Collagen ribbon augmentation of Achilles tendon tears: a biomechanical evaluation.

Early motion of a repaired Achilles tendon has been accepted to improve both clinical and biomechanical outcomes. It has been postulated that augmenting a primary Achilles tendon repair with a collagen ribbon will improve the repair construct's initial strength, thereby facilitating early motion. The purpose of the present study was to compare the failure load of Achilles tendon defects repaired with suture, with or without augmentation with a collagen ribbon. Ten matched pairs of cadaveric feet and tibiae underwent simulated Achilles tendon tear in the watershed area and were then repaired with 4-strand Krackow sutures only or were sutured and augmented with a box weave collagen ribbon xenograft. The specimens were prepared for testing by keeping the insertion of the Achilles to the calcaneus intact and dissecting the gastrocnemius at its origin, leaving the repair undisturbed. The mean load at failure for the augmented (suture plus collagen ribbon) specimens was 392.4 ± 74.9 N. In contrast, the mean load at failure for the suture-only (control) construct was 98.0 ± 17.6 N (p < .001). The augmented specimens demonstrated a greater mean strength of 4.1 ± 0.9 N (range 3.2 to 5.6). After cyclic loading, the mean gap across the Achilles repair was significantly smaller in the augmented group than in the control group (p = .006). We have concluded that box weave collagen ribbon augmentation of the primary suture Achilles tendon repairs can provide enhanced gap resistance and strength under cyclic loading and ramped tensile testing.

Surface functionalization of electro-deposited nickel.

A new in situ electrochemical method of functionalizing an oxide-free Ni surface is demonstrated using octanethiol. Initial adsorption results in a multilayer molecular film, which blocks both the hydrogen evolution reaction (HER) and re-oxidation of the Ni by ambient oxygen. However, excess octanethiol can be removed by rinsing with ethanol, leaving behind a monolayer that continues to protect against re-oxidation but gives rise to an unexpected enhancement in the HER, with a greater enhancement for longer film formation times. The presence of an octanethiol monolayer on the surface was confirmed by spectroscopic observation of the CH(2), CH(3) and thiolate groups using infra red spectroscopy, while X-ray photo-electron spectroscopy demonstrated the effectiveness of the thiol layer as a barrier to surface oxidation. The electrochemically prepared octanethiol film impedes oxidation of the Ni in air more effectively than a film formed by immersion in a solution of octanethiol in ethanol.

A new angiographic method to assess coronary flow reserve-validation in humans.

BACKGROUND: Coronary flow reserve (CFR) is defined as the ratio between coronary artery flow during maximal hyperemia and rest. It is considered as a marker for the integrity of the epicardial coronary circulation and the microcirculation. CFR measurement typically requires the introduction of a guide wire into a diseased coronary artery. We tested a new algorithm, which allows to estimate CFR by analysis of coronary angiograms without the need for direct intracoronary measurements. METHODS: Twenty seven patients (10 female, mean age 64 +/- 11 years) underwent diagnostic cardiac catheterization for the evaluation of chest pain. A Doppler wire was introduced into the diseased coronary artery and CFR(doppler) was calculated by the flow velocity ratio between rest and maximal hyperemia, induced by intravenous administration of 140 microg of adenosine per kg bodyweight. This was compared to the angiographically determined CFR (CFR(angio)) under the same conditions (rest and induced maximal hyperemia) by densitometry. CFR(angio) was based on the creation of two time density curves representing the disappearance of contrast over time. CFR(angio) was the resulting ratio between the density values during hyperemia and rest. RESULTS: An excellent correlation was found between CFR(doppler) and CFR(angio): CFR(angio) = 1 x CFR(doppler) (r = 0.87; P < 0.0001). The average absolute difference between both indeces was 0.36 +/- 0.31. CONCLUSION: Measurement of CFR(angio) by densitometry is feasible and provides results, which are comparable to Doppler-derived intracoronary flow velocity measurements.

Special segment: soft tissue matrices--one form of acellular human dermis for use in tendon and ligament repairs in the foot and ankle.

