Type I collagen self-assembly: the roles of substrate and concentration

Preparation and Characterization of Nanocomposite Hydrogels Based on Self-Assembling Collagen and Cellulose Nanocrystals

Collagen (Col) hydrogels are an important biomaterial with many applications in the biomedical sector. However, deficiencies, including insufficient mechanical properties and a rapid rate of biodegradation, hamper their application. In this work, nanocomposite hydrogels were prepared by combining a cellulose nanocrystal (CNC) with Col without any chemical modification. The high-pressure, homogenized CNC matrix acts as nuclei in the collagen's self-aggregation process. The obtained CNC/Col hydrogels were characterized in terms of their morphology, mechanical and thermal properties and structure by SEM, rotational rheometer, DSC and FTIR, respectively. Ultraviolet-visible spectroscopy was used to characterize the self-assembling phase behavior of the CNC/Col hydrogels. The results showed an accelerated assembling rate with the increasing loading of CNC. The triple-helix structure of the collagen was preserved with a dosage of CNC of up to 15 wt%. The CNC/Col hydrogels demonstrated an improvement in both the storage modulus and thermal stability which is attributed to the interaction between the CNC and collagen by the hydrogen bonds.

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.

Formation of β-Lactoglobulin Self-Assemblies via Liquid-Liquid Phase Separation for Applications beyond the Biological Functions

Proteins are like miracle machines, playing important roles in living organisms. They perform vital biofunctions by further combining together and/or with other biomacromolecules to form assemblies or condensates such as membraneless organelles. Therefore, studying the self-assembly of biomacromolecules is of fundamental importance. In addition to their biological activities, protein assemblies also exhibit extra properties that enable them to achieve applications beyond their original functions. Herein, this study showed that in the presence of monosaccharides, ethylene glycols, and amino acids, β-lactoglobulin (β-LG) can form assemblies with specific structures, which were highly reproducible. The mechanism of the assembly process was studied through multi-scale observations and theoretical analysis, and it was found that the assembling all started from the formation of solute-rich liquid droplets via liquid-liquid phase separation (LLPS). These droplets then combined together to form condensates with elaborate structures, and the condensates finally evolved to form assemblies with various morphologies. Such a mechanism of the assembly is valuable for studying the assembly processes that frequently occur in living organisms. Detailed studies concerning the properties and applications of the obtained β-LG assemblies showed that the assemblies exhibited significantly better performances than the protein itself in terms of autofluorescence, antioxidant activity, and metal ion absorption, which indicates broad applications of these assemblies in bioimaging, biodetection, biodiagnosis, health maintenance, and pollution treatment. This study revealed that biomacromolecules, especially proteins, can be assembled via LLPS, and some unexpected application potentials could be found beyond their original biological functions.

D-band strain underestimates fibril strain for twisted collagen fibrils at low strains

Collagen fibrils are the main structural component of load-bearing tissues such as tendons, ligaments, skin, the cornea of the eye, and the heart. The D-band of collagen fibrils is an axial periodic density modulation that can be easily characterized by tissue-level X-ray scattering. During mechanical testing, D-band strain is often used as a proxy for fibril strain. However, this approach ignores the coupling between strain and molecular tilt. We examine the validity of this approximation using an elastomeric collagen fibril model that includes both the D-band and a molecular tilt field. In the low strain regime, we show that the D-band strain substantially underestimates fibril strain for strongly twisted collagen fibrils - such as fibrils from skin or corneal tissue.

The effect of collagen hydrogels on chondrocyte behaviors through restricting the contraction of cell/hydrogel constructs

