Cryogenically fabricated three-dimensional chitosan scaffolds with pore size-controlled structures for biomedical applications

A route toward fabrication of 3D printed bone scaffolds based on poly(vinyl alcohol)-chitosan/bioactive glass by sol-gel chemistry

Among different methods for the fabrication of bone scaffolds, 3D printing has created great advances in tissue engineering and regenerative medicine owing to its ability to make objects mimicking native tissues. Thanks to its abundant availability, structural features, and favorable biological properties, chitosan (CS) hydrogel was selected to be used for preparation of the bone scaffolds. However, the 3D printing of CS-based hydrogels is still under early exploration. Knowing the fact that natural polymers are not so competent at holding large amounts of water, poly(vinyl alcohol) as the second polymer was employed. The novelty of the present research lies in the concept of employing sol-gel chemistry in order to attain proper viscosity and rheological behavior to give self-standing filaments of the polymer blends. Employing sol-gel reaction in the preparation of the hybrid hydrogels had the advantage of endowing shape fidelity to the polymer blend without any solidifying in the needle. The obtained organic-inorganic hybrids were directly printed and subsequently cross-linked. The best performance in terms of mechanical strength, cell viability, and bio-mineralization was observed for the 50:50 ratio. The in vitro cell culture and the bioactivity results showed that the printed scaffolds with this method have great potential in bone tissue engineering. Further, this method could be expandable to print other hydrogels with diverse applications such as implantable devices, soft robotics, etc.

Current application and modification strategy of marine polysaccharides in tissue regeneration: A review

Marine polysaccharides (MPs) are exceptional bioactive materials that possess unique biochemical mechanisms and pharmacological stability, making them ideal for various tissue engineering applications. Certain MPs, including agarose, alginate, carrageenan, chitosan, and glucan have been successfully employed as biological scaffolds in animal studies. As carriers of signaling molecules, scaffolds can enhance the adhesion, growth, and differentiation of somatic cells, thereby significantly improving the tissue regeneration process. However, the biological benefits of pure MPs composite scaffold are limited. Therefore, physical, chemical, enzyme modification and other methods are employed to expand its efficacy. Chemically, the structural properties of MPs scaffolds can be altered through modifications to functional groups or molecular weight reduction, thereby enhancing their biological activities. Physically, MPs hydrogels and sponges emulate the natural extracellular matrix, creating a more conducive environment for tissue repair. The porosity and high permeability of MPs membranes and nanomaterials expedite wound healing. This review explores the distinctive properties and applications of select MPs in tissue regeneration, highlighting their structural versatility and biological applicability. Additionally, we provide a brief overview of common modification strategies employed for MP scaffolds. In conclusion, MPs have significant potential and are expected to be a novel regenerative material for tissue engineering.

High-Throughput Dispensing of Viscous Solutions for Biomedical Applications

Cells cultured in three-dimensional scaffolds express a phenotype closer to in vivo cells than cells cultured in two-dimensional containers. Natural polymers are suitable materials to make three-dimensional scaffolds to develop disease models for high-throughput drug screening owing to their excellent biocompatibility. However, natural polymer solutions have a range of viscosities, and none of the currently available liquid dispensers are capable of dispensing highly viscous polymer solutions. Here, we report the development of an automated scaffold dispensing system for rapid, reliable, and homogeneous creation of scaffolds in well-plate formats. We employ computer-controlled solenoid valves to regulate air pressure impinging upon a syringe barrel filled with scaffold solution to be dispensed. Automated dispensing of scaffold solution is achieved via a programmable software interface that coordinates solution extrusion and the movement of a dispensing head. We show that our pneumatically actuated dispensing system can evenly distribute high-viscosity, chitosan-based polymer solutions into 96- and 384-well plates to yield highly uniform three-dimensional scaffolds after lyophilization. We provide a proof-of-concept demonstration of high-throughput drug screening by culturing glioblastoma cells in scaffolds and exposing them to temozolomide. This work introduces a device that can hasten the creation of three-dimensional cell scaffolds and their application to high-throughput testing.

