Browsing by Author "Ajdary, Rubina"
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Item 3D-Printed Thermoset Biocomposites Based on Forest Residues by Delayed Extrusion of Cold Masterbatch (DECMA)(AMERICAN CHEMICAL SOCIETY, 2021-10-18) Trifol, Jon; Jayaprakash, Siddharth; Baniasadi, Hossein; Ajdary, Rubina; Kretzschmar, Niklas; Rojas, Orlando J.; Partanen, Jouni; Seppälä, Jukka V.; Department of Chemical and Metallurgical Engineering; Department of Mechanical Engineering; Department of Bioproducts and Biosystems; Polymer technology; Advanced Manufacturing and Materials; Bio-based Colloids and MaterialsWe developed a 3D-printing process based on thermoset biocomposites termed Delayed Extrusion of Cold Masterbatch (DECMA). DECMA is a processing method, based on controlling the degree of curing, that takes some responsibility of the 3D printing from materials and as such can be used to 3D print otherwise unprintable materials. First, a masterbatch was produced by mixing a bio-based resin (bioepoxy) and sawdust and lignin. This paste was partially cured at room temperature until reaching an apparent viscosity suitable for extrusion (≈105 mPa·s at 1 s-1). The system was next cooled (5-10 °C) to delay subsequent hardening prior to 3D printing. The printability of the biocomposite paste was systematically investigated and the merits of the delayed extrusion, via DECMA, were assessed. It was found that DECMA allowed the revalorization of sawdust and lignin via 3D printing, as direct printing led to failed prints. Our approach afforded cost-effective, shear-thinning dopes with a high bio-based content (58-71%). The bio-based 3D-printed materials demonstrated good machinability by computer numerical control (CNC). Overall, the benefits of the introduced DECMA method are shown for processing bio-based materials and for on-demand solidification during additive manufacturing.Item Absorbent Filaments from Cellulose Nanofibril Hydrogels through Continuous Coaxial Wet Spinning(2018-08-15) Lundahl, Meri J.; Klar, Ville; Ajdary, Rubina; Norberg, Nicholas; Ago, Mariko; Cunha, Ana Gisela; Rojas, Orlando J.; Department of Bioproducts and Biosystems; Department of Mechanical Engineering; Bio-based Colloids and Materials; Spectris plcA continuous and scalable method for the wet spinning of cellulose nanofibrils (CNFs) is introduced in a core/shell configuration. Control on the interfacial interactions was possible by the choice of the shell material and coagulant, as demonstrated here with guar gum (GG) and cellulose acetate (CA). Upon coagulation in acetone, ethanol, or water, GG and CA formed supporting polymer shells that interacted to different degrees with the CNF core. Coagulation rate was shown to markedly influence the CNF orientation in the filament and, as a result, its mechanical strength. The fastest coagulation noted for the CNF/GG core/shell system in acetone led to an orientation index of ∼0.55 (Herman's orientation parameter of 0.40), Young's modulus of ∼2.1 GPa, a tensile strength of ∼70 MPa, and a tenacity of ∼8 cN/tex. The system that underwent the slowest coagulation rate (CNF/GG in ethanol) displayed a limited CNF orientation but achieved an intermediate level of mechanical resistance, owing to the strong core/shell interfacial affinity. By using CA as the supporting shell, it was possible to spin CNF into filaments with high water absorption capacity (43 g water/g dry filament). This was explained by the fact that water (used as the coagulant for CA) limited the densification of the CNF core structure, yielding filaments with high accessible area and pore density.Item Acetylated Nanocellulose for Single-Component Bioinks and Cell Proliferation on 3D-Printed Scaffolds(AMER CHEMICAL SOC, 2019-05-22) Ajdary, Rubina; Huan, Siqi; Zanjanizadeh Ezazi, Nazanin; Xiang, Wenchao; Grande, Rafael; Santos, Hélder A.; Rojas, Orlando J.; Department of Bioproducts and Biosystems; Bio-based Colloids and Materials; University of HelsinkiNanocellulose has been demonstrated as a suitable material for cell culturing, given its similarity to extracellular matrices. Taking advantage of the shear thinning behavior, nanocellulose suits three-dimensional (3D) printing into scaffolds that support cell attachment and proliferation. Here, we propose aqueous suspensions of acetylated nanocellulose of a low degree of substitution for direct ink writing (DIW). This benefits from the heterogeneous acetylation