Linear and Multi-Photon Fluorescence of Thiophene Based Copolymer with Electron-Accepting Side Chains.

A novel copolymer poly(thiophene-2,5-diyl-2,5-di-n-octyloxycarbonyl-1,4-phenylene), denoted as P33, is introduced as potential material for photovoltaics, polymer light-emitting diodes, and/or organic transistors. P33 dissolved in chloroform is investigated by steady-state absorption, linear/non-linear fluorescence spectroscopies and time-resolved fluorescence spectroscopy. Molar extinction coefficient, fluorescence quantum yield, and singlet fluorescence lifetime of P33 are determined to be 18,315 M-1 cm-1, 0.4, and 810 ps, respectively. The P33 fluorescence fast components of decay times are 1.2 ps, 2.0 ps, and 0.5 ps for increasing wavelengths of 480 nm, 500 nm, and 520 nm, respectively. The fast component is attributed to a transport of nearly instantaneously formed excitons to localized states known as downhill energy transfer. Additionally multi-photon excited fluorescence is observed for pumping with wavelengths of 800 nm and 1200 nm. Two-photon absorption cross-section is determined to be 6.9 GM. These spectroscopic studies provide basic fluorescence characteristics of the novel thiophene copolymer P33.

A cell-free nanofiber composite scaffold regenerated osteochondral defects in miniature pigs.

The aim of the study was to evaluate the effect of a cell-free hyaluronate/type I collagen/fibrin composite scaffold containing polyvinyl alcohol (PVA) nanofibers enriched with liposomes, basic fibroblast growth factor (bFGF) and insulin on the regeneration of osteochondral defects. A novel drug delivery system was developed on the basis of the intake effect of liposomes encapsulated in PVA nanofibers. Time-controlled release of insulin and bFGF improved MSC viability in vitro. Nanofibers functionalized with liposomes also improved the mechanical characteristics of the composite gel scaffold. In addition, time-controlled release of insulin and bFGF stimulated MSC recruitment from bone marrow in vivo. Cell-free composite scaffolds containing PVA nanofibers enriched with liposomes, bFGF, and insulin were implanted into seven osteochondral defects of miniature pigs. Control defects were left untreated. After 12 weeks, the composite scaffold had enhanced osteochondral regeneration towards hyaline cartilage and/or fibrocartilage compared with untreated defects that were filled predominantly with fibrous tissue. The cell-free composite scaffold containing PVA nanofibers, liposomes and growth factors enhanced migration of the cells into the defect, and their differentiation into chondrocytes; the scaffold was able to enhance the regeneration of osteochondral defects in minipigs.

Correlation of dynamic impact testing, histopathology and visual macroscopic assessment in human osteoarthritic cartilage.

OBJECTIVE: Improved staging of cartilage degeneration is required, particularly during the early stages. We correlated mechanical properties with histological and macroscopic findings. METHODS: One hundred and twenty cartilage samples were obtained during total knee arthroplasty. Two adjacent plugs were harvested--one for histological classification and one for macroscopic and biomechanical purposes. Dynamic impact testing was performed; normal stress, dissipated energy (∆E), tangent modulus and stiffness were evaluated. RESULTS: Samples were classified according to six categories of the ICRS histological scale. Mechanical characteristics revealing significant differences between the groups (p < 0.01) were specific damping and related absolute ∆E. A significant correlation was found between the macroscopic score and specific damping, as well as absolute and relative ∆E (p < 0.01). A strong relation was revealed between relative ∆E and cartilage thickness (p < 0.001; R (2) = 0.69). CONCLUSIONS: Only ∆E correlated with the condition of the cartilage--the value increased with decreasing quality-and is the most suitable characteristic. This change appears substantial in initial stages of cartilage deterioration.

Reconstruction of the anterior cruciate ligament: dynamic strain evaluation of the graft.

The study is focused on the biomechanical aspects of the anterior cruciate ligament (ACL) reconstruction procedures with an emphasis on evaluating the dynamic strain of materials commonly used for this purpose. Separate and multiple, equally tensioned strands of hamstring grafts used for the reconstruction of the ACL were biomechanically tested and compared to original ACL and bone-patellar tendon-bone (BPTB) grafts, using tissue samples from cadavers. The study was focused on measuring such material properties as the strength, stiffness, maximum load, and elongation at maximum load of the original ACL, BPTB graft, and single tendon hamstring (gracilis and semitendinosus) grafts, continued by double strands and finally by four-strand graft (STG) evaluation. Fresh-frozen cadaveric knees were used, which had been clamped and tensioned equally. The measurement was performed by drop-weight testing, using a Laser Doppler Vibrometer as a basic sensor of the dynamic movements of the gripping clamps, with parallel correlation by a piezoelectric transducer. The grafts for experiments were obtained from 21-paired knees. The measurement was performed at room temperature (21 degrees C) after 24 h of thawing at 4 degrees C. All the specimens were measured for their response to the dynamic tensile load. The maximum strength values were obtained and calculated for the appropriate section area of the specimen. The tensioned strands of the original ACL showed a maximum average load of 1,246 +/- 243 N in the section area of about 30 mm(2) (max. stress 41.3 MPa); the strands of BPTB grafts showed values of 3,855 +/- 550 N in the section area of 80 mm(2) (max. stress 40.6 MPa); the gracilis tendons showed 925 +/- 127 N in the section area of 10 mm(2) (max. stress 95.1 MPa) and the semitendinosuss yielded a result of 2,050 +/- 159 N in the area of 20 mm(2) (max. stress 88.7 MPa). Of all the materials, the original ACL have the lowest strength and stiffness in respect of their biomechanical properties. BPTB grafts showed a slightly higher value of maximum stress, while both the gracilis and semitendinosus tendons showed double the value of maximum load per section area-tensile stress. Two- and four- combined hamstring strands clamped together and equally tensioned with a drop-weight had the combined tensile strength properties of the individual strands within the estimated range of measurement errors. No significant changes in maximum loads/stresses were observed under impact loading conditions. The results of this study demonstrate that equally tensioned four-strand hamstring-tendon grafts have higher initial tensile properties than those in other varieties of samples. From a biomechanical point of view, they seem to be a reasonable alternative procedure for ACL reconstruction.