Intermolecular interactions in collagen self-assembly as revealed by Fourier transform infrared spectroscopy

Silver carp swim bladder collagen derived from deep eutectic solvents: Enhanced solubility against pH and NaCl stresses

Deep eutectic solvents (DESs) are renowned in chemical and food industries for their eco-friendly extraction efficacy. Silver carp swim bladders, a collagen-rich byproduct of surimi production, are underutilized, resulting in considerable protein waste. Traditionally, collagen extraction has relied on harsh acids, contributing to environmental pollution and producing collagens with limited solubility, thus constraining their applications. This study evaluated DESs compared to conventional acids in extracting collagen, focusing on structural and solubility variations. Notably, urea-based DESs (urea-lactic acid: U-LA, 1:10, w/v) achieved the highest hydroxyproline recovery rates (∼ 94 %), comparable to acetic acid (AA, 1:20, w/v), but with half the solid-liquid ratio. Unlike acid-extracted collagen, which preserved the triple-helical structure, urea-based DESs partially disrupted this configuration by reducing intramolecular hydrogen bonding within collagen. However, these solvents simultaneously increased intermolecular hydrogen bonding. This alteration significantly enhanced collagen's solubility, maintaining over 60 % across a broad pH range (1-10) and various NaCl concentrations (0-6 %, w/v). Furthermore, urea-acetic acid (U-AA) extracted collagen exhibited the highest maximum transition temperature (solid state, Tmax = 101.94 °C) and gel strength (165 g). The findings suggest that urea-based DESs not only enhance collagen recovery rates but also its solubility and gelation properties, broadening its potential applications in cosmetics, food products, and biomaterials.

Elucidating the role of water in collagen self-assembly by isotopically modulating collagen hydration

Water is known to play an important role in collagen self-assembly, but it is still largely unclear how water-collagen interactions influence the assembly process and determine the fibril network properties. Here, we use the H[Formula: see text]O/D[Formula: see text]O isotope effect on the hydrogen-bond strength in water to investigate the role of hydration in collagen self-assembly. We dissolve collagen in H[Formula: see text]O and D[Formula: see text]O and compare the growth kinetics and the structure of the collagen assemblies formed in these water isotopomers. Surprisingly, collagen assembly occurs ten times faster in D[Formula: see text]O than in H[Formula: see text]O, and collagen in D[Formula: see text]O self-assembles into much thinner fibrils, that form a more inhomogeneous and softer network, with a fourfold reduction in elastic modulus when compared to H[Formula: see text]O. Combining spectroscopic measurements with atomistic simulations, we show that collagen in D[Formula: see text]O is less hydrated than in H[Formula: see text]O. This partial dehydration lowers the enthalpic penalty for water removal and reorganization at the collagen-water interface, increasing the self-assembly rate and the number of nucleation centers, leading to thinner fibrils and a softer network. Coarse-grained simulations show that the acceleration in the initial nucleation rate can be reproduced by the enhancement of electrostatic interactions. These results show that water acts as a mediator between collagen monomers, by modulating their interactions so as to optimize the assembly process and, thus, the final network properties. We believe that isotopically modulating the hydration of proteins can be a valuable method to investigate the role of water in protein structural dynamics and protein self-assembly.

The Structural Interactions of Molecular and Fibrillar Collagen Type I with Fibronectin and Its Role in the Regulation of Mesenchymal Stem Cell Morphology and Functional Activity

The observed differences in the structure of native tissue and tissue formed in vitro cause the loss of functional activity of cells cultured in vitro. The lack of fundamental knowledge about the protein mechanism interactions limits the ability to effectively create in vitro native tissue. Collagen is able to spontaneously assemble into fibrils in vitro, but in vivo, other proteins, for example fibronectin, have a noticeable effect on this process. The molecular or fibrillar structure of collagen plays an equally important role. Therefore, we studied the interaction of the molecular and fibrillar structure of collagen with fibronectin. Atomic force and transmission electron microscopy showed that the presence of fibronectin does not affect the native structure and diameter of collagen fibrils. Confocal microscopy demonstrated that the collagen structure affects the cell morphology. Cells are better spread on molecular collagen compared with cells cultured on fibrillar collagen. Fibronectin promotes the formation of a large number of focal contacts, while in combination with collagen of both forms, its effect is leveled. Thus, understanding the mechanisms of the relationship between the protein structure and composition will effectively manage the creation in vitro of a new tissue with native properties.

