Development of chitosan-tripolyphosphate non-woven fibrous scaffolds for tissue engineering application

Porous Chitosan Hydrogels Produced by Physical Crosslinking: Physicochemical, Structural, and Cytotoxic Properties

Chitosan hydrogels are biomaterials with excellent potential for biomedical applications. In this study, chitosan hydrogels were prepared at different concentrations and molecular weights by freeze-drying. The chitosan sponges were physically crosslinked using sodium bicarbonate as a crosslinking agent. The X-ray spectroscopy (XPS and XRD diffraction), equilibrium water content, microstructural morphology (confocal microscopy), rheological properties (temperature sweep test), and cytotoxicity of the chitosan hydrogels (MTT assay) were investigated. XPS analysis confirmed that the chitosan hydrogels obtained were physically crosslinked using sodium bicarbonate. The chitosan samples displayed a semi-crystalline nature and a highly porous structure with mean pore size between 115.7 ± 20.5 and 156.3 ± 21.8 µm. In addition, the chitosan hydrogels exhibited high water absorption, showing equilibrium water content values from 23 to 30 times their mass in PBS buffer and high thermal stability from 5 to 60 °C. Also, chitosan hydrogels were non-cytotoxic, obtaining cell viability values ≥ 100% for the HT29 cells. Thus, physically crosslinked chitosan hydrogels can be great candidates as biomaterials for biomedical applications.

Measuring Physical Properties of Electrospun Nanofiber Mats for Different Biomedical Applications

Electrospun nanofiber mats are nowadays often used for biotechnological and biomedical applications, such as wound healing or tissue engineering. While most studies concentrate on their chemical and biochemical properties, the physical properties are often measured without long explanations regarding the chosen methods. Here, we give an overview of typical measurements of topological features such as porosity, pore size, fiber diameter and orientation, hydrophobic/hydrophilic properties and water uptake, mechanical and electrical properties as well as water vapor and air permeability. Besides describing typically used methods with potential modifications, we suggest some low-cost methods as alternatives in cases where special equipment is not available.

Development and in vitro assessment of a bi-layered chitosan-nano-hydroxyapatite osteochondral scaffold

An innovative approach was developed to engineer a multi-layered chitosan scaffold for osteochondral defect repair. A combination of freeze drying and porogen-leaching out methods produced a porous, bioresorbable scaffold with a distinct gradient of pore size (mean = 160-275 μm). Incorporation of 70 wt% nano-hydroxyapatite (nHA) provided additional strength to the bone-like layer. The scaffold showed instantaneous mechanical recovery under compressive loading and did not delaminate under tensile loading. The scaffold supported the attachment and proliferation of human mesenchymal stem cells (MSCs), with typical adherent cell morphology found on the bone layer compared to a rounded cell morphology on the chondrogenic layer. Osteogenic and chondrogenic differentiation of MSCs preferentially occurred in selected layers of the scaffold in vitro, driven by the distinct pore gradient and material composition. This scaffold is a suitable candidate for minimally invasive arthroscopic delivery in the clinic with potential to regenerate damaged cartilage and bone.

Stimuli-responsive electrospun nanofibers based on PNVCL-PVAc copolymer in biomedical applications

Poly(N-vinylcaprolactam) (PNVCL) is a suitable alternative for biomedical applications due to its biocompatibility, biodegradability, non-toxicity, and showing phase transition at the human body temperature range. The purpose of this study was to synthesize a high molecular weight PNVCL-PVAc thermo-responsive copolymer with broad mass distribution suitable for electrospun nanofiber fabrication. The chemical structure of the synthesized materials was detected by FTIR and ¹HNMR spectroscopies. N-Vinyl caprolactam/vinyl acetate copolymers (159,680 molecular weight (g/mol) and 2.51 PDI) were synthesized by radical polymerization. The phase transition temperature of N-vinyl caprolactam/vinyl acetate copolymer was determined by conducting a contact angle test at various temperatures (25, 26, 28, and 30 [Formula: see text]). The biocompatibility of the nanofibers was also evaluated, and both qualitative and quantitative results showed that the growth and proliferation of 929L mouse fibroblast cells increased to 80% within 48 h. These results revealed that the synthesized nanofibers were biocompatible and not cytotoxic. The results confirmed that the synthesized copolymers have good characteristics for biomedical applications.

