bluuebunny/crossref_metadata_2025 huggingface dataset:
Makrocyclische [4n + 2]‐Hückel‐Aromaten bis n = 9 und [4n]‐Antiaromaten bis n = 10: Homologe Reihen vom Tetraepoxy[24]‐annulen(2.0.2.0) zum Tetraepoxy[40]annulen(12.0.12.0) und vom ‘Tetraoxa‐[22]porphyrin(2.0.2.0)’‐zum ‘Tetraepoxa[38]porphyrin(12.0.12.0)’‐Dikation
Authors: Märkl Gottfried , Knott Th. , Kreitmeier Peter , Burgemeister Thomas , Kastner F.
Published: December 2004

Macrocyclic [4n + 2]‐Hückel Aromatic Systems up to n = 9 and [4n] Antiaromatic Systems up to n = 10: Homologous Sequences from Tetraepoxy[24]annulene(2.0.2.0) to Tetraepoxy[40]annulene(12.0.12.0) and from the ‘Tetraoxa[22]porphyrin(2.0.2.0)‐’ to the ‘Tetraoxa[38]porphyrin(12.0.12.0’‐Dication1)2)

Tetraepoxy[32]annulene(8.0.8.0) 3, tetraepoxy[36]annulene(10.0.10.0) 4, and tetraepoxy[40]annulene(12.0.12.0) 5 are synthesized and oxidized to give the ‘tetraoxa[30]‐’, ‘tetraoxa[34]‐’, and ‘tetraoxa[38]porphyrin’ dications 8–10. The annulenes as well as the ‘porphyrins’ are mixtures of at least two different configurational isomers, which can be analyzed by 1H‐NMR techniques. Together with systems described already earlier, a complete homologous sequence from tetraepoxy[24]annulene(2.0.2.0) to tetraepoxy[40]annulene(12.1.12.0) and from ‘tetraoxa[22]porphyrin(2.0.2.0)’ to ‘tetraoxa[38]porphyrin(12.0.12.0)’ dications are available for the first time. The UV/VIS‐absorptionmaxima in the annulene series are shifted to longer wavelengths with an increment of 12 nm per additional CC bonds, and the Δδ values of the 1H‐NMR spectra demonstrate a decreasing paratropic character (Δδ = 5.97 (1), 2.80 (3), and 4.23 ppm (4). The averaged λmax values of the Soret bands of the ‘tetraoxaporphyrin’ dications show a linear bathochromic shift with an increment Δδ of 58 nm per two additional double bonds, the absorptions of the most intensive Q‐bands also increase linearly with an increment of ca. 160 nm. The Δδ values of the 1H‐NMR spectra of the ‘tetraoxaporphyrin’ dications are increasing with the ring size (Δδ = 24.04 (7a) to 25.17 (9a) ppm), respectively, decreasing (Δδ = 21.55 (6) to 21.50 (9b) ppm) with a small maximum of 22.60 ppm for 7b, depending on the configuration of the isomers. The results confirm the antiaromatic character of the annulenes with up to 40π electrons and the aromatic character of the ‘tetraoxaporphyrin’ dications with up to 38π electrons.
Evolution of the mandibular mesh implant
Authors: Salyer Kenneth E. , Johns Donnell F. , Holmes Ralph E. , Layton James G.
Published: December 2004

Between 1960 and 1972, the Dallas Veterans Administration Hospital Maxillofacial Research Laboratory developed and made over 150 cast‐mesh implants. Successive designs were ovoid, circular, and double‐lumened in cross section to improve implant strength, surface area for bioattachment, and adjustability. Sleeves, collars, and bows were employed in the assembly of these implants, with an acrylic condylar head attached when indicated. In 1972, our laboratory developed a mandibular mesh tray, cast in one piece on a single sprue, with preservation of the vertically adjustable ramus. Stainless steel replaced Vitallium because of its greater malleability. Essentially, a lost‐wax technique is used to cast the mesh tray. The model of a mandibular segment is duplicated as a refractory model. Mesh wax, made in our own custom‐made die, is adapted to the refractory model. The unit is then sprued and invested. The wax is fired our of the mold in a gas furnace. Casting is done by the transferral of molten stainless steel from the crucible to the mold by centrifugal force in an electroinduction casting machine. Other mesh implants that have been developed are made from wire mesh, Dacron mesh, cast Ticonium, and hydroformed titanium.
Evaluation of wound‐covering materials
Authors: Schwope A. D. , Wise D. L. , Sell K. W. , Dressler D. P. , Skornick W. A.
Published: December 2004

