Characteristics of Precipitation-formed Polyethylene Glycol Microgels Are Controlled by Molecular Weight of Reactants

Abstract

This work describes the formation of poly(ethylene glycol) (PEG) microgels via a photopolymerized precipitation reaction. Precipitation reactions offer several advantages over traditional microsphere fabrication techniques. Contrary to emulsion, suspension, and dispersion techniques, microgels formed by precipitation are of uniform shape and size, i.e. low polydispersity index, without the use of organic solvents or stabilizers. The mild conditions of the precipitation reaction, customizable properties of the microgels, and low viscosity for injections make them applicable for in vivo purposes. Unlike other fabrication techniques, microgel characteristics can be modified by changing the starting polymer molecular weight. Increasing the starting PEG molecular weight increased microgel diameter and swelling ratio. Further modifications are suggested such as encapsulating molecules during microgel crosslinking. Simple adaptations to the PEG microgel building blocks are explored for future applications of microgels as drug delivery vehicles and tissue engineering scaffolds. Video LinkThe video component of this article can be found at

Polyethlyene glycol microgels to deliver bioactive nerve growth factor

“…PLA‐b‐PEG‐b‐PLA microgels were formed via precipitation reaction as described in detail in previous publications . Microgels were formed from both molecular weights, and were termed 3K microgels or 6K microgels.…”

“…Swollen mass ( M s ) of the microgels, defined as the mass after equilibrium swelling (48 h), was measured by washing the microgels in Type I H 2 O 5× and swelling for a minimum of 48 h before centrifuging in preweighed microcentrifuge tubes for 10 min at 4000× g . After removing the supernatant, samples were lyophilized to constant mass to obtain dry mass ( M d ) . The water content in the microgels was calculated by Eq.…”

“…The gradient was then centrifuged for 10 min at 4000× g and 5°C. Microgel position after centrifugation allowed for a simple density calculation …”

Injectable PEGylated fibrinogen cell-laden microparticles made with a continuous solvent- and oil-free preparation method

“…Ideally, these 55 materials can be delivered locally and undergo a liquid-to-gel tran-56 sition at the site of injection in order to form the final implant [1,2]. 57 A number of different in situ chemistries have been employed to 58 achieve this effect with biomaterials, but problems can arise with 59 the rapid liquid-to-gel transition reaction, which hinders their 60 widespread applicability in tissue engineering, requiring in situ cell 61 encapsulation [3]. For example, it is very difficult to predict the 62 reliability of the reaction and its end products, as well as to miti- 63 gate the reaction's cytotoxicity to the surrounding tissues and 64 encapsulated cells, when reacting the materials in situ [4].…”

“…Viscosity analysis of the PF/cell mixtures for cell densities of 3 Â 10 6 , 6 Â 10 6 and 1.2 Â 10 7 cells ml À1 during time of exposure to UV irradiation at 2 mW cm À2 intensity (UV irradiation initiated 30 s into the time-sweep measurements). [61]. The type of photopolymerizable polymer system can also be 567 tailored using this approach, provided that crosslinking kinetics 568 is known.…”