Electrospun biodegradable nanofibers scaffolds for bone tissue engineering

Many polymeric materials have been developed and introduced for bone regeneration. Especially, their nanofibrous forms are mostly applied for artificial extracellular matrices. Polymeric materials in their nanofibrous form show some potent properties such as high surface‐to‐volume ratio, tunable porosity, and ease of surface functionalization. Benefiting from the properties of their main polymer and additives, they can provide new opportunities for cell seeding, proliferation, and new 3D‐tissue formation. This article focuses on most cited polymeric nanofibrous scaffolds fabricated by electrospinning and recent achievements. They were divided into two main categories: natural (collagen, silk, keratin, gelatin, chitosan, and alginate) and synthetic (e.g., polycaprolactone, polylactic acid, and polyglycolic acid) polymers. The role of several additives like hydroxyapatite, bone morphogenetic proteins (BMPs), tricalcium phosphate, and collagen type I in improving the adhesion, differentiation, and tissue formation of stem cells were discussed. Finally, the osteogenic capacity and ability of nanofibrous scaffolds to support the growth of clinically relevant bone tissue were briefly studied. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42883.     

Biocompatible graphene-embedded PCL/PGS-based nanofibrous scaffolds: A potential application for cardiac tissue regeneration

Research in the field of tissue engineering, especially heart tissue engineering, is growing rapidly. Herein, the morphological, chemical, mechanical and biological properties of poly (caprolactone) (PCL)/poly (glycerol sebacate) (PGS) and PCL/PGS/graphene nanofibrous scaffolds are investigated. Initially, PGS pre-polymer is synthesized and characterized by nuclear magnetic resonance and Fourier transform infrared spectroscopies. Then, in order to use the benefits of PGS, this polymer is mixed with PCL. Blending PGS with PCL resulted in the enhancement of ultimate elongation and reduction in the elastic modulus due to the intrinsic properties of PGS. The hydrophobicity of PCL nanofibers is reduced by adding PGS as hydrophilic polymer (105 ± 3° vs. 44 ± 2°). Also, the addition of graphene to the blend nanofibers is balanced the hydrophilicity. Degradation rate of pure PCL nanofibers is very slow but it is increased in the presence of PGS. All nanofibrous scaffolds are biocompatible and non-toxic. The highest cell adhesion (covered area = 0.916 ± 0.032) and biocompatibility (98.79 ± 1%) are related to PCL/PGS loaded with 1% wt of graphene (PCL/PGS/graphene ₁). Thus, this sample can be a good candidate for further examinations of cardiac tissue engineering.     

In vivo bioactivity of herbal‐drug‐incorporated nanofibrous matrixes

Aloe‐vera‐incorporated polycaprolactone nanofibrous matrixes were prepared by an electrospinning method. These developed matrixes were evaluated for their water absorption capacity, water vapor permeability, and contact angle, and, in an in vivo animal model, wound‐healing ability. The incorporation of the herbal drug made the matrixes hydrophilic with improved water retention and permeability properties. The in vivo studies were carried out in a rat model and showed improved results with respect to healing. Thus, this study confirmed that the developed matrixes could be used for wound‐healing applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42178.     

Biomimetic mineralization of chitosan/gelatin cryogels and in vivo biocompatibility assessments for bone tissue engineering

The objective of this study is to develop biomimetic chitosan: gelatin (CH:Gel) cryogels for bone tissue engineering, combining the biological recognition of natural polymers with the distinguished interconnected porosity of cryogels, and biomimicking properties of bone like hydroxyapatite. The control of the biomineralization process onto biomaterials should be evaluated before clinical application. Therefore, the effect of chitosan and gelatin ratios on the final properties of the cryogels were investigated. FTIR, XRD, and SEM analysis indicated that the SBF coating exhibited similar characteristics to hydroxyapatite. The cryogels showed good biocompatibility with L929 mouse fibroblasts. Clinical outcomes and gross pathological examination showed that neither necrosis nor foreign body reaction was noted at the end of implantation. The biomimetically mineralized scaffold was found to be non-irritant and non-toxic for bone tissue. The biological performance and favorable properties demonstrated that the SBF coated CH:Gel cryogel can be a promising biomimetic scaffold for bone tissue engineering applications.     

