Effect of Polymer Composition on Rheological and Degradation Properties of Temperature-Responsive Gelling Systems Composed of Acyl-Capped PCLA-PEG-PCLA

Abstract

In this study, the ability to modulate the rheological and degradation properties of temperature-responsive gelling systems composed of acyl-capped poly(ε-caprolactone-co-lactide)-b-poly(ethylene glycol)-b-poly(ε-caprolactone-co-lactide) (PCLA-PEG-PCLA) triblock copolymers was investigated. Eight polymers with varying molecular weight of PCLA, caproyl/lactoyl ratio (CL/LA) and capped with either acetyl- or propionyl-groups were synthesized by ring-opening polymerization of L-lactide and ε-caprolactone in toluene using PEG as initiator and tin(II) 2-ethylhexanoate as catalyst, and subsequently reacted in solution with an excess of acyl chloride to yield fully acyl-capped PCLA-PEG-PCLA. The microstructure of the polymers was determined by (1)H NMR, and the thermal properties and crystallinity of the polymers in dry state and in 25 wt % aqueous systems were studied by differential scanning calorimetry and X-ray diffraction. Rheological and degradation/dissolution properties of aqueous systems composed of the polymers in 25 wt % aqueous systems were studied. (1)H NMR analysis revealed that the monomer sequence in the PCLA blocks was not fully random, resulting in relatively long CL sequences, even though transesterification was demonstrated by the enrichment with lactoyl units and the presence of PEG-OH end groups. Except the most hydrophilic polymer composed of acetyl-capped PCLA1400-PEG1500-PCLA1400 having a CL/LA molar ratio of 2.5, the polymers at 25 wt % in buffer were sols below room temperature and transformed into gels between room temperature and 37 °C, which makes them suitable as temperature-responsive gelling systems for drug delivery. Over a period of weeks at 37 °C, the systems containing polymers with long CL sequences (~8 CL) and propionyl end-groups became semicrystalline as shown by X-ray diffraction analysis. Degradation of the gels by dissolution at 37 °C took 100-150 days for the amorphous gels and 250-300 days for the semicrystalline gels. In conclusion, this study shows that changes in the polymer composition allow an easy but significant modulation of rheological and degradation properties.

Effect of drug loading on the properties of temperature‐responsive polyester–poly(ethylene glycol)–polyester hydrogels

“…Therefore, the suspensions appear transparent to the naked eye. The vial inversion method was used to differentiate gels from viscous liquids at 37 °C . Vials containing the formulations were brought to 37 °C for 30 min, then inverted and examined after 10 min (Fig.…”

“…These hydrogels showed superior release kinetics compared to poloxamers when tested in vitro using ketoprofen as a hydrophilic drug and spironolactone as a hydrophobic drug . Structurally related acyl‐capped poly( ϵ ‐caprolactone‐ co ‐lactide) (PCLA)‐ block ‐PEG‐ block ‐PCLA triblock copolymers have since been shown to have improved drug release and degradation kinetics …”

Sustained intravitreal delivery of dexamethasone using an injectable and biodegradable thermogel

“…The use of organic solvents is thoroughly avoided during the whole process of application. So far, thermogelling PEG/polyester block copolymers [22][23][24][25][26][27], PEG/polypeptide block copolymers [28,29] and poly(phosphazenes) [30,31] have been reported.…”

Effect of Covalent-Functionalized Graphene Oxide with Polymer and Reactive Compatibilization on Thermal Properties of Maleic Anhydride Grafted Polypropylene

“…Simultaneously, the characteristic sharp peaks (19.5° and 23.6°; Figure S1) of NH 2 -PEG-NH 2 show almost no deviation in GO-PEG. 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 The G band at 1606 cm -1 corresponds to sp 2 -hybridized carbons and assigned to the first-order scattering of E 2g phonons. The G band demonstrates the ordered state of GO platelets.…”