Collagen is a promising material for tissue engineering, but the poor mechanical properties of collagen hydrogels, which tend to cause contraction under the action of cellular activity, make its application challengeable. In this study, the amino group of type I collagen (Col I) was modified with methacrylic anhydride (MA) and the photo-crosslinkable methacrylate anhydride modified type I collagen (CM) with three different degrees of substitution (DS) was prepared. The physical properties of CM and Col I hydrogels were tested, including micromorphology, mechanical properties and degradation properties. The results showed that the storage modulus and degradation rate of hydrogels could be adjusted by changing the DS of CM. In vitro, chondrocytes were seeded into these four groups of hydrogels and subjected to fluorescein diacetate/propidium iodide (FDA/PI) staining, cell counting kit-8 (CCK-8) test, histological staining and cartilage-related gene expression analysis. In vivo, these hydrogels encapsulating chondrocytes were implanted subcutaneously into nude mice, then histological staining and sulfated glycosaminoglycan (sGAG)/DNA assays were performed. The results demonstrated that contraction of hydrogels affected behaviors of chondrocytes, and CM hydrogels with suitable DS could resist contraction of hydrogels and promote the secretion of cartilage-specific matrix in vitro and in vivo.

Beyond temperature: controlling collagen fibrillogenesis under physiological conditions via interaction with cucurbit[7]uril

Under physiological ionic strength and pH, temperature has long been appreciated as the only stimulus that can be applied to induce in vitro self-assembly of tropocollagen. Here, we report a second, mechanistically new control strategy that uses non-covalent and selective binding of cucurbit[7]uril, a macrocyclic cavitand, with midchain aromatic residues on the tropocollagen surface. This strategy directly demonstrates the decisive role hydrophobic interactions play in collagen fibrillogenesis. It also points the way to the temporally-controllable formation of collagen fibrils in vivo that is highly desirable, yet challenging, in some biomedical scenarios.

Construction of collagen gel with high viscoelasticity and thermal stability via combining cross-linking and dehydration

Collagen gel is widely used in tissue engineering due to excellent biological properties and swollen three-dimensional network structure. To improve viscoelasticity and thermal stability, collagen gels consisting of fibrils were cross-linked with glutaraldehyde and sequentially dehydrated via ethanol or heating (named as EGC or HGC, respectively). For EGC, ethanol replaced free and loosely bound water and then combined with tightly bound water, inducing the increase in hydrogen bonds and molecular interactions. Therefore, the thermal transition temperature (T_t ) and storage modulus (G') obviously increased from 47.3 ± 0.5°C and 0.1 kPa to 92.7 ± 0.8°C and 7.8 kPa, respectively. Unfortunately, the high deformation (γ > 60%) and low recovery percentage (R < 15%) reflected the poor anti-deformation of gels due to the volatility of ethanol. For HGC, the entanglement and rigidity of fibrils increased owing to the contraction of cross-linked fibrils and cohesive action of denatured collagen. As a result, HGC were more resistant to deformation and exhibited more elasticity than native collagen gel, accompanied by the fact that G' and R increased to 28.8 kPa and 90.0% ± 0.7%. Additionally, HGC exhibited higher T_t (121.4 ± 0.5°C) due to lower water content and higher collagen concentration.

Improved structure-stability and packaging characters of crosslinked collagen fiber-based film with casein, keratin and SPI

BACKGROUND

To improve the structure-stability and packing characters of collagen fiber, we manufactured crosslinked collagen fiber (CColF)-based edible films using transglutaminase (TGase). Then we made a comparison on structure-stability and packing characteristics among the CColF-based films loaded with casein (CN), keratin (KRT) and soy protein isolate (SPI), respectively.

RESULTS

Observed from scanning electron microscopy (SEM), the CColF loaded with CN, KRT and SPI showed some unique morphology of the additional proteins. The CColF-protein films performed better packing characteristics including barrier properties, mechanical properties and thermal-stability properties, compared with CColF films. Importantly, with 500 g kg^-1 CN (of CColF) addition, CColF-based films possessed a greater thermal stability than the other films judged from differential scanning calorimetry (DSC). Meanwhile, the CColF loaded with 100 g kg^-1 CN provided a higher value of tensile strength (TS) and the CColF loaded with 100 g kg^-1 KRT showed a higher value in elongation-at-break (EAB) than the other films.

CONCLUSION

In conclusion, the collagen fiber-based edible films with better structure-stability and packing characteristics for food packaging was obtained which could be an advantage to promote the development of the application of collagen in packing products. © 2019 Society of Chemical Industry.

