Impact of Synthetic Technique on PLA−PEO−PLA Physical Hydrogel Properties

Abstract

Previous work has shown that the stiffness of poly(lactide)-b-poly(ethylene oxide)-b-poly(lactide) [PLA−PEO−PLA] hydrogels can be influenced by crystallinity. Those hydrogels with crystalline PLLA end blocks had a higher storage modulus (up to 1 order of magnitude) than the amorphous equivalents. All the previous work was done with polymers synthesized in the bulk. This paper reports the difference in mechanical properties when two different synthetic techniques are usedbulk and solution synthesis. Solution-synthesized polymers consistently formed stiffer hydrogels than bulk-synthesized polymers. Further investigation determined the following: crystalline polymers from solution synthesis still form stiffer gels than the amorphous analogues, but not to the extent previously reported; the solution synthesized polymers have narrower distributions, but this alone does not account for the mechanical differences. However, the presence of asymmetric triblock copolymers, which act like an effective diblock copolymer, within the bulk-synthesized materials appears to lower the overall stiffness of the gel. The impact on modulus is much larger for amorphous PLA than for crystalline PLLA end block materials. These findings suggest bulk-synthesized polymers likely have more asymmetric triblock copolymers, that decrease the relaxation time of the system, possibly by lowering the junction lifetime, or lead to dangling ends in the network, which cause a loss in mechanical properties when compared to solution-synthesized polymers.

Rheology of associative polymer solutions

“…Often the hydrophobic blocks were chosen for their biocompatibility and biodegradability in order to obtain hydrogels that could be used in medical applications. Examples are PLA [37][38][39][40], PCL [41][42][43], copolymers of CL and GA, CL and LA [44,45], or LA and GA [46,47], and poly(HPMAm lac ) [48]. The temperature and concentration range where gels were formed could be tuned by varying the length of the hydrophobic and hydrophilic blocks or by changing the composition of the hydrophobic block if it contained two different monomers.…”

PLA–PEO–PLA Hydrogels and Their Mechanical Properties

“…In general, the polymers can be prepared in solution or in the bulk. This can impact the mechanical properties of the resulting hydrogel since the molecular weight distribution (MWD), specifically the symmetry of the triblock copolymer, is influenced [46]. Generally, triblock copolymers produced through bulk-synthesis are more asymmetric, which reduced the mechanical stiffness of the gel phase (such as system relaxation time and junction lifetime).…”

“…Generally, triblock copolymers produced through bulk-synthesis are more asymmetric, which reduced the mechanical stiffness of the gel phase (such as system relaxation time and junction lifetime). This had a larger impact on amorphous PRLA materials than on containing crystalline PLLA [46]. Triblock formation begins by ring-opening polymerization of the lactide monomer by a preformed dihydroxylated PEG [49][50][51][52][53][54].…”

“…This includes the ability to varying the stiffness of these hydrogels by manipulating the length of the PLA endblocks [44], by changing the physical cross-links from amorphous to crystalline PLA [45], by varying the synthetic technique [46], by incorporating nanoparticles [47], and by covalently capturing the self-assembled structure [48]. This last approach is particularly intriguing since it combines the advantages of self-assembly with the stability of covalent cross-links.…”

Tetronic–Oligolactide–Heparin Hydrogel as a Multi‐Functional Scaffold for Tissue Regeneration

“…Cells will not grow properly in a mechanical environment that is not similar to their native tissue. [35] As an example, Kong et al [36] reported that increasing the viscosity of alginate hydrogels resulted in decreased cell viability. In our knowledge, it is an ambiguous hypothesis that extracellular matrix (ECM) components or ECM-like molecules can promote cell proliferation and/or differentiation or other cellular actions.…”