Structural mechanism for alteration of collagen gel mechanics by glutaraldehyde crosslinking

Self-Assembling Triple-Helix Recombinant Collagen Hydrogel Enriched with Tyrosine

The self-assembly of collagen within the human body creates a complex 3D fibrous network, providing structural integrity and mechanical strength to connective tissues. Recombinant collagen plays a pivotal role in the realm of biomimetic natural collagen. However, almost all of the reported recombinant collagens lack the capability of self-assembly, severely hindering their application in tissue engineering and regenerative medicine. Herein, we have for the first time constructed a series of self-assembling tyrosine-rich triple helix recombinant collagens, mimicking the structure and functionality of natural collagen. The recombinant collagen consists of a central triple-helical domain characterized by the (Gly-Xaa-Yaa)n sequence, along with N-terminal and C-terminal domains featuring the GYY sequence. The introduction of GYY has a negligible impact on the stability of the triple-helical structure of recombinant collagen while simultaneously promoting its self-assembly into fibers. In the presence of [Ru(bpy)3]Cl2 and APS as catalysts, tyrosine residues in the recombinant collagen undergo covalent cross-linking, resulting in a hydrogel with exceptional mechanical properties. The recombinant collagen hydrogel exhibits outstanding biocompatibility and bioactivity, significantly enhancing the proliferation, adhesion, migration, and differentiation of HFF-1 cells. This innovative self-assembled triple-helix recombinant collagen demonstrates significant potential in the fields of tissue engineering and medical materials.

Review paper: The importance of consideration of collagen cross-links in computational models of collagen-based tissues

Collagen as the main protein in Extra Cellular Matrix (ECM) is the main load-bearing component of fibrous tissues. Nanostructure and architecture of collagen fibrils play an important role in mechanical behavior of these tissues. Extensive experimental and theoretical studies have so far been performed to capture these properties, but none of the current models realistically represent the complexity of network mechanics because still less is known about the collagen's inner structure and its effect on the mechanical properties of tissues. The goal of this review article is to emphasize the significance of cross-links in computational modeling of different collagen-based tissues, and to reveal the need for continuum models to consider cross-links properties to better reflect the mechanical behavior observed in experiments. In addition, this study outlines the limitations of current investigations and provides potential suggestions for the future work.

A Glutaraldehyde-Free Crosslinking Method for the Treatment of Collagen-Based Biomaterials for Clinical Application

Biological bioprostheses such as grafts, patches, and heart valves are often derived from biological tissue like the pericardium. These bioprostheses can be of xenogenic, allogeneic, or autologous origin. Irrespective of their origin, all types are pre-treated via crosslinking to render the tissue non-antigenic and mechanically strong or to minimize degradation. The most widely used crosslinking agent is glutaraldehyde. However, glutaraldehyde-treated tissue is prone to calcification, inflammatory degradation, and mechanical injury, and it is incapable of matrix regeneration, leading to structural degeneration over time. In this work, we are investigating an alternative crosslinking method for an intraoperative application. The treated tissue's crosslinking degree was evaluated by differential scanning calorimetry. To confirm the findings, a collagenase assay was conducted. Uniaxial tensile testing was used to assess the tissue's mechanical properties. To support the findings, the treated tissue was visualized using two-photon microscopy. Additionally, fourier transform infrared spectroscopy was performed to study the overall protein secondary structure. Finally, a crosslinking procedure was identified for intraoperative processing. The samples showed a significant increase in thermal and enzymatic stability after treatment compared to the control, with a difference of up to 22.2 °C and 100%, respectively. Also, the tissue showed similar biomechanics to glutaraldehyde-treated tissue, showing greater extensibility, a higher failure strain, and a lower ultimate tensile strength than the control. The significant difference in the structure band ratio after treatment is proof of the introduction of additional crosslinks compared to the untreated control with regard to differences in the amide-I region. The microscopic images support these findings, showing an alteration of the fiber orientation after treatment. For collagen-based biomaterials, such as pericardial tissue, the novel phenolic crosslinking agent proved to be an equivalent alternative to glutaraldehyde regarding tissue characteristics. Although long-term studies must be performed to investigate superiority in terms of longevity and calcification, our novel crosslinking agent can be applied in concentrations of 1.5% or 2.0% for the treatment of biomaterials.