Comparison of Physicochemical Characteristics and Fibril Formation Ability of Collagens Extracted from the Skin of Farmed River Puffer (Takifugu obscurus) and Tiger Puffer (Takifugu rubripes)

Acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC) from the skin of river puffer (ASC-RP and PSC-RP) and tiger puffer (ASC-TP and PSC-TP) were extracted and physicochemically examined. Denaturation temperature (T_d) for all the collagens was found to be 25.5–29.5 °C, which was lower than that of calf skin collagen (35.9 °C). Electrophoretic patterns indicated all four samples were type I collagen with molecular form of (α₁)₂α₂. FTIR spectra confirmed the extracted collagens had a triple-helical structure, and that the degree of hydrogen bonding in ASC was higher than PSC. All the extracted collagens could aggregate into fibrils with D-periodicity. The fibril formation rate of ASC-RP and PSC-RP was slightly higher than ASC-TP and PSC-TP. Turbidity analysis revealed an increase in fibril formation rate when adding a low concentration of NaCl (less than 300 mM). The fibril formation ability was suppressed with further increasing of NaCl concentration, as illustrated by a reduction in the turbidity and formation degree. SEM analysis confirmed the well-formed interwoven structure of collagen fibrils after 24 h of incubation. Summarizing the experimental results suggested that the extracted collagens from the skin of river puffer and tiger puffer could be considered a viable substitute to mammalian-derived collagens for further use in biomaterial applications.

Improving linking interface between collagen-based hydrogels and bone-like substrates

Regenerative medicine requires the use of heterogeneous scaffolds when the tissue that needs to be repaired presents a gradient in its properties and cannot be replaced by a homogeneous graft. Then, an intimate contact between the different layers is critical to guarantee the optimal performance of the construct. This work presents a procedure that allows the immobilization of collagen-based hydrogels by self-assembly onto any desired substrate, by means of a pentafluorophenyl methacrylate (PFM) coating obtained by plasma enhanced chemical vapor deposition and a collagen monolayer. The latter is attached onto the PFM-coated substrate thanks to its high reactivity towards amines and it will act as anchoring point for the subsequent collagen fibrillation and hydrogel formation. The interaction between collagen and PFM-coated substrates has been evaluated using the quartz crystal microbalance with dissipation (QCM-D) technique. In addition, QCM-D has been used to design and monitor the collagen fibril formation process. A correlation between QCM-D data and optical microscopy has been established, and fibril formation has been confirmed by atomic force microscopy (AFM).

Evaluation of biocompatibility and immunogenicity of micro/nanofiber materials based on tilapia skin collagen

Type I collagen, used as a raw material, plays a pivotal role in the development of medical devices and tissue engineering. Due to the risk of zoonotic transmission and religious constraints for mammalian collagen, fish collagen gains increased attention and is widely seen as an alternative. In this study, two collagen micro/nanofiber materials, self-assembled collagen nanofiber and electrospun collagen nanofiber, were prepared by tilapia skin collagen and their biocompatibility and immunogenicity was thoroughly investigated. The result revealed that the state of tilapia skin collagen in self-assembled collagen nanofiber and electrospun collagen nanofiber was different. The circular dichroism spectrum indicated that collagen in self-assembled collagen nanofiber retained the triple helical structure of the native collagen, while collagen in electrospun collagen nanofiber was denatured into gelatin. Nevertheless, the evaluation according to ISO10993, including tests of cytotoxicity, hemolysis, skin sensitization, acute systemic toxicity, mouse immunization and lymphocyte proliferation, demonstrated good biocompatibility and low immunogenicity for both self-assembled and electrospun collagen nanofiber materials. Overall, the present study highlighted that type I collagen from tilapia skin would be a promising biomaterial for the development of regenerate medical products.