Benefit of coupling heparin to crosslinked collagen I/III scaffolds for human dermal fibroblast subpopulations' tissue growth

Currently, there is a lack of models representing the skin dermal heterogeneity for relevant research and skin engineering applications. This is the first study reporting production of dermal equivalents reproducing features of papillary and reticular dermal compartments. Inspired from our current knowledge on the architecture and composition differences between the papillary and reticular dermis, we evaluated different collagen-based porous materials to serve as scaffolds for the three-dimensional expansion of freshly isolated papillary and/or reticular fibroblasts. The scaffolds, composed of either collagen I or collagen I and III mixtures, were prepared by lyophilization. Pore size and hydrolytic stability were controlled by crosslinking with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) or EDC/NHS with covalently bound heparin. The evaluation of the resultant "papillary" and "reticular" dermal equivalents was based on the analysis of characteristic features of each dermal compartment, such as cell density and deposition of newly synthetized extracellular matrix components in histological sections. Crosslinking supported cell growth during dermal tissue formation independent on the fibroblast subpopulation. The presence of collagen III seemed to have some positive but non-specific effect only on the maintenance of the mechanical strength of the scaffolds during dermal formation. Histological analyses demonstrated a significant and specific effect of heparin on generating dermal equivalents reproducing the respective higher papillary than reticular cell densities and supporting distinct extracellular matrix components deposition (three to five times more carbohydrate material deposited by papillary fibroblasts in all scaffolds containing heparin, while higher collagen production was observed only in the presence of heparin).

On Force and Form: Mechano-Biochemical Regulation of Extracellular Matrix

The extracellular matrix is well-known for its structural role in supporting cells and tissues, and its important biochemical role in providing signals to cells has increasingly become apparent. These structural and biochemical roles are closely coupled through mechanical forces: the biochemistry of the extracellular matrix determines its mechanical properties, mechanical forces control release or display of biochemical signals from the extracellular matrix, and the mechanical properties of the matrix in turn influence the mechanical set point at which signals are sent. In this Perspective, we explain how the extracellular matrix is regulated by strain and mechanical forces. We show the impact of biochemistry and mechanical forces on in vivo assembly of extracellular matrix and illustrate how matrix can be generated in vitro using a variety of methods. We cover how the matrix can be characterized in terms of mechanics, composition, and conformation to determine its properties and to predict interactions. Finally, we explore how extracellular matrix remodeling, ligand binding, and hemostasis are regulated by mechanical forces. These recently discovered mechano-biochemical interactions have important functions in wound healing and disease progression. It is likely that mechanically altered extracellular matrix interactions are a commonly recurring theme, but due to limited tools to generate extracellular matrix fibers in vitro and lack of high-throughput methods to detect these interactions, it is hypothesized that many of these interactions have yet to be discovered.

Structural studies on Demospongiae sponges from Gökçeada Island in the Northern Aegean Sea

The Demospongiae is the largest Class in the phylum Porifera (sponges). Most sponge species in the Class Demospongiae have a skeleton of siliceous spicules and/or protein spongin or both. The first aim of this study was to perform the morphological and structural characterization of the siliceous spicules of four species belonging to Class Demospongiae (Suberites domuncula, Axinella polypoides, Axinella damicornis and Agelas oroides) collected around Gökçeada Island-Turkey (Northern Aegean Sea). The characterizations were carried out using a combination of Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM/EDX), Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Small Angle X-ray Scattering (SAXS) techniques. The sponge Chondrosia reniformis (Porifera, Demospongiae) lacks a structural skeleton of spicules or the spongin. It consists mainly of a collagenous tissue. The collagen with sponge origin is an important source in biomedical and pharmaceutical applications. The second aim of this study was to provide more information on the molecular structure of collagen of outer (ectosome) and inner (choanosome) regions of the Chondrosia reniformis using ATR-FTIR spectroscopy. Hierarchical clustering analysis (HCA) was also used for the discrimination of ATR-FTIR spectra of species.

Facile construction of mechanically tough collagen fibers reinforced by chitin nanofibers as cell alignment templates

Reconstituted collagen fibers with excellent mechanical performance were successfully fabricated with sodium alginate as coagulate and chitin nanofibers as reinforcing filler and applied as a fibroblast alignment templated scaffold.

