Nano and micro mechanical properties of uncross-linked and cross-linked chitosan films

The Importance of Chitosan Coatings in Dentistry

A Chitosan is a copolymer of N-acetyl-D-glucose amine and D-glucose amine that can be easily produced. It is a polymer that is widely utilized to create nanoparticles (NPs) with specific properties for applications in a wide range of human activities. Chitosan is a substance with excellent prospects due to its antibacterial, anti-inflammatory, antifungal, haemostatic, analgesic, mucoadhesive, and osseointegrative qualities, as well as its superior film-forming capacity. Chitosan nanoparticles (NPs) serve a variety of functions in the pharmaceutical and medical fields, including dentistry. According to recent research, chitosan and its derivatives can be embedded in materials for dental adhesives, barrier membranes, bone replacement, tissue regeneration, and antibacterial agents to improve the management of oral diseases. This narrative review aims to discuss the development of chitosan-containing materials for dental and implant engineering applications, as well as the challenges and future potential. For this purpose, the PubMed database (Medline) was utilised to search for publications published less than 10 years ago. The keywords used were "chitosan coating" and "dentistry". After carefully selecting according to these keywords, 23 articles were studied. The review concluded that chitosan is a biocompatible and bioactive material with many benefits in surgery, restorative dentistry, endodontics, prosthetics, orthodontics, and disinfection. Furthermore, despite the fact that it is a highly significant and promising coating, there is still a demand for various types of coatings. Chitosan is a semi-synthetic polysaccharide that has many medical applications because of its antimicrobial properties. This article aims to review the role of chitosan in dental implantology.

Green Additives in Chitosan-Based Bioplastic Films: Physical, Mechanical, and Chemical Properties

To switch to alternatives for fossil-fuel-based polymer materials, renewable raw materials from green resources should be utilized. Chitosan is such a material that is a strong, but workable derivative from chitin, obtained from crustaceans. However, various applications ask for specific plastic properties, such as certain flexibility, hardness and transparency. With different additives, also obtainable from green resources, chitosan-based composites in the form of self-supporting films, ranging from very hard and brittle to soft and flexible were successfully produced. The additives turned out to belong to one of three categories, namely linear, non-linear, or crosslinking additives. The non-linear additives could only be taken up to a certain relative amount, whereas the uptake of linear additives was not limited within the range of our experiments. Additives with multiple functional groups tend to crosslink chitosan even at room temperature in an acidic medium. Finally, it was shown that dissolving the chitosan in acetic acid and subsequently drying the matrix as a film results in reacetylation compared to the starting chitosan source, resulting in a harder material. With these findings, it is possible to tune the properties of chitosan-based polymer materials, making a big step towards application of this renewable polymer within consumer goods.

Application of atomic force microscopy in the characterization of fruits and vegetables and associated substances toward improvement in quality, preservation, and processing: nanoscale structure and mechanics perspectives

Fruits and vegetables are essential horticultural crops for humans. The quality of fruits and vegetables is critical in determining their nutritional value and edibility, which are decisive to their commercial value. Besides, it is also important to understand the changes in key substances involved in the preservation and processing of fruits and vegetables. Atomic force microscopy (AFM), a powerful technique for investigating biological surfaces, has been widely used to characterize the quality of fruits and vegetables and the substances involved in their preservation and processing from the perspective of nanoscale structure and mechanics. This review summarizes the applications of AFM to investigate the texture, appearance, and nutrients of fruits and vegetables based on structural imaging and force measurements. Additionally, the review highlights the application of AFM in characterizing the morphological and mechanical properties of nanomaterials involved in preserving and processing fruits and vegetables, including films and coatings for preservation, bioactive compounds for processing purposes, nanofiltration membrane for concentration, and nanoencapsulation for delivery of bioactive compounds. Furthermore, the strengths and weaknesses of AFM for characterizing the quality of fruits and vegetables and the substances involved in their preservation and processing are examined, followed by a discussion on the prospects of AFM in this field.

