Lyophilised Platelet-Rich Fibrin: Physical and Biological Characterisation

Background: Platelet-rich fibrin (PRF) has gained popularity in craniofacial surgery, as it provides an excellent reservoir of autologous growth factors (GFs) that are essential for bone regeneration. However, the low elastic modulus, short-term clinical application, poor storage potential and limitations in emergency therapy use restrict its more widespread clinical application. This study fabricates lyophilised PRF (Ly-PRF), evaluates its physical and biological properties, and explores its application for craniofacial tissue engineering purposes. Material and methods: A lyophilisation method was applied, and the outcome was evaluated and compared with traditionally prepared PRF. We investigated how lyophilisation affected PRF’s physical characteristics and biological properties by determining: (1) the physical and morphological architecture of Ly-PRF using SEM, and (2) the kinetic release of PDGF-AB using ELISA. Results: Ly-PRF exhibited a dense and homogeneous interconnected 3D fibrin network. Moreover, clusters of morphologically consistent cells of platelets and leukocytes were apparent within Ly-PRF, along with evidence of PDGF-AB release in accordance with previously reports. Conclusions: The protocol established in this study for Ly-PRF preparation demonstrated versatility, and provides a biomaterial with growth factor release for potential use as a craniofacial bioscaffold.

Surface Modification of Porous Polyethylene Implants with an Albumin-Based Nanocarrier-Release System

Background: Porous polyethylene (PPE) implants are used for the reconstruction of tissue defects but have a risk of rejection in case of insufficient ingrowth into the host tissue. Various growth factors can promote implant ingrowth, yet a long-term gradient is a prerequisite for the mediation of these effects. As modification of the implant surface with nanocarriers may facilitate a long-term gradient by sustained factor release, implants modified with crosslinked albumin nanocarriers were evaluated in vivo. Methods: Nanocarriers from murine serum albumin (MSA) were prepared by an inverse miniemulsion technique encapsulating either a low- or high-molar mass fluorescent cargo. PPE implants were subsequently coated with these nanocarriers. In control cohorts, the implant was coated with the homologue non-encapsulated cargo substance by dip coating. Implants were consequently analyzed in vivo using repetitive fluorescence microscopy utilizing the dorsal skinfold chamber in mice for ten days post implantation. Results: Implant-modification with MSA nanocarriers significantly prolonged the presence of the encapsulated small molecules while macromolecules were detectable during the investigated timeframe regardless of the form of application. Conclusions: Surface modification of PPE implants with MSA nanocarriers results in the alternation of release kinetics especially when small molecular substances are used and therefore allows a prolonged factor release for the promotion of implant integration.

Hyaluronic Acid Accelerates VEGF and PDGF Release from Advance Platelet Rich Fibrin in Diabetic Foot Ulcer

BACKGROUND: Hyaluronic acid (HA) is an essential component of extracellular matrix and mediates signaling in wound healing. HA could induce growth factor release from Advanced Platelet Rich Fibrin (A-PRF), including Vascular Endothelial Growth Factor (VEGF) and Platelet-derived Growth Factor (PDGF). However, concentrations of the released-VEGF and PDGF have not been clearly disclosed. Therefore, current study was conducted to measure the release of these growth factors in HA + A-PRF gel of diabetic foot ulcer (DFU) subjects.METHODS: Twenty DFU subjects were included in the study and treated with A-PRF or HA+A-PRF. A-PRF was derived from autologous peripheral blood and processed with low-speed centrifugation. HA was added with a ratio of 1:0.6. A-PRF or HA + A-PRF was applied topically on DFU. Upper tips of A-PRF or HA + A-PRF gels were collected on day 0, 3 and 7 for measurements of VEGF and PDGF concentrations with Enzyme-linked Immune-sorbent Assay (ELISA) methods.RESULTS: On day-3, both VEGF and PDGF concentrations of HA + A-PRF group were significantly higher than the VEGF (p=0.000) and PDGF (p=0.019) concentrations of A-PRF group. The VEGF and PDGF concentrations were continuously and significantly increased on day-7 of HA + A-PRF group, compared to the VEGF (p=0.000) and PDGF (p=0.004) concentrations of A-PRF group.CONCLUSION: Combination HA+A-PRF induces VEGF and PDGF release from A-PRF. A mixture of A-PRF and HA could be more effective than A-PRF alone for treatment of DFU.KEYWORDS: hyaluronic acid, advanced platelet rich fibrin, PRF, growth factor, VEGF, PDGF, diabetic foot ulcer

Matrix-Bound Growth Factors are Released upon Cartilage Compression by an Aggrecan-Dependent Sodium Flux that is Lost in Osteoarthritis

Articular cartilage is a dense extracellular matrix-rich tissue that degrades following chronic mechanical stress, resulting in osteoarthritis (OA). The tissue has low intrinsic repair especially in aged and osteoarthritic joints. Here we describe three pro-regenerative factors; fibroblast growth factor 2 (FGF2), connective tissue growth factor, bound to transforming growth factor-beta (CTGF-TGFβ), and hepatoma-derived growth factor (HDGF), that are rapidly released from the pericellular matrix (PCM) of articular cartilage upon mechanical injury. All three growth factors bound heparan sulfate, and were displaced by exogenous NaCl. We hypothesised that sodium, sequestered within the aggrecan-rich matrix, was freed by injurious compression, thereby enhancing the bioavailability of pericellular growth factors. Indeed, growth factor release was abrogated when cartilage aggrecan was depleted by IL-1 treatment, and in severely damaged human osteoarthritic cartilage. A flux in free matrix sodium upon mechanical compression of cartilage was visualised by 23Na magnetic resonance imaging (MRI) just below the articular surface. This corresponded to a region of reduced tissue stiffness, measured by scanning acoustic microscopy and second harmonic generation microscopy, and where Smad2/3 was phosphorylated upon cyclic compression. Our results describe a novel intrinsic repair mechanism, controlled by matrix stiffness and mediated by the free sodium concentration, in which heparan sulfate-bound growth factors are released from cartilage upon injurious load. They identify aggrecan as a depot for sequestered sodium, explaining why osteoarthritic tissue loses its ability to repair. Treatments that restore matrix sodium to allow appropriate release of growth factors upon load are predicted to enable intrinsic cartilage repair in osteoarthritis. Significance Statement Osteoarthritis is the most prevalent musculoskeletal disease, affecting 250 million people worldwide1. We identify a novel intrinsic repair response in cartilage, mediated by aggrecan-dependent sodium flux, and dependent upon matrix stiffness, which results in the release of a cocktail of pro-regenerative growth factors after injury. Loss of aggrecan in late-stage osteoarthritis prevents growth factor release and likely contributes to disease progression. Treatments that restore matrix sodium in osteoarthritis may recover the intrinsic repair response to improve disease outcome.