New Insights of Scaffolds Based on Hydrogels in Tissue Engineering

Abstract

In recent years, biomaterials development and characterization for new applications in regenerative medicine or controlled release represent one of the biggest challenges. Tissue engineering is one of the most intensively studied domain where hydrogels are considered optimum applications in the biomedical field. The delicate nature of hydrogels and their low mechanical strength limit their exploitation in tissue engineering. Hence, developing new, stronger, and more stable hydrogels with increased biocompatibility, is essential. However, both natural and synthetic polymers possess many limitations. Hydrogels based on natural polymers offer particularly high biocompatibility and biodegradability, low immunogenicity, excellent cytocompatibility, variable, and controllable solubility. At the same time, they have poor mechanical properties, high production costs, and low reproducibility. Synthetic polymers come to their aid through superior mechanical strength, high reproducibility, reduced costs, and the ability to regulate their composition to improve processes such as hydrolysis or biodegradation over variable periods. The development of hydrogels based on mixtures of synthetic and natural polymers can lead to the optimization of their properties to obtain ideal scaffolds. Also, incorporating different nanoparticles can improve the hydrogel's stability and obtain several biological effects. In this regard, essential oils and drug molecules facilitate the desired biological effect or even produce a synergistic effect. This study's main purpose is to establish the main properties needed to develop sustainable polymeric scaffolds. These scaffolds can be applied in tissue engineering to improve the tissue regeneration process without producing other side effects to the environment.

Keywords: healing process; hydrogels; polymers; regeneration; scaffolds; tissue engineering.

Figure 1

The main classes of hydrogels.

Figure 2

The main crosslinking methods are used for the development of hydrogels [78].

Figure 3

The main methods of (a) physical and (b) chemical crosslinking of hydrogels.

Figure 4

Scanning electron microscopy of hydrogels (A) without TA; (B) 10% TA; (C) 20% TA and (D) 30% TA, (1) before immersion in SBF and (2) after 7 days at 150× magnification [97].

Figure 5

SEM images (2000× magnification) of PVA scaffolds with oxidized pullulan (0.5% (OxP 0.5), 5% (OxP 5), 10% (OxP 10) and 20% (OxP 20)) and tricarboxy cellulose (0.5% (OxC 0.5), 5% (OxC 5), 10% (OxC 10) and 20% (OxC 20)) respectively [98].

Figure 6

Cell viability and proliferation assessment: (A) using MTT assay (** p > 0.01 and *** p > 0.001); (B) LDH assay for cytotoxicity evaluation; (C) Confocal microscopy: dead (red) and live (green) cells, scale bar 100 µm using L929 murine fibroblast cells [111].

Figure 7

(a) Wound surface percentage for: Control Group (G_CTR), group with hydrogel sodium alginate/gelatin (80:20) (G_H), and group hydrogel with AgNP 4 mM AgNO₃ (G_HP) with mean ± S.E. * p < 0.05 in relation to G_HP, G_CTR and G_H, respectively (n = 21/group). (b) Photomicrographs of histological sections stained with hematoxylin/eosin (scale = 100 µm) [140].

Figure 8

The main applications that can be applied in bone regeneration [158].

Figure 9

SEM and immunofluorescence assessment of cell morphology on MHA-MFu and MHA hydrogels after 7 days. Scale bar: 2 μm for SEM and 50 μm for immunofluorescence images [159].

Figure 10

Hydrogels based on PVA/Se-doped TiO₂ NPs/HA [164] (a) MTT assay of BMMSCs with PVA-based composites after 72 h incubation, and (b) Differentiation potential of BMMSCs to osteogenic, adipogenic, and chondrogenic lineages, of PVA nanocomposites after 72 h of incubation.