Gene expression of markers of osteogenic differentiation of human mesenchymal cells on collagen I-modified microrough titanium surfaces.

Microrough, doubly acid etched titanium surfaces (Ti) were further modified by amination and covalent coupling of fibrillar collagen type I (ColTi). Human Mesenchymal Cells (HMC) adhesion and growth, and relevant osteogenic differentiation in nonosteogenic (basal) medium were evaluated by fluorescence microscopy, scanning electron microscopy, and RT-PCR for a three-week period. Results show strongly enhanced HMC adhesion and cell density at short experimental time on ColTi, together with complete spreading of the cell body over the microrough surface topography. RT-PCR analysis of several genes involved in osteogenesis indicate, since the first week of culturing, significant progression of HMC on ColTi along the osteogenic pathway. These results indicate that the adopted process of surface immobilization of collagen, mandatory to impart collagenase resistance in implant sites, does not impair biospecific interactions between HMC and collagen. Thus, it is possible to upgrade properties arising from the control of Ti surfaces topography by surface-chemistry driven enhanced recruitment of precursor osteogenic cells and pro-osteogenic stimula.

Multifunctional implant surfaces: surface characterization and bone response to acid-etched Ti implants surface-modified by fibrillar collagen I.

The goal of the study was the evaluation of the effect of biochemical surface modification by collagen on the bone response to acid-etched titanium surfaces. Fibrillar type I porcine collagen was adsorbed and covalently linked to acid-etched Ti disks and implants. Adhesion, growth, and specific alkaline phosphatase (ALP) activity of osteoblast-like SaOS2 cells were evaluated. Implants in the femur and tibia of rabbit were performed for 2 and 4 weeks and relevant bone to implant contact (BIC) was evaluated by histomorphometry. Results show that cell morphology and growth are controlled by the rough acid-etched implants topography. Specific metabolic activity (ALP) is significantly increased by the collagen overlayer. Importantly, surface modification by collagen increases the speed of periimplant bone formation, resulting in significantly higher BIC both in femur and tibia at 2 weeks. These results suggest that morphological (surface topography) and biochemical (surface linking of bioactive molecules) cues can cooperate and yield multifunctional implant surfaces. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

Inhibition of LPS-induced proinflammatory responses of J774.2 macrophages by immobilized enzymatically tailored pectins.

The surface of an implant device can be modified by immobilizing biological molecules on it to improve its integration into the host tissue. We have previously demonstrated that enzymatically tailored plant pectins are promising nanocoatings for biomaterials. This study investigates whether a coating of modified hairy region (rhamnogalacturonan-I) from apple pectin (MHR-alpha) which has anti-adhesive properties can inhibit the generation of inflammatory mediators by lipopolysaccharide (LPS)-activated macrophages. For that purpose, J774.2 murine macrophages were cultured for 24h on MHR-alpha-coated Petri dishes and tissue culture polystyrene controls, with and without LPS. Cell morphology, cell growth, nitrite and TNF-alpha secretion were studied. The results indicate that MHR-alpha coating inhibits the LPS-induced activation of macrophages.

Physical-chemical and biological characterization of silk fibroin-coated porous membranes for medical applications.

Membranes in artificial organs and scaffolds for tissue engineering are often coated with biomimetic molecules (e.g., collagen) to improve their biocompatibility and promote primary cell adhesion and differentiation. However, animal proteins are expensive and may be contaminated with prions. Silk fibroin (SF) made by Bombyx Mori silk worms, used as a scaffold or grafted to other polymers, reportedly promotes the adhesion and growth of many human cell types. This paper describes how commercial porous membranes were physically coated with SF, and their physical-chemical properties were characterized by SEM, AFM, tensile stress analysis and dynamic contact angle measurements. The effect of the SF coating on membrane biocompatibility and resistance to bacterial colonization is also examined. The proposed technique yields SF coats of different thickness that strengthen the membranes and make their surface remarkably more wettable. The SF coat is not cytotoxic, and promotes the adhesion and proliferation of an immortalized fibroblast cell line. Similarly to collagen, SF-coated membranes also exhibit a much better resistance to the adhesion of S. epidermidis bacteria than uncoated membranes. These preliminary results suggest that SF is a feasible alternative to collagen as a biomimetic coating for 3D scaffolds for tissue engineering or bioartificial (as well as artificial) prosthesis.

