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Modification of polymeric particles via surface grafting for 3D scaffold design
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Surface modification techniques have played important roles in various aspects of modern technology. They have been employed to improve substrates by altering surface physicochemical properties. An ideal surface modifying technique would be a method that is applicable to any kind of materials prepared from a wide range of polymers and that can occur under mild reaction conditions. The work in this thesis has utilized four main concepts: I) the development of a ‘grafting-from’ technique by covalently growing polymer grafts from particle surfaces, II) the presence of steric and electrosteric forces due to long-range repulsive interactions between particles, III) a combined surface grafting and layer-by-layer approach to create polyelectrolyte multilayers (PEMs) on particle surfaces to fabricate strong and functional materials, and IV) the roles of hydrophilic polymer grafts and substrate geometry on surface degradation.

A non-destructive surface grafting technique was developed and applied to polylactide (PLA) particle surfaces. Their successful modification was verified by observed changes to the surface chemistry, morphology and topography of the particles. To quantify the aggregation behavior of grafted and non-grafted particles, force interaction measurements were performed using colloidal probe atomic force microscopy (AFM). Long-range repulsive interactions were observed when symmetric systems, i.e., hydrophilic polymer grafts on two interacting surfaces, and asymmetric system were applied. Electrosteric forces were observed when the symmetric substrates interacted at pH 7.4. When PEMs were alternately assembled on the surface of poly(L-lactide) (PLLA) particles, the grafted surfaces played a dominated role in altering the surface chemistry and morphology of the particles. Three-dimensional scaffolds of surface grafted particle coated with PEMs demonstrated high mechanical performance that agreed well with the mechanical performance of cancellous bone. Nanomaterials were used to functionalize the scaffolds and further influence their physicochemical properties. For example, when magnetic nanoparticles were used to functionalize the scaffolds, a high electrical conductivity was imparted, which is important for bone tissue regeneration. Furthermore, the stability of the surface grafted particles was evaluated in phosphate buffered saline (PBS) solution. The nature of the hydrophilic polymer grafts and the geometry of the PLLA substrates played central roles in altering the surface properties of films and particles. After 10 days of PBS immersion, larger alterations in the surface morphology were observed on the film compared with microparticles grafted with poly(acrylic acid) (PAA). In contrast to the PAA-grafted substrates, the morphology of poly(acrylamide) (PAAm)-grafted substrates was not affected by PBS immersion. Additionally, PAAm-grafted microparticulate substrates encountered surface degradation more rapidly than PAAm-grafted film substrates.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , 61 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:48
Keyword [en]
surface grafting, PLA, PLLA, hydrophilic polymers, particles, geometry, steric stabilization, atomic force microscopy (AFM), polyelectrolyte multilayers, 3D scaffold, bone tissue engineering, surface degradation
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-174295ISBN: 978-91-7595-686-2 (print)OAI: oai:DiVA.org:kth-174295DiVA: diva2:858601
Public defence
2015-10-29, E3, Osquars backe 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20151002

Available from: 2015-10-02 Created: 2015-10-02 Last updated: 2015-10-02Bibliographically approved
List of papers
1. Nondestructive Covalent "Grafting-from" of Poly(lactide) Particles of Different Geometries
Open this publication in new window or tab >>Nondestructive Covalent "Grafting-from" of Poly(lactide) Particles of Different Geometries
2012 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 4, no 6, 2978-2984 p.Article in journal (Refereed) Published
Abstract [en]

A nondestructive "grafting-from" method has been developed using poly(lactide) (PLA) particles of different shapes as substrates and three hydrophilic monomers as grafts. Irregularly shaped particles and spheres of PLA were covalently surface functionalized using a versatile method of photoinduced free radical polymerization. The preservation of the molecular weight of the PLA particle bulk and the retention of the original particle shape confirmed the negligible effect of the grafting method. The changes in surface composition were determined by FTIR for both spherical and irregular particles and by XPS for the irregular particles showing the versatility of the method. Changes in the surface morphology of the PLA spherical particles were observed using microscopy techniques showing a full surface coverage of one of the grafted monomers. The method is applicable to a wide set of grafting monomers and provides a permanent alteration of the surface chemistry of the PLA particles creating hydrophilic PIA surfaces in addition to creating sites for further modification and drug delivery in the biomedical fields.

