DLP 3D Printing Meets Lignocellulosic Biopolymers: Carboxymethyl Cellulose Inks for 3D Biocompatible Hydrogels

Design considerations for digital light processing bioprinters

With the rapid development and popularization of additive manufacturing, different technologies, including, but not limited to, extrusion-, droplet-, and vat-photopolymerization-based fabrication techniques, have emerged that have allowed tremendous progress in three-dimensional (3D) printing in the past decades. Bioprinting, typically using living cells and/or biomaterials conformed by different printing modalities, has produced functional tissues. As a subclass of vat-photopolymerization bioprinting, digital light processing (DLP) uses digitally controlled photomasks to selectively solidify liquid photocurable bioinks to construct complex physical objects in a layer-by-layer manner. DLP bioprinting presents unique advantages, including short printing times, relatively low manufacturing costs, and decently high resolutions, allowing users to achieve significant progress in the bioprinting of tissue-like complex structures. Nevertheless, the need to accommodate different materials while bioprinting and improve the printing performance has driven the rapid progress in DLP bioprinters, which requires multiple pieces of knowledge ranging from optics, electronics, software, and materials beyond the biological aspects. This raises the need for a comprehensive review to recapitulate the most important considerations in the design and assembly of DLP bioprinters. This review begins with analyzing unique considerations and specific examples in the hardware, including the resin vat, optical system, and electronics. In the software, the workflow is analyzed, including the parameters to be considered for the control of the bioprinter and the voxelizing/slicing algorithm. In addition, we briefly discuss the material requirements for DLP bioprinting. Then, we provide a section with best practices and maintenance of a do-it-yourself DLP bioprinter. Finally, we highlight the future outlooks of the DLP technology and their critical role in directing the future of bioprinting. The state-of-the-art progress in DLP bioprinter in this review will provide a set of knowledge for innovative DLP bioprinter designs.

Preparation of an injectable and photocurable carboxymethyl cellulose/hydroxyapatite composite and its application in cranial regeneration

Limited bone regeneration, uncontrollable degradation rate, mismatched defect zone and poor operability have plagued the reconstruction of irregular bone defect by tissue-engineered materials. A combination of biomimetic scaffolds with hydroxyapatite has gained great popularity in promoting bone regeneration. Therefore, we designed an injectable, photocurable and in-situ curing hydrogel by methacrylic anhydride -modified carboxymethyl cellulose (CMC-MA) loading with spherical hydroxyapatite (HA) to highly simulate the natural bony matrix and match any shape of damaged tissue. The prepared carboxymethyl cellulose-methacrylate/ hydroxyapatite(CMC-MA/HA) composite presented good rheological behavior, swelling ratio and mechanical property under light illumination. Meanwhile, this composite hydrogel promoted effectively proliferation, supported adhesion and upregulated the osteogenic-related genes expression of MC3T3-E1 cells in vitro, as well as the activity of the osteogenic critical protein, Integrin α1, β1, Myosin 9, Myosin 10, BMP-2 and Smad 1 in Integrin/BMP-2 signal pathway. Together, the composite hydrogels realized promotion of bone regeneration, deformity improvement, and the enhanced new bone strength in skull defect. It also displayed a good histocompatibility and stability of subcutaneous implantation in vivo. Overall, this study laid the groundwork for future research into developing a novel biomaterial and a minimally invasive therapeutic strategies for reconstructing bone defects and contour deficiencies.

Pharmaceutical applications and requirements of resins for printing by digital light processing (DLP)

The digital light processing (DLP) printer has proven to be effective in biomedical and pharmaceutical applications, as its printing method does not induce shear and a strong temperature on the resin. In addition, the DLP printer has good resolution and print quality, which makes it possible to print complex structures with a customized shape, being used for various purposes ranging from jewelry application to biomedical and pharmaceutical areas. The big disadvantage of DLP is the lack of a biocompatible and non-toxic resin on the market. To overcome this limitation, an ideal resin for biomedical and pharmaceutical use is needed. The resin must have appropriate properties, so that the desired format is printed when with a determined wavelength is applied. Thus, the aim of this work is to bring the basic characteristics of the resins used by this printing method and the minimum requirements to start printing by DLP for pharmaceutical and biomedical applications. The DLP method has proven to be effective in obtaining pharmaceutical devices such as drug delivery systems. Furthermore, this technology allows the printing of devices of ideal size, shape and dosage, providing the patient with personalized treatment.