of precursor cellulosic fibers, which eases their deconstruction and confers the characteristics required for extrusion in DIW. Accordingly, the morphology of related 3D-printed architectures and their performance during drying and rewetting as well as interactions with living cells are compared with those produced from typical unmodified and TEMPO-oxidized nanocelluloses. We find that a significantly lower concentration of acetylated nanofibrils is needed to obtain bioinks of similar performance, affording more porous structures. Together with their high surface charge and axial aspect, acetylated nanocellulose produces dimensionally stable monolithic scaffolds that support drying and rewetting, required for packaging and sterilization. Considering their potential uses in cardiac devices, we discuss the interactions of the scaffolds with cardiac myoblast cells. Attachment, proliferation, and viability for 21 days are demonstrated. Overall, the performance of acetylated nanocellulose bioinks opens the possibility for reliable and scale-up fabrication of scaffolds appropriate for studies on cellular processes and for tissue engineering.Item Ascorbic acid-loaded polyvinyl alcohol/cellulose nanofibril hydrogels as precursors for 3D printed materials(Elsevier Science B.V., 2021-11) Bani Asadi, Hossein; Madani, Zahraalsadat; Ajdary, Rubina; Rojas Gaona, Orlando; Seppälä, Jukka; Department of Chemical and Metallurgical Engineering; Department of Bioproducts and Biosystems; Polymer technology; Bio-based Colloids and MaterialsWe proposed a simple method to process hydrogels containing polyvinyl alcohol and cellulose nanofibrils (PVA/CNF) to prepare volumetric architectures by direct ink writing (DIW). The presence of CNF in the aqueous PVA suspensions conferred rheology profiles that were suitable for extrusion and solidification in pre-designed shapes. The viscoelastic behavior of the hybrid inks enabled precise control on processability and shape retention, for instance, as demonstrated in multilayered lattice structures of high fidelity. After lyophilization, the obtained 3D-printed hydrogels presented a very high porosity, with open and interconnected pores, allowing a high-water uptake capacity (up to 1600%). The mechanical strength of the composite 3D-printed materials matched those of soft tissues, opening opportunities for skin applications. As such, drug-loaded samples revealed a controlled and efficient delivery of an antioxidant (ascorbic acid) in PBS buffer media at 23 °C (~80% for 8 h). Altogether, PVA/CNF hydrogels were introduced as suitable precursors of 3D-lattice geometries with excellent physical and mechanical characteristics.Item Bacterial nanocellulose enables auxetic supporting implants(ELSEVIER SCI LTD, 2022-05-15) Ajdary, Rubina; Abidnejad, Roozbeh; Lehtonen, Janika; Kuula, Jani; Raussi-Lehto, Eija; Kankuri, Esko; Tardy, Blaise; Rojas, Orlando J.; Department of Bioproducts and Biosystems; Department of Neuroscience and Biomedical Engineering; Bio-based Colloids and Materials; University of HelsinkiOwing to its purity and exceptional mechanical performance, bacterial nanocellulose (BNC) is well suited for tissue engineering applications. BNC assembles as a network that features similarities with the extracellular matrix (ECM) while exhibiting excellent integrity in the wet state, suitable for suturing and sterilization. The development of complex 3D forms is shown by taking advantage of the aerobic process involved in the biogenesis of BNC at the air/culture medium interphase. Hence, solid supports are used to guide the formation of BNC biofilms that easily form auxetic structures. Such biomaterials are demonstrated as implantable meshes with prescribed opening size and infill density. The measured mechanical strength is easily adjustable (48–456 MPa tensile strength) while ensuring shape stability (>87% shape retention after 100 burst loading/unloading cycles). We further study the cytotoxicity, monocyte/macrophage pro-inflammatory activation, and phenotype to demonstrate the prospective use of BNC as supportive implants with long-term comfort and minimal biomaterial fatigue.Item Cellulose dissolution in aqueous NaOH–ZnO : cellulose reactivity and the role of ZnO(SPRINGER, 2021-02) Väisänen, Saija; Ajdary, Rubina; Altgen, Michael; Nieminen, Kaarlo; Kesari, Kavindra K.; Ruokolainen, Janne; Rojas, Orlando J.; Vuorinen, Tapani; Department of Bioproducts and