Inflammatory cell response to ultra-thin amorphous and crystalline hydroxyapatite surfaces

Area of Science:

• Biomaterials Science
• Implantology
• Cell Biology

Background:

• Hydroxyapatite (HA) coatings on titanium (Ti) implants are proposed to improve osseointegration.
• The specific biological mechanisms underlying HA-induced responses, particularly concerning different HA phases, remain unclear.
• Understanding the inflammatory cell response to varying HA surface properties is crucial for optimizing implant design.

Purpose of the Study:

• To investigate the differential inflammatory cell response of human mononuclear cells to amorphous versus crystalline thin HA coatings on titanium implants.
• To correlate surface characteristics (chemistry, phase, wettability, topography) with biological responses, including cytokine secretion and cell adhesion.

Main Methods:

• Human mononuclear cells were cultured on machined Ti, amorphous HA-coated Ti, and crystalline HA-coated Ti surfaces.
• Cells were cultured for 24 and 96 hours, with and without lipopolysaccharide (LPS) stimulation.
• Surface characterization included chemistry, phase composition, wettability, and topography; biological analysis involved cell adhesion and cytokine (TNF-α, BMP-2, TGF-β1) secretion.

Main Results:

• Amorphous HA exhibited nano-scale porosity and hydrophobicity, contrasting with the smooth crystalline HA surface.
• Amorphous HA induced higher tumor necrosis factor-alpha (TNF-α) secretion and a greater ratio of adherent cells compared to crystalline HA.
• Transforming growth factor-beta 1 (TGF-β1) was detected in all groups without significant differences; bone morphogenetic protein-2 (BMP-2) was not detected. LPS stimulation significantly increased TNF-α.
• LPS stimulation significantly increased TNF-α secretion across all groups, while TGF-β1 levels remained unaffected.

Conclusions:

• Thin HA coatings with varying phase compositions, nano-scale roughness, and wettability elicit distinct monocyte responses.
• Crystalline HA demonstrates a reduced inflammatory profile compared to amorphous HA in the absence of potent inflammatory stimuli.
• These findings highlight the importance of HA phase composition in modulating the biological response to dental and orthopedic implants.