| 1. |
- Undin, Jenny, 1985-
(författare)
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Functional Degradable Polymers by a Radical Chemistry approach
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- One class of polymers that is inherently of great value for many applications is the aliphatic polyesters. Such polymers are very suitable for use as temporary guides, scaffolds, for tissue formation and other biomedical applications, due to their biocompatibility, degradability and appropriate mechanical properties. A prominent way to incorporate sites that allow alterations and modifications of the polymer backbone could be by copolymerization of functional monomers. The focus in this thesis is the development of new monomers and subsequent polymers bestowed with functional groups.Radical ring-opening polymerization (RROP) of cyclic ketene acetals through a free-radical mechanism presents an alternative route to conventional ring-opening polymerization for the synthesis of aliphatic polyesters. By RROP, it is possible to incorporate ester functionality into the backbone of non-degradable polymers by copolymerize cyclic ketene acetals with vinyl monomers.The possibility of creating materials with high degree of functionality is achieved by copolymerization with other and possible functional monomers. Three different copolymerizations including cyclic ketene acetals were performed. First, to increase hydrophilicity of a hydrophobic polymer by copolymerization of two cyclic ketene acetals, 2-methylene-1,3,6-trioxocane (MTC) and 2-methylene-1,3-dioxepane (MDO). Second, to introduce degradability into a non-degradable backbone by copolymerize MDO and vinyl acetal (VAc). Subsequently, the acetate side-group was hydrolyzed into the more hydrophilic alcohol group. Third, to introduce reactive functionalities into the degradable backbone of poly(2-methylene-1,3-dioxepane) (PMDO), by copolymerize MDO and glycidyl methacrylate (GMA). The epoxide side-groups, originating from GMA, were subsequently used in post-polymerization reactions by coupling with the bioactive molecule heparin.The degradability of this class of copolymers was evaluated using the MDO/GMA-based material as model, showing that the materials degrade during 133 days without a rapid release of acidic degradation products or any substantial lowering of the pH. Methylthiazol tetrazolium (MTT) assays were also performed to confirm the innocuousness of the material. The results from the degradation study together with the MTT assays showed that these materials would be interesting for use in biomedical applications.Finally, a combination of controlled radical polymerization with controlled ring-opening polymerization was performed. α-Bromo-γ-butyrolactone (αBrγBL) together with ε-caprolactone (εCL) or L-lactide (LLA) was successfully copolymerized to achieve copolymers with active and available grafting sites for single electron transfer living radical polymerization (SET-LRP). Different acrylates, ranging from the hydrophobic n-butyl acrylate and methyl methacrylate to the hydrophilic 2-hydroxyethyl methacrylate, were subsequently grafted via SET-LRP. All designated acrylate monomers were successfully grafted onto the polymer backbone, thereby emphasizing the versatility and ability of αBrγBL to act as a bridge between SET-LRP and ROP for a wide range of monomers.
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| 2. |
- Benyahia Erdal, Nejla, 1991-
(författare)
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Cellulose derived carbon dots : From synthesis to evaluation as multifunctional building blocks in biomedical scaffolds
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The implementation of biobased and biodegradable polymeric materials in biomedical applications is often coupled with issues related to their insufficient mechanical properties or limited bioactivity. In this thesis, a perspective on valorization of biomass is presented, demonstrating the transformation of cellulose into biobased carbon nanomaterials with the potential to serve as multifunctional property enhancers in polycaprolactone (PCL) scaffold materials for tissue engineering.Firstly, nanographene oxide (nGO) type of carbon dots were produced through a microwave assisted hydrothermal carbonization of cellulose and subsequent oxidation in an acidic environment. The carbon dots demonstrated zero-dimensional (0D) character, ample amount of oxygen functionalities and fluorescence properties. Furthermore, a green reduction process in superheated water was developed to reduce the nGO carbon dots with and without the aid of a green reducing agent, caffeic acid (CA). The resulting r-nGO and r-nGO-CA showed in contrast to nGO decreased oxygen content and enhanced thermal stability. r-nGO-CA, in addition, maintained good cell viability towards osteoblast-like cells at a higher concentration than nGO.Secondly, incorporation of r-nGO or r-nGO-CA in PCL nanocomposites induced great enhancement in mineralization capability and creep resistance. nGO carbon dots could also due to their oxygen-rich content, be utilized to modify 3D scaffolds through surface functionalization and blending. The nGO on the surface of the PCL scaffolds, produced through optimized solvent casting particulate leaching (SCPL) techniques, could act as anchor sites for antibiotic loading and induce mineralization. It was also shown that incorporation of nGO in PCL scaffolds fabricated through high internal phase emulsion (HIPE) templating influenced the macrostructure of the scaffolds further manifesting the versatility and potential of the fabricated biobased carbon dots in biomedical applications.
