Fibrillar Diameter Research Articles

Scaling Effect of Dry Adhesion for Microfibrils and Transition Size to Flaw Insensitivity

Abstract The mechanics of detachment (e.g., a cylindrical fibril separating from a dissimilar substrate) has been treated in the perspectives of contact mechanics and fracture mechanics theory along with numerical simulations, but systematic experimental studies on the adhesion of an individual microfibril is still scarce. In this work, we conducted a detailed experiment on the adhesion tests of individual cylindrical microfibrils, within a large range of varying diameters from 4 to 400 μm, made of three different polyurethanes with moduli among ∼1–40 MPa. We confirmed the scaling effect of an individual microfibril, i.e., the adhesion σad of the individual fibril scales with fibrillar diameters D with an exponent of ∼ −0.4 to −0.45. As the fibrillar diameter is reduced below 10 μm, the adhesion becomes unchanged and size insensitive. This result is in good agreement with the theoretical predictions. Furthermore, the effects of the Young’s modulus and retraction rates during the adhesion tests on the adhesion strength were also investigated. Our experimental work will provide a guide for the optimal design of the micron-scale surfaces with improved adhesion.

Fibrillar gel self-assembly via cononsolvency of amphiphilic polymer

HypothesisPolymer with amphiphilic repeating units bathed in the mixed binary solvent can exhibit fibrillar formation and gelation via cononsolvency effect. Mechanism of gelation will be highly dependent on the solvent’s interactions and morphology of the resulting fibrillar gel can be fine-tuned by changing binary solvent composition. ExperimentsAmphiphilic homopolymers dissolved in a mixture of two solvents with different affinities to monomeric units and to each other were modeled using dissipative particle dynamics. Morphological transitions in dilute and concentrated solutions were investigated depending on the solvent-cosolvent interaction and binary solvent composition. Fibrillar gel structure was characterized via calculation of fibril’s and pore’s diameters. FindingsAmphiphilic macromolecules can combine into fibrils and form a gel as a result of the cononsolvency caused by microsegregation with one or both components of a binary solvent. In the former, the fibrils are loose, in the latter - dense. For dilute solution, state diagram in terms of solvent/cosolvent miscibility and binary solvent composition is constructed and two regions with different fibrillar gels are distinguished. For concentrated solution, the conditions, governing fibrillar diameter, pore size, number and functionality of branching points, are highlighted. These findings would be useful for the controlling synthetic matrix morphologies in the tissue engineering.

Stabilization by Nano Spray Dryer of Pioglitazone Polymeric Nanosystems: Development, In Vivo, Ex Vivo and Synchrotron Analysis.

Pioglitazone-loaded PLGA-PEG nanoparticles (NPs) were stabilized by the spray drying technique as an alternative to the treatment of ocular inflammatory disorders. Pioglitazone-NPs were developed and characterized physiochemically. Interaction studies, biopharmaceutical behavior, ex vivo corneal and scleral permeation, and in vivo bioavailability evaluations were conducted. Fibrillar diameter and interfibrillar corneal spacing of collagen was analyzed by synchrotron X-ray scattering techniques and stability studies at 4 °C and was carried out before and after the spray drying process. NPs showed physicochemical characteristics suitable for ocular administration. The release was sustained up to 46 h after drying; ex vivo corneal and scleral permeation profiles of pioglitazone-NPs before and after drying demonstrated higher retention and permeation through cornea than sclera. These results were correlated with an in vivo bioavailability study. Small-angle X-ray scattering (SAXS) analysis did not show a significant difference in the organization of the corneal collagen after the treatment with pioglitazone-NPs before and after the drying process, regarding the negative control. The stabilization process by Nano Spray Dryer B-90 was shown to be useful in preserving the activity of pioglitazone inside the NPs, maintaining their physicochemical characteristics, in vivo bioavailability, and non-damage to corneal collagen function after SAXS analysis was observed.

Animal model with structural similarity to human corneal collagen fibrillar arrangement.

