Development of silk fibroin/nanohydroxyapatite composite hydrogels for bone tissue engineering

Preparation of nanofibrous poly (L-lactic acid) scaffolds using the thermally induced phase separation technique in dioxane/polyethylene glycol solution

Porous nanofibrous poly (L-lactic acid) (PLLA) scaffolds were fabricated in combination with a thermally induced phase separation technique using a dioxane/polyethylene glycol (PEG) system. The effect of factors such as molecular weight of PEG, aging treatment, aging or gelation temperature, and the ratio of PEG to dioxane were investigated. The results revealed that all scaffolds had high porosity, and had a significant impact on the formation of nanofibrous structures. The decrease in the molecular weight and aging or gelation temperature leads to a thinner and more uniform fibrous structure.

Silk fibroin hydrogel membranes prepared by a sequential cross-linking strategy for guided bone regeneration

Silk fibroin hydrogel is a widely used material for tissue engineering. However, its mechanical properties are the main obstacle to its application to medical bone regeneration barrier membranes. Here, we developed a new hydrogel membrane for guided bone regeneration (GBR). In this study, a sequential crosslinking strategy including photo crosslinking and organic solvent (ethanol) treatment was used to obtain silk fibroin hydrogel membrane (EA-SF). The mechanical properties of EA-SF were significantly enhanced compared to the hydrogel prepared only by photocrosslinking (E-SF). The compressive and tensile strengths of the hydrogel film treated with 75% ethanol for 6 h were 1.18 ± 0.36 MPa and 0.43 ± 0.03 MPa, respectively. In vitro cell culture results showed that EA-SF has good biocompatibility and can effectively shield fibroblasts (L929). EA-SF also has excellent in vitro protein hydrolysis stability. In vivo experiments (subcutaneous implantation and calvarial defect experiment) confirmed the stability and barrier functionality of EA-SF. In conclusion, this study demonstrated that ethanol could improve the mechanical properties of silk fibroin hydrogel and extend the scope of their application, making silk fibroin hydrogel a promising GBR material.

Silk fibroin carriers with sustained release capacity for treating neurological diseases

Neurological diseases such as traumatic brain injury, cerebral ischemia, Parkinson's, and Alzheimer's disease usually occur in the central and peripheral nervous system and result in nervous dysfunction, such as cognitive impairment and motor dysfunction. Long-term clinical intervention is necessary for neurological diseases where neural stem cell transplantation has made substantial progress. However, many risks remain for cell therapy, such as puncture bleeding, postoperative infection, low transplantation success rate, and tumor formation. Sustained drug delivery, which aims to maintain the desired steady-state drug concentrations in plasma or local injection sites, is considered as a feasible option to help overcome side effects and improve the therapeutic efficiency of drugs on neurological diseases. Natural polymers such as silk fibroin have excellent biocompatibility, which can be prepared for various end-use material formats, such as microsphere, gel, coating/film, scaffold/conduit, microneedle, and enables the dynamic release of loaded drugs to achieve a desired therapeutic response. Sustained-release drug delivery systems are based on the mechanism of diffusion and degradation by altering the structures of silk fibroin and drugs, factors, and cells, which can induce nerve recovery and restore the function of the nervous system in a slow and persistent manner. Based on these desirable properties of silk fibroin as a carrier with sustained-release capacity, this paper discusses the role of various forms of silk fibroin-based drug delivery materials in treating neurological diseases in recent years.

Chitosan/silk fibroin/nitrogen-doped carbon quantum dot/α-tricalcium phosphate nanocomposite electrospinned as a scaffold for wound healing application: In vitro and in vivo studies

A highly porous nanofibrous network that can functionalize antibacterial and therapeutic agents can be considered a suitable option for skin wound healing. In this study, α-tricalcium phosphate (α-TCP)/nitrogen-doped carbon quantum dots (N-CQDs) nanocomposite was synthesized and then applied to the fabrication of novel chitosan (CS)/silk fibroin (SF)/N-CQDs/α-TCP wound dressing via electrospinning system. The prepared nanomaterials were well characterized using X-ray diffraction, Fourier-transform infrared, scanning and transmission electron microscopes analyses, and antibacterial assay. Furthermore, nanofibers were evaluated regarding their physical properties, such as tensile behavior, water uptake capacity, and water contact angle. The results reveal that CS/SF/N-CQDs/α-TCP showed lower MIC values against E. coli and S. aureus (1.45 ± 0.26 mg/mL and 1.59 ± 0.12 mg/mL) compared to other synthesized materials. Also, in-vitro investigations were performed, and the MTT assay on the HFF cell line revealed that CS/SF/N-CQDs/α-TCP nanofiber could possess good biocompatibility. Interestingly, the scratch test proved that faster cell migration and proliferation occurred in the presence of CS/SF/N-CQDs/α-TCP (73 ± 3.12 %). Finally, we examined the wound healing ability of CS/SF/N-CQDs/α-TCP nanofiber using an animal model. The results confirmed that produced nanofiber could efficiently promote wound closure by 96.73 ± 1.25 % in 12 days. Histopathological analyses verified accelerated re-epithelization and well-structured epidermis in CS/SF/N-CQDs/α-TCP nanofiber-treated group. Based on our findings, the CS/SF/N-CQDs/α-TCP nanofiber with excellent antimicrobial properties is highly suitable for wound healing and skin tissue regeneration applications.