Application Progress of Modified Chitosan and Its Composite Biomaterials for Bone Tissue Engineering

In recent years, bone tissue engineering (BTE), as a multidisciplinary field, has shown considerable promise in replacing traditional treatment modalities (i.e., autografts, allografts, and xenografts). Since bone is such a complex and dynamic structure, the construction of bone tissue composite materials has become an attractive strategy to guide bone growth and regeneration. Chitosan and its derivatives have been promising vehicles for BTE owing to their unique physical and chemical properties. With intrinsic physicochemical characteristics and closeness to the extracellular matrix of bones, chitosan-based composite scaffolds have been proved to be a promising candidate for providing successful bone regeneration and defect repair capacity. Advances in chitosan-based scaffolds for BTE have produced efficient and efficacious bio-properties via material structural design and different modifications. Efforts have been put into the modification of chitosan to overcome its limitations, including insolubility in water, faster depolymerization in the body, and blood incompatibility. Herein, we discuss the various modification methods of chitosan that expand its fields of application, which would pave the way for future applied research in biomedical innovation and regenerative medicine.

Facile fabrication and nanoscale assembly of polydopamine-functionalized, flexible chitosan films

Substrates that are simultaneously thin, strong, optically transparent, and biocompatible have diverse applications in a range of fundamental and applied fields. While nature-derived materials offer advantages of sustainability and inherent biocompatibility compared to synthetic polymers, their brittleness and swelling, as well as surface charge and chemical functionalization non-conducive to cell growth, can hinder widespread application. In this work, we discuss the fabrication and systematic characterization of polydopamine-coated chitosan thin films. Chitosan is a widely used, partially deacetylated form of chitin, derived from crustaceans and arthropods. Polydopamine (PDA) is derived from chemistries mimicking mussel foot adhesive proteins. A facile dip-coating process of thin and flexible, uncrosslinked chitosan films in aqueous dopamine solutions leads to dramatic changes in physical and chemical properties. We show how the PDA forms time-dependent assemblies on the film surfaces, affecting surface roughness, hydrophilicity, and mechanical strength. Coating the surface for even a few seconds provides functional changes to the films. Our results shows that the optimal coating time is on the order of few hours, whereby the films are optically transparent with excellent extensibility and Young’s modulus, while further coating reduces the benefits of this surface coating. These materials are biocompatible, serving as substrates for cell adhesion and growth while maintaining good viability. Overall, these findings give insight to the effects of PDA assembly on surfaces, and illustrate how a simple, quick, and robust bioinspired coating process can prime substrates for biomedical applications such as tissue engineering, biosensing, and wound healing.

Controlled release of enrofloxacin by vanillin-crosslinked chitosan-polyvinyl alcohol blends

In transdermal drug delivery applications uniform drug distribution and sustained release are of great importance to decrease the side effects. In this direction in the present research, vanillin crosslinked chitosan (CS) and polyvinyl alcohol (PVA) blend based matrix-type transdermal system was prepared by casting and drying of aqueous solutions for local delivery of enrofloxacin (ENR) drug. Subsequently, the properties including the morphology, chemical structure, thermal behavior, tensile strength, crosslinking degree, weight uniformity, thickness, swelling and drug release of the CS-PVA blend films before and after crosslinking were characterized. In vitro drug release profiles showed the sustained release of ENR by the incorporation of vanillin as a crosslinker into the CS-PVA polymer matrix. Furthermore, the release kinetic profiles revealed that the followed mechanism for all samples was Higuchi and the increase of vanillin concentration in the blend films resulted in the change of diffusion mechanism from anomalous transport to Fickian diffusion. Overall, the obtained results suggest that the investigated vanillin crosslinked CS-PVA matrix-type films are potential candidates for transdermal drug delivery system.