Physical and in vivo (burned rat model) evaluations as wound coverings were performed for 1) a freeze‐dried collagen/poly (ϵ‐caprolactone) (PCL) film laminate, 2) a freeze‐dried PCL “foam”/PCL film laminate, and 3) a heat‐dried collagen/PCL film laminate. Porcine skin and cadaver skin were also evalulated in vivo for the purpose of comparison. Water‐vapor transmission rates and Young's moduli were measured. The degrees of adherence of the coverings to the wound were measured. Grafts which became significantly adherent (>150 dyne/cm2) to the wound within 1 day were most successful in promoting the formation of a viable tissue bed which appeared ready to accept further grafting. The force required to remove the PCL foam laminate from a full‐thickness excision wound was found to increase from 170 dyne/cm2 on the first day postgraft to 1500 dyne/cm2 by the tenth day. The force required to remove freeze‐dried collagen laminate remained constant at 200 dyne/cm2 over the 10 day test period. For the heat‐dried collagen laminate, a force of only 50 dyne/cm2 was required on day 1, increasing to 200 dyne/cm2 on day 6. Insensible water‐loss rates of animals grafted with the laminates were found to be similar to those from animals with human cadaver skin grafts and less than that from animals with porcine skin grafts. When moistened, the laminates prepared using the freeze‐dried materials were flexible and somewhat transparent permitting observation of the wound.
Analysis of the ingredients and determination of the residual components of acrylic bone cements
Authors: Brauer G. M. , Termini D. J. , Dickson G.
Published: December 2004

Rapid and reliable methods for the characterization and quantitative determination of ingredients usually present in self‐curing methacrylate bone cements were developed using spectrophotometric, gas chromatographic (GC), and conventional gravimetric procedures. These procedures are applicable to non‐crosslinked methacrylate resins. In the presence of some copolymers, polymer blends or crosslinking agents, or other ingredients which will result in the formation of insoluble methacrylate resins, some modification of the identification procedures and quantitative estimation of the resin components will be required. Molecular weight and molecular weight distribution of the powder and cured cement were obtained from viscosity and gel‐permeation measurements. Residual low molecular weight materials in the cured cement were determined for various storage times. Residual and water‐leachable monomer and residual dimethyl‐p‐toluidine (DMPT) were measured by GC. In air, the monomer content of the cured resin decreased from 3.3% after 1 hr to 2.4% after 215 days. When stored in water at 37°C, over 65% of the extractable monomer is leached out within 10 min. After 6 hr, the rate of diffusion of monomer into the aqueous phase is low. The cured cement contains as much as 0.6% DMPT, which does not leach out. Residual peroxide, estimated spectrophotometrically, amounts to 0.8%, but decreases to 0.14% after 15 months in water at 37°C. A semiquantitative colorimetric test indicated that the hydroquinone content of specimens analyzed within 24 hr after curing amounted to 9 ppm.
Effect of comonomer ratio on hydrocortisone diffusion from sustained‐release composite capsules
Authors: Fu J. C. , Moyer D. L. , Hagemeier C.
Published: December 2004