Experimental Investigation on the Penetrability Mechanism of Gel Slug During Well Completion Processes

Reservoir formation damage is an essential problem which troubled oil and gas well production, a smart packer is a promising technology to maintain sustainable development for the oil and gas fields. Currently, the "gel valve" technology has been proved to be feasible with gel slug to seal casing and descend the completion pipe string, while the systemic performance of ideal gel is still not clear. In the underbalanced completion stage with the gel valve, the downward completion string needs to penetrate the gel slug to form an oil and gas passage in the wellbore. The penetration of rod string to gel is a dynamic process. The gel-casing structure often shows a time-dependent mechanical response, which is different from the static response. In the process of penetration, the interaction force between the rod and gel is not only related to the properties of the interface between gel and string but also affected by the moving speed, rod diameter, and thickness of the gel. The dynamic penetration experiment was carried out to determine the penetrating force varied with depth. The research showed that the force curve was mainly composed of three parts, the rising curve of elastic deformation, decline curve for the surface worn out, and another curve of the rod wear into. By changing the rod diameter, gel thickness, and penetration speed, the change rules of forces in each stage were further analyzed, which would provide a scientific basis for a well completion design with a gel valve.

An indentation-based framework for probing the glycosaminoglycan-mediated interactions of collagen fibrils

Microscale deformation processes, such as reorientation, buckling, and sliding of collagen fibrils, determine the mechanical behavior and function of collagenous tissue. While changes in the structure and composition of tendon have been extensively studied, the deformation mechanisms that modulate the interaction of extracellular matrix (ECM) constituents are not well understood, partly due to the lack of appropriate techniques to probe the behavior. In particular, the role of glycosaminoglycans (GAGs) in modulating collagen fibril interactions has remained controversial. Some studies suggest that GAGs act as crosslinkers between the collagen fibrils, while others have not found such evidence and postulate that GAGs have other functions. Here, we introduce a new framework, relying on orientation-dependent indentation behavior of tissue and computational modeling, to evaluate the shear-mediated function of GAGs in modulating the collagen fibril interactions at a length scale more relevant to fibrils compared to bulk tests. Specifically, we use chondroitinase ABC to enzymatically deplete the GAGs in tendon; measure the orientation-dependent indentation response in transverse and longitudinal orientations; and infer the microscale deformation mechanisms and function of GAGs from a microstructural computational model and a modified shear-lag model. We validate the modeling approach experimentally and show that GAGs facilitate collagen fibril sliding with minimal crosslinking function. We suggest that the molecular reconfiguration of GAGs is a potential mechanism for their microscale, strain-dependent viscoelastic behavior. This study reveals the mechanisms that control the orientation-dependent indentation response by affecting the shear deformation and provides new insights into the mechanical function of GAGs and collagen crosslinkers in collagenous tissue.

The interface stiffness and topographic feature dictate interfacial invasiveness of cancer spheroids

During cancer metastasis, tumor cells likely navigate, in a collective manner, discrete tissue spaces comprising inherently heterogeneous extracellular matrix microstructures where interfaces may be frequently encountered. Studies have shown that cell migration modes can be determined by adaptation to mechanical/topographic cues from interfacial microenvironments. However, less attention has been paid to exploring the impact of interfacial mechnochemical attributes on invasive and metastatic behaviors of tumor aggregates. Here, we excogitated a collagen matrix-solid substrate interface platform to investigate the afore-stated interesting issue. Our data revealed that stiffer interfaces stimulated spheroid outgrowth by motivating detachment of single cells and boosting their motility and velocity. However, stronger interfacial adhesive strength between matrix and substrate led to the opposite outcomes. Besides, this interfacial parameter also affected the morphological switch between migration modes of the detached cells and their directionality. Mechanistically, myosin II-mediated cell contraction, compared to matrix metalloproteinases-driven collagen degradation, was shown to play a more crucial role in the invasive outgrowth of tumor spheroids in interfacial microenvironments. Thus, our findings highlight the importance of heterogeneous interfaces in addressing and combating cancer metastasis.

Crosslinker-free collagen gelation for corneal regeneration

Development of an artificial cornea can potentially fulfil the demand of donor corneas for transplantation as the number of donors is far less than needed to treat corneal blindness. Collagen-based artificial corneas stand out as a regenerative option, having promising clinical outcomes. Collagen crosslinked with chemical crosslinkers which modify the parent functional groups of collagen. However, crosslinkers are usually cytotoxic, so crosslinkers need to be removed from implants completely before application in humans. In addition, crosslinked products are mechanically weak and susceptible to enzymatic degradation. We developed a crosslinker free supramolecular gelation strategy using pyrene conjugated dipeptide amphiphile (PyKC) consisting of lysine and cysteine; in which collagen molecules are intertwined inside the PyKC network without any functional group modification of the collagen. The newly developed collagen implants (Coll-PyKC) are optically transparent and can effectively block UV light, are mechanically and enzymatically stable, and can be sutured. The Coll-PyKC implants support the growth and function of all corneal cells, trigger anti-inflammatory differentiation while suppressing the pro-inflammatory differentiation of human monocytes. Coll-PyKC implants can restrict human adenovirus propagation. Therefore, this crosslinker-free strategy can be used for the repair, healing, and regeneration of the cornea, and potentially other damaged organs of the body.

