Enhancing Immunomodulation and Osseointegration of Bone Implants via Thrombin-Activated Platelet-Rich Plasma Self-Assembly

Chemistry Medicinal Chemistry Immunology Biochemistry Life Sciences Bioengineering Orthopedics Medicine
bone implants thrombin platelet-rich plasma immunomodulation osseointegration self-assembly tissue repair

Enhancing Immunomodulation and Osseointegration of Bone Implants: A Detailed Overview of Thrombin-Activated Platelet-Rich Plasma (PRP) Self-Assembly Technology

Background Introduction

To address the challenge of bone defect repair, bone implants play a critical role in modern medicine. However, existing bone implant materials like Polyetheretherketone (PEEK), despite their significant advantages in chemical stability, elastic modulus, and imaging compatibility, face a major limitation: biological inertness. This inertness hinders the integration process between implants and surrounding bone tissue, potentially leading to postoperative inflammation, bone resorption, and even implant failure.

To solve this issue, bioactive substances are often introduced to implant surfaces. However, these exogenous substances raise concerns about immune rejection or negatively impact the mechanical properties of the implant surface. On the other hand, Platelet-Rich Plasma (PRP), an autologous-derived bioactive liquid, is rich in growth factors (e.g., Transforming Growth Factor [TGF], Platelet-Derived Growth Factor [PDGF], and Vascular Endothelial Growth Factor [VEGF]) and has demonstrated tremendous potential in promoting osteogenesis, angiogenesis, and immunomodulation. However, it remains a scientific challenge to effectively anchor PRP onto PEEK surfaces and create a gel layer for sustained release of biological factors.

To address this challenge, this study for the first time attempted to graft thrombin onto the PEEK surface via chemical bonding technology, preserving its enzymatic activity to enable PRP self-assembly into a gel state on the surface. Thrombin, a multifunctional serine protease, plays a key role in activating PRP, and protecting its precise molecular structure and active site is critical for the success of this research.

Source and Author Information

This research was conducted by Xiaotong Shi, Zongliang Wang, and colleagues from the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, the Capital Medical University Affiliated Beijing Friendship Hospital, and the First Hospital of Jilin University. The paper was published in 2025 in the high-impact journal Advanced Healthcare Materials (Adv. Healthcare Mater.).

Detailed Research Process

1. Immobilizing Thrombin on PEEK Surface

The first step in the study involved multi-step chemical modifications to firmly anchor thrombin onto the PEEK surface: - Surface Activation of PEEK: Using 220-grit sandpaper, the PEEK samples were mechanically treated to create a rough texture for enhanced adhesion during subsequent modifications. - Surface Hydroxylation: The PEEK surface was activated using sodium borohydride reduction to convert carbonyl groups into hydroxyl groups, followed by activation with N,N’-Disuccinimidyl Carbonate (DSC) to generate reactive chemical groups. - Thrombin Immobilization: The samples were treated with thrombin solutions of varying concentrations (50, 100, and 200 U/ml) for 24 hours, resulting in thrombin-modified PEEK (sp-pk-thr).

2. Characterization of Thrombin Modification

Through SEM imaging, FTIR spectroscopy, water contact angle measurements, and enzymatic activity evaluations, the study confirmed the following: - Significant changes in the surface microstructure due to modification (SEM and EDX results showed a marked increase in nitrogen content). - The optimal thrombin concentration was determined to be 100 U/ml, as higher concentrations did not further enhance enzyme activity.

3. Self-Assembly of PRP Gel on PEEK Surface

Using thrombin-modified PEEK as a substrate, the researchers explored PRP self-assembly behavior under thrombin activation, employing PRP solutions with different platelet concentrations (1x, 3x, and 5x): - Self-Assembly Surface Testing: SEM images confirmed that low platelet concentration PRP struggled to form a continuous gel layer, while PRP at 3x and 5x concentrations formed gels with complete porous structures. - Growth Factor Release: ELISA experiments revealed that high platelet concentration PRP gels could sustainably release PDGF-BB and VEGF for up to 16 days.

Research Results and Analysis

  1. Cell Experiments: Experiments on MC3T3-E1, HUVEC, and RAW264.7 cells demonstrated that PRP-functionalized PEEK significantly improved cell adhesion, proliferation, and migration. PRP gels with 5x platelet concentration exhibited optimal cell proliferation effects.

  2. Osteogenesis and Angiogenesis:

    • ALP and ARS Tests: After 7 or 14 days, PRP-coated groups exhibited significantly higher alkaline phosphatase activity and calcium deposition.
    • Tubule Formation Assay: PRP-functionalized PEEK remarkably enhanced HUVEC tubule formation.

  3. Immunomodulatory Functionality: PRP-modified groups showed reduced iNOS expression and enhanced CD206 expression in RAW264.7 cells, suggesting an ability to promote M1-to-M2 macrophage polarization, suppress inflammation, and enhance repair.

  4. Animal Experiments: In a rat tibial defect model, PRP-modified groups demonstrated significantly higher BV/TV, Tb.N, and Tb.Th, alongside reduced Tb.Sp. Histology and immunofluorescence showed significantly elevated OCN and OPN expression in PRP groups, confirming their superior osteogenic capabilities.

Scientific Significance and Application Value

This study pioneered the application of thrombin immobilization techniques to integrate PRP functionalities onto PEEK surfaces, not only imparting bioactivity to PEEK but also leveraging PRP’s unique immunomodulatory and tissue repair properties to greatly enhance osseointegration. Potential applications include: - Broad use in clinical bone defect repair and implant development; - A paradigm for efficient utilization of autologous bio-materials; - Advanced tools and methods for bio-surface modifications.

The study solved the problem of anchoring PRP to PEEK surfaces and provided theoretical and technological foundations for the evolution of next-generation implant materials. Future optimization directions include refining platelet enrichment levels for maximal bioactivity and applying this approach to 3D-printed PEEK scaffolds.

Study Highlights

  1. Introduced and validated the thrombin-PRP technique for PEEK surface self-assembly functionalization.
  2. Pioneered new pathways for optimizing PRP loading and long-term growth factor release.
  3. Emphasized the multifunctional enhancements of PEEK surfaces in bioactivity, osteogenesis, angiogenesis, and immunomodulation.

This research advances implant material studies toward greater biofunctionality, efficiency, and reduced risks.