Synthesis and properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/chitin nanocrystals composite scaffolds for tissue engineering

Design of Chitin Cell Culture Matrices for 3D Tissue Engineering: The Importance of Chitin Types, Solvents, Cross-Linkers, and Fabrication Techniques

This review focuses on factors and the fabrication techniques affecting the microarchitecture of tissue engineering scaffolds from the second most abundant biopolymer, chitin. It emphasizes the unique potentiality of this polymer in tissue engineering (TE) applications and highlights the variables important to achieve tailored scaffold properties. First, we describe aspects of scaffolds' design, and the complex interplay between chitin types, solvent systems, additives, and fabrication techniques to incorporate porosity, with regard to best practices. In the following section, we provide examples of scaffolds' use, with a focus on in vitro cell studies. Finally, an analysis of their biodegradability is presented. Our review emphasizes the potentiality of chitin and the pressing need for further research to overcome existing challenges and fully harness its capabilities in tissue engineering.

Covalent Immobilization of Natural Biomolecules on Chitin Nanocrystals

As a highly crystalline and renewable natural polymer nanomaterial, chitin nanocrystals (ChNCs) have attracted intense interest in the biomedical field. The structure of a ChNC is composed of an acetylglucosamine unit containing two hydroxyl groups and an acetyl group. The acetyl group can be converted to the active amino group through deacetylation, which is under the condition of maintaining the rod-like morphology and high crystalline property and is beneficial for the following modification and potential application. We investigated the relationship between different treatments and varied crystallinities of the modified ChNC, which obtained surface amino groups and aldehyde groups and retained high crystallinity. The natural biomolecules were covalently immobilized on the surface of the ChNC. The etherification was performed based on the hydroxyl groups. Based on the amino groups and the aldehyde groups, the carboxyamine and Knoevenagel condensation reactions were realized on ChNCs. Finally, natural biomolecule-modified ChNCs showed no or low cytotoxicity, antibacterial properties, and high antioxidant properties, which extended their potential biomedical applications.

Chitin Nanocrystals: Environmentally Friendly Materials for the Development of Bioactive Films

Biobased nanomaterials have gained growing interest in recent years for the sustainable development of composite films and coatings, providing new opportunities and high-performance products. In particular, chitin and cellulose nanocrystals offer an attractive combination of properties, including a rod shape, dispersibility, outstanding surface properties, and mechanical and barrier properties, which make these nanomaterials excellent candidates for sustainable reinforcing materials. Until now, most of the research has been focused on cellulose nanomaterials; however, in the last few years, chitin nanocrystals (ChNCs) have gained more interest, especially for biomedical applications. Due to their biological properties, such as high biocompatibility, biodegradability, and antibacterial and antioxidant properties, as well as their superior adhesive properties and promotion of cell proliferation, chitin nanocrystals have emerged as valuable components of composite biomaterials and bioactive materials. This review attempts to provide an overview of the use of chitin nanocrystals for the development of bioactive composite films in biomedical and packaging systems.

One-Step Preparation of Chitin Nanofiber Dispersion in Full pH Surroundings Using Recyclable Solid Oxalic Acid and Evaluation of Redispersed Performance

This study proposed an efficient and economical preparation pathway from purified chitin to nanofibers that can be dispersed in full pH surroundings. Recyclable oxalic acid was applied to prepare chitin nanofibers in a mild environment along with concurrent modifications of the carboxylic groups on the surface. Pretreatment with oxalic acid significantly improved the mechanical disintegration of chitin into nanofibers, the length of nanofibers reached ∼1100 nm, and the crystallinity and thermal stability of the chitin were basically unchanged with mild treatment. Oxalic acid can be reused many times with a high recovery of over 91%. Most importantly, the obtained nanofibers can be fabricated into films and hydrogels with certain mechanical properties, which can be redispersed into nanofibers using mild mechanical treatment. This method not only produces nanofibers in a green, reusable system but also provides a reference for the potential application of chitin nanofibers in commercial transportation and wide applicability.

Chitin nanocrystals based complex fluids: A green nanotechnology

Chitin biopolymer has received significant attention recently by many industries as a green technology. Nanotechnology has been used to make chitin nanocrystals (ChiNCs) that are rod-shaped natural nanomaterials with nanoscale size. Owing to the unique features such as biodegradability, biocompatibility, renewability, rod-shape, and excellent surface and interfacial, physiochemical, and thermo-mechanical properties; ChiNCs have been green and attractive products with wide applications specifically in medical and pharmaceutical, food and packaging, cosmetic, electrical, and electronic, and also in the oil and gas industry. This review aims to give a comprehensive and applied insight into ChiNCs technology. It starts with reviewing different sources of chitin and their extraction methods followed by the characterization of ChiNCs. Furthermore, a detailed investigation into various complex fluids (dispersions, emulsions, foams, and gels) stabilized by ChiNCs and their characterisation have been thoroughly deliberated. Finally, the current status including ground-breaking applications, untapped investigations, and future prospective have been presented.