Silk fibroin scaffolds: A promising candidate for bone regeneration

It remains a big challenge in clinical practice to repair large-sized bone defects and many factors limit the application of autografts and allografts, The application of exogenous scaffolds is an alternate strategy for bone regeneration, among which the silk fibroin (SF) scaffold is a promising candidate. Due to the advantages of excellent biocompatibility, satisfying mechanical property, controllable biodegradability and structural adjustability, SF scaffolds exhibit great potential in bone regeneration with the help of well-designed structures, bioactive components and functional surface modification. This review will summarize the cell and tissue interaction with SF scaffolds, techniques to fabricate SF-based scaffolds and modifications of SF scaffolds to enhance osteogenesis, which will provide a deep and comprehensive insight into SF scaffolds and inspire the design and fabrication of novel SF scaffolds for superior osteogenic performance. However, there still needs more comprehensive efforts to promote better clinical translation of SF scaffolds, including more experiments in big animal models and clinical trials. Furthermore, deeper investigations are also in demand to reveal the degradation and clearing mechanisms of SF scaffolds and evaluate the influence of degradation products.

Enhanced formation of bioactive and strong silk-bioglass hybrid materials through organic-inorganic mutual molecular nucleation induction and templating

Materials based on silk fibroin (SF) are important for many biomedical applications due to their excellent biocompatibility and tunable biodegradability. However, the insufficient mechanical strength and low bioactivity of these materials have limited their applications. For silk hydrogels, slow gelation is also a crucial problem. In this work, a simple approach is developed to address these challenging problems all at once. By mixing SF solution with bioglass (BG) sol, instant gelation of silk is induced, the storage modulus of the hydrogel and the compressive modulus of the aerogel are significantly enhanced. The formation of a complex of SF and tetraethyl orthosilicate (TEOS), either through hydrogen bonding or TEOS condensation on SF, facilitated the aggregation of SF and, on the other hand, created active sites for the condensation of TEOS and BG formation on the surface of silk nanofibrils. The resultant hybrid gels have much higher capacity for biomineralization, indicating their higher bioactivity, compared with the pristine silk gels. This organic (SF)-inorganic (BG) mutual nucleation induction and templating can be used for a general approach to produce bioactive silk materials of various formats not limited to gels and may also inspire the formation of other functional protein-BG hybrid materials.

Bioselectivity of silk protein-based materials and their bio-inspired applications

Adhesion to material surfaces is crucial for almost all organisms regarding subsequent biological responses. Mammalian cell attachment to a surrounding biological matrix is essential for maintaining their survival and function concerning tissue formation. Conversely, the adhesion and presence of microbes interferes with important multicellular processes of tissue development. Therefore, tailoring bioselective, biologically active, and multifunctional materials for biomedical applications is a modern focus of biomaterial research. Engineering biomaterials that stimulate and interact with cell receptors to support binding and subsequent physiological responses of multicellular systems attracted much interest in the last years. Further to this, the increasing threat of multidrug resistance of pathogens against antibiotics to human health urgently requires new material concepts for preventing microbial infestation and biofilm formation. Thus, materials exhibiting microbial repellence or antimicrobial behaviour to reduce inflammation, while selectively enhancing regeneration in host tissues are of utmost interest. In this context, protein-based materials are interesting candidates due to their natural origin, biological activity, and structural properties. Silk materials, in particular those made of spider silk proteins and their recombinant counterparts, are characterized by extraordinary properties including excellent biocompatibility, slow biodegradation, low immunogenicity, and non-toxicity, making them ideally suited for tissue engineering and biomedical applications. Furthermore, recombinant production technologies allow for application-specific modification to develop adjustable, bioactive materials. The present review focusses on biological processes and surface interactions involved in the bioselective adhesion of mammalian cells and repellence of microbes on protein-based material surfaces. In addition, it highlights the importance of materials made of recombinant spider silk proteins, focussing on the progress regarding bioselectivity.

Use of Bombyx mori silk fibroin in tissue engineering: From cocoons to medical devices, challenges, and future perspectives

Silk fibroin has become a prominent material in tissue engineering (TE) over the last 20 years with almost 10,000 published works spanning in all the TE applications, from skeleton to neuronal regeneration. Fibroin is an extremely versatile biopolymer that, due to its ease of processing, has enabled the development of an entire plethora of materials whose properties and architectures can be tailored to suit target applications. Although the research and development of fibroin TE materials and devices is mature, apart from sutures, only a few medical products made of fibroin are used in the clinical routines. <40 clinical trials of Bombyx mori silk-related products have been reported by the FDA and few of them resulted in a commercialized device. In this review, after explaining the structure and properties of silk fibroin, we provide an overview of both fibroin constructs existing in the literature and fibroin devices used in clinic. Through the comparison of these two categories, we identified the burning issues faced by fibroin products during their translation to the market. Two main aspects will be considered. The first is the standardization of production processes, which leads both to the standardization of the characteristics of the issued device and the correct assessment of its failure. The second is the FDA regulations, which allow new devices to be marketed through the 510(k) clearance by demonstrating their equivalence to a commercialized medical product. The history of some fibroin medical devices will be taken as a case study. Finally, we will outline a roadmap outlining what actions we believe are needed to bring fibroin products to the market.