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| 3. |
- Höglund, Anders, 1979-
(författare)
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Controlled Degradation of Polyester-Ethers Revealed by Mass Spectrometry Techniques
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The use of degradable biomedical materials in e.g. tissue engineering and controlled drug delivery has changed medical science during recent decades. The key question is to adapt the material with respect to mechanical properties, surface characteristics, and degradation profile to suit its intended application. Products formed during the degradation of bioresorbable materials are generally considered non-toxic and they are excreted from the human body. However, large amounts of specific degradation products such as hydroxyacids and oligomers may induce a pH decrease and a subsequent inflammatory response at the implantation site. In this study, macromolecular design and a combination of cross-linking and adjusted hydrophilicity are utilized as tools to control and tailor the degradation rate and the subsequent release of degradation products from polyester-ethers. A series of different homo- and copolymers of e-caprolactone (CL) and 1,5-dioxepan-2-one (DXO) were synthesized and their hydrolytic degradation was monitored in aqueous media at 37 °C for up to 546 days. The low and medium molar mass degradation products released during hydrolysis were monitored by various mass spectrometry techniques. The materials studied included linear DXO/CL triblock and multiblock copolymers, PCL and PDXO linear homopolymers, and cross-linked homo- and random copolymers of CL/DXO where 2,2’-bis-(ε-caprolactone-4-yl) propane (BCP) was used as a cross-linking agent. The results show that macromolecular engineering and controlled hydrophilicity of cross-linked networks are useful tools for customizing the release rate of acidic degradation products. Thereby, the formation of local acidic environments is prevented and the risk of inflammatory responses in the body is reduced.
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| 4. |
- Olofsson, Martin, 1975-
(författare)
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Microalgae : future bioresource of the sea?
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Unicellular microalgae are a renewable bioresource that can meet the challenge forfood and energy in a growing world population. Using sunlight, CO2, nutrients,and water, algal cells produce biomass in the form of sugars, proteins and oils, allof which carry commercial value as food, feed and bioenergy. Flue gas CO2 andwastewater nutrients are inexpensive sources of carbon and fertilizers. Microalgaecan mitigate CO2 emissions and reduce nutrients from waste streams whileproducing valuable biomass.My focus was on some of the challenging aspects of cultivating microalgae ascrop: the response of biomass production and quality to seasonality, nutrients andbiological interactions. Approach spans from laboratory experiments to large-scaleoutdoor cultivation, using single microalgal strains and natural communities insouthern (Portugal) and northern (Sweden) Europe.Half of the seasonal variation in algal oil content was due to changes in light andtemperature in outdoor large-scale cultures of a commercial strain (Nannochloropsisoculata). Seasonal changes also influence algal oil composition with more neutrallipids stored in cells during high light and temperature. Nitrogen (N) stress usuallyenhances lipid storage but suppresses biomass production. Our manipulationshowed that N stress produced more lipids while retaining biomass. Thus,projecting annual biomass and oil yields requires accounting for both seasonalchanges and N stress to optimize lipid production in commercial applications.Baltic Sea microalgae proved to be a potential biological solution to reduce CO2emissions from cement flue gas with valuable biomass production. A multi-speciescultivation approach rather than single-species revealed that natural or constructedcommunities of microalgae can produce equivalent biomass quality. Diversecommunities of microalgae can offer resilience and stability due to more efficientresource utilization with less risk of contamination, less work and cost for culturemaintenance.Stable algal biomass production (annual basis) was achieved in outdoor pilot-scale(1600 L) cultivation of Baltic Sea natural communities using cement flue gas as aCO2 source. Results indicate favorable algal oil content at northern Europeanlatitudes compared to southern European latitudes.My thesis establishes the potential of cultivating microalgae as a bioresource inScandinavia, and using a community approach may be one step towardssustainable algal technology.
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