Development of Cellulose Nanofibril/Casein-Based 3D Composite Hemostasis Scaffold for Potential Wound-Healing Application

Excessive bleeding in traumatic hemorrhage is the primary concern for natural wound healing and the main reason for trauma deaths. The three-dimensional (3D) bioprinting of bioinks offers the desired structural complexity vital for hemostasis activity and targeted cell proliferation in rapid and controlled wound healing. However, it is challenging to develop suitable bioinks to fabricate specific 3D scaffolds desirable in wound healing. In this work, a 3D composite scaffold is designed using bioprinting technology and synergistic hemostasis mechanisms of cellulose nanofibrils (TCNFs), chitosan, and casein to control blood loss in traumatic hemorrhage. Bioinks that consist of casein bioconjugated TCNF (with a casein content of 104.5 ± 34.1 mg/g) using the carbodiimide cross-linker chemistry were subjected to bioprinting for customizable 3D scaffold fabrication. Further, the 3D composite scaffolds were in situ cross-linked using a green ionic complexation approach. The covalent conjugation among TCNF, casein, and chitosan was confirmed by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and X-ray diffraction (XRD) studies. The in vitro hemostasis activity of the 3D composite scaffold was analyzed by a human thrombin-antithrombin (TAT) assay and adsorption of red blood cells (RBCs) and platelets. The 3D composite scaffold had a better swelling behavior and a faster whole blood clotting rate at each time point than the 3D TCNF scaffold and commercial cellulose-based dressings. The TAT assay demonstrated that the 3D composite scaffold could form a higher content of thrombin (663.29 pg/mL) and stable blood clot compared to a cellulosic pad (580.35 pg/mL), 3D TCNF (457.78 pg/mL), and cellulosic gauze (328.92 pg/mL), which are essential for faster blood coagulation. In addition, the 3D composite scaffold had a lower blood clotting index (23.34%) than the 3D TCNF scaffold (41.93%), suggesting higher efficiencies for RBC entrapping to induce blood clotting. The in vivo cytocompatibility was evaluated by a 3D cell culture study, and results showed that the 3D composite scaffold could promote growth and proliferation of NIH 3T3 fibroblast cells, which is vital for wound healing. Cellulase-based in vitro deconstruction of the 3D composite scaffold showed significant weight loss (80 ± 5%) compared to the lysozyme hydrolysis (22 ± 5%) after 28 days of incubation, suggesting the biodegradation potential of the composite scaffold. In conclusion, this study proposes efficient prospects to develop a 3D composite scaffold from bioprinting of TCNF-based bioinks that can accelerate blood clotting and wound healing, suggesting its potential application in reducing blood loss during traumatic hemorrhage.

Photopolymerizable chitosan hydrogels with improved strength and 3D printability

Chitosan hydrogel have presented great potential in biomedical applications due to its biocompatibility, biodegradability and characteristic similarity to native extracellular matrix. However, 3D printing of chitosan hydrogel often suffers from weak formability and poor mechanical property, limiting its further utilization. In this study, a novel chiotsan hydrogel is prepared from maleic chitosan (MCS) with high acrylate group substitution (i.e. 1.67) and thiol-terminated poly (ethylene glycol) (TPEG) via step-chain growth photopolymerization approach, which can overcome significantly the oxygen inhibition effect. Rheological property, microstructure, mechanical properties and in vitro degradation can be regulated by changing the thiol/acrylate molar ratio. There is strong intermolecular action between MCS and TPEG. Notably, photopolymerized MCS/TPEG hydrogel exhibited ~2-fold and ~ 10-fold increase in gelling rate and compressive strength, respectively, compared to pure chitosan hydrogel. Based on these results, 3D printing of chitosan hydrogel fabricated by simultaneous extrusion deposition and thiol-acrylate photopolymerization, demonstrates printing accuracy and improved scaffold stability. This 3D printing of chitosan hydrogel shows no cytotoxicity and can support adherence of L929 cells, suggesting its potential in biomedical applications such as tissue engineering and drug delivery.