Nano-hydroxyapatite incorporated quince seed mucilage bioscaffolds for osteogenic differentiation of human adipose-derived mesenchymal stem cells

In this study, the therapeutic hydrocolloid quince seed mucilage (QSM) from Cydonia oblonga Miller fruit is enriched with needle-like nano-hydroxyapatite (nHAp) crystals to fabricate a novel biomimetic osteogenic bioscaffold. The molecular weight (M_w) of water-based extracted QSM was measured with GPC (8.67 × 10⁵ g/mol), and the composite blend was prepared at a ratio of 1:1 (w/w) QSM_aq and nHAp. The porous bioscaffolds were manufactured by the freeze-drying method, and evaluated in-depth with advanced analyses. The XRD, ATR-FTIR, SEM-EDX, and elemental mapping analyses revealed a uniform coated semi-crystalline structure with no covalent bindings between QSM and nHAp. Moreover, due to the hydrocolloid backbone, a supreme swelling ratio (w/w, 6523 ± 190%) with suitable pore size (208.12 ± 99.22 μm) for osteogenic development was obtained. Further, the cytocompatible bioscaffolds were evaluated for osteogenic differentiation in vitro using human adipose-derived mesenchymal stem cells (hAMSCs). The immuno/histochemical (I/HC) staining revealed that the cells with the spherical morphology invaded the pores of the prepared bioscaffolds. Also, relatively early up-regulated osteogenic markers were observed by the qRT-PCR analyses. Overall, it is believed that the QSM-nHAp bioscaffolds might be favorable in non-load bearing applications, especially in the cranio-maxillofacial region, due to their regenerative, bendable, and durable features.

Bone Scaffolds: An Incorporation of Biomaterials, Cells, and Biofactors

Large injuries to bones are still one of the most challenging musculoskeletal problems. Tissue engineering can combine stem cells, scaffold biomaterials, and biofactors to aid in resolving this complication. Therefore, this review aims to provide information on the recent advances made to utilize the potential of biomaterials for making bone scaffolds and the assisted stem cell therapy and use of biofactors for bone tissue engineering. The requirements and different types of biomaterials used for making scaffolds are reviewed. Furthermore, the importance of stem cells and biofactors (growth factors and extracellular vesicles) in bone regeneration and their use in bone scaffolds and the key findings are discussed. Lastly, some of the main obstacles in bone tissue engineering and future trends are highlighted.

Enzymatically Crosslinked In Situ Synthesized Silk/Gelatin/Calcium Phosphate Hydrogels for Drug Delivery

Our research focuses on combining the valuable properties of silk fibroin (SF) and calcium phosphate (CaP). SF is a natural protein with an easily modifiable structure; CaP is a mineral found in the human body. Most of the new age biocomposites lack interaction between organic/inorganic phase, thus SF/CaP composite could not only mimic the natural bone, but could also be used to make drug delivery systems as well, which can ensure both healing and regeneration. CaP was synthesized in situ in SF at different pH values, and then crosslinked with gelatin (G), horseradish peroxide (HRP), and hydrogen peroxide (H₂O₂). In addition, dexamethasone phosphate (DEX) was incorporated in the hydrogel and drug delivery kinetics was studied. Hydrogel made at pH 10.0 was found to have the highest gel fraction 110.24%, swelling degree 956.32%, and sustained drug delivery for 72 h. The highest cell viability was observed for the hydrogel, which contained brushite (pH 6)-512.43%.

Preparation and biological properties of silk fibroin/nano-hydroxyapatite/hyaluronic acid composite scaffold

In this study, the silk fibroin/nano-hydroxyapatite/hyaluronic acid (SF/nHAp/HA) composite scaffolds with different HA contents were developed by blending, cross-linking and freeze-drying, and their physicochemical properties and cell biocompatibilityin vitrowere subsequently studied. It was observed that the molecular conformation of the composite scaffolds was mainly composed of silk I and a small amount of theβ-sheets structure. On enhancing the HA content, the pore size of the scaffold decreased, while the porosity, water absorption, swelling ratio and mechanical properties were observed to increase. In particular, the SF/nHAp/HA scaffold with a 5.0 wt% ratio exhibited the highest water absorption and mechanical properties among the developed materials. In addition, thein vitrocytocompatibility analysis showed that the bone marrow mesenchymal stem cells exhibited excellent cell proliferation and osteogenic differentiation ability on the SF/nHAp/5.0 wt%HA scaffolds, as compared with the other scaffolds. It can be concluded that the developed composite scaffolds represent a promising class of materials for the bone tissue repair and regeneration.

Silk Biomaterials for Bone Tissue Engineering

Silk is a natural fibrous polymer with application potential in regenerative medicine. Increasing interest remains for silk materials in bone tissue engineering due to their characteristics in biocompatibility, biodegradability and mechanical properties. Plenty of the in vitro and in vivo studies confirmed the advantages of silk in accelerating bone regeneration. Silk is processed into scaffolds, hydrogels, and films to facilitate different bone regenerative applications. Bioactive factors such as growth factors and drugs, and stem cells are introduced to silk-based matrices to create friendly and osteogenic microenvironments, directing cell behaviors and bone regeneration. The recent progress in silk-based bone biomaterials is discussed and focused on different fabrication and functionalization methods related to osteogenesis. The challenges and potential targets of silk bone materials are highlighted to evaluate the future development of silk-based bone materials.

