Application of Collagen Scaffold in Tissue Engineering: Recent Advances and New Perspectives

Polyelectrolyte Multilayer Capsule (PEMC)-Based Scaffolds for Tissue Engineering

Tissue engineering (TE) is a highly multidisciplinary field that focuses on novel regenerative treatments and seeks to tackle problems relating to tissue growth both in vitro and in vivo. These issues currently involve the replacement and regeneration of defective tissues, as well as drug testing and other related bioapplications. The key approach in TE is to employ artificial structures (scaffolds) to support tissue development; these constructs should be capable of hosting, protecting and releasing bioactives that guide cellular behaviour. A straightforward approach to integrating bioactives into the scaffolds is discussed utilising polyelectrolyte multilayer capsules (PEMCs). Herein, this review illustrates the recent progress in the use of CaCO3 vaterite-templated PEMCs for the fabrication of functional scaffolds for TE applications, including bone TE as one of the main targets of PEMCs. Approaches for PEMC integration into scaffolds is addressed, taking into account the formulation, advantages, and disadvantages of such PEMCs, together with future perspectives of such architectures.

Collagen scaffold for mesencyhmal stem cell from stromal vascular fraction (biocompatibility and attachment study): Experimental paper

Background

One of the most important part of tissue engineering (TE) is a matrix called scaffold. A good scaffold integrates with the host tissue and support the growth and differentiation of the cells. Collagen is the most abundant protein in the ECM and has been considered to be a group of proteins with a characteristic molecular structure—fibrillar structure, which contributes to the extracellular scaffolding.

Objective

In this research we study the biocompatibility and attachment of collagen scaffold by measuring the level of availability of mesenchymal stem cell (MSC) cluster from stromal vascular fraction (SVF).

Method

This study was experimental invitro on MSC culture derived from SVF, with post-test control group design. Biocompatibility was measured by viability of MSC from SVF with marker Propidium Iodine through flowcytometry and electron microscope was used to assess the population density of MSC from SVF by measuring the number of cluster cells seen.

Result

Oxidize cellulose has the greatest value of MSC cluster with average number of 2003 cell cluster. This result was significant with p < 0.05 using One-Way Anova and Tukey Test.

Conclusion

Collagen scaffold is ideal for MSC from SVF because of its compatibility and attachment.

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Biocompatibility and attachment of collagen scaffold.

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Measuring the level of availability of mesenchymal stem cell (MSC) cluster from stromal vascular fraction (SVF).

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Experimental in vitro study on MSC culture derived from SVF.

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Biocompatibility was measured by viability of MSC from SVF with marker Propidium Iodine through flowcytometry.

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Electron microscope was used to assess the population density of MSC from SVF.

Coral-Derived Collagen Fibers for Engineering Aligned Tissues

There is a growing need for biomaterial scaffolds that support engineering of soft tissue substitutes featuring structure and mechanical properties similar to those of the native tissue. This work introduces a new biomaterial system that is based on centimeter-long collagen fibers extracted from Sarcophyton soft corals, wrapped around frames to create aligned fiber arrays. The collagen arrays displayed hyperelastic and viscoelastic mechanical properties that resembled those of collagenous-rich tissues. Cytotoxicity tests demonstrated that the collagen arrays were nontoxic to fibroblast cells. In addition, fibroblast cells seeded on the collagen arrays demonstrated spreading and increased growth for up to 40 days, and their orientation followed that of the aligned fibers. The possibility to combine the collagen cellular arrays with poly(ethylene glycol) diacrylate (PEG-DA) hydrogel, to create integrated biocomposites, was also demonstrated. This study showed that coral collagen fibers in combination with a hydrogel can support biological tissue-like growth, with predefined orientation over a long period of time in culture. As such, it is an attractive scaffold for the construction of various engineered tissues to match their native oriented morphology.

Mesenchymal stromal cell-derived factors promote the colonization of collagen 3D scaffolds with human skin cells

The development of stem cell technology in combination with advances in biomaterials has opened new ways of producing engineered tissue substitutes. In this study, we investigated whether the therapeutic potential of an acellular porous scaffold made of type I collagen can be improved by the addition of a powerful trophic agent in the form of mesenchymal stromal cells conditioned medium (MSC-CM) in order to be used as an acellular scaffold for skin wound healing treatment. Our experiments showed that MSC-CM sustained the adherence of keratinocytes and fibroblasts as well as the proliferation of keratinocytes. Moreover, MSC-CM had chemoattractant properties for keratinocytes and endothelial cells, attributable to the content of trophic and pro-angiogenic factors. Also, for the dermal fibroblasts cultured on collagen scaffold in the presence of MSC-CM versus serum control, the ratio between collagen III and I mRNAs increased by 2-fold. Furthermore, the gene expression for α-smooth muscle actin, tissue inhibitor of metalloproteinase-1 and 2 and matrix metalloproteinase-14 was significantly increased by approximately 2-fold. In conclusion, factors existing in MSC-CM improve the colonization of collagen 3D scaffolds, by sustaining the adherence and proliferation of keratinocytes and by inducing a pro-healing phenotype in fibroblasts.

Conductive carbon nanofibers incorporated into collagen bio-scaffold assists myocardial injury repair

Currently, treatment of myocardial infarction considered as unmet clinical need. Nanomaterials have been used in the regeneration of tissues such as bone, dental and neural tissue in the body and have increased hope for revitalizing of damaged tissues. Conductive carbon base nanomaterials with its superior physicochemical properties have emerged as promising materials for cardiovascular application. In this study, we applied a biosynthetic collagen scaffold containing carbon nanofiber for regenerating of damaged heart tissue. The collagen-carbon nanofiber scaffold was fabricated and fully characterised. The scaffold was grafted on the affected area of myocardial ischemia, immediately after ligation of the left anterior descending artery in the wistar rat's model. After 4 weeks, histological analyses were performed for investigation of formation of immature cardio-myocytes, epicardial cells, and angiogenesis. Compared to untreated hearts, this scaffold significantly protects heart tissue against injury. This improvement is accompanied by a reduction in fibrosis and the increased formation of a blood vessel network and immature cardio-myocytes in the infarction heart. No toxicity detected with apoptotic and TUNEL assays. In conclusion, the mechanical support of the collagen scaffold with carbon nanofiber enhanced the regeneration of myocardial tissue.

