Abstract
Microgels are intra-molecular crosslinked macromolecules that can be used as vehicles to deliver and release drugs at the point-of-need in the patient’s body. Here, gelatin microgels were formed from microfluidics droplets, stabilised by aldehydes and frozen into a spheroidal shape. Microgel morphology and response to external stimuli were characterised. It was found that the behaviour of the spheroidal microgels was sensitive to both pH and ionic strength and that the distribution of charges into the microgels affected the behaviour of swelling and uptake. The uptake of molecules such as Rhodamine B and Methylene Blue were investigated as a model for drug uptake/release mechanisms. Under physiological conditions, the uptake of Rhodamine was rapid and a uniform distribution of the fluorescent molecules was recorded inside the microgels. However, the mechanism of release became slower at lower pH, which mimics the stomach environment. Under physiological conditions, Methylene Blue release occurred faster than for Rhodamine. Anionic and neutral molecules were also tested. In conclusion, the dependence of uptake and release of model drugs on basic/acid conditions shows that microgels could be used for targeted drug delivery. Different shaped microgels, such as spheres, spheroids, and rods, could be useful in tissue engineering or during vascularisation.
Highlights
Microgels, which constitute a new form of polymer, are structures with intra-molecular crosslinked macromolecules[1,2,3]
Methods of microgel preparation are widely documented and range from solution bulk protocols[10], intended as the formation and stabilisation in an emulsion, to the most recent based on microfluidics[11], which enables a deep control on the dimensions and shape of the microgels as well as on their composition
Assembling heterogeneous and homogeneous architectures from crosslinked microgel building blocks is in great demand in various applications, in tissue engineering[12] for mimicking biological functions and in the production of novel materials with engineered properties[13]
Summary
At the pI, the zeta potential is about null and the microgels displayed a modest swelling[28, 29] At this pH, the carboxylate anions and the amine groups not linked with the glutaraldehyde in the reaction of crosslinking are protonated, so that the microgels charge resulted almost null. As a consequence of the last phenomenon, the microgels underwent an anisotropic swelling along the two main directions (length and diameter)[30] This anomalous behaviour of the microgels could be the consequence of network constrictions formed inside the protein structure, which reduced the capability of the microgels to grasp the water molecules and constrained the movement of the chains[31]. Microgels can be digested in a few hours in the presence of trypsin[21]
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