Polymorphism of amyloid fibrils formed by a peptide from the yeast prion protein Sup35: AFM and Tip-Enhanced Raman Scattering studies

Aggregation of prion proteins is the cause of various prion related diseases. The infectious form of prions, amyloid aggregates, exist as multiple strains. The strains are thought to represent structurally different prion protein molecules packed into amyloid aggregates, but the knowledge on the structure of different types of aggregates is limited. Here we report on the use of AFM (Atomic Force Microscopy) and TERS (Tip-Enhanced Raman Scattering) to study morphological heterogeneity and access underlying conformational features of individual amyloid aggregates. Using AFM we identified the morphology of amyloid fibrils formed by the peptide (CGNNQQNY) from the yeast prion protein Sup35 that is critically involved in the aggregation of the full protein. TERS results demonstrate that morphologically different amyloid fibrils are composed of a distinct set of conformations. Fibrils formed at pH 5.6 are composed of a mixture of peptide conformations (β-sheets, random coil and α-helix) while fibrils formed in pH~2 solution primarily have β-sheets. Additionally, peak positions in the amide III region of the TERS spectra suggested that peptides have parallel arrangement of β-sheets for pH~2 fibrils and antiparallel arrangement for fibrils formed at pH 5.6. We also developed a methodology for detailed analysis of the peptide secondary structure by correlating intensity changes of Raman bands in different regions of TERS spectra. Such correlation established that structural composition of peptides is highly localized with large contribution of unordered secondary structures on a fibrillar surface.

Structure of collagen adsorbed on a model implant surface resolved by polarization modulation infrared reflection-absorption spectroscopy

The polarization modulation infrared reflection-absorption spectra of collagen adsorbed on a titania surface and quantum chemical calculations are used to describe components of the amide I mode to the protein structure at a sub-molecular level. In this study, imino acid rich and poor fragments, representing the entire collagen molecule, are taken into account. The amide I mode of the collagen triple helix is composed of three absorption bands which involve: (i) (∼1690cm(-1)) the CO stretching modes at unhydrated groups, (ii) (1655-1673cm(-1)) the CO stretching at carbonyl groups at imino acids and glycine forming intramolecular hydrogen bonds with H atoms at both NH2 and, unusual for proteins, CH2 groups at glycine at a neighbouring chain and (iii) (∼1640cm(-1)) the CO stretching at carbonyl groups forming hydrogen bonds between two, often charged, amino acids as well as hydrogen bonds to water along the entire helix. The IR spectrum of films prepared from diluted solutions (c<50μgml(-1)) corresponds to solution spectra indicating that native collagen molecules interact with water adsorbed on the titania surface. In films prepared from solutions (c⩾50μgml(-1)) collagen multilayers are formed. The amide I mode is blue-shifted by 18cm(-1), indicating that intramolecular hydrogen bonds at imino acid rich fragments are weakened. Simultaneous red-shift of the amide A mode implies that the strength of hydrogen bonds at the imino acid poor fragments increases. Theoretically predicted distortion of the collagen structure upon adsorption on the titania surface is experimentally confirmed.

Enhanced Critical Size Defect Repair in Rabbit Mandible by Electrospun Gelatin/β‐TCP Composite Nanofibrous Membranes

The design and fabrication of biodegradable barrier membranes with satisfactory structure and composition remain a considerable challenge for periodontal tissue regeneration. We have developed a biomimetic nanofibrous membrane made from a composite of gelatin and β‐tricalcium phosphate (β‐TCP). We previously confirmed the in vitro biological performance of the membrane material, but the efficacy of the membranes in promoting bone repair in situ has not yet been examined. Gelatin/β‐TCP composite nanofibers were fabricated by incorporation of 20 wt.% β‐TCP nanoparticles into electrospun gelatin nanofibers. Electron microscopy showed that the composite membranes presented a nonwoven structure with an interconnected porous network and had a rough surface due to the β‐TCP nanoparticles, which were distributed widely and uniformly throughout the gelatin‐fiber matrix. The repair efficacy of rabbit mandible defects implanted with bone substitute (Bio‐Oss) and covered with the gelatin/β‐TCP composite nanofibrous membrane was evaluated in comparison with pure gelatin nanofibrous membrane. Gross observation, histological examination, and immunohistochemical analysis showed that new bone formation and defect closure were significantly enhanced by the composite membranes compared to the pure gelatin ones. From these results, we conclude that nanofibrous gelatin/β‐TCP composite membranes could serve as effective barrier membranes for guided tissue regeneration.

