The shape and size of hydroxyapatite particles dictate inflammatory responses following implantation

• Published in: Scientific reports Vol. 7; no. 1; pp. 2922 - 13
• Main Authors: Lebre, Filipa, Sridharan, Rukmani, Sawkins, Michael J, Kelly, Daniel J, O'Brien, Fergal J, Lavelle, Ed C
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 07.06.2017; Nature Publishing Group UK; Nature Portfolio
• Subjects: Animals; Biocompatible Materials - adverse effects; Biocompatible Materials - chemistry; Cellular Microenvironment - immunology; Chemical Phenomena; Cytokines; Cytokines - biosynthesis; Dendritic Cells - immunology; Dendritic Cells - metabolism; Durapatite - adverse effects; Durapatite - chemistry; Female; Flow Cytometry; Hydroxyapatite; IL-1β; Immune response; Inflammasomes; Inflammation; Inflammation - etiology; Inflammation - pathology; Innate immunity; Macrophages - immunology; Macrophages - metabolism; Mice; NLR Family, Pyrin Domain-Containing 3 Protein - genetics; NLR Family, Pyrin Domain-Containing 3 Protein - metabolism; Prosthesis Implantation - adverse effects; Structure-function relationships; Transplants & implants
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-017-03086-0

The extent of regeneration following biomaterial implantation is dependent on the microenvironment surrounding the implant. Since implant composition can have a profound effect on inflammation, it is essential to understand this process as a non-resolving inflammatory response can lead to fibrous encapsulation and insufficient integration. Incorporation of particulates into implants confers structural and functional benefits, thus optimizing particulate characteristics to enhance immune mediated efficacy is important. We investigated the relationship between the nature of hydroxyapatite (HA) particles and the innate immune response, focusing on how particle size (0.1 µm, 5 µm, 20 µm, 100 µm) and morphology (needle-shaped/spherical; smooth/rough surface) modulates inflammatory responses. We observed a shape and size-dependent activation of the NLRP3 inflammasome and IL-1β secretion; while needle-shaped and smaller HA particles significantly enhanced cytokine secretion, larger particles did not. Moreover, HA particle characteristics profoundly influenced patterns of innate immune cell recruitment and cytokine production following injection. While small, needle-shaped particles induced a strong inflammatory response, this was not observed with smooth, spherical particles of comparable size or with larger particles. These findings indicate that hydroxyapatite particle characteristics dictate immune cell recruitment and the ensuing inflammatory response, providing an opportunity to tailor HA particle characteristics to regulate immune responses induced after biomaterial implantation.