Collagen banded fibril structure and the collagen-platelet reaction

An in-vitro evaluation of residual dentin retained after using novel enzymatic-based chemomechanical caries removal agents

To assess the biochemical, mechanical and structural characteristics of retained dentin after applying three novel bromelain-contained chemomechanical caries removal (CMCR) formulations in comparison to the conventional excavation methods (hand and rotary) and a commercial papain-contained gel (Brix 3000). Seventy-two extracted permanent molars with natural occlusal carious lesions (score > 4 following the International Caries Detection and Assessment System (ICDAS-II)) were randomly allocated into six groups (n = 12) according to the excavation methods: hand excavation, rotary excavation, Brix 3000, bromelain-contained gel (F1), bromelain-chloramine-T (F2), and bromelain-chlorhexidine gel (F3). The superficial and deeper layers of residual dentin were examined by Raman microspectroscopy and Vickers microhardness, while the surface morphology was assessed by the scanning electron microscope (SEM). A multivariate analysis of variance followed by Tukey's test (p > 0.05) was performed for data analysis. The novel formulations showed an ability to preserve the partially demineralized dentin that showed a reduced phosphate content with a higher organic matrix. This was associated with lower Vickers microhardness values in comparison to sound dentin and rotary excavation. The collagen integration ratio in all methods was close to sound dentin (0.9-1.0) at the deeper dentin layer. The bromelain-chloramine-T gel (F2) produced the smoothest smear-free dentin surface with a higher number of opened dentinal tubules. In contrast, dense smearing covering the remaining dentin was observed in the manual and rotary methods with obstructed dentin tubule orifices. The bromelain-contained formulations can be considered a new minimally invasive approach for selectively removing caries in deep cavitated dentin lesions.

Theaflavin -3,3'-digallate/ethanol: a novel cross-linker for stabilizing dentin collagen

Objectives

To study the ability of theaflavin-3,3'-digallate (TF3)/ethanol solution to crosslink demineralized dentin collagen, resist collagenase digestion, and explore the potential mechanism.

Methods

Fully demineralized dentin blocks were prepared using human third molars that were caries-free. Then, these blocks were randomly allocated into 14 separate groups (n = 6), namely, control, ethanol, 5% glutaraldehyde (GA), 12.5, 25, 50, and 100 mg/ml TF3/ethanol solution groups. Each group was further divided into two subgroups based on crosslinking time: 30 and 60 s. The efficacy and mechanism of TF3's interaction with dentin type I collagen were predicted through molecular docking. The cross-linking, anti-enzymatic degradation, and biomechanical properties were studied by weight loss, hydroxyproline release, scanning/transmission electron microscopy (SEM/TEM), in situ zymography, surface hardness, thermogravimetric analysis, and swelling ratio. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy were utilized to explore its mechanisms. Statistical analysis was performed using one and two-way analysis of variance and Tukey's test.

Results

TF3/ethanol solution could effectively crosslink demineralized dentin collagen and improve its resistance to collagenase digestion and biomechanical properties (p < 0.05), showing concentration and time dependence. The effect of 25 and 50 mg/ml TF3/ethanol solution was similar to that of 5% GA, whereas the 100 mg/mL TF3/ethanol solution exhibited better performance (p < 0.05). TF3 and dentin type I collagen are mainly cross-linked by hydrogen bonds, and there may be covalent and hydrophobic interactions.

Conclusion

TF3 has the capability to efficiently cross-link demineralized dentin collagen, enhancing its resistance to collagenase enzymatic hydrolysis and biomechanical properties within clinically acceptable timeframes (30 s/60 s). Additionally, it exhibits promise in enhancing the longevity of dentin adhesion.

Longitudinal bond strength of a universal adhesive and chemical dentin characterization under different acid etching protocols

OBJECTIVE

This study aimed to analyze the longitudinal bond strength of a universal adhesive and chemically characterize the dentin substrate under different acid etching protocols.

METHODOLOGY

Dentin samples were etched with polyacrylic acid 25% (PAA) for 10 seconds (n=3) and phosphoric acid 32% (PA) for 15 seconds (n=3) and analyzed by Fourier transform infrared spectroscopy - attenuated total reflectance (FTIR-ATR) before and after treatment. For collagen degradation, samples (n=12) were divided into 3 groups: PAA, PA, and Deionized water (control), and analyzed by the quantity of solubilized type I collagen C-terminal cross-linked telopeptides and solubilized C-terminal peptide in relation to total protein concentration (ICTPtp and CTXtp) and by their ultimate tensile strength (UTS). For the adhesive interface analysis, dentin samples (n=72) were divided into 3 groups: PAA, PA, and Self-etch (SE), and subdivided into 2 groups: 24 h (baseline) and 1 year. The following tests were performed: microtensile bond strength (μTBS) (n=48), scanning electron microscopy (SEM) (n=12), and nanoleakage (n=12).

RESULTS

The FTIR of PAA showed lower reduction of the peaks in the phosphate group when compared to PA. For ICTPtp, PA showed a significantly higher value. For CTXtp, PA and PAA groups failed to statically differ from each other. UTS was significantly lower for PA. For μTBS, storage time significantly affected bond strength. The results were unaffected by the etching protocol. For SEM, after 1 year, PA had little evidence of degradation in the upper third of the adhesive interface in comparison to the other groups. Nanoleakage showed no considerable silver impregnation after 1 year in the SE group.

CONCLUSION

The use of PAA prior to a universal adhesive (when compared to PA) represents a less aggressive type of etching to dentin. However, self-etching still seems to be the best option for universal adhesive systems that have functional monomers in their composition.

Effect of Different Crosslinkers on Denatured Dentin Collagen's Biostability, MMP Inhibition and Mechanical Properties

OBJECTIVE

Sound, natural dentin collagen can be stabilized against enzymatic degradation through exogenous crosslinking treatment for durable bonding; however, the effect on denatured dentin (DD) collagen is unknown. Hence, the ability of different crosslinkers to enhance/restore the properties of DD collagen was assessed.