Use of ultrasonic and pepsin treatment in tandem for collagen extraction from meat industry by-products

BACKGROUND

Relatively little attention is paid to collagen-rich cattle short tendons (musculus extensor communis, musculus flexor digitorum, musculus digitorum profundis) as a source of high content and relatively pure collagen, a meat-processing by-product that is used to a minimal extent. Thus, suitable extraction processes from a meat production by-product to gain intact collagen is promising, which thus become interesting from an economic and environmental point of view.

RESULTS

Two extraction methods were compared: a 48 h pepsin treatment using 0.5 mol L⁻¹ acetic acid and an extraction using pepsin treatment after ultrasonic treatment in a 0.5 mol L⁻¹ acetic acid solution (the total ultrasonic and pepsin treatment time was 48 h). The results indicated that the optimal conditions for the extraction of collagen from cattle tendon with the ultrasonic-pepsin tandem method is: 4°C, tendon pre-swollen for 12 h in 0.5 mol L⁻¹ acetic acid, pepsin amount: 50 U mg⁻¹ of sample, ultrasonic-pepsin tandem treatment time for 18 h and 30 h, respectively. Extracted cattle tendon collagen using ultrasonic and pepsin treatment in tandem was characterised by amino acid analysis, SDS-PAGE, FT-IR, solubility and thermal denaturation temperature. The results show that the ultrasonic-pepsin tandem method can effectively improve the efficiency of pepsin extraction of natural collagen without any compromise of the resultant collagen quality.

CONCLUSION

This study provides a favourable process to deal with poorly extractable residue by use of ultrasonic and pepsin treatment in tandem. Extracted collagen possesses an intact molecular structure, which is useful and particularly important for its biomedical applications, such as drug delivery systems, wound dressings, and scaffolds.

Synthesis and character investigation of new collagen Hydrolysate/polyvinyl alcohol/hydroxyapatite Polymer-Nano-Porous Membranes: I. Experimental design optimization in thermal and structural properties

ABSTRACT

Development of bioorganic-inorganic composites has drawn eyes to extensive attention in biomedical fields and tissue engineering. So many attempts to prepare hydroxyapatite (HA), in conjunction with various binders including polyvinyl alcohol (PVA), and collagen has performed for late 20 years. We applied a method based on the phase separation for making of polymer porous membranes. This procedure is induced through the addition of a small quantity of water (polymer-rich phase) to a solution with HA precursors (polymer-poor phase). Thermal and structural composite properties of collagen Hydrolysate (CH)-PVA/HA Polymer-Nano-Porous Membranes were analyzed by Design of experiment that was undertaken using D-optimal approach, to select the optimal combination of nano composites precursor. The resulted composite characters were investigated by Fourier transform infrared, scanning electron microscopy (SEM) and thermal gravimetric analysis. Based on the SEM images, this new method could be clearly concluded to porous CH-PVA/HA hybrid materials. Finally the hemocompatibility of nanocomposite membranes were evaluated by the hemolysis study.

Collagen characteristics of farmed Atlantic salmon with firm and soft fillet texture

The possible role of collagen in texture variations among Atlantic salmon (Salmo salar L.) grown under commercial conditions at a Norwegian farm was studied. The texture was determined instrumentally as the breaking strength, and collagen and its salt (SSC), acid (ASC), pepsin (PSC) and insoluble (IF) fractions were analysed in order to determine the collagen aggregation degree. The collagen solubility and its overall amino acid (AA) composition showed no correlation to the breaking strength, but a positive correlation was observed between the breaking strength and glycine (r=0.74) and alanine (r=0.87) contents of the PSC fraction. Salmon with high breaking strength had higher T(peak) (temperature of transition) and ΔH (enthalpy of transition), and the collagen seemed to have triple helix structures mainly stabilized by covalent associations as compared to salmon with low breaking strength. The glycosylation degree was also positively correlated to the breaking strength (r=0.88, p ≤ 0.05). It is concluded that firmness of salmon muscle was not related to the total amount of collagen in the muscle, but rather higher collagen stability.

