Axillary vein approach for pulmonic valvuloplasty in infants with iliac vein obstruction

Repeated pulmonic balloon valvuloplasty from the axillary vein was performed in two infants with initial transvalvular gradients of 131 and 162 mm Hg. The first angioplasty was performed through the femoral vein and improved the valve gradient in both patients. Because of obstruction of the iliac system the axillary vein approach was used for the second angioplasty. The transaxillary pulmonic valvuloplasty decreased the gradient to acceptable levels, and no complications were noticed. The axillary vein approach can be the alternative to the femoral one in cases with obstructed iliac system or interrupted inferior vena cava.     

Effect of biomaterial properties on bone healing in a rabbit tooth extraction socket model

In this work we sought to understand the effect of biomaterial properties upon healing bone tissue. We hypothesized that a hydrophilic polymer gel implanted into a bone tissue defect would impede the healing process owing to the biomaterial's prevention of protein adsorption and thus cell adhesion. To test this hypothesis, healing bone was investigated within a rabbit incisor extraction socket, a subcritical size bone defect that resists significant soft tissue invasion by virtue of its conformity. After removal of the incisor teeth, one tooth socket was left as an empty control, one was filled with crosslinked polymer networks formed from the hydrophobic polymer poly(propylene fumarate) (PPF), and one was filled with a hydrogel formed from the hydrophilic oligomer oligo(poly(ethylene glycol) fumarate) (OPF). At five different times (4 days as well as 1, 2, 4, and 8 weeks), jaw bone specimens containing the tooth sockets were removed. We analyzed bone healing by histomorphometrical analysis of hematoxylin and eosin stained sections as well as immunohistochemically stained sections. The proposed hypothesis, that a hydrophilic material would hinder bone healing, was supported by the histomorphometrical results. In addition, the immunohistochemical results reflect molecular signaling indicative of the early invasion of platelets, the vascularization of wound-healing tissue, the differentiation of migrating progenitor cells, and the formation and remodeling of bone tissue. Finally, the results emphasize the need to consider biomaterial properties and their differing effects upon endogenous growth factors, and thus bone healing, during the development of tissue engineering devices.     

In vitro degradation of polymeric networks of poly(propylene fumarate) and the crosslinking macromer poly(propylene fumarate)-diacrylate

Polymeric networks of poly(propylene fumarate) (PPF) crosslinked with poly(propylene fumarate)-diacrylate (PPF-DA) are currently being investigated as an injectable, biodegradable bone cement. This study examined the effect of crosslinking density, medium pH, and the incorporation of a beta-tricalcium phosphate (beta-TCP) filler on the in vitro degradation of PPF/PPF-DA. Cylindrical specimens were submerged in buffered saline at 37 degrees C and the change in weight, geometry, and compressive mechanical properties were monitored over a 52-week period. All formulations showed an initial increase in modulus and yield strength over the first 12 weeks, achieving maxima of 1307+/-101 and 51+/-3MPa, respectively, for the beta-TCP composite. PPF/PPF-DA networks with the lower crosslinking density demonstrated the greatest degradation with a 17% mass loss. Samples in the lower buffer pH 5.0 compared to physiological pH 7.4 did not show any differences in mass loss, but exhibited a faster decrease in the compressive strength over time. The beta-TCP composites maintained their mechanical properties at the level following their initial increase. These results show that the degradation of PPF/PPF-DA networks can be controlled by the crosslinking density, accelerated at a lower pH, and prolonged with the incorporation of the beta-TCP filler.     

Increased frequency of the rare PstI allele (P2) in a population of CAD patients in Northern Greece

Restriction fragment length polymorphisms (RFLPs) at the apolipoprotein AI-CIII-AIV gene cluster and their association with coronary artery disease (CAD) and lipid levels were studied in a Northern Greek population. Ninety-five patients with CAD and fifty-four normal controls, angio-graphically proven, were included in this study. Using genomic hybridization techniques, three polymorphic restriction sites were identified at this locus: the PstI at the 3' end of the apoAI gene, the SacI at the 3' non-coding region of the apoCIII gene and the PvuII at the intergenic region between the apoCIII-AIV genes. The rare allele (P2) arising from the absence of the PstI restriction site was observed with a significantly higher frequency (p<0.01) in patients compared to normals (0.11 vs 0.02). In contrast, the rare allele for the SacI polymorphic site had a similar distribution among patients and controls (0.12 vs 0.16). The same was observed for the PvuII RFLP (0.04 vs 0.05). Correlation of lipid and apolipoprotein AI levels with the three RFLPs revealed no significant association, although apo AI and HDL were lower in patients with the P2 allele. Thus, in this Greek population, only the PstI polymorphism, among the polymorphic restriction sites examined, appears to be associated with CAD.     

Flow Perfusion Culture of Marrow Stromal Cells Seeded on Porous Biphasic Calcium Phosphate Ceramics

Calcium phosphate ceramics have been widely used for filling bone defects to aid in the regeneration of new bone tissue. Addition of osteogenic cells to porous ceramic scaffolds may accelerate the bone repair process. This study demonstrates the feasibility of culturing marrow stromal cells (MSCs) on porous biphasic calcium phosphate ceramic scaffolds in a flow perfusion bioreactor. The flow of medium through the scaffold porosity benefits cell differentiation by enhancing nutrient transport to the scaffold interior and by providing mechanical stimulation to cells in the form of fluid shear. Primary rat MSCs were seeded onto porous ceramic (60% hydroxyapatite, 40% β-tricalcium phosphate) scaffolds, cultured for up to 16 days in static or flow perfusion conditions, and assessed for osteoblastic differentiation. Cells were distributed throughout the entire scaffold by 16 days of flow perfusion culture whereas they were located only along the scaffold perimeter in static culture. At all culture times, flow perfused constructs demonstrated greater osteoblastic differentiation than statically cultured constructs as evidenced by alkaline phosphatase activity, osteopontin secretion into the culture medium, and histological evaluation. These results demonstrate the feasibility and benefit of culturing cell/ceramic constructs in a flow perfusion bioreactor for bone tissue engineering applications.     

Use of stereolithography to manufacture critical-sized 3D biodegradable scaffolds for bone ingrowth

A novel approach to the manufacture of biodegradable polymeric scaffolds for tissue-engineering utilizing stereolithography (SLA) is presented. SLA is a three-dimensional (3D) printing method that uses an ultraviolet laser to photo-crosslink a liquid polymer substrate. The current generation of SLA devices provide a 3D printing resolution of 0.1 mm. The experiments utilized a biodegradable resin mixture of diethyl fumarate (DEF), poly(propylene fumarate) (PPF), and a photoinitiator, bisacylphosphine oxide (BAPO). The PPF is crosslinked with the use of the SLA's UV laser (325-nm wavelength). An SLA device was retrofitted with a custom fixture build tank enclosing an elevator-driven build table. A 3D prototype model testing the manufacturing control this device provides was created in a computer-aided-design package. The resulting geometric data were used to drive the SLA process, and a DEF/PPF prototype part was successfully manufactured. These scaffolds have application in the tissue engineering of bony substrates.