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- Ben Amara, Heithem, 1984, et al.
(author)
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Immunomodulation by biodegradable Mg-implants promotes soft and hard tissues responses in vivo
- 2023
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In: Scandinavian Society of Biomaterials conference, 21–24 March 2023, Røros, Norway.
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Conference paper (other academic/artistic)abstract
- INTRODUCTION: Magnesium (Mg)-based degradable implants are an attractive treatment solution for musculoskeletal injuries, avoiding second-stage surgical removal. In multiple clinical applications, the implant is in contact with both the bone and the overlying soft tissue. Although Mg implants are often presented to hold anti-inflammatory properties, less attention has been paid to the sequential response to these implants including initial immune response and subsequent tissue repair. The present study investigated the molecular, cellular, and structural events taking place at the Mg implant interface to soft tissue and bone after in vivo implantation in dedicated experimental rat models. METHODS: Male Sprague Dawley rats received disc-shaped implants in the dorsum subcutis or screw-shaped implants in the proximal tibial metaphysis. Implants were manufactured from pure magnesium (99.99% - high purity; Mg) or from pure titanium (grade 4; Ti) as control. Animals were euthanized after 1, 3, 6, 14, and 28 day of soft tissue implantation, and after 3 and 28 days of bone implantation. Two types of samples were collected: 1-Implants with the adherent cells (n=7-8/group/time-point). These were allocated for cell counting and /or gene expression analyses of implant-adherent cells. 2-Peri-implant tissue with implants (n = 8/group/time-point). These enabled histological and histomorphometric analyses of the fibrous capsule organization around implants inserted in soft tissues and of osseointegration parameters at the bone-implant interface. Statistical comparisons between experimental groups were run using Kruskal-Wallis, and Mann-Whitney tests (p<0.05). RESULTS: Cells adherent to the surface of the implants featured different gene regulation patterns between Mg and Ti groups (Fig. 1). Consistently in soft tissue and in bone, macrophage polarization markers indicated higher expression of proinflammatory macrophage gene inducible nitric oxide synthase (iNos) initially at Mg versus Ti (3 d in bone and 1-6 d in soft tissue). Afterward, gene expression of both macrophage subtypes markers (proinflammatory – iNos and prohealing – Mannose receptor c1; Mrc1) was comparable between implants, irrespective of their insertion site. Histomorphometry evidenced superior bone-implant contact (at 28 d in bone) and thinner fibrous capsule (at 6-28 d in soft tissue) for Mg versus Ti. CONCLUSIONS: In comparison to non-degradable Ti, both soft tissue and bone responses to biodegradable Mg featured an initial yet transient gene activation of the macrophage proinflammatory subtype. Such immunomodulation by Mg resulted in the reduction of fibrous encapsulation in soft tissue and in the promotion of bone formation at the bone-implant interface. ACKNOWLEDGEMENTS: Mg implants were generously provided by Helmholtz-Zentrum Hereon, Geesthacht, Germany. This project is part of the European Training Network within the framework of Horizon 2020 Marie Skłodowska-Curie Action No 811226.
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| 2. |
- Ben Amara, Heithem, 1984, et al.
(author)
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In vivo interaction between biodegradable magnesium implants and soft tissue Part II: Kinetics of the cellular response at the host-implant interface
- 2021
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In: 13th Biometal Conference, 23-26 August 2021, Virtual Conference..
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Conference paper (other academic/artistic)abstract
- INTRODUCTION: Regenerative therapies often engage multiple tissues. Soft tissue complications (e.g. dehiscences and infection) may violate successful bone regeneration. Magnesium (Mg)-based degradable implants is a promising treatment alternative for musculoskeletal injuries, avoiding second-stage surgical removal. In several clinical applications, the implant is in contact with both the bone and the overlying soft tissue. Whereas the bone response to Mg implants has been a major research focus, less attention has been paid to the soft tissue response. The present study investigated the spatial and temporal molecular, cellular and structural events taking place at the soft tissue-Mg implant interface after in vivo implantation in an experimental rat model. METHODS: Following approval by the Local Ethical Committee at the University of Gothenburg (Dnr 02437/2018), female Sprague-Dawley rats (n=90) were implanted with discs manufactured from pure magnesium (99.99% - high purity; Mg) or from pure titanium (grade 4; Ti) (herein, employed as a control, possessing biocompatibility properties). Subcutaneous pockets were surgically created in the animal dorsum and were implanted with: 1- Ti; or 2- Mg discs; or 3- left without implants (Sham Ti or Sham Mg). After 1, 3, 6, 14 and 28 days, animals were euthanized, and three types of samples were retrieved: 1-Implants with the adherent cells (n=8/group/time-point): for cell counting and molecular gene expression of the implant-adherent cells. 