Polydopamine coating of uncrosslinked chitosan as an acellular scaffold for full thickness skin grafts

There is an unmet need for skin grafting materials that are readily available for large area wounds, due to complex, lengthy and costly manufacturing processes that are not compatible with this type of wounds. Here we developed an acellular skin graft material based on surface coating of uncrosslinked porous (UCLP) chitosan. UCLP chitosan membranes had mechanical properties in ranges suitable for skin grafting. Polydopamine (PDA) coating improved hydrophilicity and resulted in a significant increase in attachment and metabolic activity of mammalian cells in vitro. PDA coating also decreased the attachment of pseudomonas aeruginosa - a common bacteria infecting skin wounds. Finally, the PDA-coated membranes were implanted in full thickness surgical wounds in a rodent model and resulted in complete would closure in 5 days. The current study suggests that PDA-coated UCLP chitosan membranes could be a simple and effective strategy for the development of grafting materials for large area wounds.

Electrophoretic Deposition of Copper(II)-Chitosan Complexes for Antibacterial Coatings

Bacterial infection associated with medical implants is a major threat to healthcare. This work reports the fabrication of Copper(II)–Chitosan (Cu(II)–CS) complex coatings deposited by electrophoretic deposition (EPD) as potential antibacterial candidate to combat microorganisms to reduce implant related infections. The successful deposition of Cu(II)–CS complex coatings on stainless steel was confirmed by physicochemical characterizations. Morphological and elemental analyses by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy verified the uniform distribution of copper in the Chitosan (CS) matrix. Moreover, homogeneous coatings without precipitation of metallic copper were confirmed by X-ray diffraction (XRD) spectroscopy and SEM micrographs. Controlled swelling behavior depicted the chelation of copper with polysaccharide chains that is key to the stability of Cu(II)–CS coatings. All investigated systems exhibited stable degradation rate in phosphate buffered saline (PBS)–lysozyme solution within seven days of incubation. The coatings presented higher mechanical properties with the increase in Cu(II) concentration. The crack-free coatings showed mildly hydrophobic behavior. Antibacterial assays were performed using both Gram-positive and Gram-negative bacteria. Outstanding antibacterial properties of the coatings were confirmed. After 24 h of incubation, cell studies of coatings confirms that up to a certain threshold concentration of Cu(II) were not cytotoxic to human osteoblast-like cells. Overall, our results show that uniform and homogeneous Cu(II)–CS coatings with good antibacterial and enhanced mechanical stability could be successfully deposited by EPD. Such antibiotic-free antibacterial coatings are potential candidates for biomedical implants.

Glycine-Chitosan-Based Flexible Biodegradable Piezoelectric Pressure Sensor

This paper presents flexible pressure sensors based on free-standing and biodegradable glycine-chitosan piezoelectric films. Fabricated by the self-assembly of biological molecules of glycine within a water-based chitosan solution, the piezoelectric films consist of a stable spherulite structure of β-glycine (size varying from a few millimeters to 1 cm) embedded in an amorphous chitosan polymer. The polymorphic phase of glycine crystals in chitosan, evaluated by X-ray diffraction, confirms formation of a pure ferroelectric phase of glycine (β-phase). Our results show that a simple solvent-casting method can be used to prepare a biodegradable β-glycine/chitosan-based piezoelectric film with sensitivity (∼2.82 ± 0.2 mV kPa-1) comparable to those of nondegradable commercial piezoelectric materials. The measured capacitance of the β-glycine/chitosan film is in the range from 0.26 to 0.12 nF at a frequency range from 100 Hz to 1 MHz, and its dielectric constant and loss factor are 7.7 and 0.18, respectively, in the high impedance range under ambient conditions. The results suggest that the glycine-chitosan composite is a promising new biobased piezoelectric material for biodegradable sensors for applications in wearable biomedical diagnostics.

