New injectable two-step forming hydrogel for delivery of bioactive substances in tissue regeneration Pérez-Herrero, Edgar Gómez Morales, Jaime Hydrogel Collagen–cyclodextrin–chitosan Rheology Mass transfer Estradiol FITC-dextran The authors would like to thank Dr Alberto Fernández-Medarde (Instituto de Biología Molecular y Celular del Cáncer, Centro de Investigación del Cáncer, CSIC-USAL) for proofreading the article. Moreover, the help and the advice in the interpretation on FTIR spectra given by Dr Jose Adrián Gavin (Organic Chemistry Department, ULL) and Dr Antonio Manuel Hernández-Daranas (Instituto de Productos Naturales y Agrobiología, CSIC) is appreciated. A hydrogel based on chitosan, collagen, hydroxypropyl-γ-cyclodextrin and polyethylene glycol was developed and characterized. The incorporation of nano-hydroxyapatite and pre-encapsulated hydrophobic/hydrophilic model drugs diminished the porosity of hydrogel from 81.62 ± 2.25% to 69.98 ± 3.07%. Interactions between components of hydrogel, demonstrated by FTIR spectroscopy and rheology, generated a network that was able to trap bioactive components and delay the burst delivery. The thixotropic behavior of hydrogel provided adaptability to facilitate its implantation in a minimally invasive way. Release profiles from microspheres included or not in hydrogel revealed a two-phase behavior with a burst- and a controlled-release period. The same release rate for microspheres included or not in the hydrogel in the controlled-release period demonstrated that mass transfer process was controlled by internal diffusion. Effective diffusion coefficients, Deff, that describe internal diffusion inside microspheres, and mass transfer coefficients, h, i.e. the contribution of hydrogel to mass transfer, were determined using ‘genetic algorithms’, obtaining values between 2.64·10−15 and 6.67·10−15 m2/s for Deff and 8.50·10−10 to 3.04·10−9 m/s for h. The proposed model fits experimental data, obtaining an R2-value ranged between 95.41 and 98.87%. In vitro culture of mesenchymal stem cells in hydrogel showed no manifestations of intolerance or toxicity, observing an intense proliferation of the cells after 7 days, being most of the scaffold surface occupied by living cells. 2020-05-12T11:42:33Z 2020-05-12T11:42:33Z 2019-05-10 info:eu-repo/semantics/article Edgar Pérez-Herrero, Patricia García-García, Jaime Gómez-Morales, Matias Llabrés, Araceli Delgado, Carmen Évora, New injectable two-step forming hydrogel for delivery of bioactive substances in tissue regeneration, Regenerative Biomaterials, Volume 6, Issue 3, June 2019, Pages 149–162, [https://doi.org/10.1093/rb/rbz018] http://hdl.handle.net/10481/61976 10.1093/rb/rbz018 eng http://creativecommons.org/licenses/by/3.0/es/ info:eu-repo/semantics/openAccess Atribución 3.0 España Oxford University Press