METHODS

Demineralized natural and DD collagen films (7 mm × 7 mm × 7 µm) and beams (0.8 mm × 0.8 mm × 7 mm) were prepared. DD collagen was experimentally produced by heat or acid exposure, which was then assessed by various techniques. All specimens were then treated with 1 wt% of chemical crosslinker 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/n-hydroxysuccinimide (EDC/NHS) and two structurally different flavonoids-theaflavins (TF) from black tea and type-A proanthocyanidins from cranberry juice (CR) for either 30 s or 1 h. The controls were untreated. Dentin films were assessed for chemical interaction and cross-linking effect by FTIR, biostability against exogenous collagenase by weight loss (WL) and hydroxyproline release (HYP), and endogenous matrix metalloproteinases (MMPs) activity by confocal laser microscopy. Dentin beams were evaluated for tensile properties. Data were analyzed using ANOVA and Tukey's test (α = 0.05).

RESULTS

Compared with natural collagen, DD collagen showed pronounced structural changes, altered biostability and decreased mechanical properties, which were then improved to various degrees that were dependent on the crosslinkers used, with EDC/NHS being the least effective. Surprisingly, the well-known MMP inhibitor EDC/NHS showed negligible effect on or even increased MMP activity in DD collagen. As compared with control, cross-linking induced by TF and CR significantly increased collagen biostability (reduced WL and HYP release, p < 0.05), MMP inhibition (p < 0.001) and mechanical properties (p < 0.05), regardless of denaturation.

CONCLUSIONS

DD collagen cannot or can only minimally be stabilized via EDC/NHS crosslinking; however, the challenging substrate of DD collagen can be enhanced or restored using the promising flavonoids TF and CR.

Strategy Based on Michael Addition Reaction for the Development of Bioinspired Multilayered and Multiphasic 3D Constructs

The high incidence of osteochondral defects has increased the interest in the development of improved repairing alternatives, with tissue engineering being considered a promising approach. The hierarchical, complex structure of osteochondral tissue requires the design of a biomimetic multilayered scaffold. Here, a multilayered and multiphasic 3D macroporous structure was achieved at subzero temperature by the Michael addition reaction of amino functionalities of collagen with acryloyl groups of a bifunctionalized poly(ε-caprolactone). This green approach has been successfully applied to crosslink layers of different composition, both for their efficient sequential formation and connection. Polyethylenimine functionalized nano-hydroxyapatite (nHApLPEI) was added to the bottom layer. The resulting hybrid cryogels were characterized by morphology, equilibrium swelling ratios, compressive strength analysis, and MTS assay. They presented good stability, integrity, and biocompatibility. The results revealed that the properties of the prepared constructs may be tuned by varying the composition, number, and thickness of the layers. The Young modulus values were between 3.5 ± 0.02 and 10.5 ± 0.6 kPa for the component layers, while for the multilayered structures they were more than 7.3 ± 0.2 kPa. The equilibrium swelling ratio varied between 4.6 and 14.2, with a value of ~10.5 for the trilayered structure, correlated with the mean pore sizes (74–230 µm).

Biochemical and Mechanical Analysis of Occlusal and Proximal Carious Lesions

A precise evaluation of caries excavation endpoint is essential in clinical and laboratory investigations. Caries invasion differentiates dentin into structurally altered layers. This study assessed these changes using Raman spectroscopy and Vickers microhardness. Ten permanent molars with occlusal and proximal carious lesions were assessed and compared at 130 points utilizing four Raman spectroscopic peaks: phosphate v1 at 960 cm^-1, amide I (1650 cm^-1), amide III (1235 cm^-1) and the C-H bond of the pyrrolidine ring (1450 cm^-1). The phosphate-to-amide I peak ratio and collagen integrity peak ratio (amide III: C-H bond) of carious zones were calculated and compared in both lesions. The former ratio was correlated to 130 Vickers microhardness indentations through lesions. The caries-infected dentin (CID) exhibited low phosphate peak, but higher amide I, III and C-H bond peaks than other zones in both lesions. The peaks in amide regions (I and III) varied in occlusal versus proximal lesions. A high correlation was found between mineral: matrix peak ratio and equivalent microhardness number within carious lesions, while the collagen integrity peak ratio was applied in proximal lesions only. Raman spectroscopy detected changes in the mineral and matrix contents within different carious zones and regions.

Structurally abnormal collagen fibrils in abdominal aortic aneurysm resist platelet adhesion

BACKGROUND

Platelet adhesion to the subendothelial collagen fibrils is one of the first steps in hemostasis. Understanding how structural perturbations in the collagen fibril affect platelet adhesion can provide novel insights into disruption of hemostasis in various diseases. We have recently identified the presence of abnormal collagen fibrils with compromised D-periodic banding in the extracellular matrix remodeling present in abdominal aortic aneurysms (AAA).

OBJECTIVE

In this study, we employed multimodal microscopy approaches to characterize how collagen fibril structure impacts platelet adhesion in clinical AAA tissues.

METHODS

Ultrastructural atomic force microscopy (AFM) analysis was performed on tissue sections after staining with fluorescently labeled collagen hybridizing peptide (CHP) to recognize degraded collagen. Second harmonic generation (SHG) microscopy was used on CHP-stained sections to identify regions of intact versus degraded collagen. Finally, platelet adhesion was identified via SHG and indirect immunofluorescence on the same tissue sections.

RESULTS

Our results indicate that ultrastructural features characterizing collagen fibril abnormalities coincide with CHP staining. SHG signal was absent from CHP-positive regions. Additionally, platelet binding was primarily localized to regions with SHG signal. Abnormal collagen fibrils present in AAA (in SHG negative regions) were thus found to inhibit platelet adhesion compared to normal fibrils.

CONCLUSIONS

Our investigations reveal how the collagen fibril structure in the vessel wall can serve as another regulator of platelet-collagen adhesion. These results can be broadly applied to understand the role of collagen fibril structure in regulating thrombosis or bleeding disorders.

