In Vivo Biocompatibility Investigation of an Injectable Calcium Carbonate (Vaterite) as a Bone Substitute including Compositional Analysis via SEM-EDX Technology.

Ronald E. Unger,Stevo Najman,Oliver Görke,Laura Besch,Caroline Bogram,Ole Jung,Said Alkildani,Wolfgang Tremel,Romina Schröder,Mike Barbeck,Sanja Stojanovic

doi:10.3390/ijms23031196

Abstract

Injectable bone substitutes (IBS) are increasingly being used in the fields of orthopedics and maxillofacial/oral surgery. The rheological properties of IBS allow for proper and less invasive filling of bony defects. Vaterite is the most unstable crystalline polymorph of calcium carbonate and is known to be able to transform into hydroxyapatite upon contact with an organic fluid (e.g., interstitial body fluid). Two different concentrations of hydrogels based on poly(ethylene glycol)-acetal-dimethacrylat (PEG-a-DMA), i.e., 8% (w/v) (VH-A) or 10% (w/v) (VH-B), were combined with vaterite nanoparticles and implanted in subcutaneous pockets of BALB/c mice for 15 and 30 days. Explants were prepared for histochemical staining and immunohistochemical detection methods to determine macrophage polarization, and energy-dispersive X-ray analysis (EDX) to analyze elemental composition was used for the analysis. The histopathological analysis revealed a comparable moderate tissue reaction to the hydrogels mainly involving macrophages. Moreover, the hydrogels underwent a slow cellular infiltration, revealing a different degradation behavior compared to other IBS. The immunohistochemical detection showed that M1 macrophages were mainly found at the material surfaces being involved in the cell-mediated degradation and tissue integration, while M2 macrophages were predominantly found within the reactive connective tissue. Furthermore, the histomorphometrical analysis revealed balanced numbers of pro- and anti-inflammatory macrophages, demonstrating that both hydrogels are favorable materials for bone tissue regeneration. Finally, the EDX analysis showed a stepwise transformation of the vaterite particle into hydroxyapatite. Overall, the results of the present study demonstrate that hydrogels including nano-vaterite particles are biocompatible and suitable for bone tissue regeneration applications.

Highlights

Most tissues in the human body have the capacity to repair themselves via physiological processes
At 30 days post implantation the analysis showed that markers for the pro-inflammatory macrophages were found at the material surfaces and especially by the cells invading both hydrogels (Figure 3E,G)
Preclinical in vivo studies and clinical studies analyzing the tissue reactions and integration behavior of an Injectable bone substitutes (IBS) based on β-TCP granules and a hydrogel based on modified cellulose and sodium hyaluronate as well as an IBS composed of a water-based gel combined with nano-hydroxyapatite (HA) particles and biphasic calcium phosphate granules showed that this material class allows for an integration and degradation pattern moving from the periphery to the implant center according to the concept of Guided

Summary

Introduction

Most tissues in the human body have the capacity to repair themselves via physiological processes. The capacity to repair larger defects (so-called critical-size defects), for example caused by extensive traumatic damage or disease, can be too substantial to allow for a normal physiological repair to take place [2,3] This type of defect is often a challenging problem encountered in maxillofacial and oral surgery for Guided Bone Regeneration (GBR). The method aims to enhance natural bone regrowth at the defect site via the implantation of so-called bone substitute materials (BSM), which act as a scaffold structure for host cells to grow on [4,5,6] This process, known as bone tissue regeneration, has clinically been used for several decades

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