Abstract: BACKGROUND: Drug-loaded bone scaffolds for tuberculosis treatment suffer from problems such as drug burst release in the early stages of treatment and insufficient drug release in the later stages, which leads to low drug concentration at the lesion, therefore, it is imperative to build a drug controlled-release system on the tissue-engineered bone scaffolds.
OBJECTIVE: To prepare photothermal composite scaffolds with different isoniazid liposome doping ratios and characterize their mechanical and biological properties.
METHODS: Isoniazid liposomes were prepared using the thin-film hydration method. The microstructure, encapsulation efficiency, drug loading capacity, particle size, and Zeta potential of liposomes were characterized. 15 mg of isoniazid was selected as the total drug amount for a single drug-loaded scaffold. Isoniazid drug powder, isoniazid liposome powder at 2%, 5%, and 8% of the total drug amount, respectively, were mixed uniformly with the scaffold base material (hydroxyapatite and β-tricalcium phosphate in a mass ratio of 6:4) and 3% of the photothermal agent polypyrrole nanoparticles (by mass fraction of the scaffold base material) to prepare extrusion printing powders. 13% polyvinyl alcohol gel was added to the extrusion printing powder in a 1:1 mass ratio. Pure isoniazid scaffolds and three kinds of isoniazid liposome photothermal scaffolds were fabricated using extrusion-based 3D bioprinting. The microstructure, porosity, mechanical properties, and drug release performance of the photothermal scaffolds were characterized. Mouse embryonic osteoblasts (MC3T3 cells) were cultured with extracts from the four kinds of scaffolds. The cytotoxicity of the scaffolds was detected using the MTT assay.
RESULTS AND CONCLUSION: (1) Under transmission electron microscopy, isoniazid liposomes appeared as spherical vesicles with a relatively regular shape. The encapsulation efficiency of isoniazid liposomes was (28.67±0.62)%, the drug loading capacity was (3.54±0.19)%, the average particle size was (363.63±10.42) nm, and the average Zeta potential was (-4.68±0.72) mV. (2) Scanning electron microscopy showed that compared with the pure isoniazid scaffold, the isoniazid liposome photothermal scaffold had more pores internally. With the increase of isoniazid liposome content, the porosity of the photothermal scaffold showed an increasing trend, while the compressive strength and elastic modulus showed a decreasing trend, but still met the minimum compressive strength required for tissue implantation experiments in animals. The incorporation of isoniazid liposomes effectively solved the problem of drug burst release in the early stage of drug release from the scaffold, and the cumulative drug release rate in the early stage was inversely proportional to the amount of isoniazid liposomes incorporated. After irradiation with an 808 nm near-infrared laser, the cumulative drug release rate of the isoniazid liposome photothermal scaffold increased compared with that without near-infrared laser irradiation. With the increase of isoniazid liposome content, the photothermal controlled release performance of the scaffold became more significant in the later stage of drug release. MTT assay showed that the relative proliferation rate of MC3T3 cells cultured with the extracts of the four kinds of scaffolds for 24, 72, and 120 hours was all greater than 70%, indicating no significant cytotoxicity. The results show that the isoniazid liposome photothermal scaffold has good mechanical properties, drug-controlled release performance, and cytocompatibility.

Key words: bone tuberculosis, 3D printing, drug-loaded scaffolds, liposome, polypyrrole, controlled drug release, biomaterials