Biodegradable 131 Iodine-Labeled Microspheres: Potential Transarterial Radioembolization Biomaterial for Primary Hepatocellular Carcinoma Treatment

Transarterial radioembolization with radionuclide-labeled microspheres is successfully used in hepatocellular carcinoma (HCC) treatment, but the non-biodegradability and rapid settlement of the microsphere material are associated with unsatisfied distribution and unable for multiple administrations. In this study, a novel biodegradable chitosan-collagen composite microsphere (CCM) with ideal settlement rate is prepared. The Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) results indicate CCMs have desirable shapes with diameters around 10 µm, and considerable biodegradability within 12 weeks. These CCMs are successfully radiolabeled with ¹³¹ I and processed efficiency of 70.4 MBq mg^-1 of microspheres as well as favorable stability in vitro. Then, ¹³¹ I-CCMs are injected into rats with orthotopic HCC via the hepatic artery which effectively improves the median overall survival from 19 to 44 days (p < 0.05). Single photon emission computed tomography (SPECT/CT) imaging and immunohistochemical analysis indicate well-localized biodistribution and consistent stability of ¹³¹ I-CCMs in the liver over 28 days. Magnetic resonance imaging (MRI) and gross specimens monitoring confirm the inhibited tumor growth after ¹³¹ I-CCMs treatment. In conclusion, these biodegradable ¹³¹ I-CCMs exhibit optimal radiolabeling efficiency, stability, and favorably radioembolization effect for orthotopic HCC in a rodent model, suggesting potential for interventional cancer therapy.

Type I Collagen Suspension Induces Neocollagenesis and Myodifferentiation in Fibroblasts In Vitro

The ability of a collagen-based matrix to support cell proliferation, migration, and infiltration has been reported; however, the direct effect of an aqueous collagen suspension on cell cultures has not been studied yet. In this work, the effects of a high-concentration aqueous suspension of a micronized type I equine collagen (EC-I) have been evaluated on a normal mouse fibroblast cell line. Immunofluorescence analysis showed the ability of EC-I to induce a significant increase of type I and III collagen levels, parallel with overexpression of crucial proteins in collagen biosynthesis, maturation, and secretion, prolyl 4-hydroxylase (P4H) and heat shock protein 47 (HSP47), as demonstrated by western blot experiments. The treatment led, also, to an increase of α-smooth muscle actin (α-SMA) expression, evaluated through western blot analysis, and cytoskeletal reorganization, as assessed by phalloidin staining. Moreover, scanning electron microscopy analysis highlighted the appearance of plasma membrane extensions and blebbing of extracellular vesicles. Altogether, these results strongly suggest that an aqueous collagen type I suspension is able to induce fibroblast myodifferentiation. Moreover, our findings also support in vitro models as a useful tool to evaluate the effects of a collagen suspension and understand the molecular signaling pathways possibly involved in the effects observed following collagen treatment in vivo.

Dexamethasone- loaded polymeric porous sponge as a direct pulp capping agent

This study aims to achieve the principles of tissue engineering using biopolymers to be applied in the field of vital endodontic treatment to stimulate stem cells and engineering and regeneration of dentin tissue. the polymer blend was loaded with the steroidal anti-inflammatory drug, dexamethasone, and the porous drug-loaded bio-sponge was produced by lyophilization. Bio-sponge, as a direct pulp capping agent, was histologically studied compared to calcium hydroxide Ca(OH)₂ in an animal experiment. The results indicated the effectiveness of the bio-sponge as a direct pulp capping agent where the dentin bridge was formed faster than Ca(OH)₂ treated samples. There was no inflammatory response in the pulp tissue throughout the follow-up period. The porous bio-sponge loaded with dexamethasone with a neutral pH resulted in enhancement of the odontoblast differentiation from stem cells, resulting in the formation of a renewed dentin bridge without the slightest inflammatory response in the pulp.

Biodegradable Nanopolymers in Cardiac Tissue Engineering: From Concept Towards Nanomedicine

Cardiovascular diseases are the number one cause of heart failure and death in the world, and the transplantation of the heart is an effective and viable choice for treatment despite presenting many disadvantages (most notably, transplant heart availability). To overcome this problem, cardiac tissue engineering is considered a promising approach by using implantable artificial blood vessels, injectable gels, and cardiac patches (to name a few) made from biodegradable polymers. Biodegradable polymers are classified into two main categories: natural and synthetic polymers. Natural biodegradable polymers have some distinct advantages such as biodegradability, abundant availability, and renewability but have some significant drawbacks such as rapid degradation, insufficient electrical conductivity, immunological reaction, and poor mechanical properties for cardiac tissue engineering. Synthetic biodegradable polymers have some advantages such as strong mechanical properties, controlled structure, great processing flexibility, and usually no immunological concerns; however, they have some drawbacks such as a lack of cell attachment and possible low biocompatibility. Some applications have combined the best of both and exciting new natural/synthetic composites have been utilized. Recently, the use of nanostructured polymers and polymer nanocomposites has revolutionized the field of cardiac tissue engineering due to their enhanced mechanical, electrical, and surface properties promoting tissue growth. In this review, recent research on the use of biodegradable natural/synthetic nanocomposite polymers in cardiac tissue engineering is presented with forward looking thoughts provided for what is needed for the field to mature.

Hyaluronic acid biomaterial for human tissue-engineered skin substitutes: Preclinical comparative in vivo study of wound healing

BACKGROUND

There is not an ideal biomaterial for tissue-engineered skin substitutes (TESSs), and most of the studies or existing therapies use xenogeneic origin natural biomaterials or biosynthetic scaffolds.

OBJECTIVE

To analyse clinical, histological integration and homeostasis parameters of a human TESS manufactured with fibrin-hyaluronic acid biomaterial (HA-Skin), grafted in immunodeficient mice for 8 weeks, and compared with the gold standard treatment (Autograft), a human TESS manufactured with fibrin-agarose biomaterial (AG-Skin) and secondary wound healing dressings.