Rabbit and porcine corneas have been used in scientific research due to their structural similarity to the human cornea. Currently, there are no studies that have compared corneal collagen fibrillar diameter, interfibrillar distance and interlamellar distance between human and animal models. Ten pairs of porcine, rabbit, and human corneas were used. These were analysed using light and Transmission Electron microscopy. The collagen fibrillar diameter, interfibrillar distance and interlamellar distance were statistically compared between porcine, rabbit and human corneas. The human, porcine and rabbit; mean collagen fibrillar diameters were: 24.52 ± 2.09nm; 32.87 ± 0.87nm; and 33.67 ± 1.97nm. The mean interfibrillar distances were: 46.10 ± 2.44nm; 53.33 ± 2.24nm; and 52.87 ± 2.73nm, respectively. The collagen fibrillar diameter and interfibrillar distance of porcine and rabbit corneas were significantly different (p < 0.001) to the human corneal values but not form each other. The interlamellar distance of human, porcine and rabbit corneas was: 2190 ± 820nm; 6460 ± 1180nm; and 4410 ± 1330nm, respectively. All the comparisons were statistically different, in porcine versus rabbit at the p < 0.01 level and both porcine and rabbit versus human at the p < 0.001 level. Histologically, all five layers (epithelium, Bowman's layer, stroma, Descemet membrane and endothelium) of the cornea were visible in all the three species. While neither animal model was structurally identical to the human cornea, they are both relatively close to being used as models to study the biomechanical effects of external insults/treatments to be extrapolated to the human cornea.

Accelerated Amyloid Beta Pathogenesis by Bacterial Amyloid FapC.

The gut–brain axis has attracted increasing attention in recent years, fueled by accumulating symptomatic, physiological, and pathological findings. In this study, the aggregation and toxicity of amyloid beta (Aβ), the pathogenic peptide associated with Alzheimer's disease (AD), seeded by FapC amyloid fragments (FapCS) of Pseudomonas aeruginosa that colonizes the gut microbiome through infections are examined. FapCS display favorable binding with Aβ and a catalytic capacity in seeding the peptide amyloidosis. Upon seeding, twisted Aβ fibrils assume a much‐shortened periodicity approximating that of FapC fibrils, accompanied by a 37% sharp rise in the fibrillar diameter, compared with the control. The robust seeding capacity for Aβ by FapCS and the biofilm fragments derived from P. aeruginosa entail abnormal behavior pathology and immunohistology, as well as impaired cognitive function of zebrafish. Together, the data offer the first concrete evidence of structural integration and inheritance in peptide cross‐seeding, a crucial knowledge gap in understanding the pathological correlations between different amyloid diseases. The catalytic role of infectious bacteria in promoting Aβ amyloidosis may be exploited as a potential therapeutic target, while the altered mesoscopic signatures of Aβ fibrils may serve as a prototype for molecular assembly and a biomarker for screening bacterial infections in AD.

Scaling law and microstructure of alginate hydrogel

The gelation of alginate in aqueous solution was studied as a function of Ca2+ concentration. At each given concentration of alginate, a critical gel concentration cg, Ca2+, was successfully determined for the first time using the Winter–Chambon criterion. The critical gel concentration cg, Ca2+ was found to increase linearly with alginate concentration. At the same time, the critical relaxation exponent n decreased and the critical gel strength Sg increased linearly with alginate concentration. An improved egg-box model was proposed to describe the change in gel junction and gel network. In the stable gel state, the plateau modulus Ge of alginate gel depended on Ca2+ concentration according to a power-law scaling, Ge=kɛ1.5, where ɛ is the relative distance of a gelling variable (Ca2+ concentration in this case) from the gel point (cg, Ca2+). The FESEM images verified the microstructure of alginate gel in which alginate chains associated into fibrils in the presence of Ca2+ ions. The fibrillar diameter and network density increased with increasing Ca2+ ion concentration while alginate concentration had a weak influence on fibrillar diameter.

Hybrid supramolecular and colloidal hydrogels that bridge multiple length scales.