Novel chitosan-poly(vinyl acetate) biomaterial suitable for additive manufacturing and bone tissue engineering applications

Chitosan, a biocompatible and biodegradable natural polymer, offers great promise as a biomaterial for tissue engineering applications. Chitosan scaffolds have previously been fabricated using additive manufacturing techniques, however, the use of crosslinkers, weak mechanical stability and structural resolution remain problematic. In this study Chitosan-PVAc biopolymer blends were prepared using a non-organic solvent that can prepare a three-dimensional printable biopolymer in less time than conventional methods. Prepared films were characterised using SEM, FTIR and thermogravimetric analysis. Additionally, the swelling properties, biodegradability and printability of the scaffolds were also studied. The fabricated films were biodegradable within a 3-week period and showed controllable swelling properties. Results indicated no toxicity and cells attached onto films. Additionally, hydrogels showed antibacterial activity against S. aureus, S. epidermidis and E.coli, which could potentially prevent implant related infections. Additive manufacturing simulation of PVAc composite 3% chitosan and PVAc composite 4% chitosan were able to produce a layered scaffold without using crosslinkers and therefore confirming printability. Cytocompabability were assessed using a resazurin assay and cell attachment. From these results, we concluded that the printable PVAc composite 3% chitosan and PVAc composite 4% chitosan biopolymer blends meet the requirements of a biomaterial and can potentially be used for biomedical implants.

Chitosan-based 3D-printed scaffolds for bone tissue engineering

Despite the spontaneous regenerative properties of autologous bone grafts, this technique remains dilatory and restricted to fractures and injuries. Conventional grafting strategies used to treat bone tissue damage have several limitations. This highlights the need for novel approaches to overcome the persisting challenges. Tissue-like constructs that can mimic natural bone structurally and functionally represent a promising strategy. Bone tissue engineering (BTE) is an approach used to develop bioengineered bone with subtle architecture. BTE utilizes biomaterials to accommodate cells and deliver signaling molecules required for bone rejuvenation. Among the various techniques available for scaffold creation, 3D-printing technology is considered to be a superior technique as it enables the design of functional scaffolds with well-defined customizable properties. Among the biomaterials obtained from natural, synthetic, or ceramic origins, naturally derived chitosan (CS) polymers are promising candidates for fabricating reliable tissue constructs. In this review, the physicochemical-biological properties and applications of CS-based 3D-printed scaffolds and their future perspectives in BTE are summarized.

Cryogenically printed flexible chitosan/bioglass scaffolds with stable and hierarchical porous structures for wound healing

Wound healing is a dynamic and well-orchestrated process that can be promoted by creating an optimal environment with wound dressing. An ideal wound dressing material should possess a suitable matrix, structure and bioactive components, functioning synergistically to accelerate wound healing. Wound dressings that allow reproducibility and customizability are highly desirable in clinical practice. In this study, using chitosan (CS) as the matrix and bioglass (BG) as the biological component, a spatially designed dressing scaffold was fabricated from a home-made cryogenic printing system. The micro- and macro-structures of the scaffold were highly controllable and reproducible. The printed scaffold exhibited interconnected and hierarchical pore structures, as well as good flexibility and water absorption capacity, and these properties were not affected by the content of BG. Nevertheless, when the content of BGs exceeded 20% that of CS, the tension strength and elongation rate reduced, but in vitro antibacterial, cell proliferation and migration performance were enhanced. In vivo examinations revealed that the composite scaffold significantly promoted wound healing process, with the group having 30% bioglass showing better wound closure, neovascularization and collagen deposition than other groups. These results indicate that the 3D printed CS/BG composite scaffold is a promising dressing material that accelerates wound healing.

Chitosan-Nanocellulose Composites for Regenerative Medicine Applications

Regenerative medicine represents an emerging multidisciplinary field that brings together engineering methods and complexity of life sciences into a unified fundamental understanding of structure-property relationship in micro/nano environment to develop the next generation of scaffolds and hydrogels to restore or improve tissue functions. Chitosan has several unique physico-chemical properties that make it a highly desirable polysaccharide for various applications such as, biomedical, food, nutraceutical, agriculture, packaging, coating, etc. However, the utilization of chitosan in regenerative medicine is often limited due to its inadequate mechanical, barrier and thermal properties. Cellulosic nanomaterials (CNs), owing to their exceptional mechanical strength, ease of chemical modification, biocompatibility and favorable interaction with chitosan, represent an attractive candidate for the fabrication of chitosan/ CNs scaffolds and hydrogels. The unique mechanical and biological properties of the chitosan/CNs bio-nanocomposite make them a material of choice for the development of next generation bio-scaffolds and hydrogels for regenerative medicine applications. In this review, we have summarized the preparation method, mechanical properties, morphology, cytotoxicity/ biocompatibility of chitosan/CNs nanocomposites for regenerative medicine applications, which comprises tissue engineering and wound dressing applications.