Mimicking the Hierarchical Organization of Natural Collagen: Toward the Development of Ideal Scaffolding Material for Tissue Regeneration

Biological materials found in living organisms, many of which are proteins, feature a complex hierarchical organization. Type I collagen, a fibrous structural protein ubiquitous in the mammalian body, provides a striking example of such a hierarchical material, with peculiar architectural features ranging from the amino acid sequence at the nanoscale (primary structure) up to the assembly of fibrils (quaternary structure) and fibers, with lengths of the order of microns. Collagen plays a dominant role in maintaining the biological and structural integrity of various tissues and organs, such as bone, skin, tendons, blood vessels, and cartilage. Thus, "artificial" collagen-based fibrous assemblies, endowed with appropriate structural properties, represent ideal substrates for the development of devices for tissue engineering applications. In recent years, with the ultimate goal of developing three-dimensional scaffolds with optimal bioactivity able to promote both regeneration and functional recovery of a damaged tissue, numerous studies focused on the capability to finely modulate the scaffold architecture at the microscale and the nanoscale in order to closely mimic the hierarchical features of the extracellular matrix and, in particular, the natural patterning of collagen. All of these studies clearly show that the accurate characterization of the collagen structure at the submolecular and supramolecular levels is pivotal to the understanding of the relationships between the nanostructural/microstructural properties of the fabricated scaffold and its macroscopic performance. Several studies also demonstrate that the selected processing, including any crosslinking and/or sterilization treatments, can strongly affect the architecture of collagen at various length scales. The aim of this review is to highlight the most recent findings on the development of collagen-based scaffolds with optimized properties for tissue engineering. The optimization of the scaffolds is particularly related to the modulation of the collagen architecture, which, in turn, impacts on the achieved bioactivity.

Light Cross-Linkable Marine Collagen for Coaxial Printing of a 3D Model of Neuromuscular Junction Formation

Collagen is a major component of the extracellular matrix (ECM) that modulates cell adhesion, growth, and migration, and has been utilised in tissue engineering applications. However, the common terrestrial sources of collagen carry the risk of zoonotic disease transmission and there are religious barriers to the use of bovine and porcine products in many cultures. Marine based collagens offer an attractive alternative and have so far been under-utilized for use as biomaterials for tissue engineering. Marine collagen can be extracted from fish waste products, therefore industry by-products offer an economical and environmentally sustainable source of collagen. In a handful of studies, marine collagen has successfully been methacrylated to form collagen methacrylate (ColMA). Our work included the extraction, characterization and methacrylation of Red Snapper collagen, optimisation of conditions for neural cell seeding and encapsulation using the unmodified collagen, thermally cross-linked, and the methacrylated collagen with UV-induced cross-linking. Finally, the 3D co-axial printing of neural and skeletal muscle cell cultures as a model for neuromuscular junction (NMJ) formation was investigated. Overall, the results of this study show great potential for a novel NMJ in vitro 3D bioprinted model that, with further development, could provide a low-cost, customizable, scalable and quick-to-print platform for drug screening and to study neuromuscular junction physiology and pathogenesis.

Optimization of the collagen extraction from Nile tilapia skin (Oreochromis niloticus) and its hydrogel with hyaluronic acid

Nile tilapia skin, an abundant waste from fish processing, can be used for collagen extraction, which has a high aggregated value for biomedical applications. Collagen extraction was conducted under different reaction conditions (time, temperature, and concentration of acetic acid) in order to optimize the yield without compromising the integrity of the collagen. Temperature and time were responsible for increased yield. The extraction at 4 and 20 °C produced the acid-solubilized collagen (ASC) with the intact triple helix and was analysed by Fourier-transform infrared spectroscopy (FT-IR) and circular dichroism (CD). The optimized ASC (which used 0.35 mol/L of acetic acid at 20 °C) was consumed to obtain for the first-time fish-based hydrogels with hyaluronic acid (HA) crosslinked with 1-ethyl-3-(3-dimethylaminopropryl carbodiimide (EDC) and N-hydroxysuccinimide (NHS). The hydrogel was characterized by FT-IR, rheology, swelling, and scanning electron microscopy (SEM), confirming that cross-linking was accomplished. It possesses a robust organized network, swells 255 % in PBS and bears interconnected pores with a diameter in the range of 10-100 μm. Until now, col-HA hydrogels crosslinked with EDC/NHS have not been reported in literature with collagen from Nile Tilapia skin. Fish collagen can be a better option than those from land-based animals (cow and pig).

Dimeric Proanthocyanidins on the Stability of Dentin and Adhesive Biointerfaces

A dentin biomodification strategy with selective proanthocyanidin (PAC)-enriched extracts reinforces dentin and dentin-resin interfaces. Enrichment of the extracts according to the degree of polymerization allows exploration of bioactive principles of PACs and structure-activity relationships. This study investigated the sustained dentin matrix biomodification and dentin-resin bioadhesion of 2 fractions consisting exclusively of B-type PAC dimers with or without a single galloyl motif (specifically, DIMER_G and DIMER_NG) and their precursor material, enriched grape seed extract (e-GSE; Vitis vinifera). The biomodification potential was determined by long-term evaluation of the apparent modulus of elasticity and collagen solubility (hydroxyproline release). Chemical characterization of the dentin matrix was performed by attenuated total reflectance-Fourier-transform infrared spectroscopy. The bioadhesive properties were assessed by a microtensile bond strength test at different time points, and macro-hybrid layers were produced to verify the degree of conversion of the adhesive resin. Fractions consisting of DIMER_G, DIMER_NG, and their precursor, e-GSE, increased the modulus of elasticity at all time points and reduced collagen degradation. Specimens treated with DIMER_NG remained stable throughout 12 mo of storage, whereas a significant drop in the modulus of elasticity was observed for the DIMER_G and e-GSE groups at 6 mo. The fractions and precursor did not affect the degree of resin conversion at the hybrid layer. Changes in infrared resonances corresponding to collagen cross-links in the dentin matrix occurred for all treatments. Higher bond strength was observed for dentin treated with e-GSE as compared with DIMER_G and DIMER_NG; all biointerfaces remained stable after 12 mo. Nongalloylated PACs mediate stable dentin biomodification, which includes protective activity against collagen degradation and reinforcement of the anchoring dentin matrix. Collectively, PACs with a higher degree of oligomerization offer a robust bioadhesion between the hydrophilic dentin matrix and the hydrophobic adhesive.