Nanostructured biomaterials for tissue engineered bone tissue reconstruction

Bone tissue engineering strategies are emerging as attractive alternatives to autografts and allografts in bone tissue reconstruction, in particular thanks to their association with nanotechnologies. Nanostructured biomaterials, indeed, mimic the extracellular matrix (ECM) of the natural bone, creating an artificial microenvironment that promotes cell adhesion, proliferation and differentiation. At the same time, the possibility to easily isolate mesenchymal stem cells (MSCs) from different adult tissues together with their multi-lineage differentiation potential makes them an interesting tool in the field of bone tissue engineering. This review gives an overview of the most promising nanostructured biomaterials, used alone or in combination with MSCs, which could in future be employed as bone substitutes. Recent works indicate that composite scaffolds made of ceramics/metals or ceramics/polymers are undoubtedly more effective than the single counterparts in terms of osteoconductivity, osteogenicity and osteoinductivity. A better understanding of the interactions between MSCs and nanostructured biomaterials will surely contribute to the progress of bone tissue engineering.

Thermodynamic modeling and investigation of the formation of electrospun collagen fibers

Electrospun type I collagen fibers are very promising materials for tissue scaffold applications, but are typically fabricated from toxic solvents. Recently, electrospinning of type I collagen fibers by using environmentally friendly phosphate buffer saline (PBS)/ethanol solution has been explored. PBS/ethanol solvent systems offer better cell compatibility, but the high surface tension and high boiling point of the solvent system make the collagen difficult to electrospin and can cause inferior fiber morphology. In this study, the influence of solvent surface tension on the morphology of electrospun collagen fibers has been experimentally investigated and analyzed from a thermodynamics perspective. The analytical results indicate that solvents with high surface tension drive the formation of beads along the smaller, thinner fibers. In addition, beads with relatively small angular eccentricity were thermodynamically favorable. The experimental results presented herein corroborate the theoretical analysis and conclusions drawn from this study. The surface tension of the solvent has significant influence on the bead formation, especially in an aqueous system. The environmental humidity for the electrospinning process and the collagen concentration were also investigated. These parameters may result in variations of the evaporation-solidification rates, which consequently impact the formation and morphologies of electrospun collagen fibers. According to the thermodynamic analysis, uniform electrospun collagen fibers without beads can be obtained by manipulating solvent surface tension during the electrospinning process.

Tissue engineering for intervertebral disk degeneration

Many challenges confront intervertebral disk engineering owing to complexity and the presence of extraordinary stresses. Rebuilding a disk of native function could be useful for removal of the symptoms and correction of altered spine kinematics. Improvement in understanding of disk properties and techniques for disk engineering brings promise to the fabrication of a functional motion segment for the treatment of disk degeneration. Increasing sophistication of techniques available in biomedical sciences will bring its application into clinics. This review provides an account of current progress and challenges of intervertebral disk bioengineering and discusses means to move forward and toward bedside translation.

Microspectroscopic evidence of cretaceous bone proteins

Low concentrations of the structural protein collagen have recently been reported in dinosaur fossils based primarily on mass spectrometric analyses of whole bone extracts. However, direct spectroscopic characterization of isolated fibrous bone tissues, a crucial test of hypotheses of biomolecular preservation over deep time, has not been performed. Here, we demonstrate that endogenous proteinaceous molecules are retained in a humerus from a Late Cretaceous mosasaur (an extinct giant marine lizard). In situ immunofluorescence of demineralized bone extracts shows reactivity to antibodies raised against type I collagen, and amino acid analyses of soluble proteins extracted from the bone exhibit a composition indicative of structural proteins or their breakdown products. These data are corroborated by synchrotron radiation-based infrared microspectroscopic studies demonstrating that amino acid containing matter is located in bone matrix fibrils that express imprints of the characteristic 67 nm D-periodicity typical of collagen. Moreover, the fibrils differ significantly in spectral signature from those of potential modern bacterial contaminants, such as biofilms and collagen-like proteins. Thus, the preservation of primary soft tissues and biomolecules is not limited to large-sized bones buried in fluvial sandstone environments, but also occurs in relatively small-sized skeletal elements deposited in marine sediments.