METHODS

Human TESSs and autografts were implanted into BALB/c mice after surgical excision. Secondary wound healing approach was achieved with biosynthetic collagen wound dressing (Biobrane^® ) and fibrin-hyaluronic acid or fibrin-agarose biomaterial without cells (Total N = 44). Clinical integration and homeostasis parameters were evaluated every two weeks for two months. Histological and immunohistochemical analyses were performed four and eight weeks after grafting.

RESULTS

HA-Skin, AG-Skin and Autograft groups showed a proper clinical integration and epithelization eight weeks later. Scar evaluation revealed better results for Autograft and HA-Skin. Homeostasis analysis indicated similar values of transepidermal water loss and elasticity between HA-Skin (6.42 ± 0.75 g/h/m² , 0.42 ± 0.08 AU), Autograft (6.91 ± 1.28 g/h/m² , 0.40 ± 0.08 AU) and healthy mouse skin (6.40 ± 0.43 g/h/m² , 0.35 ± 0.03 AU). Histological results showed that human TESSs and autografts presented better skin structuration and higher expression of cytokeratins.

CONCLUSIONS

This study suggests that human TESS based on fibrin-hyaluronic acid biomaterial could be suitable for clinical application in the treatment of several dermatological pathologies (wound healing).

Tissue Integration and Degradation of a Porous Collagen-Based Scaffold Used for Soft Tissue Augmentation

Collagen-based scaffolds hold great potential for tissue engineering, since they closely mimic the extracellular matrix. We investigated tissue integration of an engineered porous collagen-elastin scaffold developed for soft tissue augmentation. After implantation in maxillary submucosal pouches in 6 canines, cell invasion (vimentin), extracellular matrix deposition (collagen type I) and scaffold degradation (cathepsin k, tartrate-resistant acid phosphatase (TRAP), CD86) were (immuno)-histochemically evaluated. Invasion of vimentin⁺ cells (scattered and blood vessels) and collagen type I deposition within the pores started at 7 days. At 15 and 30 days, vimentin⁺ cells were still numerous and collagen type I increasingly filled the pores. Scaffold degradation was characterized by collagen loss mainly occurring around 15 days, a time point when medium-sized multinucleated cells peaked at the scaffold margin with simultaneous labeling for cathepsin k, TRAP, and CD86. Elastin was more resistant to degradation and persisted up to 90 days in form of packages well-integrated in the newly formed soft connective tissue. In conclusion, this collagen-based scaffold maintained long-enough volume stability to allow an influx of blood vessels and vimentin⁺ fibroblasts producing collagen type I, that filled the scaffold pores before major biomaterial degradation and collapse occurred. Cathepsin k, TRAP and CD86 appear to be involved in scaffold degradation.

Natural Polymeric Scaffolds in Bone Regeneration

Despite considerable advances in microsurgical techniques over the past decades, bone tissue remains a challenging arena to obtain a satisfying functional and structural restoration after damage. Through the production of substituting materials mimicking the physical and biological properties of the healthy tissue, tissue engineering strategies address an urgent clinical need for therapeutic alternatives to bone autografts. By virtue of their structural versatility, polymers have a predominant role in generating the biodegradable matrices that hold the cells in situ to sustain the growth of new tissue until integration into the transplantation area (i.e., scaffolds). As compared to synthetic ones, polymers of natural origin generally present superior biocompatibility and bioactivity. Their assembly and further engineering give rise to a wide plethora of advanced supporting materials, accounting for systems based on hydrogels or scaffolds with either fibrous or porous architecture. The present review offers an overview of the various types of natural polymers currently adopted in bone tissue engineering, describing their manufacturing techniques and procedures of functionalization with active biomolecules, and listing the advantages and disadvantages in their respective use in order to critically compare their actual applicability potential. Their combination to other classes of materials (such as micro and nanomaterials) and other innovative strategies to reproduce physiological bone microenvironments in a more faithful way are also illustrated. The regeneration outcomes achieved in vitro and in vivo when the scaffolds are enriched with different cell types, as well as the preliminary clinical applications are presented, before the prospects in this research field are finally discussed. The collection of studies herein considered confirms that advances in natural polymer research will be determinant in designing translatable materials for efficient tissue regeneration with forthcoming impact expected in the treatment of bone defects.

A review on recent advances and applications of fish collagen

During the processing of the fishery resources, the significant portion is either discarded or used to produce low-value fish meal and oil. However, the discarded portion is the rich source of valuable proteins such as collagen, vitamins, minerals, and other bioactive compounds. Collagen is a vital protein in the living body as a component of a fibrous structural protein in the extracellular matrix, connective tissue and building block of bones, tendons, skin, hair, nails, cartilage and joints. In recent years, the use of fish collagen as an increasingly valuable biomaterial has drawn considerable attention from biomedical researchers, owing to its enhanced physicochemical properties, stability and mechanical strength, biocompatibility and biodegradability. This review focuses on summarizing the growing role of fish collagen for biomedical applications. Similarly, the recent advances in various biomedical applications of fish collagen, including wound healing, tissue engineering and regeneration, drug delivery, cell culture and other therapeutic applications, are discussed in detail. These applications signify the commercial importance of fish collagen for the fishing industry, food processors and biomedical sector.

Efficient smooth muscle cell differentiation of iPS cells on curcumin-incorporated chitosan/collagen/polyvinyl-alcohol nanofibers

Bladder dysfunction is one of the most common diseases that occur for a number of reasons and the current treatment modalities do not improve much in its recovery process. Tissue engineering in the last two decades has given great hope for the treatment of these disorders. In this study, a composite nanofibrous scaffold was fabricated from chitosan, collagen, and polyvinyl-alcohol polymer blend while curcumin incorporated in scaffold fibers. The scaffold supportive functions from smooth muscle cell differentiation were studied when human-induced pluripotent stem cells were cultured on the scaffolds under differentiation medium. Biocompatibility of the fabricated scaffold increased significantly by incorporating curcumin in the scaffold fibers, where protein adsorption, cell attachment, and viability were increased in the nanofiber/curcumin group compared with the other groups. In addition, the expression level of smooth muscle cell-related genes, including alpha-smooth muscle actin (αSMA), smooth muscle 22 alpha (SM-22a), Caldesmon1, and Calponin1in the stem cells upregulated while cultured in the presence of curcumin, but this increase was significantly improved while cells cultured on the nanofibers/curcumin. In addition, αSMA protein in the cells cultured on the nanofibers/curcumin expressed significantly higher than those cells cultured on the nanofibers without curcumin. It can be concluded that smooth muscle cell differentiation of the induced pluripotent stem cells promoted by curcumin and this promotion was synergistically improved while curcumin incorporated in the nanofibers.