Hybrid nanocomposites were constructed based on colloidal nanofibrillar hydrogels with interpenetrating supramolecular hydrogels, displaying enhanced rheological yield strain and a synergistic improvement in storage modulus. The supramolecular hydrogel consists of naphthyl-functionalized hydroxyethyl cellulose and a cationic polystyrene derivative decorated with methylviologen moieties, physically cross-linked with cucurbit[8]uril macrocyclic hosts. Fast exchange kinetics within the supramolecular system are enabled by reversible cross-linking through the binding of the naphthyl and viologen guests. The colloidal hydrogel consists of nanofibrillated cellulose that combines a mechanically strong nanofiber skeleton with a lateral fibrillar diameter of a few nanometers. The two networks interact through hydroxyethyl cellulose adsorption to the nanofibrillated cellulose surfaces. This work shows methods to bridge the length scales of molecular and colloidal hybrid hydrogels, resulting in synergy between reinforcement and dynamics.

Hybrid Supramolecular and Colloidal Hydrogels that Bridge Multiple Length Scales.

Hybrid nanocomposites were constructed based on colloidal nanofibrillar hydrogels with interpenetrating supramolecular hydrogels, displaying enhanced rheological yield strain and a synergistic improvement in storage modulus. The supramolecular hydrogel consists of naphthyl‐functionalized hydroxyethyl cellulose and a cationic polystyrene derivative decorated with methylviologen moieties, physically cross‐linked with cucurbit[8]uril macrocyclic hosts. Fast exchange kinetics within the supramolecular system are enabled by reversible cross‐linking through the binding of the naphthyl and viologen guests. The colloidal hydrogel consists of nanofibrillated cellulose that combines a mechanically strong nanofiber skeleton with a lateral fibrillar diameter of a few nanometers. The two networks interact through hydroxyethyl cellulose adsorption to the nanofibrillated cellulose surfaces. This work shows methods to bridge the length scales of molecular and colloidal hybrid hydrogels, resulting in synergy between reinforcement and dynamics.

Seed micromorphology of central European Orobanche and Phelipanche (Orobanchaceae) in relation to preferred hosts and systematic implications

Holoparasitic genera within family Orobanchaceae are characterised by greatly reduced vegetative organs; therefore, seed micromorphology has proved to be a useful complementary taxonomic criterion. Seeds of 160 samples from 54 localities of 26 taxa of the Orobanche and Phelipanche genera occurring in central Europe, specifically from Poland, the Czech Republic, Austria and Slovakia, supplemented by samples from Spain, France and Ukraine, were investigated using scanning electron microscopy. Thirteen quantitative or qualitative morphological characters of seeds were analysed. The following three types of periclinal wall sculpture of seeds were identified: veined and fibrillar in Phelipanche; with oval or elliptic perforations (pitted) in almost all species of Orobanche; with outer periclinal wall smooth, granular or rugged (very rarely visibly pitted), impeding vision of the inner one, occurring only in O. gracilis Sm. and O. coerulescens Stephan in Willd. The influence of different hosts on the features of seeds of eight species is also presented, as well as relationships between seed morphology and taxonomic classification, including problematic taxa. The best diagnostic features include type of ornamentation of the periclinal wall, perforation diameter (in pitted sculpture), fibrillar diameter (in fibrillar sculpture) and width of anticlinal walls. Size and shape of the seeds and cells and the presence of median troughs are variable; however, these features can be helpful when using larger samples. The usefulness of micromorphological studies on seeds of Orobanche and Phelipanche is demonstrated.

