EDC cross-linking improves skin substitute strength and stability

Antibiotic-eluting scaffolds with responsive dual-release kinetics facilitate bone healing and eliminate S. aureus infection

Osteomyelitis (OM) is a progressive, inflammatory infection of bone caused predominately by Staphylococcus aureus. Herein, we engineered an antibiotic-eluting collagen-hydroxyapatite scaffold capable of eliminating infection and facilitating bone healing. An iterative freeze-drying and chemical crosslinking approach was leveraged to modify antibiotic release kinetics, resulting in a layered dual-release system whereby an initial rapid release of antibiotic to clear infection was followed by a sustained controlled release to prevent reoccurrence of infection. We observed that the presence of microbial collagenase accelerated antibiotic release from the crosslinked layer of the scaffold, indicating that the material is responsive to microbial activity. As exemplar drugs, vancomycin and gentamicin-eluting scaffolds were demonstrated to be bactericidal, and supported osteogenesis in vitro. In a pilot murine model of OM, vancomycin-eluting scaffolds were observed to reduce S. aureus infection within the tibia. Finally, in a rabbit model of chronic OM, gentamicin-eluting scaffolds both facilitated radial bone defect healing and eliminated S. aureus infection. These results show that antibiotic-eluting collagen-hydroxyapatite scaffolds are a one-stage therapy for OM, which when implanted into infected bone defects simultaneously eradicate infection and facilitate bone tissue healing.

Repair of tendons treated with peracetic acid-ethanol and gamma irradiation by EDC combined with NHS: a morphological, biochemical and biomechanical study in vitro

The purpose of this study was to investigate whether 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) combined with n-hydroxysuccinimide (NHS) can repair tendon damage caused by peracetic acid-ethanol and gamma irradiation sterilization. The semitendinosus tendons of 15 New Zealand white rabbits were selected as experimental materials, and the tendons were sterilized in a solution containing 1% (v/w) peracetic acid and 24% (v/w) ethanol. After 15 kGy gamma irradiation sterilization, the tendons were randomly divided into three groups (n = 10). The tendons were repaired with EDCs of 0, 2.5 and 5 mM combined with 5 mM NHS for 6 h, the tendons were temporarily stored at - 80 ± °C. The arrangement and spatial structure of collagen fibers were observed by light microscopy and scanning electron microscopy, the collagen type and collagen crimp period were observed under a polarizing microscope, and the collagen fibril diameter and its distribution were measured by transmission electron microscopy, from which the collagen fibril index and mass average diameter were calculated. The resistance of collagen to enzymolysis was detected by the free hydroxyproline test, and tensile fracture and cyclic loading tests of each group of tendons were carried out, from which the elastic modulus, maximum stress, maximum strain, strain energy density and cyclic creep strain were calculated. The obtained results showed that the gap between loose collagen fibers in the 0 mM control group was wider, the parallel arrangement of tendons in the 2.5 and 5 mM groups was more uniform and regular and the fiber space decreased, the crimp period in the 5 mM group was lower than that in the 0 mM group (P < 0.05), and the concentration of hydroxyproline in the 5 mM group (711.64 ± 77.95 μg/g) was better than that in the control group (1150.57 ± 158.75 μg/g). The elastic modulus of the 5 mM group (424.73 ± 150.96 MPa) was better than that of the 0 mM group (179.09 ± 37.14 MPa). Our results show that EDC combined with NHS can repair damaged tendons after peracetic acid-ethanol and gamma radiation treatment, and 5 mM EDC has better morphological performance, anti-enzymolysis ability and biomechanical properties than 2.5 mM EDC.

In vitro and in silico investigation of glycyrrhizic acid encapsulated zein nanoparticles: A synergistic targeted drug delivery approach for breast cancer

This study presents an innovative approach for targeted drug delivery through the development of Glycyrrhizic acid-loaded zein nanoparticles (GA-LNPs) as a proficient carrier system. The juxtaposition of zein, a hydrophobic biological macromolecule as a protein carrier, and Glycyrrhizic acid (GA), a hydrophilic therapeutic compound, exemplifies the adaptability of hydrocolloids within cutting-edge drug delivery systems. The characterization and functional traits of research encompass multifaceted analyses of natural macromolecules, which elucidate the homogeneous and spherical morphology of GA-LNPs with an average size of 170.49 nm. The controlled drug release profile of GA, orchestrated under simulated gastrointestinal conditions, adheres to diffusion-based Higuchi kinetics, reflecting the controlled release of the natural macromolecules. The intermolecular interactions among Zein, GA, and cross-linker EDC, facilitated through molecular dynamics simulations, fortify the structural integrity of the encapsulation matrix. In Vitro studies revealed enhanced cellular uptake of GA-LNPs in MCF-7 breast cancer cells. This cellular internalization was further confirmed through cytotoxicity assessments using MTT and apoptosis assays (fluorescence microscopy), which demonstrated the prominent anticancer effects of GA-LNPs on MCF-7 in time/dose-dependent manner. The successful formulation of GA-LNPs, coupled with their sustained release and potent anticancer properties, makes them a potential platform for advanced targeted therapeutic strategies in biomedical applications.

Swim bladder-derived biomaterials: structures, compositions, properties, modifications, and biomedical applications

Animal-derived biomaterials have been extensively employed in clinical practice owing to their compositional and structural similarities with those of human tissues and organs, exhibiting good mechanical properties and biocompatibility, and extensive sources. However, there is an associated risk of infection with pathogenic microorganisms after the implantation of tissues from pigs, cattle, and other mammals in humans. Therefore, researchers have begun to explore the development of non-mammalian regenerative biomaterials. Among these is the swim bladder, a fish-derived biomaterial that is rapidly used in various fields of biomedicine because of its high collagen, elastin, and polysaccharide content. However, relevant reviews on the biomedical applications of swim bladders as effective biomaterials are lacking. Therefore, based on our previous research and in-depth understanding of this field, this review describes the structures and compositions, properties, and modifications of the swim bladder, with their direct (including soft tissue repair, dural repair, cardiovascular repair, and edible and pharmaceutical fish maw) and indirect applications (including extracted collagen peptides with smaller molecular weights, and collagen or gelatin with higher molecular weights used for hydrogels, and biological adhesives or glues) in the field of biomedicine in recent years. This review provides insights into the use of swim bladders as source of biomaterial; hence, it can aid biomedicine scholars by providing directions for advancements in this field.

Naturally derived highly resilient and adhesive hydrogels with application as surgical adhesive

The inadequacy of conventional surgical techniques for wound closure and repair in soft and resilient tissues may lead to poor healing outcomes such as local tissue fibrosis and contracture. Therefore, the development of adhesive and resilient hydrogels that can adhere firmly to irregular and dynamic wound interfaces and provide a "tension-free proximity" environment for tissue regeneration has become extremely important. Herein, we describe an integrated modeling-experiment-application strategy for engineering a promising hydrogel-based bioadhesive based on recombinant human collagen (RHC) and catechol-modified hyaluronic acid (HA-Cat). Molecular modeling and simulations were used to verify and explore the hypothesis that RHC and HA-Cat can form an assembly complex through physical interactions. The complex was synergistically crosslinked via a catechol/o-quinone coupling reaction and a carbodiimide coupling reactions, resulting in superior hydrogels with strong adhesion and resilience properties. The application of this bioadhesive to tissue adhesion and wound sealing in vivo was successfully demonstrated, with an optimum collagen index, epidermal thickness, and lowest scar width. Furthermore, subcutaneous implantation demonstrated that the bioadhesive exhibited good biocompatibility and degradability. This newly developed hydrogel may be a highly promising surgical adhesive for medical applications, including wound closure and repair.