Graphene-Oxide-Based FRET Platform for Sensing Xenogeneic Collagen Coassembly

Xenogeneic collagen coassembly (XCCA) offers a new view for the design and performance regulation of novel collagen-based biomaterials. But there is still a lack of accurate and sensitive method for monitoring XCCA. In this study, a simple and efficient graphene-oxide (GO)-based fluorescence resonance energy transfer (FRET) platform has been developed to sense XCCA. We first designed a fluorescein isothiocyanate (FITC)-labeled porcine skin collagen (PSC) that adsorbed on the GO surface and effectively quenched its fluorescence. Upon the addition of grass carp skin collagen (GCSC), the XCCA between PSC and GCSC resulted in desorption of FITC-PSC from GO surface and thus caused an increase in fluorescence signal. Under the optimal conditions, the fluorescence signal linearly increased with the increase in the GCSC concentration in the range of 50-1000 μg/mL, with a sensitivity of 22 μg/mL (S/N = 3). Furthermore, the developed strategy also exhibited excellent specificity and anti-interference ability. More interestingly, the thermal stability of collagen fibrils formed by XCCA is linearly related to the GCSC concentration. These results open a facile, effective, and sensitive approach for sensing XCCA and provide a new strategy for arbitrarily regulating the thermal stability of collagen fibrils.

Development of an In Vitro 3D Brain Tissue Model Mimicking In Vivo-Like Pro-inflammatory and Pro-oxidative Responses

To analyze complex inflammatory responses in an in vitro system, we constructed a new 3D in vitro brain tissue model that exhibits in vivo-like tissue responses (e.g. immune cell phenotypes, and molecular response) to inflammatory stimuli. Finite element modeling of oxygen diffusion and cellular oxygen consumption predicted the oxygen profile within 3D structures, consisting of Type I collagen hydrogel embedded with murine microglia. Viability and cytotoxicity analyses supported the mathematical analysis, determining optimal cell growth conditions for 3D construct development. Real-time RT-PCR and ELISA demonstrated significant up-regulation of pro-inflammatory mediators, such as TNF-α, MCP-1, IL-6 and IL-1β, in lipopolysaccharide (LPS)-stimulated in vitro cell culture (2D and 3D) and in vivo mouse model systems. Interestingly, levels of inflammatory responses from the in vitro 3D model system were more similar to in vivo than in vitro 2D. Additionally, in situ dihydroethidium (DHE) assay and immunofluorescence staining revealed that levels of LPS-stimulated reactive oxygen species (ROS) generation and microglial activation from in vitro 3D model system were closer to in vivo than in vitro 2D. These results demonstrated that an in vitro 3D model provides more physiologically relevant pro-oxidative and pro-inflammatory environments in brain than an in vitro 2D model.

Preparation and characterization of soy protein isolate-collagen self-assembled nanomicelles

This paper describes the preparation and characterization of soy protein isolate (SPI)-collagen self-assembled nanomicelles. Novel SPI-collagen self-assembled nanomicelles via hydrogen bonding and electrostatic interactions were developed. SPI-collagen soluble complexes were formed at pH 6.4, which was lower than the isoelectric point of collagen (pI = 7.8) and higher than that of SPI (pI = 4.5). This research mainly focuses on the intermolecular force between the SPI and collagen. The diameter distribution, critical association concentration, and stability of the SPI-collagen self-assembled nanomicelles were investigated in this research. It was found that the SPI and collagen had hydrogen bonding and electrostatic interactions, and then formed natural complex nanomicelles in a weakly acidic environment. The preparation of SPI-collagen self-assembled nanomicelles was performed in an aqueous environment without surfactants or toxic agents. As a fixing agent, transglutaminase (TGase) promoted the intra- and intermolecular cross-linking of the nanomicelles, which improved the stability of the self-assembled nanomicelles. The SPI-collagen nanomicelles had a good stability. This research may provide a reference for the utilization of SPI-collagen self-assembled nanomicelles.

This paper describes the preparation and characterization of soy protein isolate (SPI)-collagen self-assembled nanomicelles.

Biomimetic tumor microenvironments based on collagen matrices

This review provides an overview of the current approaches to engineer defined 3D matrices for the investigation of tumor cell behaviorin vitro, with a focus on collagen-based fibrillar systems.

Self-assembly of collagen-based biomaterials: preparation, characterizations and biomedical applications

By combining regulatory parameters with characterization methods, researchers can selectively fabricate collagenous biomaterials with various functional responses for biomedical applications.

