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  • 1. Ajalloueian, Fatemeh
    et al.
    Zeiai, Said
    Rojas, Ramiro
    Department of Chemistry, Division of Polymer Chemistry, Uppsala University, Sweden.
    Fossum, Magdalena
    Hilborn, Jöns
    One-Stage Tissue Engineering of Bladder Wall Patches for an Easy-To-Use Approach at the Surgical Table2013In: Tissue Engineering. Part C, Methods, ISSN 1937-3384, E-ISSN 1937-3392, Vol. 19, no 9, p. 688-696Article in journal (Refereed)
    Abstract [en]

    We present a method for producing a cell-scaffold hybrid construct at the bedside. The construct is composed of plastic-compressed collagen together with a poly(e-caprolactone) (PCL)-knitted mesh that yields an integrated, natural-synthetic scaffold. This construct was evaluated by seeding of minced bladder mucosa, followed by proliferation in vitro. High mechanical strength in combination with a biological environment suitable for tissue growth was achieved through the creation of a hybrid construct that showed an increased tensile strength (17.9 +/- 2.6 MPa) when compared to plastic-compressed collagen (0.6 +/- 0.12 MPa). Intimate contact between the collagen and the PCL fabric was required to ensure integrity without delamination of the construct. This contact was achieved by surface alkaline hydrolysis of the PCL, followed by adsorption of poly(vinyl) alcohol. The improvement in hydrophilicity of the PCL-knitted mesh was confirmed through water contact angle measurements, and penetration of the collagen into the mesh was evaluated by scanning electron microscopy (SEM). Particles of minced bladder mucosa tissue were seeded onto this scaffold, and the proliferation was followed for 6 weeks in vitro. Results obtained from phase contrast microscopy, SEM, and histological staining indicated that cells migrated from the minced tissue particles and reorganized on the scaffold. Cells were viable and proliferative, with morphological features characteristic of urothelial cells. Proliferation reached the point at which a multilayer with a resemblance to stratified urothelium was achieved. This successful method could potentially be used for in vivo applications in reconstructive urology as an engineered autologous tissue transplant without the requirement for in vitro culture before transplantation.

  • 2.
    Herrera, Martha
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Thitiwutthisakul, Kasinee
    SCG Packaging Publ Co Ltd, Prod & Technol Dev Ctr, Ban Pong 70110, Ratchaburi, Thailand..
    Yang, Xuan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. KTH Royal Inst Technol, Dept Fibre & Polymer Technol, S-10044 Stockholm, Sweden.;KTH Royal Inst Technol, Wallenberg Wood Sci Ctr, S-10044 Stockholm, Sweden..
    Rujitanaroj, Pim-on
    SCG Packaging Publ Co Ltd, Prod & Technol Dev Ctr, Ban Pong 70110, Ratchaburi, Thailand..
    Rojas, Ramiro
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Berglund, Lars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Biocomposites.
    Preparation and evaluation of high-lignin content cellulose nanofibrils from eucalyptus pulp2018In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 25, no 5, p. 3121-3133Article in journal (Refereed)
    Abstract [en]

    High Klason lignin content (23 wt%) cellulose nanofibrils (LCNF) were successfully isolated from eucalyptus pulp through catalyzed chemical oxidation, followed by high-pressure homogenization. LCNFs had a diameter of ca. 13 nm according to AFM evaluation. Dense films were obtained through vacuum filtration (nanopaper) and subjected to different drying methods. When drying under heat and mild vacuum (93 degrees C, 95 kPa) a higher water contact angle, lower roughness and oxygen transmission rate were observed, compared to those drying at room temperature under compression conditions. DSC experiments showed difference in signals associated to T-g of LCNF compared to CNF produced from spruce bleached pulp through enzymatic pre-treatment. The LCNF-based nanopaper showed mechanical properties slightly lower than for those made from cellulose nanofibrils, yet with increased hydrophobicity. In summary, the high-lignin content cellulose nanofibrils proved to be a suitable material for the production of low oxygen permeability nanopaper, with chemical composition close to native wood.