Functional silk fibroin hydrogels: preparation, properties and applications

Over the past decade, the hydrogels prepared from silk fibroin have received immense research attention due to the advantages of safe nature, biocompatibility, controllable degradation and capability to combine with other materials. They have broad application prospects in biomedicine and other fields. However, the traditional silk protein hydrogels have a simple network structure and single functionality, thus, leading to poor adaptability towards complex application environments. As a result, the application fields and development have been significantly restricted. However, the development of functional silk protein hydrogels has provided the opportunities to overcome the limitations of the silk protein hydrogels. In recent years, the functional design of the silk protein hydrogels and their potential applications have attracted the attention of scholars worldwide. Nevertheless, a comprehensive review on functional silk protein hydrogels is missing so far. In order to gain an in-depth understanding of the development status of the functional silk protein hydrogels, this article reviews the current status of the preparation, properties and application of the functional silk protein hydrogels. The article first briefly introduces the current cross-linking methods (including physical and chemical cross-linking), principles, advantages and limitations of the silk protein hydrogels. Subsequently, the types of functional silk protein hydrogels (e.g., high strength, injectable, self-healing, adhesive, conductive, environmental stimuli-responsive, 3D printable, etc.) and design principles for functional implementation have been introduced. Next, based on the advantages of the various functional aspects of the silk protein hydrogels, the applications of these hydrogels in the biomedical field (tissue engineering, sustained drug release, wound repair, adhesives, etc.) and bioelectronics are reviewed. Finally, the development prospects and challenges associated with silk protein functional hydrogels have been analyzed. It is hoped that this study will contribute towards the future innovation of the silk protein hydrogels by promoting the rational design of new mechanisms and successful realization of the target applications.

Effect of Cerium-Containing Hydroxyapatite in Bone Repair in Female Rats with Osteoporosis Induced by Ovariectomy

Osteoporosis is a public health problem, with bone loss being the main consequence. Hydroxyapatite (HA) has been largely used as a bioceramic to stimulate bone growth. In our work, a cerium-containing HA (Ce-HA) has been proposed and its effects on the antimicrobial and bone-inducing properties were investigated. The synthesis of the materials occurred by the suspension–precipitation method (SPM). The XRD (X-ray Diffraction) confirmed the crystalline phase, and the Rietveld refinement confirmed the crystallization of HA and Ce-HA in a hexagonal crystal structure in agreement with ICSD n° 26205. Characterizations by FT-IR (Fourier Transform Infrared Spectroscopy), XPS (X-ray Photoemission Spectroscopy), and FESEM-EDS (Field Emission Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy) confirmed the presence of cerium (Ce3+ and Ce4+). The antibacterial activity of Has was evaluated against Staphylococcus aureus 25,923 and Escherichia coli 25,922 strains, which revealed that the material has antimicrobial properties and the cytotoxicity assay indicated that Ce-containing HA was classified as non-toxic. The effects of Ce-HA on bone repair, after application in bone defects in the tibia of female rats with osteoporosis induced by ovariectomy (OVX), were evaluated. After 15 and 30 days of implantation, the samples were analyzed by Raman, histology and X-ray microtomography. The results showed that the animals that had the induced bone defects filled with the Ce-HA materials had more expressive bone neoformation than the control group.

Biomaterials with Potential Use in Bone Tissue Regeneration-Collagen/Chitosan/Silk Fibroin Scaffolds Cross-Linked by EDC/NHS

Blending of different biopolymers, e.g., collagen, chitosan, silk fibroin and cross-linking modifications of these mixtures can lead to new materials with improved physico-chemical properties, compared to single-component scaffolds. Three-dimensional scaffolds based on three-component mixtures of silk fibroin, collagen and chitosan, chemically cross-linked, were prepared and their physico-chemical and biological properties were evaluated. A mixture of EDC (N-(3-dimethylaminopropyl)-N’-ethylcarbodiimide hydrochloride) and NHS (N-hydroxysuccinimide) was used as a cross-linking agent. FTIR was used to observe the position of the peaks characteristic for collagen, chitosan and silk fibroin. The following properties depending on the scaffold structure were studied: swelling behavior, liquid uptake, moisture content, porosity, density, and mechanical parameters. Scanning Electron Microscopy imaging was performed. Additionally, the biological properties of these materials were assessed, by metabolic activity assay. The results showed that the three-component mixtures, cross-linked by EDC/NHS and prepared by lyophilization method, presented porous structures. They were characterized by a high swelling degree. The composition of scaffolds has an influence on mechanical properties. All of the studied materials were cytocompatible with MG-63 osteoblast-like cells.