Simultaneous electrospin-electrosprayed biocomposite nanofibrous scaffolds for bone tissue regeneration

Currently, the application of nanotechnology in bone tissue regeneration is a challenge for the fabrication of novel bioartificial bone grafts. These nanostructures are capable of mimicking natural extracellular matrix with effective mineralization for successful regeneration of damaged tissues. The simultaneous electrospraying of nanohydroxyapatite (HA) on electrospun polymeric nanofibrous scaffolds might be more promising for bone tissue regeneration. In the current study, nanofibrous scaffolds of gelatin (Gel), Gel/HA (4:1 blend), Gel/HA (2:1 blend) and Gel/HA (electrospin-electrospray) were fabricated for this purpose. The morphology, chemical and mechanical stability of nanofibres were evaluated by means of field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy and with a universal tensile machine, respectively. The in vitro biocompatibility of different nanofibrous scaffolds was determined by culturing human foetal osteoblasts and investigating the proliferation, alkaline phosphatase (ALP) activity and mineralization of cells. The results of cell proliferation, ALP activity and FESEM studies revealed that the combination of electrospinning of gelatin and electrospraying of HA yielded biocomposite nanofibrous scaffolds with enhanced performances in terms of better cell proliferation, increased ALP activity and enhanced mineralization, making them potential substrates for bone tissue regeneration.

Influence of telopeptides, fibrils and crosslinking on physicochemical properties of type I collagen films

Type I collagen is widely used in various different forms for research and commercial applications. Different forms of collagen may be classified according to their source, extraction method, crosslinking and resultant ultrastructure. In this study, afibrillar and reconstituted fibrillar films, derived from acid soluble and pepsin digested Type I collagen, were analysed using Lateral Force Microscopy (LFM), Fourier Transform Infra-Red Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and enzymatic stability assays to asses the influence of telopeptides, fibrils and crosslinking. LFM proved to be a useful technique to confirm an afibrillar/fibrillar ultrastructure and to elucidate fibril diameters. FTIR has proved insensitive to ultrastructural differences involving telopeptides and fibrils. DSC results showed a significant increase in T(d) for crosslinked samples (+22-28 degrees C), and demonstrated that the thermal behaviour of hydrated, afibrillar films is more akin to reconstituted fibrillar films than monomeric solutions. The enzymatic stability assay has provided new evidence to show that afibrillar films of Type I collagen can be significantly more resistant to collagenase (by up to 3.5 times), than reconstituted fibrillar films, as a direct consequence of the different spatial arrangement of collagen molecules. A novel mechanism for this phenomenon is proposed and discussed. Additionally, the presence of telopeptide regions in afibrillar tropocollagen samples has been shown to increase resistance to collagenase by greater than 3.5 times compared to counterpart afibrillar atelocollagen samples. One-factor ANOVA analysis, with Fisher's LSD post-hoc test, confirms these key findings to be of statistical significance (P < 0.05). The profound physicochemical effects of collagen ultrastructure demonstrated in this study reiterates the need for comprehensive materials disclosure and classification when using these biomaterials.

Preparation and characterization of homogeneous chitosan-polylactic acid/hydroxyapatite nanocomposite for bone tissue engineering and evaluation of its mechanical properties

Homogeneous nanocomposites composed of hydroxyapatite and chitosan in the presence of polylactic acid were synthesized by a novel in situ precipitation method. The morphological and compositional properties of composites were investigated. Hydroxyapatite nanoparticles in a special rod-like shape with a diameter of about 50nm and a length of about 300nm were distributed homogeneously within the chitosan-polylactic acid matrix. The interaction between the organic matrix and the inorganic crystallite and the formation mechanism of the rod-like nanoparticles were also studied. The results suggested that the formation of the special rod-like nanoparticles could be controlled by a multiple-order template effect. High-resolution images showed that the rod-like inorganic particles were composed of randomly orientated subparticles about 10nm in diameter. The mechanical properties of the composites were evaluated by measuring their compressive strength and elastic modulus. The data indicated that the addition of polylactic acid can make homogeneous composites scaffold resist significantly higher stress. The elastic modulus of the composites was also improved by the addition of polylactic acid, which can make them more beneficial for surgical applications.