Biosystems; Department of Applied Physics; Wood Chemistry; Bio-based Colloids and Materials; Wood Material Science; Biorefineries; Molecular MaterialsAbstract: Cellulose utilization at its full potential often requires its dissolution which is challenging. Aqueous NaOH is the solvent of choice due to the rapid, non-toxic, low cost and environmentally friendly dissolution process. However, there are several limitations, such as the required low temperature and cellulose´s moderately low degree of polymerization and concentration. Moreover, there is a tendency for gelation of semidilute solutions with time and temperature. The addition of ZnO aids cellulose dissolution and hinders self-aggregation in the NaOH solution; however, the exact role of ZnO has remained as an open question. In this work, we studied cellulose dissolution in the aqueous NaOH–ZnO system as well as the reactivity of the dissolved cellulose by oxidation with 4-AcNH-TEMPO+ (TEMPO+). Based on Raman spectroscopic studies and the TEMPO+-reactivities, we propose a new structure for cellulose dissolved in aqueous NaOH–ZnO. Graphic abstract: [Figure not available: see fulltext.]Item Cellulose gelation in NaOH(aq) by CO2 absorption: Effects of holding time and concentration on biomaterial development(Elsevier Science Ltd., 2023-02-15) Reyes, Guillermo; Ajdary, Rubina; Kankuri, Esko; Kaschuk, Joice J.; Kosonen, Harri; Rojas, Orlando J.; Department of Bioproducts and Biosystems; Bio-based Colloids and Materials; University of Helsinki; UPM Research CenterWe address the limited solubility and early onset of gelation of aqueous sodium hydroxide to position it as a preferred green solvent for cellulose. For this purpose, we expand the concentration window (up to 12 wt%) by using a CO2-depleted air and adjusting the time the dope remains in the given atmosphere, before further processing (holding time) and regeneration conditions. Cellulose solutions are extruded following characteristic (rheology and extrusion) parameters to yield aligned filaments reaching tenacities up to 2.3 cN·dtex−1, similar to that of viscose. Further material demonstrations are achieved by direct ink writing of auxetic biomedical meshes (Poisson's ratio of −0.2, tensile strength of 115 kPa) and transparent films, which achieved a tensile strength and toughness of 47 MPa and 590 kJ·m−3, respectively. The results suggest an excellent outlook for cellulose transformation into bioproducts. Key to this development is the control of the gelation ensuing solution flow and polymer alignment, which depend on CO2 absorption, cellulose concentration, and holding time.Item Cellulose Nanofibrils Endow Phase-Change Polyethylene Glycol with Form Control and Solid-to-gel Transition for Thermal Energy Storage(AMERICAN CHEMICAL SOCIETY, 2021-02-10) Yazdani, Maryam R.; Ajdary, Rubina; Kankkunen, Ari; Rojas, Orlando J.; Seppälä, Ari; Department of Mechanical Engineering; Department of Bioproducts and Biosystems; Energy Conversion; Bio-based Colloids and MaterialsGreen energy-storage materials enable the sustainable use of renewable energy and waste heat. As such, a form-stable phase-change nanohybrid (PCN) is demonstrated to solve the fluidity and leakage issues typical of phase-change materials (PCMs). Here, we introduce the advantage of solid-to-gel transition to overcome the drawbacks of typical solid-to-liquid counterparts in applications related to thermal energy storage and regulation. Polyethylene glycol (PEG) is form-stabilized with cellulose nanofibrils (CNFs) through surface interactions. The cellulosic nanofibrillar matrix is shown to act as an organogelator of highly loaded PEG melt (85 wt %) while ensuring the absence of leakage. CNFs also preserve the physical structure of the PCM and facilitate handling above its fusion temperature. The porous CNF scaffold, its crystalline structure, and the ability to hold PEG in the PCN are characterized by optical and scanning electron imaging, infrared spectroscopy, and X-ray diffraction. By the selection of the PEG molecular mass, the lightweight PCN provides a tailorable fusion temperature in the range between 18 and 65 °C for a latent heat storage of up to 146 J/g. The proposed PCN shows remarkable repeatability in latent heat storage after 100 heating/cooling cycles as assessed by differential scanning calorimetry. The thermal regulation and light-to-heat conversion of the PCN are confirmed via infrared thermal imaging