Silk Polymers and Nanoparticles: A Powerful Combination for the Design of Versatile Biomaterials

Silk fibroin (SF) is a natural protein largely used in the textile industry but also in biomedicine, catalysis, and other materials applications. SF is biocompatible, biodegradable, and possesses high tensile strength. Moreover, it is a versatile compound that can be formed into different materials at the macro, micro- and nano-scales, such as nanofibers, nanoparticles, hydrogels, microspheres, and other formats. Silk can be further integrated into emerging and promising additive manufacturing techniques like bioprinting, stereolithography or digital light processing 3D printing. As such, the development of methodologies for the functionalization of silk materials provide added value. Inorganic nanoparticles (INPs) have interesting and unexpected properties differing from bulk materials. These properties include better catalysis efficiency (better surface/volume ratio and consequently decreased quantify of catalyst), antibacterial activity, fluorescence properties, and UV-radiation protection or superparamagnetic behavior depending on the metal used. Given the promising results and performance of INPs, their use in many different procedures has been growing. Therefore, combining the useful properties of silk fibroin materials with those from INPs is increasingly relevant in many applications. Two main methodologies have been used in the literature to form silk-based bionanocomposites: in situ synthesis of INPs in silk materials, or the addition of preformed INPs to silk materials. This work presents an overview of current silk nanocomposites developed by these two main methodologies. An evaluation of overall INP characteristics and their distribution within the material is presented for each approach. Finally, an outlook is provided about the potential applications of these resultant nanocomposite materials.

Synthesis and characterization of photocrosslinkable albumin-based hydrogels for biomedical applications

Protein-based biomaterials are widely used to generate three-dimensional (3D) scaffolds for tissue regeneration as well as compact delivery systems for drugs, genes, and peptides. Specifically, albumin-based biomaterials are of particular interest for their ability to facilitate controlled delivery of drugs and other therapeutic agents. These hydrogels possess non-toxic and non-immunogenic properties that are desired in tissue engineering scaffolds. This work employs a rapid ultraviolet (UV) light induced crosslinking to fabricate bovine serum albumin (BSA) hydrogels. Using four different conditions, the BSA hydrogel properties were modulated based on the extent of glycidyl methacrylate modification in each polymer. The highly tunable mechanical behavior of the material was determined through compression tests which yielded a range of material strengths from 4.4 ± 1.5 to 122 ± 7.4 kPa. Pore size measurements also varied from 7.7 ± 1.7 to 23.5 ± 6.6 μm in the photocrosslinked gels. The physical properties of materials such as swelling and degradation were also characterized. In further evaluation, 3D scaffolds were used in cell encapsulation and in vivo implantation studies. The biocompatibility and degradability of the material demonstrated effective integration with the native tissue environment. These modifiable chemical and mechanical properties allow BSA hydrogels to be fine-tuned to a plethora of biomedical applications including regenerative medicine, in vitro cancer study models, and wound healing approaches.

Consecutive dephosphorylation by alkaline phosphatase-directed in situ formation of porous hydrogels of SF with nanocrystalline calcium phosphate ceramics for bone regeneration

Alkaline phosphatase, as an enzyme involved in the process of bone mineralization and regeneration, was incorporated into a solution of SF to induce its gelation and mineralization through consecutive dephosphorylation actions on different substrates. In these processes, alkaline phosphatase firstly worked on a small peptide of NapGFFYp by removing its hydrophilic phosphate group. The resulted NapGFFY performed supramolecular assembly in the solution of SF and synergistically induced the conformation transition of SF from random coil to β-sheet structures, leading to the formation of a stable SF hydrogel under physiological conditions. And then, the entrapped ALP within the SF-NY gel network retained its catalytic activity, released phosphate ions from glycerophosphate, and catalysed the formation of calcium phosphate minerals within the porous gel. Because of the mild conditions of these processes and good biocompatibility of the scaffold, the mineralized SF gel can work as a biomimetic scaffold to promote the osteogenic differentiation of rBMSCs and stimulate femoral defect regeneration in a rat model.

Silk Fibroin/Collagen/Chitosan Scaffolds Cross-Linked by a Glyoxal Solution as Biomaterials toward Bone Tissue Regeneration

In this study, three-dimensional materials based on blends of silk fibroin (SF), collagen (Coll), and chitosan (CTS) cross-linked by glyoxal solution were prepared and the properties of the new materials were studied. The structure of the composites and the interactions between scaffold components were studied using FTIR spectroscopy. The microstructure was observed using a scanning electron microscope. The following properties of the materials were measured: density and porosity, moisture content, and swelling degree. Mechanical properties of the 3D materials under compression were studied. Additionally, the metabolic activity of MG-63 osteoblast-like cells on materials was examined. It was found that the materials were characterized by a high swelling degree (up to 3000% after 1 h of immersion) and good porosity (in the range of 80–90%), which can be suitable for tissue engineering applications. None of the materials showed cytotoxicity toward MG-63 cells.