Modulation of keratocyte phenotype by collagen fibril nanoarchitecture in membranes for corneal repair

Type I collagen membranes with tailored fibril nanoarchitectures were fabricated through a vitrification processing, which mimicked, to a degree, the collagen maturation process of corneal stromal extracellular matrix in vivo. Vitrification was performed at a controlled temperature of either 5 °C or 39 °C at a constant relative humidity of 40% for various time periods from 0.5 wk up to 8 wk. During vitrification, the vitrified collagen membranes (collagen vitrigels, CVs) exhibited a rapid growth in fibrillar density through the evaporation of water and an increase in fibrillar stiffness due to the formation of new and/or more-stable interactions. On the other hand, the collagen fibrils in CVs maintained their D-periodicity and showed no significant difference in fibrillar diameter, indicating preservation of the native states of the collagen fibrils during vitrification. Keratocyte phenotype was maintained on CVs to varying degrees that were strongly influenced by the collagen fibril nanoarchitectures. Specifically, the vitrification time of CVs mainly governed the keratocyte morphology, showing significant increases in the cell protrusion number, protrusion length, and cell size along with CV vitrification time. The CV vitrification temperature affected the regulation of keratocyte fibroblasts' gene expressions, including keratocan and aldehyde dehydrogenase (ALDH), demonstrating a unique way to control the expression of specific genes in vitro.

Solvents effects in the formation and viscoelasticity of DBS organogels

The gel behavior of dibenzylidene sorbitol (DBS) in different solvents was studied by rheology, optical microscopy and transmission electron microscopy. It was found that DBS molecules would self-assemble into fibrils with a helical structure, and the fibrillar diameter decreased with increasing solvent polarity. The gel dissolution temperature was extremely sensitive to the DBS concentration and solvent polarity, which could be explained by the Gibbs–Thomson equation through interfacial stress. The phase diagram, which classified the sol, the gel and the cluster regime in different solvents was determined by rheology and optical microscopy. The critical gel concentration was found to increase as the difference in the polar and hydrogen-bonding components of the solubility parameter (Δδph) between the gelator and solvents decreased. Meanwhile, the difference in the critical gel concentration in different solvents could explain the difference in the relaxation exponent and the gel strength at the gel point well. In the stable gel state, the plateau modulus depended on the gelator concentration according to a power-law scaling, GoN ∝ c2, which was consistent with entanglement theory and independent of the type of solvent. However, the gelator–solvent interaction and its temperature dependence were found to affect the stability of the gel substantially under large amplitude oscillatory shear. The critical strain would increase as Δδph decreased, and showed more evident temperature dependence on solvents with a smaller Δδph.

Characterization of Methacrylated Type-I Collagen as a Dynamic, Photoactive Hydrogel

Type-I collagen is an attractive scaffold material for tissue engineering due to its ability to self-assemble into a fibrillar hydrogel, its innate support of tissue cells through bioactive adhesion sites, and its biodegradability. However, a lack of control of material properties has hampered its utility as a scaffold. We have modified collagen via the addition of methacrylate groups to create collagen methacrylamide (CMA) using a synthesis reaction that allows retention of fundamental characteristics of native collagen, including spontaneous fibrillar self-assembly and enzymatic biodegradability. This method allows for a rapid, five-fold increase in storage modulus upon irradiation with 365 nm light. Fibrillar diameter of CMA was not significantly different from native collagen. Collagenolytic degradability of uncrosslinked CMA was minimally reduced, while photocrosslinked CMA was significantly more resistant to degradation. Live/Dead staining demonstrated that a large majority (71%) of encapsulated mesenchymal stem cells remained viable 24 h after photocrosslinking, which further increased to 81% after 72 h. This material represents a novel platform for creating mechanically heterogeneous environments.

Improved mechanical and photophysical properties of chitosan incorporated folic acid gel possessing the characteristics of dye and metal ion absorption