The daily in vitro release of hydrocortisone from composite polymer capsules is reported here for over 120 days. Increase in vinyl acetate comonomer content of the ethylene–vinyl acetate copolymer matrix brought about an increase in the diffusion rate. Variation in the initial drug content of the capsules from 40 mg to 20 mg affects the daily drug release less significantly than the variation in copolymer ratio. The correlation between vinyl acetate comonomer content and the percent crystallinity of the copolymer matrix is suggested as one of the possible major factors in controlling diffusion rate from this drug–polymer system. The diffusion constant (D) calculated was 0.212 × 10−10 cm2/sec when the copolymer carrier has 30% vinyl acetate content and 0.430 × 10−11 cm2/sec when the copolymer carrier has 20% vinyl acetate content for capsules with 20 mg initial drug content, and 0.118 × 10−11 cm2/sec and 0.226 × 10−11 cm2/sec, respectively, for capsules with 40 mg initial drug content.
Thrombus formation in a staged capillary membrane oxygenator associated with a microaggregate blood filter: A scanning electron microscope study
Authors: Guidoin R. G. , Awad J. A. , Domurado D. , Haggis G. H.
Published: December 2004

Blood contact at interfaces in extracorporeal devices is a source of traumas. Proteins are very rapidly adsorbed; then, depending on which proteins are left various degrees of platelet aggregation follow and thrombi develop. The scanning electron microscope reveals very instructive information on the morphology of the blood deposits which adhere to foreign surfaces. Oxygenators such as the Awad D, which is a staged one made of silicone rubber, become “thrombus invaded” after prolonged extracorporeal circulation in spite of adequate heparinization of the blood. In most cases, evaluation of membranes and devices is assessed with respect to transfer of blood gases. Careful examination of the morphology of deposits should be developed. This study shows the importance of blood flow rate, design, and materials.
Antiinflammatory activities of polymers of o‐methacryloyloxybenzoic acid
Authors: Grimová J. , Hrabák F.
Published: December 2004

Antiinflammatory activities of low‐ and high‐ molecular‐weight polymers of o‐methacryloyloxybenzoic acid were compared with the antiinflammatory activity of o‐acetoxybenzoic (acetylsalicylic) acid in tests on hind‐leg inflammations in rats induced by injection of either Freund's adjuvant or aqueous suspension of kaolin. The antiinflammatory activies of the orally administered polymers cooresponded to 40–90% of the activity of o‐acetoxybenzoic acid, and were not substantially dependent on the degree of polymerization.
Experimental infections along subcutaneous conduits
Authors: Myojin Kazuhiro , Von Recum Andreas F.
Published: December 2004

To determine whether progressive infection along percutaneous conduits (PC) usually leads to infection of cardiac assist devices, two PCs each were implanted into the subcutis of 11 dogs. One month later, one end of one conduit was inoculated with either E. coli or S. aureus. The resulting infections in all dogs progressed little during the first two weeks and in 10 of the 11 animals involved less than 40% of the total length of the PC. Bacteriological tests one month after the infecting organisms were introduced showed that they were no longer present at the site of inoculation in 4 of the 11 dogs and no bacteria were found at the opposite end of the inoculated PCs or in the noninoculated PCs. Histological observations confirmed these results and indicated that in all animals encapsulation of the infected area prevented its further enlargement.
Identification of wear particles in tissue after implantation of different plastic materials
Authors: Leugering H. J. , Püschner H.
Published: December 2004

A method is shown by which to identify wear particles of implanted plastic materials in tissue. A Mettler FP2 hot stage was used to determine the melting point of different elastomer particles in normal histological sections between the crossed nicols. By using a microcolorimeter Type MPE (Leitz, Wetzlar, Germany), additional information about the molecular degradation of wear particles was obtained.
Antibiotics in acrylic bone cement. In vitro studies
Authors: Welch Ardyce B.
Published: December 2004