under simulated sunlight and in a thermal chamber, outperforming those of a reference, commercial insulation material. Our PCN is easily processed as a structurally stable design, including three-dimensional, two-dimensional (films), and one-dimensional (filaments) materials; they are, respectively, synthesized by direct ink writing, casting/molding, and wet spinning. We demonstrate the prospects of the lightweight, green nanohybrid for smart-energy buildings and waste heat-generating electronics for thermal energy storage and management.Item Direct CO2 capture by alkali-dissolved cellulose and sequestration in building materials and artificial reef structures(WILEY-VCH VERLAG, 2023-03-16) Reyes, Guillermo; Vega-Coloma, Mabel; Antonova, Anna; Ajdary, Rubina; Jonveaux, Solene; Flanigan, Colleen; Lautenbacher, Nathalie; Rojas, Orlando J.; Department of Bioproducts and Biosystems; Department of Civil Engineering; Department of Design; Bio-based Colloids and Materials; Mineral Based Materials and Mechanics; Universidad del Bío-Bío; Université de Sherbrooke; Zoe – A Living Sea Sculpture in CozumelCurrent carbon capture and utilization (CCU) technologies require high energy input and costly catalysts. Here, an effective pathway is offered that addresses climate action by atmospheric CO2 sequestration. Industrially relevant highly reactive alkali cellulose solutions are used as CO2 absorption media. The latter lead to mineralized cellulose materials (MCM) at a tailorable cellulose-to-mineral ratio, forming organic-inorganic viscous systems (viscosity from 102 to 107 mPa s and storage modulus from 10 to 105 Pa). CO2 absorption and conversion into calcium carbonate and associated minerals translate to maximum absorption of 6.5 gCO2 gcellulose−1, tracking inversely with cellulose loading. Cellulose lean gels are easily converted into dry powders, shown as a functional component of ceramic glazes and cementitious composites. Meanwhile, cellulose-rich gels are moldable and extrudable, yielding stone-like structures tested as artificial substrates for coral reef restoration. Life Cycle Assessment (LCA) suggests new CCU opportunities for building materials, as demonstrated in underwater deployment for coral reef ecosystem restoration.Item Direct ink writing of aloe vera/cellulose nanofibrils bio-hydrogels(ELSEVIER SCI LTD, 2021-08-15) Bani Asadi, Hossein; Ajdary, Rubina; Trifol Guzman, Jon; Rojas, Orlando J.; Seppälä, Jukka; Department of Chemical and Metallurgical Engineering; Department of Bioproducts and Biosystems; Polymer technology; Bio-based Colloids and MaterialsDirect-ink-writing (DIW) of hydrogels has become an attractive research area due to its capability to fabricate intricate, complex, and highly customizable structures at ambient conditions for various applications, including biomedical purposes. In the current study, cellulose nanofibrils reinforced aloe vera bio-hydrogels were utilized to develop 3D geometries through the DIW technique. The hydrogels revealed excellent viscoelastic properties enabled extruding thin filaments through a nozzle with a diameter of 630 μm. Accordingly, the lattice structures were printed precisely with a suitable resolution. The 3D-printed structures demonstrated significant wet stability due to the high aspect ratio of the nano- and microfibrils cellulose, reinforced the hydrogels, and protected the shape from extensive shrinkage upon drying. Furthermore, all printed samples had a porosity higher than 80% and a high-water uptake capacity of up to 46 g/g. Altogether, these fully bio-based, porous, and wet stable 3D structures might have an opportunity in biomedical fields.Item Direct Ink Writing of Biocompatible Nanocellulose and Chitosan Hydrogels for Implant Mesh Matrices(ACS Publications, 2022-04-13) Ajdary, Rubina; Reyes Torres, Guillermo; Kuula, Jani; Raussi-Lehto, Eija; Mikkola, Tomi S.; Kankuri, Esko; Rojas Gaona, Orlando; Department of Bioproducts and Biosystems; Department of Neuroscience and Biomedical Engineering; Bio-based Colloids and Materials; University of HelsinkiDirect ink writing via single or multihead extrusion is used to synthesize layer-by-layer (LbL) meshes comprising renewable polysaccharides. The best mechanical performance (683 ± 63 MPa modulus and 2.5 ± 0.4 MPa tensile strength) is observed for 3D printed structures with full infill density, given the role of electrostatic complexation between the oppositely charged components (chitosan and cellulose nanofibrils). The LbL structures develop an unexpectedly high wet stability that undergoes gradual weight loss at neutral and slightly acidic pH. The excellent biocompatibility and noncytotoxicity toward human monocyte/macrophages and controllable shrinkage upon solvent exchange make the cellular meshes appropriate for use as biomedical implants.Item Electrochemically synthesized graphene/TEMPO-oxidized cellulose nanofibrils hydrogels: Highly conductive green inks for 3D printing of robust structured EMI shielding aerogels(Elsevier Ltd, 2023-06-15) Erfanian, Elnaz; Moaref, Roxana; Ajdary, Rubina; Tam, Kam C.; Rojas, Orlando J.; Kamkar, Milad; Sundararaj, Uttandaraman; Department of Bioproducts and Biosystems; Bio-based Colloids and Materials; University of Calgary; University of British ColumbiaWe report on the design and synthesis of bio-based, electrically conductive green inks for direct ink writing (DIW) of lightweight electronics and electromagnetic interference (EMI) shields. The inks incorporate fibrillated cellulose and electrochemically synthesized graphene oxide (EGO), with no production and/or consumption of hazardous chemicals. The cellulosic component, TOCNF ((2,2,6,6-tetrame-thylpiperidin-1-yl) oxidanyl (TEMPO)-oxidized cellulose nanofibrils), improves the colloidal dispersion and the rheological properties of EGO-based inks for high-resolution 3D printing via DIW. The printing fidelity and shape retention significantly rely on the EGO/TOCNF loading and ratio in the precursor hydrogel inks. Aerogels result from freeze drying, allowing the production of 3D ultra-lightweight materials with prescribed macro-scale design featuring excellent stability and ease of handling. It is shown that the nano- and micro-scale design of the aerogels can be readily tuned by the solid content and EGO/TOCNF ratio in the inks. This multi-scale materials design provides a unique opportunity to control the mechanical and electrical properties of the printed structures. For instance, aerogels with compression modulus in the range of 250–1096 kPa are obtained based on the composition of the inks. For the optimized ink, an excellent EMI shielding effectiveness, as high as 55.6 dB, is achieved.Item Fabrication and Characterization of Drug-Loaded Conductive Poly(glycerol sebacate)/Nanoparticle-Based Composite Patch for Myocardial Infarction Applications(AMERICAN CHEMICAL SOCIETY, 2020-02-12) Zanjanizadeh Ezazi, Nazanin; Ajdary, Rubina; Correia, Alexandra; Mäkilä, Ermei; Salonen, Jarno; Kemell, Marianna; Hirvonen, Jouni; Rojas, Orlando J.; Ruskoaho, Heikki J.; Santos, Hélder A.; Department of Bioproducts and Biosystems; Bio-based Colloids and Materials; University of Helsinki; University of TurkuHeart tissue engineering is critical in the treatment of myocardial infarction, which may benefit from drug-releasing smart materials. In this study, we load a small molecule (3i-1000) in new biodegradable and conductive patches for application in infarcted myocardium. The composite patches consist of a biocompatible elastomer, poly(glycerol sebacate) (PGS), coupled with collagen type I, used to promote cell attachment. In addition, polypyrrole is incorporated because of its electrical conductivity and to induce cell signaling. Results from the in vitro experiments indicate a high density of cardiac myoblast cells attached on the patches, which stay viable for at least 1 month. The degradation of the patches does not show any cytotoxic effect, while 3i-1000 delivery induces cell proliferation. Conductive patches show high blood wettability and drug release, correlating with the rate of degradation of the PGS matrix. Together with the electrical conductivity and elongation characteristics, the developed biomaterial fits the mechanical, conductive, and biological demands required for cardiac treatment.Item Fiber-based superabsorbents(2017-08-29) Ajdary, Rubina; Ago, Mariko; Kemian tekniikan korkeakoulu; Rojas, OrlandoItem Functionalized nanocellulose supported phase change materials for thermal energy storage(2019-10-22) Shi, Xuetong; Ajdary, Rubina; Yazdani, Roza; Kemian tekniikan korkeakoulu; Rojas, OrlandoItem High-resolution 3D printing of xanthan gum/nanocellulose bio-inks(Elsevier, 2022-06-01) Baniasadi, Hossein; Kimiaei, Erfan; Teixeira Polez, Roberta; Ajdary, Rubina; Rojas Gaona, Orlando; Österberg, Monika; Seppälä, Jukka; Department of Chemical and Metallurgical