Bioinspired 3D porous human placental derived extracellular matrix/silk fibroin sponges for accelerated bone regeneration

Critical bone defects arising from traumatic injury and diseases are of major health concern since they are unable to heal spontaneously without clinical intervention. In this context, bone tissue engineering provides an attractive approach to treat bone defects by providing a bioactive template which has the potential to guide osseous tissue regeneration. In this study, porous hybrid placental extracellular matrix sponge (PIMS) was fabricated by a combinatorial method using silk fibroin (SF)/placental derived extracellular matrix and subsequently evaluated its efficacy towards bone tissue regeneration. The presence of intrinsic growth factors was evidenced by immunoblotting of the extracted proteins derived from the placental derived extracellular matrix. This growth factor rich PIMS lends a unique bioactive scaffolding to human amniotic mesenchymal stem cells (HAMSCs) which supported enhanced proliferation as well as superior osteogenic differentiation. Gene expression studies demonstrated significant up-regulation of osteogenic related genes in the PIMS group. PIMS when implanted in the chick chorioallantoic membrane, significantly attracted allantoic vessels revealing its potential to stimulate angiogenesis ex vivo. Furthermore, no severe immune response to the host was observed on subcutaneous implantation of PIMS in vivo. Instead, it supported the formation of blood vessels, revealing its outstanding biocompatibility. Additionally, critical tibial defects treated with PIMS demonstrated higher bone volume after six weeks when analyzed by micro-CT, which was accompanied by high mineral density. Histological and immunofluorescence studies validated the results and revealed enhanced osseous tissue regeneration after six weeks of surgery. All these findings recapitulated that the growth factors incorporated bioactive PIMS could perform as an appropriate matrix for osteogenic differentiation and efficient bone regeneration.

Physico-Chemical Characterization and Biological Tests of Collagen/Silk Fibroin/Chitosan Scaffolds Cross-Linked by Dialdehyde Starch

In this study, three-dimensional (3D) biopolymeric scaffolds made from collagen, silk fibroin and chitosan were successfully prepared by the freeze drying method. Dialdehyde starch (DAS) was used as a cross-linking agent for the materials. The properties of the materials were studied using density and porosity measurements, scanning electron microscope (SEM) imaging, swelling and moisture content measurements. Additionally, cytocompatibility of the materials in contact with MG-63 osteoblast-like cells was tested by live/dead staining and resazurin reduction assay on days 1, 3 and 7. It was found that new 3D materials made from collagen/silk fibroin/chitosan binary or ternary mixtures are hydrophilic with a high swelling ability (swelling rate in the range of 1680–1900%). Cross-linking of such biopolymeric materials with DAS increased swelling rate up to about 2100%, reduced porosity from 96–97% to 91–93%, and also decreased density and moisture content of the materials. Interestingly, presence of DAS did not influence the microstructure of the scaffolds as compared to non-cross-linked samples as shown by SEM. All the tested samples were found to be cytocompatible and supported adhesion and growth of MG-63 cells as shown by live–dead staining and metabolic activity test.

Overviews of Biomimetic Medical Materials

This chapter describes the overviews of biomimetic medical materials which covers innovation and significance of terminology, diverse fabrication methods, and technologies ranges from nanotechnology to 3D printing to develop biomimetic materials for medical applications. It also depicts specific fundamental characteristics required for a material to be a model biomimetic material for particular medical application. It basically outlines current statuses of biomimetic medical materials used for tissue engineering and regenerative medicine, drug/protein delivery, bioimaging, biosensing, and 3D bioprinting technology. It also illustrates the effect of functionalization of a material through chemical and biological approaches towards different applications. Not only, the key properties and potential applications of the biomimetic materials, but it also explains the protection and utilization of intellectual property associated with biomedical materials.

Additive effect of pulp pequi oil (Caryocar brasiliense Camb.) on the biocompatibility of collagen and gelatin membranes in subcutaneous implants

ABSTRACT Trauma or disease inflicted by tissue injuries may cause tissue degeneration. The use of biomaterials for direct or indirect repair has emerged as a promising alternative, and has become an important research topic. The pequi fruit (Caryocar brasiliense Camb.) has shown antifungal, antibacterial, anti-inflammatory, healing, antitumor, and antioxidant properties. The objective of this study was to develop a new biomaterial using a combination of collagen, gelatin, and pulp pequi oil, and to evaluate its biocompatibility in comparison with that of biomaterials produced without pulp pequi oil. Membranes were prepared from a mixture of bovine tendon collagen, commercial gelatin, and pulp pequi oil. The inflammatory and cicatricial processes were assessed via histopathology of the tissue interface/implants in the subcutaneous tissues and quantitative evaluation of leukocyte and collagen production in Wistar rats. It was observed that the presence of pequi oil reduced the amount of foreign-body giant cells and favored the recruitment of fibroblasts (P< 0.01), thereby promoting greater production of collagen membrane than that in the membranes of control samples. Therefore, it can be concluded that the addition of pequi oil improved the biocompatibility of collagen and accelerated the healing process.

Fabrication and characterization of hydroxypropyl guar-poly (vinyl alcohol)-nano hydroxyapatite composite hydrogels for bone tissue engineering

Biocompatible bone implants composed of natural materials are highly desirable in orthopedic reconstruction procedures. In this study, novel and ecofriendly bionanocomposite hydrogels were synthesized using a blend of hydroxypropyl guar (HPG), poly vinyl alcohol (PVA), and nano-hydroxyapatite (n-HA) under freeze-thaw and mild reaction conditions. The hydrogel materials were characterized using various techniques. TGA studies indicate that both composites, HPG/PVA and HPG/PVA/n-HA, have higher thermal stability compared to HPG alone whereas HPG/PVA/n-HA shows higher stability compared to PVA alone. The HPG/PVA hydrogel shows porous morphology as revealed by the SEM, which is suitable for bone tissue regeneration. Additionally, the hydrogels were found to be transparent and flexible in nature. In vitro biomineralization study performed in simulated body fluid shows HPG/PVA/n-HA has an apatite like structure. The hydrogel materials were employed as extracellular matrices for biocompatibility studies. In vitro cell viability studies using mouse osteoblast MC3T3 cells were performed by MTT, Trypan blue exclusion, and ethidium bromide/acridine orange staining methods. The cell viability studies reveal that composite materials support cell growth and do not show any signs of cytotoxicity compared to pristine PVA. Osteoblastic activity was confirmed by an increased alkaline phosphatase enzyme activity in MC3T3 bone cells grown on composite hydrogel matrices.