3D printing of high-strength chitosan hydrogel scaffolds without any organic solvents

Here, a novel direct ink printing method was developed to print high-strength chitosan hydrogel scaffolds without any organic solvents.

3D Plotting using Camphene as Pore-regulating Agent to Produce Hierarchical Macro/micro-porous Poly(ε-caprolactone)/calcium phosphate Composite Scaffolds

This study demonstrates the utility of camphene as the pore-regulating agent for phase separation-based 3D plotting to produce hierarchical macro/micro-porous poly(ε-caprolactone) (PCL)-calcium phosphate (CaP) composite scaffolds, specifically featuring highly microporous surfaces. Unlike conventional particulate porogens, camphene is highly soluble in acetone, the solvent for PCL polymer, but insoluble in coagulation medium (water). In this study, this unique characteristic supported the creation of numerous micropores both within and at the surfaces of PCL and PCL-CaP composite filaments when using high camphene contents (40 and 50 wt%). In addition, the incorporation of the CaP particles into PCL solutions did not deteriorate the formation of microporous structures, and thus hierarchical macro/micro-porous PCL-CaP composite scaffolds could be successfully produced. As the CaP content increased, the in vitro biocompatibility, apatite-forming ability, and mechanical properties (tensile strength, tensile modulus, and compressive modulus) of the PCL-CaP composite scaffolds were substantially improved.

Cryogenic free-form extrusion bioprinting of decellularized small intestinal submucosa for potential applications in skin tissue engineering

A novel strategy of cryogenic 3D bioprinting assisted by free-from extrusion printing has been developed and applied to printing of a decellularized small intestinal submucosa (dSIS) slurry. The rheological properties, including kinetic viscosity, storage modulus (G'), and loss modulus (G″), were appropriate for free-from extrusion printing of dSIS slurry. Three different groups of scaffolds, including P₅₀₀, P₆₀₀, and P₇₀₀, with filament distances of 500, 600, and 700 μm, respectively were fabricated at a 5 mm s^-1 working velocity of the platform (V _xy) and 25 kPa air pressure of the dispensing system (P) at -20 °C. The fabricated scaffolds were crosslinked via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) which resulted in a polyporous microstructure. The variations in the filament diameter and pore size were evaluated in the initial frozen state after printing, the lyophilized state, and after immersion in a PBS solution. The Young's modulus of the P₅₀₀, P₆₀₀, and P₇₀₀ scaffolds was measured in wet and dry states for EDC-crosslinked scaffolds. The cell experiment results showed improved cell adhesion, viability, and proliferation both on the surface and within the scaffold, indicating the biocompatibility and suitability of the scaffold for 3D cell models. Further, gene and protein expression of normal skin fibroblasts on dSIS scaffolds demonstrated their ability to promote the production of some extracellular matrix proteins (i.e. collagen I, collagen III, and fibronectin) in vitro. Overall, this study presents a new potential strategy, by combining cryogenic 3D bioprinting with decellularized extracellular matrix materials, to manufacture ideal scaffolds for skin tissue engineering applications.

Towards the Development of Artificial Bone Grafts: Combining Synthetic Biomineralisation with 3D Printing

A synthetic technique inspired by the biomineralisation process in nacre has been previously reported to be effective in replicating the nanostructural elements of nacre in 2D chitosan hydrogel films. Here we evaluate the applicability of this synthetic biomineralisation technique, herein called the McGrath method, in replicating the flat tabular morphology of calcium carbonate and other nanostructural elements obtained when 2D chitosan hydrogel films were used, on a 3D porous chitosan hydrogel-based scaffold, hence developing 3D chitosan-calcium carbonate composites. Nozzle extrusion-based 3D printing technology was used to develop 3D porous scaffolds using chitosan hydrogel as the printing ink in a custom-designed 3D printer. The rheology of the printing ink and print parameters were optimised in order to fabricate 3D cylindrical structures with a cubic lattice-based internal structure. The effects of various dehydration techniques, including air-drying, critical point-drying and freeze-drying, on the structural integrity of the as-printed scaffolds from the nano to macroscale, were evaluated. The final 3D composite materials were characterised using scanning electron microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy. The study has shown that McGrath method can be used to develop chitosan-calcium carbonate composites wherein the mineral and matrix are in intimate association with each other at the nanoscale. This process can be successfully integrated with 3D printing technology to develop 3D compartmentalised polymer-mineral composites.