Engineering; Department of Bioproducts and Biosystems; Polymer technology; Bioproduct Chemistry; Bio-based Colloids and MaterialsThe current study provides a comprehensive rheology study and a survey on direct ink writing of xanthan gum/cellulose nanocrystal (XG/CNC) bio-inks for developing 3D geometries that mimic soft tissue engineering scaffolds' physical and mechanical properties. The presence of CNC was found to be a critical prerequisite for the printability of XG bio-inks; accordingly, the hybrid XG/CNC bio-inks revealed the excellent viscoelastic properties that enabled precise control of hydrogel shaping and printing of lattice structures composed of up to eleven layers with high fidelity and fair resolution without any deformation after printing. The lyophilized 3D scaffolds presented a porous structure with open and interconnected pores and a porosity higher than 70%, vital features for tissue engineering scaffolds. Moreover, they showed a relatively high swelling of approximately 11 g/g, facilitating oxygen and nutrient exchange. Furthermore, the elastic and compressive moduli of the scaffolds that enhanced significantly upon increasing CNC content were in the range of a few kPa, similar to soft tissues. Finally, no significant cell cytotoxicity was observed against human liver cancer cells (HepG2), highlighting the potential of these developed 3D printed scaffolds for soft tissue engineering applications.Item Hollow Filaments Synthesized by Dry-Jet Wet Spinning of Cellulose Nanofibrils: Structural Properties and Thermoregulation with Phase-Change Infills(AMERICAN CHEMICAL SOCIETY, 2022-04-08) Reyes, Guillermo; Ajdary, Rubina; Yazdani, Maryam R.; Rojas, Orlando J.; Department of Bioproducts and Biosystems; Department of Mechanical Engineering; Bio-based Colloids and Materials; Energy ConversionWe use dry-jet wet spinning in a coaxial configuration by extruding an aqueous colloidal suspension of oxidized nanocellulose (hydrogel shell) combined with airflow in the core. The coagulation of the hydrogel in a water bath results in hollow filaments (HF) that are drawn continuously at relatively high rates. Small-angle and wide-angle X-ray scattering (SAXS/WAXS) reveals the orientation and order of the cellulose sheath, depending on the applied shear flow and drying method (free-drying and drying under tension). The obtained dry HF show Young's modulus and tensile strength of up to 9 GPa and 66 MPa, respectively. Two types of phase-change materials (PCM), polyethylene glycol (PEG) and paraffin (PA), are used as infills to enable filaments for energy regulation. An increased strain (9%) is observed in the PCM-filled filaments (HF-PEG and HF-PA). The filaments display similar thermal behavior (dynamic scanning calorimetry) compared to the neat infill, PEG, or paraffin, reaching a maximum latent heat capacity of 170 J·g-1 (48-55 °C) and 169 J·g-1 (52-54 °C), respectively. Overall, this study demonstrates the facile and scalable production of two-component core-shell filaments that combine structural integrity, heat storage, and thermoregulation properties.Item Leakage-proof microencapsulation of phase change materials by emulsification with acetylated cellulose nanofibrils(ELSEVIER SCI LTD, 2021-02-15) Shi, Xuetong; Yazdani, Maryam R.; Ajdary, Rubina; Rojas, Orlando J.; Department of Bioproducts and Biosystems; Department of Mechanical Engineering; Bio-based Colloids and Materials; Energy Conversion; Department of Bioproducts and BiosystemsWe use acetylated cellulose nanofibrils (AcCNF) to stabilize transient emulsions with paraffin that becomes shape-stable and encapsulated phase change material (PCM) upon cooling. Rheology measurements confirm the gel behavior and colloidal stability of the solid suspensions. We study the effect of nanofiber content on PCM leakage upon melting and compare the results to those from unmodified CNF. The nanostructured cellulose promotes paraffin phase transition, which improves the efficiency of thermal energy exchange. The leakage-proof microcapsules display high energy absorption capacity (ΔHm = 173 J/g) at high PCM loading (up to 80 wt%), while effectively controlling the extent of supercooling. An excellent thermal stability is observed during at least 100 heating/cooling cycles. Degradation takes place at 291 °C, indicating good thermal stability. The high energy density and the effective shape and thermal stabilization of the AcCNF-encapsulated