Synthetic materials, particularly graphene composites have been identified to transform healthcare. Unfortunately, irrespective of graphene oxide having excellent properties, its biomedical applications are limited owing to insufficient functionality. Oxidation of graphene produces water-dispersible graphene oxide. However, its feature is majorly damaged compared to purely sp2 hybridized graphene. In addition, any attempts to reduce graphene oxide in a bid to restore its mechanical as well as electronic attributes leads to a loss of functional groups and water dispersibility. For these reasons, most modifications have to tradeoff between bulk properties and chemical functionalization.
The levels of oxidation are necessary in compatibility, where reduced graphene oxide reduces oxidative stress, therefore improving compatibility. For the case of implantable biomaterials, materials surface is critical as it is contact with the body. Therefore, for graphene oxide-containing implant, functionalities and chemistry added to graphene oxide have a considerable effect on biocompatibility. Various levels of oxidation have been investigated in a move to improve compatibility of graphene oxide for applications in biomedicine.
Non-covalently modifying graphene oxide with bioactive molecules via physical interactions have been considered to add extra features to graphene oxide without injuring its bulk attributes. Non-covalent method of modifying graphene oxides has many benefits, but has the drawbacks of limited control over interaction, lack of permanent functionalization, and difficulty in forecasting materials as well as interfacial-host interactions in vivo and in vitro.
Reduced Claisen graphene can be customized for applications in biomedicine by implementing primary alcohols to trigger ring-opening polymerization of peptides. Peptides that have been polymerized from amino acids may have an array of sequences that can allow for control of properties, structures, and biological response. For this reason, indicating the ability to functionalize reduced Claisen graphene with peptides will enable a number of bioactive applications based on peptide features and sequence.
Researchers led by Professor Stefanie Sydlik at Carnegie Mellon University applied reduced Claisen graphene to initiate the ring-opening polymerization of lysine peptides and glutamate in order to come up with 3-D scaffolds for applications in biomedicine. Lysine and glutamate were used owing to their bioactive features and the fact that polymerization could be extended to any peptide of choice. Their research work is published in journal, Polymer International.
The authors polymerized from reduced Claisen graphene short homopeptides from α-amino acid N-carboxyyanhydride monomers to lysine and glutamate and resulted in functionalized graphenes that were degradable, bioactive, and cytocompatible. When the authors exposed them to NIH-3T3 fibroblasts and RAW 264.7 macrophages indicated that the materials were cytocompatible, even at high doses, and did not affect necessary subcellular compartment.
The researchers hot-pressed the powders to form strong, mechanically stiff, and tough three-dimensional constructs with tunable mechanical attributes based on functionalization. The proposed bioactive, stiff, tough, and strong, peptide-functionalized reduced Claisen graphene pellets developed by Stefanie Sydlik team will be useful in further advancements in biomedical applications of graphene composites.
Brian D Holt, Anne M Arnold and Stefanie A Sydlik. Peptide-functionalized reduced graphene oxide as a bioactive mechanically robust tissue regeneration scaffold. Polymer International, volume 66 (2017), pages 1190–1198.
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