Low-Concentration Gelatin Methacryloyl Hydrogel with Tunable 3D Extrusion Printability and Cytocompatibility: Exploring Quantitative Process Science and Biophysical Properties

Three-dimensional (3D) bioprinting of hydrogels with a wide spectrum of compositions has been widely investigated. Despite such efforts, a comprehensive understanding of the correlation among the process science, buildability, and biophysical properties of the hydrogels for a targeted clinical application has not been developed in the scientific community. In particular, the quantitative analysis across the entire developmental path for 3D extrusion bioprinting of such scaffolds is not widely reported. In the present work, we addressed this gap by using widely investigated biomaterials, such as gelatin methacryloyl (GelMA), as a model system. Using extensive experiments and quantitative analysis, we analyzed how the individual components of methacrylated carboxymethyl cellulose (mCMC), needle-shaped nanohydroxyapatite (nHAp), and poly(ethylene glycol)diacrylate (PEGDA) with GelMA as baseline matrix of the multifunctional bioink can influence the biophysical properties, printability, and cellular functionality. The complex interplay among the biomaterial ink formulations, viscoelastic properties, and printability toward the large structure buildability (structurally stable cube scaffolds with 15 mm edge) has been explored. Intriguingly, the incorporation of PEGDA into the GelMA/mCMC matrix offered improved compressive modulus (∼40-fold), reduced swelling ratio (∼2-fold), and degradation rates (∼30-fold) compared to pristine GelMA. The correlation among microstructural pore architecture, biophysical properties, and cytocompatibility is also established for the biomaterial inks. These photopolymerizable bio(material)inks served as the platform for the growth and development of bone and cartilage matrix when human mesenchymal stem cells (hMSCs) are either seeded on two-dimensional (2D) substrates or encapsulated on 3D scaffolds. Taken together, this present study unequivocally establishes a significant step forward in the development of a broad spectrum of shape-fidelity compliant bioink for the 3D bioprinting of multifunctional scaffolds and emphasizes the need for invoking more quantitative analysis in establishing process-microstructure-property correlation.

Gelatin Methacryloyl (GelMA)-Based Biomaterial Inks: Process Science for 3D/4D Printing and Current Status

Tissue engineering for injured tissue replacement and regeneration has been a subject of investigation over the last 30 years, and there has been considerable interest in using additive manufacturing to achieve these goals. Despite such efforts, many key questions remain unanswered, particularly in the area of biomaterial selection for these applications as well as quantitative understanding of the process science. The strategic utilization of biological macromolecules provides a versatile approach to meet diverse requirements in 3D printing, such as printability, buildability, and biocompatibility. These molecules play a pivotal role in both physical and chemical cross-linking processes throughout the biofabrication, contributing significantly to the overall success of the 3D printing process. Among the several bioprintable materials, gelatin methacryloyl (GelMA) has been widely utilized for diverse tissue engineering applications, with some degree of success. In this context, this review will discuss the key bioengineering approaches to identify the gelation and cross-linking strategies that are appropriate to control the rheology, printability, and buildability of biomaterial inks. This review will focus on the GelMA as the structural (scaffold) biomaterial for different tissues and as a potential carrier vehicle for the transport of living cells as well as their maintenance and viability in the physiological system. Recognizing the importance of printability toward shape fidelity and biophysical properties, a major focus in this review has been to discuss the qualitative and quantitative impact of the key factors, including microrheological, viscoelastic, gelation, shear thinning properties of biomaterial inks, and printing parameters, in particular, reference to 3D extrusion printing of GelMA-based biomaterial inks. Specifically, we emphasize the different possibilities to regulate mechanical, swelling, biodegradation, and cellular functionalities of GelMA-based bio(material) inks, by hybridization techniques, including different synthetic and natural biopolymers, inorganic nanofillers, and microcarriers. At the close, the potential possibility of the integration of experimental data sets and artificial intelligence/machine learning approaches is emphasized to predict the printability, shape fidelity, or biophysical properties of GelMA bio(material) inks for clinically relevant tissues.