  • 3. Huo, Jinxing
    et al.
    Rojas, Ramiro
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Bohlin, Jan
    Hilborn, Jöns
    Gamstedt, E. Kristofer
    Parametric elastic analysis of coupled helical coils for tubular implant applications: experimental characterization and numerical analysis.2014In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 29, no SI, p. 462-469Article in journal (Refereed)
    Abstract [en]

    Coupled helical coils show promising mechanical behavior to be used as tubular organ constructs, e.g., in trachea or urethra. They are potentially easy to manufacture by filament winding of biocompatible and resorbable polymers, and could be tailored for suitable mechanical properties. In this study, coupled helical coils were manufactured by filament winding of melt-extruded polycaprolactone, which was reported to demonstrate desired in vivo degradation speed matching tissue regeneration rate. The tensile and bending stiffness was characterized for a set of couple helical coils with different geometric designs, with right-handed and left-handed polymer helices fused together in joints where the filaments cross. The Young's modulus of unidirectional polycaprolactone filaments was characterized, and used as input together with the structural parameters of the coupled coils in finite element simulations of tensile loading and three-point bending of the coils. A favorable comparison of the numerical and experimental results was found, which paves way for use of the proposed numerical approach in stiffness design under reversible elastic conditions of filament wound tubular constructs.

  • 4.
    Ingverud, Tobias
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Larsson, Emma
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Hemmer, Guillaume
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Rojas, Ramiro
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Malkoch, Michael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Carlmark, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    High water-content thermoresponsive hydrogels via electrostatic macrocrosslinking of cellulose nanofibrils2016In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 54, no 21, p. 3415-3424Article in journal (Refereed)
    Abstract [en]

    Atom transfer radical polymerization (ATRP) has been utilized to synthesize tri- and star-block copolymers of poly(di(ethylene glycol)methyl ether methacrylate) (PDEGMA) and quaternized poly(2-(dimethylamino)ethyl methacrylate) (qPDMAEMA). The block copolymers, all with a minimum of two cationically charged blocks, were sequentially used for electrostatic macrocrosslinking of a dilute dispersion of anionic TEMPO-oxidized cellulose nanofibrils (CNF, 0.3 wt%), forming free-standing hydrogels. The cationic block copolymers adsorbed irreversibly to the CNF, enabling the formation of ionically crosslinked hydrogels, with a storage modulus of up to 2.9 kPa. The ability of the block copolymers to adsorb to CNF was confirmed by quartz crystal microbalance with dissipation monitoring (QCM-D) and infrared spectroscopy (FT-IR), and the thermoresponsive properties of the hydrogels were investigated by rheological stress and frequency sweep, and gravimetric measurements. This method was shown to be promising for the facile production of thermoresponsive hydrogels based on CNF.

  • 5. Kohn, Joachim B
    et al.
    Bolikal, Durgadas
    Rojas, Ramiro
    Bioresorbable polymers synthesized from monomer analogs of natural metabolites2009Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    This invention discloses biocompatible polymers prepared from monomers (IV), and (IVa), or derivatives thereof, for which the variables are described in the claims and specification. These polymers may be bioresorbable and thus useful for manufacture of medical devices. Therefore, methods for preparing these polymers and medical devices prepared therefrom are also encompassed by this disclosure.

  • 6.
    Larsson, Emma
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Ingverud, Tobias
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Hemmer, Guillaume
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Rojas, Ramiro
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Malkoch, Michael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Carlmark, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Thermoresponsive hydrogels of cellulose nanofibrils and triblock copolymersManuscript (preprint) (Other academic)
    Abstract [en]

    Atom transfer radical polymerization (ATRP) has been utilized to synthesize triblock and star-block copolymers of quaternized poly(2-(dimethylamino)ethyl methacrylate) (qPDMAEMA) and poly(di(ethylene glycol) methyl ether methacrylate (PDEGMA). The block copolymers, that all contained a minimum of two charged blocks, were sequential adsorbed to negatively charged cellulose nanofibrils (CNF) in dilute water suspension, forming thermoresponsive hydrogels. The presence of more than one charge block allowed for the polymers to form permanent, physically crosslinked, gels when adsorbed to the CNF. The ability of the polymers to adsorb to CNF was confirmed by quartz crystal microbalance with dissipation monitoring (QCM-D), and the thermoresponsive properties of the gels were investigated by rheological measurements and gravimetric measurements. This method was shown to be promising for the facile, production of thermoresponsive hydrogels composed of CNF.

