Collagen fibres with improved strength for the repair of soft tissue injuries

Self-Assembly Behavior of Collagen and Its Composite Materials: Preparation, Characterizations, and Biomedical Engineering and Allied Applications

Collagen is the oldest and most abundant extracellular matrix protein and has many applications in biomedical, food, cosmetic, and other industries. Previous reviews have already introduced collagen's sources, structures, and biosynthesis. The biological and mechanical properties of collagen-based composite materials, their modification and application forms, and their interactions with host tissues are pinpointed. It is worth noting that self-assembly behavior is the main characteristic of collagen molecules. However, there is currently relatively little review on collagen-based composite materials based on self-assembly. Herein, we briefly reviewed the biosynthesis, extraction, structure, and properties of collagen, systematically presented an overview of the various factors and corresponding characterization techniques that affect the collagen self-assembly process, and summarize and discuss the preparation methods and application progress of collagen-based composite materials in different fields. By combining the self-assembly behavior of collagen with preparation methods of collagen-based composite materials, collagen-based composite materials with various functional reactions can be selectively prepared, and these experiences and outcomes can provide inspiration and practical techniques for the future development directions and challenges of collagen-based composite biomaterials in related applications fields.

Comparative Study of the Dehydrothermal Crosslinking of Electrospun Collagen Nanofibers: The Effects of Vacuum Conditions and Subsequent Chemical Crosslinking

Collagen nanofibrous materials have become integral to tissue engineering due to their exceptional properties and biocompatibility. Dehydrothermal crosslinking (DHT) enhances stability and maintains structural integrity without the formation of toxic residues. The study involved the crosslinking of electrospun collagen, applying DHT with access to air and under vacuum conditions. Various DHT exposure times of up to 72 h were applied to examine the time dependance of the DHT process. The DHT crosslinked collagen was subsequently chemically crosslinked using carbodiimides. The material crosslinked in this way evinced elevated Young's modulus values and ultimate tensile strength values, a lower swelling rate and lower shrinkage ratio during crosslinking, and a higher degree of resistance to degradation than the material crosslinked solely with DHT or carbodiimides. It was shown that the crosslinking mechanism using DHT occupies different binding sites than those using chemical crosslinking. Access to air for 12 h or less did not exert a significant impact on the material properties compared to DHT under vacuum conditions. However, concerning longer exposure times, it was determined that access to air results in the deterioration of the properties of the material and that reactions take place that occupy the free bonding sites, which subsequently reduces the effectiveness of chemical crosslinking using carbodiimides.

Electron Beam-Modified Collagen Type I Fibers: Synthesis and Characterization of Mechanical Response

Ten MeV electron beam treatment facilitates a biomimetic introduction of cross-links in collagenous biopolymer systems, modifying their viscoelastic properties, mechanical stability, and swelling behavior. For reconstituted collagen type I fibers, electron-induced cross-linking opens up new perspectives regarding future biomedical applications in terms of tissue and ligament engineering. We demonstrate how electron irradiation affects stiffness both in low-strain regimes and in postyield regimes of biocompatible reconstituted rat tail collagen type I fibers. Stress-strain tests show a dose-dependent increase in modulus in the nonlinear elastic response, indicating a central role of induced cross-links in mechanical stability. Environmental scanning electron microscopy after fiber rupture reveals aligned distributed collagen fibril domains under the fiber surface for as-prepared fibers, accompanied by a ductile fracture behavior, whereas, in tensile tests imaged by light microscopy after 10 MeV electron treatment, isotropic network topologies are observed until the occurrence of a brittle type of rupture. Based on the biomimicry of the process, these findings might pave the way for a novel type of synthesis of tailored tendon or ligament substitutes.

In Situ Cross-Linked Collagen-Based Biological Patch Integrating Anti-Infection and Anti-Calcification Properties

Acellular dermal matrix (ADM) can be used as collagen-based biological patches for regeneration and repair of soft tissues in vivo. However, the problems of calcification and infection during treatment with patches can lead to premature patch failure and even to a severely increased risk of recurrence. In this study, first, porcine ADM (pADM) grafted with vinyl underwent an in situ cross-linking reaction in the presence of an initiator, while quaternary ammonium groups were introduced into the pADM during the cross-linking process to obtain MA-DMC-pADM, which is a biological patch with anti-infection and anti-calcification properties. The results of physicochemical property tests of the material showed that the pADM after cross-linking had better physical and mechanical properties. Importantly, antibacterial and anti-calcification experiments showed that MA-DMC-pADM had a good antibacterial and anti-calcification effect. Therefore, the MA-DMC-pADM biological patch facilitates their longer-lasting effectiveness, allowing pADM to be used in a wider range of applications.