Marine Collagen from Alternative and Sustainable Sources: Extraction, Processing and Applications

Due to its unique properties, collagen is used in the growing fields of pharmaceutical and biomedical devices, as well as in the fields of nutraceuticals, cosmeceuticals, food and beverages. Collagen also represents a valid resource for bioplastics and biomaterials, to be used in the emerging health sectors. Recently, marine organisms have been considered as promising sources of collagen, because they do not harbor transmissible disease. In particular, fish biomass as well as by-catch organisms, such as undersized fish, jellyfish, sharks, starfish, and sponges, possess a very high collagen content. The use of discarded and underused biomass could contribute to the development of a sustainable process for collagen extraction, with a significantly reduced environmental impact. This addresses the European zero-waste strategy, which supports all three generally accepted goals of sustainability: sustainable economic well-being, environmental protection, and social well-being. A zero-waste strategy would use far fewer new raw materials and send no waste materials to landfills. In this review, we present an overview of the studies carried out on collagen obtained from by-catch organisms and fish wastes. Additionally, we discuss novel technologies based on thermoplastic processes that could be applied, likewise, as marine collagen treatment.

Enzymatic Hydrolysis of Marine Collagen and Fibrinogen Proteins in the Presence of Thrombin

: Enzymatic hydrolysis of native collagen and fibrinogen was carried out under comparable conditions at room temperature. The molecular weight parameters of proteins before and after hydrolysis by thrombin were monitored by gel-penetrating chromatography (GPC). An analysis of the experiment results shows that the molecular weight parameters of the initial fibrinogen (Fn) and cod collagen (CC) are very similar. High molecular CC decays within the first minute, forming two low molecular fractions. The main part (~80%) falls on the fraction with a value of Mw less than 10 kDa. The initial high molecular fraction of Fn with Mw ~320-340 kDa is not completely hydrolyzed even after three days of control. The presence of low molecular fractions with Mw ~17 and Mw ~10 kDa in the solution slightly increases within an hour and noticeably increases for three days. The destruction of macromolecules of high molecular collagen to hydrolysis products appears almost completely within the first minute mainly to the polymer with Mw ~10 kDa, and enzymatic hydrolysis of fibrinogen proceeds slower than that of collagen, but also mainly to the polymer with Mw ~10 kDa. Comparative photos of the surfaces of native collagen, fibrinogen and the scaffold based on them were obtained.

Proteins and Peptides as Important Modifiers of the Polymer Scaffolds for Tissue Engineering Applications-A Review

Polymer scaffolds constitute a very interesting strategy for tissue engineering. Even though they are generally non-toxic, in some cases, they may not provide suitable support for cell adhesion, proliferation, and differentiation, which decelerates tissue regeneration. To improve biological properties, scaffolds are frequently enriched with bioactive molecules, inter alia extracellular matrix proteins, adhesive peptides, growth factors, hormones, and cytokines. Although there are many papers describing synthesis and properties of polymer scaffolds enriched with proteins or peptides, few reviews comprehensively summarize these bioactive molecules. Thus, this review presents the current knowledge about the most important proteins and peptides used for modification of polymer scaffolds for tissue engineering. This paper also describes the influence of addition of proteins and peptides on physicochemical, mechanical, and biological properties of polymer scaffolds. Moreover, this article sums up the major applications of some biodegradable natural and synthetic polymer scaffolds modified with proteins and peptides, which have been developed within the past five years.

Enhanced biological properties of collagen/chitosan-coated poly(ε-caprolactone) scaffold by surface modification with GHK-Cu peptide and 58S bioglass

Bioactive glasses and peptides have shown promising results in improving wound healing and skin repair. The present study explores the effectiveness of surface modification of collagen/chitosan-coated electrospun poly(ε-caprolactone) scaffold with 58S bioactive glass or GHK-Cu peptide. To coat scaffolds with the bioactive glass, we prepared suspensions of silanized bioactive glass powder with three different concentrations and the scaffolds were pipetted with suspensions. Similarly, GHK-Cu-coated scaffolds were prepared by pipetting adequate amount of 1-mM solution of peptide (in milli-Q) on the surface of scaffolds. ATR-FTIR spectroscopy indicated the successful modification of collagen/chitosan-coated electrospun poly(ε-caprolactone) scaffold with bioactive glass and GHK-Cu. Microstructural investigations and in vitro studies such as cell adhesion, cell viability and antibacterial assay were performed. All samples demonstrated desirable cell attachment. Compared to poly(ε-caprolactone)/collagen/chitosan, the cell proliferation of GHK-Cu and bioactive glass-coated (concentrations of 0.01 and 0.1) scaffolds increased significantly at days 3 and 7, respectively. Poly(ε-caprolactone)/collagen/chitosan-uncoated scaffold and scaffolds coated with GHK-Cu and bioactive glass revealed desirable antibacterial properties but the antibacterial activity of GHK-Cu-coated sample turned out to be superior. These findings indicated that biological properties of collagen/chitosan-coated synthetic polymer could be improved by GHK-Cu and bioactive glass.

Biomaterials for Personalized Cell Therapy

Cell therapy has already had an important impact on healthcare and provided new treatments for previously intractable diseases. Notable examples include mesenchymal stem cells for tissue regeneration, islet transplantation for diabetes treatment, and T cell delivery for cancer immunotherapy. Biomaterials have the potential to extend the therapeutic impact of cell therapies by serving as carriers that provide 3D organization and support cell viability and function. With the growing emphasis on personalized medicine, cell therapies hold great potential for their ability to sense and respond to the biology of an individual patient. These therapies can be further personalized through the use of patient-specific cells or with precision biomaterials to guide cellular activity in response to the needs of each patient. Here, the role of biomaterials for applications in tissue regeneration, therapeutic protein delivery, and cancer immunotherapy is reviewed, with a focus on progress in engineering material properties and functionalities for personalized cell therapies.

