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  • 1.
    Albertsson, Ann-Christine
    et al.
    KTH, School of Chemical Science and Engineering (CHE).
    Plikk, Peter
    KTH, School of Chemical Science and Engineering (CHE).
    PMSE 484-Mixed brushes as selective self-adoptive patterns that enhance polymer adsorption2006In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 232, p. 212-212Article in journal (Other academic)
  • 2. Idris, Shaza Bushra
    et al.
    Arvidson, Kristina
    Plikk, Peter
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Ibrahim, Lah
    Finne-Wistrand, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Bolstad, Anne Isine
    Mustafa, Kama
    Polyester copolymer scaffolds enhance expression of bone markers in osteoblast-like cells2010In: J BIOMED MATER RES PART A, ISSN 1549-3296, Vol. 94A, no 2, p. 631-639Article in journal (Refereed)
    Abstract [en]

    In tissue engineering, the resorbable aliphatic polyester poly(L-lactide) (PLLA) is used as scaffolds in bone regeneration. Copolymers of poly(L-lactide)-co-(epsilon-caprolactone) [poly(LLA-co-CL)] and poly(L-lactide)-co-(1,5-dioxepan-2-one) [poly(LLA-co-DXO)], with superior mechanical properties to PLLA, have been developed to be used as scaffolds, but the influence on the osteogenic potential is unclear. This in vitro study of test scaffolds of poly(LLA-co-CL) and poly(LLA-co-DXO) using PLLA scaffolds as a control demonstrates the attachment and proliferation of human osteoblast-like cells (HOB) as measured by SEM and a methylthiazol tetrazolium (MTT) colorimetric assay, and the progression of HOB osteogenesis for up to 3 weeks; expressed as synthesis of the osteoblast differentiation markers: collagen type 1 (Col 1), alkaline phosphatase, bone sialoprotein, osteocalcin (OC), osteopontin and runt related gene 2 (Runx2). Surface analysis disclosed excellent surface attachment, spread and penetration of the cells into the pores of the test scaffolds compared to the PLLA. MTT results indicated that test scaffolds enhanced the proliferation of HOBs. Cells grown on the test scaffolds demonstrated higher synthesis of Col 1 and OC and also increased bone markers mRNA expression. Compared to scaffolds of PLLA, the poly(LLA-co-CL) and poly(LLA-co-DXO) scaffolds enhanced attachment, proliferation, and expression of osteogenic markers by HOBs in vitro. Therefore, these scaffolds might be appropriate carriers for bone engineering. (C) 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 94A: 631-639, 2010

  • 3.
    Målberg, Sofia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Plikk, Peter
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Finne Wistrand, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Design of Elastomeric Homo- and Copolymer Networks of Functional Aliphatic Polyester for Use in Biomedical Applications2010In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 22, no 9, p. 3009-3014Article in journal (Refereed)
    Abstract [en]

    An unsaturated aliphatic polyester was synthesized by condensation polymerization to yield the pre-polymer, poly(but-2-ene-1,4-diyl malonate) (PBM), which is applicable as an elastomeric network and as a macroinitiator for the polymerization of cyclic ester monomers. The method of preparation was simple and straightforward with no need to purify the monomers or add a potentially harmful catalyst. The number average molecular weight of the pre-polymer could easily be increased from 5000 to 12000 by extending the reaction time. The pre-polymer PBM was successfully cross-linked with UV-radiation to form a clear, transparent, colorless, flexible, and strong film. PBM as a macroinitiator for L-lactide (LLA) and epsilon-caprolactone (CL) polymerizations highly increased the ductility of the LLA-polymer, while maintaining the strength, compared to PLLA polymerized with common initiators. The tensile properties of PCL were also improved. The linear PCL-PBM and PLLA-PBM polymers were easily cross-linked to give polymers with greater strength and higher modulus as the result.