Effectively improved 3-dimensional structural stability of atelocollagen-gelatin sponge biomaterial by heat treatment

Atelocollagen-gelatin (ACG) sponge was fabricated from atelocollagen and gelatin by lyophilization without introducing toxic substances. This study aimed to investigate the effects of heat treatment on the 3-dimensional structural stability of ACG sponge biomaterial. ACG sponge samples were fabricated and heat treated at 125^oC for 12 h in the vacuum. The results revealed that heat treatment did not affect porosity, pore size and mechanical compressive strength. Heat-treated ACG sponge showed decreased absorbance and peak shift of amid I (C=O) stretches, slightly higher water uptake degree and significantly decreased in vitro degradation rate. Moreover, heat-treated ACG sponge maintained good 3-dimensional surface morphology and porous microstructure throughout 7 days, while non-heat-treated ACG sponge collapsed in less than 24 h. The human mesenchymal stromal cells (hMSCs) were shown to adhere and grow well on heat-treated ACG sponges. These results indicate that heat treatment is effective and safe to stabilize 3-dimensional ACG sponge biomaterial for tissue engineering.

Isotropic and Anisotropic Scaffolds for Tissue Engineering: Collagen, Conventional, and Textile Fabrication Technologies and Properties

In this review article, tissue engineering and regenerative medicine are briefly explained and the importance of scaffolds is highlighted. Furthermore, the requirements of scaffolds and how they can be fulfilled by using specific biomaterials and fabrication methods are presented. Detailed insight is given into the two biopolymers chitosan and collagen. The fabrication methods are divided into two categories: isotropic and anisotropic scaffold fabrication methods. Processable biomaterials and achievable pore sizes are assigned to each method. In addition, fiber spinning methods and textile fabrication methods used to produce anisotropic scaffolds are described in detail and the advantages of anisotropic scaffolds for tissue engineering and regenerative medicine are highlighted.

Comprehensive collagen crosslinking comparison of microfluidic wet-extruded microfibers for bioactive surgical suture development

Collagen microfiber-based constructs have garnered considerable attention for ligament, tendon, and other soft tissue repairs, yet with limited clinical translation due to strength, biocompatibility, scalable manufacturing, and other challenges. Crosslinking collagen fibers improves mechanical properties; however, questions remain regarding optimal crosslinking chemistries, biocompatibility, biodegradation, long-term stability, and potential for biotextile assemble at scale, limiting their clinical usefulness. Here, we assessed over 50 different crosslinking chemistries on microfluidic wet-extruded collagen microfibers made with clinically relevant collagen to optimize collagen fibers as a biotextile yarn for suture or other medical device manufacture. The endogenous collagen crosslinker, glyoxal, provides extraordinary fiber ultimate tensile strength near 300MPa, and Young's modulus of over 3GPa while retaining 50% of the initial load-bearing capacity through 6 months as hydrated. Glyoxal crosslinked collagen fibers further proved cytocompatible and biocompatible per ISO 10993-based testing, and further elicits a predominantly M2 macrophage response. Remarkably these strong collagen fibers are amenable to industrial braiding to form strong collagen fiber sutures. Collagen microfluidic wet extrusion with glyoxal crosslinking thus progress bioengineered, strong, and stable collagen microfibers significantly towards clinical use for potentially promoting efficient healing compared to existing suture materials. STATEMENT OF SIGNIFICANCE: Towards improving clinical outcomes for over 1 million ligament and tendon surgeries performed annually, we report an advanced microfluidic extrusion process for type I collagen microfiber manufacturing for biological suture and other biotextile manufacturing. This manuscript reports the most extensive wet-extruded collagen fiber crosslinking compendium published to date, providing a tremendous recourse to the field. Collagen fibers made with clinical-grade collagen and crosslinked with glyoxal, exhibit tensile strength and stability that surpasses all prior reports. This is the first report demonstrating that glyoxal, a native tissue crosslinker, has the extraordinary ability to produce strong, cytocompatible, and biocompatible collagen microfibers. These collagen microfibers are ideal for advanced research and clinical use as surgical suture or other tissue-engineered medical products for sports medicine, orthopedics, and other surgical indications.

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.