The folic acid (F) gel, prepared in a 1:1 dimethyl sulfoxide (DMSO)–water mixture (v/v), at 0.2% (w/v) concentration has a nano-fibrous network morphology. FTIR spectra indicate the presence of intermolecular H-bonding interactions in the gel. The folic acid–chitosan (C) hybrid (FC) gel (prepared by mixing 0.1 ml of 1% (w/v) C solution with 2 ml 0.2% (w/v) F solution) appears as a yellow transparent semi-solid mass consisting of a nano-fibrous network with a higher density of branches. The fibrillar diameter of the FC hybrid gel (10.5 nm) is much lower than that of F gel (17.3 nm). The FTIR band at 3390 cm−1 of F gel shows a shift to 3435 cm−1 in the FC hybrid gel indicting a hydrogen bonding interaction between C and F. The fluorescence intensity of the FC hybrid gel is enhanced by 2.75 times than that of F gel. The shear viscosity of FC hybrid gel is 3 orders higher than that of the F gel and both gels exhibit shear thickening at a low shear rate (<10−3 s−1) but above that, shear-thinning occurs. In the creep phase, the FC hybrid gel exhibits strain recovery but the F gel does not. The complex modulus (G*) of both systems initially exhibit a sharp increase, followed by a slow increase with time (t) and dG*/dt varies with C concentration in the FC hybrid gel showing a maximum. The WAXS pattern of the FC hybrid xerogel does not exhibit any crystalline peak, suggesting that the additive (C) inhibits the crystallization of F. The dye absorption by the hybrid gel material is maximum for Eosin Yellow, (83.5%), however, Methyl Orange and Methylene Blue are absorbed to a lesser extent (∼40%). The FC hybrid gel absorbs 55% of Cu2+, 67.2% of Cr3+ and 49% of Co2+ from their respective solutions.

Collagen ultrastructural changes during stromal wound healing in organ cultured bovine corneas

Corneal collagen ultrastructural changes occur during the healing process. The present study was designed to compare collagen ultrastructural changes after trephine wounding or flap creation. Bovine corneas were injured and maintained in organ culture for up to 4 weeks. Samples were removed from culture at 0, 1, 2, 3 and 4 weeks and snap frozen in liquid N(2). X-ray scattering was used to measure changes in collagen interfibrillar spacing, intermolecular spacing and fibrillar diameter. Some samples were fixed in 10% Neutral Buffered Formalin solution and wax embedded for immunohistochemistry to monitor myofibroblast differentiation in corneal flaps. Swelling effects (i.e. changes in interfibrillar spacing) were more severe in trephined corneas than in those with stromal flaps. Collagen fibrillar diameter remained normal in the periphery of injured corneas, but increased significantly in areas within and around the wound in trephined samples and in the epithelial incision site in corneal flaps. Intermolecular spacing was unchanged in all samples. In the flaps, alphaSMA expression was only detected in an area adjacent to the epithelial plug, and cell numbers gradually increased during the culture. We conclude that stromal swelling is more rapid for trephine-wounded corneas than in stromal flaps, indicating that the intensity of the corneal healing response depends on the type of injury.

Conductive polymer preparation under extreme or non-classical conditions

Polyaniline (PANI) emeraldine salt form and PANI/silver composites have been synthesized by sonochemical and ionizing radiation methods. These composite materials were obtained through sonication and γ irradiation of an aqueous solution of aniline and silver nitrate, in room temperature, respectively. The mechanisms suggested to explain the formation of these products are based on the fact that both methods produce hydroxyl radical •OH and hydrogen radical •H, where hydroxyl radical •OH acts as an oxidizing agent in the polymerization process of aniline monomer; and hydrogen radical •H, as a reducing agent for silver ions. Spectroscopic, X-ray, and SEM measures show that PANI and silver nano particles of 40 nm average diameter are produced with ultrasonic methods, whereas silver nano particles of 60 nm average, and fibrillar, highly network morphology for PANI with 60 nm fibrillar diameter average are obtained using γ radiation).