  • 7. Lewitus, Dan Y.
    et al.
    Rios, Fabian
    Rojas, Ramiro
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. New Jersey Center for Biomaterials, Rutgers, The State University of New Jersey, United States .
    Kohn, Joachim
    Molecular design and evaluation of biodegradable polymers using a statistical approach2013In: Journal of materials science. Materials in medicine, ISSN 0957-4530, E-ISSN 1573-4838, Vol. 24, no 11, p. 2529-2535Article in journal (Refereed)
    Abstract [en]

    The challenging paradigm of bioresorbable polymers, whether in drug delivery or tissue engineering, states that a fine-tuning of the interplay between polymer properties (e.g., thermal, degradation), and the degree of cell/tissue replacement and remodeling is required. In this paper we describe how changes in the molecular architecture of a series of terpolymers allow for the design of polymers with varying glass transition temperatures and degradation rates. The effect of each component in the terpolymers is quantified via design of experiment (DoE) analysis. A linear relationship between terpolymer components and resulting T-g (ranging from 34 to 86 A degrees C) was demonstrated. These findings were further supported with mass-per-flexible-bond analysis. The effect of terpolymer composition on the in vitro degradation of these polymers revealed molecular weight loss ranging from 20 to 60 % within the first 24 h. DoE modeling further illustrated the linear (but reciprocal) relationship between structure elements and degradation for these polymers. Thus, we describe a simple technique to provide insight into the structure property relationship of degradable polymers, specifically applied using a new family of tyrosine-derived polycarbonates, allowing for optimal design of materials for specific applications.

  • 8.
    Li, Yuanyuan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Fu, Qiliang
    Rojas, Ramiro
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Yan, Min
    KTH, School of Electrical Engineering (EES).
    Lawoko, Martin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Berglund, Lars
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology. KTH, Superseded Departments (pre-2005), Fibre and Polymer Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Lignin-Retaining Transparent Wood2017In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 10, no 17, p. 3445-3451Article in journal (Refereed)
    Abstract [en]

    Optically transparent wood, combining optical and mechanical performance, is an emerging new material for light-transmitting structures in buildings with the aim of reducing energy consumption. One of the main obstacles for transparent wood fabrication is delignification, where around 30wt% of wood tissue is removed to reduce light absorption and refractive index mismatch. This step is time consuming and not environmentally benign. Moreover, lignin removal weakens the wood structure, limiting the fabrication of large structures. A green and industrially feasible method has now been developed to prepare transparent wood. Up to 80wt% of lignin is preserved, leading to a stronger wood template compared to the delignified alternative. After polymer infiltration, a high-lignin-content transparent wood with transmittance of 83%, haze of 75%, thermal conductivity of 0.23WmK(-1), and work-tofracture of 1.2MJm(-3) (a magnitude higher than glass) was obtained. This transparent wood preparation method is efficient and applicable to various wood species. The transparent wood obtained shows potential for application in energy-saving buildings.

  • 9.
    Li, Yuanyuan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Yu, Shun
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Chen, Pan
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Rojas, Ramiro
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Hajian, Alireza
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Cellulose nanofibers enable paraffin encapsulation and the formation of stable thermal regulation nanocomposites2017In: Nano Energy, ISSN 2211-2855, Vol. 34, p. 541-548Article in journal (Refereed)
    Abstract [en]

    Non-leaking, green materials with high content of phase change materials (PCM) can conserve solar energy and contribute to a sustainable society. Here, paraffin was encapsulated by nanocellulose (CNF) through a pickering emulsion method, while simultaneously forming a composite material. The thermodynamic drive for phase separation was confirmed by molecular modeling. Particle formation was characterized by dynamic light scattering and they were processed into stable PCM/CNF composites in the form of PCM paper structures with favorable mechanical properties. The PCM composite was lightweight and showed a solid content of paraffin of more than 72 wt%. Morphology was characterized using FE-SEM. The thermal regulation function of the PCM composite was demonstrated in the form of a model roof under simulated sunlight. No obvious leakage was observed during heating/cooling cycles, as supported by DSC and SAXS data. The PCM composite can be extended to panels used in energy-efficient smart buildings with thermal regulation integrated in load-bearing structures.