Electrospun Nanofibers of Natural and Synthetic Polymers as Artificial Extracellular Matrix for Tissue Engineering

Many types of polymer nanofibers have been introduced as artificial extracellular matrices. Their controllable properties, such as wettability, surface charge, transparency, elasticity, porosity and surface to volume proportion, have attracted much attention. Moreover, functionalizing polymers with other bioactive components could enable the engineering of microenvironments to host cells for regenerative medical applications. In the current brief review, we focus on the most recently cited electrospun nanofibrous polymeric scaffolds and divide them into five main categories: natural polymer-natural polymer composite, natural polymer-synthetic polymer composite, synthetic polymer-synthetic polymer composite, crosslinked polymers and reinforced polymers with inorganic materials. Then, we focus on their physiochemical, biological and mechanical features and discussed the capability and efficiency of the nanofibrous scaffolds to function as the extracellular matrix to support cellular function.

Fibrous bone tissue engineering scaffolds prepared by wet spinning of PLGA

Having a self-healing capacity, bone is very well known to regenerate itself without leaving a scar. However, critical size defects due to trauma, tumor, disease, or infection involve bone graft surgeries in which complication rate is relatively at high levels. Bone tissue engineering appears as an alternative for grafting. Fibrous scaffolds are useful in tissue engineering applications since they have a high surface-to-volume ratio, and adjustable, highly interconnected porosity to enhance cell adhesion, survival, migration, and proliferation. They can be produced in a wide variety of fiber sizes and organizations. Wet spinning is a convenient way to produce fibrous scaffolds with consistent fiber size and good mechanical properties. In this study, a fibrous bone tissue engineering scaffold was produced using poly(lactic-co-glycolic acid) (PLGA). Different concentrations (20%, 25%, and 30%) of PLGA (PLA:PGA 75:25) (Mw = 66,000-107,000) were wet spun using coagulation baths composed of different ratios (75:25, 60:40, 50:50) of isopropanol and distilled water. Scanning electron microscopy (SEM) and in vitro degradation studies were performed to characterize the fibrous PLGA scaffolds. Mesenchymal stem cells were isolated from rat bone marrow, characterized by flow cytometry and seeded onto scaffolds to determine the most appropriate fibrous structure for cell proliferation. According to the results of SEM, degradation studies and cell proliferation assay, 20% PLGA wet spun in 60:40 coagulation bath was selected as the most successful condition for the preparation of wet-spun scaffolds. Wet spinning of different concentrations of PLGA (20%, 25%, 30%) dissolved in dichloromethane using different isopropanol:distilled water ratios of coagulation baths (75:25, 60:40, 50:50) were shown in this study.

Multi-functional carboxylic acids for chitosan scaffold

In general, CS scaffold is prepared by lyophilizing CS hydrogel which traditionally can be prepared by dissolving CS in acetic acid and crosslinking with dialdehyde. However, this method expresses unpleasant odor and toxicity leading to obstruct the practical applications. Here, the aqueous solution of multi-functional carboxylic acids is considered as the alternative and ordorless solvents to provide dual functions, i.e. (i) protonation of CS for the dissolution, and (ii) providing the preferable structure to give crosslink networks under amide bond through the conjugation reaction. The present work demonstrates the potential use of multi-functional carboxylic acids for preparation of CS scaffold and shows the tunable physicochemical and mechanical properties. The work also extends to the basic studies on biological properties to propose as the potential material for dental tissue engineering.

On the Correlation between the Microscopic Structure and Properties of Phosphate-Cross-Linked Chitosan Gels

Ionic chitosan gels fabricated using multivalent anions, tripolyphosphate (TPP) or pyrophosphate (PPi), respectively, have been investigated as potential biomaterials to be used in tissue engineering. Starting from the hypothesis that the polymer mesh texture at the microscale affects the final performance of the resulting materials, an innovative image analysis approach is presented in the first part of the article, which is aimed at deriving quantitative information from transmission electron microscopy images. The image analysis of the (more extended) central area of the gel networks revealed differences between both the cross-linking densities and pore size distributions of the two systems, the TPP gels showing a higher connectivity. Chitosan-TPP gels showed a limited degradation in simulated physiological media up to 6 weeks, reasonably ascribed to the texture of the (more extended) central area of the gels, whereas PPi counterparts degraded almost immediately. The release profiles and the calculation of diffusion coefficients for bovine serum albumin and cytochrome c, herein used as model payloads, indicated a different release behavior depending on the polymer network homogeneity/inhomogeneity and molecular weight of loaded molecules. This finding was ascribed to the marked inhomogeneity of the PPi gels (at variance with the TPP ones), which had been demonstrated in our previous work. Finally, thorough in vitro studies demonstrated good biocompatibility of both chitosan gels, and because of this feature, they can be used as suitable scaffolds for cellular colonization and metabolic activity.