Development and characterization of a photo-cross-linked functionalized type-I collagen (Oreochromis niloticus) and polyethylene glycol diacrylate hydrogel

Collagen hydrogels have been widely investigated as scaffolds for tissue engineering due to their biocompatibility and capacity to promote cell adhesion. However, insufficient mechanical strength and rapid degradation properties remain the major obstacles for their applications. In the present study, type-I tilapia collagen (TC) was functionalized to form methacrylated tilapia collagen (MATC) by introducing methacrylic acid, developing a photo-cross-linked PEGDA-MATC hydrogel. The mechanical strength of PEGDA-MATC hydrogel could be tuned by adjusting the pH of the precursor solutions, which was decreased with the pH increased. At a pH 5 condition, PEGDA-MATC showed the highest compressive fracture stress (1.31 MPa). Compared to the PEGDA-TC hydrogel, PEGDA-MATC hydrogel exhibited similar swelling behavior to PEGDA-TC hydrogel in PBS solutions, but higher residual mass ratio (PEGDA-MATC, 213.2 ± 2.8%) than PEGDA-TC hydrogel (199.4 ± 3.8%) when cultured with type-I collagenase. PEGDA-MATC hydrogel showed sustained BSA release capacity for 6 days, and the BSA release ratio was significantly (p < 0.05) decreased with increasing concentration of loaded-BSA (68.6% at 4 mg mL^-1, 42.2% at 8 mg mL^-1). The PEGDA-MATC hydrogel allowed cell adhesion and proliferation in vitro. These results demonstrated that PEGDA-MATC hydrogel might be a potential scaffold for tissue engineering applications.

Biomimetic mineralizable collagen hydrogels for dynamic bone matrix formation to promote osteogenesis

The simulation of the native bone matrix formation process is crucial for the construction of the cellular microenvironment for bone regeneration. However, it is still challenging to design bioactive materials that simultaneously mimic the composition and dynamic mineralization process of the bone matrix, let alone realize osteoinduction by a biomimetic dynamic microenvironment. In this study, we prepared a biomimetic mineralizable collagen hydrogel (CAV) and explored the effects of a dynamic mineralized matrix on the osteogenesis of stem cells both in vitro and in vivo. We showed the feasibility of the biomimetic CAV hydrogel to induce mineralization in simulated media including simulated body fluid (SBF), glycerol phosphate calcium salt hydrate (CaGP) solution and cell co-cultured systems. The participation of cells in the mineralization process is more likely to induce matrix remodeling due to the synergistic effects of CAV mineralization and cellular secretion, resulting in higher matrix strength. We also demonstrated that the biomimetic mineralized hydrogel could up-regulate osteogenic genes and protein expression of bone marrow mesenchymal stem cells (BMSCs), thus enhancing osteogenesis in vivo. The interactions between the mineralizable hydrogel and cells play an important role in regulating dynamic matrix mineralization and osteogenesis. Our findings prove that the biomimetic mineralizable hydrogel is a promising candidate for implantable orthopedic applications and provides essential implications for the future design of materials for bone regeneration.

Extracellular matrix-mimetic composite hydrogels of cross-linked hyaluronan and fibrillar collagen with tunable properties and ultrastructure

A platform of enzymatically-crosslinked Collagen/Tyramine hyaluronan derivative (Col/HA-Tyr) hydrogels with tunable compositions and gelation conditions was developed to evaluate the impact of the preparation conditions on their physical, chemical and biological properties. At low HA-Tyr content, hydrogels exhibited a fibrillar structure, with lower mechanical properties compared to pure Col hydrogels. At high HA-Tyr and Horse Radish Peroxydase (HRP) content, a microfibrillar network was formed beside the banded Col fibrils and a synergistic effect of the hybrid structure on mechanical properties was observed. These hydrogels were highly resistant against enzymatic degradation while keeping a high degree of hydration. Unlike HA-Tyr hydrogels, encapsulation of human dermal fibroblasts within Col/HA-Tyr hydrogels allowed for high cell viability. These results showed that high HA-Tyr and HRP concentrations are required to positively impact the physical properties of hydrogels while preserving collagen fibrils. Those Col/HA-Tyr hydrogels appear promising for novel tissue engineering applications following a biomimetic approach.

Recent Development in the Fabrication of Collagen Scaffolds for Tissue Engineering Applications: A Review

Tissue engineering focuses on developing biological substitutes to restore, maintain or improve tissue functions. The three main components of its application are scaffold, cell and growthstimulating signals. Scaffolds composed of biomaterials mainly function as the structural support for ex vivo cells to attach and proliferate. They also provide physical, mechanical and biochemical cues for the differentiation of cells before transferring to the in vivo site. Collagen has been long used in various clinical applications, including drug delivery. The wide usage of collagen in the clinical field can be attributed to its abundance in nature, biocompatibility, low antigenicity and biodegradability. In addition, the high tensile strength and fibril-forming ability of collagen enable its fabrication into various forms, such as sheet/membrane, sponge, hydrogel, beads, nanofibre and nanoparticle, and as a coating material. The wide option of fabrication technology together with the excellent biological and physicochemical characteristics of collagen has stimulated the use of collagen scaffolds in various tissue engineering applications. This review describes the fabrication methods used to produce various forms of scaffolds used in tissue engineering applications.

Natural polypeptides-based electrically conductive biomaterials for tissue engineering

Fabrication of an appropriate scaffold is the key fundamental step required for a successful tissue engineering (TE). The artificial scaffold as extracellular matrix in TE has noticeable role in the fate of cells in terms of their attachment, proliferation, differentiation, orientation and movement. In addition, chemical and electrical stimulations affect various behaviors of cells such as polarity and functionality. Therefore, the fabrication approach and materials used for the preparation of scaffold should be more considered. Various synthetic and natural polymers have been used extensively for the preparation of scaffolds. The electrically conductive polymers (ECPs), moreover, have been used in combination with other polymers to apply electric fields (EF) during TE. In this context, composites of natural polypeptides and ECPs can be taken into account as context for the preparation of suitable scaffolds with superior biological and physicochemical features. In this review, we overviewed the simultaneous usage of natural polypeptides and ECPs for the fabrication of scaffolds in TE.