Glutaraldehyde fixation of venous valve tissue: A benchmark for alternative fixation methods

Objective

Bioprosthetic venous valves have yet to achieve long-term patency due to issues with calcification following implantation that is influenced by current xenograft fixation methods, most notably glutaraldehyde. The goal of this study was to investigate the effects of glutaraldehyde fixation on the functional properties of venous tissue to establish a benchmark for the evaluation of alternative fixation methods.

Methods

The degree of crosslinking was evaluated by determining shrink temperature and the stability of tissue with pronase and collagenase digestion.

Results

Glutaraldehyde fixation of venous tissue was confirmed by a significant difference in the shrink temperature between fresh and glutaraldehyde treated samples. Significant differences in the amount of tissue remaining following digestion were observed for venous versus cardiac tissue.

Conclusions

This study demonstrates the importance of tissue-specific evaluation in the development of alternative xenograft fixation methods to improve outcomes with bioprosthetic venous valves.

Nature-Based Biomaterials and Their Application in Biomedicine

Natural polymers, based on proteins or polysaccharides, have attracted increasing interest in recent years due to their broad potential uses in biomedicine. The chemical stability, structural versatility, biocompatibility and high availability of these materials lend them to diverse applications in areas such as tissue engineering, drug delivery and wound healing. Biomaterials purified from animal or plant sources have also been engineered to improve their structural properties or promote interactions with surrounding cells and tissues for improved in vivo performance, leading to novel applications as implantable devices, in controlled drug release and as surface coatings. This review describes biomaterials derived from and inspired by natural proteins and polysaccharides and highlights their promise across diverse biomedical fields. We outline current therapeutic applications of these nature-based materials and consider expected future developments in identifying and utilising innovative biomaterials in new biomedical applications.

Skeletal muscle progenitors are sensitive to collagen architectural features of fibril size and cross linking

Muscle stem cells (MuSCs) are essential for the robust regenerative capacity of skeletal muscle. However, in fibrotic environments marked by abundant collagen and altered collagen organization, the regenerative capability of MuSCs is diminished. MuSCs are sensitive to their extracellular matrix environment but their response to collagen architecture is largely unknown. The present study aimed to systematically test the effect of underlying collagen structures on MuSC functions. Collagen hydrogels were engineered with varied architectures: collagen concentration, cross linking, fibril size, and fibril alignment, and the changes were validated with second harmonic generation imaging and rheology. Proliferation and differentiation responses of primary mouse MuSCs and immortal myoblasts (C2C12s) were assessed using EdU assays and immunolabeling skeletal muscle myosin expression, respectively. Changing collagen concentration and the corresponding hydrogel stiffness did not have a significant influence on MuSC proliferation or differentiation. However, MuSC differentiation on atelocollagen gels, which do not form mature pyridinoline cross links, was increased compared with the cross-linked control. In addition, MuSCs and C2C12 myoblasts showed greater differentiation on gels with smaller collagen fibrils. Proliferation rates of C2C12 myoblasts were also higher on gels with smaller collagen fibrils, whereas MuSCs did not show a significant difference. Surprisingly, collagen alignment did not have significant effects on muscle progenitor function. This study demonstrates that MuSCs are capable of sensing their underlying extracellular matrix (ECM) structures and enhancing differentiation on substrates with less collagen cross linking or smaller collagen fibrils. Thus, in fibrotic muscle, targeting cross linking and fibril size rather than collagen expression may more effectively support MuSC-based regeneration.

Optimization of Collagen Chemical Crosslinking to Restore Biocompatibility of Tissue-Engineered Scaffolds

Collagen scaffolds, one of the most used biomaterials in corneal tissue engineering, are frequently crosslinked to improve mechanical properties, enzyme tolerance, and thermal stability. Crosslinkers such as 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) are compatible with tissues but provide low crosslinking density and reduced mechanical properties. Conversely, crosslinkers such as glutaraldehyde (GTA) can generate mechanically more robust scaffolds; however, they can also induce greater toxicity. Herein, we evaluated the effectivity of double-crosslinking with both EDC and GTA together with the capability of sodium metabisulfite (SM) and sodium borohydride (SB) to neutralize the toxicity and restore biocompatibility after crosslinking. The EDC-crosslinked collagen scaffolds were treated with different concentrations of GTA. To neutralize the free unreacted aldehyde groups, scaffolds were treated with SM or SB. The chemistry involved in these reactions together with the mechanical and functional properties of the collagen scaffolds was evaluated. The viability of the cells grown on the scaffolds was studied using different corneal cell types. The effect of each type of scaffold treatment on human monocyte differentiation was evaluated. One-way ANOVA was used for statistical analysis. The addition of GTA as a double-crosslinking agent significantly improved the mechanical properties and enzymatic stability of the EDC crosslinked collagen scaffold. GTA decreased cell biocompatibility but this effect was reversed by treatment with SB or SM. These agents did not affect the mechanical properties, enzymatic stability, or transparency of the double-crosslinked scaffold. Contact of monocytes with the different scaffolds did not trigger their differentiation into activated macrophages. Our results demonstrate that GTA improves the mechanical properties of EDC crosslinked scaffolds in a dose-dependent manner, and that subsequent treatment with SB or SM partially restores biocompatibility. This novel manufacturing approach would facilitate the translation of collagen-based artificial corneas to the clinical setting.