Label-Free Characterization of Collagen Crosslinking in Bone-Engineered Materials Using Nonlinear Optical Microscopy

Engineered biomaterials provide unique functions to overcome the bottlenecks seen in biomedicine. Hence, a technique for rapid and routine tests of collagen is required, in which the test items commonly include molecular weight, crosslinking degree, purity, and sterilization induced structural change. Among them, the crosslinking degree mainly influences collagen properties. In this study, second harmonic generation (SHG) and coherent anti-Stokes Raman scattering (CARS) microscopy are used in combination to explore the collagen structure at molecular and macromolecular scales. These measured parameters are applied for the classification and quantification among the different collagen scaffolds, which were verified by other conventional methods. It is demonstrated that the crosslinking status can be analyzed from SHG images and presented as the coherency of collagen organization that is correlated with the mechanical properties. Also, the comparative analyses of SHG signal and relative CARS signal of amide III band at 1,240 cm−1 to δCH2 band at 1,450 cm−1 of these samples provide information regarding the variation of the molecular structure during a crosslinking process, thus serving as nonlinear optical signatures to indicate a successful crosslinking.

The influence of animal species, gender and tissue on the structural, biophysical, biochemical and biological properties of collagen sponges

Although collagen type I is extensively used in biomedicine, no study to-date has assessed how the properties of the produced scaffolds are affected as a function of species, gender and tissue from which the collagen was extracted. Herein, we extracted and characterised collagen from porcine and bovine, male and female and skin and tendon tissues and we subsequently fabricated and assessed the structural, biophysical, biochemical and biological properties of collagen sponges. All collagen preparations were of similar purity and free-amine content (p > 0.05). In general, the porcine groups yielded more collagen; had higher (p < 0.05) denaturation temperature and resistance to enzymatic degradation; and lower (p < 0.05) swelling ratio and compression stress and modulus than the bovine groups of the same gender and tissue. All collagen preparations supported growth of human dermal fibroblasts and exhibited similar biological response to human THP-1 monocytes. These results further illustrate the need for standardisation of collagen preparations for the development of reproducible collagen-based devices. Assessment of the physicochemical and biological properties of collagen sponges as a function of animal species (bovine versus porcine), gender (male versus female) and tissue (skin versus tendon).

Fiber engagement accounts for geometry-dependent annulus fibrosus mechanics: A multiscale, Structure-Based Finite Element Study

A comprehensive understanding of biological tissue mechanics is crucial for designing engineered tissues that aim to recapitulate native tissue behavior. Tensile mechanics of many fiber-reinforced tissues have been shown to depend on specimen geometry, which makes it challenging to compare data between studies. In this study, a validated multiscale, structure-based finite element model was used to evaluate the effect of specimen geometry on multiscale annulus fibrosus tensile mechanics through a fiber engagement analysis. The relationships between specimen geometry and modulus, Poisson's ratio, tissue stress-strain distributions, and fiber reorientation behaviors were investigated at both tissue and sub-tissue levels. It was observed that annulus fibrosus tissue level tensile properties and stress transmission mechanisms were dependent on specimen geometry. The model also demonstrated that the contribution of fiber-matrix interactions to tissue mechanical response was specimen size- and orientation-dependent. The results of this study reinforce the benefits of structure-based finite element modeling in studies investigating multiscale tissue mechanics. This approach also provides guidelines for developing optimal combined computational-experimental study designs for investigating fiber-reinforced biological tissue mechanics. Additionally, findings from this study help explain the geometry dependence of annulus fibrosus tensile mechanics previously reported in the literature, providing a more fundamental and comprehensive understanding of tissue mechanical behavior. In conclusion, the methods presented here can be used in conjunction with experimental tissue level data to simultaneously investigate tissue and sub-tissue scale mechanics, which is important as the field of soft tissue biomechanics advances toward studies that focus on diminishing length scales.

Cross-Linked Nanocellulosic Materials and Their Applications

Nanocelluloses (NCs) have remarkable mechanical properties and contain abundant surface functional groups that can be modified or cross-linked with other materials. They have been widely used as an environment-friendly reinforcing agent in polymer composites. However, for applications that are carried out in humid environments or aqueous suspensions, hydrophilicity of NCs lower their mechanical integrity. Hence, cross-linking techniques have been investigated in recent years for preparing NC-based materials that are dimensionally stable under humid or aqueous environments and have better physicochemical properties. This Minireview examines the quickly growing field of cross-linked NC-based materials, which have many benefits including improved aqueous, structural, mechanical, and thermal stability. In addition, the potential application of cross-linked NC-based materials in adsorption of heavy metal is discussed.