Improved mechanical properties and thermal-stability of collagen fiber based film by crosslinking with casein, keratin or SPI: Effect of crosslinking process and concentrations of proteins

This study utilized three different thermo-stable proteins of casein, keratin and soy protein isolate (SPI) to improve the thermal stabilities and mechanical properties of collagen fiber films using transglutaminase (TGase) crosslinking. The crosslinking greatly enhanced the thermal- stability of collagen fiber films, especially that of the collagen fiber crosslinking with 50% casein composite films, judged from thermogravimetric analysis (TGA). Furthermore, the TGase treatment improved the mechanical properties of the collagen fiber films interms of tensile strength (TS) and elongation at break (EAB). Importantly, a prominent improvement in EAB at wet and heated state was noted when collagen fiber crosslinked with 50% keratin or 50% casein, respectively. Moreover, different addition patterns of proteins in the collagen fiber films offered altered morphology as observed by scanning electron microscopy (SEM). Meanwhile, the conformational changes of the films revealed by fourier transform infrared spectroscopy (FTIR) confirmed a greater stabilization of film in the group of collagen fiber crosslinking with other proteins. In conclusion, the crosslinking action induced by TGase between collagen fiber and higher thermo-stable proteins promoted heat-resistance and mechanical properties of collagen fiber based film.

Removal of dentin non-collagenous structures results in the unraveling of microfibril bundles in collagen type I

AIMS

The structural organization of collagen from mineralized tissues, such as dentin and bone, has been a topic of debate in the recent literature. Recent reports have presented novel interpretations of the complexity of collagen type I at different hierarchical levels and in different tissues. Here, we investigate the nanostructural organization of demineralized dentin collagen following the digestion of non-collagenous components with a trypsin enzyme.

MATERIALS AND METHODS

Dentin specimens were obtained from healthy third-molars, cut into small cubes, and polished down to 1 µm roughness. Samples were then demineralized with 10% citric acid for 2 min. Selected specimens were further treated with a solution containing 1 mg/ml trypsin for 48 hours at 37 °C (pH 7.9-9.0). Both untreated and trypsin digested samples were analyzed using SDS-PAGE, Field Emission Scanning Electron Microscopy (FE-SEM), and nanoindentation, where surface hardness and creep properties were compared before and after treatments.

RESULTS

FE-SEM images of demineralized dentin showed the banded morphology of D-periodical collagen type I, which upon enzymatic digestion with trypsin appeared to dissociate longitudinally, consistently unraveling ~20 nm structures (microfibril bundles). Such nanoscale structures, to the best of our knowledge, have not been characterized in dentin previously. Mechanical characterization via nanoindentation showed that the unraveling of such microfibril bundles affected the creep displacement and creep rate of demineralized dentin.

CONCLUSION

In summary, our results provide novel evidence of the organization of collagen type I from dentin, which may have important implications for the interaction of dental materials with the organic dentin matrix and the mechanical properties of mineralized tissues.

Myosin phosphorylation on stress fibers predicts contact guidance behavior across diverse breast cancer cells

During cancer progression the extracellular matrix is remodeled, forming aligned collagen fibers that proceed radially from the tumor, resulting in invasion. We have recently shown that different invasive breast cancer cells respond to epitaxially grown, aligned collagen fibrils differently. This article develops insight into why these cells differ in their contact guidance fidelity. Small changes in contractility or adhesion dramatically alter directional persistence on aligned collagen fibrils, while migration speed remains constant. The directionality of highly contractile and adhesive MDA-MB-231 cells can be diminished by inhibiting Rho kinase or β1 integrin binding. Inversely, the directionality of less contractile and adhesive MTLn3 cells can be enhanced by activating contractility or integrins. Subtle, but quantifiable alterations in myosin II regulatory light chain phosphorylation on stress fibers explain the tuning of contact guidance fidelity, separate from migration per se indicating that the contractile and adhesive state of the cell in combination with collagen organization in the tumor microenvironment determine the efficiency of migration. Understanding how distinct cells respond to contact guidance cues will not only illuminate mechanisms for cancer invasion, but will also allow for the design of environments to separate specific subpopulations of cells from patient-derived tissues by leveraging differences in responses to directional migration cues.