Rap1a Regulates Cardiac Fibroblast Contraction of 3D Diabetic Collagen Matrices by Increased Activation of the AGE/RAGE Cascade

Cardiovascular disease is a common diabetic complication that can arise when cardiac fibroblasts transition into myofibroblasts. Myofibroblast transition can be induced by advanced glycated end products (AGEs) present in the extracellular matrix (ECM) activating RAGE (receptor for advanced glycated end products) to elicit intracellular signaling. The levels of AGEs are higher under diabetic conditions due to the hyperglycemic conditions present in diabetics. AGE/RAGE signaling has been shown to alter protein expression and ROS production in cardiac fibroblasts, resulting in changes in cellular function, such as migration and contraction. Recently, a small GTPase, Rap1a, has been identified to overlap the AGE/RAGE signaling cascade and mediate changes in protein expression. While Rap1a has been shown to impact AGE/RAGE-induced protein expression, there are currently no data examining the impact Rap1a has on AGE/RAGE-induced cardiac fibroblast function. Therefore, we aimed to determine the impact of Rap1a on AGE/RAGE-mediated cardiac fibroblast contraction, as well as the influence isolated diabetic ECM has on facilitating these effects. In order to address this idea, genetically different cardiac fibroblasts were embedded in 3D collagen matrices consisting of collagen isolated from either non-diabetic of diabetic mice. Fibroblasts were treated with EPAC and/or exogenous AGEs, which was followed by assessment of matrix contraction, protein expression (α-SMA, SOD-1, and SOD-2), and hydrogen peroxide production. The results showed Rap1a overlaps the AGE/RAGE cascade to increase the myofibroblast population and generation of ROS production. The increase in myofibroblasts and oxidative stress appeared to contribute to increased matrix contraction, which was further exacerbated by diabetic conditions. Based off these results, we determined that Rap1a was essential in mediating the response of cardiac fibroblasts to AGEs within diabetic collagen.

Diverse and Productive Source of Biopolymer Inspiration: Marine Collagens

Marine biodiversity is expressed through the huge variety of vertebrate and invertebrate species inhabiting intertidal to deep-sea environments. The extraordinary variety of "forms and functions" exhibited by marine animals suggests they are a promising source of bioactive molecules and provides potential inspiration for different biomimetic approaches. This diversity is familiar to biologists and has led to intensive investigation of metabolites, polysaccharides, and other compounds. However, marine collagens are less well-known. This review will provide detailed insight into the diversity of collagens present in marine species in terms of their genetics, structure, properties, and physiology. In the last part of the review the focus will be on the most common marine collagen sources and on the latest advances in the development of innovative materials exploiting, or inspired by, marine collagens.

Cell attachment effects of collagen nanoparticles on crosslinked electrospun nanofibers

Since collagen is naturally a main extracellular matrix protein, it has been applied widely in skin's tissue engineering scaffolds to mimics the characteristics of extracellular matrix for proper transplantation of living cells. However, there are challenges that come with application of this natural polymer such as high solubility in aqueous environments which requires further consideration such as chemically cross-linking in order to stabilization. But these treatments also affect its functionality and finally cellular behaviors on scaffold. In this research we evaluated the suitability of collagen nanofibers versus collagen nanoparticles for cell adhesion and viability on glutaraldehyde cross-linked scaffolds. Appling a dual-pump electrospining machine a blend PCL-Gelatin from one side and collagen nanofibers or collagen nanoparticles from the other side were collected on the collector. The fabricated scaffolds were characterized by scanning electron microscopy, contact angle, and mechanical analysis. The cell viability, adhesion and morphology were studied respectively using MTT assay, hoechst staining and scanning electron microscopy. The results indicated significantly improvement of cell viability, adhesion and better spreading on scaffolds with collagen nanoparticles than collagen nanofibers. It seems changes in surface morphology, viscoelastic moduli and swelling ability following cross-linking with glutaraldehyde in scaffold with collagen nanoparticles are still favorable for cellular proliferation. Based on these results, in the case of glutaraldehyde cross-linking, application of collagen nanoparticles rather than collagen nanofibers in tissue regeneration scaffolds will better mimic the extracellular matrix characteristics; and preserve the viability and adhesion of seeded cells.