Influence of elastin on the properties of hybrid PCL/elastin scaffolds for tissue engineering

Developing scaffolds by combining different polymers in order to improve the properties of the bare polymers has become an extensively applied practice. Polycaprolactone (PCL) is a synthetic polyester with outstanding properties for tissue engineering (TE), although it does have certain drawbacks that can be counteracted by combining it with other biopolymers. The biopolymer elastin is an essential functional component of the dermal extracellular matrix. Therefore, the aim of this work was to produce binary systems comprising a combination of PCL (16 wt/vol%) and different concentrations of elastin (2 and 4 wt/vol%) to evaluate how the protein affects the matrix. To this end, the morphological, physicochemical, mechanical and biological properties of the aforementioned scaffolds were further characterized, observing that PCL/elastin is a suitable mixture as it improves the wettability of PCL when combined with elastin (the contact angles were reduced from 102 to ca. 70°). In addition, mixing PCL with a small quantity of elastin (2%) improved the mechanical properties of PCL-based scaffolds (Young's modulus increased from 36 to 69 MPa and the maximum stress increased from 11 to 34 MPa).     

Modified poly(caprolactone trifumarate) with embedded gelatin microparticles as a functional scaffold for bone tissue engineering

Bone tissue engineering offers high hopes in reconstructing bone defects that result from trauma, infection, tumors, and other conditions. However, there remains a need for novel scaffold materials that can effectively stimulate ossification with appropriate functional properties. Therefore, a novel injectable, biodegradable, and biocompatible scaffold made by incorporating modified poly(caprolactone trifumarate) (PCLTF) with embedded gelatin microparticles (GMPs) as porogen is developed. Specifically, in vitro and in vivo tests were carried out. For the latter, to determine the osteogenic ability of PCLTF‐GMPs scaffolds, and to characterize bone‐formation, these scaffolds were implanted into critical‐sized defects of New Zealand white rabbit craniums. Field Emission Scanning Electron Microscope (FESEM) demonstrated cells of varying shapes attached to the scaffold surface in vitro. The PCLTF‐GMPs demonstrated improved biocompatibility in vivo. Polyfluorochrome tracers detected bone growth occurring in the PCLTF‐GMPs filled defects. By incorporating PCLTF with GMPs, we have fabricated a promising self‐crosslinkable biocompatible and osteoconducive scaffold for bone tissue engineering. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43711.     

Surface‐modified pliable PDLLA/PCL/β‐TCP scaffolds as a promising delivery system for bone regeneration

Surface‐modified poly(d , l ‐lactide)/polycaprolactone/β‐tricalcium phosphate complex scaffold was fabricated in this study and we hypothesized that pliable and mechanical strong scaffold would be achieved by regulation of ternary compositions; while superficial modification strategy conduced to preserve and controlled‐release of bioactive growth factors. Properties of the composite scaffolds were systematically investigated, including mechanical properties, surface morphology, porosity, wettability, and releasing behavior. Moreover, the representative cytokine, recombinant human bone morphogenetic protein‐2 (rhBMP‐2), was loaded and implanted into muscular pouch of mouse to assess bone formation in vivo. Improved osteogenesis was achieved ascribed to both amplified β‐tricalcium phosphate (β‐TCP) content and retarded initial burst release. Particularly, scaffold doped with hydroxypropyl methylcellulose (HPMC) displayed optimal osteogenic capability. The results indicated that the PDLLA/PCL/β‐TCP complex scaffold along with HPMC‐coating and rhBMP‐2 loading was a promising candidate for bone regeneration. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40951.     