Computational investigation of a 3D-printed skin substitute with orthotropy in mechanical property

As a promising treatment for third-degree burns, grafting with bioengineering skin substitutes shows a capability to overcome the deficiency of donor skin. Similar mechanical properties with human skin are required for employed skin substitutes to avoid secondary damage to patients. Given the representativeness of orthotropy in mechanical properties, there is a need for developing orthotropic skin substitutes. This paper presents computational investigation as well as structural design for the fabrication of orthotropic skin substitutes. A finite element method (FEM) based mechanics simulation model for analyzing the stress field in the skin substitute was developed, by which the stress distribution in mimetic structures of the epidermis and dermis can be acquired. Moreover, the equation of Young's modulus was deduced based on the simulation result, which expressed the mechanical property of designed skin substitutes. Furthermore, several structures of skin substitutes were proposed and their calculated Young's modulus ranged from 21.87 kPa to 213.32 kPa, which was similar to the human skin. Ultimately, uniaxial tensile tests were performed for three types of 3D-printed orthotropic skin substitutes, which validates the feasibility to regulate Young's modulus by regulating the structure of fabricated skin substitutes.

Dual gene-activated dermal scaffolds regulate angiogenesis and wound healing by mediating the coexpression of VEGF and angiopoietin-1

The vascularization of dermal substitutes is a key challenge in efforts to heal deep skin defects. In this study, dual gene-activated dermal scaffolds (DGADSs-1) were fabricated by loading nanocomposite particles of polyethylenimine (PEI)/multiple plasmid DNAs (pDNAs) encoding vascular endothelial growth factor and angiopoietin-1 at a ratio of 1:1. In a similar manner, DGADSs-2 were loaded with a chimeric plasmid encoding both VEGF and Ang-1. In vitro studies showed that both types of DGADSs released PEI/pDNA nanoparticles in a sustained manner; they demonstrated effective transfection ability, leading to upregulated expression of VEGF and Ang-1. Furthermore, both types of DGADSs promoted fibroblast proliferation and blood vessel formation, although DGADSs-1 showed a more obvious promotion effect. A rat full-thickness skin defect model showed that split-thickness skin transplanted using a one-step method could achieve full survival at the 12th day after surgery in both DGADSs-1 and DGADSs-2 groups, and the vascularization time of dermal substitutes was significantly shortened. Compared with the other three groups of scaffolds, the DGADSs-1 group had significantly greater cell infiltration, collagen deposition, neovascularization, and vascular maturation, all of which promoted wound healing. Thus, compared with single-gene-activated dermal scaffolds, DGADSs show greater potential for enhancing angiogenesis. DGADSs with different loading modes also exhibited differences in terms of angiogenesis; the effect of loading two genes (DGADSs-1) was better than the effect of loading a chimeric gene (DGADSs-2). In summary, DGADSs, which continuously upregulate VEGF and Ang-1 expression, offer a new functional tissue-engineered dermal substitute with the ability to activate vascularization.

Polymer nanomaterials for use as adjuvant surgical tools

Materials employed in the treatment of conditions encountered in surgical and clinical practice frequently face barriers in translation to application. Shortcomings can be generalized through their reduced mechanical stability, difficulty in handling, and inability to conform or adhere to complex tissue surfaces. To overcome an amalgam of challenges, research has sought the utilization of polymer-derived nanomaterials deposited in various fashions and formulations to improve the application and outcomes of surgical and clinical interventions. Clinically prevalent applications include topical wound dressings, tissue adhesives, surgical sealants, hemostats, and adhesion barriers, all of which have displayed the potential to act as superior alternatives to current materials used in surgical procedures. In this review, emphasis will be placed not only on applications, but also on various design strategies employed in fabrication. This review is designed to provide a broad and thought-provoking understanding of nanomaterials as adjuvant tools for the assisted treatment of pathologies prevalent in surgery. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Implantable Materials and Surgical Technologies > Nanoscale Tools and Techniques in Surgery.

Effect of extracellular matrix fiber cross-linkage on cancer cell motility and surrounding matrix deformation

Cancer incidence is increasing annually, and the invasion of cancer into the stroma significantly affects cancer metastasis. The stroma primarily comprises an abundant extracellular matrix (ECM) that interacts closely with cancer cells. Cancer cells use the ECM as a scaffold to migrate from a tumor via mechanical actions such as pushing and pulling the fibers. The purpose of this study is to clarify the effects of elastic modulus differences on cell migration behavior based on the same ECM fiber structure. We observe temporal changes in the morphology of cancer cells and the surrounding ECM to elucidate the relationship between changes in the mechanical properties of the ECM and the invasive behavior of cancer cells. We analyze the shape and migration distance of cancer cells and the displacement field of the ECM by varying the fiber elastic modulus but fixing the ECM density. Increasing the elastic modulus results in a protruding cell shape, which indicates the maximum displacement of the ECM around the cell. Additionally, differences in cell migration speed and dispersion based on the elastic modulus are observed. The behavior of cells with increasing elasticity is classified via cluster analysis. Owing to the chemical cross-linking of the fibers, some cells cannot deform the surrounding tissue. This is attributable to the gel state of the ECM and microscopic fluctuations in the fiber density around the cells. We successfully assessed the effect of changes in the ECM modulus on cell mortality and morphology to reveal the mechanism of cancer invasion.

Human beta defensin-2 loaded PLGA nanoparticles impregnated in collagen-chitosan composite scaffold for the management of diabetic wounds

Diabetic wound (DW) is the most devastating complication resulting in significant mortality and morbidity in diabetic patients. The standard treatment of DW care fails to address the prerequisites of treating DW owing to its multifactorial pathophysiology. Henceforth, developing a single treatment strategy to handle all the loopholes may effectively manage DW. The objective of the current study was to formulate Human beta defensin-2 (HBD-2) loaded Poly (lactic-co-glycolic acid) (PLGA) nanoparticle impregnated in collagen/chitosan (COL-CS) composite scaffolds for the accelerated healing of DW. Upon investigation, the developed biodegradable crosslinked scaffold possesses low matrix degradation, optimum porosity, and sustained drug release than the non-crosslinked scaffold. In vitro studies revealed that the HBD-2 COL-CS scaffold was biocompatible and accelerated cell migration and angiogenesis. The HBD-2 COL-CS scaffold showed significant antimicrobial activity in S. aureus, E. coli, and P. aeruginosa. The in vivo studies revealed that the HBD-2 COL-CS treated group accelerated healing compared to those in COL-CS and control groups. The ELISA results indicated a significant decrease in MMP-9, TNF-α, MPO, NAG, and NO with an increase in IL-10 in HBD-2 COL-CS treated group. The accelerated healing in HBD-2 COL-CS treated group might be due to the synergistic effects of PLGA (collagen synthesis and deposition and positive angiogenic effect), HBD-2 (anti-inflammatory, antibacterial, positive angiogenic effect, cell proliferation, and migration), COL (established wound healer and stabilizer) and CS (antibacterial, controlled drug release).