Promising cellulose-based functional gels for advanced biomedical applications: A review

Novel biomedical materials provide a new horizon for the diagnosis/treatment of diseases and tissue repair in medical engineering. As the most abundant biomass polymer on earth, cellulose is characterized by natural biocompatibility, good mechanical properties, and structure-performance designability. Owing to these outstanding features, cellulose as a biomacromolecule can be designed as functional biomaterials via hydrogen bonding (H-bonding) interaction or chemical modification for human tissue repair, implantable tissue organs, and controlling drug release. Moreover, cellulose can also be used to construct medical sensors for monitoring human physiological signals. In this study, the structural characteristics, functionalization approaches, and advanced biomedical applications of cellulose are reviewed. The current status and application prospects of cellulose and its functional materials for wound dressings, drug delivery, tissue engineering, and electronic skin (e-skin) are discussed. Finally, the key technologies and methods used for designing cellulosic biomaterials and broadening their application prospects in biomedical fields are highlighted.

4D-Printable Photocrosslinkable Polyurethane-Based Inks for Tissue Scaffold and Actuator Applications

4D printing recently emerges as an exciting evolution of conventional 3D printing, where a printed construct can quickly transform in response to a specific stimulus to switch between a temporary variable state and an original state. In this work, a photocrosslinkable polyethylene-glycol polyurethane ink is synthesized for light-assisted 4D printing of smart materials. The molecular weight distribution of the ink monomers is tunable by adjusting the copolymerization reaction time. Digital light processing (DLP) technique is used to program a differential swelling response in the printed constructs after humidity variation. Bioactive microparticles are embedded into the ink and the improvement of biocompatibility of the printed constructs is demonstrated for tissue engineering applications. Cell studies reveal above 90% viability in 1 week and ≈50% biodegradability after 4 weeks. Self-folding capillary scaffolds, dynamic grippers, and film actuators are made and activated in a humid environment. The approach offers a versatile platform for the fabrication of complex constructs. The ink can be used in tissue engineering and actuator applications, making the ink a promising avenue for future research.

Photocrosslinkable Cellulose Derivatives for the Manufacturing of All-Cellulose-Based Architectures

Replacing petroleum-based polymers with biopolymers such as polysaccharides is essential for protecting our environment by saving fossil resources. A research field that can benefit from the application of more sustainable and renewable materials is photochemistry. Therefore, cellulose-based photoresists that could be photocrosslinked via UV irradiation (λ = 254 nm and λ = 365 nm) were developed. These biogenic polymers enable the manufacturing of sustainable coatings, even with imprinted microstructures, and cellulose-based bulk materials. Thus, herein, cellulose was functionalized with organic compounds containing carbon double bonds to introduce photocrosslinkable side groups directly onto the cellulose backbone. Therefore, unsaturated anhydrides such as methacrylic acid anhydride and unsaturated and polyunsaturated carboxylic acids such as linoleic acid were utilized. Additionally, these cellulose derivatives were modified with acetate or tosylate groups to generate cellulose-based polymers, which are soluble in organic solvents, making them suitable for multiple processing methods, such as casting, printing and coating. The photocurable resist was basically composed of the UV-crosslinkable biopolymer, an appropriate solvent and, if necessary, a photoinitiator. Moreover, these bio-based photoresists were UV-crosslinkable in the liquid and solid states after the removal of the solvent. Further, the manufactured cellulose-based architectures, even the bulk structures, could be entirely regenerated into pure cellulose devices via a sodium methoxide treatment.

Methacrylated Cellulose Nanocrystals as Fillers for the Development of Photo-Cross-Linkable Cytocompatible Biosourced Formulations Targeting 3D Printing

Cellulose nanocrystals (CNCs) from cotton were functionalized in aqueous medium using methacrylic anhydride (MA) to produce methacrylated cellulose nanocrystals (mCNCs) with a degree of methacrylation (DM) up to 12.6 ± 0.50%. Dispersible as-prepared CNCs and mCNCs were then considered as reinforcing fillers for aqueous 3D-printable formulations based on methacrylated carboxymethylcellulose (mCMC). The rheological properties of such photo-cross-linkable aqueous formulations containing nonmodified CNCs or mCNCs at 0.2 or 0.5 wt% in 2 wt% mCMC were fully investigated. The influence of the presence of nanoparticles on the UV-curing kinetics and dimensions of the photo-cross-linked hydrogels was probed and 13C CP-MAS NMR spectroscopy was used to determine the maximum conversion ratio of methacrylates as well as the optimized time required for UV postcuring. The viscoelasticity of cross-linked hydrogels and swollen hydrogels was also studied. The addition of 0.5 wt% mCNC with a DM of 0.83 ± 0.040% to the formulation yielded faster cross-linking kinetics, better resolution, more robust cross-linked hydrogels, and more stable swollen hydrogels than pure mCMC materials. Additionally, the produced cryogels showed no cytotoxicity toward L929 fibroblasts. This biobased formulation could thus be considered for the 3D printing of hydrogels dedicated to biomedical purposes using vat polymerization techniques, such as stereolithography or digital light processing.

