Structures and Applications of Thermoresponsive Hydrogels and Nanocomposite-Hydrogels Based on Copolymers with Poly (Ethylene Glycol) and Poly (Lactide-Co-Glycolide) Blocks

Abstract

Thermoresponsive hydrogels showing biocompatibility and degradability have been under intense investigation for biomedical applications, especially hydrogels composed of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic poly(lactic acid-co-glycolic acid) (PLGA) as first-line materials. Even though various aspects such as gelation behavior, degradation behavior, drug-release behavior, and composition effect have been studied for 20 years since the first report of these hydrogels, there are still many outputs on parameters affecting their gelation, structure, and application. In this review, the current trends of research on linear block copolymers composed of PEG and PLGA during the last 5 years (2014-2019) are summarized. In detail, this review stresses newly found parameters affecting thermoresponsive gelation, findings from structural analysis by simulation, small-angle neutron scattering (SANS), etc., progress in biomedical applications including drug delivery systems and regeneration medicine, and nanocomposites composed of block copolymers with PEG and PLGA and nanomaterials (laponite).

Polymers Exhibiting Lower Critical Solution Temperatures as a Route to Thermoreversible Gelators for Healthcare

“…However, temperature enhances the hydrophobic effect driving a greater fraction of micelles to form, potentially altering micelle shape, and enhancing inter‐micelle interactions which in turn induces gelation. [ 15 ] Poloxamers, in particular, have been widely studied and are appealing due to their history of use in human medicine. [ 16,17 ] However, there are several limitations of these materials, including a high dependence of T gel on polymer concentration leading to a reverse gel–sol transition upon dilution, [ 18 ] weak gel strengths for some applications such as mucosal drug delivery and 3D printing, [ 17,19 ] and low long‐term cell viability in their presence for tissue engineering and cell culture purposes.…”

Recent Advances in Injectable Hydrogels for Controlled and Local Drug Delivery

“…When the solution temperature is increased, polymer-water hydrogen bonding becomes weaker, while the hydrophobic interactions between micelles become stronger; this results in the formation of a networks or aggregates of micelles. [170] In one study, Singh et al reported thermo-and pH-sensitive injectable hydrogels composed of poly( -caprolactone lactide) (PCLA)-PEG-PCLA-PAEU multiblock copolymers. The nega-tively charged human growth hormone (hGH) was interacted with the positively charged surface of 2D-layered double hydroxide NPs (LDH).…”

From Supramolecular Hydrogels to Multifunctional Carriers for Biologically Active Substances

“…The gel strength depends on the number, size, and geometry of hydrophobic domains. The properties can also be modified by surfactant or salt addition [ 34 , 35 ]. The ease of recreating hydrophobic interactions makes these gels exhibit excellent self-healing properties.…”

“…The ease of recreating hydrophobic interactions makes these gels exhibit excellent self-healing properties. The damaged hydrogel usually can be repaired at room temperature, regaining its mechanical properties [ 1 , 11 , 26 , 35 , 36 , 37 , 38 ]. The hydrogels which are formed by hydrophobic interactions often exhibit interesting negatively thermo-responsive behavior (the temperature increase causes the gelation process).…”