Trauma to tendons and ligaments represents a significant part of orthopaedic and podiatric injuries. To improve the outcome of repair, complex or chronic injuries may require reinforcement of the primary repair with a graft. Biologic grafts currently available provide different handling, strength, and biological responses. One of the currently available grafts, an acellular human dermal membrane with specific properties, has been successfully used in the augmentation of tendon and ligament repairs for more than 6 years.

Gas phase formation of dense alkanethiol layers on GaAs(110).

We present a study of the growth and thermal stability of hexanethiol (C6) films on GaAs(110) by direct recoil spectroscopy with time-of-flight analysis. We compare our results with the better known case of C6 adsorption on Au(111). In contrast to the two-step adsorption kinetics observed for Au surfaces after lengthy exposures, data for C6 adsorption on the GaAs(110) surface are consistent with the formation of a single dense phase of C6 molecules at lower exposures. On the contrary, in solution preparation, dense phases can only be obtained on GaAs for long alkanethiols and after lengthy immersions. The C6 layer has a first desorption peak at 325 K, where partial desorption of the alkanethiol molecules takes place. Fits to the desorption curves result in a 1 eV adsorption energy, in agreement with a chemisorption process. Increasing the temperature to 500 K results in the S-C bond scission with only S remaining on the GaAs(110) surface. The possibility of forming dense, short-alkanethiol layers on semiconductor surfaces from the vapor phase could have a strong impact for a wide range of self-assembled monolayer applications, with only minimal care not to surpass room temperature once the layer has been formed in order to avoid molecular desorption.

Room-temperature kinetics of short-chain alkanethiol film growth on Ag(111) from the vapor phase.

We have used time-of-flight (TOF) direct recoiling spectroscopy (DRS) to follow propanethiol adsorption at 300 K from the vapor phase on an Ag(111) surface, for exposures ranging from 10(-1) to 10(5) L. Results show that the adsorption proceeds with changes in the sticking coefficient, consistent with at least three phases. At low exposures, the alkanethiol molecules adsorb with high probability at defect sites, followed by a slower growth mode that essentially covers the whole surface. A third change in the sticking coefficient is associated with the final saturation stage, corresponding to a thicker layer related to molecules in a more upright orientation. The adsorption kinetics for hexanethiol is similar to that of propanethiol but taking place at higher rates, stressing the importance of the hydrocarbon chain length in the growth process. ISS-TOF measurements during thermal desorption show that most of the C, H, and S go away together, suggesting that the molecules adsorb and desorb from flat regions without S-C bond cleavage. Fitting the desorption maximum at 450 K with a first-order desorption curve gives a desorption energy of 1.43 eV. A small final S content that is correlated with the initial Ag(111) surface roughness is observed after desorption.

Electrochemical self-assembly of alkanethiolate molecules on Ni(111) and polycrystalline Ni surfaces.

In this work, the electrochemical formation of alkanethiolate self-assembled monolayers (SAMs) on Ni(111) and polycrystalline Ni surfaces from alkanethiol-containing aqueous 1 M NaOH solutions was studied by combining Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), electrochemical techniques, and density functional theory (DFT) calculations. Results show that alkanethiolates adsorb on Ni concurrent with NiO electroreduction. The resulting surface coverage depends on the applied potential and hydrocarbon chain length. Electrochemical and XPS data reveal that alkanethiolate electroadsorption at room temperature takes place without S-C bond scission, in contrast to previous results from gas-phase adsorption. A complete and dense monolayer, which is stable even at very high cathodic potentials (-1.5 V vs SCE), is formed for dodecanethiol. DFT calculations show that the greater stability against electrodesorption found for alkanethiolate SAMs on Ni, with respect to SAMs on Au, is somewhat related to the larger alkanethiolate adsorption energy but is mainly due to the larger barrier to interfacial electron transfer present in alkanethiolate-covered Ni. A direct consequence of this work is the possibility of using electrochemical self-assembly as a straightforward route to build stable SAMs of long-chained alkanethiolates on Ni surfaces at room temperature.