  • 4.
    Odelius, Karin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Plikk, Peter
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Elastomeric hydrolyzable porous scaffolds: Copolymers of aliphatic polyesters and a polyether-ester2005In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 6, no 5, p. 2718-2725Article in journal (Refereed)
    Abstract [en]

    Porous scaffolds of 1,5-dioxepan-2-one (DXO), L-lactide (LLA), and epsilon-caprolactone (CL) were prepared by a solvent casting, salt particulate leaching technique in which the composites were detached from their mold using a novel methanol swelling procedure. By incorporating DXO segments into polymers containing LLA or CL, an increase in hydrophilicity is achieved, and incorporating soft amorphous domains in the crystalline sections enables tailoring of the mechanical properties. The porosities of the scaffolds ranged from 89.2% to 94.6%, and the pores were shown to be interconnected. The materials were synthesized by bulk copolymerization of 1,5-dioxepan-2-one (DXO), L-lactide (LLA), and epsilon-caprolactone (CL) using stannous 2-ethylhexanoate as catalyst. The copolymers formed varied in structure; poly(DXO-co-CL) is random in its arrangement, whereas poly(DXO-co-LLA) and poly(LLA-co-CL) are more blocky in their structures.

  • 5.
    Odelius, Karin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Plikk, Peter
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    The influence of composition of porous copolyester scaffolds on reactions induced by irradiation sterilization2008In: Biomaterials, ISSN 0142-9612, E-ISSN 1878-5905, Vol. 29, no 2, p. 129-140Article in journal (Refereed)
    Abstract [en]

    In our previous work regarding radiation sterilization of porous scaffolds we have concluded that the composition and microstructure of the polymer chain are a key factor influencing the degradation reactions occurring upon irradiation. In this work we in contrast reported on the effects of high-energy irradiation on the thermal and mechanical properties. Electron beam (EB)- and T-irradiation sterilization were used in order to finalize the properties of a series of porous scaffolds comprised of different aliphatic polyester copolymers. The results presented here show that, for both sterilization methods, the crystallinity increased for all copolymers of 1,5-dioxepan-2-one (DXO) and L,L-lactide (LLA) at the minimum sterilization dose. The same was true of the P.-caprolactone (CL)- and LLA-containing copolymers upon EB sterilization, while a reduction in crystallinity were found upon gamma-irradiation. As was anticipated, it was shown that crystallinity also is a characteristic of the copolymer influencing the effects of the irradiation-induced reactions. Both the onset temperature and the temperature corresponding to the maximum rate of weight loss increased after irradiation and hence the thermal stability was increased. This is a result of a simultaneous lengthening of the chains by cross-linking reactions and a shortening by random chain-scissions occurring throughout the molecule, which lead to the formation of new endgroups with higher thermal stability. Scaffolds of crystalline polymers retained more of their initial tensile properties after irradiation compared to amorphous materials. The result previously published, showing that the composition was a key factor influencing the degradation reactions occurring upon irradiation, was augmented here.

  • 6.
    Plikk, Peter
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Design of Functional Degradable Aliphatic Polyesters and Porous Tissue Engineering Scaffolds2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The regeneration of damaged tissues or organs using porous scaffolds which act as temporary guides for the patient’s own cells, i.e. tissue engineering, is a means to overcome the shortcomings of current standard medical treatments. The large number of tissue engineering applications and the high demands on materials make it necessary to design materials and scaffolds with innovative characteristics tailored to suit specific applications. The purpose of the work presented in this thesis was to design aliphatic polyester (co)polymers and porous scaffolds in order to tailor material and scaffold properties and to control the property changes induced by radiation sterilization.

    Porous scaffolds were created, with an emphasis on tailoring the scaffolds thermal and mechanical properties. Stannous octoate was used in ring-opening polymerizations of L,L-lactide (LLA), ε-caprolactone (CL) and 1,5-dioxepane-2-one (DXO) to attain three copolymer types with a wide assortment of monomer compositions. A solvent casting and salt leaching scaffold fabrication technique was developed, and highly porous scaffolds possessing a range of predetermined properties were obtained.

    Highly porous tubular scaffolds of different designs for use in nerve regeneration were developed using copolymers of LLA, CL, DXO or trimethylene carbonate (TMC) and a versatile immersion coating and porogen leaching technique.

