A comparative study on culture conditions and routine expansion of amniotic fluid-derived mesenchymal progenitor cells.

BACKGROUND: Amniotic fluid (AF) cell populations will be applied in perinatology. We aimed to test the feasibility of large-scale cell expansion. STUDY METHODS: We determined the best out of three published expansion protocols for mesenchymal progenitors (AF samples, n = 4) in terms of self-renewal ability. Characterization was performed based on morphology, surface marker analysis, cytogenetic stability, and differentiation potential. The conditions for the best self-renewal ability were further determined in a consecutive series (n = 159). RESULTS: The medium containing fetal bovine serum (FBS), epidermal growth factor, insulin, transferrin, and tri-iodothyronine, combined with seeding on gelatin-coated wells, best stimulated the growth of cells with mesenchymal features, as demonstrated by flow cytometry; however, only osteogenic differentiation was possible. Large-scale testing (n = 44) failed to confirm a robust self-renewal ability. Better results were obtained (n = 88) using optimized FBS or an increased initial cell density. Eventually over 81% of cultures continued growing after the initial medium change and had mesenchymal features but failed differentiation assays. DISCUSSION: Routine in vitro expansion of AF-derived mesenchymal cells remains problematic. Despite an increase in successful cell cultures from 40 up to 80% using optimized serum and an increased cell density, eventually cells failed to demonstrate differentiation abilities. Routine isolation and expansion from unselected AF samples remains a challenge.

Combined biaxial and uniaxial mechanical characterization of prosthetic meshes in a rabbit model.

The present experimental study is aimed at a combined uniaxial and biaxial mechanical characterization of the deformation behavior of two types of prosthetic meshes, SPMM (heavy-weight) and Gynemesh M (light-weight, partly absorbable), after integration in the host tissue. Explants from a full-thickness-abdominal-wall-defect-rabbit-model were tested in the two loading conditions. Corresponding protocols and data analysis procedures for biaxial inflation tests and uniaxial tensile tests were developed. Biaxial responses were observed to be by factor 2-4 stiffer compared to corresponding uniaxial experiments, depending on the material tested. In biaxial loading conditions, SPMM explants were stiffest. Gynemesh M explants and native tissue were similarly compliant at low membrane tensions (<5N/cm) (abdominal wall: 40±23N/cm, Gynemesh M: 59±44N/cm, SPMM: 145±36N/cm). At high membrane tensions (>5N/cm), there were distinct differences in the stiffness of the three groups, SPMM explants being the stiffest, followed by Gynemesh M explants and native tissue being the most compliant. In uniaxial loading conditions, the two explants were similarly stiff and distinctly stiffer than native tissue at low membrane tensions (<5N/cm) (abdominal wall: 9±1N/cm, Gynemesh M: 21±5N/cm, and SPMM: 24±5N/cm). At high membrane tension (>5N/cm), differences between all groups vanished. Biaxial and uniaxial tests yield different results with respect to the mechanical behavior of mesh explants. These findings demonstrate that an evaluation of the mechanical biocompatibility of prosthetic meshes should be based on an experimental configuration (uniaxial or biaxial tension) which reproduces the expected in vivo conditions of mechanical loading and deformation.

Persistence of polypropylene mesh anisotropy after implantation: an experimental study.

OBJECTIVE: To determine whether anisotropy persisted after incorporation into the host, using a standardised rabbit model for abdominal wall reconstruction. DESIGN: Investigator-initiated prospective-controlled experimental study. SETTING: Centre for Surgical Technologies, Medical Faculty KU-Leuven. SAMPLE: Fifteen New Zealand White rabbits. METHODS: In each rabbit, four full thickness primarily repaired abdominal wall defects were covered by a 4 × 5-cm Prolift+M implant (Johnson & Johnson, Norderstedt, Germany), either with the stiffest (n = 6 rabbits) or most elastic (n = 6) direction parallel to the body axis. Prolift+M contains 32 g/m² polypropylene, reinforced with polyglecaprone fibres. Harvesting was performed after 30, 60 and 120 days (n = 2 each time-point). The abdominal wall of three unoperated rabbits was used as negative control. MAIN OUTCOME MEASURES: Contraction, compliance and maximal strain and stress determined by uniaxial tensiometry. RESULTS: Anisotropy properties persist at lower, more physiological displacements, but not at higher displacements. The stiffness of a mesh-augmented repair in the lower strain range remains above that of native tissue. Eventual mesh contraction was limited to 4.3%. CONCLUSIONS: Anisotropic properties of Prolift+M persist in vivo and shrinkage is minimal. Compliance of mesh-augmented repair remains less than that of native tissue. The functional consequences of this remain to be studied.

Biomechanical findings in rats undergoing fascial reconstruction with graft materials suggested as an alternative to polypropylene.

AIMS: Graft materials used for pelvic floor reinforcement should still be considered as investigational and, therefore, evaluated experimentally and within clinical trials. The present report describes our biomechanical findings in rats implanted with selected novel implant materials, which in recent years have been suggested as alternatives to plain polypropylene (PP) meshes. METHODS: Full thickness abdominal wall defects were primarily repaired by the implant of interest. Experiments involved eight different implant materials: two partly degradable synthetic implants, that is, a hybrid of polyglactin 910 with PP (Vypro II) and collagen coated PP (Pelvitex); two non-cross linked (Surgisis, InteXen LP) and two cross-linked materials (Pelvicol, Pelvisoft) and two porous modifications of InteXen LP and Pelvicol implants. At different time points (7, 14, 30, and 90 days), the implants and surrounding host tissue (explant) were harvested and tensiometry was performed. Tensile strength and location of breakage were recorded. RESULTS: In general resorbable non-cross linked collagen matrices and porous materials were weaker after 90 days; similar behavior was seen for implant materials alone and their construction with the surrounding native tissue. Both non-porous and porous modification of InteXen LP appeared at 90 days as a very thin layer of collagen that was two-thirds, respectively one-third of the initial thickness. CONCLUSIONS: In experimental conditions, sufficient strength was obtained only after 3 months, and PP containing constructs appeared as the strongest though reconstruction with Pelvicol showed comparable outcomes. Lower values for strength of non-cross linked and porous collagen materials are questioning their efficacy for pelvic floor reconstruction.