Obtaining and Characterization of the PLA/Chitosan Foams with Antimicrobial Properties Achieved by the Emulsification Combined with the Dissolution of Chitosan by CO2 Saturation

A new method of obtaining functional foam material has been proposed. The materials were created by mixing the poly lactic acid (PLA) solution in chloroform, chitosan (CS) dissolved in water saturated with CO₂ and polyethylene glycol (PEG), and freeze-dried for removal of the solvents. The composite foams were characterized for their structural (SEM, FT-IR, density, porosity), thermal (DSC), functional (hardness, elasticity, swelling capacity, solubility), and biological (antimicrobial and cytotoxic) properties. Chitosan in the composites was a component for obtaining their foamed form with 7.4 to 22.7 times lower density compared to the neat PLA and high porosity also confirmed by the SEM. The foams had a hardness in the range of 70-440 kPa. The FT-IR analysis confirmed no new chemical bonds between the sponge ingredients. Other results showed low sorption capacity (2.5-7.2 g/g) and solubility of materials (less than 0.2%). The obtained foams had the lower T_g value and improved ability of crystallization compared to neat PLA. The addition of chitosan provides the bacteriostatic and bactericidal properties against Escherichia coli and Staphylococcus aureus. Biocompatibility studies have shown that the materials obtained are not cytotoxic to the L929 cell line.

Therapeutic options and drug delivery strategies for the prevention of intrauterine adhesions

Intrauterine adhesions (IUAs) are bands of fibrous tissue that form in the endometrial cavity and associated with the increased risk of abnormal menstruation, recurrent pregnancy loss, secondary infertility, and pregnancy complications. Physical barriers, including intrauterine device and hydrogel, were clinical available to prevent the post-operational IUAs. But physically separation of the injured endometrium relies on the own limited healing power and often ends with recurrence. In recent years, the mechanisms driving IUAs treatment has validated the application of hormones, and further stem cell therapy has also led to the development of novel therapeutic agents with promising efficacy in pre-clinical and initial clinical studies. Still, it is challenging to delivery the therpaeutic factors to the injured uterus. Herein, in this review, we discuss the traditional intervention methods for the prevention of IUAs, as well as novel therapeutics and delivery strategies that will most likely change the treatment paradigms for better clinical outcomes. The combination strategy that using physical barriers as the delivery carriers for therapeutics might provide new alternatives for the prevention of IUAs.

Cell-Electrospinning and Its Application for Tissue Engineering

Electrospinning has gained great interest in the field of regenerative medicine, due to its fabrication of a native extracellular matrix-mimicking environment. The micro/nanofibers generated through this process provide cell-friendly surroundings which promote cellular activities. Despite these benefits of electrospinning, a process was introduced to overcome the limitations of electrospinning. Cell-electrospinning is based on the basic process of electrospinning for producing viable cells encapsulated in the micro/nanofibers. In this review, the process of cell-electrospinning and the materials used in this process will be discussed. This review will also discuss the applications of cell-electrospun structures in tissue engineering. Finally, the advantages, limitations, and future perspectives will be discussed.

Hydrogel scaffolds based on blood plasma cryoprecipitate and collagen derived from various sources: Structural, mechanical and biological characteristics

At present there is a growing need for tissue engineering products, including the products of scaffold-technologies. Biopolymer hydrogel scaffolds have a number of advantages and are increasingly being used to provide means of cell transfer for therapeutic treatments and for inducing tissue regeneration. This work presents original hydrogel biopolymer scaffolds based on a blood plasma cryoprecipitate and collagen and formed under conditions of enzymatic hydrolysis. Two differently originated collagens were used for the scaffold formation. During this work the structural and mechanical characteristics of the scaffold were studied. It was found that, depending on the origin of collagen, scaffolds possess differences in their structural and mechanical characteristics. Both types of hydrogel scaffolds have good biocompatibility and provide conditions that maintain the three-dimensional growth of adipose tissue stem cells. Hence, scaffolds based on such a blood plasma cryoprecipitate and collagen have good prospects as cell carriers and can be widely used in regenerative medicine.

Biocompatibility Investigation of Hybrid Organometallic Polymers for Sub-Micron 3D Printing via Laser Two-Photon Polymerisation

Hybrid organometallic polymers are a class of functional materials which can be used to produce structures with sub-micron features via laser two-photon polymerisation. Previous studies demonstrated the relative biocompatibility of Al and Zr containing hybrid organometallic polymers in vitro. However, a deeper understanding of their effects on intracellular processes is needed if a tissue engineering strategy based on these materials is to be envisioned. Herein, primary rat myogenic cells were cultured on spin-coated Al and Zr containing polymer surfaces to investigate how each material affects the viability, adhesion strength, adhesion-associated protein expression, rate of cellular metabolism and collagen secretion. We found that the investigated surfaces supported cellular growth to full confluency. A subsequent MTT assay showed that glass and Zr surfaces led to higher rates of metabolism than did the Al surfaces. A viability assay revealed that all surfaces supported comparable levels of cell viability. Cellular adhesion strength assessment showed an insignificantly stronger relative adhesion after 4 h of culture than after 24 h. The largest amount of collagen was secreted by cells grown on the Al-containing surface. In conclusion, the materials were found to be biocompatible in vitro and have potential for bioengineering applications.