Cutting Edge Aquatic-Based Collagens in Tissue Engineering

Aquatic-based collagens have attracted much interest due to their great potential application for biomedical sectors, including the tissue engineering sector, as a major component of the extracellular matrix in humans. Their physical and biochemical characteristics offer advantages over mammalian-based collagen; for example, they have excellent biocompatibility and biodegradability, are easy to extract, and pose a relatively low immunological risk to mammalian products. The utilization of aquatic-based collagen also has fewer religious restrictions and lower production costs. Aquatic-based collagen also creates high-added value and good environmental sustainability by aquatic waste utilization. Thus, this study aims to overview aquatic collagen's characteristics, extraction, and fabrication. It also highlights its potential application for tissue engineering and the regeneration of bone, cartilage, dental, skin, and vascular tissue. Moreover, this review highlights the recent research in aquatic collagen, future prospects, and challenges for it as an alternative biomaterial for tissue engineering and regenerative medicines.

Are Natural Compounds a Promising Alternative to Synthetic Cross-Linking Agents in the Preparation of Hydrogels?

The main aim of this review is to assess the potential use of natural cross-linking agents, such as genipin, citric acid, tannic acid, epigallocatechin gallate, and vanillin in preparing chemically cross-linked hydrogels for the biomedical, pharmaceutical, and cosmetic industries. Chemical cross-linking is one of the most important methods that is commonly used to form mechanically strong hydrogels based on biopolymers, such as alginates, chitosan, hyaluronic acid, collagen, gelatin, and fibroin. Moreover, the properties of natural cross-linking agents and their advantages and disadvantages are compared relative to their commonly known synthetic cross-linking counterparts. Nowadays, advanced technologies can facilitate the acquisition of high-purity biomaterials from unreacted components with no additional purification steps. However, while planning and designing a chemical process, energy and water consumption should be limited in order to reduce the risks associated with global warming. However, many synthetic cross-linking agents, such as N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate, poly (ethylene glycol) diacrylates, epichlorohydrin, and glutaraldehyde, are harmful to both humans and the environment. One solution to this problem could be the use of bio-cross-linking agents obtained from natural resources, which would eliminate their toxic effects and ensure the safety for humans and the environment.

Comparison of biopolymer scaffolds for the fabrication of skin substitutes in a porcine wound model

This study compared three acellular scaffolds as templates for the fabrication of skin substitutes. A collagen-glycosaminoglycan (C-GAG), a biodegradable polyurethane foam (PUR) and a hybrid combination (PUR/C-GAG) were investigated. Scaffolds were prepared for cell inoculation. Fibroblasts and keratinocytes were serially inoculated onto the scaffolds and co-cultured for 14 days before transplantation. Three pigs each received four full-thickness 8 cm × 8 cm surgical wounds, into which a biodegradable temporising matrix (BTM) was implanted. Surface seals were removed after integration (28 days), and three laboratory-generated skin analogues and a control split-thickness skin graft (STSG) were applied for 16 weeks. Punch biopsies confirmed engraftment and re-epithelialisation. Biophysical wound parameters were also measured and analysed. All wounds showed greater than 80% epithelialisation by day 14 post-transplantation. The control STSG displayed 44% contraction over the 16 weeks, and the test scaffolds, C-GAG 64%, Hybrid 66.7% and PUR 67.8%. Immunohistochemistry confirmed positive epidermal keratins and basement membrane components (Integrin alpha-6, collagens IV and VII). Collagen deposition and fibre organisation indicated the degree of fibrosis and scar produced for each graft. All scaffold substitutes re-epithelialised by 4 weeks. The percentage of original wound area for the Hybrid and PUR was significantly different than the STSG and C-GAG, indicating the importance of scaffold retainment within the first 3 months post-transplant. The PUR/C-GAG scaffolds reduced the polymer pore size, assisting cell retention and reducing the contraction of in vitro collagen. Further investigation is required to ensure reproducibility and scale-up feasibility.

The influence of UV irradiation on fish skin collagen films in the presence of xanthohumol and propanediol

Fish skin collagen films are widely used as adhesives in medicine and cosmetology. Ultraviolet (UV) irradiation can be considered as an effective sterilization method for biomaterials, however, it may also lead to material photodegradation. In this work, the influence of xanthohumol and propanediol on the physico-chemical properties of collagen films before and after UV irradiation was studied. Collagen for this research was extracted from silver carp skin and thin films were fabricated by the solution casting methods. The structure of films was researched using infrared spectroscopy. The surface properties of films were investigated using Atomic Force Microscopy (AFM) and contact angle measurements. Mechanical properties were measured as well. It was found that the addition of xanthohumol and propanediol modified the roughness of collagen films and their mechanical properties. UV irradiation led to the water loss from the film and modification of the collagen structure. In the presence of propanediol and xanthohumol the water loss after UV irradiation was smaller than in UV-irradiated collagen films without these additives.

Preparation of Cross-Linked Bovine Tendon Acellular Fibers and Study of Their Biophysical and Chemical Properties

To explore the effect of glutaraldehyde (GA) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) cross-linking on the biophysical and chemical properties of acellular scaffold to better provide suitable donor materials for tendon reconstruction. GA and EDC with different concentrations and action time gradients were used to cross-link the acellular scaffold. By detecting the collagen content in the cross-linked scaffold and the cytotoxicity, the cross-linking scheme with minimal damage to the scaffold and minimal cytotoxicity was explored for subsequent studies. The biomechanical properties (durability, elastic modulus, stressmax) of the scaffolds in GA, EDC, acellular scaffold, and tendon groups were compared, and the scaffold rat models were constructed to further evaluate their in vivo histocompatibility. Under different concentration gradients, the collagen content of the scaffolds in the GA and EDC groups had no obvious difference. When 0.5% GA was cross-linked for 24 h, and the mass ratio of EDC (1:2) was cross-linked for 4 h, the inhibition rate of the scaffold extract on fibroblasts was the lowest. In the mechanical property test, the Stressmax, durability, and elastic modulus of the cross-linked acellular scaffolds were significantly improved than those before cross-linking, and the elastic modulus of the EDC acellular scaffold was similar to that of the bovine tendon. In the compatibility test, compared with the acellular scaffold group, fibroblast activity in the GA group decreased obviously, and the scaffold implanted in rat models led to a persistent chronic inflammatory reaction. However, cells in the EDC group could maintain good activity. Moreover, the scaffold had good compatibility with rats and did not cause an obvious inflammatory reaction. EDC cross-linking scheme will not damage the acellular scaffold, and the cytotoxicity of the obtained scaffold is controllable. Additionally, EDC cross-linked acellular scaffold has mechanical properties similar to normal tendons and excellent histocompatibility.

Fabrication Strategies Towards Hydrogels for Biomedical Application: Chemical and Mechanical Insights

This review aims at giving selected chemical and mechanical insights on design criteria that should be taken into account in hydrogel production for biomedical applications. Particular emphasis will be given to the chemical aspects involved in hydrogel design: macromer chemical composition, cross-linking strategies and chemistry towards "conventional" and smart/stimuli responsive hydrogels. Mechanical properties of hydrogels in view of regenerative medicine applications will also be considered.