Quercetin Inlaid Silk Fibroin/Hydroxyapatite Scaffold Promotes Enhanced Osteogenesis

There is a significant rise in the bone grafts demand worldwide to treat bone defects owing to continuous increase in conditions such as injury, trauma, diseases, or infections. Therefore, development of three-dimensional scaffolds has evolved as a reliable technology to address the current limitations for bone tissue regeneration. Mimicking the natural bone, in this study, we have designed a silk fibroin/hydroxyapatite scaffold inlaid with a bioactive phytochemical (quercetin) at different concentrations for promoting osteogenesis, especially focusing on quercetin ability for enhancing bone health. Characterization of the quercetin/silk fibroin/hydroxyapatite (Qtn/SF/HAp) scaffolds showed an increased pore size and irregular porous microstructure with good mechanical strength. The Qtn (low-content)/SF/HAp scaffold was found to be an efficient cell carrier facilitating cellular growth, osteogenic differentiation, and proliferation as compared to SF/HAp and Qtn (high-content)/SF/HAp scaffolds. However, Qtn (high-content)/SF/HAp was observed to inhibit cell proliferation without any effects on cell viability. In vitro and in vivo outcomes studied using bone marrow-derived mesenchymal stem cells (rBMSCs) confirm the cytocompatibility, osteogenic differentiation ability, and prominent upregulation of the bone-specific gene expressions for the rBMSCs-seeded Qtn/SF/HAp scaffolds. In particular, the implanted Qtn (low-content)/SF/HAp scaffolds at the bone defect site were found to be well-attached and amalgamated with the surrounding tissues with approximately 80% bone volume recovery at 6 weeks after surgery as compared with other groups. Based on the aforementioned observations highlighting the quercetin efficiency for bone regeneration, the as-synthesized Qtn (low-content)/SF/HAp scaffolds can be envisioned to provide a biomimetic bone-like microenvironment promoting rBMSCs differentiation into osteoblast, thus suggesting a potential alternative graft for high-performance regeneration of bone tissues.

Simultaneous structuring and mineralization of silk fibroin scaffolds

Silk fibroin is commonly used as scaffold material for tissue engineering applications. In combination with a mineralization with different calcium phosphate phases, it can also be applied as material for bone regeneration. Here, we present a study which was performed to produce mineralized silk fibroin scaffolds with controlled macroporosity. In contrast to former studies, our approach focused on a simultaneous gelation and mineralization of silk fibroin by immersion of frozen silk fibroin monoliths in acidic calcium phosphate solutions. This was achieved by thawing frozen silk fibroin monoliths in acidic calcium phosphate solution, leading to the precipitation of monocalcium phosphate within the silk fibroin matrix. In the second approach, a conversion of incorporated β-tricalcium phosphate particles into brushite was successfully achieved. Furthermore, a controlled cryostructuring process of silk fibroin scaffolds was carried out leading to the formation of parallel-oriented pores with diameters of 30–50 µm.

Silk fibroin/nanohydroxyapatite hydrogels for promoted bioactivity and osteoblastic proliferation and differentiation of human bone marrow stromal cells

Silk fibroin (SF) is a natural, biocompatible, and biodegradable polymer having a great potential for the successful regeneration of damaged bone tissue. In the present work, nanohydroxyapatite (nanoHA) was incorporated into SF polymer to form a bioactive composite hydrogel for applications as bone implants. The degradation and bioactive properties of SF/nanoHA composite hydrogels were evaluated. Additionally, biological investigations of human bone marrow stromal cells (hBMSCs) viability, proliferation and differentiation to the osteoblastic phenotype were conducted. The incorporation of nanoHA in SF polymer matrices improved the bioactivity of the hydrogels. The biological results highlighted that the SF/nanoHA composite hydrogels are suitable for hBMSCs attachment and proliferation, while a test for alkaline phosphatase (ALP) and bone morphogenetic protein 2 (BMP-2) expression suggested osteoblast differentiation. Additionally, a cell staining method for ALP allowed to observe cell infiltration with active production of ALP by the infiltrated cells, paving the way to use the proposed composite hydrogel for bone tissue regeneration.

Synthesis, characterization and in vitro screening of a nano-hydroxyapatite/chitosan/Euryale ferox nanoensemble – an inimitable approach for bone tissue engineering

In order to explore novel synthetic bone scaffolds, a biomimmetic, osteoinductive, tricomposite scaffold has been synthesized incorporating Euryale ferox (EF) with nano-hydroxyapatite and chitosan.