A novel technique of taking tendon biopsies in the horse

SummaryTo evaluate a novel tendon biopsy technique for use in the horse and to assess the effect of different exercise levels on the healing process of minimally damaged superficial digital flexor tendons (SDFT), 24 Dutch Warmblood foals were randomly divided into 3 equally sized groups one week after birth. One group was box rested, one group got box rest with additional enforced exercise, and one group got free pasture exercise. Biopsies from the peripheral region of the SDFT were taken at age 2 months using a new micro-biopsy technique. At age 5 months the foals were euthanized and samples from the biopsy site and a control site were harvested. Collagen fibrillar index (CFI, the total amount of collagen as a percentage of the measured area), mass-average diameter (MAvD, mean of the diameter versus area distribution) and collagen fibrillar diameter frequency (the distribution of collagen fibril sizes expressed as a percentage of the number of collagen fibrils) were calculated. The CFI, MAvD values were significantly lower in the wound samples. It is concluded that the biopsy technique may be a useful tool for research applications. The absence of exercise-induced effects on the collagen fibril population in the wound samples suggests that the first phase of the process of tendon healing in immature equine SDFT’s sustaining a minor surgically-induced wound, is not exercise-dependent. However, findings may be different in mature horses sustaining accidental trauma.A novel technique to take biopsies from immature equine flexor tendons was developed and used to evaluate the effect of various levels of exercise on the development of the collagen fibril diameter distribution in the resulting wounds. The technique appeared to be minimally invasive, but complication rate was deemed too high for clinical use. There was no effect of exercise on mass average diameter of collagen fibrils, suggesting that the repair process, at least in its initial stage, is exercise-independent.

Electron microscopic investigation of the effects of diabetes mellitus on the Achilles tendon

Fine structural changes in the Achilles tendons of patients with long-term diabetes mellitus were investigated. All patients had clinical and electrophysiological evidence of diabetic neuropathy and had ulceration and/or Charcot neuroarthropathy. Several differences between tendons of diabetic (n = 12) and nondiabetic (n = 5) individuals were observed by electron microscopy. In diabetics, these differences included increased packing density of collagen fibrils, decreases in fibrillar diameter, and abnormal fibril morphology. In one diabetic patient, individual collagen fibrils were tightly apposed so that many areas of tendon appeared as a single mass of closely adhering fibrillae. In addition, foci in which collagen fibrils appeared twisted, curved, overlapping and otherwise highly disorganized were common in specimens from most patients (11 of 12). These morphologic abnormalities in the Achilles tendons of diabetics appear to reflect a poorly known process of structural reorganization that may be the result of nonenzymatic glycation expressed over many years. Such structural changes could contribute to the tightening of the Achilles tendor a phenomenon consistent with clinical observations of extreme shortening of the Achilles tendon-gastrocnemius-soleus complex common in advanced diabetic neuropaths. In patients with diabetic neuropathy, tendon shortening causes severe equinus that may precipitate serious ulceration, stress fractures, and Charcot collapse of the foot. However, in nondiabetics, the fine structure of the Achilles tendon appears normal, consistent with the finding that the ultrastructural changes result from diabetes rather than neuropathy.

Dinoflagellate evolution: speculation and evidence.

Nuclear features of dinoflagellates that were used originally to support the Mesocaryota concept are reviewed. The fibrillar diameter of dinoflagellage chromatin, low level of chromosomal basic proteins, membrane attachment of chromosomes and swirl pattern observed in sectioned chromosomes are features that support a prokaryotic affinity. The presence of repeated and highly complex DNA, a S-phase of DNA synthesis in the cell cycle, presence of basic proteins, and the reinterpretation of extranuclear microtubules as a spindle support the contention that dinoflagellates are eukaryotes. This combination of prokaryotic and eukaryotic features suggests that dionflagellates are a geologically old group and that perhaps they diverged from the higher eukaryotic lineage before evolution of eukaryotic chromatin but after the evolution of repeated DNA. The 2 patterns of carotenoid composition exemplified by the presence of peridinin or fucoxanthin suggest separate origins of dinoflagellate plastids, perhaps by prokaryotic and eukaryotic capture. It is suggested that the species possessing fucoxanthin obtained their plastids by capture of photosynthetic eukaryotes.

Study of transverse heterogeneity of oriented crystalline polymers

Small- and wide-angle X-ray diffraction were used to study transverse dimension changes of fibrils and crystals during stretching of crystalline polymers. The crystal dimensions were found to change little when the degree of stretching λ was increased from 3–4-fold to the critical value but there was a considerable decrease of the fibrillar diameter. The latter was 2–3 times larger than the transverse dimension of the crystals at small λ, but the two parameters became similar at larger λ. The conclusion was reached that the fibrils separate during polymer orientation in crystalline zones at the boundary between crystals.