Effect of temperature on the actomyosin-paramyosin structure from giant squid mantle (Dosidicus gigas)

BACKGROUND

The secondary structure of a protein determines its functional properties, such as its gelling capacity. The α-helix and β-sheet comprise its main structures. Myofibrillar proteins from jumbo squid are composed mainly of the actomyosin-paramyosin complex; this complex contains a high percentage of α-helix, because actin, paramyosin, and myosin constitute 30%, 100%, and 55% of the α-helix, respectively. It is important to elucidate the role of the secondary structures in the gelation of giant squid proteins as they form gel. The role of the secondary structures in the gelation of giant squid proteins is therefore very important. For this reason, the objective of this work was to evaluate the effect of temperature on the structural behavior of actomyosin-paramyosin isolate (API) from Dosidicus gigas.

RESULTS

The unfolding of the API system, which is composed of the actomyosin-paramyosin complex, was clarified by studying surface hydrophobicity and viscosity. Three characteristic peaks were found, associated with myosin, paramyosin, and actin. Infrared and circular dichroism corroborated the view that API undergoes major structural changes, because it proceeds from mostly an α-helix structure to 100% β-sheet.

CONCLUSION

The structural rearrangement favors gelation by cross-linking, generating new protein-protein and water-protein interactions, which create a more stable structure compared to mantle proteins (MP). Likewise, the presence of sarcoplasmic and stromal proteins in D. gigas muscle prevents the unfolding of myofibrillar proteins, favoring gelation by agglomeration, decreasing the ability to trap water and thus its gelling capacity. © 2019 Society of Chemical Industry.

The effects of photodynamic therapy with blue light and papain-based gel associated with Urucum, on collagen and fibroblasts: a spectroscopic and cytotoxicity analysis

Papacarie Duo™ is clinically used and has proven effectiveness; however, it is necessary to improve its antimicrobial action. The combined treatment of Papacarie Duo™ with Urucum (Bixa Orellana) could create a potential tool for dental caries treatment; its extract obtained from the seeds' pericarp contains a water-soluble primary pigment (cis-bixin) with smaller amounts of other carotenoids. The dicarboxylic acid salts of cis-norbixin and trans-norbixin occur in heated alkaline solutions. To analyze the absorption spectra and cytotoxicity (with human dermal fibroblasts) in different concentrations of Urucum, associated or not with Papacarie Duo™, we performed this in vitro study. The effects of pure Urucum, Papacarie Duo™, and PapaUrucum™ on the microstructure of collagen were also analyzed. The application of papain-based gel with Urucum did not present cytotoxicity, its exhibit UV absorption spectrum peak around 460 ± 20 nm. Also, it showed that the compound used did not alter the chemical structure of collagen. Consequently, this product could be used as a chemomechanical method to remove dentin caries as well as being a potential product for antimicrobial photodynamic therapy (aPDT) application.

Papain gel containing methylene blue for simultaneous caries removal and antimicrobial photoinactivation against Streptococcus mutans biofilms

This study intended to evaluate the effects of a papain-gel with a red-light absorbing pigment (methylene blue – MB) to mediate photodynamic therapy (PDT) against Streptococcus mutans biofilms. The PapaMBlue was compared with free MB to generate reactive oxygen species using fluorescence probes (SOSG and HPF). PDT (660-nm light) was carried out against S. mutans biofilms grown on either plastic dishes or on collagen membrane and assayed by CFU, live-dead staining using confocal microscopy, transmission electron microscopy and H&E staining for collagen films. Cytotoxicity and subcellular localization was studied in human fibroblasts. Sponges of bioabsorbable type I collagen membrane were exposed to papain based gel, irradiated with laser and analyzed about their integrity by ATR-FTIR. The PapaMBlue produced higher amounts of singlet oxygen and hydroxyl radicals than free MB, possibly due to better disaggregation of the dye in solution. The PapaMBlue antimicrobial effects on biofilms proved to be capable of reducing the S. mutans. Both MTT and PrestoBlue assays showed higher cell viability and metabolism scores in fibroblasts treated with PapaMBlue and MB, possibly due to stimulation of mitochondrial activity and that collagen triple helix is unaffected. The PapaMBlue is equally effective as MB in destroying S. mutans biofilms growing on plastic or collagen without affecting fibroblasts.

Surface biology of collagen scaffold explains blocking of wound contraction and regeneration of skin and peripheral nerves

We review the details of preparation and of the recently elucidated mechanism of biological (regenerative) activity of a collagen scaffold (dermis regeneration template, DRT) that has induced regeneration of skin and peripheral nerves (PN) in a variety of animal models and in the clinic. DRT is a 3D protein network with optimized pore size in the range 20-125 µm, degradation half-life 14 ± 7 d and ligand densities that exceed 200 µM α1β1 or α2β1 ligands. The pore has been optimized to allow migration of contractile cells (myofibroblasts, MFB) into the scaffold and to provide sufficient specific surface for cell-scaffold interaction; the degradation half-life provides the required time window for satisfactory binding interaction of MFB with the scaffold surface; and the ligand density supplies the appropriate ligands for specific binding of MFB on the scaffold surface. A dramatic change in MFB phenotype takes place following MFB-scaffold binding which has been shown to result in blocking of wound contraction. In both skin wounds and PN wounds the evidence has shown clearly that contraction blocking by DRT is followed by induction of regeneration of nearly perfect organs. The biologically active structure of DRT is required for contraction blocking; well-matched collagen scaffold controls of DRT, with structures that varied from that of DRT, have failed to induce regeneration. Careful processing of collagen scaffolds is required for adequate biological activity of the scaffold surface. The newly understood mechanism provides a relatively complete paradigm of regenerative medicine that can be used to prepare scaffolds that may induce regeneration of other organs in future studies.

