Biopolymers for Tissue Engineering: Crosslinking, Printing Techniques, and Applications

Currently, tissue engineering has been dedicated to the development of 3D structures through bioprinting techniques that aim to obtain personalized, dynamic, and complex hydrogel 3D structures. Among the different materials used for the fabrication of such structures, proteins and polysaccharides are the main biological compounds (biopolymers) selected for the bioink formulation. These biomaterials obtained from natural sources are commonly compatible with tissues and cells (biocompatibility), friendly with biological digestion processes (biodegradability), and provide specific macromolecular structural and mechanical properties (biomimicry). However, the rheological behaviors of these natural-based bioinks constitute the main challenge of the cell-laden printing process (bioprinting). For this reason, bioprinting usually requires chemical modifications and/or inter-macromolecular crosslinking. In this sense, a comprehensive analysis describing these biopolymers (natural proteins and polysaccharides)-based bioinks, their modifications, and their stimuli-responsive nature is performed. This manuscript is organized into three sections: (1) tissue engineering application, (2) crosslinking, and (3) bioprinting techniques, analyzing the current challenges and strengths of biopolymers in bioprinting. In conclusion, all hydrogels try to resemble extracellular matrix properties for bioprinted structures while maintaining good printability and stability during the printing process.

Multicore-shell MnO2@Ppy@N-doped porous carbon nanofiber ternary composites as electrode materials for high-performance supercapacitors

In this study, a multicore-shell ternary composite electrode material (MnO₂@Ppy@NPCNFs) with excellent electrochemical performances was prepared by using surface modification, in which core-shell Ppy@N-doped porous carbon nanofibers (Ppy@NPCNFs) with large specific surface area and high conductivity were used as the substrate (a multicore layer), and MnO₂ was loaded on the substrate by hydrothermal synthesis to form a shell layer, further improving the SC of electrode material. The parameters of hydrothermal growth of MnO₂ on Ppy@NPCNFs were explored by means of the control variable method and response surface methodology, and the optimal parameters were predicted and verified. Electrochemical test results showed that the SC of MnO₂@Ppy@NPCNFs prepared under the optimal reaction parameters was as high as 595.77 F g^-1, and its capacitance retention was 96.2 % after 1000 cycles. Moreover, a symmetric supercapacitor prepared with the optimal multicore-shell electrode showed an energy density of 9.36 Wh kg^-1 at a power density of 1000 W kg^-1 and a retention rate of 92.46 % after 1000 cycles, indicating the promising application of multicore-shell ternary composite electrode material in high-performance supercapacitors.

3D Bioprinting of Gelatin-Xanthan Gum Composite Hydrogels for Growth of Human Skin Cells

In recent years, bioprinting has attracted much attention as a potential tool for generating complex 3D biological constructs capable of mimicking the native tissue microenvironment and promoting physiologically relevant cell-cell and cell-matrix interactions. The aim of the present study was to develop a crosslinked 3D printable hydrogel based on biocompatible natural polymers, gelatin and xanthan gum at different percentages to be used both as a scaffold for cell growth and as a wound dressing. The CellInk Inkredible 3D printer was used for the 3D printing of hydrogels, and a glutaraldehyde solution was tested for the crosslinking process. We were able to obtain two kinds of printable hydrogels with different porosity, swelling and degradation time. Subsequently, the printed hydrogels were characterized from the point of view of biocompatibility. Our results showed that gelatin/xanthan-gum bioprinted hydrogels were biocompatible materials, as they allowed both human keratinocyte and fibroblast in vitro growth for 14 days. These two bioprintable hydrogels could be also used as a helpful dressing material.