Characterization of biocompatible pig skin collagen and application of collagen-based films for enzyme immobilization

Based on the excellent biocompatibility of collagen, collagen was extracted from pig skin by acid-enzymatic method. The films were prepared by the self-aggregation behavior of collagen, and the catalase was immobilized by adsorption, cross-linking and embedding. The experiment investigated the effects of glutaraldehyde on the mechanical properties, external sensory properties, and denaturation temperature of the films. The results showed that self-aggregating material could maintain the triple helix structure of pig skin collagen. The self-aggregation treatment and cross-linking treatment can improve the mechanical properties to 53 MPa, while the glutaraldehyde cross-linking agent can increase the denaturation temperature of the pig skin collagen self-aggregating membrane by 20.35% to 84.48 °C. This means that its application to immobilized catalase has better stability. The comparison shows that the catalase immobilized by the adsorption method has strong activity and high operational stability, and the cross-linking agent glutaraldehyde and the initial enzyme concentration have a significant effect on the immobilization, and the activity can reach 175 U g⁻¹. After 16 uses of the film, the catalase was completely inactivated. This study provides a reference for the preparation of a catalase sensor that can be used to detect hydrogen peroxide in food by a catalase sensor.

Based on the excellent biocompatibility of collagen, collagen was extracted from pig skin by acid-enzymatic method.

Confinement of Candida Antarctica Lipase B in a Multifunctional Cyclodextrin-Derived Silicified Hydrogel and Its Application as Enzymatic Nanoreactor

Supramolecular hydrogels with a three-dimensional cross-linked macromolecular network have attracted growing scientific interest in recent years because of their ability to incorporate high loadings of bioactive molecules such as drugs, proteins, antibodies, peptides, and genes. Herein, we report a versatile approach for the confinement of Candida antarctica lipase B (CALB) within a silica-strengthened cyclodextrin-derived supramolecular hydrogel and demonstrate its potential application in the selective oxidation of 2,5-diformylfuran (DFF) to 2,5-furandicarboxylic acid (FDCA) under mild conditions. The enzymatic nanoreactor was deeply characterized using thermogravimetric analysis, Fourier transform infrared spectroscopy, N₂-adsorption, dynamic light scattering, UV-visible spectroscopy, transmission electron microscopy, scanning electron microscopy, and confocal laser scanning microscopy, while the reaction products were established on the basis of ¹H nuclear magnetic resonance spectroscopy combined with high-performance liquid chromatography. Our results revealed that while CALB immobilized in conventional sol-gel silica yielded exclusively 5-formylfuran-2-carboxylic acid (FFCA), confinement of the enzyme in the silicified hydrogel imparted a 5-fold increase in DFF conversion and afforded 67% FDCA yield in 7 h and almost quantitative yields in less than 24 h. The hierarchically interconnected pore structure of the host matrix was found to provide a readily accessible diffusion path for reactants and products, while its flexible hydrophilic-hydrophobic interface was extremely beneficial for the interfacial activation of the immobilized lipase.

Comparative evaluation of the physicochemical properties of nano-hydroxyapatite/collagen and natural bone ceramic/collagen scaffolds and their osteogenesis-promoting effect on MC3T3-E1 cells

The use of various types of calcium phosphate has been reported in the preparation of repairing materials for bone defects. However, the physicochemical and biological properties among them might be vastly different. In this study, we prepared two types of calcium phosphates, nano-hydroxyapatite (nHA) and natural bone ceramic (NBC), into 3D scaffolds by mixing with type I collagen (CoL), resulting in the nHA/CoL and NBC/CoL scaffolds. We then evaluated and compared the physicochemical and biological properties of these two calcium phosphates and their composite scaffold with CoL. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction spectroscopy (XRD) and compressive tests were used to, respectively, characterize the morphology, composition, distribution and the effect of nHA and NBC to collagen. Next, we examined the biological properties of the scaffolds using cytotoxicity testing, flow cytometry, immunofluorescence staining, biocompatibility testing, CCK-8 assays and RT-PCR. The results reflected that the Ca2+ released from nHA and NBC could bind chemically with collagen and affect its physicochemical properties, including the infrared absorption spectrum and compression modulus, among others. Furthermore, the two kinds of scaffolds could promote the expression of osteo-relative genes, but showed different gene induction properties. In short, NBC/CoL could promote the expression of early osteogenic genes, while nHA/CoL could upregulate late osteogenic genes. Conclusively, these two composite scaffolds could provide MC3T3-E1 cells with a biomimetic surface for adhesion, proliferation and the formation of mineralized extracellular matrices. Moreover, nHA/CoL and NBC/CoL had different effects on the period and extent of MC3T3-E1 cell mineralization.