Synthesis of highly interconnected 3D scaffold from Arothron stellatus skin collagen for tissue engineering application

The substrate which is avidly used for tissue engineering applications should have good mechanical and biocompatible properties, and all these parameters are often considered as essential for dermal reformation. Highly interconnected three dimensional (3D) wound dressing material with enhanced structural integrity was synthesized from Arothron stellatus fish skin (AsFS) collagen for tissue engineering applications. The synthesized 3D collagen sponge (COL-SPG) was further characterized by different physicochemical methods. The scanning electron microscopy analysis of the material demonstrated that well interconnected pores with homogeneous microstructure on the surface aids higher swelling index and that the material also possessed good mechanical properties with a Young's modulus of 0.89±0.2 MPa. Biocompatibility of the 3D COL-SPG showed 92% growth for both NIH 3T3 fibroblasts and keratinocytes. Overall, the study revealed that synthesized 3D COL-SPG from fish skin will act as a promising wound dressing in skin tissue engineering.

Effect of papain-based gel on type I collagen--spectroscopy applied for microstructural analysis

Considering the improvement of biomaterials that facilitate atraumatic restorative techniques in dentistry, a papain-based gel can be used in the chemomechanical removal of decayed dental tissue. However, there is no information regarding the influence of this gel on the structure of sound collagen. The aim of the present study was to investigate the adsorption of a papain-based gel (Papacarie^TM) to collagen and determine collagen integrity after treatment. A pilot study was first performed with 10 samples of type I collagen membrane obtained from bovine Achilles deep tendon to compare the influence of hydration (Milli-Q water) on infrared bands of collagen. In a further experiment, 10 samples of type I collagen membrane were used to evaluate the effects of Papacarie^TM on the collagen microstructure. All analyses were performed using the attenuated total reflectance technique of Fourier transform infrared (ATR-FTIR). The results demonstrated that the application of Papacarie^TM does not lead to the degradation of collagen and this product can be safely used in minimally invasive dentistry. As the integrity of sound collagen is preserved after the application of the papain-based gel, this product is indicated for the selective removal of infected dentin, leaving the affected dentin intact and capable of re-mineralization.

A Fourier transform infrared spectroscopy analysis of carious dentin from transparent zone to normal zone

It is well known that caries invasion leads to the differentiation of dentin into zones with altered composition, collagen integrity and mineral identity. However, understanding of these changes from the fundamental perspective of molecular structure has been lacking so far. In light of this, the present work aims to utilize Fourier transform infrared spectroscopy (FTIR) to directly extract molecular information regarding collagen's and hydroxyapatite's structural changes as dentin transitions from the transparent zone (TZ) into the normal zone (NZ). Unembedded ultrathin dentin films were sectioned from carious teeth, and an FTIR imaging system was used to obtain spatially resolved FTIR spectra. According to the mineral-to-matrix ratio image generated from large-area low-spectral-resolution scan, the TZ, the NZ and the intermediate subtransparent zone (STZ) were identified. High-spectral-resolution spectra were taken from each zone and subsequently examined with regard to mineral content, carbonate distribution, collagen denaturation and carbonate substitution patterns. The integrity of collagen's triple helical structure was also evaluated based on spectra collected from demineralized dentin films of selected teeth. The results support the argument that STZ is the real sclerotic layer, and they corroborate the established knowledge that collagen in TZ is hardly altered and therefore should be reserved for reparative purposes. Moreover, the close resemblance between the STZ and the NZ in terms of carbonate content, and that between the STZ and the TZ in terms of being A-type carbonate-rich, suggest that the mineral that initially occludes dentin tubules is hydroxyapatite newly generated from odontoblastic activities, which is then transformed into whitlockite in the demineralization/remineralization process as caries progresses.

Proanthocyanidins' efficacy in stabilizing dentin collagen against enzymatic degradation: MALDI-TOF and FTIR analyses

OBJECTIVES

To investigate grape seed extract proanthocyanidins' (PA) capability in improving dentin collagen's sustainability in an enzymatic environment, given that the size and shape of the collagen samples, and the manner to apply PA are both clinically relevant.

METHODS

Human dentin was sectioned into 6-μm-thick films. After demineralisation in 35wt% phosphoric acid for 15s, the films were subject to 30s of treatment at PA concentrations of 0% (control), 0.5%, 1%, 2%, 3.75%, 7.5% and 15% (w/w), respectively. The films were then digested in 0.1wt% collagenase for 1h and 24h. The amount of degraded collagen in the liquid digests was determined by MALDI-TOF mass spectroscopy. The trend of PA's incorporation into dentin collagen was analysed by ATR-FTIR.

RESULTS

The control exhibited complete digestion in 1h. In contrast, collagen treated with 0.5% and 1% PA afforded 13.84±4.69% and an undetectable level of degradation, respectively in the first 1h of digestion, and additional 17.48±4.38% and 4.50±1.68%, respectively in the following 23h. Collagen treated with ≥2wt% PA was not significantly digested regardless of digestion time. FTIR spectroscopy revealed that PA incorporation was saturated at ≥2wt% PA.

CONCLUSION

Thirty seconds of PA treatment at 2wt% and above could provide optimal protection for dentin collagen against collagenase digestion.

CLINICAL SIGNIFICANCE

This study demonstrated PA's extraordinary efficiency in stabilizing demineralised dentin collagen when it is applied in a clinical relevant manner, and identified the optimal conditions for its utilization.

Biologically active collagen-based scaffolds: advances in processing and characterization

A small number of type I collagen-glycosaminoglycan scaffolds (collagen-GAG scaffolds; CGSs) have unusual biological activity consisting primarily in inducing partial regeneration of organs in the adult mammal. Two of these are currently in use in a variety of clinical settings. CGSs appear to induce regeneration by blocking the adult healing response, following trauma, consisting of wound contraction and scar formation. Several structural determinants of biological activity have been identified, including ligands for binding of fibroblasts to the collagen surface, the mean pore size (which affects ligand density) and the degradation rate (which affects the duration of the wound contraction-blocking activity by the scaffold). Processing variables that affect these determinants include the kinetics of swelling of collagen fibres in acetic acid, freezing of the collagen-GAG suspension and cross-linking of the freeze-dried scaffold. Recent developments in the processing of CGSs include fabrication of scaffolds that are paucidisperse in pore size, scaffolds with gradients in physicochemical properties (and therefore biological activity) and scaffolds that incorporate a mineral component. Advances in the characterization of the pore structure of CGSs have been made using confocal and nonlinear optical microscopy (NLOM). The mechanical behaviour of CGSs, as well as the resistance to degradative enzymes, have been studied. Following seeding with cells (typically fibroblasts), contractile forces in the range 26-450 nN per cell are generated by the cells, leading to buckling of scaffold struts. Ongoing studies of cell-seeded CGSs with NLOM have shown an advantage over the use of confocal microscopy due to the ability of the former method to image the CGS surfaces without staining (which alters its surface ligands), reduced cell photodamage, reduced fluorophore photobleaching and the ability to image deeper inside the scaffold.

