New injectable two-step forming hydrogel for delivery of bioactive substances in tissue regeneration

Abstract

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, D eff , 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 m 2 /s for D eff and 8.50·10 −10 to 3.04·10 −9 m/s for h . The proposed model fits experimental data, obtaining an R 2 -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.

PLGA-BMP-2 and PLA-17β-Estradiol Microspheres Reinforcing a Composite Hydrogel for Bone Regeneration in Osteoporosis

“…The release profile of 17β-estradiol as liposoluble drug in a MeOH:water (60:40) release medium was previously characterized [21]. By contrast, here two release media were used, MeOH:water (50:50) and an aqueous solution of SLS, because we suspected that the solvent affected the release rate of the lipophilic substance.…”

“…To prepare the core system, approximately 20 mg of microspheres were dispersed in 50 µL of the hydrogel composed by a mixture of collagen type I (5 mg/mL), HP-γ-CD (34 mg/mL), RB (0.4 mg/mL), CHT (5 mg/mL), PEG-400 (150 mg/mL), and 5 mg of nano-HAP. Then, the hydrogel was cross-linked with 5% w/w TPP sterile aqueous solution (0.5 µL/µL of hydrogel) and visible light blue at 468 nm (Dental device) for 3 min [21]. The dose of BMP-2 was 6 µg in microspheres and the total 17β-estradiol dose was 200 µg in three different forms: electrospun films, microspheres, or dispersed into the gel.…”

“…The quality of the core system was checked according to its rheological characteristics and porosity previously described [21]. In addition, water uptake and mass loss assays were carried out by incubation of aliquots of 300 µL of the core system in 5 mL of sterile MilliQ water (37 • C) under orbital agitation (25 rpm).…”

“…The released 17β-estradiol was measured in the supernatant using the spectrophotometric method. The effective diffusion coefficient, D eff in the matrix of the microspheres and the mass transfer coefficient of the drug in the boundary layer h, were calculated according to the non-steady-state Fick law, as previously described in detail [21]. Whether or not the released fraction of 17β-estradiol from the microspheres dispersed in the core system was analyzed, and Equations (3)-(6) were applied for D eff and h calculation.…”

“…As stated previously, to minimize the residual sum of squares, "genetic algorithms" already implanted in R software (R Foundation for Statistical Computing, version 3.6.1., 2019, Vienna, Austria) were used [21].…”