Evaluation of dense collagen matrices as medicated wound dressing for the treatment of cutaneous chronic wounds.

Cutaneous chronic wounds are characterized by an impaired wound healing which may lead to infection and amputation. When current treatments are not effective enough, the application of wound dressings is required. To date, no ideal biomaterial is available. In this study, highly dense collagen matrices have been evaluated as novel medicated wound dressings for the treatment of chronic wounds. For this purpose, the structure, mechanical properties, swelling ability and in vivo stability of matrices concentrated from 5 to 40 mg mL(-1) were tested. The matrix stiffness increased with the collagen concentration and was associated with the fibril density and thickness. Increased collagen concentration also enhanced the material resistance against accelerated digestion by collagenase. After subcutaneous implantation in rats, dense collagen matrices exhibited high stability without any degradation after 15 days. The absence of macrophages and neutrophils evidenced their biocompatibility. Subsequently, dense matrices at 40 mg mL(-1) were evaluated as drug delivery system for ampicillin release. More concentrated matrices exhibited the best swelling abilities and could absorb 20 times their dry weight in water, allowing for an efficient antibiotic loading from their dried form. They released efficient doses of antibiotics that inhibited the bacterial growth of Staphylococcus Aureus over 3 days. In parallel, they show no cytotoxicity towards human fibroblasts. These results show that dense collagen matrices are promising materials to develop medicated wound dressings for the treatment of chronic wounds.

Grafting of dermatan sulfate on polyethylene terephtalate to enhance biointegration.

The aim of the present study was to achieve the immobilization of dermatan sulfate (DS) on polyethylene terephthalate (PET) surfaces and to evaluate its biocompatibility. DS obtained from the skin of Scyliorhinus canicula shark was immobilized via carbodiimide on knitted PET fabrics, modified with carboxyl groups. PET-DS characterization was performed by SEM, ATR-FTIR and contact angle measurements. Biocompatibility was evaluated by investigating plasma protein adsorption and endothelial cell proliferation, as well as by subcutaneous implantations in rats. The results indicated that DS immobilization on PET was achieved at ~8 µg/cm². ATR-FTIR evidenced the presence of sulfate groups on the PET surface. In turn, contact angle measurements indicated an increase in the surface wettability. DS immobilization increased albumin adsorption on the PET surface, whereas it decreased that of fibrinogen. In vitro cell culture revealed that endothelial cell proliferation was also enhanced on PET-DS. Histological results after 15 days of subcutaneous implantation showed a better integration of PET-DS samples in comparison to those of nonmodified PET. In summary, DS was successfully grafted onto the surface of PET, providing it new physicochemical characteristics and biological properties for PET, thus enhancing its biointegration.

Influence of polysaccharide composition on the biocompatibility of pullulan/dextran-based hydrogels.

The implantation of a biomaterial for tissue engineering requires the presence of a suitable scaffold on which the tissue repair and regeneration will take place. Polymers have been frequently used for that purpose because they show similar properties to that of the natural extracellular matrix. Scaffold properties and biocompatibility are modulated by the composition of the polymers used. In this work four polysaccharide-based hydrogels (PSH) made of dextran and pullulan were synthesized. Their in vitro properties were determined and then tested in vivo in a rat model. As pullulan concentration increased in dextran hydrogels, the glass transition temperature and the maximum modulus decreased. In vitro degradation studies for 30 days demonstrated no significant degradation of PSH except for 100% pullulan hydrogel. In vivo tissue response evaluated 30 days after PSH subcutaneous implantation in rats indicated that all PSH were surrounded by a fibrous capsule. Adding pullulan to dextran induced an increased inflammatory reaction compared to PSH-D(100% dextran) or PSH-D(75)P(25)(75% dextran). This in vitro and in vivo data can be used in the design of hydrogels appropriate for tissue engineering applications.

Synthesis and in vivo integration of improved concentrated collagen hydrogels.

Normal collagen hydrogels, currently used as the dermal layer of skin substitute Apligraf®, are obtained by encapsulating dermal fibroblasts in a collagen hydrogel at low concentration (0.66 mg/ml). However they suffer from extensive contraction by cells and weak resistance against degradation, which limits their use as permanent graft. We have previously shown that concentrated collagen hydrogels at 3 mg/ml exhibit an improved performance in this respect but nevertheless degrade in vivo to ca. 50% of their initial area after 1 month. We have now investigated a new procedure to synthesize more concentrated collagen hydrogels at 5 mg/ml in order to improve hydrogel resistance and integration capability. The constructs were implanted in subcutaneous pockets in a rat model and analysed after 15 and 30 days. They were still visible after 1 month without any reduction of their area. Histological analysis revealed rapid colonization of the implants by host cells. Neovascularization was observed and reached the core of the implant at day 15. Moreover, cell colonization was not associated with a severe host response. The absence of apoptotic cells evidenced cell viability and the neosynthesis of collagen III a remodelling process. These novel non-crosslinked and cost-effective materials show superior stability and in vivo integration compared to less concentrated collagen hydrogels and appear promising for the treatment of skin lesions.

Lecturing to 200 students and its effects on cytokine concentration and salivary markers of adrenal activation.