Nanofibrous Foams of Poly(3-hydroxybutyrate)/Cellulose Nanocrystal Composite Fabricated Using Nonsolvent-Induced Phase Separation

In this study, we fabricated nanofibrous foams of neat poly(3-hydroxybutyrate) (PHB) and PHB/cellulose nanocrystal (CNC) nanocomposite using nonsolvent-induced phase separation (NIPS) followed by solvent extraction. Two different nonsolvents, tetrahydrofuran (THF) and 1,4-dioxane (Diox), in combination with the solvent, chloroform (CF), were used for NIPS. The parameters of NIPS-derived crystallization kinetics were calculated using Avrami analysis of time-dependent infrared spectral measurements. The lower viscosity and poorer PHB affinity of THF than those of Diox resulted in rapid crystallization and gelation rate, which in turn resulted in higher strength of the foam. The mechanical reinforcement by the incorporation of CNCs was achieved for the composite foam prepared in Diox/CF but not in THF/CF, owing to the relatively better dispersion of the CNCs in Diox than that in THF. A rapid rate of NIPS-derived crystallization and gelation was achieved in THF/CF with the incorporation of CNCs, indicating the effective crystal nucleation of CNCs. However, the presence of CNCs deaccelerated the crystallization in Diox/CF, indicating that the inhibition effect of PHB mobility became more dominant than the nucleation effect of CNCs; this was because the CNC dispersion became more homogeneous in Diox/CF. In vitro cell viability assays exhibited excellent cytocompatibility of the foams, thereby showing potential for use in biomedical applications.

Comparison of acidic deep eutectic solvents in production of chitin nanocrystals

Five different acidic deep eutectic solvents (DESs) composed of choline chloride and organic acids were applied to fabricate chitin nanocrystals (ChNCs). All DESs resulted in high transmittance and stable ChNCs suspensions with very high mass yield ranging from 78 % to 87.5 % under proper reaction conditions. The acidic DESs had a dual role in ChNCs fabrication, i.e. they promoted hydrolysis of chitin and acted as an acylation reagent. Physicochemical characterization of chitin revealed that the removal of amorphous area during DES treatments led to increased crystallinity of ChNCs and a dimension diversity correlated the DES used. The average diameter and length of individual ChNCs ranged from 42 nm to 49 nm and from 257 nm to 670 nm, respectively. The thermal stability of ChNCs was comparable to that of pristine chitin. Thus, acidic DESs showed to be non-toxic and environmentally benign solvents for production of functionalized chitin nanocrystals.

Designing of PLA scaffolds for bone tissue replacement fabricated by ordinary commercial 3D printer

BACKGROUND

The primary objective of Tissue engineering is a regeneration or replacement of tissues or organs damaged by disease, injury, or congenital anomalies. At present, Tissue engineering repairs damaged tissues and organs with artificial supporting structures called scaffolds. These are used for attachment and subsequent growth of appropriate cells. During the cell growth gradual biodegradation of the scaffold occurs and the final product is a new tissue with the desired shape and properties. In recent years, research workplaces are focused on developing scaffold by bio-fabrication techniques to achieve fast, precise and cheap automatic manufacturing of these structures. Most promising techniques seem to be Rapid prototyping due to its high level of precision and controlling. However, this technique is still to solve various issues before it is easily used for scaffold fabrication. In this article we tested printing of clinically applicable scaffolds with use of commercially available devices and materials. Research presented in this article is in general focused on "scaffolding" on a field of bone tissue replacement.

RESULTS

Commercially available 3D printer and Polylactic acid were used to create originally designed and possibly suitable scaffold structures for bone tissue engineering. We tested printing of scaffolds with different geometrical structures. Based on the osteosarcoma cells proliferation experiment and mechanical testing of designed scaffold samples, it will be stated that it is likely not necessary to keep the recommended porosity of the scaffold for bone tissue replacement at about 90%, and it will also be clarified why this fact eliminates mechanical properties issue. Moreover, it is demonstrated that the size of an individual pore could be double the size of the recommended range between 0.2-0.35 mm without affecting the cell proliferation.

CONCLUSION

Rapid prototyping technique based on Fused deposition modelling was used for the fabrication of designed scaffold structures. All the experiments were performed in order to show how to possibly solve certain limitations and issues that are currently reported by research workplaces on the field of scaffold bio-fabrication. These results should provide new valuable knowledge for further research.

Novel Poly(3-hydroxybutyrate-g-vinyl alcohol) Polyurethane Scaffold for Tissue Engineering

The design of new synthetic grafted poly(3-hydroxybutyrate) as composite 3D-scaffolds is a convenient alternative for tissue engineering applications. The chemically modified poly(3-hydroxybutyrate) is receiving increasing attention for use as biomimetic copolymers for cell growth. As of yet, these copolymers cannot be used efficiently because of the lack of good mechanical properties. Here, we address this challenge, preparing a composite-scaffold of grafted poly(3-hydroxybutyrate) polyurethane for the first time. However, it is unclear if the composite structure and morphology can also offer a biological application. We obtained the polyurethane by mixing a polyester hydroxylated resin with polyisocyanate and the modified polyhydroxyalkanoates. The results show that the poly(3-hydroxybutyrate) grafted with poly(vinyl alcohol) can be successfully used as a chain extender to form a chemically-crosslinked thermosetting polymer. Furthermore, we show a proposal for the mechanism of the polyurethane synthesis, the analysis of its morphology and the ability of the scaffolds for growing mammalian cells. We demonstrated that astrocytes isolated from mouse cerebellum, and HEK293 can be cultured in the prepared material, and express efficiently fluorescent proteins by adenoviral transduction. We also tested the metabolism of Ca(2+) to obtain evidence of the biological activity.

Biomedical Applications of Biodegradable Polyesters

The focus in the field of biomedical engineering has shifted in recent years to biodegradable polymers and, in particular, polyesters. Dozens of polyester-based medical devices are commercially available, and every year more are introduced to the market. The mechanical performance and wide range of biodegradation properties of this class of polymers allow for high degrees of selectivity for targeted clinical applications. Recent research endeavors to expand the application of polymers have been driven by a need to target the general hydrophobic nature of polyesters and their limited cell motif sites. This review provides a comprehensive investigation into advanced strategies to modify polyesters and their clinical potential for future biomedical applications.