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Tissue responses around polymethylmethacrylate particles implanted into bone: analysis of expression of bone matrix
1Department of Orthopedic Surgery, Graduate School of Medicine, Kyoto University, Japan. kunitaka@kuhp.kyoto-u.ac.jp
Abstract:
Tissue responses around implanted polymethylmethacrylate (PMMA) particles were analyzed by in situ hybridization with digoxigenin-labeled procollagen alpha1(I) (COL), osteonectin, osteocalcin, and osteopontin (OPN) mRNA probes. PMMA particles (150-300 microm in diameter) were implanted into rat tibiae, and specimens were collected at 3, 5, 7, and 10 days after operation. New bone was formed centripetally, and bone-forming osteoblasts expressed all four kinds of mRNAs. A COL signal was expressed most strongly and widely. In the early stage, COL-positive cells were detected on and among particles sporadically. A COL signal was rarely detected in cells on the surfaces of the particles, suggesting that PMMA particles may suppress osteoblast differentiation. Osteonectin and osteocalcin mRNAs were expressed in bone-forming osteoblasts in a similar pattern by day 7. By contrast, an OPN signal was detected mainly on the particles, not only in COL-positive osteoblasts but also in COL-negative round cells. The latter cells had acid phosphatase activity, suggesting that they might be macrophages responding to a foreign body. At day 10, an OPN signal was detected continuously in multinucleated cells on PMMA particles, whereas new bone was formed away from particles. Our approach helped us to understand the initial cellular reaction to materials, which may determine their biocompatibility.
Insights
Polymethylmethacrylate (PMMA) particles implanted in rat tibiae showed limited osteoblast differentiation on particle surfaces. Macrophages responded to particles, influencing tissue reactions and biocompatibility.
Area of Science:
- Biomaterials Science
- Tissue Engineering
- Cellular Biology
Background:
- Understanding cellular responses to implanted biomaterials is crucial for developing biocompatible materials.
- Polymethylmethacrylate (PMMA) is a common biomaterial, but its interaction with bone tissue requires detailed investigation.
Purpose of the Study:
- To investigate the in situ tissue response around implanted PMMA particles.
- To analyze the expression of key bone matrix proteins and cellular markers during bone formation.
Main Methods:
- In situ hybridization using digoxigenin-labeled mRNA probes for procollagen alpha1(I) (COL), osteonectin, osteocalcin, and osteopontin (OPN).
- PMMA particles (150-300 microm) were implanted into rat tibiae, with specimens collected at 3, 5, 7, and 10 days post-operation.
Main Results:
- Bone formation occurred centripetally around PMMA particles, with osteoblasts expressing all four mRNAs.
- A strong COL signal was observed, but its presence on particle surfaces was sporadic, suggesting suppressed osteoblast differentiation.
- Osteopontin (OPN) was detected on particles in both osteoblasts and acid phosphatase-positive round cells, potentially macrophages, and later in multinucleated cells.
Conclusions:
- PMMA particles may inhibit direct osteoblast differentiation on their surfaces.
- Macrophages appear to be involved in the cellular response to PMMA particles.
- The initial cellular reactions, including macrophage involvement and suppressed osteoblast differentiation, are critical for determining the biocompatibility of implanted materials.