Injectable hydrogels for quasi hypersoft tissue

2022-05-06 0 By

Injectable hydrogel is a water-soluble polymer solution that gelates in situ when applied to a target environment, such as the human body or a porous scaffold.These materials are minimally invasive, can fill irregular cavities, and can inject drugs and biologics simultaneously, making them significant for reconstructive surgery, tissue engineering, and drug delivery applications.However, the current injection hydrogels have some problems, such as mechanical mismatch with tissue, fragility, water excretion and high viscosity, which greatly limit their clinical application.To solve this problem,Sergei S. Sheiko and Mohammad Vatankhah-Varnosfaderani of the University of North Carolina at Chapel Hill and Krzysztof Carnegie Mellon UniversityMatyjaszewski et al. designed bottle brush macromolecules that provide softness, firmness, strength, fluidity, and expansibility at the same time.The resulting hydrogel mimics the deformation response of super-soft tissues such as fat and brain, withholding 700 percent of the deformation while preventing water loss during gelation.Due to its low cytotoxicity and other biological properties, the materials developed based on this will have an important role in reconstructive surgery, tissue engineering and drug delivery applications.The work was published in Science Advances under the title “Injectable Bottlebrush Hydrogels with Organo-mimetic Mechanical Properties.”A hydrophilic thermosensitive wire-brush – line (LBL) triblock copolymer was synthesized from thermosensitive polyethylene glycol (PEG) bottle brush block and poly (N-isopropylacrylamide) linear block.In this copolymer, the synthetic LBL copolymer helps to improve the injectivity of the material because the compact conformation of the bottle brush block leads to reduced solution viscosity, while the thermal responsive linear segment allows rapid gelation at 37°C.Different from the existing soft tissue filling designs, this copolymer has the following advantages :(I) it can simulate j-shaped tissue deformation under the condition of controlling the water content, reducing the mechanical mismatch between implants and natural tissues;(ii) Exhibits low viscosity properties at high polymer concentrations, which is conducive to improved injectable properties;(iii) The copolymer is based on physical cross-linking and can eliminate the infiltration of chemical substances into the body;(iv) Excellent mechanical elasticity, able to withstand deformation up to 700% at low moduli of less than 1 kPa.Based on the above LBL copolymers, two kinds of polymer networks were prepared.Hydrogels formed by self-assembly at internal temperature and elastomers formed by subsequent evaporation of water.Both the hydrogel and the elastomers exhibit mechanical properties similar to those of the tissue, characterized by combined optimization of softness and hardness, resulting in a typical J-shaped stress-strain curve.Due to the high polymerization number f of about 150 and the equilibrium nature of the gelation process, LBL hydrogels have mechanical stability and can maintain about 700% deformation, instant rupture and rapid recombination.The reversible network can be transformed into a permanent hydrogel by adding uv or temperature-induced crosslinking agent to the L-domain.In vitro and in vivo tests have shown that injectable hydrogels have low toxicity (causing only mild inflammation) and can be used as body fillers in reconstructive surgery or as bio-inks mixed with tissue-engineered cells.Not only that, but the large molecular material is also expected to play an important role in additive manufacturing of certain shaped objects, such as organs.Figure 2 groups of heat sensitive hydrogels and elastomer literature links: source: polymer science frontiers