paraffin points to a sustainable solution for thermal energy storage and conversion.Item Low Solids Emulsion Gels Based on Nanocellulose for 3D-Printing(2019-02-11) Huan, Siqi; Ajdary, Rubina; Bai, Long; Klar, Ville; Rojas, Orlando J.; Department of Bioproducts and Biosystems; Department of Mechanical Engineering; Bio-based Colloids and MaterialsMultiphase (emulsion) gels with internal phase fractions between 0.1 and 0.5 were formulated at low loadings of cellulose nanofibrils (CNF), alginate, and polylactide (PLA). Their properties (rheology and morphology) fitted those of inks used for direct ink writing (DIW). The effect of formulation and composition variables were elucidated after printing cubic scaffolds and other solid designs. The distinctive microstructures that were developed allowed high printing fidelity and displayed limited shrinkage after room temperature and freeze-drying (0 and 5% shrinkage in the out-of-plane and in-plane directions upon freeze-drying, respectively). The CNF added in the continuous phase was shown to be critical to achieve rheology control as an effective interfacial stabilizer and to ensure the printability of the ink toward high structural reliability. We found that the extent of shape retention of the dried scaffolds resulted from the tightly locked internal structure. The PLA that was initially added in the nonpolar or organic phase (0 to 12%) was randomly embedded in the entire scaffold, providing a strong resistance to shrinkage during the slow water evaporation at ambient temperature. No surface collapse or lateral deformation of the dried scaffolds occurred, indicating that the incorporation of PLA limited drying-induced shape failure. It also reduced compression strain by providing better CNF skeletal support, improving the mechanical strength. Upon rewetting, the combination of the hydrophilicity imparted by CNF and alginate together with the highly porous structure of the 3D material and the internal microchannels contributed to high water absorption via capillary and other phenomena (swelling % between ∼400 and 900%). However, no shape changes occurred compared to the initial 3D-printed shape. The swelling of the scaffolds correlated inversely with the PLA content in the precursor emulsion gel, providing a means to regulate the interaction with water given its low surface energy. Overall, the results demonstrate that by compatibilization of the CNF-based hydrophilic and the PLA-based hydrophobic components, it is possible to achieve shape control and retention upon 3D printing, opening the possibility of adopting low-solids inks for DIW into dry objects. The dryable CNF-based 3D structural materials absorb water while being able to support load (high elastic modulus) and maintain the shape upon hydration.Item Microfibers synthesized by wet-spinning of chitin nanomaterials : Mechanical, structural and cell proliferation properties(ROYAL SOC CHEMISTRY, 2020-08-11) Wang, Ling; Ezazi, Nazanin Zanjanizadeh; Liu, Liang; Ajdary, Rubina; Xiang, Wenchao; Borghei, Maryam; Santos, Helder A.; Rojas, Orlando J.; Department of Bioproducts and Biosystems; Bio-based Colloids and Materials; Nanjing Forestry University; University of HelsinkiPartially deacetylated chitin nanofibers (ChNF) were isolated from shell residues derived from crab biomass and used to prepare hydrogels, which were easily transformed into continuous microfibers by wet-spinning. We investigated the effect of ChNF solid content, extrusion rate and coagulant type, which included organic (acetone) and alkaline (NaOH and ammonia) solutions, on wet spinning. The properties of the microfibers and associated phenomena were assessed by tensile strength, quartz crystal microgravimetry, dynamic vapor sorption (DVS), thermogravimetric analysis and wide-angle X-ray scattering (WAXS). The as-spun microfibers (14 GPa stiffness) comprised hierarchical structures with fibrils aligned in the lateral direction. The microfibers exhibited a remarkable water sorption capacity (up to 22 g g(-1)), while being stable in the wet state (50% of dry strength), which warrants consideration as biobased absorbent systems. In addition, according to cell proliferation and viability of rat cardiac myoblast H9c2 and mouse bone osteoblast K7M2, the wet-spun ChNF microfibers showed excellent results and can be considered as fully safe for biomedical uses, such as in sutures, wound healing patches and cell culturing.
