3D printing technology offers a vast range of applications for tissue engineering applications. Over the past decade a vast range of new equipment has been developed; while, 3D printable biomaterials, especially hydrogels, are investigated to fit the printability requirements. The current candidates for bioprinting often require post‐printing cross‐linking to maintain their shape. On the other hand, dynamic hydrogels are considered as the most promising candidate for this application with their extrudability and self‐healing properties. However, it proves to be very difficult to match the required rheological in a simple material. Here, this study presents for the first time the simplest formulation of a dynamic hydrogel based on thiol‐functionalized hyaluronic acid formulated with gold ions that fulfill all the requirements to be printed without the use of external stimuli, as judged by the rheological studies. The printability is also demonstrated with a 3D printer allowing for the printing of the dynamic hydrogel as it is, achieving 3D construct with a relatively good precision and up to 24 layers, corresponding to 10 mm high. This material is the simplest 3D printable hydrogel and its mixture with cells and biological compounds is expected to open a new era in 3D bioprinting.
Purpose: Growth factors found in the amniotic membrane (AM) help accelerate epithelium regeneration in the damaged cornea or conjunctiva. This study compares the effects of hydrogels releasing the AM proteins on the proliferation, migration, and time‐to‐closure (healing) of the conjunctival epithelium. Methods: Proteins extracted from the AM using sonication were incorporated into two hydrogels used as ocular inserts. The tested inserts materials were the self‐healing, dynamic hyaluronic‐acid hydrogel based on gold‐thiolate/disulfide exchange (Hydrogel A) and a physically cross‐linked hydrogel based on a combination between Eudragit S100 and hyaluronic acid with a reinforced matrix by polyvinyl alcohol, polyvinyl pyrrolidone and polyethylene glycol (Hydrogel B). In an in vitro experiment, a scratch was made on the human conjunctival epithelium cells (Chang Conjunctiva, Clone 1‐5c‐4) to mimic an incision wound. The cells were cultured with hydrogels for 48 hours to study the effect of these materials on epithelium repair. The samples were examined using a Zeiss Observer Z1 inverted microscope, and the results were evaluated employing the Image‐J program to obtain the cell migration rate (μm/h). Results: Hydrogel A increased the rate of closure at 22 h (121 ± 19 μm) in comparison with Hydrogel B (394 ± 78 μm). After 46 h, the scratches in Hydrogel A and control cultures were completely closed, while the Hydrogel B samples had an unclosed area of 54 ± 4 μm. Conclusions: Both hydrogels promoted wound healing in cultured conjunctival epithelium cells. However, a lower rate of wound closure was observed for Hydrogel B than for Hydrogel A and the control, probably because the speed of cell proliferation was slower in Hydrogel B. The wound‐healing assay showed that the Hydrogel A and B increased cell viability and significantly stimulated cell migration.
Purpose: To compare the effect on corneal healing of two novel hydrogels releasing proteins obtained from amniotic membrane (AM). Methods: Forty‐four New Zealand White rabbits underwent corneal wounding with NAOH 1 M and received different treatments: Control (group 1), AM transplantation (group 2), model A hydrogel (group 3) and model B hydrogel (group 4). The progression of wound healing was recorded with photographs and assessed by measuring the remaining epithelial defect over time. Histology was performed to examine acute and chronic changes. Results: There were no statistically significant differences between groups in epithelial defect areas (mm2) at days 0, 7, 14, 21 and 28. The percentage of wound closure (%) showed statistically significant differences on day 7 between Group 1 and Group 4 (p = 0.03). The percentage of completely healed corneas showed no statistically significant differences between the control and treated groups on days 14, 21 and 28, but on day 7, there were differences between Group 4 and Control (p = 0.02). On days 14 and 21 the rate of completely healed corneas was higher in Group 3 and Group 4 (55% on day 14 and 30% on day 21) compared to Group 1 (44.4% on day 14 and 11.1% on day 21). Conclusions: The novel biodegradable hydrogels with AM proteins could promote corneal re‐epithelialization. The chosen animal model showed a high rate of wound reopening once closed. Group 4 hydrogels showed low adhesiveness so the implant movement and the fragile regenerated epithelium could justify the higher de‐epithelized areas on day 7. The results show a higher number of wounds with complete epithelialization and a smaller epithelial defect area (mm2) in the treated groups compared to control, even after removal of the AM proteins, which might indicate that proteins secreted in the early stages of epithelialization could enhance corneal wound closure.
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