Electrospinning of chitosan-based nanofibers: from design to prospective applications

Chitosan is a biopolymer originating from renewable resources, with great properties which make it an attractive candidate for plenty of applications of contemporary interest. By manufacturing chitosan into nanofibers using the electrospinning method, its potential is amplified due to the enhancement of the active surface and the low preparation cost. Many attempts were made with the aim of preparing chitosan-based nanofibers with controlled morphology targeting their use for tissue engineering, wound healing, food packaging, drug delivery, air and water purification filters. This was a challenging task, which resulted in a high amount of data, sometimes with apparent contradictory results. In this light, the goal of the paper is to present the main routes reported in the literature for chitosan electrospinning, stressing the advantages and disadvantages of each of them. Special emphasis is placed on the influence of various electrospinning parameters on the morphological characteristics of the fibers and their suitability for distinct applications.

Electrospun Biomaterials from Chitosan Blends Applied as Scaffold for Tissue Regeneration

Our objective in this work was to summarize the main results obtained in processing pure chitosan and chitosan/hyaluronan complex in view of biomedical applications, taking advantage of their original properties. In addition, an electrospinning technique was selected to prepare nanofiber mats well adapted for tissue engineering in relation to the large porosity of the materials, allowing an exchange with the environment. The optimum conditions for preparation of purified and stable nanofibers in aqueous solution and phosphate buffer pH = 7.4 are described. Their mechanical properties and degree of swelling are given. Then, the prepared biomaterials are investigated to test their advantage for chondrocyte development after comparison of nanofiber mats and uniform films. For that purpose, the adhesion of cells is studied by atomic force microscopy (AFM) using single-cell force spectroscopy, showing the good adhesion of chondrocytes on chitosan. At the end, adhesion and proliferation of chondrocytes in vitro are examined and clearly show the interest of chitosan nanofiber mats compared to chitosan film for potential application in tissue engineering.

Microenvironment Influence of a Novel Bioengineered Wound Product, APIS®: A Preliminary In Vitro Analysis of Inflammatory Marker and Growth Factor Secretion

Objective

Preliminary biological activity assessment of a novel bioengineered wound product (APIS®, SweetBio, Inc., Memphis, TN, USA), a synthesis of gelatin, Manuka honey, and hydroxyapatite, with in vitro indications to protect, instill balance to, and progress the wound microenvironment. Approach. The biological activity the bioengineered wound product (BWP) elicits on human cells in vitro was assessed by evaluating matrix metalloproteinase- (MMP-) related proteins expressed by macrophages and secretion of growth factors in fibroblasts. Cells were cultured with no treatment, stimulated with lipopolysaccharides (LPS), or seeded directly on the BWP for 24 hours. An additional 72-hour time point for the BWP was assessed to determine if the BWP maintained its activity compared to itself at 24 hours. Cell culture supernatants were assayed to quantify secreted protein levels.

Results

MMP-9 secretion from macrophages seeded on the BWP were nondetectable (P < 0.01), while a tissue inhibitor of MMP (TIMP-1) was detected. This decreased the overall MMP-9/TIMP-1 ratio secreted from macrophages seeded on the BWP compared to the controls. Additionally, the secretion of prohealing growth factors such as basic fibroblast growth factor (FGFb) and vascular endothelial growth factor (VEGF) was observed.

Conclusion

Results from this preliminary in vitro evaluation suggest that the BWP has the potential to instill balance to the wound microenvironment by reducing the MMP-9/TIMP-1 ratio secretion from macrophages and progress previously stalled chronic wounds towards healing by triggering the release of growth factors from fibroblasts.

Cinnamon extract loaded electrospun chitosan/gelatin membrane with antibacterial activity

This study develops chitosan/gelatin nanofiber membranes with sustained release capacity to prevent infection by delivering cinnamon extract (CE) in the implanted site. The effects of the incorporation of CE content (2-6%) on the properties of the nanofibers were evaluated. Morphological studies using SEM indicated that loading the extract did not affect the average diameter of nanofiber mats, which remained around 140-170 nm. TGA and FTIR spectroscopy results confirmed successful CE loading. Furthermore, the results showed that incorporating extract into the nanofibers enhanced their degradation behavior, antibacterial activity, and biocompatibility. Cultured cells attached to and proliferate on the nanofiber membrane with high cell viability capacity until the CE content reached 4%. The extract release profile consisted of a burst release in the first 6 h, followed by a controlled release in the next 138 h. Therefore, CE loaded chitosan/gelatin nanofiber is an excellent construct for biomedical applications.