Organic-inorganic interaction between hydroxyapatite and gelatin with the aging of gelatin in aqueous phosphoric acid solution

Hydroxyapatite (HAp)/gelatin (GEL) nanocomposite was prepared by the solution-precipitation process using Ca(OH)(2) in water and aqueous solution of H(3)PO(4) in GEL. Before the co precipitation process the GEL powders were dissolved in the aqueous phosphoric acid solution for the phosphorylation of GEL molecules. The chemical variation of the phosphorylated GEL macromolecules was investigated by using attenuated total reflection (ATR) measurement. The crystal growth of HAp became bigger with the long-time aging of the GEL molecules in the phosphoric acid solution, and it resulted from the reduction of length scale of the GEL molecules. The degree of the organic-inorganic interaction was decreased because of the degradation of the GEL macromolecules.

FTIR studies of collagen model peptides: complementary experimental and simulation approaches to conformation and unfolding

X-ray crystallography of collagen model peptides has provided high-resolution structures of the basic triple-helical conformation and its water-mediated hydration network. Vibrational spectroscopy provides a useful bridge for transferring the structural information from X-ray diffraction to collagen in its native environment. The vibrational mode most useful for this purpose is the amide I mode (mostly peptide bond C=O stretch) near 1650 cm-1. The current study refines and extends the range of utility of a novel simulation method that accurately predicts the infrared (IR) amide I spectral contour from the three-dimensional structure of a protein or peptide. The approach is demonstrated through accurate simulation of the experimental amide I contour in solution for both a standard triple helix, (Pro-Pro-Gly)10, and a second peptide with a Gly --> Ala substitution in the middle of the chain that models the effect of a mutation in the native collagen sequence. Monitoring the major amide I peak as a function of temperature gives sharp thermal transitions for both peptides, similar to those obtained by circular dichroism spectroscopy, and the Fourier transform infrared (FTIR) spectra of the unfolded states were compared with polyproline II. The simulation studies were extended to model early stages of thermal denaturation of (Pro-Pro-Gly)10. Dihedral angle changes suggested by molecular dynamics simulations were made in a stepwise fashion to generate peptide unwinding from each end, which emulates the effect of increasing temperature. Simulated bands from these new structures were then compared to the experimental bands obtained as temperature was increased. The similarity between the simulated and experimental IR spectra lends credence to the simulation method and paves the way for a variety of applications.

Effects of collagen fiber orientation on the response of biologically derived soft tissue biomaterials to cyclic loading

In the present study, the effects of initial collagen fiber orientation on the medium-term (up to 50 x 10(6) cycles) fatigue response of heart valve soft tissue biomaterials was investigated. Glutaraldehyde treated bovine pericardium (GLBP), preselected for uniform structure and collagen fiber orientation, was used as the representative heart valve biomaterial. Using specialized instrumentation, GLBP specimens were subjected to cyclic tensile loading to maximum stress levels of 500 +/- 50 kPa at a frequency of 22 Hz. Two sample groups were examined, one with the preferred collagen fiber direction parallel (PD) and perpendicular (XD) to the direction of applied strain. The primary findings indicated that GLBP fatigue response was highly sensitive to the direction of loading with respect to fiber orientation. Specifically, when loading perpendicular to the preferred collagen fiber orientation, fiber reorientation is the dominant mechanism. In contrast, when loaded parallel to the preferred fiber direction a reduction in both collagen fiber crimp and fiber reorientation occurred. Moreover, alterations in the degree and direction of mechanical anisotropy can be inducted by cyclic loading when specimens are loaded perpendicular to the preferred fiber direction. Fourier Transform Infrared Spectroscopy (FT-IR) results indicate that molecular-level damage to collagen occurs in both groups after only 20 x 10(6) cycles. Taken as a whole, the results of this study suggest that initial collagen orientation plays a critical role in bioprosthetic heart valve biomaterial fatigue response.