The effect of combining gentamicin and cephalothin with Surgical Simplex bone cement was tested in vitro. Experiments were designed to determine (1) quantitative elution rates and period of time the antibiotics were eluted and (2) effective bactericidal qualities. Both antibiotics were eluted from polymerized acrylic cement in large quantities within 24–48 hr after coming in contact with fluid and continued to be released in smaller amounts for 21 days to more than 175 days. This varied with the antibiotic, concentration of antibiotic in the cement, surface area of cement, and volume of elution fluid. Quantitative determinations of numbers of bacteria in broth cultures demonstrated that sufficient quantities of antibiotics were released to be bactericidal to microorganisms within 45 min to 20 hr. This was dependent on the type of antibiotic, type of bacteria, concentration of antibiotic in the cement, and time of contact.
Age hardening of orthodontic beta titanium alloys
Authors: Goldberg A. Jon , Shastry C. V.
Published: December 2004

Metastable beta titanium alloys have been shown to be effective in orthodontic therapy because of their low modulus of elasticity and good springback, forming, and welding characteristics. Although used in the as‐drawn condition, these alloys are also age hardenable through precipitation of the alpha phase in the beta matrix. The effect of aging temperature, aging time, and prior cold work on the mechanical properties of fine wires of Ti‐13V‐11Cr‐3Al and Ti‐11.5Mo‐6Zr‐4.5Sn were determined. The latter alloy was more responsive to aging. Aging at 900°F for 14 h produced increases of approximately 40% in the modulus of elasticity, the yield and ultimate strengths. There was a corresponding decrease in ductility. The resulting wires could be useful in clinical situations requiring a high‐yield strength and a stiffness intermediate between as‐drawn beta titanium and stainless steel, the elastic moduli of which are 10 and 28 × 106 psi, respectively.
Enzyme histochemistry of the tissue response to pure metal implants
Authors: McNamara A. , Williams D. F.
Published: December 2004

Techniques of enzyme histochemistry have been used to augment those of histology and scanning electron microscopy in the study of the tissue response to pure metals. In this article the distribution of acid and alkaline phosphatase, lactate and succinate dehydrogenases, leucine aminopeptidase, and nonspecific esterase in association with implants of aluminium, copper, cobalt, nickel, and lead is described, and its significance for the tissue response is discussed. The toxic nature of cobalt was demonstrated especially by the intense acid phosphatase activity associated with macrophages and the virtual absence of LDH and SDH activity, implying a low level of respiration. Pigmented deposits noted previously from histological examination of the tissue surrounding copper implants was shown to be cellular in origin with many individual cells of macrophagic morphology being discernible following histochemical staining, suggesting that pigmentation has resulted from copper overload, similar to that of liver cells in Wilson's Disease. Generally, observations with nickel were qualitatively similar to those with copper, but not so prominent. Although lead is well known as a toxic metal, and indeed its effect on nervous tissue was apparent in this study from observation of unusual enzyme activity in muscle, the local response was minimal in contrast to that associated with several other pure metals. On the other hand, aluminium, normally considered a relatively nontoxic metal, induced intense activity of certain enzymes, noticeably acid phosphatase and leucine aminopeptidase, indicating its toxicity under implant conditions.
Cell growth on metallic glasses: The interaction of amorphous metal alloys with cultured neuronal, osteoblast, endothelial, and fibroblast cells
Authors: McAuslan B. R. , Johnson G. , Delamore G. W. , Gibson M. A. , Steele J. G.
Published: December 2004

Ferrous based, corrosion resistant amorphous alloys supported the adhesion and growth of cultured chick neuronal cells, human marrow stromal cells (presumptive osteoblasts), bovine aortal endothelial cells, and hamster kidney fibroblasts. Alloys of compositions Fe60Ni10Cr10P13C7, Fe70Cr10P13C7, and Fe70Cr10P13B7 were found to be suitable. In contrast the crystalline form of these alloys was markedly less effective. Outgrowth of neurites from neuronal cells was promoted by precoating the metal surface with either laminin or neurite promotion factor. The adhesion of osteoblasts and fibroblasts suggests that corrosion resistant metal glasses should be considered as biomaterials useful for orthopedic applications. The adhesion of neuronal cells accompanied by neurite outgrowth indicates that the system might provide a functional interface between the neuromuscular system and an electromagnetic material that could be useful in bionic engineering.
Polymerization of multifunctional methacrylates and acrylates
Authors: Miyazaki Koji , Horibe Takashi
Published: December 2004