2-Peri-implant exudate (n=8/group/time-point): for analyses of the number, type, viability, and gene expression of cells in the peri-implant space. 3-Peri-implant tissue with implants (n=8/group/time-point): enabling histological and histomorphometric analyses of soft tissue and fibrous capsule organization around the implant. Statistical comparisons were made between experimental groups at each time point and between time-points for each experimental group. (Kruskal-Wallis, Mann-Whitney and Wilcoxon signed-rank tests; p<0.05). RESULTS: Cells recruited to the exudates and adherent to the surface of the implants featured different kinetics between Mg and Ti groups. At the surface of Mg implant, the number of adherent cells sharply increased from 1 day to reach a peak at 6 days, thereafter decreasing toward 28 days. The ratio of implant-adherent/exudate cells was significantly higher at Mg vs Ti after 6 days, whereas the reverse was detected after 28 days. RNA extracted from cells from the different compartments revealed good quality, allowing detailed molecular analysis. After 28d, the fibrous capsule around Mg implants was significantly thinner than around Ti. CONCLUSIONS: In comparison to non-degradable Ti controls, soft tissue healing around biodegradable Mg implants is characterized by an early, intense, but yet transient, cellular influx in the immediate vicinity of the implant surface, and, at later stage, with a reduced fibrotic encapsulation. ACKNOWLEDGEMENTS: Mg implants were generously provided by the Helmholtz-Zentrum Hereon, Geesthacht, Germany. This project is part of the European Training Network within the framework of Horizon 2020 Marie Skodowska-Curie Action No 811226.
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| 3. |
- Ben Amara, Heithem, 1984, et al.
(author)
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Promoting soft and hard tissue repair via immunomodulation by the surface degradation of magnesium implants in vivo
- 2023
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In: Materials for Tomorrow conference by Chalmers University of Technology, 8-10 November 2023, Gothenburg, Sweden.
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Conference paper (other academic/artistic)abstract
- INTRODUCTION: Magnesium (Mg) is a reactive metallic biomaterial that degrades via surface corrosion upon contact with body fluids. By virtue of its degradation and mechanical properties, Mg implants are currently employed with success to treat musculoskeletal injuries and avoid second-stage surgical removal 1. While these implants are claimed to possess anti-inflammatory properties, this notion contrasts with the initial signs of inflammation observed in the soft tissue of patients treated with Mg implants. This study investigated how the surface degradation of Mg implants in vivo influences the molecular, cellular, and structural events during initial inflammation and subsequent healing of the interfacing soft tissue and bone in comparison to nondegradable titanium (Ti) implants using experimental rat models. METHODS: Rats received disc-shaped implants in their dorsum subcutis or screw-shaped implants in the proximal metaphysis of their tibiae. Implants were manufactured from pure Mg (>99.995% - high purity) or from pure Ti (grade 4). Animals were euthanized after 1, 3, 6, 14, and 28 days of soft tissue implantation, and after 3 and 28 days of bone implantation. Two types of samples were collected: i) Implants only (n = 7-8/group/time-point): for counting and/or gene expression analyses of implant-adherent cells. ii) Implants with peri-implant tissues (n = 5-8/group/time-point): for compositional analysis of the Mg degradation layer in conjunction with the histomorphometry of the fibrous capsule around implants in soft tissues and of osseointegration at the bone–implant interface. Statistical comparisons were run using Kruskal-Wallis and Mann-Whitney tests (p<0.05). RESULTS: Cells adherent to the implant surfaces featured different gene regulation patterns between Mg and Ti groups (Fig. 1). Initially in soft tissue (1–6 d) and bone (3 d), a higher expression of proinflammatory macrophage polarization markers, e.g. inducible nitric oxide synthase (iNos), was shown in Mg versus Ti groups. Afterward, by 28 d, gene expression of both macrophage subtype markers (proinflammatory – iNos, and prohealing – Mannose receptor c1; Mrc1) was comparable between implants, irrespective of their insertion site. Histomorphometry revealed superior bone–implant contact (at 28 d in bone) and thinner fibrous capsule (at 6–28 d in soft tissue) for Mg versus Ti (Fig. 1). The 28 d-degradation layer at the Mg surface was enriched in Ca and P in both soft tissue and bone. CONCLUSIONS: In comparison to Ti implants, both soft tissue and bone responses to Mg implants featured an initial, amplified, yet transient, inflammation marked by the gene activation of the macrophage proinflammatory subtype. Such immunomodulation by the surface degradation of Mg implant promoted more bone deposition, at the bone–implant interface, and less fibrous encapsulation, at the soft tissue–implant interface. REFERENCES: 1. Han et al. Mater Today 2019, 23: 57-71. ACKNOWLEDGEMENTS: Horizon 2020 Marie Skłodowska-Curie Action (No 811226) and Area of Advance Materials/Chalmers and GU Biomaterials. Mg implants were generously provided by Hereon, Geesthacht, Germany.
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