Adventitial Collagen Crosslink Reduces Intimal Hyperplasia in a Rabbit Arteriovenous Graft Model

BACKGROUND

Intimal hyperplasia (IH) is the initial lesion of vein graft failure after coronary artery bypass grafting. The weak venous wall is likely one of the primary reasons for IH after exposure to the arterial environment. We investigate whether adventitial collagen cross-link by glutaraldehyde (GA) reinforces the venous wall and then reduces IH.

MATERIALS AND METHODS

Adventitial collagen cross-link by 0.3% GA was performed on the rabbit jugular veins. The degree of cross-link was accessed by tensile test. The jugular vein with or without cross-link was implanted into the carotid artery of rabbit. Vein dilatation at the immediate anastomosis and pathological remodeling of vein graft after 4 wk was assessed.

RESULTS

Tensile test indicated that the mechanical property of 3-min cross-linked veins more closely resembled that of the carotid artery. In rabbit arteriovenous graft models, 3-min adventitial collagen cross-link limited overdistension (diameter: 3.24 mm versus 4.65 mm, P < 0.01) at the immediate anastomosis and reduced IH (intima thickness: 78.83 μm versus 140.19 μm, P < 0.01) of vein grafts 4 wk after implantation in the cross-link group as compared with the graft group (without cross-link). Compared with the cross-link group, the expression of proliferating cell nuclear antigen and vascular cell adhesion molecule-1 increased significantly at both the mRNA and protein levels within the graft group (P < 0.01), but the expression of smooth muscle-22α decreased significantly (P < 0.01).

CONCLUSIONS

Adventitial collagen cross-link by GA increased the vessel stiffness and remarkably reduced IH in a rabbit arteriovenous graft model.

Effect of Modified Bovine Pericardium on Human Gingival Fibroblasts in vitro

Supportive membranes have recently been applied to treat periodontal disease in order to achieve periodontal tissue regeneration. The crucial role of these membranes is to facilitate the restoration of the structural and functional periodontium. Bovine pericardium (BP) is mainly composed of collagen type I, which was demonstrated to have good mechanical properties and biological regenerative potential. Our research aimed to extend the application of membrane derived from BP to periodontal disease treatment. However, the fabrication method to achieve a xenogenic-free membrane with the mechanical properties required for periodontal treatment is rarely mentioned. Therefore, a procedure for the extraction and modification of BP using sodium dodecyl sulfate (SDS) and glutaraldehyde (GA) was developed. BP was harvested and decellularized using different SDS concentrations (0.05-0.3%). GA was used to further modify the membranes to achieve suitable thickness, mechanical strength, and pore size. A combination protocol of 0.15% SDS treatment for 12 h with continuous agitation combined with 0.1% GA for 6 h for membrane fabricating was applied. The modified BP (mBP) had the targeted characteristics, such as 0.2-0.5 mm thickness, approximately 10 MPa in tensile strength, 30% in strain force, and a pore size <5 µm, which is comparable to commercially available collagen membranes. Findings from this study demonstrated that the established method was effective in preparing BP membrane for periodontal treatment while decreasing the concentration of reagents and processing time. Moreover, our modified membrane was found to have no cytotoxicity but supports the migration, attachment, and proliferation of human gingival fibroblasts in vitro. Taken together, these results confirmed that mBP is suitable for application in periodontal disease treatment and regeneration.

Capturing 3D large-strain Euler-bending filament dynamics in fibrous media simulations; sample case of compression collapse in dendritic actin network

Cytoskeletal networks to transmission towers are comprised of slender elements. Slender filaments bend and buckle more easily than stretch. Therefore a deforming network is expected to exhaust all possible bending-based modes before engaging filament stretch. While the large-strain bending critically determines fibrous-media response, simulations use small-strain and jointed approximations. At low resolution, these approximations inflate bending resistance and delay buckling onset. The proposed string-of-continuous-beams (SOCB) approach captures 3D nonlinear Euler bending of filaments with high fidelity at low cost. Bending geometry (i.e. angles and its differentials) is solved as primary variables, to fit a 5th order polynomial of the contour angle. Displacement, solved simultaneously as length conservation, is predicted with C3 and C6 smoothness between and within segments, using only 2 nodes. In the chosen analysis frame, in-plane and out-plane moments can be decoupled for arbitrarily-curved segments. Complex crosslink force-transfers can be specified. Simulations show that when a daughter branch is appended, the buckling resistance of a filament changes from linear to nonlinear before reversible collapse. An actin outcrop with 8 generations of mother-daughter branching produced the linear, nonlinear, and collapse regimes observed in compression experiments. 'Collapse' was a redistribution of outcrop forces following the buckling of few strands.