Development and characterisation of 3D collagen-gelatin based scaffolds for breast cancer research

While 2D culture presents a useful tool for cancer research, it fails to replicate the tumor microenvironment as it lacks proper three-dimensional cell-cell/cell-matrix interactions, often resulting in exaggerated responses to therapeutic agents. 3D models that aim to overcome the issues associated with 2D culture research offer a new frontier for cancer research with cell growth, morphology and genetic properties that more closely match in vivo cancers. Herein, we aim to develop a collagen-based scaffold that supports the attachment and proliferation of breast cancer (BC) cells as a 3D culture model. Scaffolds were produced on a repeatable basis using a freeze-drying procedure. The constructs were highly porous (>99%) with homogenous pore sizes (150-300 μm) and an interconnected structure. The application of 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDAC) crosslinking resulted in scaffolds with elastic moduli in the range of 1-2 kPa, mimicking cancerous breast tissue stiffness. Furthermore, the incorporation of gelatin into the scaffolds enabled the porosity, pore size and mechanical properties to be tailored, resulting in scaffolds with stiffness values that accurately replicate the stiffness of human BC extracellular matrix (ECM) (1.3-1.7 kPa). Scaffolds displayed high in vitro stability with 90% of mass remaining after 14 days of culture. The scaffolds were shown to be highly biocompatible, and capable of supporting the attachment, infiltration and proliferation of MCF7 breast cancer (BC) cells over +14 days. These results confirm the suitability of these scaffolds as culture models for BC cells. These collagen-based scaffolds offer significant potential for the exploration of aspects of BC, such as gene expression profiles and patterns, and for the assessment of the efficacy of therapeutic agents in treating BC.

Bioprinting and plastic compression of large pigmented and vascularized human dermo-epidermal skin substitutes by means of a new robotic platform

Extensive availability of engineered autologous dermo-epidermal skin substitutes (DESS) with functional and structural properties of normal human skin represents a goal for the treatment of large skin defects such as severe burns. Recently, a clinical phase I trial with this type of DESS was successfully completed, which included patients own keratinocytes and fibroblasts. Yet, two important features of natural skin were missing: pigmentation and vascularization. The first has important physiological and psychological implications for the patient, the second impacts survival and quality of the graft. Additionally, accurate reproduction of large amounts of patient’s skin in an automated way is essential for upscaling DESS production. Therefore, in the present study, we implemented a new robotic unit (called SkinFactory) for 3D bioprinting of pigmented and pre-vascularized DESS using normal human skin derived fibroblasts, blood- and lymphatic endothelial cells, keratinocytes, and melanocytes. We show the feasibility of our approach by demonstrating the viability of all the cells after printing in vitro, the integrity of the reconstituted capillary network in vivo after transplantation to immunodeficient rats and the anastomosis to the vascular plexus of the host. Our work has to be considered as a proof of concept in view of the implementation of an extended platform, which fully automatize the process of skin substitution: this would be a considerable improvement of the treatment of burn victims and patients with severe skin lesions based on patients own skin derived cells.

Cationic, anionic and neutral polysaccharides for skin tissue engineering and wound healing applications

Today, chronic wound care and management can be regarded as a clinically critical issue. However, the limitations of current approaches for wound healing have encouraged researchers and physicians to develop more efficient alternative approaches. Advances in tissue engineering and regenerative medicine have resulted in the development of promising approaches that can accelerate wound healing and improve the skin regeneration rate and quality. The design and fabrication of scaffolds that can address the multifactorial nature of chronic wound occurrence and provide support for the healing process can be considered an important area requiring improvement. In this regard, polysaccharide-based scaffolds have distinctive properties such as biocompatibility, biodegradability, high water retention capacity and nontoxicity, making them ideal for wound healing applications. Their tunable structure and networked morphology could facilitate a number of functions, such as controlling their diffusion, maintaining wound moisture, absorbing a large amount of exudates and facilitating gas exchange. In this review, the wound healing process and the influential factors, structure and properties of carbohydrate polymers, physical and chemical crosslinking of polysaccharides, scaffold fabrication techniques, and the use of polysaccharide-based scaffolds in skin tissue engineering and wound healing applications are discussed.

Advances in Skin Tissue Bioengineering and the Challenges of Clinical Translation

Skin tissue bioengineering is an emerging field that brings together interdisciplinary teams to promote successful translation to clinical care. Extensive deep tissue injuries, such as large burns and other major skin loss conditions, are medical indications where bioengineered skin substitutes (that restore both dermal and epidermal tissues) are being studied as alternatives. These may not only reduce mortality but also lessen morbidity to improve quality of life and functional outcome compared with the current standards of care. A common objective of dermal-epidermal therapies is to reduce the time required to accomplish stable closure of wounds with minimal scar in patients with insufficient donor sites for autologous split-thickness skin grafts. However, no commercially-available product has yet fully satisfied this objective. Tissue engineered skin may include cells, biopolymer scaffolds and drugs, and requires regulatory review to demonstrate safety and efficacy. They must be scalable for manufacturing and distribution. The advancement of technology and the introduction of bioreactors and bio-printing for skin tissue engineering may facilitate clinical products' availability. This mini-review elucidates the reasons for the few available commercial skin substitutes. In addition, it provides insights into the challenges faced by surgeons and scientists to develop new therapies and deliver the results of translational research to improve patient care.

Collagen-Alginate Composite Hydrogel: Application in Tissue Engineering and Biomedical Sciences

Alginate (ALG), a polysaccharide derived from brown seaweed, has been extensively investigated as a biomaterial not only in tissue engineering but also for numerous biomedical sciences owing to its wide availability, good compatibility, weak cytotoxicity, low cost, and ease of gelation. Nevertheless, alginate lacks cell-binding sites, limiting long-term cell survival and viability in 3D culture. Collagen (Col), a major component protein found in the extracellular matrix (ECM), exhibits excellent biocompatibility and weak immunogenicity. Furthermore, collagen contains cell-binding motifs, which facilitate cell attachment, interaction, and spreading, consequently maintaining cell viability and promoting cell proliferation. Recently, there has been a growing body of investigations into collagen-based hydrogel trying to overcome the poor mechanical properties of collagen. In particular, collagen-alginate composite (CAC) hydrogel has attracted much attention due to its excellent biocompatibility, gelling under mild conditions, low cytotoxicity, controllable mechanic properties, wider availability as well as ease of incorporation of other biomaterials and bioactive agents. This review aims to provide an overview of the properties of alginate and collagen. Moreover, the application of CAC hydrogel in tissue engineering and biomedical sciences is also discussed.

Antibacterial efficacy of quaternized chitosan/poly (vinyl alcohol) nanofiber membrane crosslinked with blocked diisocyanate

N-[(2-hydroxyl-3-trimethylammonium) propyl] chitosan chloride (HTCC), which is a type of chitosan derivative with quaternary ammonium groups, possesses a higher antibacterial activity as compared to the pristine chitosan. The nanofiber membranes made of HTCC are attractive for applications demanding for antibacterial function. However, the hydrophilic nature of HTCC makes it unsuitable for electrospinning of nanofibers. Hence, biodegradable polyvinyl alcohol (PVA) was proposed as an additive to improve the electrospinnability of HTCC. In this work, PVA/HTCC nanofiber membrane was crosslinked with the blocked diisocyanate (BI) to enhance the stability of nanofiber membrane in water. Microbiological assessments showed that the PVA/HTCC/BI nanofiber membranes possessed a good antibacterial efficacy (∼100 %) against E. coli. Moreover, the biocompatibility of PVA/HTCC/BI nanofiber membrane was proven by the cytotoxicity test on mouse fibroblasts. These promising results indicated that the PVA/HTCC/BI nanofiber membrane can be a promising material for food packaging and as a potential wound dressing for skin regeneration.