Preparation and Optimization of a Biomimetic Triple-Layered Vascular Scaffold Based on Coaxial Electrospinning

Electrospinning is a promising method for preparing bionic vascular scaffolds. In particular, coaxial electrospinning can encapsulate polymer materials in biological materials and provide vascular scaffolds with good biomechanical properties. However, it is difficult to produce a stable Taylor cone during the coaxial electrospinning process. Moreover, glutaraldehyde cross-linked natural biomaterials are cytotoxic. To address these issues, a novel electrospinning process is proposed in this report. A non-ionic surfactant (Tween 80) was added to poly(lactic-co-glycolic acid) electrospinning solution and gelatin-collagen electrospinning solution, which prevented the interfacial effect of coaxial electrospinning due to different core/shell solutions. The as-prepared materials were then cross-linked with the non-toxic coupling agents N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide/N-hydroxysuccinimide (EDC/NHS). By comparing the biomechanical properties of EDC/NHS cross-linked vascular scaffold with glutaraldehyde vapor-cross-linked vascular scaffold, it was found that the fracture strain and biological performance of EDC/NHS cross-linked vascular scaffold were better than those of the glutaraldehyde cross-linked scaffold. Finally, a three-layer bionic vascular scaffold was prepared by the proposed electrospinning process. Biomechanical performance tests were carried out and the prepared scaffold was found to meet the requirements of tissue-engineered blood vessels. The research in this paper provides a useful reference for the preparation and optimization of vascular scaffolds.

Bioactive yet antimicrobial structurally stable collagen/chitosan/lysine functionalized hyaluronic acid - based injectable hydrogels for potential bone tissue engineering applications

Novel, biocompatible, multifunctional, injectable genipin crosslinked collagen/chitosan/lysine-modified hyaluronic acid based hydrogels (ColChHA_mod) were prepared in a facile, one-step procedure. The novelty of the current approach lies in the functionalization of hyaluronic acid (HA) with primary amine groups by lysine attachment, and its further use as a component of the injectable sol. The obtained derivative, HA_mod, could form, upon crosslinking with genipin, covalent bonds with other components of the hydrogel network, resulting in structurally stable, better-defined hydrogels. We have demonstrated that, by adjusting HA_mod content and genipin concentration, hydrogels with tunable physicochemical characteristics (swelling, wettability, tendency for enzymatic degradation) and properties adequate for the potential bone tissue regeneration can be prepared. Storage modulus measurements indicated that HA_mod has positive effect on mechanical characteristics of hydrogels prepared. It was also revealed that the ColChHA_mod-based hydrogels are characterized by a high porosity (85-95%). The in situ rheological measurements confirmed the injectability of the obtained hydrogels. The in vitro cell culture studies showed that the surface of all materials prepared was biocompatible, as they supported proliferation and adhesion of osteoblast-like cells followed by ALP expression. The intrinsic antibacterial activity of the hydrogels against Escherichia coli was also demonstrated in in vitro experiment.

Current progress in application of polymeric nanofibers to tissue engineering

Tissue engineering uses a combination of cell biology, chemistry, and biomaterials to fabricate three dimensional (3D) tissues that mimic the architecture of extracellular matrix (ECM) comprising diverse interwoven nanofibrous structure. Among several methods for producing nanofibrous scaffolds, electrospinning has gained intense interest because it can make nanofibers with a porous structure and high specific surface area. The processing and solution parameters of electrospinning can considerably affect the assembly and structural morphology of the fabricated nanofibers. Electrospun nanofibers can be made from natural or synthetic polymers and blending them is a straightforward way to tune the functionality of the nanofibers. Furthermore, the electrospun nanofibers can be functionalized with various surface modification strategies. In this review, we highlight the latest achievements in fabricating electrospun nanofibers and describe various ways to modify the surface and structure of scaffolds to promote their functionality. We also summarize the application of advanced polymeric nanofibrous scaffolds in the regeneration of human bone, cartilage, vascular tissues, and tendons/ligaments.

Halloysite Nanoclay/Biopolymers Composite Materials in Tissue Engineering

Biocompatible materials for the fabrication of tissue substitutes are crucially important in the advancement of modern medicinal biotechnology. These materials, to serve their function, should be similar in physical, chemical, biological, and structural properties to native tissues which they are aimed to mimic. The porosity of artificial scaffolds is essential for normal nutrient transmission to cells, gas diffusion, and cell attachment and proliferation. Nanoscale inorganic additives and dopants are widely used to improve the functional properties of the polymer materials for tissue engineering. Among these inorganic dopants, halloysite nanotubes are arguably the most perspective candidates because of their biocompatibility and functional properties allowing to enhance significantly the mechanical and chemical stability of tissue engineering scaffolds. Here, this vibrant field of biotechnology for regenerative medicine is overviewed.

Chitosan films for regenerative medicine: fabrication methods and mechanical characterization of nanostructured chitosan films

Regenerative medicine is continuously facing new challenges and it is searching for new biocompatible, green/natural polymer materials, possibly biodegradable and non-immunogenic. Moreover, the critical importance of the nano/microstructuring of surfaces is overall accepted for their full biocompatibility and in vitro/in vivo performances. Chitosan is emerging as a promising biopolymer for tissue engineering and its application can be further improved by exploiting its nano/microstructuration. Here, we report the state of the art of chitosan films and scaffolds nano/micro-structuration. We show that it is possible to obtain, by solvent casting, chitosan thin films with good mechanical properties and to structure them at the microscale and even nanoscale level, with resolutions down to 100 nm.

Healing of Bone Defects in Pig's Femur Using Mesenchymal Cells Originated from the Sinus Membrane with Different Scaffolds

Objective

Repairing bone defects, especially in older individuals with limited regenerative capacity, is still a big challenge. The use of biomimetic materials that can enhance the restoration of bone structure represents a promising clinical approach. In this study, we evaluated ectopic bone formation after the transplantation of human maxillary Schneiderian sinus membrane- (hMSSM-) derived cells embedded within various scaffolds in the femur of pigs.

Methods

The scaffolds used were collagen, gelatin, and hydroxyapatite/tricalcium phosphate (HA/βTCP) where fibrin/thrombin was used as a control. Histological analysis was performed for the new bone formation. Quantitative real-time PCR (qRT-PCR) and immunohistochemistry (IHC) were used to assess mRNA and protein levels of specific osteoblastic markers, respectively.