Collagen multifilament spinning

The benefits of fiber based implants and scaffolds for tissue engineering applications are their anisotropic, highly porous, and controllable macro-, micro-, and nanostructure. Collagen is one of the most commonly used material for the fabrication of scaffolds, as this biopolymer is present in the natural extracellular matrix. For textile processing and textile scaffold fabrication methods, multifilament yarns are required, however, only monofilaments can be generated by state-of-the-art collagen spinning. Hence, the research presented in here aimed at the development of a collagen multifilament wet-spinning process in reproducible quality as well as the characterization of non-crosslinked and crosslinked wet-spun multifilament yarns. Wet spun collagen yarns were comprised of 6 single filaments each having a fineness of 5 tex and a diameter of 80 μm. The tensile strength of the glutaraldehyde crosslinked yarns was 169 MPa (Young's modulus 3534 MPa) in the dry state and 40 MPa (Young's modulus 281 MPa) in the wet state. Furthermore, wet spun collagen filaments showed a characteristic fibrillar structure, which was similar the morphological structure of natural collagen fibers. The textile processing of collagen multifilament yarn was demonstrated by means of knitting technology.

Light-Activated Tissue-Integrating Sutures as Surgical Nanodevices

Sutures are typically the primary means of soft tissue repair in surgery and trauma. Despite their widespread use, sutures do not result in immediate sealing of approximated tissues, which can result in bacterial infection and leakage. Nonabsorbable sutures and staples can be traumatic to tissue, and the trauma can be exacerbated by their subsequent removal. Use of cyanoacrylate glues is limited because of their brittleness and toxicity. In this work, laser-activated tissue-integrating sutures (LATIS) are described as novel nanodevices for soft tissue approximation and repair. Incorporation of gold nanorods within fibers generated from collagen result in LATIS fibers which demonstrate robust photothermal responses following irradiation with near infrared laser light. Compared to conventional sutures, LATIS fibers result in greater biomechanical recovery of incised skin in a mouse model of skin closure after spine surgeries. Histopathology analyses show improved repair of the epidermal gap in skin, which indicate faster tissue recovery using LATIS. The studies indicate that LATIS-facilitated approximation of skin in live mice synergizes the benefits of conventional suturing and laser-activated tissue integration, resulting in new approaches for faster sealing, tissue repair, and healing.

The Collagen Suprafamily: From Biosynthesis to Advanced Biomaterial Development

Collagen is the oldest and most abundant extracellular matrix protein that has found many applications in food, cosmetic, pharmaceutical, and biomedical industries. First, an overview of the family of collagens and their respective structures, conformation, and biosynthesis is provided. The advances and shortfalls of various collagen preparations (e.g., mammalian/marine extracted collagen, cell-produced collagens, recombinant collagens, and collagen-like peptides) and crosslinking technologies (e.g., chemical, physical, and biological) are then critically discussed. Subsequently, an array of structural, thermal, mechanical, biochemical, and biological assays is examined, which are developed to analyze and characterize collagenous structures. Lastly, a comprehensive review is provided on how advances in engineering, chemistry, and biology have enabled the development of bioactive, 3D structures (e.g., tissue grafts, biomaterials, cell-assembled tissue equivalents) that closely imitate native supramolecular assemblies and have the capacity to deliver in a localized and sustained manner viable cell populations and/or bioactive/therapeutic molecules. Clearly, collagens have a long history in both evolution and biotechnology and continue to offer both challenges and exciting opportunities in regenerative medicine as nature's biomaterial of choice.

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

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

The Relationship of Collagen Structural and Compositional Heterogeneity to Tissue Mechanical Properties: A Chemical Perspective

Collagen is the primary protein component in mammalian connective tissues. Over the last 20 years, evidence has mounted that collagen matrices exhibit substantial heterogeneity in their hierarchical structures and that this heterogeneity plays important roles in both structure and function. Herein, an overview of studies addressing the nanoscale compositional and structural heterogeneity is provided and connected to work exploring the mechanical implications for a number of tissues.