Observing Effects of Calcium/Magnesium Ions and pH Value on the Self-Assembly of Extracted Swine Tendon Collagen by Atomic Force Microscopy

Self-assembly of extracted collagen from swine trotter tendon under different conditions was firstly observed using atomic force microscopy; then the effects of collagen concentration, pH value, and metal ions to the topography of the collagen assembly were analyzed with the height images and section analysis data. Collagen assembly under 0.1 M, 0.2 M, 0.3 M CaCl2, and MgCl2 solutions in different pH values showed significant differences (P < 0.05) in the topographical properties including height, width, and roughness. With the concentration being increased, the width of collagen decreased significantly (P < 0.05). The width of collagen fibers was first increased significantly (P < 0.05) and then decreased with the increasing of pH. The collagen was assembled with network structure on the mica in solution with Ca2+ ions. However, it had shown uniformed fibrous structure with Mg2+ ions on the new cleaved mica sheet. In addition, the width of collagen fibrous was 31~58 nm in solution with Mg2+ but 21~50 nm in Ca2+ solution. The self-assembly collagen displayed various potential abilities to construct fibers or membrane on mica surfaces with Ca2+ ions and Mg2+ irons. Besides, the result of collagen self-assembly had shown more relations among solution pH value, metal ions, and collagen molecular concentration, which will provide useful information on the control of collagen self-assembly in tissue engineering and food packaging engineering.

Estrogen depletion and drug treatment alter the microstructure of type I collagen in bone

The impact of estrogen depletion and drug treatment on type I collagen fibril nanomorphology and collagen fibril packing (microstructure) was evaluated by atomic force microscopy (AFM) using an ovariectomized (OVX) rabbit model of estrogen deficiency induced bone loss. Nine month-old New Zealand white female rabbits were treated as follows: sham-operated (Sham; n = 11), OVX + vehicle (OVX + Veh; n = 12), OVX + alendronate (ALN, 600 μg/kg/wk., s.c.; n = 12), and OVX + cathepsin-K inhibitor L-235 (CatKI, 10 mg/kg, daily, p.o.; n = 13) in prevention mode for 27 weeks. Samples from the cortical femur and trabecular lumbar vertebrae were polished, demineralized, and imaged using AFM. Auto-correlation of image patches was used to generate a vector field for each image that mathematically approximated the collagen fibril alignment. This vector field was used to compute an information-theoretic entropy that was employed as a quantitative fibril alignment parameter (FAP) to allow image-to-image and sample-to-sample comparison. For all samples, no change was observed in the average FAP values; however significant differences in the distribution of FAP values were observed. In particular, OVX + Veh lumbar vertebrae samples contained a tail of lower FAP values representing regions of greater fibril alignment. OVX + ALN treatment resulted in a FAP distribution with a tail indicating greater alignment for cortical femur and less alignment for trabecular lumbar vertebrae. OVX + CatKI treatment gave a distribution of FAP values with a tail indicating less alignment for cortical femur and no change for trabecular lumbar vertebrae. Fibril alignment was also evaluated by considering when a fibril was part of discrete bundles or sheets (classified as parallel) or not (classified as oblique). For this analysis, the percentage of parallel fibrils in cortical femur for the OVX group was 17% lower than the Sham group. OVX + ALN treatment partially prevented the proportion of parallel fibrils from decreasing and OVX + CatKI treatment completely prevented a change. In trabecular lumbar vertebrae, there was no difference in the percentage of parallel fibrils between Sham and any of the other treatment groups.

