Mapas de densidad acústica

As mentioned, one of the benefits of polymersomes over liposomes is the unique

ability to tune to degradation and release kinetics of the polymer backbone for enhanced

control of drug delivery rates. To that end, we sought to stabilize the membrane structure

and decrease the permeation of drug across the membrane prior to membrane hydrolysis

by forming biodegradable membrane stabilized vesicles through the use of a acryl group

on the terminal hydroxyl end of the PCL block, a photoiniator, and a light source. Once

assembled into polymersomes and in the presence of a photoinitiator, UV light exposure

induces a radical polymerization through the functional groups (Figure 2.14). This

approach does not hinder hydrolysis of the PCL chain and yields oligo-caprolactone

units, PEG, and kinetic chains of poly(acrylic acid) as the degradation products [84].

Figure 2.14- Schematic of Hydrophobic End Group Polymerization for Stabilization of Polymersome Membranes

Joshua S. Katz determined that only in the case where DMPA, the photoinitiator

polymerization of the acrylate groups observed (i.e., disappearance of acrylate peaks in

NMR spectra, Figure 2.15

the NMR spectrum of the UV exposed polymersomes containing DMPA, indicative of an

increase in molecular weight that would be expected to accompany acrylate

polymerization. UV light alone or simply the presence of DMPA were both insufficient

to induce polymerization

conversion of the acrylate groups was also investigated (

1:1 mol/mol ratio of DMPA to polymer was necessary for complete conversion of

acrylates.

Figure 2.15- (A) NMR spectra of dehydrated polymersomes of AcPCL

or without DMPA loaded into the membrane before and after UV light exposure as indicated. The -DMPA+UV sample received a 30min dose of UVlight, while the +DMPA+UV sample received a 5 min dose

polymersomes with varying amounts of DMPA loaded into the membrane (reported as molar ratio of polymer:DMPA). All samples received a 10 min dose of UV light. Lowercase letters indicate assignment of peaks to the chemical

e acrylate groups observed (i.e., disappearance of acrylate peaks in

15A). Additionally, significant peak broadening can be seen in

ectrum of the UV exposed polymersomes containing DMPA, indicative of an

increase in molecular weight that would be expected to accompany acrylate

polymerization. UV light alone or simply the presence of DMPA were both insufficient

to induce polymerization. Furthermore, the amount of DMPA necessary for complete

conversion of the acrylate groups was also investigated (Figure 2.14, Figure

1:1 mol/mol ratio of DMPA to polymer was necessary for complete conversion of

(A) NMR spectra of dehydrated polymersomes of AcPCL

or without DMPA loaded into the membrane before and after UV light exposure as DMPA+UV sample received a 30min dose of UVlight, while the +DMPA+UV sample received a 5 min dose. (B) NMR spectra of AcPCL

polymersomes with varying amounts of DMPA loaded into the membrane (reported as molar ratio of polymer:DMPA). All samples received a 10 min dose of UV light. Lowercase letters indicate assignment of peaks to the chemical structure shown.

e acrylate groups observed (i.e., disappearance of acrylate peaks in

A). Additionally, significant peak broadening can be seen in

ectrum of the UV exposed polymersomes containing DMPA, indicative of an

increase in molecular weight that would be expected to accompany acrylate

polymerization. UV light alone or simply the presence of DMPA were both insufficient

. Furthermore, the amount of DMPA necessary for complete

Figure 2.15B). A

1:1 mol/mol ratio of DMPA to polymer was necessary for complete conversion of

(A) NMR spectra of dehydrated polymersomes of AcPCL-b-PEG with or without DMPA loaded into the membrane before and after UV light exposure as DMPA+UV sample received a 30min dose of UVlight, while the . (B) NMR spectra of AcPCL-b-PEG polymersomes with varying amounts of DMPA loaded into the membrane (reported as molar ratio of polymer:DMPA). All samples received a 10 min dose of UV light.

To demonstrate membrane stabilization as a method of controlling the release of

drug from the polymersome, doxorubicin was encapsulated in PEO-b-PCL-Ac

polymersomes loaded with DMPA in the membrane and the release was monitored via

fluorescence dequenching of the drug as discussed in Section 2.3 EXPERIMENTAL

METHODS. We compared formulations with and without 15 min exposure to UV light

(Figure 2.16A). As mentioned, as DOX releases from the polymersome and is diluted

into the surrounding solution, its fluorescence increases over a baseline level [85],

enabling tracking of the release from the polymersomes. Results are normalized to the

initial amount of DOX encapsulated (determined by membrane disruption through Triton

exposure to an additional sample for each group) less the baseline fluorescence.

Formulations were also highly stable, exhibiting negligible release (<1%) when stored at

4 C over the same period of time. The characteristic initial burst phase release, seen

with PEO-b-PCL vesicles, was seen for both stabilized and non-stabilized polymersomes;

however, the amount of drug released was slightly more when encapsulated in the non-

stabilized polymersomes. The drug molecules released during this burst phase are likely

from the DOX that partitioned into the membrane prior to stabilization (DOX is

amphiphilic). However, following the burst phase release, the rate of release was much

slower for stabilized polymersomes compared to the non-stabilized polymersomes

(Figure 2.16B). By 7 days, only an additional ∼5% more of the drug from that released during the burst phase was observed to be released for the stabilized vesicles, compared

to the additional ∼25% more being released for the non-stabilized samples, similar to what was observed with PEO-b-PCL vesicles in Section 2.4.1. Due to degradation of

DOX in aqueous solutions

method. However, from the two observed profiles (

release is significantly retarded by stabilization of the membrane.

Figure 2.16- Doxorubicin Release from PEO

(a) Percent cumulative released and (b) release rates of DOX encapsulated in PEO b-PCL-Ac polymersomes with 1:1 DMPA either without exposure (circles) or with exposure to 15 min UV light (squares). The amount released was normalized to the initial amount encapsulated and is reported as means (

deviations.