    Reactions induced by electron beam and gamma irradiation were used to finalize the scaffold properties. By changing the nature of the radiation, the radiation dose, the type of monomers, the monomer composition and the chain microstructure, it was possible to alter the susceptibility and the degradation mechanisms of the polymers. Predicted end-properties were obtainable and the sterilization procedure was incorporated as a final step in the scaffold fabrication.

    The free radical ring-opening polymerization of the cyclic ketene acetal 2-methylene-1,3-dioxe-5-pene was developed, a reaction mechanism was proposed and the reaction products were characterized as a first step towards the creation of an innovative multifunctional aliphatic polyester. The reaction mechanism was shown to be temperature-dependent and propagation was inhibited by the formation of an allylic radical in the ring-opening step. The primary reaction product at higher temperatures was the cyclic ester 3-vinyl-1,4-butyrolactone. At lower temperatures, the main product was oligomers of ring-opened and ring-retained repeating units.

  • 7.
    Plikk, Peter
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Porous degradable polyester scaffolds2006Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Tissue engineering is a growing research field in which degradable porous scaffolds are used to regenerate tissue from the patients own cells. The problems due to donor shortage or the lack of full property restoration from prosthetic implants can thereby be overcome. It is important that the polymers used in tissue engineering, as in any medical application, have well controlled properties. Equally important is the ability to tailor these properties to suite a specific application. The development of fabrication processes that enables tailoring, without any uncontrolled changes in characteristics, is thereby imperative.

    In this thesis, the creation of porous scaffolds focusing on tailoring and customizing the scaffold properties is described. Tailoring was achieved by selecting the proper monomers and their compositions when copolymerizing different cyclic aliphatic ester monomers and an ether-ester monomer. Porous structures applicable for both soft and hard tissue regeneration were obtained comprising a range of predetermined mechanical and thermal properties. In detail, stannous octoate was used as the catalyst in ring-opening polymerization of L,L-lactide (LLA), ε-caprolactone (CL) and 1,5-dioxepane-2-one (DXO) to attain the wide assortment of copolymers with different monomers and monomer compositions. Highly porous scaffolds having well interconnected pores were obtained through the development of a versatile solvent casting and porogen leaching technique.

    The reactions induced by high energy radiation in the form of electron beam and gamma-ray were used to finalize the scaffold properties. This was achieved by creating polymers possessing predetermined reaction mechanisms when irradiated. Changes in the nature of the radiation, the radiation dose, the type of monomers, the composition and thus the microstructure of the chain gave ways to alter the susceptibility and the reaction mechanism of the polymers. Thus, predicted end-products are obtainable and the sterilization procedure is consequently incorporated as a final step in the scaffold fabrication.

  • 8.
    Plikk, Peter
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Målberg, Sofia
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Design of Resorbable Porous Tubular Copolyester Scaffolds for Use in Nerve Regeneration2009In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 10, no 5, p. 1259-1264Article in journal (Refereed)
    Abstract [en]

    Copolymers of L,L-lactide (LLA), epsilon-caprolactone (CL), trimethylene carbonate (TMC), or 1,5-dioxepane-2-one (DXO) were used to design porous tubular scaffolds with various mechanical properties, porosities, and numbers of layers in the tube wall. The mechanical properties of the tubular scaffold types showed good suitability for nerve regeneration and other nonload-bearing tissue engineering applications and were easy to handle without damaging the porous structure. A low stannous 2-ethylhexanoate-to-monomer ratio of 1:10000 did not change the tensile properties of the copolymer tubes significantly compared to those of scaffolds made using a Sn(Oct)(2)-to-monomer ratio of 1:600. The adaptability of the immersion coating and porogen leaching technique was demonstrated by creating tubes with different designs. Tubes with different wall layers were created by varying the immersion solutions, and the ease of altering the porosity, pore shape, and pore size was exemplified by using sodium chloride alone or mixed with poly(ethylene glycol) as porogen.