Recombinant human collagen/chitosan-based soft hydrogels as biomaterials for soft tissue engineering

Animal-derived collagen may contain viruses, and its impurity can cause immunological reactions. Chitosan, always required a neutralization step in fabricating it into the biocompatible tissue engineering scaffolds. To avoid these risks and simplify the production process, a series of recombinant human collagen/carboxylated chitosan (RHC-CHI) based soft hydrogel scaffolds were prepared by crosslinking-induced gelation and then investigated their feasibilities for use as soft tissue engineering scaffolds. The gelation time was optimized by modulating the biopolymer concentration or reaction temperature. The hydrogel swelling, degradation rate, and mechanical properties were also investigated. The results showed that these parameters could be tuned by adjusting either the RHC-to-chitosan ratio or the total polymer concentration. The mechanical properties of the hydrogels were improved by adding chitosan, but excess chitosan reduced the hydrogel mechanical strength and accelerated the degradation speed. Cytotoxicity tests showed that all fabricated soft hydrogels were biocompatible and displayed no cytotoxicity. Cytocompatibility tests and qRT-PCR studies indicated that the hydrogel system promoted the adhesion and proliferation of NIH-3T3 cells, and cellular activities were directly up-regulated by RHC. Finally, our in vivo study proved these hydrogels were able to accelerate the cell infiltration and wound closure. These results show that the soft RHC-CHI hydrogels show promise in soft-tissue engineering.

Advances in biofabrication techniques for collagen-based 3D in vitro culture models for breast cancer research

Collagen is the most abundant component of the extracellular matrix (ECM), therefore it represents an ideal biomaterial for the culture of a variety of cell types. Recently, collagen-based scaffolds have shown promise as 3D culture platforms for breast cancer-based research. Two-dimensional (2D) in vitro culture models, while useful for gaining preliminary insights, are ultimately flawed as they do not adequately replicate the tumour microenvironment. As a result, they do not facilitate proper 3D cell-cell/cell-matrix interactions and often an exaggerated response to therapeutic agents occurs. The ECM plays a crucial role in the development and spread of cancer. Alterations within the ECM have a significant impact on the pathogenesis of cancer, the initiation of metastasis and ultimate progression of the disease. 3D in vitro culture models that aim to replicate the tumour microenvironment have the potential to offer a new frontier for cancer research with cell growth, morphology and genetic properties that more closely match in vivo cancers. While initial 3D in vitro culture models used in breast cancer research consisted of simple hydrogel platforms, recent advances in biofabrication techniques, including freeze-drying, electrospinning and 3D bioprinting, have enabled the fabrication of biomimetic collagen-based platforms that more closely replicate the breast cancer ECM. This review highlights the current application of collagen-based scaffolds as 3D in vitro culture models for breast cancer research, specifically for adherence-based scaffolds (i.e. matrix-assisted). Finally, the future perspectives of 3D in vitro breast cancer models and their potential to lead to an improved understanding of breast cancer diagnosis and treatment are discussed.

Impact of Digestive Inflammatory Environment and Genipin Crosslinking on Immunomodulatory Capacity of Injectable Musculoskeletal Tissue Scaffold

The paracrine and autocrine processes of the host response play an integral role in the success of scaffold-based tissue regeneration. Recently, the immunomodulatory scaffolds have received huge attention for modulating inflammation around the host tissue through releasing anti-inflammatory cytokine. However, controlling the inflammation and providing a sustained release of anti-inflammatory cytokine from the scaffold in the digestive inflammatory environment are predicated upon a comprehensive understanding of three fundamental questions. (1) How does the release rate of cytokine from the scaffold change in the digestive inflammatory environment? (2) Can we prevent the premature scaffold degradation and burst release of the loaded cytokine in the digestive inflammatory environment? (3) How does the scaffold degradation prevention technique affect the immunomodulatory capacity of the scaffold? This study investigated the impacts of the digestive inflammatory environment on scaffold degradation and how pre-mature degradation can be prevented using genipin crosslinking and how genipin crosslinking affects the interleukin-4 (IL-4) release from the scaffold and differentiation of naïve macrophages (M0). Our results demonstrated that the digestive inflammatory environment (DIE) attenuates protein retention within the scaffold. Over 14 days, the encapsulated protein released 46% more in DIE than in phosphate buffer saline (PBS), which was improved through genipin crosslinking. We have identified the 0.5 (w/v) genipin concentration as an optimal concentration for improved IL-4 released from the scaffold, cell viability, mechanical strength, and scaffold porosity, and immunomodulation studies. The IL-4 released from the injectable scaffold could differentiate naïve macrophages to an anti-inflammatory (M2) lineage; however, upon genipin crosslinking, the immunomodulatory capacity of the scaffold diminished significantly, and pro-inflammatory markers were expressed dominantly.

Decellularization of Skin Tissue

Biomaterials science encompasses elements of medicine, biology, chemistry, materials, and tissue engineering. They are engineered to interact with biological systems to treat, augment, repair, or replace lost tissue function. The choice of biomaterial depends on the procedure being performed, the severity of the patient's condition, and the surgeon's preference. Prostheses made from natural-derived biomaterials are often derived from decellularized extracellular matrix (ECM) of animal (xenograft) or human (allograft) origin. Advantages of using ECM include their resemblance in morphology and three-dimensional structures with that of tissue to be replaced. Due to this, scientists all over are now focusing on naturally derived biomaterials which have been shown to possess several advantages compared to synthetic ones, owing to their biocompatibility, biodegradability, and remodeling properties. Advantages of a naturally derived biomaterial enhance their application for replacement or restoration of damaged organs/tissues. They adequately support cell adhesion, migration, proliferation, and differentiation. Naturally derived biomaterials can induce extracellular matrix formation and tissue repair when implanted into a defect by enhancing attachment and migration of cells from surrounding environment. In the current chapter, we will focus on the natural and synthetic dermal matrix development and all of the progress in this field.

Current Advances in 3D Bioprinting Technology and Its Applications for Tissue Engineering

Three-dimensional (3D) bioprinting technology has emerged as a powerful biofabrication platform for tissue engineering because of its ability to engineer living cells and biomaterial-based 3D objects. Over the last few decades, droplet-based, extrusion-based, and laser-assisted bioprinters have been developed to fulfill certain requirements in terms of resolution, cell viability, cell density, etc. Simultaneously, various bio-inks based on natural-synthetic biomaterials have been developed and applied for successful tissue regeneration. To engineer more realistic artificial tissues/organs, mixtures of bio-inks with various recipes have also been developed. Taken together, this review describes the fundamental characteristics of the existing bioprinters and bio-inks that have been currently developed, followed by their advantages and disadvantages. Finally, various tissue engineering applications using 3D bioprinting are briefly introduced.

