Advanced fabrication and characterization of robocasted halloysite-hydroxyapatite nanocomposite scaffolds for hard tissue regeneration

Abstract

The rising frequency of bone injury and disease necessitates the need for bone replacement materials and scaffolds. Hydroxyapatite (HAP), a natural element of hard tissue, is frequently employed for bone defects treatment due to its biocompatibility and identical structure. But its brittleness limits its application in load bearing. In this present study, porous scaffolds with improved mechanical and biological performances were fabricated by combining HAP with Halloysite nanoclay (HNC 1 wt.% to 3 wt.%) using the Robocasting technique. Hydroxypropyl methylcellulose (HPMC, 1–2 wt.%) was used as the binder to prepare printable pastes. An optimal concentration of 1.5 wt% for the HPMC binder was identified from rheological measurements. The green scaffolds were printed, dried, and sintered at 1,100 °C. The microstructure and distribution of HNC within the scaffolds were characterized by FESEM. The reinforcement concentration was limited to 3wt.% due to the microcracks and agglomeration observed in the 3 wt.% scaffold. Vickers hardness increased from 245.7 H V (pure HAP) to 271.7 H V (2 wt.% HNC + HAP scaffold) with a plateau from agglomeration. Also, the porosity is observed between 38% and 40%. The biological evaluation comprised Alamar Blue proliferation, MTT cell viability (MG-63), and antimicrobial testing against Staphylococcus aureus . The antimicrobial assays showed comparatively limited zones of inhibition for HAP and HAP–HNC composites (max ∼8.7 mm for HAP) in comparison to ciprofloxacin (25.3 mm). All HAP–HNC scaffolds demonstrated in vitro cytocompatibility, wherein the addition of HNC increased cell survival and proliferation compared to the pure HAP. The 2–3 wt.% HNC demonstrated the highest biological response. Hence, the improved cytocompatibility, tolerable antibacterial behavior, and superior mechanical qualities of the HAP–HNC scaffolds make them suitable candidates for bone tissue engineering applications.