Optimization of Glutaraldehyde Vapor Treatment for Electrospun Collagen/Silk Tissue Engineering Scaffolds

Freestanding fibrous matrices with proper protein composition and desirable mechanical properties, stability, and biocompatibility are in high demand for tissue engineering. Electrospun (E-spun) collagen-silk composite fibers are promising tissue engineering scaffolds. However, as-spun fibers are mechanically weak and unstable. In this work, we applied glutaraldehyde (GA) vapor treatment to improve the fiber performance, and the effect on the properties of E-spun collagen-silk fibers was studied systematically. GA treatment was found to affect collagen and silk distinctively. Whereas GA chemically links collagen peptides, it induces conformational transitions to enrich β-sheets in silk. The combined effects impose a control of the mechanical properties, stability, and degradability of the composite fibers, which are dependent on the extent of GA treatment. In addition, a mild treatment of the fibers did not diminish cell proliferation and viability. However, overly treated fibers demonstrated reduced cell-matrix adhesion. The understanding of GA treatment effects on collagen, silk, and the composite fibers enables effective control and fine tuning of the fiber properties to warrant their diverse in vitro and in vivo applications.

The use of nanoscaffolds and dendrimers in tissue engineering

To avoid tissue rejection during organ transplantation, research has focused on the use of tissue engineering to regenerate required tissues or organs for patients. The biomedical applications of hyperbranched, multivalent, structurally uniform, biocompatible dendrimers in tissue engineering include the mimicking of natural extracellular matrices (ECMs) in the 3D microenvironment. Dendrimers are unimolecular architects that can incorporate a variety of biological and/or chemical substances in a 3D architecture to actively support the scaffold microenvironment during cell growth. Here, we review the use of dendritic delivery systems in tissue engineering. We discuss the available literature, highlighting the 3D architecture and preparation of these nanoscaffolds, and also review challenges to, and advances in, the use dendrimers in tissue engineering. Advances in the manufacturing of dendritic nanoparticles and scaffold architectures have resulted in the successful incorporation of dendritic scaffolds in tissue engineering.

Harnessing the Versatility of Bacterial Collagen to Improve the Chondrogenic Potential of Porous Collagen Scaffolds

Collagen I foams are used in the clinic as scaffolds to promote articular cartilage repair as they provide a bioactive environment for cells with chondrogenic potential. However, collagen I as a base material does not allow for precise control over bioactivity. Alternatively, recombinant bacterial collagens can be used as "blank slate" collagen molecules to offer a versatile platform for incorporation of selected bioactive sequences and fabrication into 3D scaffolds. Here, we show the potential of Streptococcal collagen-like 2 (Scl2) protein foams modified with peptides designed to specifically and noncovalently bind hyaluronic acid and chondroitin sulfate to improve chondrogenesis of human mesenchymal stem cells (hMSCs) compared to collagen I foams. Specific compositions of functionalized Scl2 foams lead to improved chondrogenesis compared to both nonfunctionalized Scl2 and collagen I foams, as indicated by gene expression, extracellular matrix accumulation, and compression moduli. hMSCs cultured in functionalized Scl2 foams exhibit decreased collagens I and X gene and protein expression, suggesting an advantage over collagen I foams in promoting a chondrocytic phenotype. These highly modular foams can be further modified to improve specific aspects chondrogenesis. As such, these scaffolds also have the potential to be tailored for other regenerative medicine applications.

Harnessing Hierarchical Nano- and Micro-Fabrication Technologies for Musculoskeletal Tissue Engineering

Cells within a tissue are able to perceive, interpret and respond to the biophysical, biomechanical, and biochemical properties of the 3D extracellular matrix environment in which they reside. Such stimuli regulate cell adhesion, metabolic state, proliferation, migration, fate and lineage commitment, and ultimately, tissue morphogenesis and function. Current scaffold fabrication strategies in musculoskeletal tissue engineering seek to mimic the sophistication and comprehensiveness of nature to develop hierarchically assembled 3D implantable devices of different geometric dimensions (nano- to macrometric scales) that will offer control over cellular functions and ultimately achieve functional regeneration. Herein, advances and shortfalls of bottom-up (self-assembly, freeze-drying, rapid prototype, electrospinning) and top-down (imprinting) scaffold fabrication approaches, specific to musculoskeletal tissue engineering, are discussed and critically assessed.

The past, present and future in scaffold-based tendon treatments

Tendon injuries represent a significant clinical burden on healthcare systems worldwide. As the human population ages and the life expectancy increases, tendon injuries will become more prevalent, especially among young individuals with long life ahead of them. Advancements in engineering, chemistry and biology have made available an array of three-dimensional scaffold-based intervention strategies, natural or synthetic in origin. Further, functionalisation strategies, based on biophysical, biochemical and biological cues, offer control over cellular functions; localisation and sustained release of therapeutics/biologics; and the ability to positively interact with the host to promote repair and regeneration. Herein, we critically discuss current therapies and emerging technologies that aim to transform tendon treatments in the years to come.