  • 10. Luk, Arnold
    et al.
    Sanjeeva Murthy, N
    Wang, Wenjie
    Rojas, Ramiro
    Kohn, Joachim
    Study of nanoscale structures in hydrated biomaterials using small-angle neutron scattering2011In: Acta Biomaterialia, ISSN 1742-7061, Vol. 8, no 4, p. 1459-1468Article in journal (Refereed)
    Abstract [en]

    Distribution of water in three classes of biomedically relevant and degradable polymers was investigated using small-angle neutron scattering. In semicrystalline polymers, such as poly(lactic acid) and poly(glycolic acid), water was found to diffuse preferentially into the non-crystalline regions. In amorphous polymers, such as poly(D,L-lactic acid) and poly(lactic-co-glycolic acid), the scattering after 7 days of incubation was attributed to water in microvoids that form following the hydrolytic degradation of the polymer. In amorphous copolymers containing hydrophobic segments (desaminotyrosyl-tyrosine ethyl ester) and hydrophilic blocks (poly(ethylene glycol) (PEG)), a sequence of distinct regimes of hydration were observed: homogeneous distribution (similar to 10 angstrom length scales) at <13 wt.% PEG (similar to 1 water per EG), clusters of hydrated domains (similar to 50 angstrom radius) separated at 24 wt.% PEG (1-2 water per EG), uniformly distributed hydrated domains at 41 wt.% PEG (similar to 4 water per EG) and phase inversion at >50 wt.% PEG (>6 water per EG). Increasing the PEG content increased the number of these domains with only a small decrease in distance between the domains. These discrete domains appeared to coalesce to form submicron droplets at similar to 60 degrees C, above the melting temperature of crystalline PEG. The significance of such observations on the evolution of micrometer-size channels that form during hydrolytic erosion is discussed.

  • 11. López, Alejandro
    et al.
    Persson, Cecilia
    Hilborn, Jöns
    Rojas, Ramiro
    Department of Materials Chemistry, Division of Polymer Chemistry, The Ångström Laboratory, Uppsala University, Sweden .
    Comparative characterization of oligomeric precursors intended for injectable implants2013In: Polymers for Advanced Technologies, ISSN 1042-7147, E-ISSN 1099-1581, Vol. 24, no 1, p. 15-21Article in journal (Refereed)
    Abstract [en]

    The use of injectable materials is a simple approach for drug delivery and tissue repair, in, e. g. minimally invasive surgery applications. If these materials are used past their glass transition temperature and have a low viscosity, they will be able to flow while delivered in situ. Whether these materials are to be used as low viscosity drug carriers or further crosslinked for tissue repair, there is a need for a better understanding of their handling properties. In this study, oligo(trimethylene carbonate) (oTMC) and oligo[D, L-lactide-co-(epsilon-caprolactone)] (oDLLA-co-CL) of various molecular weights within a relevant injectability range were synthesized via ring-opening polymerization. The materials were comparatively characterized by H-1 NMR spectroscopy, differential scanning calorimetry, gel permeation chromatography, and rheological measurements. After comparing the viscosities and molecular weights of the materials, it was concluded that oDLLA-co-CLs were, generally, better suited as an injectable in situ crosslinking network, whereas oTMCs were found to be better candidates as injectable drug carriers. This study provides useful data and guidelines on the use of these and other similar oligomers intended for injectable implants.

  • 12. Ohm, Wiebke
    et al.
    Rothkirch, Andre
    Pandit, Pallavi
    Koerstgens, Volker
    Mueller-Buschbaum, Peter
    Rojas, Ramiro
    Yu, Shun
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Polymer Technology.
    Brett, Calvin J.
    Soderberg, Daniel L.
    Roth, Stephan V.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Biocomposites.
    Morphological properties of airbrush spray-deposited enzymatic cellulose thin films2018In: JOURNAL OF COATINGS TECHNOLOGY AND RESEARCH, ISSN 1945-9645, Vol. 15, no 4, p. 759-769Article in journal (Refereed)
    Abstract [en]

    We investigate the layer formation of enzymatic cellulose by airbrush spray coating on silicon oxide surfaces. The layer structure and morphology of enzymatic cellulose films in the thickness range between 86 nm and 2.1 A mu m is determined as a function of the spray coating procedures. For each spray coating step, layer buildup, surface topography, crystallinity as well as the nanoscale structure are probed with atomic force microscopy and surface-sensitive X-ray scattering methods. Without intermittent drying, the film thickness saturates; with intermittent drying, a linear increase in layer thickness with the number of spray pulses is observed. A closed cellulose layer was always observed. The crystallinity remains unchanged; the nanoscale structures show three distinct sizes. Our results indicate that the smallest building blocks increasingly contribute to the morphology inside the cellulose network for thicker films, showing the importance of tailoring the cellulose nanofibrils. For a layer-by-layer coating, intermittent drying is mandatory.