Influence of hydroxyapatite and BMP‐2 on bioactivity and bone tissue formation ability of electrospun PLLA nanofibers

An excellent bioactive scaffold material which could induce and promote new bone formation is essential in the bone repair field. In this study, the bioactive material hydroxyapatite (HA) and the bone morphogenetic protein‐2 (BMP‐2) were added to poly‐l‐lactic acid (PLLA) using the electrospinning method. Scanning electron microscopy investigations performed on four different fiber scaffolds, PLLA, PLLA/HA, PLLA/BMP‐2 and PLLA/HA/BMP‐2, revealed that the fibers of all scaffolds are closely interwoven, and the presence of large interconnected voids between the fibers, resulting in a three‐dimensional porous network structure that was similar to the structure of the extracellular matrix of healthy bones. In the MG63 cell culture growth experiments, the composite scaffold material PLLA/HA/BMP‐2 showed a higher bioactivity than the other three scaffold materials. The four scaffold materials were implanted in rabbits’ tibia for 30 and 90 days. The results of the animal experiments indicate that the capability of the PLLA/HA/BMP‐2 composite to induce and promote bone tissue formation was better compared with PLLA/HA or PLLA/BMP‐2, suggesting that PLLA combined with HA/BMP‐2 is a promising material for bone tissue repair. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42249.     

Bioprinting a cell-laden matrix for bone regeneration: A focused review

Although many efforts have been made to regenerate the bone lesions, existing challenges can be mitigated through the development of tissue engineering scaffolds. However, the weak control on the microstructure of constructs, limitation in preparation of patient-specific and multilayered scaffolds, restriction in the fabrication of cell-laden matrixes, and challenges in preserving the drug/growth factors' efficacy in conventional methods have led to the development of bioprinting technology for regeneration of bone defects. So in this review, conventional 3D printers are classified, then the priority of the different types of bioprinting technologies for the preparation of the cell/growth factor-laden matrixes are focused. Besides, the bio-ink compositions, including polymeric/hybrid hydrogels and cell-based bio-inks are classified according to fundamental and recent studies. Herein, different effective parameters, such as viscosity, rheological properties, cross-linking methods, biodegradation biocompatibility, are considered. Finally, different types of cells and growth factors that can encapsulate in the bio-inks to promote bone repair are discussed, and both in vitro and in vivo achievement are considered. This review provides current and future perspectives of cell-laden bioprinting technologies. The restrictions and challenges are identified, and proper strategies for the development of cell-laden matrixes and high-performance printable bio-inks are proposed.     

3D printing-assisted combinatorial approach for designing mechanically-tunable and vascular supportive nanofibrous membranes to repair perforated eardrum

Perforation of eardrum or tympanic membrane (TM) is a common clinical condition, which occurs due to infection or injury of the eardrum, and could results in varying degrees of conductive hearing loss among all ages. In this study, the authors report the combinatorial approach of designing mechanically-tunable and vascular supportive nanofibrous membranes by 3D printing-assisted electrospinning (e-spin) using polycaprolactone (PCL) and gelatin with different mass ratios suitable to repair a perforated eardrum. The physicochemical, mechanical, and biological properties of the membranes were characterized. The results show that the membrane has nanofibrous morphology with fibers are of varying size (400–600 nm in diameter) depending on processing conditions. The wettability and mechanical properties of the membrane can be tuned by regulating the gelatin content. Moreover, a biomimetic repair strategy inspired by chicken eggshell membrane, often used in wound dressings, was also presented for study and results show that the suture retention strength of the fabricated membrane can meet clinical translational requirements to promote TM healing. The vascular cell responsiveness of PCL/gelatin nanofibrous membrane was evaluated using human umbilical vein endothelial cells (HUVECs) and the results showed satisfactory biocompatibility, vascular cell responsiveness, and cell proliferation. The findings of this study demonstrate that the combinatorically engineered PCL/gelatin nanofibrous membrane has great potential for repairing perforated eardrum.     