The Impact of Cross-linking Mode on the Physical and Antimicrobial Properties of a Chitosan/Bacterial Cellulose Composite

The bacteriostatic performance of a chitosan film is closely related to its ionic and physical properties, which are significantly influenced by the mode of cross-linking. In the current work, chitosan with or without bacterial cellulose was cross-linked with borate, tripolyphosphate, or the mixture of borate and tripolyphosphate, and the composite films were obtained by a casting of dispersion. Mechanical measurements indicated that different modes of cross-linking led to varying degrees of film strength and elongation increases, while the films treated with the borate and tripolyphosphate mixture showed the best performance. Meanwhile, changes in the fractured sectional images showed a densified texture induced by cross-linkers, especially for the borate and tripolyphosphate mixture. Measurements of Fourier transform infrared showed the enhanced interaction between the matrix polymers treated by borate, confirmed by a slight increase in the glass transitional temperature and a higher surface hydrophobicity. However, the reduced antimicrobial efficiency of composite films against E. coli, B. cinerea, and S. cerevisiae was obtained in cross-linked films compared with chitosan/bacterial cellulose films, indicating that the impact on the antimicrobial function of chitosan is a noteworthy issue for cross-linking.

Preparation of Nanocellulose Reinforced Chitosan Films, Cross-Linked by Adipic Acid

Adipic acid, an abundant and nontoxic compound, was used to dissolve and cross-link chitosan. After the preparation of chitosan films through casting technique, the in situ amidation reaction was performed at 80-100 °C as verified by Fourier transform infrared (FT-IR). The reaction was accompanied by the release of water which was employed to investigate the reaction kinetics. Accordingly, the reaction rate followed the first-order model and Arrhenius equation, and the activation energy was calculated to be 18 kJ/mol. Furthermore, the mechanical properties of the chitosan films were comprehensively studied. First, optimal curing conditions (84 °C, 93 min) were introduced through a central composite design. In order to evaluate the effects of adipic acid, the mechanical properties of physically cross-linked (uncured), chemically cross-linked (cured), and uncross-linked (prepared by acetic acid) films were compared. The use of adipic acid improved the tensile strength of uncured and chemically cross-linked films more than 60% and 113%, respectively. Finally, the effect of cellulose nanofibrils (CNFs) on the mechanical performance of cured films, in the presence of glycerol as a plasticizer, was investigated. The plasticized chitosan films reinforced by 5 wt % CNFs showed superior properties as a promising material for the development of chitosan-based biomaterials.

Bone regeneration using injectable BMP-7 loaded chitosan microparticles in rat femoral defect

Injectable chitosan microparticles were prepared using a simple coacervation method under physiologically friendly conditions by eliminating oil or toxic chemical, and employing low temperature and pressure for growth factor stability. Amount of 200 ng of bone morphogenetic protein-7 (BMP-7) was incorporated in the chitosan microparticles by two methods: encapsulating and coating techniques. These microparticles were tested in vivo to determine the biological response in a rat femoral bone defect at 6 and 12 weeks. Four groups (n=10) were tested which include two groups for BMP-7 incorporated microparticles (by two techniques), microparticles without BMP-7, and defect itself (negative control). Healthy bone formation was observed around the microparticles, which were only confined to the defect site and did not disperse. Histology indicated minor inflammatory response around the microparticles at 6 weeks, which reduced by 12 weeks. Micro-CT analysis of bone surface density and porosity was found to be significantly more (p<0.05) for microparticles containing groups, in comparison with controls, which suggests that the new bone formed in the presence of microparticles is more interconnected and porous. Collagen fibrils analysis conducted using multiphoton microscopy showed significant improvement in the formation of bundled collagen area (%) in microparticles containing groups in comparison with controls, indicating higher cross-linking between the fibrils. Microparticles were biocompatible and did not degrade in the 12 week implant period.