  • 13. Piskounova, Sonya
    et al.
    Rojas, Ramiro
    Bergman, Kristoffer
    Hilborn, Jöns
    The Effect of Mixing on the Mechanical Properties of Hyaluronan-Based Injectable Hydrogels2011In: Macromolecular Materials and Engineering, ISSN 1438-7492, Vol. 296, no 10, p. 944-951Article in journal (Refereed)
    Abstract [en]

    A method for determining the correlation between the mixing of two reactive polymers and the structural and mechanical properties of the formed hydrogels is presented. Rheological measurements show that insufficient mixing gives rise to soft and not fully crosslinked hydrogels while excessive mixing beyond gel point results in weaker hydrogels due to potential breakage of their 3D network. Furthermore, the hydrogels swell significantly more in cell culture medium than in phosphate-buffered saline, attributed to interactions with additional molecules such as proteins. Thus, moderate mixing gives rise to the most homogenous and mechanically stable hydrogels and the choice of medium e. g., for release experiments, should be consistent in order to avoid unnecessary variations in the data caused by different swelling profiles.

  • 14. Rojas, Ramiro
    et al.
    Harris, Nicole K
    Piotrowska, Karolina
    Kohn, Joachim
    Evaluation of automated synthesis for chain and step-growth polymerizations: Can robots replace the chemists?2008In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, Vol. 47, no 1, p. 49-58Article in journal (Refereed)
    Abstract [en]

    This article explores current challenges in the use of automated parallel synthesizers in polymeric materials research. Four types of polymerizations were investigated: carbodiimide-mediated polyesterification, diphenol phosgenation, free radical, and reversible addition-fragmentation chain-transfer (RAFT). Synthetic challenges of condensation polymerization, such as liquid and solid dispensing accuracy, dropwise addition, and toxic chemical handling, were successfully met using the automated synthesizer. Both solid and liquid dosing of the diphenol and diacid were successful for polyarylate synthesis. The high precision of liquid dispensing made it possible to achieve stoichiometric balance using reagent stock solutions. For all reactions, molecular weights and their reproducibility were comparable to those obtained with manual synthesis. For RAFT polymerizations, solvent and mol ratio of chain transfer reagent to initiator were successfully optimized on the automated synthesizer and a library of over 60 polymethacrylate copolymer compositions was generated. Considerable savings in time relative to manual methods were achieved when generating polymer libraries (e.g., 4.5x faster for 96 polymethacrylates and 20x faster for 45 for polycarbonates).

  • 15. Schizas, Nikos
    et al.
    Rojas, Ramiro
    Kootala, Sujit
    Andersson, Brittmarie
    Pettersson, Jennie
    Hilborn, Jons
    Hailer, Nils P
    Hyaluronic acid-based hydrogel enhances neuronal survival in spinal cord slice cultures from postnatal mice2013In: Journal of biomaterials applications, ISSN 0885-3282, E-ISSN 1530-8022, Vol. 28, no 6, p. 825-836Article in journal (Refereed)
    Abstract [en]

    Numerous biomaterials based on extracellular matrix-components have been developed. It was our aim to investigate whether a hyaluronic acid-based hydrogel improves neuronal survival and tissue preservation in organotypic spinal cord slice cultures. Organotypic spinal cord slice cultures were cultured for 4 days in vitro (div), either on hyaluronic acid-based hydrogel (hyaluronic acid-gel group), collagen gel (collagen group), directly on polyethylene terephthalate membrane inserts (control group), or in the presence of soluble hyaluronic acid (soluble hyaluronic acid group). Cultures were immunohistochemically stained against neuronal antigen NeuN and analyzed by confocal laser scanning microscopy. Histochemistry for choline acetyltransferance, glial fibrillary acidic protein, and Griffonia simplicifolia isolectin B4 followed by quantitative analysis was performed to assess motorneurons and different glial populations. Confocal microscopic analysis showed a 4-fold increase in the number of NeuN-positive neurons in the hyaluronic acid-gel group compared to both collagen (p < 0.001) and control groups (p < 0.001). Compared to controls, organotypic spinal cord slice cultures maintained on hyaluronic acid-based hydrogel showed 5.9-fold increased survival of choline acetyltransferance-positive motorneurons (p = 0.008), 2-fold more numerous resting microglial cells in the white matter (p = 0.031), and a 61.4% reduction in the number of activated microglial cells within the grey matter (p = 0.05). Hyaluronic acid-based hydrogel had a shear modulus (G′) of ≈1200 Pascals (Pa), which was considerably higher than the ≈25 Pa measured for collagen gel. Soluble hyaluronic acid failed to improve tissue preservation. In conclusion, hyaluronic acid-based hydrogel improves neuronal and - most notably - motorneuron survival in organotypic spinal cord slice cultures and microglial activation is limited. The positive effects of hyaluronic acid-based hydrogel may at least in part be due to its mechanical properties.