Trackable and highly fluorescent nanocellulose-based printable bio-resins for image-guided tissue regeneration

Dynamic tracking of cell migration during tissue regeneration remains challenging owing to imaging techniques that require sophisticated devices, are often lethal to healthy tissues. Herein, we developed a 3D printable non-invasive polymeric hydrogel based on 2,2,6,6-(tetramethylpiperidin-1-yl) oxyl (TEMPO)-oxidized nanocellulose (T-CNCs) and carbon dots (CDs) for the dynamic tracking of cells. The as-prepared T-CNC@CDs were used to fabricate a liquid bio-resin containing gelatin methacryloyl (GelMA) and polyethylene glycol diacrylate (GPCD) for digital light processing (DLP) bioprinting. The shear-thinning properties of the GPCD bio-resin were further improved by the addition of T-CNC@CDs, allowing high-resolution 3D printing and bioprinting of human cells with higher cytocompatibility (viability ∼95 %). The elastic modulus of the printed GPCD hydrogel was found to be ∼13 ± 4.2 kPa, which is ideal for soft tissue engineering. The as-fabricated hydrogel scaffold exhibited tunable structural color property owing to the addition of T-CNC@CDs. Owing to the unique fluorescent property of T-CNC@CDs, the human skin cells could be tracked within the GPCD hydrogel up to 30 days post-printing. Therefore, we anticipate that GPCD bio-resin can be used for 3D bioprinting with high structural stability, dynamic tractability, and tunable mechanical stiffness for image-guided tissue regeneration.

Development of Chitosan/Sodium Carboxymethylcellulose Complexes to Improve the Simvastatin Release Rate: Polymer/Polymer and Drug/Polymer Interactions' Effects on Kinetic Models

Simvastatin (SIM) is a potent lipid-lowering drug used to control hyper-cholesterolemia and prevent cardiovascular diseases. SIM presents low oral bioavailability (5%) because of its low aqueous solubility. In this work, polyelectrolyte complexes (PEC) are developed with different chitosan (CS) and carboxymethylcellulose (CMC) ratios that will allow for an increase in the SIM dissolution rate (2.54-fold) in simulated intestinal medium (pH 4.5). Scanning Electron Microscopy (SEM) images revealed highly porous structures. The changes between both complexes, PEC-SIM:CS:CMC (1:1:2) and (1:2:1), were related to the relaxation of the polymer chains upon absorption of the dissolution medium. Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and powder X-ray diffraction (XRPD) studies were used to evaluate the polymer/polymer and drug/polymer interactions on the different PEC-SIM:CS:CMC ratios. In addition, the PEC-SIM:CS:CMC (1:2:1) complex exhibited a high ratio of protonated amino groups (NH3+) and an increase in intramolecular hydrogen bonds, which were correlated with a high expansion of the interpolymer chains and an increase in the SIM dissolution rate. Different kinetic models such as zero-order, first-order, Higuchi and Korsmeyer-Peppas were studied to evaluate the influence of CS/CMC ionic interactions on the ability to improve the release rate of poorly soluble drugs.

Consequence of Synthetic Bone Substitute Used for Alveolar Cleft Graft Reconstruction (Preliminary Clinical Study)

Background  The outcome of alveolar grafting with synthetic bone substitute (Osteon III) in various bone defect volumes is highlighted. Methods  A prospective study was accomplished on 55 patients (6-13 years of age) with unilateral alveolar bone cleft. Osteon III, consisting of hydroxyapatite and tricalcium phosphate, is used to reconstruct the defect. Alveolus defect diameter was calculated before surgery (V1), after 3 months (V2), and finally after 6 months (V3) postsurgery. In the t -test, a significant difference and correlation between V1, V2, and V3 are stated. A p- value of 0.01 is considered a significant difference between parameters. Results  The degree of cleft is divided into three categories: small (9 cases), medium (20 patients), and large (26 cases).The bone volume of the clefted site is divided into three steps: volume 1: (mean 18.1091 mm 3 ); step 2: after 3 months, volume 2 resembles the amount of unhealed defect (mean 0.5109 mm 3 ); and the final bone volume assessment is made after 6 months (22.5455 mm 3 ). Both show statistically significant differences in bone volume formation. Conclusion  An alloplastic bone substitute can also be used as a graft material because of its unlimited bone retrieval. Osteon III can be used to reconstruct the alveolar cleft smoothly and effectively.