Simultaneous cell death and desquamation of the embryonic diffusion barrier during epidermal development.

The periderm is an epithelial layer covering the emerging epidermis in early embryogenesis of vertebrates. In the chicken embryo, an additional cellular layer, the subperiderm, occurs at later embryonic stages underneath the periderm. The questions arose what is the function of both epithelial layers and, as they are transitory structures, by which mechanism are they removed. By immunocytochemistry, the tight junction (TJ) proteins occludin and claudin-1 were localized in the periderm and in the subperiderm, and sites of close contact between adjacent cells were detected by electron microscopy. Using horseradish peroxidase (HRP) as tracer, these contacts were identified as tight junctions involved in the formation of the embryonic diffusion barrier. This barrier was lost by desquamation at the end of the embryonic period, when the cornified envelope of the emerging epidermis was formed. By TUNEL and DNA ladder assays, we detected simultaneous cell death in the periderm and the subperiderm shortly before hatching. The absence of caspases-3, -6, and -7 activity, key enzymes of apoptosis, and the lack of typical morphological criteria of apoptosis such as cell fragmentation or membrane blebbing point to a special form of programmed cell death (PCD) leading to the desquamation of the embryonic diffusion barrier.

Measurement of bone morphogenetic proteins and other growth factors in demineralized bone matrix.

Osteoinductivity of demineralized bone matrix has been attributed to bone morphogenetic proteins (BMP). Other growth factors, including insulin-like growth factor-1 (IGF-1) and transforming growth factor-beta1 (TGF-beta1), have also been detected in demineralized bone matrix. Success of bone graft substitutes containing demineralized bone matrix has been assumed to be closely associated with osteoinductivity of the demineralized bone matrix. Because of differences in bone characteristics between donors and tissue banks, confirmation and measurement of osteoinductivity may play a crucial role in predicting the success of the bone graft substitute. In the current studies, BMP-2, BMP-4, TGF-beta1, and IGF-1 were measured in demineralized bone matrix. A strong association was noted between BMP-2 and TGF-beta1 levels. A strong association was also found between BMP-2 and new bone formation in an ectopic nude rat model.

The use of acellular dermal matrix as a scaffold for periosteum replacement.

Three preclinical models were used to evaluate GraftJacket Acellular Periosteum Replacement Scaffold (Wright Medical Technology, Inc, Arlington, Tenn). The studies assessed the ability of the acellular dermal matrix to repopulate with cells, revascularize, provide a protected environment for bone defect restoration, and minimize fibrous tissue infiltration. An athymic nude rat muscle implantation study demonstrated a steady increase in cellular repopulation through days 2-21. The formation of blood vessels occurred between days 7-14 in this study. Results from a porcine femoral drill hole study indicated that the scaffold material was intact and adherent to surrounding bone and allowed cellular repopulation and vascular infiltration at a 5-week time period. A preliminary porcine segmental bone defect model at a 6-week time period demonstrated the ability of the scaffold material to protect the bone defect site as revealed by new bone formation within the margins of the defect and adjacent to the scaffold. The segmental model also indicated minimal to no soft tissue invasion into the defect site. The combined studies provided preliminary evidence that the dermal membrane material may be used as a scaffold for periosteum regeneration by allowing for cellular repopulation, revascularization, and bone defect restoration.

Dynamics of solid growth under a gravitational field: influence of the formation of a diffusive layer.

We discuss the gravitational sedimentation of particles in terms of a stochastic model considering, in view of experimental evidence, that the aggregation to the growing surface (deposit) is mediated by the formation of a layer of suspended particles subject to gravitational forces, thermal agitation, as well as aggregation (contact) forces. The aggregation of such partially buoyant particles is ruled by the rates of occurrence of the different stochastic events: incorporation to the layer of suspended particles, sedimentation, and gravitationally biased diffusion. The model introduces bridges across different standard solid on solid deposition models which can be considered as limit cases of the present one. Analytical and numerical results show that for finite (realistic) deposits there are different regimes of aggregation including situations in which the deposit is grown completely during the transient time of the system.