PEGylated curcumin-loaded nanofibrous mats with controlled burst release through bead knot-on-spring design

APEGylatedcurcumin (PCU) loaded electrospuns based on poly(ε-caprolactone) (PCL) andpolyvinyl alcohol (PVA) were fabricated for wound dressing applications. The main reason for this wound dressing design is antibacterialactivity enhancement, and wound exudates management. PEGylation increases curcuminsantibacterial properties and PVA can help exudates management. For optimal wound dressing, first, response surface methodology (RSM) was applied to optimize the electrospinning parameters to achieve appropriate nanofibrous mats. Then a three-layer electrospun was designed by considering the water absorbability, PCU release profile as well as antibacterial and biocompatibility of the final wound dressing. The burst release in controlled release systems could be evaluated for prevention of the higher initial drug release and control the effective life time. The PCU release results illustrated that the bead knot plays a positive role in controlling the release profile andby increase in the number of beads per unit area from 3000 to 9000 mm^-2,the PCU burst release will be reduced; Also in vitro studies show that optimized three-layer dressing based on PCL/PVA/PCU can support water vapour transmission rate in optimal range and also absorb more than three times exudates in comparison with mono-layerdressing. Antibacterial tests show that the electrospun wound dressing containing 5% PCU exhibits100% antibacterial activityas well as cell viability level within an acceptable range.

Fabrication of Dissolvable Microneedle Patches Using an Innovative Laser-Cut Mould Design to Shortlist Potentially Transungual Delivery Systems: In Vitro Evaluation

There has been a great interest towards transungual delivery systems due to limited drug penetration for the treatment of nail diseases. More important, antifungal oral medicaments used may cause serious side effects including liver damage. Therefore, we propose non-oral dissolvable microneedle (MN) patch to strike the poor permeability of the nail. We report the design of MN patch mould using a laser-cutting machine and solvent casting of several hydrophilic polymers to fabricate these MN patches. Formulations were evaluated for their in vitro release and penetration properties and selected based on physical characterization for compatibility (differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD)), dimension repeatability and drug content uniformity. A 72-array of cone-shaped MN patch mould was successfully constructed on polymethylmethacrylate sheets. Interval and frequency of laser exposure were pivotal to determine the needle sharpness, attained unexpectedly at a low level of circa 30 μm. F1 platform of polyvinyl alcohol, kollicoat IR®, ethylene glycol and gelatin showed circa 74% penetration of methylhydroxy-4-benzoate (F1(A)) over 24 h, whereas F2 (same as F1-A with the addition of poloxamer 338) resulted in an almost 42% of this drug retention in the bovine hoof (24 h). Both formulations are likely to be useful for onychomycosis treatment. F1 polymers also afford enhanced permeability (almost 73.5% after 24 h) of terbinafine hydrochloride into the hoof (F1(B)). However, F3 (chitosan, gelatin and ethylene glycol) presents the prospect of developing MN patch for this drug with almost complete hoof penetration (circa 96.3% after 24 h). All medicated formulations have shown similar mechanical properties after ageing for 1 year under dry conditions.

Cold atmospheric plasma as a promising approach for gelatin immobilization on poly(ε-caprolactone) electrospun scaffolds