Innovative Cryopreservation Process Using a Modified Core/Shell Cell-Printing with a Microfluidic System for Cell-Laden Scaffolds

This work investigated the printability and applicability of a core/shell cell-printed scaffold for medium-term (for up to 20 days) cryopreservation and subsequent cultivation with acceptable cellular activities including cell viability. We developed an innovative cell-printing process supplemented with a microfluidic channel, a core/shell nozzle, and a low-temperature working stage to obtain a cell-laden 3D porous collagen scaffold for cryopreservation. The 3D porous biomedical scaffold consisted of core/shell struts with a cell-laden collagen-based bioink/dimethyl sulfoxide mixture in the core region and an alginate/poly(ethylene oxide) mixture in the shell region. Following 2 weeks of cryopreservation, the cells (osteoblast-like cells or human adipose stem cells) in the scaffold showed good viability (over 90%), steady growth, and mineralization similar to those of a control scaffold fabricated using a conventional cell-printing process without cryopreservation. We believe that these results are attributable to the optimized fabrication processes the cells underwent, including safe freezing/thawing processes. On the basis of these results, this fabrication process has great potential for obtaining core/shell cell-laden collagen scaffolds for cryopreservation, which have various tissue engineering applications.

Preparation of alginate-chitosan fibers with potential biomedical applications

The preparation of alginate-chitosan fibers, through wet spinning technique, as well as the study of their properties as a function of chitosan's molecular weight and retention time in the coagulation bath, is presented and discussed in this work. Scanning electron microscopy (SEM) revealed that the fibers presented irregular and rough surfaces, with a grooved and heavily striated morphology distributed throughout the structure. Dynamic mechanical analysis (DMA) showed that, with the exception of elongation at break, the incorporation of chitosan into the fibers improved their tensile properties. The in vitro release profile of sulfathiazole as a function of chitosan's molecular weight indicated that the fibers are viable carriers of drugs. Kinetic models showed that the release of the model drug is first-order, and the release mechanism is governed by the Korsmeyer-Peppas model. Likewise, fibers loaded with sulfathiazole showed excellent inhibition of Escherichia coli growth after an incubation time of 24h at 37 °C.

Composite chitosan/silk fibroin nanofibers for modulation of osteogenic differentiation and proliferation of human mesenchymal stem cells

Nanofibrous membrane scaffolds of chitosan (CS), silk fibroin (SF) and CS/SF blend were prepared by electrospinning and studied for growth and osteogenic differentiation of human bone marrow mesenchymal stem cells (hMSCs). The morphology and physico-chemical properties of all membrane scaffolds were compared. The influence of CS and SF on cell proliferation was assessed by the MTS assay, whereas osteogenic differentiation was determined from the Alizarin Red staining, alkaline phosphatase activity and expression of osteogenic marker genes. The osteogenic differentiation and proliferation of hMSCs were enhanced by CS and SF nanofibers, respectively. Blending CS with SF retained the osteogenesis nature of CS without negatively influencing the cell proliferative effect of SF. By taking advantage of the differentiation/proliferation cues from individual components, the electrospun CS/SF composite nanofibrous membrane scaffold is suitable for bone tissue engineering.

Cationic polymers and their therapeutic potential

The last decade has witnessed enormous research focused on cationic polymers. Cationic polymers are the subject of intense research as non-viral gene delivery systems, due to their flexible properties, facile synthesis, robustness and proven gene delivery efficiency. Here, we review the most recent scientific advances in cationic polymers and their derivatives not only for gene delivery purposes but also for various alternative therapeutic applications. An overview of the synthesis and preparation of cationic polymers is provided along with their inherent bioactive and intrinsic therapeutic potential. In addition, cationic polymer based biomedical materials are covered. Major progress in the fields of drug and gene delivery as well as tissue engineering applications is summarized in the present review.