To cross-link or not to cross-link? Cross-linking associated foreign body response of collagen-based devices

Collagen-based devices, in various physical conformations, are extensively used for tissue engineering and regenerative medicine applications. Given that the natural cross-linking pathway of collagen does not occur in vitro, chemical, physical, and biological cross-linking methods have been assessed over the years to control mechanical stability, degradation rate, and immunogenicity of the device upon implantation. Although in vitro data demonstrate that mechanical properties and degradation rate can be accurately controlled as a function of the cross-linking method utilized, preclinical and clinical data indicate that cross-linking methods employed may have adverse effects on host response, especially when potent cross-linking methods are employed. Experimental data suggest that more suitable cross-linking methods should be developed to achieve a balance between stability and functional remodeling.

Water distribution in dentin matrices: bound vs. unbound water

OBJECTIVE

This work measured the amount of bound versus unbound water in completely-demineralized dentin.

METHODS

Dentin beams prepared from extracted human teeth were completely demineralized, rinsed and dried to constant mass. They were rehydrated in 41% relative humidity (RH), while gravimetrically measuring their mass increase until the first plateau was reached at 0.064 (vacuum) or 0.116 gH2O/g dry mass (Drierite). The specimens were then exposed to 60% RH until attaining the second plateau at 0.220 (vacuum) or 0.191 gH2O/g dry mass (Drierite), and subsequently exposed to 99% RH until attaining the third plateau at 0.493 (vacuum) or 0.401 gH2O/g dry mass (Drierite).

RESULTS

Exposure of the first layer of bound water to 0% RH for 5 min produced a -0.3% loss of bound water; in the second layer of bound water it caused a -3.3% loss of bound water; in the third layer it caused a -6% loss of bound water. Immersion in 100% ethanol or acetone for 5 min produced a 2.8 and 1.9% loss of bound water from the first layer, respectively; it caused a -4 and -7% loss of bound water in the second layer, respectively; and a -17 and -23% loss of bound water in the third layer. Bound water represented 21-25% of total dentin water. Chemical dehydration of water-saturated dentin with ethanol/acetone for 1 min only removed between 25 and 35% of unbound water, respectively.

SIGNIFICANCE

Attempts to remove bound water by evaporation were not very successful. Chemical dehydration with 100% acetone was more successful than 100% ethanol especially the third layer of bound water. Since unbound water represents between 75 and 79% of total matrix water, the more such water can be removed, the more resin can be infiltrated.

Influence of water content on the ablation of skin with a 532 nm nanosecond Nd:YAG laser

This work reports that the ablation volume and rate of porcine skin changed significantly with the change of skin water content. Under the same laser irradiation conditions (532 nm Nd:YAG laser, pulse width = 11.5 ns, pulse energy = 1.54 J, beam radius = 0.54 mm), the ablation volume dropped by a factor of 4 as the skin water content decreased from 40 wt. % (native) to 19 wt. % with a change in the ablation rate below and above around 25 wt. %. Based on the ablation characteristics observed by in situ shadowgraph images and the calculated tissue temperatures, it is considered that an explosive rupture by rapid volumetric vaporization of water is responsible for the ablation of the high water content of skin, whereas thermal disintegration of directly irradiated surface layer is responsible for the low water content of skin.

The process of EDC-NHS Cross-linking of reconstituted collagen fibres increases collagen fibrillar order and alignment

We describe the production of collagen fibre bundles through a multi-strand, semi-continuous extrusion process. Cross-linking using an EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide), NHS (N-hydroxysuccinimide) combination was considered. Atomic Force Microscopy (AFM) and Raman spectroscopy focused on how cross-linking affected the collagen fibrillar structure. In the cross-linked fibres, a clear fibrillar structure comparable to native collagen was observed which was not observed in the non-cross-linked fibre. The amide III doublet in the Raman spectra provided additional evidence of alignment in the cross-linked fibres. Raman spectroscopy also indicated no residual polyethylene glycol (from the fibre forming buffer) or water in any of the fibres.