Effect of surfactants on surface activity and rheological properties of type I collagen at air/water interface

We describe the effect of three synthetic surfactants (anionic - sodium dodecyl sulfate (SDS), cationic - cetyltrimethylammonium bromide (CTAB) and nonionic - Triton X-100 (TX-100)) on surface properties of the type I calf skin collagen at the air/water interface in acidic solutions (pH 1.8). The protein concentration was fixed at 5×10^-6molL^-1 and the surfactant concentration was varied in the range 5×10^-6molL^-1-1×10^-4molL^-1, producing the protein/surfactant mixtures with molar ratios of 1:1, 1:2, 1:5, 1:10 and 1:20. An Axisymmetric Drop Shape Analysis (ADSA) method was used to determine the dynamic surface tension and surface dilatational moduli of the mixed adsorption layers. Two spectroscopic techniques: UV-vis spectroscopy and fluorimetry allowed us to determine the effect of the surfactants on the protein structure. The thermodynamic characteristic of the mixtures was studied using isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC). Modification of the collagen structure by SDS at low surfactant/protein ratios has a positive effect on the mixture's surface activity with only minor deterioration of the rheological properties of the adsorbed layers. The collagen/CTAB mixtures do not show that pronounced improvement in surface activity, while rheological properties are significantly deteriorated. The mixtures with non-ionic TX-100 do not show any synergistic effects in surface activity.

In Vitro Analysis of the Co-Assembly of Type-I and Type-III Collagen

An important step towards achieving functional diversity of biomimetic surfaces is to better understand the co-assembly of the extracellular matrix components. For this, we study type-I and type-III collagen, the two major collagen types in the extracellular matrix. By using atomic force microscopy, custom image analysis, and kinetic modeling, we study their homotypic and heterotypic assembly. We find that the growth rate and thickness of heterotypic fibrils decrease as the fraction of type-III collagen increases, but the fibril nucleation rate is maximal at an intermediate fraction of type-III. This is because the more hydrophobic type-I collagen nucleates fast and grows in both longitudinal and lateral directions, whereas more hydrophilic type-III limits lateral growth of fibrils, driving more monomers to nucleate additional fibrils. This demonstrates that subtle differences in physico-chemical properties of similar molecules can be used to fine-tune their assembly behavior.

Intense Raman scattering on hybrid Au/Ag nanoplatforms for the distinction of MMP-9-digested collagen type-I fiber detection

Well-ordered Au-nanorod arrays were fabricated using the focused ion beam method (denoted as fibAu_NR). Au or Ag nanoclusters (NCs) of various sizes and dimensions were then deposited on the fibAu_NR arrays using electron beam deposition to improve the surface-enhanced Raman scattering (SERS) effect, which was verified using a low concentration of crystal violet (10(-)(5)M) as the probe molecule. An enhancement factor of 6.92 × 10(8) was obtained for NCsfibAu_NR, which is attributed to the combination of intra-NC and NR localized surface plasmon resonance. When 4-aminobenzenethiol (4-ABT)-coated Au or Ag nanoparticles (NPs) were attached to NCsfibAu_NR, the small gaps between 4-ABT-coated NPs and intra-NCs allowed detection at the single-molecule level. Hotspots formed at the interfaces of NCs/NRs and NPs/NCs at a high density, producing a strong local electromagnetic effect. Raman spectra from as-prepared type I collagen (Col-I) and Ag-NP-coated Col-I fibers on NCsfibAu_NR were compared to determine the quantity of amino acids in their triple helix structure. Various concentrations of matrix-metalloproteinase-9-digested Col-I fibers on NCsfibAu_NR were qualitatively examined at a Raman laser wavelength of 785nm to determine the changes of amino acids in the Col-I fiber structure. The results can be used to monitor the growth of healing Col-I fibers in a micro-environment.

Influence on the physicochemical properties of fish collagen gels using self-assembly and simultaneous cross-linking with the N-hydroxysuccinimide adipic acid derivative