Biocompatible scaffolds composed of chemically crosslinked chitosan and gelatin for tissue engineering

Chitosan‐based scaffolds are widely studied in tissue regeneration because of their biocompatibility and biodegradability. Scaffolds are obtained by different techniques and can be modified with other polymers allowing controlling their properties. This article discusses the assembling of three‐dimensional chitosan porous scaffolds blended with gelatin. Gelatin was used to enhance cells attachment due to the presence of cell adhesion motifs, while improving mechanical strength. 2,5‐dimethoxy‐2,5‐dihydrofurane (DHF) was used as the crosslinking agent, because it allowed to control the reaction kinetics through temperature, time and DHF concentration. The results indicate that scaffolds morphology, pore sizes and distribution, compressive moduli and biodegradation in vitro with lysozyme, can be customized with variations of gelatin content and crosslinking degree. Scaffolds were neither cytotoxic nor genotoxic for human keratinocytes, exhibiting cell–substrate interactions. Our findings demonstrated that chitosan–gelatin scaffolds crosslinked with DHF, as a new crosslinking agent, are suitable in tissue engineering applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43814.     

Hybrid biomimetic electrospun fibrous mats derived from poly(ε‐caprolactone) and silk fibroin protein for wound dressing application

To achieve excellent biofunctionality of Bombyx mori silk fibroin (SF), we explored a novel hybridization method to combine the unique properties of SF with poly(ε‐caprolactone) (PCL) electrospun fibers. The hybrid electrospun fibers demonstrate excellent hydrophilicity and biocompatibility that are important to tissue engineering applications. The biomimetic fibrous structure was fabricated by conventional electrospinning of PCL. The individual surfaces of PCL electrospun fibers were coated with silk fibroin protein using a lyophilization technique. The SF coating layers were durable which were further developed by surface modification with fibronectin to improve their biological function. The hybrid electrospun fibers show excellent support for normal human dermal fibroblast (NHDF) cells adhesion and proliferation than neat PCL fibers, while the surface‐modified hybrid electrospun fibers show significantly enhanced proliferation of NHDF cells on their surface. This study indicates the new opportunity of fabrication technique that can construct a biomimetic fibrous structure while the original function as a biomaterial remained existing. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41653.     

Electrospun vascular graft properties following femtosecond laser ablation

For polymers in tissue engineering to reach their full potential, the three‐dimensional integration of cells with scaffolds must become more complex. In vascular grafts this is particularly challenging as specific physical property requirements must be met. We apply a combination of polymer processing techniques—electrospinning and femtosecond laser ablation—to produce microchannels inside the walls of electrospun tubes providing for spatially‐controlled cell seeding. To determine if such a scaffold can provide the desired physical properties, a greater understanding of the relationship between manufacturing and mechanics is needed. As the strength of these scaffolds is an important functional component, the relative properties of single, bi‐ and tri‐layer combinations produced using different solvents were compared. The effect of fiber layer thickness was also investigated. The thickness of the hexafluorisopropanol‐derived layer dominated the overall scaffold properties regardless of the nature of the other two layers. Although laser‐machined microchannels had substantial effects on single layer and some of the bilayers, in the “final” trilayer scaffold, little effect on mechanical properties was observed. The concept of “vascular wall engineering” could successfully produce trilayer composite scaffolds that maintain the targeted mechanical properties while allowing intricate, three‐dimensional cell seeding. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Biomimetic phospholipid polymers for suppressing adsorption of saliva proteins on dental hydroxyapatite substrate

To prevent infectious diseases induced by the adhesion of microorganisms and their metabolic products to dental implants, saliva protein adsorption, which induces the plaque deposition to the intraoral substrates should be inhibited. We used a water-soluble 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer to modify the surface of hydroxyapatite (HAp) substrate, the main component of dental implant surface. The MPC polymer containing a catechol group at the terminal of polymer chain and amino groups in the side chain was synthesized by mimicking the mussel adhesive protein. The MPC polymer containing 2% of the primary amino groups showed effective adhesion to the HAp substrate. Mucin, the dental plaque protein, adsorbs on the HAp surface; however, the MPC polymer modification could reduce this adsorption amount by more than 98% compared to the original HAp substrate surface. Thus, the treatment of the MPC polymer has potential to reduce oral infection due to plaque deposition.     