Injectable nanosilica-chitosan microparticles for bone regeneration applications

This study was aimed at assessing the effects of silica nanopowder incorporation into chitosan-tripolyphosphate microparticles with the ultimate goal of improving their osteogenic properties. The microparticles were prepared by simple coacervation technique and silica nanopowder was added at 0% (C), 2.5% (S1), 5% (S2) and 10% (S3) (w/w) to chitosan. We observed that this simple incorporation of silica nanopowder improved the growth and proliferation of osteoblasts along the surface of the microparticles. In addition, the composite microparticles also showed the increased expression of alkaline phosphatase and osteoblast specific genes. We observed a significant increase ( p < 0.05) in the expression of alkaline phosphatase by the cells growing on all sample groups compared to the control (C) groups at day 14. The morphological characterization of these microparticles through scanning electron microscopy showed that these microparticles were well suited to be used as the injectable scaffolds with perfectly spherical shape and size. The incorporation of silica nanopowder altered the nano-roughness of the microparticles as observed through atomic force microscopy scans with roughness values going down from C to S3. The results in this study, taken together, show the potential of chitosan-tripolyphosphate-silica nanopowder microparticles for improved bone regeneration applications.

Highly monodisperse colloidal coacervates based on a bioactive lactose-modified chitosan: From synthesis to characterization

The present contribution aims at describing the fabrication of coacervates in the nano-size range starting from a 1-deoxylactit-1-yl chitosan (in this manuscript termed as CTL60) and the multivalent anion tripolyphosphate (TPP). Colloidal coacervates have been obtained for precise values of the molar ratio of TPP to CTL60 repeating unit. Coacervation is ensured only at pH 4.5 and not at 7.4, thus demonstrating the key role of electrostatic interactions in the stabilization of the coacervates. At a variance with chitosan, CTL60 favors the formation of highly homogeneous coacervates with very low values of the polydispersity index (PDI). Moreover, CTL60 coacervates can be freeze-dried without any cryoprotectant, they can host a model molecule and are stable up to three weeks at 4°C. Conversely, such coacervates dissolve upon increasing pH and ionic strength. By considering the bioactive polycation CTL60, the present system can be suggested as a first step in the development of innovative biologically-active nano-carriers to be used as drug delivery systems.

Microstructured chitosan/poly(γ-glutamic acid) polyelectrolyte complex hydrogels by computer-aided wet-spinning for biomedical three-dimensional scaffolds

The application of additive manufacturing principles to hydrogel processing represents a powerful route to develop porous three-dimensional constructs with a variety of potential biomedical applications, such as scaffolds for tissue engineering and three-dimensional in vitro tissue models. The aim of this study was to develop novel porous hydrogels based on a microstructured polyelectrolyte complex between chitosan and poly(γ-glutamic acid) by applying a computer-aided wet-spinning technique. The developed fabrication process was used to build up three-dimensional porous hydrogels by collecting microstructured layers made of chitosan/poly(γ-glutamic acid) on top of the other. Microstructured polyelectrolyte complex hydrogels were characterized and compared to chitosan/poly(γ-glutamic acid) porous hydrogels with similar composition prepared by conventional freeze-drying technique. Fourier transform infrared analysis confirmed the formation of an electrostatic interaction between the two processed polymers in all the developed chitosan/poly(γ-glutamic acid) hydrogels. The composition of the porous constructs as well as the employed processing techniques had a significant influence on the resulting swelling, thermal, and mechanical properties. In particular, the combination of the ionic interaction between chitosan/poly(γ-glutamic acid) and the defined internal microarchitecture of microstructured polyelectrolyte complex hydrogels provided a significant improvement of the compressive mechanical properties. Preliminary in vitro biological investigations revealed that microstructured polyelectrolyte complex hydrogels were suitable for the adhesion and proliferation of Balb/3T3 clone A31 mouse embryo fibroblasts. The encouraging results in terms of cytocompatibility and stability of the microstructure in aqueous solutions due to the ionic crosslinking suggest the investigation of the developed microstructured polyelectrolyte complex hydrogels as suitable scaffolds for three-dimensional cells’ culture.