Design of a multiphase osteochondral scaffold. I. Control of chemical composition

This is the first in a series of articles that describe the design and development of a family of osteochondral scaffolds based on collagen-glycosaminoglycan (collagen-GAG) and calcium phosphate technologies, engineered for the regenerative repair of defects in articular cartilage. The osteochondral scaffolds consist of two layers: a mineralized type I collagen-GAG scaffold designed to regenerate the underlying subchondral bone and a nonmineralized type II collagen-GAG scaffold designed to regenerate cartilage. The subsequent articles in this series describe the fabrication and properties of a mineralized scaffold as well as a two-layer (one mineralized, the other not) osteochondral scaffold for regeneration of the underlying bone and cartilage, respectively. This article describes a technology through which the chemical composition-particularly the calcium phosphate mass fraction-of triple coprecipitated nanocomposites of collagen, glycosaminoglycan, and calcium phosphate can be accurately and reproducibly varied without the need for titrants or other additives. Here, we describe how the mineral:organic ratio can be altered over a range that includes that for articular cartilage (0 wt % mineral) and for bone (75 wt % mineral). This technology achieves the objective of mimicking the composition of two main tissue types found in articular joints, with particular emphasis on the osseous compartment of an osteochondral scaffold. Exclusion of titrants avoids the formation of potentially harmful contaminant phases during freeze-drying steps crucial for scaffold fabrication, ensuring that the potential for binding growth factors and drugs is maintained.

Similarities and differences between induced organ regeneration in adults and early foetal regeneration

At least three organs (skin, peripheral nerves and the conjunctiva) have been induced to regenerate partially in adults following application of porous, degradable scaffolds with highly specific structure (templates). Templates blocked contraction and scar formation by inducing a reduction in the density of contractile fibroblasts (probably myofibroblasts) and by preventing these cells to organize themselves appropriately in the wound. In contrast, during early foetal healing, myofibroblasts were absent and wounds did not close by contraction but rather by spontaneous regeneration. The adult regenerative process has so far led to imperfect recovery of the physiological anatomy of skin (skin appendages were missing), while early foetal healing has led to apparently complete restoration. Furthermore, the mechanism of the adult regenerative process involves thwarting of myofibroblast function while, during early foetal healing, differentiation of myofibroblasts has not yet occurred. The data suggest that induced organ regeneration in the adult is the result of partial reversion to early foetal healing. If so, the adult may conceal a foetal response that may be subject to activation following application of highly active scaffolds or of other substances or cells.

Pexiganan-incorporated collagen matrices for infected wound-healing processes in rat

The use of peptide-based drugs is limited by their rapid degradability and toxicity at high concentration during their therapeutic application. These problems could be managed by the use of a peptide delivery agent for sustained release in the site of action. Collagen is one of the most proven biomaterials of good biocompatibility with an exceptional ligand encapsulating property. In this work, we have shown that pexiganan, an antimicrobial, 22-amino-acid peptide could be incorporated and delivered to the wound-healing site against bacterial strains Pseudomonas aeruginosa and Staphylococcus aureus. The release profiles of pexiganan collagen films with different collagen concentration were studied. The release of pexiganan from 2.5% w/w of collagen film showed a sustainable activity over 72 h with effective antimicrobial concentrations. Pexiganan-incorporated collagen (PIC)-treated groups were compared with open wound (OW)- and collagen film (CF)-treated rats. PIC-treated animals showed a diminishing level of bacterial growth as compared with OW- and CF-treated animals. The biochemical parameters such as hydroxyproline, protein, DNA, uronic acid, hexosamine, SOD, and catalase content in the granulation tissue of the healing wound revealed increased proliferation of cells involved in tissue reconstruction in PIC-treated groups when compared with OW- and CF-treated groups. Furthermore, spectroscopic studies suggested that collagen structure is not perturbed by pexiganan incorporation. This study provides rationale for application of collagen membrane for antimicrobial peptide delivery in infected wounds.

A novel method for the simultaneous, titrant-free control of pH and calcium phosphate mass yield

Calcium phosphate (CaP) bioceramics have long been of interest for the unique properties that they exhibit as bone substitute materials. By harnessing the unique bone-bonding capacity of CaP's, biomaterials scientists have made great strides over the past 2 decades to produce novel materials to assist in the treatments of defects caused by trauma, disease, or both. In recent years, however, it has become apparent that the traditional set of techniques used to produce calcium phosphates does not satisfy all of the requirements necessary to meet the challenges of emerging applications. In particular, recent interest in (i) the synthesis of coprecipitated CaP/bioorganic composites and (ii) the investigation of the mechanisms of biomineralization has highlighted the need for new methods to control pH and CaP mass yield.

Injectable gels of anionic collagen: Rhamsan composites for plastic correction: Preparation, characterization, and rheological properties