Potency of fish collagen as a scaffold for regenerative medicine

Cells, growth factors, and scaffold are the crucial factors for tissue engineering. Recently, scaffolds consisting of natural polymers, such as collagen and gelatin, bioabsorbable synthetic polymers, such as polylactic acid and polyglycolic acid, and inorganic materials, such as hydroxyapatite, as well as composite materials have been rapidly developed. In particular, collagen is the most promising material for tissue engineering due to its biocompatibility and biodegradability. Collagen contains specific cell adhesion domains, including the arginine-glycine-aspartic acid (RGD) motif. After the integrin receptor on the cell surface binds to the RGD motif on the collagen molecule, cell adhesion is actively induced. This interaction contributes to the promotion of cell growth and differentiation and the regulation of various cell functions. However, it is difficult to use a pure collagen scaffold as a tissue engineering material due to its low mechanical strength. In order to make up for this disadvantage, collagen scaffolds are often modified using a cross-linker, such as gamma irradiation and carbodiimide. Taking into account the possibility of zoonosis, a variety of recent reports have been documented using fish collagen scaffolds. We herein review the potency of fish collagen scaffolds as well as associated problems to be addressed for use in regenerative medicine.

Generation of spatially aligned collagen fiber networks through microtransfer molding

The unique biomechanical properties of native tissue are governed by the organization and composition of integrated collagen and elastin networks. An approach for fabricating spatially aligned, fiber-reinforced composites with adjustable collagen fiber dimensions, layouts, and distribution within an elastin-like protein matrix yielding a biocomposite with controllable mechanical responses is reported. Microtransfer molding is employed for the fabrication of hollow and solid collagen fibers with straight or crimped fiber geometries. Collagen fibers (width: 2-50 μm, thickness: 300 nm to 3 μm) exhibit a Young's modulus of 126 ± 61 MPa and an ultimate tensile strength of 7 ± 3.2 MPa. As fiber networks within composite structures, straight fiber layouts display orthotropic responses with Young's modulus ranging from 0.95 ± 0.35 to 10.4 ± 0.5 MPa and tensile strength from 0.22 ± 0.08 to 0.87 ± 0.5 MPa with increasing fraction of collagen fibers (1-10%, v/v). In contrast, composites based on crimped fiber layouts exhibit strain-dependent stiffness with an increase in Young's modulus from 0.7 ± 0.14 MPa to 3.15 ± 0.49 MPa, at a specific transition strain. Through controlling the microstructure of engineered collagen fiber networks, a facile means is established to control macroscale mechanical responses of composite protein-based materials.

Microablation of collagen-based substrates for soft tissue engineering

Noting the abundance and importance of collagen as a biomaterial, we have developed a facile method for the production of a dense fibrillar extracellular matrix mimicking collagen-elastin hybrids with tunable mechanical properties. Through the use of excimer-laser technology, we have optimized conditions for the ablation of collagen lamellae without denaturation of protein, maintenance of fibrillar ultrastructure and preservation of native D-periodicity. Strengths of collagen-elastin hybrids ranged from 0.6 to 13 MPa, elongation at break from 9 to 70% and stiffness from 2.9 to 94 MPa, allowing for the design of a wide variety of tissue specific scaffolds. Further, large (centimeter scale) lamellae can be fabricated and embedded with recombinant elastin to generate collagen-elastin hybrids. Exposed collagen in hybrids act as cell adhesive sites for rat mesenchymal stem cells that conform to ablate waveforms. The ability to modulate these features allows for the generation of a class of biopolymers that can architecturally and physiologically replicate native tissue.

Incorporation of bioactive polyvinylpyrrolidone-iodine within bilayered collagen scaffolds enhances the differentiation and subchondral osteogenesis of mesenchymal stem cells

Polyvinylpyrrolidone-iodine (Povidone-iodine, PVP-I) is widely used as an antiseptic agent for lavation during joint surgery; however, the biological effects of PVP-I on cells from joint tissue are unknown. This study examined the biocompatibility and biological effects of PVP-I on cells from joint tissue, with the aim of optimizing cell-scaffold based joint repair. Cells from joint tissue, including cartilage derived progenitor cells (CPC), subchondral bone derived osteoblast and bone marrow derived mesenchymal stem cells (BM-MSC) were isolated. The concentration-dependent effects of PVP-I on cell proliferation, migration and differentiation were evaluated. Additionally, the efficacy and mechanism of a PVP-I loaded bilayer collagen scaffold for osteochondral defect repair was investigated in a rabbit model. A micromolar concentration of PVP-I was found not to affect cell proliferation, CPC migration or extracellular matrix production. Interestingly, micromolar concentrations of PVP-I promote osteogenic differentiation of BM-MSC, as evidenced by up-regulation of RUNX2 and Osteocalcin gene expression, as well as increased mineralization on the three-dimensional scaffold. PVP-I treatment of collagen scaffolds significantly increased fibronectin binding onto the scaffold surface and collagen type I protein synthesis of cultured BM-MSC. Implantation of PVP-I treated collagen scaffolds into rabbit osteochondral defect significantly enhanced subchondral bone regeneration at 6 weeks post-surgery compared with the scaffold alone (subchondral bone histological score of 8.80±1.64 vs. 3.8±2.19, p<0.05). The biocompatibility and pro-osteogenic activity of PVP-I on the cells from joint tissue and the enhanced subchondral bone formation in PVP-I treated scaffolds would thus indicate the potential of PVP-I for osteochondral defect repair.