Preliminary Study of In Vitro Three-Dimensional Skin Model Using an Ovine Collagen Type I Sponge Seeded with Co-Culture Skin Cells: Submerged versus Air-Liquid Interface Conditions

Three-dimensional (3D) in vitro skin models have been widely used for cosmeceutical and pharmaceutical applications aiming to reduce animal use in experiment. This study investigate capability of ovine tendon collagen type I (OTC-I) sponge suitable platform for a 3D in vitro skin model using co-cultured skin cells (CC) containing human epidermal keratinocytes (HEK) and human dermal fibroblasts (HDF) under submerged (SM) and air-liquid interface (ALI) conditions. Briefly, the extracted OTC-I was freeze-dried and crosslinked with genipin (OTC-I_GNP) and carbodiimide (OTC-I_EDC). The gross appearance, physico-chemical characteristics, biocompatibility and growth profile of seeded skin cells were assessed. The light brown and white appearance for the OTC-I_GNP scaffold and other groups were observed, respectively. The OTC-I_GNP scaffold demonstrated the highest swelling ratio (~1885%) and water uptake (94.96 ± 0.14%). The Fourier transformation infrared demonstrated amide A, B and I, II and III which represent collagen type I. The microstructure of all fabricated sponges presented a similar surface roughness with the presence of visible collagen fibers and a heterogenous porous structure. The OTC-I_EDC scaffold was more toxic and showed the lowest cell attachment and proliferation as compared to other groups. The micrographic evaluation revealed that CC potentially formed the epidermal- and dermal-like layers in both SM and ALI that prominently observed with OTC-I_GNP compared to others. In conclusion, these results suggest that OTC_GNP could be used as a 3D in vitro skin model under ALI microenvironment.

Evaluation of 1-Ethyl-3-(3-Dimethylaminopropyl) Carbodiimide Cross-Linked Collagen Membranes for Guided Bone Regeneration in Beagle Dogs

The purpose of this study was to evaluate the bone regeneration efficacy of an 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)-cross-linked collagen membrane for guided bone regeneration (GBR). A non-cross-linked collagen membrane (Control group), and an EDC-cross-linked collagen membrane (Test group) were used in this study. In vitro, mechanical, and degradation testing and cell studies were performed. In the animal study, 36 artificial bone defects were formed in the mandibles of six beagles. Implants were inserted at the time of bone grafting, and membranes were assigned randomly. Eight weeks later, animals were sacrificed, micro-computed tomography was performed, and hematoxylin-eosin stained specimens were prepared. Physical properties (tensile strength and enzymatic degradation rate) were better in the Test group than in the Control group. No inflammation or membrane collapse was observed in either group, and bone volumes (%) in defects around implants were similar in the two groups (p > 0.05). The results of new bone areas (%) analysis also showed similar values in the two groups (p > 0.05). Therefore, it can be concluded that cross-linking the collagen membranes with EDC is the method of enhancing the physical properties (tensile strength and enzymatic degradation) of the collagen membranes without risk of toxicity.

Rose Bengal Crosslinking to Stabilize Collagen Sheets and Generate Modulated Collagen Laminates

For medical application, easily accessible biomaterials with tailored properties are desirable. Collagen type I represents a biomaterial of choice for regenerative medicine and tissue engineering. Here, we present a simple method to modify the properties of collagen and to generate collagen laminates. We selected three commercially available collagen sheets with different thicknesses and densities and examined the effect of rose bengal and green light collagen crosslinking (RGX) on properties such as microstructure, swelling degree, mechanical stability, cell compatibility and drug release. The highest impact of RGX was measured for Atelocollagen, for which the swelling degree was reduced from 630% (w/w) to 520% (w/w) and thickness measured under force application increased from 0.014 mm to 0.455 mm, indicating a significant increase in mechanical stability. Microstructural analysis revealed that the sponge-like structure was replaced by a fibrous structure. While the initial burst effect during vancomycin release was not influenced by crosslinking, RGX increased cell proliferation on sheets of Atelocollagen and on Collagen Solutions. We furthermore demonstrate that RGX can be used to covalently attach different sheets to create materials with combined properties, making the modification and combination of readily available sheets with RGX an attractive approach for clinical application.

Understanding interfacial fracture behavior between microinterlocked soft layers using physics-based cohesive zone modeling

We examine the underlying fracture mechanics of the human skin dermal-epidermal layer's microinterlocks using a physics-based cohesive zone finite-element model. Using microfabrication techniques, we fabricated highly dense arrays of spherical microstructures of radius ≈50μm without and with undercuts, which occur in an open spherical cavity whose centroid lies below the microstructure surface to create microinterlocks in polydimethylsiloxane layers. From experimental peel tests, we find that the maximum density microinterlocks without and with undercuts enable the respective ≈4-fold and ≈5-fold increase in adhesion strength as compared to the plain layers. Critical visualization of the single microinterlock fracture from the cohesive zone model reveals a contact interaction-based phenomena where the primary propagating crack is arrested and the secondary crack is initiated in the microinterlocked area. Strain energy energetics confirmed significantly lower strain energy dissipation for the microinterlock with the undercut as compared to its nonundercut counterpart. These phenomena are completely absent in a plain interface fracture where the fracture propagates catastrophically without any arrests. These events confirm the difference in the experimental results corroborated by the Cook-Gordon mechanism. The findings from the cohesive zone simulation provide deeper insights into soft microinterlock fracture mechanics that could prominently help in the rational designing of sutureless skin grafts and electronic skin.

In Vivo Analysis of the Biocompatibility and Immune Response of Jellyfish Collagen Scaffolds and its Suitability for Bone Regeneration

Jellyfish collagen, which can be defined as "collagen type 0" due to its homogeneity to the mammalian types I, II, III, V, and IX and its batch-to-batch consistent producibility, is of special interest for different medical applications related to (bone) tissue regeneration as an alternative to mammalian collagen-based biomaterials. However, no in vivo studies regarding the induction of M1- and M2-macrophages and their time-dependent ration as well as the analysis of the bone regeneration capacity of jellyfish collagen scaffolds have been conducted until now. Thus, the goal of this study was to determine the nature of the immune response to jellyfish collagen scaffolds and their bone healing capacities. Two in vivo studies using established implantation models, i.e., the subcutaneous and the calvarian implantation model in Wistar rats, were conducted. Furthermore, specialized histological, histopathological, and histomorphometrical methods have been used. As a control biomaterial, a collagen scaffold, originating from porcine pericardium, which has already been stated as biocompatible, was used for the subcutaneous study. The results of the present study show that jellyfish collagen scaffolds are nearly completely resorbed until day 60 post implantation by stepwise integration within the subcutaneous connective tissue mediated mainly by macrophages and single multinucleated giant cells. Interestingly, the degradation process ended in a vessel rich connective tissue that is understood to be an optimal basis for tissue regeneration. The study results showed an overall weaker immune response to jellyfish collagen than to porcine pericardium matrices by the induction of significantly lower numbers of macrophages together with a more balanced occurrence of M1- and M2-macrophages. However, both collagen-based biomaterials induced balanced numbers of both macrophage subtypes, which supports their good biocompatibility. Moreover, the histomorphometrical results for the calvarial implantation of the jellyfish scaffolds revealed an average of 46.20% de novo bone formation at day 60, which was significantly higher compared to the control group. Thereby, the jellyfish collagen scaffolds induced also significantly higher numbers of anti-inflammatory macrophages within the bony implantation beds. Altogether, the results show that the jellyfish collagen scaffolds allowed for a directed integration behavior, which is assumed to be in accordance with the concept of Guided Bone Regeneration (GBR). Furthermore, the jellyfish collagen scaffolds induced a long-term anti-inflammatory macrophage response and an optimal vascularization pattern within their implant beds, thus showing excellent biocompatibility and (bone) tissue healing properties.

