The use of cell transplantation to treat enzyme deficiency disorders is limited by
the immune response targeted against foreign tissue or the use of life-long
immunosuppressants. Hiding cells from the immune system in an encapsulation device is
promising. Cells encapsulated within an anionic calcium alginate hydrogel bead are
protected through a semi-permeable membrane formed by polycation, poly-L-lysine
(PLL). A final layer of alginate is added to hide the cationic PLL surface but this has
proved to be difficult creating capsules which are prone to fibrotic overgrowth, blocking
exchange of nutrients, waste and therapeutic enzymes through the capsule. For long term
applications these capsules need to be both biocompatible and mechanically robust.
This thesis aims to address the biocompatibility issue of high cationic surface
charge by synthesizing polycations of reduced charge using N-(3-
aminopropyl)methacrylamide hydrochloride (APM) and N-(2-
hydroxypropyl)methacrylamide (HPM) and study the associated mechanical properties of
the capsules using micropipette aspiration. Micropipette aspiration was applied and
validated for alginate based capsules (gel and liquid core) to quantify stiffness.
Varying ratios of APM were used to control the overall charge of the polycations
formed while HPM was incorporated as a neutral, hydrophilic, nonfouling comonomer.
The molecular weight (MW) was controlled by using reversible addition-fragmentation
chain transfer (RAFT) polymerization. The biocompatibility of these polymers was tested
by cell adhesion and proliferation of 3T3 fibroblasts onto APM/HPM copolymer
functionalized surfaces and by solution toxicity against C2C12 myoblasts. The ability for the APM/HPM copolymers to bind to alginate and form capsules was also assessed, along
with the integrity and stiffness of the capsule membrane with or without additional
covalent cross-linking by reactive polyanion, poly(methacrylic acid-co-2-vinyl-4,4-
dimethylazlactone) (PMV60).
Thermo-responsive block copolymers of N-isopropylacrylamide (NIPAM) and 2-
hydroxyethylacrylamide (HEA) were also synthesized as potential drug delivery
nanoparticles, showing control over micelle morphology with varying NIPAM to HEA
ratios. / Thesis / Doctor of Science (PhD) / The treatment of enzyme deficiency disorders by cell transplantation is limited by
the immune attack of foreign tissue in absence of immunosuppressants. Cells protected in
an encapsulation device has shown promise. Poly-L-lysine, a widely used membrane
material in these protective capsules, binds to the anionic gel entrapping living cells
because it is highly cationic. The high cationic charge is difficult to hide causing the
immune system to build tissue around the capsule, preventing the encapsulated cells from
exchanging nutrients and therapeutic enzymes. This thesis aims to replace poly-L-lysine
by synthesizing a series of more biocompatible materials of decreasing cationic charge.
These materials were studied for the ability to support tissue growth and form stable
capsules. The membrane strength was measured using an aspiration method validated for
these types of capsules. Reducing the cationic charge of the materials increased the
biocompatibility of the capsule membrane but also made for weaker membranes.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/27614 |
| Date | 04 1900 |
| Creators | Kleinberger, Rachelle |
| Contributors | Stover, Harald, Chemistry |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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