Synthetic collagen fascicles for the regeneration of tendon tissue

The structure of an ideal scaffold for tendon regeneration must be designed to provide a mechanical, structural and chemotactic microenvironment for native cellular activity to synthesize functional (i.e. load bearing) tissue. Collagen fibre scaffolds for this application have shown some promise to date, although the microstructural control required to mimic the native tendon environment has yet to be achieved allowing for minimal control of critical in vivo properties such as degradation rate and mass transport. In this report we describe the fabrication of a novel multi-fibre collagen fascicle structure, based on type-I collagen with failure stress of 25-49 MPa, approximating the strength and structure of native tendon tissue. We demonstrate a microscopic fabrication process based on the automated assembly of type-I collagen fibres with the ability to produce a controllable fascicle-like, structural motif allowing variable numbers of fibres per fascicle. We have confirmed that the resulting post-fabrication type-I collagen structure retains the essential phase behaviour, alignment and spectral characteristics of aligned native type-I collagen. We have also shown that both ovine tendon fibroblasts and human white blood cells in whole blood readily infiltrate the matrix on a macroscopic scale and that these cells adhere to the fibre surface after seven days in culture. The study has indicated that the synthetic collagen fascicle system may be a suitable biomaterial scaffold to provide a rationally designed implantable matrix material to mediate tendon repair and regeneration.

Neonatal desensitization supports long-term survival and functional integration of human embryonic stem cell-derived mesenchymal stem cells in rat joint cartilage without immunosuppression

Immunological response hampers the investigation of human embryonic stem cells (hESCs) or their derivates for tissue regeneration in vivo. Immunosuppression is often used after surgery, but exhibits side effects of significant weight loss and allows only short-term observation. The purpose of this study was to investigate whether neonatal desensitization supports relative long-term survival of hESC-derived mesenchymal stem cells (hESC-MSCs) and promotes cartilage regeneration. hESC-MSCs were injected on the day of birth in rats. Six weeks after neonatal injection, a full-thickness cylindrical cartilage defect was created and transplanted with a hESC-MSC-seeded collagen bilayer scaffold (group d+s+c) or a collagen bilayer scaffold (group d+s). Rats without neonatal injection were transplanted with the hESC-MSC-seeded collagen bilayer scaffold to serve as controls (group s+c). Cartilage regeneration was evaluated by histological analysis, immunohistochemical staining, and biomechanical test. The role of hESC-MSCs in cartilage regeneration was analyzed by CD4 immunostaining, cell death detection, and visualization of human cells in regenerated tissues. hESC-MSCs expressed CD105, CD73, CD90, CD29, and CD44, but not CD45 and CD34, and possessed trilineage differentiation potential. Group d+s+c exhibited greater International Cartilage Repair Society (ICRS) scores than group d+s or group s+c. Abundant collagen type II and improved mechanical properties were detected in group d+s+c. There were less CD4+ inflammatory cell infiltration and cell death at week 1, and hESC-MSCs were found to survive as long as 8 weeks after transplantation in group d+s+c. Our study suggests that neonatal desensitization before transplantation may be an efficient way to develop a powerful tool for preclinical study of human cell-based therapies in animal models.

Genipin crosslinking elevates the strength of electrochemically aligned collagen to the level of tendons

Collagen-based tissue mimics are important in clinical research because collagen is the main structural element in tendons. The current study aimed to improve the mechanical strength of Electronically Aligned Collagen (ELAC) threads by optimizing several crosslinking parameters. The results indicated that elevating the concentration of genipin to 2% and the solvent to 90% ethanol significantly enhanced the wet ultimate tensile stress of ELAC threads to 109 MPa with a crosslinking degree of 65%. Furthermore, significantly higher adhesion and proliferation of hMSCs was observed in ELAC threads crosslinked with 2% genipin in 90% ethanol compared to 0.625% genipin in 1X PBS. In conclusion, ELAC threads with mechanical strength on par with native tendon have significant potential to be used as scaffolds in tendon tissue engineering applications.