Temperature-responsive compounds as in situ gelling biomedical materials

Abstract

Aqueous solutions that undergo sol-to-gel transition as the temperature increases have been extensively studied during the last decade. The material can be designed by controlling the hydrophilic and hydrophobic balance of the material. Basically, the molecular weight of the hydrophilic block and hydrophobic block of a compound should be fine-tuned from the synthetic point of view. In addition, stereochemistry, microsequence, topology, and nanostructures of the compound also affect the transition temperature, gel window, phase diagram, and modulus of the gel. From a practical point of view, biodegradability, biocompatibility, and interactions between the material and drug or cell should be considered in designing a thermogelling material. The interactions are particularly important in that they control drug release profile and initial burst release of the drug in the drug delivery system, and affect cell proliferation, differentiation, and biomarker expression in three-dimensional cell culture and tissue engineering application. This review provides an in-depth summary of the recent progress of thermogelling systems including polymers, low molecular compounds, and nanoemulsions. Their biomedical applications were also comparatively discussed. In addition, perspectives on future material design of a new thermogelling material and its application are suggested.

Stimuli‐responsive polypeptide materials prepared by ring‐opening polymerization of α‐amino acid N‐carboxyanhydrides

“…19 Combining polypeptides with hydrophilic PEG can form thermo-responsive hydrogels. [20][21][22][23] For those ionic polypeptides, they can undergo solubility and conformation change upon solution pH change. Representative examples include poly-L-lysine and poly-L-glutamic acid.…”

Chemically Modified Natural Polysaccharides to Form Gels

“…Semisynthetic polysaccharides, such as carboxymethylcellulose, also undergo hydrogen bonding in a pH-sensitive manner (Barbucci et al 2000). Hydrogen bonding is sensitive towards other components in the solution, such as urea, which disrupt this form of physical bond and reduce its capacity to gel a material (Moon et al 2012). …”

Advances in drug delivery systems based on synthetic poly(hydroxybutyrate) (co)polymers

“…This response of the hydrogels is mainly governed and tuned by the hydrogel composition, the cross-linking type (chemical or physical) and the degree of cross-linking. There are numerous applications of hydrogels including in particular vehicles for drug delivery, scaffolds for tissue engineering, actuators for optics and fluidics, and model extracellular matrices for biological studies [184][185][186][187][188][189][190]. However, PHB-based hydrogels used as DDS remain quite rare in comparison to the PHB-based nanoparticles, micelles or microparticles.…”