Three-dimensional macroporous materials for tissue engineering of craniofacial bone

Repair of critical-size defects caused by trauma, removal of a tumour, or congenital abnormalities is a challenge in the craniomaxillofacial region because of the limitations associated with treatment. We have reviewed research papers and updated information relevant to the various types of macroporous scaffolds. We have included papers on several biomaterials and their use in various craniofacial defects such as mandibular, calvarial, and others, as well as the latest technological developments such as 3-dimensional printed scaffolds. We selected all papers about scaffolds, stem cells, and growth factors for review. Initial selection was by review of titles and abstracts, and the full texts of potentially suitable articles were then assessed. Methods of tissue engineering for repair of critical-size defects in the craniofacial bones seem to be viable options for surgical treatment in the future. Macroporous scaffolds with interconnected pores are of great value in regeneration of bone in the craniofacial region. In recent years, various natural or synthetic materials, or both, have been developed, on which macroporous scaffolds can be based. In this review we present a review on the various types of three-dimensional macroporous scaffolds that have been developed in recent years, and evaluate their potential for regeneration of craniofacial bone.

Recent Advances in Bioink Design for 3D Bioprinting of Tissues and Organs

There is a growing demand for alternative fabrication approaches to develop tissues and organs as conventional techniques are not capable of fabricating constructs with required structural, mechanical, and biological complexity. 3D bioprinting offers great potential to fabricate highly complex constructs with precise control of structure, mechanics, and biological matter [i.e., cells and extracellular matrix (ECM) components]. 3D bioprinting is an additive manufacturing approach that utilizes a "bioink" to fabricate devices and scaffolds in a layer-by-layer manner. 3D bioprinting allows printing of a cell suspension into a tissue construct with or without a scaffold support. The most common bioinks are cell-laden hydrogels, decellulerized ECM-based solutions, and cell suspensions. In this mini review, a brief description and comparison of the bioprinting methods, including extrusion-based, droplet-based, and laser-based bioprinting, with particular focus on bioink design requirements are presented. We also present the current state of the art in bioink design including the challenges and future directions.

A Review of Structure Construction of Silk Fibroin Biomaterials from Single Structures to Multi-Level Structures

The biological performance of artificial biomaterials is closely related to their structure characteristics. Cell adhesion, migration, proliferation, and differentiation are all strongly affected by the different scale structures of biomaterials. Silk fibroin (SF), extracted mainly from silkworms, has become a popular biomaterial due to its excellent biocompatibility, exceptional mechanical properties, tunable degradation, ease of processing, and sufficient supply. As a material with excellent processability, SF can be processed into various forms with different structures, including particulate, fiber, film, and three-dimensional (3D) porous scaffolds. This review discusses and summarizes the various constructions of SF-based materials, from single structures to multi-level structures, and their applications. In combination with single structures, new techniques for creating special multi-level structures of SF-based materials, such as micropatterning and 3D-printing, are also briefly addressed.

Composite Hydrogels for Bone Regeneration

Over the past few decades, bone related disorders have constantly increased. Among all pathological conditions, osteoporosis is one of the most common and often leads to bone fractures. This is a massive burden and it affects an estimated 3 million people only in the UK. Furthermore, as the population ages, numbers are due to increase. In this context, novel biomaterials for bone fracture regeneration are constantly under development. Typically, these materials aim at favoring optimal bone integration in the scaffold, up to complete bone regeneration; this approach to regenerative medicine is also known as tissue engineering (TE). Hydrogels are among the most promising biomaterials in TE applications: they are very flexible materials that allow a number of different properties to be targeted for different applications, through appropriate chemical modifications. The present review will focus on the strategies that have been developed for formulating hydrogels with ideal properties for bone regeneration applications. In particular, aspects related to the improvement of hydrogels' mechanical competence, controlled delivery of drugs and growth factors are treated in detail. It is hoped that this review can provide an exhaustive compendium of the main aspects in hydrogel related research and, therefore, stimulate future biomaterial development and applications.

Silk fibroin as biomaterial for bone tissue engineering

Silk fibroin (SF) is a fibrous protein which is produced mainly by silkworms and spiders. Its unique mechanical properties, tunable biodegradation rate and the ability to support the differentiation of mesenchymal stem cells along the osteogenic lineage, have made SF a favorable scaffold material for bone tissue engineering. SF can be processed into various scaffold forms, combined synergistically with other biomaterials to form composites and chemically modified, which provides an impressive toolbox and allows SF scaffolds to be tailored to specific applications. This review discusses and summarizes recent advancements in processing SF, focusing on different fabrication and functionalization methods and their application to grow bone tissue in vitro and in vivo. Potential areas for future research, current challenges, uncertainties and gaps in knowledge are highlighted.

STATEMENT OF SIGNIFICANCE

Silk fibroin is a natural biomaterial with remarkable biomedical and mechanical properties which make it favorable for a broad range of bone tissue engineering applications. It can be processed into different scaffold forms, combined synergistically with other biomaterials to form composites and chemically modified which provides a unique toolbox and allows silk fibroin scaffolds to be tailored to specific applications. This review discusses and summarizes recent advancements in processing silk fibroin, focusing on different fabrication and functionalization methods and their application to grow bone tissue in vitro and in vivo. Potential areas for future research, current challenges, uncertainties and gaps in knowledge are highlighted.