Retracted Article: A polyurethane–chitosan brush as an injectable hydrogel for controlled drug delivery and tissue engineering
Authors: Arun Kumar Mahanta
Sudipta Senapati
Pralay Maiti
Journal: Polymer Chemistry (2017)
Discipline: CHEMISTRY
Keywords: Hydrogels; Porous lyophilized hydrogels; Polyurethane brush; Chitosan backbone; Grafting
Affiliations: School of Materials Science and Technology, Indian Institute of Technology (Banaras Hindu University), Varanasi 221 005, India

Abstract: Hydrogels and porous lyophilized hydrogels have been designed using a polyurethane brush with a chitosan backbone through grafting. The degree of substitution of grafting has been varied for controlled properties and has been confirmed by 13C NMR, FTIR and UV-vis measurements. Surface modification of chitosan has been done to check the hydrophilic–hydrophobic balance which is reflected in their swelling behavior and contact angle. Porous interconnected three dimensional network structures with controlled size are observed by using a scanning electron microscope. Hydrogels or lyophilized hydrogels have sufficient mechanical strength and the brush like structure helps increase the fluidity as measured from the lesser viscosity under oscillatory shear as compared to pure chitosan and thereby the brush acts like a slipping agent. Sustained drug release is achieved using a brush copolymer as opposed to burst release noticed in pure chitosan. A controlled drug release phenomenon has been modeled both for hydrogels and lyophilized hydrogels following the Fickian diffusion (n < 0.45). Excellent cytocompatibility of the brush copolymer has been verified through cell line studies using mouse embryonic fibroblast cells. Interestingly, the cells grow nicely within the pores of a graft copolymer while predominantly the usual cell growth on the surface is observed in the lyophilized hydrogel of chitosan indicating the effect of brush like modification on the chitosan backbone towards better cell proliferation. The developed brush copolymers have the ability to form hydrogels under physiological conditions at 37 °C through sol–gel transformation which makes them suitable to be used as injectable hydrogels as evidenced from the in vivo experiment using a rat model. Hence, the developed brush copolymers are promising as potential biomaterials for drug delivery and tissue engineering applications.

Retracted: Yes

PubPeer comments:
 Figure 6b(i) is **supposed to be a control** for the experiment - Figure 6b(ii). However **these figures are the same**: Figure(ii) is a rotated resized version of Figure (i). ![file] , 
 Figure 6b of the paper describes the histopathology of the skin just after injection of hydrogel and the skin morphology after the formation of gel under the skin. We tried to take the specimen from the same location to compare in a better way and given it our Doctor who did the histopathology work for us. We put her name in the acknowledge section mentioning the entire work of histopathology was done by the same doctor, responsible for histopathology work. We believe the morphology should be similar as the hydrogel do not interact with the skin. That is how we see the things. We wish to clarify that we did not have any intention to duplicate the image and whatever we got from the doctor we tried to put that in the paper. , 
 April 2021 retraction: https: pubs.rsc.org en content articlelanding py 2021 d1py90044g#!divAbstract  The Royal Society of Chemistry hereby wholly retracts this Polymer Chemistry article due to concerns with the reliability of the data in the published article. The control, CHT10 and CHT15 panels in Fig. 5c have overlapping sections and represent cells cultured on different samples. The authors claim that the overlapping sections are similar, not identical, as the biocompatibility is similar for the control, CHT10 and CHT15 samples. An expert reviewed the author s response but concluded that it did not satisfactorily address the concerns. Fig. 6bii, which represents the skin of the hydrogel forming area, is a duplicated, rotated and scaled version of Fig. 6bi, which represents the control. The authors claim that the images are similar, not identical, as the hydrogel does not interact with the skin when compared with the control. An expert reviewed the author s response but concluded that it did not satisfactorily address the concerns. Given the significance of the concerns about the validity of the data, the findings presented in this paper are no longer reliable. The authors were contacted about this retraction notice but did not respond. Glad to see the editors did not fall for the  These images are just similar, not identical argument. As a post mortem, here are the overlapping areas in Figure 5C as described in the retraction notice. ![file] ,