Poly(Ɛ-caprolactone) (PCL) is a biocompatible polymer with a high potential to be used in tissue engineering especially in tight tissues. In the current study, cold atmospheric plasma (CAP) is used as a promising method for immobilization of gelatin as a functional biomacromolecule on PCL nanofibrous substrates. The CAP surface modification leads to oxidation of chemical groups existing on the PCL surface without doing any damage to the bulk properties of biomaterials for gelatin biomacromolecule grafting. The water contact angle (WCA) of the CAP-treated surface and gelatin-grafted PCL using CAP indicates an effective increment in the hydrophilicity of the PCL surface. Also to achieve the highest levels of gelatin grafting on the PCL surface, two different grafting methods and gelatin concentration diversity are utilized in the grafting process. The immobilization of gelatin biomacromolecules onto the CAP surface-modified PCL nanofibers is investigated using scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). The gelatin-modified PCL substrates revealed uniform nanofibrous morphology with increased average fiber diameter. The results of FTIR spectra, including hydroxyl groups, NH groups, and amide II of gelatin-grafting peaks, confirm the gelatin immobilization on the surface of nanofibers. The metabolic activity of cultured mesenchymal stem cells (MSCs) on the surface-modified scaffolds is evaluated using MTT analysis (P ≤ 0.05). The results of metabolic activity and also SEM and DAPI staining observations indicate proper attachment on the surface and viability for MSCs on the surface-immobilized nanofibrous scaffolds. Therefore, CAP treatment would be an effective method for biomacromolecule immobilization on nanofibers towards the enhancement of cell behavior.

Preparation and Characterization of Electrospun Colon-Specific Delivery System for Quercetin and Its Antiproliferative Effect on Cancer Cells

To improve the oral bioavailability of quercetin (Q) and achieve colon-specific release, a core-sheath electrospun fiber mat containing Q-loaded chitosan nanoparticle (Q-loaded EFM) was developed in this study. The nanoparticle was first fabricated, and its antioxidant activity was as effective as free Q. Then the uniform Q-loaded EFM was obtained using response surface methodology optimization, and its core-sheath structure was characterized by confocal laser scanning microscopy. In vitro release kinetics confirmed the colon targeting profile, and the release rate of Q varied inversely with fiber diameter. The data of Cell Counting Kit-8 suggested Q-loaded EFM inhibited the proliferation of Caco-2 cells in a dose- and time-dependent manner with an IC50 of 4.36, 2.81, and 2.01 mg/mL after 24, 48, and 72 h, respectively, and it was caused by arresting cell cycle on G₀/G₁ phase and triggering apoptotic cell death. This study suggests that the Q-loaded EFM represents a promising form in the oral therapy of colon disorders.

Tailoring the gelatin/chitosan electrospun scaffold for application in skin tissue engineering: an in vitro study

The nanofibrous structure containing protein and polysaccharide has good potential in tissue engineering. The present work aims to study the role of chitosan in gelatin/chitosan nanofibrous scaffolds fabricated through electrospinning process under optimized condition. The performance of chitosan in gelatin/chitosan nanofibrous scaffolds was evaluated by mechanical tests, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and in vitro cell culture on scaffolds with different gelatin/chitosan blend ratios. To assay the influence of chitosan ratio on biocompatibility of the electrospun gelatin/chitosan scaffolds for skin tissue engineering, the culturing of the human dermal fibroblast cells (HDF) on nanofibers in terms of attachment, morphology and proliferation was evaluated. Morphological observation showed that HDF cells were attached and spread well on highly porous gelatin/chitosan nanofibrous scaffolds displaying spindle-like shapes and stretching. The fibrous morphologies of electrospun gelatin/chitosan scaffolds in culture medium were maintained during 7 days. Cell proliferation on electrospun gelatin/chitosan scaffolds was quantified by MTS assay, which revealed the positive effect of chitosan content (around 30%) as well as the nanofibrous structure on the biocompatibility (cell proliferation and attachment) of substrates.

Encapsulation of Bioactive Compound in Electrospun Fibers and Its Potential Application

Electrospinning is a simple and versatile encapsulation technology. Since electrospinning does not involve severe conditions of temperature or pressure or the use of harsh chemicals, it has great potential for effectively entrapping and delivering bioactive compounds. Recently, electrospinning has been used in the food industry to encapsulate bioactive compounds into different biopolymers (carbohydrates and proteins), protecting them from adverse environmental conditions, maintaining the health-promoting properties, and achieving their controlled release. Electrospinning opens a new horizon in food technology with possible commercialization in the near future. This review summarizes the principles and the types of electrospinning processes. The electrospinning of biopolymers and their application in encapsulating of bioactive compounds are highlighted. The existing scope, limitations, and future prospects of electrospinning bioactive compounds are also presented.