Collagen I-coated titanium surfaces: mesenchymal cell adhesion and in vivo evaluation in trabecular bone implants.

The goal of the study was the evaluation of the effect of modification of titanium implants by acrylic acid surface grafting-collagen I coupling. Tests were performed on titanium samples treated by galvanostatic anodization to create a porous surface topography. Surface characterization by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) confirms the biochemical modification of the surface and shows a surface topography characterized by pores mostly below 1 mum diameter. In vitro evaluation involving human mesenchymal cells shows enhanced cell growth on collagen coated surfaces as compared to titanium ones. Four weeks in vivo evaluation of implants in rabbit femur trabecular bone shows improvements of bone-to-implant contact, while improvement of bone ingrowth is slightly not significant (p = 0.056), when compared to the control. Overall, these data indicate that integration in trabecular, or cancellous, bone can be enhanced by the surface collagen layer, confirming previous findings obtained by modification of machined surfaces by the same approach in cortical bone implants.

Adsorption of cationic antibacterial on collagen-coated titanium implant devices.

Two different cationic antimicrobial molecules, chlorhexidine (CH) and poly(hexamethylenebiguanide) (PH), were adsorbed from aqueous solution to titanium implant devices surface-modified by the covalent coupling of collagen on a polyanionic acrylic acid overlayer. Results show that more antimicrobial was adsorbed on surface modified implants as compared to control titanium devices. Moreover, the kinetic of release was affected by the interaction between the polyanionic overlayer and the cationic antimicrobial, leading to slower kinetic of release in the case of CH and stable adsorption in the case of polycationic PH . These data indicate that biochemically modified collagen coated surfaces could be endowed also by antimicrobial properties, in the spirit of present researches on multifunctional implant surfaces.

Surface engineering of titanium by collagen immobilization. Surface characterization and in vitro and in vivo studies.

Collagen was covalently linked to the surface of Titanium (Ti) by a surface modification process involving deposition of a thin film from hydrocarbon plasma followed by acrylic acid grafting. The composition and properties of surface-modified Ti were investigated by a number of surface sensitive techniques: XPS, ATR-IR, atomic force microscopy and AFM force-separation curves. In vitro tests were performed to check samples cytotoxicity and the behavior of osteoblast-like SaOS-2 cells. In vivo experiments involved 12 weeks implants in rabbit muscle as general biocompatibility assessment and 1-month implants in rabbit bone to evaluate the effect of surface modification on osteointegration rate. Results of XPS measurements show how surface chemistry is affected throughout each step of the surface modification process, finally leading to a complete and homogeneous collagen overlayer on top of the Ti samples. AFM data clearly display the modification of the surface topography and of the surface area of the samples as a consequence of the grafting and coupling process. AFM force-distance curves show that the interfacial structure responds by shrinking or swelling to variations of ionic force of the surrounding aqueous environment, suggesting that the aqueous interface of the biochemically modified Ti samples has enhanced degrees of freedom as compared to the inorganic surface of plain Ti. As to biological evaluations, the biochemically modified Ti samples are safe in terms of cytotoxicity and in vivo biocompatibility assessment. SaOS-2 cells growth rate is lower on collagen modified surfaces, and no significant difference is detected in terms of alkaline phosphatase production as compared to control Ti. Importantly, implants in rabbit femur show a significant increase of bone growth and bone-to-implant contact in the case of the collagen modified samples, confirming that biochemical modifications of Ti surface can enhance the rate of bone healing as compared to plain Ti.