Polydopamine coating of uncrosslinked chitosan as an acellular scaffold for full thickness skin grafts

There is an unmet need for skin grafting materials that are readily available for large area wounds, due to complex, lengthy and costly manufacturing processes that are not compatible with this type of wounds. Here we developed an acellular skin graft material based on surface coating of uncrosslinked porous (UCLP) chitosan. UCLP chitosan membranes had mechanical properties in ranges suitable for skin grafting. Polydopamine (PDA) coating improved hydrophilicity and resulted in a significant increase in attachment and metabolic activity of mammalian cells in vitro. PDA coating also decreased the attachment of pseudomonas aeruginosa - a common bacteria infecting skin wounds. Finally, the PDA-coated membranes were implanted in full thickness surgical wounds in a rodent model and resulted in complete would closure in 5 days. The current study suggests that PDA-coated UCLP chitosan membranes could be a simple and effective strategy for the development of grafting materials for large area wounds.

Coupled OPG-Fc on Decellularized Aortic Valves by EDC/NHS Attenuates Rat MSCs Calcification In Vitro

Valve calcification commonly damages natural human heart valves and tissue-engineered heart valves (TEHVs), and no ideal intervention is available in clinical practice. It is increasingly considered that osteoprotegerin (OPG) inhibits vascular calcification. Herein we aimed to explore whether free OPG-Fc fusion protein or coupled OPG-Fc on decellularized aortic valves attenuates calcification. Calcification of rat bone marrow-derived mesenchymal stromal cells (MSCs) was induced by osteogenic differentiation media, and the effects of free OPG-Fc or OPG-Fc coupled on the decellularized porcine aortic heart valve leaflet scaffolds by coupling agents 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS) on calcification were observed. Mineralization of the extracellular matrix, alkaline phosphatase (ALP) activity, and expression of osteoblastic markers were assessed to determine the calcification kinetics. Our results indicated that the matrix calcium content and the ALP activity, as well as the mRNA expression levels of a bone morphogenetic protein-2 (BMP-2), osteopontin (OPN), and osteocalcin (OC), of the MSCs seeded on plates with free OPG-Fc or on the OPG-Fc-coupled scaffolds decreased compared with their control MSCs without coupled OPG-Fc. The results suggest that both free and immobilized OPG-Fc on the decellularized aortic valve scaffolds by EDC/NHS can attenuate the calcification of MSCs induced by osteogenic differentiation media, implying that OPG-Fc might be a new treatment or prevention strategy for the calcification of natural human heart valves and TEHVs in the future.

Modified acellular porcine corneal matrix in deep lamellar transplantation of rabbit cornea

This study presents to develop a modified acellular porcine corneal matrix (MAPCM) to maintain high transparency, stability and biocompatibility as a rabbit deep cornea replacement using 1-ethyl-3–(3-dimethylaminopropyl)-carbodiimide crosslinking and a mild decellularization technique. Scaffolds are translucent and remain higher amount of glycosaminoglycans after decellularization than acellular porcine corneal matrix (APCM). Enzymatic degradation kinetics and mechanical properties of scaffolds are regulated by 1-ethyl-3–(3-dimethylaminopropyl)-carbodiimide -crosslinking density. The porous structure and ultrastructure of collagenous lamellae are maintained, and the pore size of MAPCM crosslinked with 0.5% (w/v) 1-ethyl-3–(3-dimethylaminopropyl)-carbodiimide is 13.26 ± 1.65 µm, similar to that of normal porcine cornea. The transmittance of MAPCM gets 79.1 ± 0.45 to 92.7 ± 1.4% in the visible light range. Results from a CCK-8 assay indicate that MAPCM gets higher cell proliferation rate of rabbit corneal stroma cells than APCM. Since collagen fibres structural integrity and regularity of MAPCM are retained after crosslinking, the opacity and stability of MAPCM are better than those of APCM within 4 weeks of animal implantation. In addition, there is no indication of an immune response or neovascularization in or around the transplanted disc. These results reveal that MAPCM may be a more suitable scaffold for corneal substitute construction.

Promotion of dermal regeneration using pullulan/gelatin porous skin substitute

Tissue-engineered dermal substitutes represent a promising approach to improve wound healing and provide more sufficient regeneration, compared with current clinical standards on care of large wounds, early excision, and grafting of autografts. However, inadequate regenerative capacity, impaired regeneration/degradation profile, and high cost of current commercial tissue-engineered dermal regeneration templates hinder their utilization, and the development of an efficient and cost-effective tissue-engineered dermal substitute remains a challenge. Inspired from our previously reported data on a pullulan/gelatin scaffold, here we present a new generation of a porous pullulan/gelatin scaffold (PG2) served as a dermal substitute with enhanced chemical and structural characteristics. PG2 shows excellent biocompatibility (viability, migration, and proliferation), assessed by in vitro incorporation of human dermal fibroblasts in comparison with the Integra® dermal regeneration template (Control). When applied on a mouse full-thickness excisional wound, PG2 shows rapid scaffold degradation, more granulation tissue, more collagen deposition, and more cellularity in comparison with Control at 20 days post surgery. The faster degradation is likely due to the enhanced recruitment of inflammatory macrophages to the scaffold from the wound bed, and that leads to earlier maturation of granulation tissue with less myofibroblastic cells. Collectively, our data reveal PG2's characteristics as an applicable dermal substitute with excellent dermal regeneration, which may attenuate scar formation.

Targeted protein delivery: carbodiimide crosslinking influences protein release from microparticles incorporated within collagen scaffolds

Tissue engineering response may be tailored via controlled, sustained release of active agents from protein-loaded degradable microparticles incorporated directly within three-dimensional (3D) ice-templated collagen scaffolds. However, the effects of covalent crosslinking during scaffold preparation on the availability and release of protein from the incorporated microparticles have not been explored. Here, we load 3D ice-templated collagen scaffolds with controlled additions of poly-(DL-lactide-co-glycolide) microparticles. We probe the effects of subsequent N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride crosslinking on protein release, using microparticles with different internal protein distributions. Fluorescein isothiocyanate labelled bovine serum albumin is used as a model protein drug. The scaffolds display a homogeneous microparticle distribution, and a reduction in pore size and percolation diameter with increased microparticle addition, although these values did not fall below those reported as necessary for cell invasion. The protein distribution within the microparticles, near the surface or more deeply located within the microparticles, was important in determining the release profile and effect of crosslinking, as the surface was affected by the carbodiimide crosslinking reaction applied to the scaffold. Crosslinking of microparticles with a high proportion of protein at the surface caused both a reduction and delay in protein release. Protein located within the bulk of the microparticles, was protected from the crosslinking reaction and no delay in the overall release profile was seen.