Ink Material Selection and Optical Design Considerations in DLP 3D Printing

Digital light processing (DLP) 3D printing has become a powerful manufacturing tool for the fast fabrication of complex functional structures. The rapid progress in DLP printing has been linked to research on optical design factors and ink selection. This critical review highlights the main challenges in the DLP printing of photopolymerizable inks. The kinetics equations of photopolymerization reaction in a DLP printer are solved, and the dependence of curing depth on the process optical parameters and ink chemical properties are explained. Developments in DLP platform design and ink selection are summarized, and the roles of monomer structure and molecular weight on DLP printing resolution are shown by experimental data. A detailed guideline is presented to help engineers and scientists to select inks and optical parameters for fabricating functional structures for multi-material and 4D printing applications.

Rational Design and Characterization of Materials for Optimized Additive Manufacturing by Digital Light Processing

Additive manufacturing technologies are developed and utilized to manufacture complex, lightweight, functional, and non-functional components with optimized material consumption. Among them, vat polymerization-based digital light processing (DLP) exploits the polymerization of photocurable resins in the layer-by-layer production of three-dimensional objects. With the rapid growth of the technology in the last few years, DLP requires a rational design framework for printing process optimization based on the specific material and printer characteristics. In this work, we investigate the curing of pure photopolymers, as well as ceramic and metal suspensions, to characterize the material properties relevant to the printing process, such as penetration depth and critical energy. Based on the theoretical framework offered by the Beer-Lambert law for absorption and on experimental results, we define a printing space that can be used to rationally design new materials and optimize the printing process using digital light processing. The proposed methodology enables printing optimization for any material and printer combination, based on simple preliminary material characterization tests to define the printing space. Also, this methodology can be generalized and applied to other vat polymerization technologies.

One-Step Preparation of Carboxymethyl Cellulose—Phytic Acid Hydrogels with Potential for Biomedical Applications

Hydrogels based on natural, biodegradable materials have gained considerable interest in the medical field due to their improved drug delivery profiles and tissue-mimicking architecture. In this regard, this study was devoted to the preparation and characterization of new physically crosslinked hydrogels based on carboxymethyl cellulose and an unconventional crosslinking agent, phytic acid. Phytic acid, in addition to its antioxidant and antibacterial effects, can improve the biological properties and stability of gels, without adding toxicity. Fourier transform infrared (FTIR) spectroscopy, rheological studies and thermal analysis confirmed the hydrogel formation. The influence of the ratio between the cellulose derivative and the crosslinker upon the morphological structure and water uptake was evidenced by scanning electron microscopy (SEM) and swelling measurements in simulated body fluids. Furthermore, procaine was entrapped within the hydrogels and used as a model drug for in vitro studies, which highlighted the dependence of the drug release on the phytic acid content of the matrix. The materials demonstrated antibacterial effects against Escherichia coli and Staphylococcus aureus bacteria. The biocompatibility was assessed on fibroblast cells, and according to our results, hydrogels can improve cell viability highlighting the potential of these systems as therapeutic scaffolds for skin tissue engineering.

Three-dimensional bioprinting: A cutting-edge tool for designing and fabricating engineered living materials

The design of engineered living materials (ELMs) is an emerging field developed from synthetic biology and materials science principles. ELMs are multi-scale bulk materials that combine the properties of self-healing and organism adaptability with the designed physicochemical or mechanical properties for functional applications in various fields, including therapy, electronics, and architecture. Among the many ELM design and manufacturing methods, three-dimensional (3D) bioprinting stands out for its precise control over the structure of the fabricated constructs and the spatial distribution of cells. In this review, we summarize the progress in the field, cell type and material selection, and the latest applications of 3D bioprinting to manufacture ELMs, as well as their advantages and limitations, hoping to deepen our understanding and provide new insights into ELM design. We believe that 3D bioprinting will become an important development direction and provide more contributions to this field.