Thermodynamic Insights and Conceptual Design of Skin-Sensitive Chitosan Coated Ceramide/PLGA Nanodrug for Regeneration of Stratum Corneum on Atopic Dermatitis

Atopic dermatitis (AD) is a complex skin disease primarily characterized by psoriasis of the stratum corneum. AD drugs have usually been used in acidic and hydrophilic solvents to supply moisture and prevent lipid defects. Ceramide is a typical treatment agent to regenerate the stratum corneum and relieve symptoms of AD. However, ceramide has limitation on direct use for skin because of its low dispersion properties in hydrophilic phase and side effects at excessive treatment. In this study, ceramide imbedded PLGA nanoparticles were developed with chitosan coating (Chi-PLGA/Cer) to overcome this problem. The chitosan coating enhanced initial adherence to the skin and prevented the initial burst of ceramide, but was degraded by the weakly acidic nature of skin, resulting in controlled release of ceramide with additional driving force of the squeezed PLGA nanoparticles. Additionally, the coating kinetics of chitosan were controlled by manipulating the reaction conditions and then mathematically modeled. The Chi-PLGA/Cer was not found to be cytotoxic and ceramide release was controlled by pH, temperature, and chitosan coating. Finally, Chi-PLGA/Cer was demonstrated to be effective at stratum corneum regeneration in a rat AD model. Overall, the results presented herein indicated that Chi-PLGA/Cer is a novel nanodrug for treatment of AD.

Cross-linked chitosan improves the mechanical properties of calcium phosphate-chitosan cement

Calcium phosphate (CaP) cements are highly applicable and valuable materials for filling bone defects by minimally invasive procedures. The chitosan (CS) biopolymer is also considered as one of the promising biomaterial candidates in bone tissue engineering. In the present study, some key features of CaP-CS were significantly improved by developing a novel CaP-CS composite. For this purpose, CS was the first cross-linked with tripolyphosphate (TPP) and then mixed with CaP matrix. A group of CaP-CS samples without cross-linking was also prepared. Samples were fabricated and tested based on the known standards. Additionally, the effect of different powder (P) to liquid (L) ratios was also investigated. Both cross-linked and uncross-linked CaP-CS samples showed excellent washout resistance. The most significant effects were observed on Young's modulus and compressive strength in wet condition as well as surface hardness. In dry conditions, the Young's modulus of cross-linked samples was slightly improved. Based on the presented results, cross-linking does not have a significant effect on porosity. As expected, by increasing the P/L ratio of a sample, ductility and injectability were decreased. However, in the most cases, mechanical properties were enhanced. The results have shown that cross-linking can improve the mechanical properties of CaP-CS and hence it can be used for bone tissue engineering applications.

Biomimetic multi-layered hollow chitosan–tripolyphosphate rod with excellent mechanical performance

Design of hollow and multi-layered features in chitosan–tripolyphosphate rod and the resulting excellent mechanical performance.

Mechanical and biological properties of chitosan/carbon nanotube nanocomposite films

In this article, different concentrations of multiwalled carbon nanotube (MWCNT) were homogeneously dispersed throughout the chitosan (CS) matrix. A simple solvent-cast method was used to fabricate chitosan films with 0.1, 0.5, and 1% of MWCNT with the average diameter around 30 nm. The CS/MWCNT films were characterized for structural, viscous and mechanical properties with optical microscopy, wide-angle X-ray diffraction, Raman spectroscopy, tensile test machine, and microindentation testing machine. Murine osteoblasts were used to examine the cell viability and attachment of the nanocomposite films at two time points. In comparison to the pure chitosan film, the mechanical properties, including the tensile modulus and strength of the films, were greatly improved by increasing the percentage of MWCNT. Furthermore, adding MWCNT up to 1% increased the viscosity of the chitosan solution by 15%. However, adding MWCNT decreased the samples ductility and transparency. In biological point of view, no toxic effect on osteoblasts was observed in the presence of different percentages of MWCNT at day 3 and day 7. This investigation suggested MWCNT could be a promising candidate for improving chitosan mechanical properties without inducing remarkable cytotoxicity on bone cells.