  • 16. Schut, J
    et al.
    Bolikal, D
    Khan, I J
    Pesnell, A
    Rege, A
    Rojas, Ramiro
    Sheihet, L
    Murthy, N S
    Kohn, J
    Glass transition temperature prediction of polymers through the mass-per-flexible-bond principle2007In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 48, no 20, p. 6115-6124Article in journal (Refereed)
    Abstract [en]

    A semi-empirical method based on the mass-per-flexible-bond (M/f) principle was used to quantitatively explain the large range of glass transition temperatures (T-g) observed in a library of 132 L-tyrosine derived homo, co- and terpolymers containing different functional groups. Polymer class specific behavior was observed in T-g vs. M/f plots, and explained in terms of different densities, steric hindrances and intermolecular interactions of chemically distinct polymers. The method was found to be useful in the prediction of polymer T-g. The predictive accuracy was found to range from 6.4 to 3.7 K, depending on polymer class. This level of accuracy compares favorably with (more complicated) methods used in the literature. The proposed method can also be used for structure prediction of polymers to match a target T-g value, by keeping the thermal behavior of a terpolymer constant while independently choosing its chemistry. Both applications of the method are likely to have broad applications in polymer and (bio)material science.

  • 17. Tummala, Gopi Krishna
    et al.
    Joffre, Thomas
    Rojas, Ramiro
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Persson, Cecilia
    Mihranyan, Albert
    Strain-induced stiffening of nanocellulose-reinforced poly(vinyl alcohol) hydrogels mimicking collagenous soft tissues2017In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 13, no 21, p. 3936-3945Article in journal (Refereed)
    Abstract [en]

    Soft tissues possess remarkable mechanical strength for their high water content, which is hard to mimic in synthetic materials. Here, we demonstrate how strain-induced stiffening in hydrogels plays a major role in mimicking the mechanical properties of collagenous soft tissues. In particular, nanocellulose reinforced polyvinyl alcohol (PVA) hydrogels of exceptionally high water content (90-93 wt%) are shown to exhibit collagen-like mechanical behavior typical for soft tissues. High water content and co-existence of both soft and rigid domains in the gel network are the main factors responsible for strain-induced stiffening. This observed effect due to the alignment of rigid components of the hydrogel is simulated through modeling and visualized through strain-induced birefringence experiments. Design parameters such as nanocellulose aspect ratio and solvent composition are also shown to be important to control the mechanical properties. In addition, owing to their transparency (90-95% at 550 nm) and hyperelastic properties (250-350% strain), the described hydrogels are promising materials for biomedical applications, especially in ophthalmology.

  • 18. Tummala, Gopi Krishna
    et al.
    Rojas, Ramiro
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Mihranyan, Albert
    Poly(vinyl alcohol) Hydrogels Reinforced with Nanocellulose for Ophthalmic Applications: General Characteristics and Optical Properties2016In: Journal of Physical Chemistry B, ISSN 1520-6106, Vol. 120, no 51, p. 13094-13101Article in journal (Refereed)
    Abstract [en]

    Globally, uncorrected refractive errors are one of the main causes of visual impairment, and contact lenses form an important part of modern day eye care and culture. Several hydrogels with varying physicochemical properties are in use to manufacture soft contact lenses. Hydrogels are generally too soft and reinforcement with appropriate materials is desirable to achieve high water content without compromising mechanical properties. In this study, we have developed a highly transparent macroporous hydrogel with water content >90%, by combining poly(vinyl alcohol) with nanocellulose. Furthermore, the results show that the composite hydrogel has refractive index close to that of water and very good UV-blocking properties.

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