Stress not only activates the SAM system and the hypothalamic-pituitary-adrenal axes, but also the immune system. The aims of this study are to assess the physiological variations in saliva (cytokines, cortisol and alpha-amylase) and perceived stress in professors when they had to lecture to 200 students. A total of eight unstimulated saliva samples were collected from nine professors: four on a working day that included the lecture and four controls on a working day without a lecture. The professors also rated subjective stress on a seven-point scale 5 min before the lecture, immediately after the lecture and at the same times on the control day. The lecture elicited substantial increases in subjective stress ratings, with the values on the lecture day significantly higher than those on the control day. Lecturing resulted in significant increases in Tumor Necrosis Factor (TNF)-α, Interleukin (IL)-2 and IL-4 concentrations, but did not affect the IL-10 values. These changes appeared to be concomitant with changes in the concentrations of the stress markers, alpha-amylase and cortisol. The mechanisms by which psychosocial stress can induce cytokine changes and modify the activity of salivary alpha-amylase are not entirely understood, and further research is thus warranted.

Concentrated collagen hydrogels as dermal substitutes.

Collagen hydrogels first appeared promising for skin repair. Unfortunately, their extensive contraction and their poor mechanical properties constituted major disadvantages toward their utilization as permanent graft. The present study has investigated a way to correct these drawbacks by increasing the collagen concentration in controlled conditions. Concentrated collagen hydrogels (CCH) at 1.5, 3 and 5mg/ml were obtained. The effect of raised collagen concentration on contraction, cell growth and remodeling activities was evaluated for 21 days in culture. Subsequently, in vivo integration of CCH and normal collagen hydrogels (NCH) was assessed. Compared to NCH, CCH contraction was delayed and smaller. At day 21, surface area of CCH at 3mg/ml was 18 times more important than that of NCH. Whatever the initial fibroblast density, CCH favored cell growth that reached about 10 times the initial cell number at day 21; cell proliferation was inhibited in NCH. Gelatinase A activities appeared lower in CCH than within NCH. In vivo studies in rats revealed a complete hydrolysis of NCH 15 days after implantation. In contrast, CCH at 3mg/ml was still present after 30 days. Moreover, CCH showed cell colonization, neovascularization and no severe inflammatory response. Our results demonstrate that concentrated collagen hydrogels can be considered as new candidates for dermal substitution because they are is easy to handle, do not contract drastically, favor cell growth, and can be quickly integrated in vivo.

An expansible aortic ring for a physiological approach to conservative aortic valve surgery.

OBJECTIVE: Dystrophic aortic insufficiency is characterized by dilation of the aortic annular base and sinotubular junction diameters preventing coaptation of thin and pliable cusps amenable to valve repair. An expansible aortic ring was designed to reduce dilated aortic root diameters to increase valvular coaptation height while maintaining root dynamics. The properties of the device were tested in vitro and in vivo in an ovine model. METHODS: Expansible rings were composed of an elastomer core covered by polyester fabric. After in vitro analysis of their mechanical properties, the rings were implanted in 6 sheep at both the level of the annular base and sinotubular junction (double subvalvular and supravalvular external aortic annuloplasty). Root dynamics were assessed by using intracardiac ultrasonography before surgical intervention and at 6 months. Histologic, scanning electron microscopic, and mechanical studies were then performed on explanted samples. RESULTS: The expansible ring produced a significant reduction of the aortic annular base and sinotubular junction diameters. Coaptation height was increased from 2.5 +/- 0.7 mm to 6.2 +/- 1.1 mm (P < .001). Mechanical testing on 6-month explanted samples revealed no significant differences in elastic modulus. Dynamics of the root were well preserved. Histomorphologic studies showed incorporation of the material without degradation. CONCLUSIONS: Expansible aortic ring implantation produces a significant annuloplasty that increases coaptation height while preserving the dynamics of the aortic root. The effectiveness of the device in treating aortic insufficiency is currently being evaluated in the prospective Conservative Aortic Valve surgery for aortic Insufficiency and Aneurysm of the Aortic Root trial comparing conservative aortic valve surgery versus mechanical valve replacement.

A biocompatible polysaccharide hydrogel-embedded polypropylene mesh for enhanced tissue integration in rats.

Prosthetic materials are largely used in surgery and tissue engineering. However, many postoperative complications are due to poor integration of the materials, which delays the healing process. The objective of our study was to develop a synthetic scaffold that, according to histopathological and biomechanical criteria, would achieve both tolerance and efficiency. In this study, we evaluated the effect of intramuscular and subcutaneous implantation of a new hybrid mesh (HM) in rats. This HM was composed of clinical grade polypropylene mesh embedded in a polysaccharide hydrogel. Histological and biomechanical studies on the polysaccharide gel alone and on HM were performed 15 and 30 days after implantation, and then compared with two clinically used materials, porcine decellularized small intestinal submucosa and a polypropylene mesh. Results showed that the incorporation of a polypropylene mesh within the polysaccharide hydrogel led to the absence of adverse effects and better tissue organization. Thus, this new synthetic biocompatible HM with suitable properties for tissue repair appears to be a promising material for clinical applications.