IGF-1 release kinetics from chitosan microparticles fabricated using environmentally benign conditions

The main objective of this study is to maximize growth factor encapsulation efficiency into microparticles. The novelty of this study is to maximize the encapsulated growth factors into microparticles by minimizing the use of organic solvents and using relatively low temperatures. The microparticles were fabricated using chitosan biopolymer as a base polymer and cross-linked with tripolyphosphate (TPP). Insulin like-growth factor-1 (IGF-1) was encapsulated into microparticles to study release kinetics and bioactivity. In order to authenticate the harms of using organic solvents like hexane and acetone during microparticle preparation, IGF-1 encapsulated microparticles prepared by the emulsification and coacervation methods were compared. The microparticles fabricated by emulsification method have shown a significant decrease (p<0.05) in IGF-1 encapsulation efficiency, and cumulative release during the two-week period. The biocompatibility of chitosan microparticles and the bioactivity of the released IGF-1 were determined in vitro by live/dead viability assay. The mineralization data observed with von Kossa assay, was supported by mRNA expression levels of osterix and runx2, which are transcription factors necessary for osteoblasts differentiation. Real time RT-PCR data showed an increased expression of runx2 and a decreased expression of osterix over time, indicating differentiating osteoblasts. Chitosan microparticles prepared in optimum environmental conditions are a promising controlled delivery system for cells to attach, proliferate, differentiate and mineralize, thereby acting as a suitable bone repairing material.

2,5-Dimethoxy 2,5-dihydrofuran crosslinked chitosan fibers enhance bone regeneration in rabbit femur defects

Chitosan fibers were fabricated via pH induced neutralization and precipitation in a 5 w/v% NaOH bath.

Catechol-functionalized chitosan/iron oxide nanoparticle composite inspired by mussel thread coating and squid beak interfacial chemistry

Biological materials offer a wide range of multifunctional and structural properties that are currently not achieved in synthetic materials. Herein we report on the synthesis and preparation of bioinspired organic/inorganic composites that mimic the key physicochemical features associated with the mechanical strengthening of both squid beaks and mussel thread coatings using chitosan as an initial template. While chitosan is a well-known biocompatible material, it suffers from key drawbacks that have limited its usage in a wider range of structural biomedical applications. First, its load-bearing capability in hydrated conditions remains poor, and second it completely dissolves at pH < 6, preventing its use in mild acidic microenvironments. In order to overcome these intrinsic limitations, a chitosan-based organic/inorganic biocomposite is prepared that mimics the interfacial chemistry of squid beaks and mussel thread coating. Chitosan was functionalized with catechol moieties in a highly controlled fashion and combined with superparamagnetic iron oxide (γ-Fe2O3) nanoparticles to give composites that represent a significant improvement in functionality of chitosan-based biomaterials. The inorganic/organic (γ-Fe2O3/catechol) interfaces are stabilized and strengthened by coordination bonding, resulting in hybrid composites with improved stability at high temperatures, physiological pH conditions, and acid/base conditions. The inclusion of superparamagnetic particles also makes the composites stimuli-responsive.