A printability study of multichannel nerve guidance conduits using projection-based three-dimensional printing

Multichannel nerve guidance conduits (NGCs) replicating the native architecture of peripheral nerves have emerged as promising alternatives to autologous nerve grafts. However, manufacturing multichannel NGCs is challenging in terms of desired structural stability and resolution. In this study, we systematically investigated the effects of photopolymer properties, inner diameter dimensions, printing parameters, and different conditions on multichannel NGCs printability using projection-based three-dimensional printing. Low viscosity and rapid photocuring properties were essential requirements. A standard model was generated to evaluate multichannel NGC printed quality. The results showed that printing deviations decreased with increased mechanical strength and inner diameter. Subsequently, gelatin methacrylate (GelMA) NGCs was selected as a representative. It was found that printing conditions, including printing temperature, peeling, and shrinkage affected final NGC accuracy and quality. PC-12 cells cultured with the GelMA NGCs displayed non-toxic and promoted cell migration. Our research provides an effective, time-saving, and high-resolution technology for manufacturing multichannel NGCs with high fidelity, which may be used as reference templates for biomedical applications.

Improving Printability of Digital-Light-Processing 3D Bioprinting via Photoabsorber Pigment Adjustment

Digital-light-processing (DLP) three-dimensional (3D) bioprinting, which has a rapid printing speed and high precision, requires optimized biomaterial ink to ensure photocrosslinking for successful printing. However, optimization studies on DLP bioprinting have yet to sufficiently explore the measurement of light exposure energy and biomaterial ink absorbance controls to improve the printability. In this study, we synchronized the light wavelength of the projection base printer with the absorption wavelength of the biomaterial ink. In this paper, we provide a stepwise explanation of the challenges associated with unsynchronized absorption wavelengths and provide appropriate examples. In addition to biomaterial ink wavelength synchronization, we introduce photorheological measurements, which can provide optimized light exposure conditions. The photorheological measurements provide precise numerical data on light exposure time and, therefore, are an effective alternative to the expendable and inaccurate conventional measurement methods for light exposure energy. Using both photorheological measurements and bioink wavelength synchronization, we identified essential printability optimization conditions for DLP bioprinting that can be applied to various fields of biological sciences.

Loose Pre-Cross-Linking Mediating Cellulose Self-Assembly for 3D Printing Strong and Tough Biomimetic Scaffolds

The lack of an effective printable ink preparation method and the usual mechanically weak performance obstruct the functional 3D printing hydrogel exploitation and application. Herein, we propose a gentle pre-cross-linking strategy to enable a loosely cross-linked cellulose network for simultaneously achieving favorable printability and a strong hydrogel network via mediating the cellulose self-assembly. A small amount of epichlorohydrin is applied to (i) slightly pre-cross-link the cellulose chains for forming the percolating network to regulate the rheological properties and (ii) form the loosely cross-linked points to mediate the cellulose chains' self-assembly for achieving superior mechanical properties. The fabrication of the complex 3D structures verifies the design flexibility. The printed cellulose hydrogels exhibit a biomimetic nanofibrous topology, remarkable tensile and compressive strength (5.22 and 11.80 MPa), as well as toughness (1.81 and 2.16 MJ/m³). As a demonstration, a bilayer scaffold (mimicking the osteochondral structure) consisting of a top pristine cellulose and a bottom cellulose/bioactive glass hydrogel is printed and exhibits superior osteochondral defect repair performance, showing a potential in tissue engineering. We anticipate that our loose pre-cross-linking 3D printing ink preparation concept can inspire the development of other polymeric inks and strong 3D printing functional hydrogels, eventually spreading the applications in diverse fields.

Solvent Mediating the in Situ Self-Assembly of Polysaccharides for 3D Printing Biomimetic Tissue Scaffolds

Intensively studied 3D printing technology is frequently hindered by the effective printable ink preparation method. Herein, we propose an elegant and gentle solvent consumption strategy to slowly disrupt the thermodynamic stability of the biopolymer (polysaccharide: cellulose, chitin, and chitosan) solution to slightly induce the molecule chains to in situ self-assemble into nanostructures for regulating the rheological properties, eventually achieving the acceptable printability. The polysaccharides are dissolved in the alkali/urea solvent. The weak Lewis acid fumed silica (as solvent mediator) is used to (i) slowly and partially consume the alkali/urea solvent to induce the polysaccharide chains to self-assemble into nanofibers to form a percolating network in a limited scale without leading to gelation and (ii) act as the support to increase the solution modulus, for achieving superior printability and scaffold design flexibility. As a demonstration, the resulting polysaccharide scaffolds with biomimetic nanofibrous structures exhibit superior performances in both the cell-free and cell-loaded bone tissue engineering strategies, showing the potential in tissue engineering. Moreover, the fumed silica could be completely removed by alkali treatment without defecting the nanofibrous structure, showing the potential in various applications. We anticipate our solvent-mediated 3D printing ink preparation concept could be used to fabricate other polymeric facile inks and for widespread applications in diverse fields.