Textile cell-free scaffolds for in situ tissue engineering applications

In this article, the benefits offered by micro-fibrous scaffold architectures fabricated by textile manufacturing techniques are discussed: How can established and novel fiber-processing techniques be exploited in order to generate templates matching the demands of the target cell niche? The problems related to the development of biomaterial fibers (especially from nature-derived materials) ready for textile manufacturing are addressed. Attention is also paid on how biological cues may be incorporated into micro-fibrous scaffold architectures by hybrid manufacturing approaches (e.g. nanofiber or hydrogel functionalization). After a critical review of exemplary recent research works on cell-free fiber based scaffolds for in situ TE, including clinical studies, we conclude that in order to make use of the whole range of favors which may be provided by engineered fibrous scaffold systems, there are four main issues which need to be addressed: (1) Logical combination of manufacturing techniques and materials. (2) Biomaterial fiber development. (3) Adaption of textile manufacturing techniques to the demands of scaffolds for regenerative medicine. (4) Incorporation of biological cues (e.g. stem cell homing factors).

Osteogenic differentiation of human mesenchymal stem cells in freeze-gelled chitosan/nano β-tricalcium phosphate porous scaffolds crosslinked with genipin

The objective of this work was to investigate material properties and osteogenic differentiation of human mesenchymal stem cells (hMSCs) in genipin (GN) crosslinked chitosan/nano β-tricalcium phosphate (CS/nano β-TCP) scaffolds, and compare the results with tripolyphosphate (TPP) crosslinked scaffolds. Porous crosslinked CS/nano β-TCP scaffolds were produced by freeze-gelation using GN (CBG scaffold) and TPP (CBT scaffold) as crosslinkers. The prepared CBT and CBG scaffolds were characterized with respect to porosity, pore size, water content, wettability, compressive strength, mass loss, and osteogenic differentiation of hMSCs. All scaffolds displayed interconnected honeycomb-like microstructures. There was a significant difference between the average pore size, porosity, contact angle, and percent swelling of CBT and CBG scaffolds. The average pore size of CBG scaffolds was higher than CBT, the porosity of CBG was lower than CBT, the water contact angle of CBG was higher than CBT, and the percent swelling of CBG was lower than CBT. At a given crosslinker concentration, there was not a significant difference in compressive modulus and mass loss of CBG and CBT scaffolds. Metabolic activity of hMSCs seeded in CBG scaffolds was slightly higher than CBT. Furthermore, CBG scaffolds displayed slightly higher extent of mineralization after 21 days of incubation in osteogenic medium compared to CBT.

Fiber-based tissue engineering: Progress, challenges, and opportunities

Tissue engineering aims to improve the function of diseased or damaged organs by creating biological substitutes. To fabricate a functional tissue, the engineered construct should mimic the physiological environment including its structural, topographical, and mechanical properties. Moreover, the construct should facilitate nutrients and oxygen diffusion as well as removal of metabolic waste during tissue regeneration. In the last decade, fiber-based techniques such as weaving, knitting, braiding, as well as electrospinning, and direct writing have emerged as promising platforms for making 3D tissue constructs that can address the abovementioned challenges. Here, we critically review the techniques used to form cell-free and cell-laden fibers and to assemble them into scaffolds. We compare their mechanical properties, morphological features and biological activity. We discuss current challenges and future opportunities of fiber-based tissue engineering (FBTE) for use in research and clinical practice.

Rapid, guanosine 5'-diphosphate-induced, gelation of chitosan sponges as novel injectable scaffolds for soft tissue engineering and drug delivery applications

Novel injectable chitosan sponges based on rapid ionic crosslinking using guanosine 5'-diphosphate are introduced. The rapid gelation, high water retention, desirable physicochemical properties, soft tissue-like mechanical properties, and excellent cytocompatibility make these injectable sponges promising candidates for tissue regeneration and drug delivery applications.