Mechanical properties of human amniotic fluid stem cells using nanoindentation

The aim of this study was to obtain nanomechanical properties of living cells focusing on human amniotic fluid stem (hAFS) cell using nanoindentation techniques. We modified the conventional method of atomic force microscopy (AFM) in aqueous environment for cell imaging and indentation to avoid inherent difficulties. Moreover, we determined the elastic modulus of murine osteoblast (OB6) cells and hAFS cells at the nucleus and cytoskeleton using force-displacement curves and Hertz theory. Since OB6 cell line has been widely used, it was selected to validate and compare the obtained results with the previous research studies. As a result, we were able to capture high resolution images through utilization of the tapping mode without adding protein or using fixation methods. The maximum depth of indentation was kept below 15% of the cell thickness to minimize the effect of substrate hardness. Nanostructural details on the surface of cells were visualized by AFM and fluorescence microscopy. The cytoskeletal fibers presented remarkable increase in elastic modulus as compared with the nucleus. Furthermore, our results showed that the elastic modulus of hAFS cell edge (31.6 kPa) was lower than that of OB6 cell edge (42.2 kPa). In addition, the elastic modulus of nucleus was 13.9 kPa for hAFS cell and 26.9 kPa for OB6 cells. Differences in cell elastic modulus possibly resulted from the type and number of actin cytoskeleton organization in these two cell types.

ZnO nanoparticles induced effects on nanomechanical behavior and cell viability of chitosan films

The aim of this paper is to develop novel chitosan-zinc oxide nanocomposite films for biomedical applications. The films were fabricated with 1, 5, 10 and 15% w/w of zinc oxide (ZnO) nanoparticles (NPs) incorporated with chitosan (CS) using a simple method. The prepared nanocomposite films were characterized using atomic force microscopy, Raman and X-ray diffraction studies. In addition, nano and micro mechanical properties were measured. It was found that the microhardness, nanohardness and its corresponding elastic modulus increased with the increase of ZnO NP percentage in the CS films. However, the ductility of films decreased as the percentage of ZnO NPs increased. Cell attachment and cytotoxicity of the prepared films at days two and five were evaluated in vitro using osteoblasts (OBs). It was observed that OB viability decreased in films with higher than 5% ZnO NPs. This result suggests that although ZnO NPs can improve the mechanical properties of pure CS films, only a low percentage of ZnO NPs can be applied for biomedical and bioengineering applications because of the cytotoxicity effects of these particles.

Comparison of chitosan/starch composite film properties before and after cross-linking

Unmodified and cross-linked chitosan/starch composite films were prepared using the solvent evaporation method. The properties of the films were studied to obtain useful information about the possible applications of composite films. FT-IR, SEM, and swelling property investigations show that the cross-linking agent glutaraldehyde reacts in the chitosan and starch blend. The compatibility of chitosan and starch blends before and after cross-linking was studied by UV-vis spectroscopy. The compatibility of the blends deteriorated after cross-linking. This finding was confirmed by the results of mechanical properties. The films show improved water barrier performance after cross-linking. The use of trace concentrations of glutaraldehyde in chitosan/starch films allows for possible application in the biomedical field.

Chitosan/Riboflavin-modified demineralized dentin as a potential substrate for bonding

Previous studies have suggested different approaches to modify dentin collagen for potential improvement in bonding to dentin. Here, we are proposing a new approach to reinforce dentin collagen fibrils network by chitosan as a reinforcement phase and UVA-activated riboflavin as crosslinking agent within clinically acceptable time-frame as potential substrate for bonding. The effect of modifying demineralized dentin substrates with chitosan/riboflavin, with a gradual increase in chitosan content, was investigated by SEM, nano-indentation, conventional-mechanical testing and hydroxyproline (HYP) release at collagenolytic and/or hydrolytic challenges. The resin/dentin interface morphology, immediate bond strength and short-term bond durability were also investigated using etch-and-rinse dentin adhesive. Modification with chitosan/riboflavin increased the mechanical properties, enhanced the mechanical stability of demineralized dentin substrates against hydrolytic and/or collagenolytic degradation challenges and decreased HYP release with collagenase exposure. When chitosan was added to riboflavin at 20%v/v ratio, significant improvement in bond strength at 24 h and 6 months in distilled water was found indicating the positive dual effect on bonding to dentin. With the gradual increase in chitosan content, obliteration of interfibrillar-spaces that might adversely affect bonding to dentin was found. Although it has a synergetic effect, chitosan content is crucial for any subsequent application in adhesive dentistry.