  • 9.
    Plikk, Peter
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Odelius, Karin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Finalizing the properties of porous scaffolds of aliphatic polyesters through radiation sterilization2006In: Biomaterials, ISSN 0142-9612, E-ISSN 1878-5905, Vol. 27, no 31, p. 5335-5347Article in journal (Refereed)
    Abstract [en]

    Porous scaffolds made of various L,L-lactide (LLA), 1,5-dioxepane-2-one (DXO) and epsilon-caprolactone (CL) copolymers were sterilized by EB- and gamma-irradiation. Differences in the comonomers, composition and the microstructure of the starting materials were used to influence the degradation mechanism and susceptibility towards irradiation and by this means to achieve sterilized scaffolds with predicted end-properties. The chemical changes and the formation of low-molecular-weight products were determined by SEC, H-1 nuclear magnetic resonance (NMR), C-13 NMR and gas chromatography-mass spectrometry (GC-MS). The degradation mechanism changed from random chain scission to cross-linking depending on the choice of monomers, the copolymer composition and the monomer sequences. Copolymerization of LLA with small amounts of CL or DXO increased the stability compared to that of the LLA homopolymer. Changing DXO to CL in a LLA copolymer also increased the stability. The type of radiation and the microstructure of the copolymer chains determined which of the monomer sequences were more prone to degrade. The most abundant low-molecular-weight product identified after sterilization was DXO monomer. Traces of LLA and CL monomers were also identified. Modification of the copolyester microstructure changed the degradation mechanism and the susceptibility towards irradiation. This allows the use of radiation sterilization to finalize the scaffold properties.

  • 10.
    Plikk, Peter
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Tyson, Therese
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Finne-Wistrand, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Mapping the Characteristics of the Radical Ring-Opening Polymerization of a Cyclic Ketene Acetal Towards the Creation of a Functionalized Polyester2009In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 47, no 18, p. 4587-4601Article in journal (Refereed)
    Abstract [en]

    Radical ring-opening polymerization of cyclic ketene acetals is a means to achieve novel types of aliphatic polyesters. 2-methylene-1,3-dioxe-5-pene is a seven-membered cyclic ketene acetal containing an unsaturation in the 5-position in the ring structure. The double bond functionality enables further reactions subsequent to polymerization. The monomer 2-methylene-1,3-dioxe-5-pene was synthesized and polymerized in bulk by free radical polymerization at different temperatures, to determine the structure of the products and propose a reaction mechanism. The reaction mechanism is dependent on the reaction temperature. At higher temperatures, ring-opening takes place to a great extent followed by a new cyclization process to form the stable five-membered cyclic ester 3-vinyl-1,4-butyrolactone as the main reaction product. Thereby, propagation is suppressed and only small amounts of other oligomeric products are formed. At lower temperatures, the cyclic ester formation is reduced and oligomeric products containing both ring-opened and ring-retained repeating units are produced at higher yield.

  • 11.
    Undin, Jenny
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Plikk, Peter
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Finne Wistrand, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Synthesis of Amorphous Aliphatic Polyester-Ether Homo- and Copolymers by Radical Polymerization of Ketene Acetals2010In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 48, no 22, p. 4965-4973Article in journal (Refereed)
    Abstract [en]

    Radical ring-opening polymerization has been efficiently used to copolymerize 2-methylene-1,3,6-trioxocane (MTC) and 2-methylene-1,3-dioxepane (MDO). The cyclic ketene acetal MTC was first synthesized and homopolymerized at different temperatures using either 2,2-azobisisobutyronitrile or dicumyl peroxide as initiator. The polymerization mechanism was not temperature-dependent, and the polymerization proceeded with 100% ring-opening at all the temperatures evaluated. The structures of MTC and PMTC were verified by H-1-nuclear magnetic resonance (NMR) and C-13-NMR spectroscopies. A number-average molecular weight of 6500 was obtained after 2 days at 70 degrees C in bulk, which was somewhat higher than the theoretical molecular weight. A significant amount of branching was detected from the high polydispersity index as well as the glass-transition temperatures. The polyester-ether was then successfully obtained by copolymerization of MTC with MDO. Different feed ratios and temperatures were used to map the reaction, and the copolymers were characterized by NMR, size exclusion chromatography, and differential scanning calorimetry. The amount of MTC within the polymer was independent of the feed ratio and always higher than the amount of MDO.

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