Tuning the mechanical and physicochemical properties of cross-linked protein films

Films derived from natural sources such as proteins provide an advantage over synthetic films due to their noncytotoxicity, biodegradability, and vast functionality. A new protein source gained from the cataractous eye protein isolate (CEPI) obtained after surgery has been investigated for this purpose. Glycerol has been employed as the plasticizer and glutaraldehyde (GD) as a cross-linker. Fourier transform infrared spectroscopy was employed to characterize the films. Nanoindentation and thermogravimetric analyses reveal improved mechanical and thermal properties of the cross-linked films. The films with 20% (w/w) GD exhibited properties such as the highest modulus and low water solubility. It is possible to tune the properties based on the extent of cross-linking. All the films were completely degraded by the enzyme trypsin. The similarity of these films was checked by using the prepared films as a delivery vehicle for a model compound, ampicillin sodium. The encapsulation efficiency was found to be 74%, and in vitro release studies showed significant amounts of drug release at physiological pH. This study will help us understand how the properties of protein films can be tuned to obtain the desired physicochemical properties. These biodegradable protein films could find use in pharmaceutical industries as delivery carriers.

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.

Fibril bending stiffness of 3D collagen matrices instructs spreading and clustering of invasive and non-invasive breast cancer cells

Extracellular matrix stiffening of breast tissues has been clinically correlated with malignant transformation and poor prognosis. An increase of collagen fibril diameter and lysyl-oxidase mediated crosslinking has been observed in advanced tumor stages. Many current reports suggest that the local mechanical properties of single fibrillar components dominantly regulate cancer cell behavior. Here, we demonstrate by an independent control of fibril diameter and intrafibrillar crosslinking of three-dimensional (3D) collagen matrices that fibril bending stiffness instructs cell behavior of invasive and non-invasive breast cancer cells. Two types of collagen matrices with fibril diameter of either 650 nm or 800 nm at a similar pore size of 10 μm were reconstituted and further modified with the zero-length crosslinker 1-ethyl-3-(3-dimethyl aminopropyl)-carbodiimide (EDC) at concentrations of 0, 20, 100 and 500 mM. This approach yields two sets of collagen matrices with overlapping variation of matrix elasticity. With these matrices we could prove the common assumption that matrix elasticity of collagen networks is bending dominated with a linear dependence on fibril bending stiffness. We derive that the measured variation of matrix elasticity is directly correlated to the variation of fibril bending stiffness, being independently controlled either by fibril diameter or by intrafibrillar crosslinking. We use these defined matrices to demonstrate that the adjustment of fibril bending stiffness allows to instruct the behavior of two different breast cancer cell lines, invasive MDA-MB-231 (human breast carcinoma) and non-invasive MCF-7 cells (human breast adenocarcinoma). Invasiveness and spreading of invasive MDA-MB-231 cells as well as clustering of non-invasive MCF-7 cells is thereby investigated over a broad parameter range. Our results demonstrate and quantify the direct dependence of cancer cell phenotypes on the matrix mechanical properties on the scale of single fibrils.

Bioactive glass based scaffolds coated with gelatin for the sustained release of icariin

Gelatin-coated, 3D sponge-like scaffolds based on 45S5 bioactive glass were produced using the foam replication technique. Compressive strength tests of gelatin-coated samples compared to uncoated scaffolds showed significant strengthening and toughening effects of the gelatin coating with compressive strength values in the range of cortical bone. Additionally, the crosslinked gelatin network (using either caffeic acid or N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC)/N-hxdroxysuccinimide (NHS) as crosslinking agent) was shown to be a suitable candidate for the sustained release of the bioactive molecule icariin. Concerning bioactivity of the produced scaffolds, characterization by FTIR and SEM indicated the formation of hydroxyapatite (HA) in all samples after immersion in simulated body fluid (SBF) for 14 days, highlighting the favorable combination of mechanical robustness, bioactivity and drug delivery capability of this new type of scaffolds.

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Foam like bioactive glass scaffolds produced by replication technique.

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Gelatin coatings confer increased compression strength to scaffolds.

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Crosslinked gelatin coating is suitable candidate for the sustained release of icariin.

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Favorable combination of bioactivity, gelatin coating and icariin release demonstrated.

Inflammatory response and biomechanical properties of coaxial scaffolds for engineered skin in vitro and post-grafting

Engineered skin (ES) offers many advantages over split-thickness skin autografts for the treatment of burn wounds. However, ES, both in vitro and after grafting, is often significantly weaker, less elastic and more compliant than normal human skin. Biomechanical properties of ES can be tuned in vitro using electrospun co-axial (CoA) scaffolds. To explore the potential for coaxial scaffold-based ES use in vivo, two CoA scaffolds were fabricated with bioactive gelatin shells and biodegradable synthetic cores of polylactic acid (PLA) and polycaprolactone (PCL), and compared with gelatin monofilament scaffolds. Fibroblast and macrophage production of inflammatory cytokines interleukin 6 (IL-6) and transforming growth factor β-1 was significantly higher when cultured on PLA and PCL monofilament scaffolds compared to gelatin monofilament scaffolds. The core-shell fiber configuration significantly reduced production of pro-inflammatory cytokines to levels similar to those of gelatin monofilament scaffolds. In vitro, ES mechanical properties were significantly enhanced using CoA scaffolds; however, after grafting CoA- and gelatin-based ES to full-thickness excisional wounds on athymic mice, the in vitro mechanical advantage of CoA grafts was lost. A substantially increased inflammatory response to CoA-based ES was observed, with upregulation of IL-6 expression and a significant M2 macrophage presence. Additionally, expression of matrix metalloproteinase I was upregulated and collagen type I alpha 1 was downregulated in CoA ES two weeks after grafting. These results suggest that while coaxial scaffolds provide the ability to regulate biomechanics in vitro, further investigation of the inflammatory response to core materials is required to optimize this strategy for clinical use. STATEMENT OF SIGNIFICANCE: Engineered skin has been used to treat very large burn injuries. Despite its ability to heal these wounds, engineered skin exhibits reduced biomechanical properties making it challenging to manufacture and surgically apply. Coaxial fiber scaffolds have been utilized to tune the mechanical properties of engineered skin while maintaining optimal biological properties but it is not known how these perform on a patient especially with regards to their inflammatory response. The current study examines the biomechanical and inflammatory properties of coaxial scaffolds and uniaxial scaffolds in vitro and in vivo. The results show that the biological response to the scaffold materials is a critical determinant of tissue properties after grafting with reduced inflammation and rapid scaffold remodeling leading to stronger skin.

Construction of low contracted 3D skin equivalents by genipin cross-linking

Continuous contraction of 3D skin equivalents in construction and use restricts their applications in clinical and pharmaceutical practices. So far, no effective method has been developed to inhibit such contraction. Hence, low cytotoxic cross-linkers, 1-ethyl-3-3-dimethylaminopropylcarbodiimide hydrochloride (EDC) and genipin, are investigated to reduce the contraction in this study. As found, both genipin and EDC at 0.2 and 0.4 mmol/L are nontoxic to collagen-entrapped fibroblasts and upregulate the extracellular matrix expression of fibroblasts in cross-linked collagen. Particularly, collagen cross-linking by intermediate concentrations of genipin, specifically 0.4 mmol/L, greatly reduces the contraction of 3D skin equivalents from 87% to 28% (n = 9, P < 0.05), while the collagen after EDC cross-linking at 0.4 mmol/L still presented severe contraction of 64% over a 21-day follow-up period. The inhibited contraction might relate to the increased gel stiffness and slowed collagen degradation. Moreover, the genipin cross-linking does not impair the formation of epidermal layers and improves the epidermal-dermal junction of skin equivalents as well. In this regard, genipin cross-linking might facilitate the applications of 3D skin equivalents in clinical practices and pharmacology testing.