Polymerizable Choline- and Imidazolium-Based Ionic Liquids Reinforced with Bacterial Cellulose for 3D-Printing

In this work, a novel approach is demonstrated for 3D-printing of bacterial cellulose (BC) reinforced UV-curable ion gels using two-component solvents based on 1-butyl-3-methylimidazolium chloride or choline chloride combined with acrylic acid. Preservation of cellulose's crystalline and nanofibrous structure is demonstrated using wide-angle X-ray diffraction (WAXD) and atomic force microscopy (AFM). Rheological measurements reveal that cholinium-based systems, in comparison with imidazolium-based ones, are characterised with lower viscosity at low shear rates and improved stability against phase separation at high shear rates. Grafting of poly(acrylic acid) onto the surfaces of cellulose nanofibers during UV-induced polymerization of acrylic acid results in higher elongation at break for choline chloride-based compositions: 175% in comparison with 94% for imidazolium-based systems as well as enhanced mechanical properties in compression mode. As a result, cholinium-based BC ion gels containing acrylic acid can be considered as more suitable for 3D-printing of objects with improved mechanical properties due to increased dispersion stability and filler/matrix interaction.

Dispersion of Micro Fibrillated Cellulose (MFC) in Poly(lactic acid) (PLA) from Lab-Scale to Semi-Industrial Processing Using Biobased Plasticizers as Dispersing Aids

In the present study, two commercial typologies of microfibrillated cellulose (MFC) (Exilva and Celish) with 2% wt % were firstly melt-compounded at the laboratory scale into polylactic acid (PLA) by a microcompounder. To reach an MFC proper dispersion and avoid the well-known aglomeration problems, the use of two kinds of biobased plasticisers (poly(ethylene glycol) (PEG) and lactic acid oligomer (OLA)) were investigated. The plasticizers had the dual effect of dispersing the MFC, and at the same time, they counterbalanced the excessive stiffness caused by the addition of MFC to the PLA matrix. Several preliminaries dilution tests, with different aqueous cellulose suspension/plasticizer weight ratios were carried out. These tests were accompanied by SEM observations and IR and mechanical tests on compression-molded films in order to select the best plasticizer content. The best formulation was then scaled up in a semi-industrial twin-screw extruder, feeding the solution by a peristaltic pump, to optimize the industrial-scale production of commercial MFC-based composites with a solvent-free method. From this study, it can be seen that the use of plasticisers as dispersing aids is a biobased and green solution that can be easily used in conventional extrusion techniques.

Recent advancements in 3D bioprinting technology of carboxymethyl cellulose-based hydrogels: Utilization in tissue engineering

3D printing technology has grown exponentially since its introduction due to its ability to print complex structures quickly and simply. The ink used in 3D printers is one of the most discussed areas and a variety of hydrogel-based inks were developed. Carboxymethyl cellulose (CMC) is derived from cellulose, which is a natural, biocompatible, biodegradable, and wildly abounded biopolymer. CMC is a very qualified candidate in the preparation of hydrogels because it has good solubility in water with multiple carboxyl groups. Various physical and chemical cross-linking methods and mechanisms have been used by researchers to prepare CMC-based hydrogels. Bioprinting is a powerful technology for tissue engineering applications that have been able to design and simulate different tissue and organs with digital control. Among many advantages, which were reported for bioprinting, its high throughput, as well as precise control of scaffolding and cells, is very valuable. Considering all these tips and capabilities, in this study, the methods of preparation and improvement of CMC-based hydrogels, applied 3D printer, and the latest inks designed using this biopolymer in terms of combination, features, and performance in tissue engineering are reported.

Recent Developments of Carboxymethyl Cellulose

Carboxymethyl cellulose (CMC) is one of the most promising cellulose derivatives. Due to its characteristic surface properties, mechanical strength, tunable hydrophilicity, viscous properties, availability and abundance of raw materials, low-cost synthesis process, and likewise many contrasting aspects, it is now widely used in various advanced application fields, for example, food, paper, textile, and pharmaceutical industries, biomedical engineering, wastewater treatment, energy production, and storage energy production, and storage and so on. Many research articles have been reported on CMC, depending on their sources and application fields. Thus, a comprehensive and well-organized review is in great demand that can provide an up-to-date and in-depth review on CMC. Herein, this review aims to provide compact information of the synthesis to the advanced applications of this material in various fields. Finally, this article covers the insights of future CMC research that could guide researchers working in this prominent field.

