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• PEEK and titanium both sustain cell adhesion, proliferation and differentiation. • Air-plasma treatment increases PEEK and titanium surface wettability. • Surface properties affect cell behavior depending on material nature. • Micropatterned titanium surface induce dental pulp stem cell differentiation. Among the materials available for implant production, titanium is the most used while polyetheretherketone (PEEK) is emerging thanks to its stability and to the mechanical properties similar to the ones of the bone tissue. Material surface properties like roughness and wettability play a paramount role in cell adhesion, cell proliferation, osteointegration and implant stability. Moreover, the bacterial adhesion to the biomaterial and the biofilm formation depend on surface smoothness and hydrophobicity. In this work, two different treatments, sandblasting and air plasma, were used to increase respectively roughness and wettability of two materials: titanium and PEEK. Their effects were analyzed with profilometry and contact angle measurements. The biological properties of the material surfaces were also investigated in terms of cell adhesion and proliferation of NIH-3T3 cells, MG63 cells and human Dental Pulp Stem Cells. Moreover, the ability of Staphylococcus aureus to adhere and form a viable biofilm on the samples was evaluated. The biological properties of both treatments and both materials were compared with samples of Synthegra® titanium, which underwent laser ablation to obtain a porous micropatterning, characterized by a smooth surface to discourage bacterial adhesion. All cell types used were able to adhere and proliferate on samples of the tested materials. Cell adhesion was higher on sandblasted PEEK samples for both MG63 and NIH-3T3 cell lines, on the contrary, the highest proliferation rate was observed on sandblasted titanium and was only slightly dependent on wettability; hDPSCs were able to proliferate similarly on sandblasted samples of both tested materials. The highest osteoblast differentiation was observed on laser micropatterned titanium samples, but similar effects, even if limited, were also observed on both sandblasted materials and air plasma treated titanium. The lowest bacterial adhesion and biofilm formation was observed on micropatterned titanium samples whereas, the highest biofilm formation was detected on sandblasted PEEK samples, and in particular on samples not treated with air-plasma, which displayed the highest hydrophobicity. The results of this work showed that all the tested materials were able to sustain osteoblast adhesion and promote cell proliferation; moreover, this work highlights the feasible PEEK treatments which allow to obtain surface properties similar to those of titanium. The results here reported, clearly show that cell behavior depends on a complex combination of surface properties like wettability and roughness and material nature, and while a rough surface is optimal for cell adhesion, a smooth and less hydrophilic surface is the best choice to limit bacterial adhesion and biofilm formation. [Display omitted] [ABSTRACT FROM AUTHOR]

Complex coacervation of two oppositely charged polysaccharides, namely a lactose-modified chitosan (CTL) and hyaluronan (HA), was investigated in this study. Coacervates of the two polysaccharides were prepared by drop-by-drop injection of HA into CTL. Transmittance and dynamic light scattering (DLS) measurements in combination with TEM analyses demonstrated the formation of spheroidal colloids in the nano-/microsize range showing good homogeneity. Strikingly, the presence of 150 mM supporting NaCl did not hamper the colloid formation. Stability studies on selected formulations demonstrated that HA/CTL coacervates were stable up to 3 weeks at 37 °C and behaved as pH-responsive colloids since transition from entangled to disentangled chains was attained for a proper pH range. The possibility of freeze-drying the coacervates for storage purposes and the ability of encapsulating selected payloads were investigated as well, for two values of the fraction of the lactitol side-chain substitution (FL). Finally, biological tests using human neutrophils were undertaken at acidic pH value (pH = 6.0): under such experimental conditions, akin to those frequently occurring in the inflammatory microenvironment, coacervates scavenged reactive oxygen species (ROS) generated by these cells in basal conditions. Given the well documented bioactivity of CTL with respect to chitosan toward cartilage regeneration, these findings point to a possible application of HA/CTL-based colloids as scavenging and bioactive carriers for the delivery of therapeutic molecules at confined inflamed sites such as knee joints.

Ionic chitosan gels fabricated using multivalent anions, tripolyphosphate (TPP) or pyrophosphate (PPi), respectively, have been investigated as potential biomaterials to be used in tissue engineering. Starting from the hypothesis that the polymer mesh texture at the microscale affects the final performance of the resulting materials, an innovative image analysis approach is presented in the first part of the article, which is aimed at deriving quantitative information from transmission electron microscopy images. The image analysis of the (more extended) central area of the gel networks revealed differences between both the cross-linking densities and pore size distributions of the two systems, the TPP gels showing a higher connectivity. Chitosan–TPP gels showed a limited degradation in simulated physiological media up to 6 weeks, reasonably ascribed to the texture of the (more extended) central area of the gels, whereas PPi counterparts degraded almost immediately. The release profiles and the calculation of diffusion coefficients for bovine serum albumin and cytochrome c, herein used as model payloads, indicated a different release behavior depending on the polymer network homogeneity/inhomogeneity and molecular weight of loaded molecules. This finding was ascribed to the marked inhomogeneity of the PPi gels (at variance with the TPP ones), which had been demonstrated in our previous work. Finally, thorough in vitro studies demonstrated good biocompatibility of both chitosan gels, and because of this feature, they can be used as suitable scaffolds for cellular colonization and metabolic activity.