Collagen gels from Southern catfish (Silurus meridionalis Chen) skins were prepared via the self-assembly of collagen molecules and simultaneous cross-linking with the N-hydroxysuccinimide adipic acid derivative (NHS-AA). The doses of NHS-AA were converted to [NHS-AA]/[NH2] ratios (0.025-1.6, calculated by the [active ester group] of NHS-AA and [ε-NH2] of lysine and hydroxylysine residues of collagen). When the ratio < 0.05, collagen gels were formed by collagen molecule self-assembly, resulting in the opalescent appearance of collagen gels and the characteristic D-periodicity of partial collagen fibrils, the collagen gel ([NHS-AA]/[NH2] = 0.05) displayed a small increase in denaturation temperature (Td, 42.8 °C), remaining weight (12.59%), specific water content (SWC 233.7) and elastic modulus (G' 128.4 Pa) compared with uncross-linked collagen gel (39.1 °C, 9.12%, 222.4 and 85.4 Pa, respectively). As the ratio > 0.05, disappearance of D-periodicity and a gradual change in appearance from opalescent to transparent suggested that the inhibition of NHS-AA in the self-assembly of collagen molecules was more obvious. As a result, the collagen gel ([NHS-AA]/[NH2] = 0.2) had the lowest Td (35.8 °C), remaining weight (7.96%), SWC (130.9) and G' (31.9 Pa). When the ratio was 1.6, the collagen molecule self-assembly was markedly suppressed and the formation of collagen gel was predominantly via the covalent cross-linking bonds which led to the transparent appearance, and the maximum values of Td (47.0 °C), remaining weight (45.92%) and G' (420.7 Pa) of collagen gel. These results indicated that collagen gels with different properties can be prepared using different NHS-AA doses.

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.

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.

Collagen mimetic peptide engineered M13 bacteriophage for collagen targeting and imaging in cancer

Collagens are over-expressed in various human cancers and subsequently degraded and denatured by proteolytic enzymes, thus making them a target for diagnostics and therapeutics. Genetically engineered bacteriophage (phage) is a promising candidate for the development of imaging or therapeutic materials for cancer collagen targeting due to its promising structural features. We genetically engineered M13 phages with two functional peptides, collagen mimetic peptide and streptavidin binding peptide, on their minor and major coat proteins, respectively. The resulting engineered phage functions as a therapeutic or imaging material to target degraded and denatured collagens in cancerous tissues. We demonstrated that the engineered phages are able to target and label abnormal collagens expressed on A549 human lung adenocarcinoma cells after the conjugation with streptavidin-linked fluorescent agents. Our engineered collagen binding phage could be a useful platform for abnormal collagen imaging and drug delivery in various collagen-related diseases.

Self-assembly of collagen on flat surfaces: the interplay of collagen-collagen and collagen-substrate interactions

Fibrillar collagens, common tissue scaffolds in live organisms, can also self-assemble in vitro from solution. While previous in vitro studies showed that the pH and the electrolyte concentration in solution largely control the collagen assembly, the physical reasons why such control could be exerted are still elusive. To address this issue and to be able to simulate self-assembly over large spatial and temporal scales, we have developed a microscopic model of collagen with explicit interactions between the units that make up the collagen molecules, as well as between these units and the substrate. We have used this model to investigate assemblies obtained via molecular dynamics deposition of collagen on a substrate at room temperature using an implicit solvent. By comparing the morphologies from our molecular dynamics simulations with those from our atomic-force microscopy experiments, we have found that the assembly is governed by the competition between the collagen-collagen interactions and those between collagen and the substrate. The microscopic model developed here can serve for guiding future experiments that would explore new regions of the parameter space.

Variation in type I collagen fibril nanomorphology: the significance and origin

Although the axial D-periodic spacing is a well-recognized nanomorphological feature of type I collagen fibrils, the existence of a distribution of values has been largely overlooked since its discovery seven decades ago. Studies based on single fibril measurements occasionally noted variation in D-spacing values, but accredited it with no biological significance. Recent quantitative characterizations supported that a 10-nm collagen D-spacing distribution is intrinsic to collagen fibrils in various tissues as well as in vitro self-assembly of reconstituted collagen. In addition, the distribution is altered in Osteogenesis Imperfecta and long-term estrogen deprivation. Bone collagen is organized into lamellar sheets of bundles at the micro-scale, and D-spacings within a bundle of a lamella are mostly identical, whereas variations among different bundles contribute to the full-scale distribution. This seems to be a very general phenomenon for the protein as the same type of D-spacing/bundle organization is observed for dermal and tendon collagen. More research investigation of collagen nanomorphology in connection to bone biology is required to fully understand these new observations. Here we review the data demonstrating the existence of a D-spacing distribution, the impact of disease on the distribution and possible explanations for the origin of D-spacing variations based on various collagen fibrillogenesis models.