Results

Histological analysis showed that the three scaffolds we used can support new bone formation with a more pronounced effect observed in the case of the gelatin scaffold. In addition, mRNA levels of the different tested osteoblastic markers Runt-Related Transcription Factor 2 (RUNX-2), osteonectin (ON), osteocalcin (OCN), osteopontin (OPN), alkaline phosphatase (ALP), and type 1 collagen (COL1) were higher, after 2 and 4 weeks, in cell-embedded scaffolds than in control cells seeded within the fibrin/thrombin scaffold. Moreover, there was a very clear and differential expression of RUNX-2, OCN, and vimentin in osteocytes, osteoblasts, hMSSM-derived cells, and bone matrix. Interestingly, the osteogenic markers were more abundant, at both time points, in cell-embedded gelatin scaffold than in other scaffolds (collagen, HA/βTCP, fibrin/thrombin).

Conclusions

These results hold promise for the development of successful bone regeneration techniques using different scaffolds embedded with hMSSM-derived cells. This trial is registered with NCT02676921.

Protein-Polymer Matrices with Embedded Carbon Nanotubes for Tissue Engineering: Regularities of Formation and Features of Interaction with Cell Membranes

This paper reveals the mechanism of nanowelding a branched network of single-walled carbon nanotubes (SWCNTs) used as a framework for the formation of protein-polymer matrices with albumin, collagen, and chitosan. It is shown that the introduction of certain point defects into the structure of SWCNTs (single vacancy, double vacancy, Stone-Wales defect, and a mixed defect) allows us to obtain strong heating in defective regions as compared to ideal SWCNTs. The wavelengths at which absorption reaches 50% are determined. Non-uniform absorption of laser radiation along with inefficient heat removal in defective regions determines the formation of hot spots, in which nanowelding of SWCNTs is observed even at 0.36 nm between contacting surfaces. The regularities of formation of layered protein-polymer matrices and the features of their interaction with cell membrane are revealed. All studies are carried out in silico using high-precision quantum approaches.

Combined Treatment with Three Natural Antioxidants Enhances Neuroprotection in a SH-SY5Y 3D Culture Model

Currently, the majority of cell-based studies on neurodegeneration are carried out on two-dimensional cultured cells that do not represent the cells residing in the complex microenvironment of the brain. Recent evidence has suggested that three-dimensional (3D) in vitro microenvironments may better model key features of brain tissues in order to study molecular mechanisms at the base of neurodegeneration. So far, no drugs have been discovered to prevent or halt the progression of neurodegenerative disorders. New therapeutic interventions can come from phytochemicals that have a broad spectrum of biological activities. On this basis, we evaluated the neuroprotective effect of three phytochemicals (sulforaphane, epigallocatechin gallate, and plumbagin) alone or in combination, focusing on their ability to counteract oxidative stress. The combined treatment was found to be more effective than the single treatments. In particular, the combined treatment increased cell viability and reduced glutathione (GSH) levels, upregulated antioxidant enzymes and insulin-degrading enzymes, and downregulated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 1 and 2 in respect to peroxide-treated cells. Our data suggest that a combination of different phytochemicals could be more effective than a single compound in counteracting neurodegeneration, probably thanks to a pleiotropic mechanism of action.

The Role of Stiffness in Cell Reprogramming: A Potential Role for Biomaterials in Inducing Tissue Regeneration

The mechanotransduction is the process by which cells sense mechanical stimuli such as elasticity, viscosity, and nanotopography of extracellular matrix and translate them into biochemical signals. The mechanotransduction regulates several aspects of the cell behavior, including migration, proliferation, and differentiation in a time-dependent manner. Several reports have indicated that cell behavior and fate are not transmitted by a single signal, but rather by an intricate network of many signals operating on different length and timescales that determine cell fate. Since cell biology and biomaterial technology are fundamentals in cell-based regenerative therapies, comprehending the interaction between cells and biomaterials may allow the design of new biomaterials for clinical therapeutic applications in tissue regeneration. In this work, we present the most relevant mechanism by which the biomechanical properties of extracellular matrix (ECM) influence cell reprogramming, with particular attention on the new technologies and materials engineering, in which are taken into account not only the biochemical and biophysical signals patterns but also the factor time.

3D Printing of Amino Resin-based Photosensitive Materials on Multi-parameter Optimization Design for Vascular Engineering Applications

Cardiovascular diseases are currently the most common cause of death globally and of which, the golden treatment method for severe cardiovascular diseases or coronary artery diseases are implantations of synthetic vascular grafts. However, such grafts often come with rejections and hypersensitivity reactions. With the emergence of regenerative medicine, researchers are now trying to explore alternative ways to produce grafts that are less likely to induce immunological reactions in patients. The main goal of such studies is to produce biocompatible artificial vascular grafts with the capability of allowing cellular adhesion and cellular proliferation for tissues regeneration. The Design of Experimental concepts is employed into the manufacturing process of digital light processing (DLP) 3D printing technology to explore near-optimal processing parameters to produce artificial vascular grafts with vascular characteristics that are close to native vessels by assessing for the cause and effect relationships between different ratios of amino resin (AR), 2-hydroxyethyl methacrylate (HEMA), dopamine, and curing durations. We found that with proper optimization of fabrication procedures and ratios of materials, we are able to successfully fabricate vascular grafts with good printing resolutions. These had similar physical properties to native vessels and were able to support cellular adhesion and proliferation. This study could support future studies in exploring near-optimal processes for fabrication of artificial vascular grafts that could be adapted into clinical applications.

The advances in nerve tissue engineering: From fabrication of nerve conduit to in vivo nerve regeneration assays

Peripheral nerve damage is a common clinical complication of traumatic injury occurring after accident, tumorous outgrowth, or surgical side effects. Although the new methods and biomaterials have been improved recently, regeneration of peripheral nerve gaps is still a challenge. These injuries affect the quality of life of the patients negatively. In the recent years, many efforts have been made to develop innovative nerve tissue engineering approaches aiming to improve peripheral nerve treatment following nerve injuries. Herein, we will not only outline what we know about the peripheral nerve regeneration but also offer our insight regarding the types of nerve conduits, their fabrication process, and factors associated with conduits as well as types of animal and nerve models for evaluating conduit function. Finally, nerve regeneration in a rat sciatic nerve injury model by nerve conduits has been considered, and the main aspects that may affect the preclinical outcome have been discussed.