Immobilization of silk fibroin on the surface of PCL nanofibrous scaffolds for tissue engineering applications

Poly(?‐caprolactone) (PCL) is explored in tissue engineering (TE) applications due to its biocompatibility, processability, and appropriate mechanical properties. However, its hydrophobic nature and lack of functional groups in its structure are major drawbacks of PCL‐based scaffolds limiting appropriate cell adhesion and proliferation. In this study, silk fibroin (SF) was immobilized on the surface of electrospun PCL nanofibers via covalent bonds in order to improve their hydrophilicity. To this end, the surface of PCL nanofibers was activated by ultraviolet (UV)–ozone irradiation followed by carboxylic functional groups immobilization on their surface by their immersion in acrylic acid under UV radiation and final immersion in SF solution. Furthermore, morphological, mechanical, contact angle, and Attenuated total reflection‐ Fourier transform infrared (ATR‐FTIR) were measured to assess the properties of the surface‐modified PCL nanofibers grafted with SF. ATR‐FTIR results confirmed the presence of SF on the surface of PCL nanofibers. Moreover, contact angle measurements of the PCL nanofibers grafted with SF showed the contact angle of zero indicating high hydrophilicity of modified nanofibers. In vitro cell culture studies using NIH 3T3 mouse fibroblasts confirmed enhanced cytocompatibility, cell adhesion, and proliferation of the SF‐treated PCL nanofibers. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46684.     

Novel bilayer electrospun poly(caprolactone)/ silk fibroin/ strontium carbonate fibrous nanocomposite membrane for guided bone regeneration

In this study, a thin layer with a thickness of about 120 μm of poly(caprolactone) (PCL) was fabricated by electrospinning method. Then, a fibrous nanocomposite composed of PCL/silk fibroin/strontium carbonate (PCL/SF/SrCO₃) was electrospun on the prepared layer. Then, they were characterized. The mechanical properties, water uptake, degradation rate, wettability, porosity, and bioactivity of the electrospun membrane were scrutinized in vitro. Cytotoxicity of the samples was assessed by using osteoblast-like cells (SAOS-2) and L929 fibroblasts. Moreover, the cell adhesion, alkaline phosphatase (ALP) activity, and calcium deposition through alizarin red staining were conducted. Results revealed that the bilayer structure doubled the optimum mechanical properties and the addition of SrCO₃ up to 15%–20% increased ALP activity, calcium deposition, and bioactivity. According to the results, the nanofibrous bilayer membrane containing 20 wt% SrCO₃, 20 wt% SF, and 60 wt% PCL was chosen as the optimum sample. Therefore, this membrane could be applied in guided bone regeneration (GBR).     

Chitosan/silk fibroin composite scaffolds for wound dressing

Three‐dimensional (3D) chitosan/silk fibroin (CS/SF) porous composite scaffolds have been prepared by simply coating a thin layer of CS onto spunlaced SF scaffolds via hydrogen‐bonding assembly technique, and they were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), X‐ray diffraction (XRD), and mechanical property measurements. The results show that porous scaffolds have a pore diameter around 50–200 μm, and improved mechanical property compared with SF, resulting from strong intermolecular hydrogen bonding interactions between CS and SF, together with the maintained β‐sheet structure of SF. The medical and biological properties of the composite scaffolds were further evaluated. The results demonstrate that they possess good biocompatibility and a broad spectrum of antimicrobial properties. The in vivo animal experiments show that the composite scaffolds promote skin regeneration of rats without any teratogenic effect and inflection, thus they are very promising in the application of wound dressings. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42503.     