Response of heterograft heart valve biomaterials to moderate cyclic loading

We have recently demonstrated that noncalcific tissue damage can lead to significant collagen degradation in clinically explanted bioprosthetic heart valves (BHVs). In the present study we quantified the early response of glutaraldehyde treated bovine pericardium (GLBP) to cyclic tensile loading to begin to elucidate the mechanisms of noncalcific tissue degeneration in BHV biomaterials. GLBP specimens were cycled at 30 Hz to a maximum uniaxial strain of 16% (corresponding to approximately 1-MPa peak stress), with the loading direction parallel to the preferred collagen fiber (PD) direction. After 30 x 10(6) cycles, specimens were subjected to biaxial mechanical testing, then cycled until 65 x 10(6) cycles. The results indicated a permanent change in the unloaded tissue dimensions of +7.1% strain in the PD direction and -7.7% strain in the cross fiber direction (XD) after 65 x 10(6) cycles and an increase of the collagen crimp period from 40.6 to 45.2 microm by 65 x 10(6) cycles (p = 0.05). Fourier transform IR spectroscopy analysis indicated that cyclic fatigue of GLBP leads to both collagen conformational changes and early denaturation. Furthermore, no significant changes in areal strain were found under 1-MPa equibiaxial stress, indicating that cyclic loading changed the collagen fiber orientation but not the overall tissue compliance. These observations suggest that while deterioration of collagen begins immediately, fiber straightening and reorientation dominates the changes in the mechanical behavior up to 65 x 10(6) cycles. The present study underscores the complexity of the response of biologically derived biomaterials to cyclic mechanical loading. Improved understanding of these phenomena can potentially guide the development of novel chemical treatment methods that seek to improve BHV durability by minimizing these degenerative processes.

Preparation of hydroxyapatite-gelatin nanocomposite

A nanocomposite of gelatin[GEL]-hydroxyapatite[HAp] was prepared using the biomimetic process. The hydroxyapatite nanocrystals were precipitated in aqueous solution of gelatin at pH 8 and 38 degrees C. The chemical bonding between calcium ions of HAp and carboxyl ions of GEL molecules induced a red-shift of the 1339 cm(-1) band of GEL in FT-IR analysis. TEM images and electron diffraction patterns for the nanocomposite strongly indicate the self-organization of HAp nanocrystals along the GEL fibrils. Electron diffraction for the nanocomposites showed a strong preferred orientation of the (002) plane in HAp nanocrystals. The development of HAp nanocrystals in an aqueous GEL solution was highly influenced by the concentration ratio of GEL to HAp. A higher concentration of GEL induced the formation of tiny crystallites (4 nm x 9 nm size), while a lower concentration of GEL contributed to the development of bigger crystallites (30 nm x 70 nm size). From DT/TGA data, the HAp-GEL nanocomposite showed typically three exothermic temperatures. The increase in decomposition temperatures indicates the formation of a primary chemical bond between HAp and GEL. The higher concentration of GEL supplies abundant reaction sites containing groups such as carboxyl, which can bind with calcium ions. The abundant supply of reaction sites leads to a very large number of HAp nuclei. However, the formation of a large number of nuclei depletes the concentration of calcium ions that available for growth to the extent that the nuclei cannot grow very large. This in turn will lead to the creation of a large number of tiny nanocrystals at this higher GEL concentration.

Fourier transform infrared evaluation of microscopic scarring in the cardiomyopathic heart: effect of chronic AT1 suppression

Our primary aim was to investigate the use of Fourier transform infrared (FTIR) spectromicroscopy as an accurate assay of cardiac extracellular matrix remodeling. Abnormal rearrangement or remodeling of the cardiac extracellular matrix is known to contribute to cardiac dysfunction. The microscopic multifocal necrosis and scarring are modulated by chronic AT(1) receptor blockade in experimental cardiomyopathy; thus, we also wished to rationalize the spectromicroscopic differences among control, untreated cardiomyopathic (CMP), and losartan-treated cardiomyopathic (LOS) hearts according to the pathogenesis of experimental cardiomyopathy. Male UM-X7.1 cardiomyopathic Syrian hamsters at early and late (65 and 200 days) stages of cardiomyopathy were subjected to 4-week losartan (15 mg/kg/day continuous infusion) treatment. Focal collagen microdomain distribution was confirmed spectroscopically by observation of the collagen IR fingerprint in the 1000-1800 cm(-1) region. Synchrotron FTIR spectromicroscopic map data were obtained from control (F1-beta strain) hamsters, nontreated cardiomyopathic, and losartan-treated CMP animals and imaged with mapping software, according to intensity of collagen fingerprint. Compared to controls, untreated late-stage CMP myocardium was characterized by elevated levels of fibrillar collagens and this was partially normalized with a 4-week losartan treatment. FTIR spectromicroscopy revealed that elevated collagen expression in focal microdomains is present in late-stage cardiomyopathy, and 4-week AT(1) blockade is associated with attenuation of collagen absorption in these lesions.