells, may pave new ways for the study of ectopic calcification.

Harnessing Hierarchical Nano- and Micro-Fabrication Technologies for Musculoskeletal Tissue Engineering

Cells within a tissue are able to perceive, interpret and respond to the biophysical, biomechanical, and biochemical properties of the 3D extracellular matrix environment in which they reside. Such stimuli regulate cell adhesion, metabolic state, proliferation, migration, fate and lineage commitment, and ultimately, tissue morphogenesis and function. Current scaffold fabrication strategies in musculoskeletal tissue engineering seek to mimic the sophistication and comprehensiveness of nature to develop hierarchically assembled 3D implantable devices of different geometric dimensions (nano- to macrometric scales) that will offer control over cellular functions and ultimately achieve functional regeneration. Herein, advances and shortfalls of bottom-up (self-assembly, freeze-drying, rapid prototype, electrospinning) and top-down (imprinting) scaffold fabrication approaches, specific to musculoskeletal tissue engineering, are discussed and critically assessed.

Collagen structure deterioration in the skin of patients with pelvic organ prolapse determined by atomic force microscopy

We used atomic force microscopy (AFM) to diagnose pathological changes in the extracellular matrix (ECM) of skin connective tissue in patients with pelvic organ prolapse (POP). POP is a common condition affecting women that considerably decreases the patients' quality of life. Deviations from normal morphology of the skin ECM from patients with POP occur including packing and arrangement of individual collagen fibers and arrangement of collagen fibrils. The nanoindentation study revealed significant deterioration of the mechanical properties of collagen fibril bundles in the skin of POP patients as compared with the skin of healthy subjects. Changes in the skin ECM appeared to correlate well with changes in the ECM of the pelvic ligament tissue associated with POP. AFM data on the ECM structure of normal and pathologically altered connective tissue were in agreement with results of the standard histological study on the same clinical specimens. Thus, AFM and related techniques may serve as independent or complementary diagnostic tools for tracking POP-related pathological changes of connective tissue.

Epitaxially grown collagen fibrils reveal diversity in contact guidance behavior among cancer cells

Invasion of cancer cells into the surrounding tissue is an important step during cancer progression and is driven by cell migration. Cell migration can be random, but often it is directed by various cues such as aligned fibers composed of extracellular matrix (ECM), a process called contact guidance. During contact guidance, aligned fibers bias migration along the long axis of the fibers. These aligned fibers of ECM are commonly composed of type I collagen, an abundant structural protein around tumors. In this paper, we epitaxially grew several different patterns of organized type I collagen on mica and compared the morphology and contact guidance behavior of two invasive breast cancer cell lines (MDA-MB-231 and MTLn3 cells). Others have shown that these cells randomly migrate in qualitatively different ways. MDA-MB-231 cells exert large traction forces, tightly adhere to the ECM, and migrate with spindle-shaped morphology and thus adopt a mesenchymal mode of migration. MTLn3 cells exert small traction forces, loosely adhere to the ECM, and migrate with a more rounded morphology and thus adopt an amoeboid mode of migration. As the degree of alignment of type I collagen fibrils increases, cells become more elongated and engage in more directed contact guidance. MDA-MB-231 cells perceive the directional signal of highly aligned type I collagen fibrils with high fidelity, elongating to large extents and migrating directionally. Interestingly, behavior in MTLn3 cells differs. While highly aligned type I collagen fibril patterns facilitate spreading and random migration of MTLn3 cells, they do not support elongation or directed migration. Thus, different contact guidance cues bias cell migration differently and the fidelity of contact guidance is cell type dependent, suggesting that ECM alignment is a permissive cue for contact guidance, but requires a cell to have certain properties to interpret that cue.

Nano-ordered surface morphologies by stereocomplexation of the enantiomeric polylactide chains: specific interactions of surface-immobilized poly(D-lactide) and poly(ethylene glycol)-poly(L-lactide) block copolymers

Both AB diblock and ABA triblock copolymers consisting of poly(L-lactide) (PLLA: A) and poly(ethylene glycol) (PEG: B) were deposited on a silicon surface on which poly(D-lactide) (PDLA) had been preimmobilized. The deposit of the diblock copolymer (PLLA-PEG) formed band structures similar to those observed when the same copolymer was directly deposited on the silicon surface. In contrast, the deposit of the triblock copolymer (PLLA-PEG-PLLA) formed many particulates scattering over the surface. When the PLLA-PEG deposit was subjected to water-soaking, the original band morphology was completely replaced by the particulate morphology that was identical to that of the PLLA-PEG-PLLA deposit. Their FT-IR analyses revealed that both copolymers had been bound through the stereocomplex (sc) formation between the preimmobilized PDLA chains and the PLLA blocks of the copolymers. Grazing-incidence small-angle X-ray scattering (GISAXS) also supported these surface morphologies. It was therefore evident that hydrophilic PEG chains can be immobilized on the PDLA-preimmobilized surface by the sc formation.

Collagen self-assembly on orthopedic magnesium biomaterials surface and subsequent bone cell attachment

Magnesium (Mg) biomaterials are a new generation of biodegradable materials and have promising potential for orthopedic applications. After implantation in bone tissues, these materials will directly interact with extracellular matrix (ECM) biomolecules and bone cells. Type I collagen, the major component of bone ECM, forms the architecture scaffold that provides physical support for bone cell attachment. However, it is still unknown how Mg substrate affects collagen assembly on top of it as well as subsequent cell attachment and growth. Here, we studied the effects of collagen monomer concentration, pH, assembly time, and surface roughness of two Mg materials (pure Mg and AZ31) on collagen fibril formation. Results showed that formation of fibrils would not initiate until the monomer concentration reached a certain level depending on the type of Mg material. The thickness of collagen fibril increased with the increase of assembly time. The structures of collagen fibrils formed on semi-rough surfaces of Mg materials have a high similarity to that of native bone collagen. Next, cell attachment and growth after collagen assembly were examined. Materials with rough surface showed higher collagen adsorption but compromised bone cell attachment. Interestingly, surface roughness and collagen structure did not affect cell growth on AZ31 for up to a week. Findings from this work provide some insightful information on Mg-tissue interaction at the interface and guidance for future surface modifications of Mg biomaterials.