Microfluidic production of bioactive fibrin micro-beads embedded in crosslinked collagen used as an injectable bulking agent for urinary incontinence treatment

Endoscopic injection of bulking agents has been widely used to treat urinary incontinence, often due to urethral sphincter complex insufficiency. The aim of the study was to develop a novel injectable bioactive collagen-fibrin bulking agent restoring long-term continence by functional muscle tissue regeneration. Fibrin micro-beads were engineered using a droplet microfluidic system. They had an average diameter of 140 μm and recombinant fibrin-binding insulin-like growth factor-1 (α₂PI_1-8-MMP-IGF-1) was covalently conjugated to the beads. A plasmin fibrin degradation assay showed that 72.5% of the initial amount of α₂PI_1-8-MMP-IGF-1 loaded into the micro-beads was retained within the fibrin micro-beads. In vitro, the growth factor modified fibrin micro-beads enhanced cell attachment and the migration of human urinary tract smooth muscle cells, however, no change of the cellular metabolic activity was seen. These bioactive micro-beads were mixed with genipin-crosslinked homogenized collagen, acting as a carrier. The collagen concentration, the degree of crosslinking, and the mechanical behavior of this bioactive collagen-fibrin injectable were comparable to reference samples. This novel injectable showed no burst release of the growth factor, had a positive effect on cell behavior and may therefore induce smooth muscle regeneration in vivo, necessary for the functional treatment of stress and other urinary incontinences.

STATEMENT OF SIGNIFICANCE

Urinary incontinence is involuntary urine leakage, resulting from a deficient function of the sphincter muscle complex. Yet there is no functional cure for this devastating condition using current treatment options. Applied physical and surgical therapies have limited success. In this study, a novel bioactive injectable bulking agent, triggering new muscle regeneration at the injection site, has been evaluated. This injectable consists of cross-linked collagen and fibrin micro-beads, functionalized with bound insulin-like growth factor-1 (α₂PI_1-8-MMP-IGF-1). These bioactive fibrin micro-beads induced human smooth muscle cell migration in vitro. Thus, this injectable bulking agent is apt to be a good candidate for regeneration of urethral sphincter muscle, ensuring a long-lasting treatment for urinary incontinence.

Tissue engineering; strategies, tissues, and biomaterials

Current tissue regenerative strategies rely mainly on tissue repair by transplantation of the synthetic/natural implants. However, limitations of the existing strategies have increased the demand for tissue engineering approaches. Appropriate cell source, effective cell modification, and proper supportive matrices are three bases of tissue engineering. Selection of appropriate methods for cell stimulation, scaffold synthesis, and tissue transplantation play a definitive role in successful tissue engineering. Although the variety of the players are available, but proper combination and functional synergism determine the practical efficacy. Hence, in this review, a comprehensive view of tissue engineering and its different aspects are investigated.

Bioinspiring Chondrosia reniformis (Nardo, 1847) Collagen-Based Hydrogel: A New Extraction Method to Obtain a Sticky and Self-Healing Collagenous Material

Collagen is a natural and abundant polymer that serves multiple functions in both invertebrates and vertebrates. As collagen is the natural scaffolding for cells, collagen-based hydrogels are regarded as ideal materials for tissue engineering applications since they can mimic the natural cellular microenvironment. Chondrosia reniformis is a marine demosponge particularly rich in collagen, characterized by the presence of labile interfibrillar crosslinks similarly to those described in the mutable collagenous tissues (MCTs) of echinoderms. As a result single fibrils can be isolated using calcium-chelating and disulphide-reducing chemicals. In the present work we firstly describe a new extraction method that directly produces a highly hydrated hydrogel with interesting self-healing properties. The materials obtained were then biochemically and rheologically characterized. Our investigation has shown that the developed extraction procedure is able to extract collagen as well as other proteins and Glycosaminoglycans (GAG)-like molecules that give the collagenous hydrogel interesting and new rheological properties when compared to other described collagenous materials. The present work motivates further in-depth investigations towards the development of a new class of injectable collagenous hydrogels with tailored specifications.

A Comparative Evaluation of the Mechanical Properties of Two Calcium Phosphate/Collagen Composite Materials and Their Osteogenic Effects on Adipose-Derived Stem Cells

Adipose-derived stem cells (ADSCs) are ideal seed cells for use in bone tissue engineering and they have many advantages over other stem cells. In this study, two kinds of calcium phosphate/collagen composite scaffolds were prepared and their effects on the proliferation and osteogenic differentiation of ADSCs were investigated. The hydroxyapatite/β-tricalcium phosphate (HA/β-TCP) composite scaffolds (HTPSs), which have an additional β-tricalcium phosphate, resulted in better proliferation of ADSCs and showed osteogenesis-promoting effects. Therefore, such composite scaffolds, in combination with ADSCs or on their own, would be promising for use in bone regeneration and potential clinical therapy for bone defects.