Crystallinity,reversibility, and injectability of physically crosslinked poly(vinyl alcohol) and poly(ethylene glycol) hydrogels

Crystallite regions within a hydrogel network contribute to its mechanical strength, which is crucial for use in load-bearing applications. However, high amounts of crystallinity can negatively impact the ability for hydrogels to be injected, an attractive property that could replace the need for highly invasive surgical procedures. The reversibility of crystallinity and its lasting impact on the injectability of poly(vinyl alcohol) and poly(ethylene glycol) hydrogels was evaluated in this paper. The relative percent crystallinity in hydrogels was evaluated after storage and autoclaving in syringes in weekly intervals using X-ray diffraction. Results indicate that crystallinity increased over time and significantly decreased after autoclaving for all samples, where postautoclaved samples contained comparable crystallinity percentages to freshly made gels (p > 0.05). Injectability was evaluated using calculated viscosity. Aged samples were able to be injected after autoclaving, yet there was no determination established between viscosity and storage times based on the data. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48706.     

Conductive multichannel PCL/gelatin conduit with tunable mechanical and structural properties for peripheral nerve regeneration

Peripheral nerve injuries remain among the most challenging medical issues despite numerous efforts to devise methods in fabrication of nerve conduits to functionally regenerate axonal defects. In this regard, the current study offers a holistic perspective in design by considering the mechanical, topographical and structural aspects which are crucial for a successful nerve guide conduit. Poly(e-caprolactone) and gelatin were employed to serve this purpose in the form of dual-electrospun films which were rolled and later shaped the assembly of a multichannel conduit. Polyaniline/graphene (PAG) nanocomposite was incorporated to endow the conduit with conductive properties. FTIR analysis, water contact angle measurements, and SEM observations as well as mechanical and conductivity tests were used to evaluate the properties of the conduits. In addition, MTT assay was conducted to assess the proliferation of rat bone marrow-derived mesenchymal stem cells cultured on the films. Incorporating 2% PAG proved to have superior cell support and proliferation, while guaranteeing electrical conductivity of 10.8 × 10⁻⁵ S/cm and remarkable tensile strength of 3.52 ± 1.3 MPa and 14.12 ± 3.1 MPa for wet and dry conditions, respectively. Overall, the observed results highlight the great potential of the fabricated conduit to be used as a candidate for peripheral nerve defects.     

Fabrication and characterization of electrospun psyllium husk-based nanofibers for tissue regeneration

The present study reports for first time the blending of psyllium husk (PH) powder/gelatin (G) in the polymer-rich composition of polyvinyl alcohol (PVA) to make an electrospinnable solution. The composite was prepared in 3 different ratios viz., 100% (wt/wt) (PVA + PH), 75% + 25% (PVA + 75PH + 25G) (wt/wt) and 50% + 50% (PVA + 50PH + 50G) (wt/wt) in 6% PVA solution. Optimum electrospinning parameters were evaluated for all the prepared blends. The fabricated nanofibers were characterized by scanning electron microscopy (SEM), attenuated total reflectance-Fourier transform infrared, differential scanning calorimetry, porosity percentage, and fiber orientation using ImageJ software. A qualitative in vitro degradation study at room temperature is supported by SEM images. The cellular interactions were characterized by MTT assay of NIH-3T3 fibroblast cells for 2 and 4 days with an optimum cell growth of >50% by fourth day of culture and long-term cultivation of L929-RFP cells was observed for 10 days. The nanofibers were formed in the range of 49–600 nm. PVA + 75PH + 25G when cultured with L929-RFP cells exhibited highest fluorescence intensity and thus supported cellular proliferation significantly. Based on the results obtained from various analyses, we anticipate that fabricated psyllium-based nanofiber can be used as a promising candidate for wound healing and other biomedical applications.