Évaluation clinique et biologique d’un ligament synthétique bioactif chez la brebis

Long-term hydrolytic degradation study of polycaprolactone films and fibers grafted with poly(sodium styrene sulfonate): Mechanism study and cell response

Polycaprolactone (PCL) is a widely used biodegradable polyester for tissue engineering applications when long-term degradation is preferred. In this article, we focused on the analysis of the hydrolytic degradation of virgin and bioactive poly(sodium styrene sulfonate) (pNaSS) functionalized PCL surfaces under simulated physiological conditions (phosphate buffer saline at 25 and 37 °C) for up to 120 weeks with the aim of applying bioactive PCL for ligament tissue engineering. Techniques used to characterize the bulk and surface degradation indicated that PCL was hydrolyzed by a bulk degradation mode with an accelerated degradation-three times increased rate constant-for pNaSS grafted PCL at 37 °C when compared to virgin PCL at 25 °C. The observed degradation mechanism is due to the pNaSS grafting process (oxidation and radical polymerization), which accelerated the degradation until 48 weeks, when a steady state is reached. The PCL surface was altered by pNaSS grafting, introducing hydrophilic sulfonate groups that increase the swelling and smoothing of the surface, which facilitated the degradation. After 48 weeks, pNaSS was largely removed from the surface, and the degradation of virgin and pNaSS grafted surfaces was similar. The cell response of primary fibroblast cells from sheep ligament was consistent with the surface analysis results: a better initial spreading of cells on pNaSS surfaces when compared to virgin surfaces and a tendency to become similar with degradation time. It is worthy to note that during the extended degradation process the surfaces were able to continue inducing better cell spreading and preserve their cell phenotype as shown by collagen gene expressions.

ToF-SIMS and XPS Characterization of Protein Films Adsorbed onto Bare and Sodium Styrenesulfonate-Grafted Gold Substrates

The adsorption of single-component bovine serum albumin (BSA), bovine fibrinogen (Fgn), and bovine immunoglobulin G (IgG) films as well as multicomponent bovine plasma films onto bare and sodium styrenesulfonate (NaSS)-grafted gold substrates was characterized. The adsorption isotherms, measured via X-ray photoelectron spectroscopy, showed that at low solution concentrations all three single-component proteins adsorb with higher affinity onto gold surfaces compared to NaSS surfaces. However, at higher concentrations, NaSS surfaces adsorb the same or more total protein than gold surfaces. This may be because proteins that adsorb onto NaSS undergo structural rearrangements, resulting in a larger fraction of irreversibly adsorbed species over time. Still, with the possible exception of BSA adsorbed onto gold, neither surface appeared to have saturated at the highest protein solution concentration studied. Principal component (PC) analysis of amino acid mass fragments from time-of-flight secondary ion mass spectra distinguished between the same protein adsorbed onto NaSS and gold surfaces, suggesting that proteins adsorb differently on NaSS and gold surfaces. Explored further using peak ratios for buried/surface amino acids for each protein, we found that proteins denature more on NaSS surfaces than on gold surfaces. Also, using peak ratios for asymmetrically distributed amino acids, potential structural differences were postulated for BSA and IgG adsorbed onto NaSS and gold surfaces. PC modeling, used to track changes in plasma adsorption with time, suggests that plasma films on NaSS and Au surfaces become more Fgn-like with increasing adsorption time. However, the PC models included only three proteins, where plasma is composed of hundreds of proteins. Therefore, while both gold and NaSS appear to adsorb more Fgn with time, further study is required to confirm that this is representative of the final state of the plasma films.

Characterization of a synthetic bioactive polymer by nonlinear optical microscopy

Tissue Engineering is a new emerging field that offers many possibilities to produce three-dimensional and functional tissues like ligaments or scaffolds. The biocompatibility of these materials is crucial in tissue engineering, since they should be integrated in situ and should induce a good cell adhesion and proliferation. One of the most promising materials used for tissue engineering are polyesters such as Poly-ε-caprolactone (PCL), which is used in this work. In our case, the bio-integration is reached by grafting a bioactive polymer (pNaSS) on a PCL surface. Using nonlinear microscopy, PCL structure is visualized by SHG and proteins and cells by two-photon excitation autofluorescence generation. A comparative study between grafted and nongrafted polymer films is provided. We demonstrate that the polymer grafting improves the protein adsorption by a factor of 75% and increase the cell spreading onto the polymer surface. Since the spreading is directly related to cell adhesion and proliferation, we demonstrate that the pNaSS grafting promotes PCL biocompatibility.

Surface initiated atom transfer radical polymerization grafting of sodium styrene sulfonate from titanium and silicon substrates

This study investigates the grafting of poly-sodium styrene sulfonate (pNaSS) from trichlorosilane/10-undecen-1-yl 2-bromo-2-methylpropionate functionalized Si and Ti substrates by atom transfer radical polymerization (ATRP). The composition, molecular structure, thickness, and topography of the grafted pNaSS films were characterized with x-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), variable angle spectroscopic ellipsometry (VASE), and atomic force microscopy (AFM), respectively. XPS and ToF-SIMS results were consistent with the successful grafting of a thick and uniform pNaSS film on both substrates. VASE and AFM scratch tests showed the films were between 25 and 49 nm thick on Si, and between 13 and 35 nm thick on Ti. AFM determined root-mean-square roughness values were ∼2 nm on both Si and Ti substrates. Therefore, ATRP grafting is capable of producing relatively smooth, thick, and chemically homogeneous pNaSS films on Si and Ti substrates. These films will be used in subsequent studies to test the hypothesis that pNaSS-grafted Ti implants preferentially adsorb certain plasma proteins in an orientation and conformation that modulates the foreign body response and promotes formation of new bone.