Advances in collagen, chitosan and silica biomaterials for oral tissue regeneration: from basics to clinical trials

Different materials have distinct surface and bulk characteristics; each of them potentially useful for the treatment of a particular wound or disease.

Inelastic behaviour of collagen networks in cell-matrix interactions and mechanosensation

The mechanical properties of extracellular matrix proteins strongly influence cell-induced tension in the matrix, which in turn influences cell function. Despite progress on the impact of elastic behaviour of matrix proteins on cell-matrix interactions, little is known about the influence of inelastic behaviour, especially at the large and slow deformations that characterize cell-induced matrix remodelling. We found that collagen matrices exhibit deformation rate-dependent behaviour, which leads to a transition from pronounced elastic behaviour at fast deformations to substantially inelastic behaviour at slow deformations (1 μm min(-1), similar to cell-mediated deformation). With slow deformations, the inelastic behaviour of floating gels was sensitive to collagen concentration, whereas attached gels exhibited similar inelastic behaviour independent of collagen concentration. The presence of an underlying rigid support had a similar effect on cell-matrix interactions: cell-induced deformation and remodelling were similar on 1 or 3 mg ml(-1) attached collagen gels while deformations were two- to fourfold smaller in floating gels of high compared with low collagen concentration. In cross-linked collagen matrices, which did not exhibit inelastic behaviour, cells did not respond to the presence of the underlying rigid foundation. These data indicate that at the slow rates of collagen compaction generated by fibroblasts, the inelastic responses of collagen gels, which are influenced by collagen concentration and the presence of an underlying rigid foundation, are important determinants of cell-matrix interactions and mechanosensation.

Dye–collagen interactions. Mechanism, kinetic and thermodynamic analysis

Dye–collagen interactions. Mechanism, kinetic and thermodynamic analysis.

Strategies for directing the structure and function of three-dimensional collagen biomaterials across length scales

Collagen type I is a widely used natural biomaterial that has found utility in a variety of biological and medical applications. Its well-characterized structure and role as an extracellular matrix protein make it a highly relevant material for controlling cell function and mimicking tissue properties. Collagen type I is abundant in a number of tissues, and can be isolated as a purified protein. This review focuses on hydrogel biomaterials made by reconstituting collagen type I from a solubilized form, with an emphasis on in vitro studies in which collagen structure can be controlled. The hierarchical structure of collagen from the nanoscale to the macroscale is described, with an emphasis on how structure is related to function across scales. Methods of reconstituting collagen into hydrogel materials are presented, including molding of macroscopic constructs, creation of microscale modules and electrospinning of nanoscale fibers. The modification of collagen biomaterials to achieve the desired structures and functions is also addressed, with particular emphasis on mechanical control of collagen structure, creation of collagen composite materials and crosslinking of collagenous matrices. Biomaterials scientists have made remarkable progress in rationally designing collagen-based biomaterials and in applying them both to the study of biology and for therapeutic benefit. This broad review illustrates recent examples of techniques used to control collagen structure and thereby to direct its biological and mechanical functions.

Development and evaluation of cross-linked collagen-hydroxyapatite scaffolds for tissue engineering

This study examines the tissue engineering potential of type I collagen cross-linked in the presence of hydroxyapatite (HAp). Scaffolds were prepared by controlled freezing followed by lyophilization of composite mixtures of collagen and HAp in acetic acid, followed by cross-linking with 0.3% glutaraldehyde. Scaffolds of three ratios were prepared, corresponding to collagen/HAp ratios of 1:2, 1:4, and 1:6. The scaffolds were evaluated for their microstructure, chemical and physical properties, swelling behavior, mechanical strength, biodegradability hemocompatability, cytocompatibility, and histopathology following subcutaneous implantation in Sprague Dawley rats. The collagen/HAp matrices showed a smaller pore size of 10-40 μm compared to 50-100 μm for pure collagen scaffolds. Pure collagen showed a mechanical strength of 0.25 MPa, and the value almost doubled for cross-linked composites with collagen/HAp ratio 1:6. The improvement in mechanical strength corresponded to a decrease in swelling and enzymatic degradation (measured by resistance to collagenases). FTIR spectra results in conjunction with scanning electron micrographs showed that cross-linking in the presence of HAp did not significantly alter the structure of collagen. MTT assay and calcein AM staining revealed prominent and healthy growth of mesenchymal stem cells in both the pure collagen as well as collagen:HAp composites of ratio 1:2. In vivo implantation in Sprague Dawley rats showed an initial acute inflammatory response during days 3 and 7, followed by a chronic, macrophage-mediated inflammatory response on days 14 and 28. Overall, a cross-linked collagen/HAp composite scaffold of ratio 1:2 was identified as having potential for further development in tissue engineering.