Fabrication of continuous apatite-graded collagen sponges via electrolysis method

Abstract

Multi-layered scaffolds of apatite and collagen for the healing of osteochondral defects have been investigated for optimized regenerative cues by distinct layers; however, multi-layered scaffolds exhibit delamination after implantation in the host body. In this study, as an alternative to multi-layered scaffolds, collagen sponges with an apatite content gradient were fabricated via an electrolytic method. Electrolysis at a constant current mode of i = 22 A m⁻² with different electrode distances of 2, 3, or 4 cm was conducted for an acidic solution at pH 3.0, including collagen at 0.5 wt% and hydroxyapatite at 0.1 wt%. During electrolysis, a high pH pocket and collagen hydrogel were concurrently formed in the vicinity of the cathode, whereas a low pH pocket was formed near the anode due to the generation of hydroxyl and hydrogen ions, respectively. The thickness of the hydrogels gradually grew to approximately one-third of the electrode distance. Subsequently, the hydrogels were freeze-dried to form sponges. Low-crystalline apatite was precipitated, and particularly, the hydrogel region closest to the cathode was more mineralized than the region farthest from the cathode. The sponge region closest to the cathode exhibited a ratio of apatite/collagen of 0.34 ± 0.04, which gradually decreased with the distance from cathode to 0.22 ± 0.04, 0.20 ± 0.05, and 0.14 ± 0.02. The biocompatibility of collagen was unaltered by the electrolysis treatment, as evidenced by the attachment and proliferation of pre-osteoblastic cells in the electrolyzed sponges. In conclusion, the electrolysis method is a powerful tool for the fabrication of collagen sponges with a continuous graded apatite composition.