Evaluation of gelatin-hyaluronic acid composite hydrogels for accelerating wound healing

Excellent wound dressings maintain a warm and moist environment, thus accelerating wound healing. In this study, we cross-linked gelatin and hyaluronic acid with ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride in different ratios (gelatin/hyaluronic acid = 8:2, gelatin/hyaluronic acid = 5:5, gelatin/hyaluronic acid = 2:8), and explored the effects and mechanisms of gelatinhyaluronic acid hydrogels on wound healing. This was done by examining dressing properties, such as fluid uptake ability, water vapor transmission rate, and the rate of water evaporation. We further verified biological function by using in vitro and in vivo wound models. The hydrogels display appropriate fluid uptake ability and good water vapor transmission rate and rate of water evaporation all of which can provide an adequate moisture environment for wound healing. Cell cytotoxicity and proliferation tests show that the hydrogels have no cytotoxicity, furthermore, gelatin/hyaluronic acid = 8:2 hydrogels have the potential to promote cell proliferation. Animal wound models demonstrate that the hydrogels can effectively promote wound healing in vivo, in particular, the gelatin/hyaluronic acid = 8:2 group which promoted the most rapid healing. Accordingly, gelatin-hyaluronic acid dressings, especially the gelatin/hyaluronic acid = 8:2 hydrogels, have a promising outlook for clinical applications in wound healing.

Designing and fabrication of curcumin loaded PCL/PVA multi-layer nanofibrous electrospun structures as active wound dressing

Active wound dressings play a significant role in burn and chronic wound treatment. In this study, electrospinning process is used to fabricate a novel three-layer active wound dressing based on ε-polycaprolactone (PCL), polyvinylalcohol (PVA), and curcumin (CU) as a biologically active compound. The main purpose for developing such a system is to control wound exudates, which remains a challenge, as well as enjoying the anti-bacterial property. Electrospinning process parameters are optimized by response surface methodology to achieve appropriate nanofibrous electrospun mats, and then, a three-layer dressing has been designed in view of water absorbability, anti-bacterial, and biocompatibility characteristics of the final dressing. The results illustrate that a three-layer dressing based on PCL/curcumin containing PVA as a middle layer with optimized thickness which is placed over the incision, absorbs three times exudates in comparison with pristine dressing. Anti-bacterial tests reveal that the dressing containing 16% curcumin exhibits anti-bacterial activity without sacrificing the acceptable level of cell viability.

Preparation of Pure and Stable Chitosan Nanofibers by Electrospinning in the Presence of Poly(ethylene oxide)

Electrospinning was employed to obtain chitosan nanofibers from blends of chitosans (CS) and poly(ethylene oxide) (PEO). Blends of chitosan (MW (weight-average molecular weight) = 102 kg/mol) and PEO (M (molecular weight) = 1000 kg/mol) were selected to optimize the electrospinning process parameters. The PEO powder was solubilized into chitosan solution at different weight ratios in 0.5 M acetic acid. The physicochemical changes of the nanofibers were determined by scanning electron microscopy (SEM), swelling capacity, and nuclear magnetic resonance (NMR) spectroscopy. For stabilization, the produced nanofibers were neutralized with K₂CO₃ in water or 70% ethanol/30% water as solvent. Subsequently, repeated washings with pure water were performed to extract PEO, potassium acetate and carbonate salts formed in the course of chitosan nanofiber purification. The increase of PEO content in the blend from 20 to 40 w% exhibited bead-free fibers with average diameters 85 ± 19 and 147 ± 28 nm, respectively. Their NMR analysis proved that PEO and the salts were nearly completely removed from the nanostructure of chitosan, demonstrating that the adopted strategy is successful for producing pure chitosan nanofibers. In addition, the nanofibers obtained after neutralization in ethanol-aqueous solution has better structural stability, at least for six months in aqueous solutions (phosphate buffer (PBS) or water).