The scaffolding of agarose hydrogel networks depends critically on the rate of cooling (quenching) after heating. Efforts are made to understand the kinetics and evolution of biopolymer self‐assembly upon cooling, but information is lacking on whether quenching might affect the final hydrogel structure and performance. Here, a material strategy for the fine modulation of quenching that involves temperature‐curing steps of agarose is reported. Combining microscopy techniques, standard and advanced macro/nanomechanical tools, it is revealed that agarose accumulates on the surface when the curing temperature is set at 121 °C. The inhomogeneity can be mostly recovered when it is reduced to 42 °C. This has a drastic effect on the stiffness of the surface, but not on the viscoelasticity, roughness, and wettability. When hydrogels are strained at small/large deformations, the curing temperature has no effect on the viscoelastic response of the hydrogel bulk but does play a role in the onset of the non‐linear region. Cells cultured on these hydrogels exhibit surface stiffness‐sensing that affects cell adhesion, spreading, F‐actin fiber tension, and assembly of vinculin‐rich focal adhesions. Collectively, the results indicate that the temperature curing of agarose is an efficient strategy to produce networks with tunable mechanics and is suitable for mechanobiology studies. Controlled quenching (cooling) of agarose after heating by temperature‐curing steps is an efficient material strategy for producing hydrogel networks with tuneable structural/mechanical properties. Fast cooling promotes the accumulation of agarose on the surface and determines the local stiffness; slow cooling provides a more homogeneous distribution of agarose with less stiffness. This clearly affects the mechanosensing of hydrogels by cells.

The employment of coaxial fibers for guided tissue regeneration can be extremely advantageous since they allow the functionalization with bioactive compounds to be preserved and released with a long-term efficacy. Antibacterial coaxial membranes based on poly-ε-caprolactone (PCL) and rifampicin (Rif) were synthesized here, by analyzing the effects of loading the drug within the core or on the shell layer with respect to non-coaxial matrices. The membranes were, therefore, characterized for their surface properties in addition to analyzing drug release, antibacterial efficacy, and biocompatibility. The results showed that the lower drug surface density in coaxial fibers hinders the interaction with serum proteins, resulting in a hydrophobic behavior compared to non-coaxial mats. The air-plasma treatment increased their hydrophilicity, although it induced rifampicin degradation. Moreover, the substantially lower release of coaxial fibers influenced the antibacterial efficacy, tested against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. Indeed, the coaxial matrices were inhibitory and bactericidal only against S. aureus, while the higher release from non-coaxial mats rendered them active even against E. coli. The biocompatibility of the released rifampicin was assessed too on murine fibroblasts, revealing no cytotoxic effects. Hence, the presented coaxial system should be further optimized to tune the drug release according to the antibacterial effectiveness.

Electrospun polycaprolactone (PCL) membranes have been widely explored in the literature as a solution for several applications in tissue engineering and regenerative medicine. PCL hydrophobicity and its lack of bioactivity drastically limit its use in the medical field. To overcome these drawbacks, many promising strategies have been developed and proposed in the literature. In order to increase the bioactivity of electrospun PCL membranes designed for guided bone and tissue regeneration purposes, in the present work, the membranes were functionalized with a coating of bioactive lactose-modified chitosan (CTL). Since CTL can be used for the synthesis and stabilization of silver nanoparticles, a coating of this compound was employed here to provide antibacterial properties to the membranes. Scanning electron microscopy imaging revealed that the electrospinning process adopted here allowed us to obtain membranes with homogeneous fibers and without defects. Also, PCL membranes retained their mechanical properties after several weeks of aging in simulated body fluid, representing a valid support for cell growth and tissue development. CTL adsorption on membranes was investigated by fluorescence microscopy using fluorescein-labeled CTL, resulting in a homogeneous and slow release over time. Inductively coupled plasma–mass spectrometry was used to analyze the release of silver, which was shown to be stably bonded to the CTL coating and to be slowly released over time. The CTL coating improved MG63 osteoblast adhesion and proliferation on membranes. On the other hand, the presence of silver nanoparticles discouraged biofilm formation by Pseudomonas aeruginosaand Staphylococcus aureuswithout being cytotoxic. Overall, the stability and the biological and antibacterial properties make these membranes a valid and versatile material for applications in guided tissue regeneration and in other biomedical fields like wound healing.