# In Vitro Evaluation of the PMN Reaction on a Collagen-Based Purified Reconstituted Bilayer Matrix (PRBM) Using the Autologous Blood Concentrate PRF

## TL;DR

This study shows that a collagen-based matrix can guide immune cells toward a healing response, potentially aiding tissue regeneration.

## Contribution

The study demonstrates that PRBM primes PMNs toward a regenerative phenotype in vitro, offering a novel therapeutic material.

## Key findings

- PRBM reduced proinflammatory cytokines like TNFα, IL15, and IL1 in PMN supernatants.
- PRBM increased regenerative cytokines such as TGFβ and IL10 in PMN supernatants.
- PRBM may promote wound healing by priming PMNs to a regenerative phenotype.

## Abstract

Background/Objectives: The body’s reaction after the implantation of a biomaterial is a non-specific inflammatory response that is mainly initiated via the recruitment of polymorphonuclear cells (PMNs) to the implant site secreting cytokines and growth factors, followed by activation of monocytes/macrophages, finally leading to wound healing. The wound healing process is dependent on the priming of the PMNs that can be guided towards an inflammatory or a regenerative phenotype with the associated characteristic PMN cytokine profiles. Since the collagen-based Purified Reconstituted Bilayer Matrix (PRBM) triggers the wound healing process at the implant site in vivo, it is hypothesized that this positive effect might be due to a material-mediated priming of the PMNs towards the regenerative phenotype. With the use of the blood concentrate platelet-rich fibrin (PRF) containing high concentrations of leukocytes, including PMNs, the natural environment of the body after the implantation of a material can be mimicked in vitro. The aim of the present study was to characterize the phenotype of native blood-derived PMNs within PRF in response to the PRBM. Methods: PMNs within PRF gained from different relative centrifugal forces were characterized in a first step before PRF was combined with the PRBM for 4 h. Supernatants were harvested to analyze the phenotype of the PMNs via the evaluation of eight different cytokines using the ELISA. Results: Analysis of the PMN phenotype could assess cytokines commonly associated with neutrophils of the proinflammatory phenotype, such as TNFα, IL15, and IL1, as lower in supernatants when PRF was incubated in the presence of the PRBM and compared to the control PRF. On the other hand, cytokines related to the PMN regenerative phenotype, like TGFβ and IL10, could be detected as higher when PRF was incubated in the presence of the PRBM. Conclusions: This might suggest that PRBM significantly activates and primes neutrophils to the regenerative phenotype, leading to the resolution of inflammation. This might trigger the process of wound healing and tissue regeneration, making the PRBM a beneficial material for therapeutic applications.