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Design of Resorbable Porous Tubular Copolyester Scaffolds for Use in Nerve Regeneration
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2009 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 10, no 5, 1259-1264 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
2009. Vol. 10, no 5, 1259-1264 p.
Keyword [en]
l-lactide; epsilon-caprolactone; trimethylene carbonate; aliphatic polyesters; molecular-weight; cyclic dimer; copolymers; 1, 5-dioxepan-2-one; polymerization; guide
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-14415DOI: 10.1021/bm900093rISI: 000265914200031Scopus ID: 2-s2.0-66149089558OAI: oai:DiVA.org:kth-14415DiVA: diva2:332436
Note
QC 20100805Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Design of Functional Degradable Aliphatic Polyesters and Porous Tissue Engineering Scaffolds
Open this publication in new window or tab >>Design of Functional Degradable Aliphatic Polyesters and Porous Tissue Engineering Scaffolds
2009 (English)Doctoral 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.

Abstract [sv]

Regenerering av skadade vävnader eller organ genom användning av porösa bionedbrytbara implantat som temporära byggnadsställningar för patientens egna celler är ett sätt att lösa de tillkortakommanden som finns i dagens medicinska behandlingsmetoder. De många möjliga applikationerna för vävnadsersättning och de höga krav som ställs på materialen skapar ett behov av nya material med innovativa egenskaper. I denna avhandling används design av alifatiska polyetrar och porösa strukturer för att skräddarsy deras egenskaper och för att kontrollera de förändringar i egenskaper som sker när materialet strålningssteriliseras.

Porösa strukturer tillverkades med fokus på design av deras materialegenskaper. Genom sampolymerisation av L,L-laktid (LLA), ε-kaprolakton (CL) och 1,5-dioxepan-2-on (DXO) med utvalda sammansättningar och monomerkombinationer kunde dessa skräddarsys. Porösa strukturer med hög porositet och ett stort register av förutbestämbara mekaniska och termiska egenskaper framställdes via en utvecklad saltlakningsteknik.

Porösa tuber för nervregenerering, med olika design, utvecklades genom användning av sampolymerer av LLA, CL, DXO eller trimetylenkarbonat (TMC) och en mångsidig stöpnings- och saltlakningsteknik.

Genom att utnyttja de reaktioner som uppstod i de polymera materialen vid sterilisering, med elektron- eller gammastrålning, erhölls förutbestämbara slutgiltiga egenskaper för de porösa strukturerna. Detta uppnåddes genom att skapa material som påverkas på ett specifikt sätt vid bestrålning. Genom att förändra strålningstyp, strålningsdos, monomerer och sammansättningar ändrades känsligheten mot strålning och de reaktionsmekanismer som inducerats. Steriliseringsprocessen blir härmed inkorporerad som ett sista steg i framställningen av de porösa strukturerna.

En fri radikal ringöppningspolymerisation utvecklades för monomeren 2-metylen-1,3-dioxe-5-pen. Reaktionsprodukterna bestämdes och en reaktionsmekanism föreslogs, som ett första steg i framställningen av en innovativ multifunktionell polyester. Reaktionsmekanismen är temperaturberoende och propagering är hämmad på grund av stabiliteten av den allylradikal som bildas vid ringöppning. Vid högre reaktionstemperaturer bildades den cykliska estern 3-vinyl-1,4-butyrolakton som huvudprodukt. Vid lägre temperaturer var den huvudsakliga produkten oligomerer bestående av både ringöppnade och ringslutna repeterande enheter.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. 58 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2009:20
Keyword
Ring-opening polymerization, Stannous octoate, 2, 2’-azoisobutyronitrile, 1, 5-dioxepane-2-one, ε-caprolactone, L-lactide, Trimethylene carbonate, 2-methylene-1, 3-dioxe-5-pene, Copolymer, Porous scaffold, Porous tubular scaffold, Electron beam, Gamma irradiation
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-10368 (URN)978-91-7415-309-5 (ISBN)
Public defence
2009-05-29, E1, KTH, Lindstedtsvägen 3, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100805Available from: 2009-05-14 Created: 2009-05-08 Last updated: 2010-08-05Bibliographically approved
2. Macromolecular synthesis of functional degradable aliphatic polyesters and porous scaffold design
Open this publication in new window or tab >>Macromolecular synthesis of functional degradable aliphatic polyesters and porous scaffold design
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

There is an increasing demand for new materials in biomedical applications with material properties that are highly specific for each application area. The search for new materials requires the creation of materials with suitable mechanical properties, functionalities, three-dimensional structures and a controlled degradation profile. The focus of the work described in this thesis has been on the synthesis of functional degradable aliphatic polyesters, on the design of porous scaffolds and on their synthesis with bio-safe catalyst/initiator systems.  

An unsaturated aliphatic polyester has been synthesized by condensation polymerization to produce poly(but-2-ene-1,4-diyl malonate) (PBM), which was applicable as a cross-linked network and as a macro-co-initiator for the ring-opening polymerization (ROP) of cyclic ester monomers. The method of preparation of PBM was simple and straightforward and there was no need to purify the monomers or add a catalyst. PBM was successfully cross-linked with UV-radiation to form a transparent, colorless, flexible and strong film. When PBM was used as a macro-co-initiator, a triblock copolymer was formed with PBM middle blocks and poly(L-lactide) (PLLA) or poly(ε-caprolactone) side blocks. The ductility of the triblock copolymer of PLLA was greatly enhanced and the strength was maintained compared to the polymer obtained when PLLA was polymerized with ethylene glycol as co-initiator. The triblock copolymers were easily cross-linked to give materials with greater strength and higher modulus as a result. When these polymers were subjected to hydrolysis, a rapid initial hydrolysis of the amorphous PBM middle block changed the microstructure from triblock to diblock, with a significant reduction in ductility and number average molecular weight. Highly porous scaffolds were created from these functional materials and the mechanical properties were evaluated by a cyclic compression test under mimicked physiological conditions.

Copolymers of L-lactide (LLA) and ε-caprolactone (CL), trimethylene carbonate (TMC) or 1,5-dioxepane-2-one (DXO) have been synthesized with a low stannous-2-ethyl hexanoate  (Sn(Oct)2) ratio and used to fabricate porous tubular scaffolds. The tubes were designed to have a range of mechanical properties suitable for nerve regeneration, with different porosities and different numbers of layers in the tube wall. The adaptability of an immersion-coating and porogen-leaching technique was demonstrated by creating tubes with different dimensions.

Although a low amount of residual tin (monomer-to-initiator ratio of 10000:1) is accepted in biomedical applications, an efficient bio-safe catalyst/initiator system would be favored. The catalytic activities of bio-safe Bi (III) acetate and creatinine towards the ROP of LLA have been compared with those of Sn(Oct)2-based systems and with those of a system catalyzed by enzymes. All these systems were shown to be suitable catalysts for the synthesis of high and moderate molecular weight PLLAs.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. 75 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2011:45
Keyword
functional polyesters, condensation polymerization, L-lactide, ε-caprolactone, triblock copolymer, mechanical properties, porous scaffolds, tissue engineering, ring-opening polymerization, Bi(III) acetate, creatinine, stannous 2-ethylhexanoate, enzyme, degradation products
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-38583 (URN)978-91-7501-060-1 (ISBN)
Public defence
2011-09-22, F3, Lindstedtsvägen 26, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
QC 20110901Available from: 2011-08-30 Created: 2011-08-29 Last updated: 2011-09-01Bibliographically approved

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