The present article describes the preparation and characterization of anionic collagen gels obtained from porcine intestinal submucosa after 72 h of alkaline treatment and in the form of rhamsan composites to develop injectable biomaterials for plastic reconstruction. All materials were characterized by SDS/polyacrylamide gel electrophoresis, infrared spectroscopy, thermal stability, potentiometric titration, rheological properties, and fluidity tests. Biocompatibility was appraised after the injection of anionic collagen: rhamsan composites at 2.5% in 60 North Folk rabbits. Independently of processing, the collagen's secondary structure was preserved in all cases, and after 72 h of hydrolysis the collagen was characterized by a carboxyl group content of 346+/-9, which, at physiological pH, corresponds to an increase of 106+/-17 negative charges, in comparison to native collagen, due to the selective hydrolysis of asparagine and glutamine carboxyamide side chain. Rheological studies of composites at pH 7.4 in concentrations of 2, 4, and 6% (in proportions of 75:1 and 50:1) showed a viscoelastic behavior dependent on the frequency, which is independent of concentration and proportion. In both, the concentration of the storage modulus always predominated over the loss modulus (G'>G'' and delta<45 degrees ). The results from creep experiments confirmed this behavior and showed that anionic collagen:rhamsan composites at pH 7.4 in the proportion of 50:1 are less elastic and more susceptible to deformation in comparison to gels in the proportion of 75:1, independent of concentration. This was further confirmed by flow experiments, indicating that the necessary force for the extrusion of anionic collagen:rhamsan composites, in comparison to anionic collagen, was significantly smaller and with a smooth flow. Biocompatibility studies showed that the tissue reaction of anionic collagen:rhamsan composites at 2.5% in the proportion of 75:1 was compatible with the application of these gels in plastic reconstruction. These results suggest that the association of collagen with rhamsan may be a good alternative in the replacement of glutaraldehyde to stabilize the microfibril assembly of commercial collagen gel preparations.

Dermal wound healing processes with curcumin incorporated collagen films

The wound healing process involves extensive oxidative stress to the system, which generally inhibits tissue remodeling. In the present study, an improvement in the quality of wound healing was attempted by slow delivery of antioxidants like curcumin from collagen, which also acts as a supportive matrix for the regenerative tissue. Curcumin incorporated collagen matrix (CICM) treated groups were compared with control and collagen treated rats. Biochemical parameters and histological analysis revealed that increased wound reduction, enhanced cell proliferation and efficient free radical scavenging in CICM group. The higher shrinkage temperature of CICM films suggests increased hydrothermal stability when compared to normal collagen films. Spectroscopic studies revealed that curcumin was bound to the collagen without affecting its triple helicity. Further we adopted the antioxidant assay using 2,2'-azobisisobutyronitrile to assess in vitro antioxidant activity of CICM. The antioxidant studies indicated that CICM quenches free radicals more efficiently. This study provides a rationale for the topical application of CICM as a feasible and productive approach to support dermal wound healing.

The effects of collagen type I topography on myoblasts in vitro

Cells respond to a variety of cues from their environment, which can include chemical, mechanical, and topographical signals. The differentiation of myoblasts requires a combination of signals. Myoblast fusion is strongly influenced by the chemical nature of the surrounding matrix and can be affected by mechanical stimulation. Studies also have shown that a large variety of cell types also are influenced by details of surface topography of a substrate as small as 44 nm. Cells grown on a collagen-coated surface differentiate more readily than those grown in the absence of the extracellular matrix protein. It is not known whether the effects of myoblast interaction with collagen are due solely to chemical interactions or if myoblasts also respond to the topography of collagen type I fibers. To determine the importance of collagen-generated topographical signals on myoblast development, cells were cultured and differentiated in vitro on surfaces that had been coated with either soluble collagen type I or fibrous collagen type I. Both surfaces present the same chemical interactions, but the additional topographical signals lead to differences in cell morphology, adhesion, spreading rates and, proliferation. Cells on the fibrous form of collagen are more stellate, form more adhesion plaques, spread faster, and proliferate at a faster, rate than cells on a surface of soluble collagen. Our data indicate that topographical signals play a role in early muscle development, but that other or additional signaling pathways regulate differentiation.

Characterization of polyanionic collagen prepared by selective hydrolysis of asparagine and glutamine carboxyamide side chains

Acellular polyanionic collagen materials intended for biomaterial and tissue engineering uses were prepared by the selective and controlled hydrolysis of carboxyamides from asparagine and glutamine residues of type I collagen present in pericardium, tendon, and intestinal submucosa, all from bovine origin. The increase in carboxyl groups was from 26 +/- 14 (12 h of hydrolysis) to 134 +/- 12 (144 h of hydrolysis). Although collagen triple helix structure of polyanionic materials was preserved in all cases, a decrease in thermal stability and a gradual loss in the ability of collagen molecules to form fibrils were detected with increasing carboxyl content, probably as a result of changes in the pattern of electrostatic interaction. The resulting materials were basically acellular polyanionic collagen matrixes associated with an elastin content dependent on the time of hydrolysis. The results showed that the procedure described in this work may be a useful process for preparation of collagen biomaterials with variable physicochemical properties and macromolecular arrangement with respect to fibril formation and with potential use in tissue engineering.

Cell adhesion and cytotoxicity studies over polyanionic collagen surfaces with variable negative charge and wettability

This work describes the cytotoxicity, and the cell adhesion behavior of K562 cell line from human erythroleukemia transfected with the DNA for the alpha(2)beta(1) integrin over type-I collagen matrices with variable degree of carboxyl group and wettability. The results showed that type-I collagen materials with variable degree of carboxyl group prepared by selective hydrolysis of carboxyamide side chains of Asn and Gln residues present in the protein, independently from the extent of side chain hydrolysis, was characterized by preserved triple helix structure for materials with a carboxyl group content up to 87 +/- 17. Imbibition and wettability increased linearly with increasing carboxyl group content from 46 +/- 12 to 87 +/- 17, and no signs of cytotoxicity were detected. Nevertheless, in comparison to native collagen, K562 cell adhesion to PACMs was significantly improved by factors ranging from 1.60 to 1.47x, with the reduction in cell adhesion observed with increasing carboxyl content attributed to a balance between the inhibition of increasing negative charge and the stimulation by increased wettability. On the other hand, the overall improvement of K562 cell adhesion to polyanionic collagen was attributed to the introduction of new distinct motifs described as the minimal active recognition sequence for alpha(2)beta(1) integrins binding with type-I collagen produced as a result of Asn-Gly Glu-Ala alpha2(I)294-297, and Gly Gln-Arg-Gly Val-Val carboxyamide side chains hydrolysis.