Photopolymerization of Bio-Based Polymers in a Biomedical Engineering Perspective

Photopolymerization is an effective method to covalently cross-link polymer chains that can be shaped into several biomedical products and devices. Additionally, polymerization reaction may induce a fluid-solid phase transformation under physiological conditions and is ideal for in vivo cross-linking of injectable polymers. The photoinitiator is a key ingredient able to absorb the energy at a specific light wavelength and create radicals that convert the liquid monomer solution into polymers. The combination of photopolymerizable polymers, containing appropriate photoinitiators, and effective curing based on dedicated light sources offers the possibility to implement photopolymerization technology in 3D bioprinting systems. Hence, cell-laden structures with high cell viability and proliferation, high accuracy in production, and good control of scaffold geometry can be biofabricated. In this review, we provide an overview of photopolymerization technology, focusing our efforts on natural polymers, the chemistry involved, and their combination with appropriate photoinitiators to be used within 3D bioprinting and manufacturing of biomedical devices. The reviewed articles showed the impact of different factors that influence the success of the photopolymerization process and the final properties of the cross-linked materials.

3D Bioprinting of Lignocellulosic Biomaterials

The interest in bioprinting of sustainable biomaterials is rapidly growing, and lignocellulosic biomaterials have a unique role in this development. Lignocellulosic materials are biocompatible and possess tunable mechanical properties, and therefore promising for use in the field of 3D-printed biomaterials. This review aims to spotlight the recent progress on the application of different lignocellulosic materials (cellulose, hemicellulose, and lignin) from various sources (wood, bacteria, and fungi) in different forms (including nanocrystals and nanofibers in 3D bioprinting). Their crystallinity, leading to water insolubility and the presence of suspended nanostructures, makes these polymers stand out among hydrogel-forming biomaterials. These unique structures give rise to favorable properties such as high ink viscosity and strength and toughness of the final hydrogel, even when used at low concentrations. In this review, the application of lignocellulosic polymers with other components in inks is reported for 3D bioprinting and identified supercritical CO₂ as a potential sterilization method for 3D-printed cellulosic materials. This review also focuses on the areas of potential development by highlighting the opportunities and unmet challenges such as the need for standardization of the production, biocompatibility, and biodegradability of the cellulosic materials that underscore the direction of future research into the 3D biofabrication of cellulose-based biomaterials.

Sustainable Photopolymers in 3D Printing: A Review on Biobased, Biodegradable, and Recyclable Alternatives

The global market for 3D printing materials has grown exponentially in the last decade. Today, photopolymers claim almost half of the material sales worldwide. The lack of sustainable resins, applicable in vat photopolymerization that can compete with commercial materials, however, limits the widespread adoption of this technology. The development of "green" alternatives is of great importance in order to reduce the environmental impact of additive manufacturing. This paper reviews the recent evolutions in the field of sustainable photopolymers for 3D printing. It highlights the synthesis and application of biobased resin components, such as photocurable monomers and oligomers, as well as reinforcing agents derived from natural resources. In addition, the design of biologically degradable and recyclable thermoset products in vat photopolymerization is discussed. Together, those strategies will promote the accurate and waste-free production of a new generation of 3D materials for a sustainable plastics economy in the near future.

Extending Cellulose-Based Polymers Application in Additive Manufacturing Technology: A Review of Recent Approaches

The materials for additive manufacturing (AM) technology have grown substantially over the last few years to fulfill industrial needs. Despite that, the use of bio-based composites for improved mechanical properties and biodegradation is still not fully explored. This limits the universal expansion of AM-fabricated products due to the incompatibility of the products made from petroleum-derived resources. The development of naturally-derived polymers for AM materials is promising with the increasing number of studies in recent years owing to their biodegradation and biocompatibility. Cellulose is the most abundant biopolymer that possesses many favorable properties to be incorporated into AM materials, which have been continuously focused on in recent years. This critical review discusses the development of AM technologies and materials, cellulose-based polymers, cellulose-based three-dimensional (3D) printing filaments, liquid deposition modeling of cellulose, and four-dimensional (4D) printing of cellulose-based materials. Cellulose-based AM material applications and the limitations with future developments are also reviewed.