Keyword
surface grafting, PLA, hydrophilic, particles, geometry
National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-99241 (URN)10.1021/am3003507 (DOI)000305716900024 ()2-s2.0-84863202182 (Scopus ID)
Note

QC 20120724

Available from: 2012-07-24 Created: 2012-07-23 Last updated: 2017-12-07Bibliographically approved
2. Force Interactions of Nonagglomerating Polylactide Particles Obtained through Covalent Surface Grafting with Hydrophilic Polymers
Open this publication in new window or tab >>Force Interactions of Nonagglomerating Polylactide Particles Obtained through Covalent Surface Grafting with Hydrophilic Polymers
Show others...
2013 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, no 26, 8873-8881 p.Article in journal (Refereed) Published
Abstract [en]

 Nonagglomerating polylactide (PLA) particles with various interaction forces were designed by covalent photografting. PLA particles were surface grafted with hydrophilic poly(acrylic acid) (PAA) or poly(acrylamide) (PAAm), and force interactions were determined using colloidal probe atomic force microscopy. Long-range repulsive interactions were detected in the hydrophilic/hydrophilic systems and in the hydrophobic/hydrophilic PLA/PLA-g-PAAm system. In contrast, attractive interactions were observed in the hydrophobic PLA/PLA and in the hydrophobic/hydrophilic PLA/PLA-g-PAA systems. AFM was also used in the tapping mode to determine the surface roughness of both neat and surface-grafted PLA film substrates. The imaging was performed in the dry state as well as in salt solutions of different concentrations. Differences in surface roughness were identified as conformational changes induced by the altered Debye screening length. To understand the origin of the repulsive force, the AFM force profiles were compared to the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory and the Alexander de Gennes (AdG) model. The steric repulsion provided by the different grafted hydrophilic polymers is a useful tool to inhibit agglomeration of polymeric particles. This is a key aspect in many applications of polymer particles, for example in drug delivery.

Keyword
Atomic force microscopy, Drug delivery, Grafting (chemical), Hydrogels, Hydrophilicity, Polyesters, Surface roughness
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-122428 (URN)10.1021/la401076m (DOI)000322059700013 ()2-s2.0-84880322768 (Scopus ID)
Funder
EU, European Research Council, 246776
Note

QC 20130909. Updated from manuscript to article in journal.

Available from: 2013-05-21 Created: 2013-05-21 Last updated: 2017-12-06Bibliographically approved
3. The nature of polymer grafts and substrate shape on the surface degradation of poly(l-lactide)
Open this publication in new window or tab >>The nature of polymer grafts and substrate shape on the surface degradation of poly(l-lactide)
2015 (English)In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628Article in journal (Refereed) Epub ahead of print
Abstract [en]

Surface grafting of functional polymers is an effective method to alter material properties and degradation behavior. Two different substrate shapes of poly(l-lactide) (PLLA), i.e., films and microparticles, were surface-grafted with hydrophilic monomers, and their surface degradation was monitored. Surface grafting with a hydrophilic and acidic polymer graft [acrylic acid (AA)] induced large alterations in the surface morphology and topography of the films. In contrast, hydrophilic and neutral polymer grafts [acrylamide (AAm)] had no significant effect on the surface degradation behavior, while the PLLA reference and co-monomeric (AA/AAm) polymer-grafted samples exhibited intermediate surface degradation rates. The grafted PAA chains induced a local acidic environment on the surface of the substrates, which in turn catalyzed the surface degradation process. This effect was more pronounced in the films than in the microparticles. Thus, the nature of the grafted chains and substrate geometry were shown to affect the surface degradation behavior of PLLA substrates.

Keyword
Degradation, Properties and characterization, Surfaces and interfaces
National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-173360 (URN)10.1002/app.42736 (DOI)
Note

QP 201509

Available from: 2015-09-10 Created: 2015-09-10 Last updated: 2017-12-04Bibliographically approved
4. Highlighting the Importance of Surface Grafting in Combination with a Layer-by-Layer Approach for Fabricating Advanced 3D Poly(L-lactide) Microsphere Scaffolds
Open this publication in new window or tab >>Highlighting the Importance of Surface Grafting in Combination with a Layer-by-Layer Approach for Fabricating Advanced 3D Poly(L-lactide) Microsphere Scaffolds
2016 (English)In: CHEMISTRY OF MATERIALS, ISSN 0897-4756, Vol. 28, no 10, 3298-3307 p.Article in journal (Other academic) Published
Place, publisher, year, edition, pages
American Chemical Society (ACS), 2016
National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-174294 (URN)10.1021/acs.chemmater.6b00133 (DOI)000376825700010 ()
Note

QC 20160629

Available from: 2015-10-02 Created: 2015-10-02 Last updated: 2016-06-29Bibliographically approved

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