Immobilization of heparin to EDC/NHS-crosslinked collagen. Characterization and in vitro evaluation

In the present study, heparin immobilization to a non-cytotoxic crosslinked collagen substrate for endothelial cell seeding was investigated. Crosslinking of collagen using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) resulted in a material containing 14 free primary amino groups per 1000 amino acid residues (E/N14C). At a fixed molar ratio NHS:EDC of 0.6, the amount of heparin covalently immobilized to E/N14C increased with increasing molar ratios of EDC to heparin carboxylic acid groups (Hep-COOH), to a maximum of approximately 5-5.5 wt% at a ratio of 2. Upon incubation in cell culture medium of endothelial cells, 4 to 7% of the immobilized heparin was released during 11 days. Immobilization of increasing amounts of heparin to E/N14C progressively reduced activation of contact activation proteases. Optimal anticoagulant activity, as measured by thrombin inhibition, was obtained after heparin immobilization using a ratio of EDC to Hep-COOH of 0.2-0.4 (14-20 mg heparin immobilized per gram of collagen). Platelets deposited to (heparinized) E/N14C showed only minor spreading and aggregation, although heparin immobilization slightly increased the number of adherent platelets. The results of this study suggest that heparin immobilization to EDC/NHS-crosslinked collagen may improve the in vivo blood compatibility of this material.

Nonstoichiometric hydroxyapatite-anionic collagen composite as support for the double sustained release of gentamicin and norfloxacin/ciprofloxacin

This work studied the sustained release of ciprofloxacin or norfloxacin and gentamicin from nonstoichiometric hydroxyapatite (nHA) and anionic collagen composite. Within the first 24 and 48 h, the total antibiotic supply was significantly higher than the minimal inhibitory concentration required for the majority of the gram-negative bacteria. Although gentamicin was completely released from the matrix after 48 h by a normal diffusion mechanism, ciprofloxacin or norfloxacin release was characterized by a 2-phase release mechanism due to binding to nHA by complexation with calcium ion. Under the conditions studied, most of the norfloxacin or ciprofloxacin only will be disposable due to bioresorption or dissociation of the complexes. In conclusion, due to its biocompatibility nHA-anionic collagen composite may be a convenient support for the double sustained release of the antibiotics gentamicin and ciprofloxacin/norfloxacin for the control of bone infection while promoting bone tissue growth.

Anionic collagen: polymer composites with improved dielectric and rheological properties

This work describes the preparation and characterization of anionic collagen composites with rhamsan and vinylidene fluoride-trifluorethylene with improved rheological and dielectric properties without loss of collagen secondary structure with an interaction occurring between both macromolecules of the composites. On a comparative basis, the force needed for the extrusion of anionic collagen:rhamsan composites was in the range from 0.088 to 0.080 J compared to that for collagen of 0.189 J. Anionic collagen:vinylidene fluoride-trifluorethylene composites were characterized, in the case of the 1:1 composite, by a pyroelectric coefficient of 1.89 x 10(-4) cm(-2) K(-1), which was significantly higher than those determined under the same conditions for native anionic collagen and vinylidene fluoride-trifluorethylene.

Géis de colágeno aniônico: ransana como biomateriais. Preparação e caracterização físico-química

Este trabalho descreve o efeito da ransana, um polissacarídeo bacteriano, sobre géis de colágeno aniônico. A interação colágeno:ransana ocorreu independentemente do pH, mesmo com baixas concentrações de ransana, e os materiais obtidos no estado sólido foram caracterizados por serem mais estáveis térmicamente à medida em que se aumenta a concentração do polissacarídeo. Nenhuma alteração na estrutura secundária em tripla hélice do tropocolágeno foi observada. O efeito mais significativo da ransana sobre os géis aniônicos de colágeno foi um aumento significativo da viscosidade, e as variações observadas em função de pH e temperatura sugerem que nesta interação, não estão envolvidas forças de natureza eletrostática ou hidrofóbica. Micrografias de colágeno aniônico e colágeno aniônico:ransana mostraram a presença de estruturas vesiculares, diferente do padrão fibrilar característico de colágeno nativo. Um modelo de interação baseado na ação da ransana sobre a água estruturada, associada à organização macromolecular do colágeno em solução é proposto. Mais importante, géis de colágeno aniônico:ransana mostraram uma estabilidade térmica compatível com aquelas desejáveis para um biomaterial injetável de colágeno, evitando o uso do glutaraldeído como agente de estabilização.

Preparação e caracterização de colágeno aniônico por hidrólise seletiva de grupos carboxamida internos

Este trabalho descreve um processo para hidrólise seletiva de grupos carboxamidas de resíduos de asparagina e glutamina presentes em matrizes colagênicas, para a obtenção de colágeno aniônico para produção de novos biomateriais. Os resultados mostraram que em meio alcalino e na presença de metais alcalinos e alcalinos terrosos, os grupos carboxamidas da proteína são seletivamente hidrolizados para dar origem a pH neutro, a materiais de colágeno com um aumento de 106 de carga negativas, em relação à matrizes não modificadas. Embora não tenham sido observadas alterações na estrutura secundária da proteína ou na organização microfibrilar da matriz, modificações significativas foram observadas no padrão da sub-periodicidade do período D da estrutura microfibrilar, que provavelmente são devidas a um aumento da intensidade de interações eletrostáticas.

Platelet adhesion to collagen-coated wells: analysis of this complex process and a comparison with the adhesion to matrigel-coated wells

The mechanisms of platelet adhesion to collagen type III-coated wells and Matrigel-coated wells were analyzed. The adhesion of 51Cr-labeled platelets to collagen-coated wells showed a biphasic pattern. The early stage of adhesion was inhibited by antibodies against platelet glycoprotein(GP)s Ia/IIa and VI. The later stage of platelet adhesion was inhibited by an antibody against the GPIIb/IIIa complex and a concomitant release of 14C-labeled serotonin was observed. The percentage of adhered platelets was increased when a higher platelet concentration was added in the reaction medium. These results indicated that the adhesion assay of platelets to collagen-coated wells was composed of two reactions: the first one is the platelet-collagen interaction that depends on GPIa/IIa and GPVI on the platelet surface; and the second reaction is the platelet-platelet interaction, platelet aggregation, which depends on GPIIb/IIIa. The adhesion of platelets to Matrigel-coated wells was indicated to involve platelet-Matrigel interactions that were partly dependent on the laminin in the Matrigel solution.