Original Article
In vivo bone formation by and inflammatory response to resorbable polymer-nanoclay constructs

https://doi.org/10.1016/j.nano.2015.06.012Get rights and content

Abstract

The development of synthetic bone grafts with requisite mechanical and morphological properties remains a key challenge in orthopaedics. Supercritical carbon dioxide (scCO2)-processed nanocomposites consisting of organically-modified montmorillonite clay dispersed in poly-d-lactide (PDLA) have shown structural and mechanical properties similar to corticocancellous bone. Using quantitative undecalcified histology and micro-computed tomography (μCT), time and material-dependent influences on in vivo bone formation, and inflammatory response were characterized. This represents the first in vivo evidence of the ability of scCO2-processed PDLA-nanoclay constructs to support osteogenesis, while eliciting an inflammatory response comparable to PDLA-hydroxyapatite materials. Histologic analyses demonstrated that the in vivo performance of nanoclay-containing PDLA constructs was similar to pure PDLA constructs, though nanocomposites demonstrated more radiodense bone at all time points (μCT analysis), and higher bone volume at 6 weeks. Taken with previous structural and mechanical studies, these in vivo analyses suggest that scCO2-processed, polymer-clay nanocomposites may be suitable structural bone graft materials.

From the Clinical Editor

With advances in science, orthopedic researchers have devoted significant amount of time in developing synthetic bone graft materials. Many of which are indeed currently in clinical use. In their previous studies, the authors described and studied supercritical carbon dioxide (scCO2)-processed nanocomposites consisting of organically modified montmorillonite clay dispersed in poly-D-lactide (PDLA) in in-vitro experiments. Here, in-vivo experiments were performed to investigate if this new material had improved mechanical properties, as well as the induction of inflammatory response. The overall positive findings may mean that this material could be used for future bone graft substitute applications.

Graphical Abstract

Nanocomposite materials consisting of organo-modified Montmorillonite clays (nanoclay) dispersed in resorbable polymer matrices via supercritical carbon dioxide (scCO2) processing have demonstrated surprising structural and compressive mechanical properties that make them candidates for bone graft substitute applications. In the present study, we demonstrate that these highly porous constructs exhibit the ability to facilitate in vivo, growth factor-induced bone formation. The in vivo inflammatory response elicited by the nanoclay-loaded constructs was similar to more traditional hydroxyapatite-based composite materials.

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Section snippets

Preparation of PDLA and PDLA-Nanoclay Debris for Inflammation Study

The inflammatory response to, and osteolytic potential of PDLA-nanoclay particulate debris was investigated, and compared to both pure PDLA, as well as PDLA filled with hydroxyapatite. Hydroxyapatite (Ca10(PO4)6(OH)2, Sigma-Aldrich) is a calcium phosphate material which has been traditionally used as a functional filler material in hard tissue engineering constructs and bone graft substitute materials.4, 7, 13, 16, 23, 24, 26, 41 As a secondary objective, two different types of nanoclay

Inflammatory Response to Nanocomposite Particulate

Given the relative lack of in vivo data regarding the inflammatory response of nanoclay and nanoclay-containing materials, a study was undertaken to characterize the response to PDLA-nanoclay constructs in particulate form. This particulate form was chosen over bulk constructs in an effort to simulate the potential shedding of nanocomposites debris during biomechanical loading and hydrolytic degradation of the constructs in vivo. The response to PDLA constructs containing one of two different

Discussion

The structural, mechanical and biologic constraints placed on bone graft substitute materials represent a significant challenge to researchers and physicians. These constructs must support significant biomechanical loads during activities of daily living, despite having an interconnected porous morphology with average pore diameters ranging from 100-300 μm.1, 2, 3 Resorbable polymers, especially lactic and glycolic acid-based materials, have been thoroughly studied as candidates for bone graft

Acknowledgment

The authors dedicate this manuscript to the memory of Harry N. Herkowitz, M.D., former Chairman of the Department of Orthopaedic Surgery at William Beaumont Hospital 1991-2013.

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      Citation Excerpt :

      However, only immature bone tissue (also called woven bone) and red blood cells (RBC) can be seen in tissue/control graft section at the same period of time (Figure 5, IV.B).7 Moreover, no aggregation of inflammatory cells such as white blood cells (WBC), macrophage or epithelioid cells were recognized in both magnified sections.24,25 A least square surgical procedure on degradation behavior of the grafts (see Figures S3-5 in supplementary data file) shows complete degradation of CZM-HA graft compared with the control graft after 4 weeks of implantation.

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    The authors declare no conflicts of interest with regard to the conduct of experiments or preparation of the present manuscript. Funding for this research was provided by a Seed/Starter Research Grant from the Cervical Spine Research Society, as well as a resident research grant from the Beaumont Research Institute.

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