In vivo biodegradability and biocompatibility of porcine type I atelocollagen newly crosslinked by oxidized glycogen.

Oxidized glycogen is used as a collagen crosslinker to prepare materials with defined crosslinking rates. Thus, films are prepared from native or denatured porcine type I atelocollagen crosslinked with three crosslinking levels defined by the ratios between the aldehyde groups of the glycogen and the amino groups of the collagen. The remaining free aldehyde groups and the imine bonds formed in the reaction are subsequently reduced or not. All the materials are subjected to in vivo biocompatibility and biodegradability evaluations by subcutaneous implantation in mice, while immunogenicity is evaluated by rabbit immunizations. As a result, cellular reactions on the implantation site are more important with nonreduced materials, and biodegradability is correlated to the structural integrity of the collagen molecule, the crosslinking rate and the reduction state of the material. No immunological reaction or calcification is detected in our in vivo experimental model. This new method for collagen crosslinking using oxidized glycogen as a crosslinking agent enables the obtention of reproducible and biocompatible materials with a large scale of biodegradability, starting from 28 days to more than 7 months.

Rolled knitted scaffolds based on PLA-pluronic copolymers for anterior cruciate ligament reinforcement: A step by step conception.

The aim of this study was to prepare a new knitted scaffold from PLA-Pluronic block copolymers for anterior cruciate ligament reconstruction. The impact of sterilization methods (beta-ray and gamma-ray sterilization) on copolymers was first evaluated in order to take into account the possible damages due to the sterilization process. Beta-ray radiation did not significantly change mechanical properties in contrast to gamma-ray sterilization. It was shown that ACL cells proliferate onto these copolymers, demonstrating their cytocompatibility. Thirdly, in order to study the influence of shaping on mechanical properties, several shapes were created with copolymers yarns: braids, ropes and linear or rolled knitted scaffolds. The rolled knitted scaffold presented interesting mechanical characteristics, similar to native anterior cruciate ligament (ACL) with a 67 MPa Young's Modulus and a stress at failure of 22.5 MPa. These findings suggest that this three dimensional rolled knitted scaffold meet the mechanical properties of ligament tissues and could be suitable as a scaffold for ligament reconstruction. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 735-743, 2017.

In vivo evaluation of hybrid patches composed of PLA based copolymers and collagen/chondroitin sulfate for ligament tissue regeneration.

Biomaterials for soft tissues regeneration should exhibit sufficient mechanical strength, demonstrating a mechanical behavior similar to natural tissues and should also promote tissues ingrowth. This study was aimed at developing new hybrid patches for ligament tissue regeneration by synergistic incorporation of a knitted structure of degradable polymer fibers to provide mechanical strength and of a biomimetic matrix to help injured tissues regeneration. PLA- Pluronic® (PLA-P) and PLA-Tetronic® (PLA-T) new copolymers were shaped as knitted patches and were associated with collagen I (Coll) and collagen I/chondroitine-sulfate (Coll CS) 3-dimensional matrices. In vitro study using ligamentocytes showed the beneficial effects of CS on ligamentocytes proliferation. Hybrid patches were then subcutaneously implanted in rats for 4 and 12 weeks. Despite degradation, patches retained strength to answer the mechanical physiological needs. Tissue integration capacity was assessed with histological studies. We showed that copolymers, associated with collagen and chondroitin sulfate sponge, exhibited very good tissue integration and allowed neotissue synthesis after 12 weeks in vivo. To conclude, PLA-P/CollCS and PLA-T/CollCS hybrid patches in terms of structure and composition give good hopes for tendon and ligament regeneration. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1778-1788, 2017.

In vitro cytocompatibility of porcine type I atelocollagen crosslinked by oxidized glycogen.

Oxidized glycogen is used as collagen crosslinker to obtain materials with defined crosslinking degrees. These materials are characterized by their swelling ratio. calorimetric properties and the crosslinking level. Direct and indirect cytotoxicities of the materials obtained as sheets, are evaluated in vitro in cultures of human fibroblasts. The crosslinking degree depends on the ratio CHO glycogen/NH2 glycogen, but whatever this ratio (4.0, 2.0 or 0.4), an important percentage of the introduced CHO groups remains free and these groups are responsible for the cytotoxicity observed with the strongly crosslinked materials. This cytotoxicity appears in cell shape modification and in significant reduction of cell growth. Whatever the crosslinking degree, this toxicity can be suppressed by a single treatment with sodium borohydride, which reduced the remaining free CHO groups in OH functions and stabilizes the materials by a concomitant reduction of the crosslinking imine bonds. After reduction, all materials allow cellular adhesion and proliferation. This new crosslinking method of the collagen by the oxidized glycogen could be promising in the preparation of matrix for in vitro and in vivo tissue regeneration.

Prevention of postcardiopulmonary bypass pericardial adhesions by a new resorbable collagen membrane.

Reduction in mediastinal adhesions is an issue in cardiac surgery. To evaluate a porcine-bioengineered collagen membrane (Cova™ CARD) intended to promote tissue regeneration, 18 sheep underwent a sternotomy and a 30 min period of cardiopulmonary bypass. They were divided into three equal groups: pericardium left open, placement of an e-polytetrafluoroethylene membrane (Preclude(®)) taken as a non-absorbable substitute comparator and placement of the absorbable Cova™ CARD membrane. Four months thereafter, the study animals underwent repeat sternotomy and were macroscopically assessed for the degree of material resorption and the intensity of adhesions. Explanted hearts were evaluated blindly for the magnitude of the inflammatory response, fibrosis and epicardial re-mesothelialization. The bioengineered membrane was absorbed by 4 months and replaced by a loosely adherent tissue leading to the best adhesion score. There was no inflammatory reaction (except for a minimal one in an animal). Fibrosis was minimal (P = 0.041 vs Preclude(®)). The highest degree of epicardial re-mesothelialization, albeit limited, was achieved by the bioengineered group in which five of six sheep demonstrated a new lining of mesothelial cells in contrast to two animals in each of the other groups. This collagen membrane might thus represent an attractive pericardial substitute for preventing post-operative adhesions.

A new absorbable collagen membrane to reduce adhesions in cardiac surgery.

Reduction of sternal adhesions is still an issue in cardiac surgery. To evaluate a new fibrillar porcine collagen absorbable membrane (Cova CARD), 16 sheep underwent a sternotomy followed by scratching of surface of the heart. They were then divided into three groups: pericardium left opened (n=4), placement of Seprafilm), the reference absorbable substitute (hyaluronic acid and carboxymethylcellulose, n=6) or of Cova CARD membrane (n=6). Four months thereafter, the animals underwent repeat sternotomy and were macroscopically assessed for the degree of resorption of the material and the intensity of adhesions. Explanted hearts were blindly evaluated for the magnitude of the inflammatory response and fibrosis. The Cova CARD membrane was almost totally absorbed by four months and replaced by a loosely adherent tissue. There was no inflammatory reaction and both the extent and density of fibrosis were minimal. The composite score (median [min;max]) integrating tightness of adhesions and histological findings of inflammation and fibrosis was two-fold lower in the Cova CARD than in the Seprafilm) group (2.0 [0;3.5] vs. 5.5 [3;7], P=0.01 by Wilcoxon test). The Cova CARD membrane might represent an attractive pericardial substitute for preventing postoperative adhesions in cardiac surgery.