Dextran-Based Injectable Hydrogel Composites for Bone Regeneration

Abstract

Currently, bone infections caused by diseases or injuries are a major health issue. In addition, the conventional therapeutic approaches used to treat bone diseases or injuries present several drawbacks. In the area of tissue engineering, researchers have been developing new alternative therapeutic approaches, such as scaffolds, to promote the regeneration of injured tissues. Despite the advantages of these materials, most of them require an invasive surgical procedure. To overcome these problems, the main focus of this work was to develop scaffolds for bone regeneration, which can be applied using injectable hydrogels that circumvent the use of invasive procedures, while allowing for bone regeneration. Throughout this work, injectable hydrogels were developed based on a natural polymer, dextran, along with the use of two inorganic compounds, calcium β-triphosphate and nanohydroxyapatite, that aimed to reinforce the mechanical properties of the 3D mesh. The materials were chemically characterized considering the requirements for the intended application: the swelling capacity was evaluated, the degradation rate in a simulated physiological environment was assessed, and compression tests were performed. Furthermore, vancomycin was incorporated into the polymeric matrices to obtain scaffolds with antibacterial performance, and their drug release profile was assessed. The cytotoxic profile of the hydrogels was assessed by an MTS assay, using osteoblasts as model cells. The data obtained demonstrated that dextran-based hydrogels were successfully synthesized, with a drug release profile with an initial burst between 50 and 80% of the drug. The hydrogels possess fair biocompatibility. The swelling capacity showed that the stability of the samples and their degradation profile is compatible with the average time period required for bone regeneration (usually about one month) and have a favorable Young's modulus (200-300 kPa). The obtained hydrogels are well-suited for bone regeneration applications such as infections that occur during implantation or bone graft substitutes with antibiotics.

Keywords: bone regeneration; drug release; injectable hydrogels; oxidized dextran.

Figure 1

Schematic representation of a two-tube syringe for the application of the hydrogels.

Figure 2

Representative scheme of the Dex oxidation through reaction with sodium periodate. (A) First oxidation, introduction of aldehyde groups at C3 and C4. (B) Second oxidation, introduction of the aldehyde group at C2 and release of formic acid.

Figure 3

Schematic representation of drug incorporation into the preparation scaffold.

Figure 4

ATR-FTIR spectra of AAD, Dex, DexOx (OD = 25% and OD = 50%), and DexOx/AAD hydrogel.

Figure 5

ATR-FTIR spectra of nHAp, β-TCP, and hydrogels with nHAp e β-TCP.

Figure 6

¹H NMR spectra of (a) (OD = 50%), (b) DexOx (OD = 25%), (c) DexOx (OD = 50%) reacted with tBC, and (d) DexOx (OD = 25%) reacted with tBC, with the peaks at 8.3 ppm (*) and 4.8 ppm (1) marked.

Figure 7

DexOx crosslinking reaction with AAD. (A) DexOx. (B) AAD. (C) Crosslinked DexOx, with hydrazone bonds formation.

Figure 8

Swelling ratio (S_r) at different pH values for the different composition samples.

Figure 9

Schematic representation of the Amadori rearrangement and scission of the glycosidic ring.

Figure 10

Degradation profiles (mass weight variation as a function of time) of the different samples (a) at pH 7.4; (b) at pH 2; (c) at pH 9; and (d) at pH 5.

Figure 11

Timeline of the bone healing/regeneration process.

Figure 12

Cumulative controlled vancomycin release profiles for the different hydrogels.

Figure 13

Cumulative controlled vancomycin release profiles during the first 6 h for (a) hydrogels with 10% AAD and (b) hydrogels with 20% AAD.

Figure 14

Cumulative controlled vancomycin release profiles during the last stage of the study for (a) hydrogels with 10% AAD and (b) hydrogels with 20% AAD.

Figure 15

Optical microscopic images of hOB cells cultured in contact with the produced hydrogels after 1, 3, and 7 days of incubation. Scale bars correspond to 100 μm.

Figure 16

Optical microscopic images of hOB cells in the negative control (K⁻, cells incubated with culture medium) and positive control (K⁺, cells incubated with EtOH 70%) after 1, 3, and 7 days of incubation. Scale bars correspond to 100 μm.

Figure 17

Characterization of the hydrogels’ biocompatibility. Evaluation of the viability of hOB cells when cultured in the presence of the produced hydrogels after 1, 3, and 7 days of incubation, through MTS analysis. K⁻ (live cells); K⁺ (dead cells). Data are presented as the mean ± standard deviation, n = 5, **** p < 0.0001, n.s. = non-significant.