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Steric Stabilization of Polylactide particles achieved by Covalent 'grafting-from' with Hydrophilic Polymers
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Despite numerous advantages of using particles in a wide range of applications, they have one drawback that is their tendency to agglomerate. One way to overcome this problem is to sterically  stabilize the particles by introducing polymeric  chains covalently attached to the surface. Surface modification by covalently attaching polymer chains to the particle surface can be achieved by e.g. a ‘grafting-from’ technique under UV irradiation.

In this thesis, polylactide (PLA) particles were surface modified, under UV irradiation, with the hydrophilic monomers: acrylamide (AAm), acrylic acid (AA), and maleic anhydride (MAH). The developed ‘grafting-from’ technique was shown to be nondestructive method for surface modification of PLA particles of two different geometries. The change in surface chemistry of the PLA particles was confirmed by FTIR and XPS, indicating the success of the surface grafting technique. Force interaction between two surface grafted PLA substrates was measured by colloidal probe AFM in different salt concentrations. In order to understand the repulsive force, the AFM force profiles were compared to the DLVO theory and AdG model. Long range repulsive interactions were mainly observed when hydrophilic polymers were covalently attached to the surface of PLA particles, leading to steric interaction. Attractive force dominated the interaction when neat PLA particle was approaching each other, resulting in particle aggregation, even though short range repulsion was observed at small separation distance, i.e. approximately 10 nm. Attractive interaction was also observed when neat PLA was approaching to PAA-grafted PLA substrate. This attractive interaction was much greater than force interaction between two neat PLA substrates.

 The surface grafted particles can be used in biomedical application where secondary interactions are important to overcome particle agglomeration such as particle-based drug delivery.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , 41 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2013:27
Keyword [en]
Steric stabilization, AFM, hydrophilicity, surface modification, poly(lactide), acrylamide, acrylic acid, maleic anhydride
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-122429OAI: oai:DiVA.org:kth-122429DiVA: diva2:622327
Presentation
2013-06-10, K2, Teknikringen 28, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
EU, European Research Council, 246776Swedish Research Council, 621-2010-3478
Note

QC 20130529

Available from: 2013-05-29 Created: 2013-05-21 Last updated: 2013-05-29Bibliographically approved
List of papers
1. 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
2. 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

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