The cross‐linking reaction of 15 dimethacrylates, one trimethacrylate and five diacrylates was studied by means of differential scanning calorimetry (DSC) and high performance liquid chromatography (HPLC) to investigate the relationship between the polymerization characteristics and the chemical structure of these monomers. The amount of pendant double bonds (Dp) and the efficiency of cross‐linking (Ec) were calculated from both the extent of polymerization (Ep) and the amount of residual monomer (Rm) obtained by DSC and HPLC analyses, respectively. The Ep and Ec values of various monomers increased with an increase in the number of chain members between the functional groups, while Rm and Dp values decreased. The dimethacrylates consisting of aliphatic chains polymerized more readily than those containing aromatic units. High Ep was obtained in the aliphatic dimethacrylates and diacrylates with more than eight chain members and the aromatic dimethacrylates with more than 20 chain members among the monomers examined. These results depend presumably on the flexibility of the functional groups in the polymer network. With most dimethacrylates and diacrylates, high Ep was also observed in thermal scanning polymerization compared to isothermal polymerization at 90°C. The diacrylates showed a high rate of polymerization compared to the corresponding dimethacrylates.
Poly(dimethylsiloxane)‐poly(ethylene oxide)‐heparin block copolymers III: Surface and bulk compositional differences
Authors: Grainger D. W. , Okano T. , Kim S. W. , Castner D. G. , Ratner B. D. , Briggs D. , Sung Y. K.
Published: December 2004

Previously observed bioactivity of poly(dimethylsiloxane)‐poly(ethyelene oxide)‐heparin (PDMS‐PEO‐Hep) triblock copolymers has prompted studies of the surface and bulk character of this copolymer using angular‐dependent electron spectroscopy for chemical analysis (ADESCA), static secondary mass spectroscopy (SIMS), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Because the low‐energy PDMS phase dominates surfaces of this copolymer when solvent cast under air or vacuum conditions, attempts were made to explain surface restructuring and rearrangements induced in hydrated or aqueous environments that permit surface accessibility and bioactivity of heparin moieties. Based on comparisons with PDMS, PEO, and heparin homopolymers, PEO/heparin blends, and an unheparinized PDMS‐PEO diblock copolymer, PDMS‐PEO‐heparin demonstrates both phase‐mixed and phase‐separated regions in DSC analysis. During annealing cycles above the Tg values of the copolymer constituents, phase‐mixed regions become increasingly phase separated and PEO enriched. TGA analysis confirmed the presence of block copolymer constituents and presented evidence of intermolecular segmental interactions, hence phase‐mixing in the copolymers. ADESCA analysis indicates that the outer 5 Å of both the PDMS‐PEO and PDMS‐PEO‐Hep copolymers is essentially pure PDMS. However, significant amounts of PEO are detected 5 to 20 Å below the surface. Static SIMS also detects the presence of PDMS at the surfaces of the PDMS‐PEO and PDMS‐PEO‐Hep copolymers. Compositional models based on ADESCA, SIMS, and DSC data are presented for desiccated and hydrated copolymer surfaces.
Stress enhancement and fatigue susceptibility of porous coated Ti‐6Al‐4V implants: An elastic analysis
Authors: Messersmith Phillip B. , Cooke Francis W.
Published: December 2004

An elastic stress analysis of porous‐coated implant surfaces was performed using the finite element method. Three‐hundred‐μm‐diameter metal beads sinter bonded onto an implant surface were modeled with sinter neck radii of 5, 10, 20, and 50 μm. Smooth‐surface, single‐bead, single‐layer, and double‐layer systems were analyzed. The finite element models were loaded to simulate bone–bead contact forces and lateral hip implant tensile forces. Results showed that, for a single bead sinter‐bonded onto an implant surface, concentration of stress occurs either at the base of the sinter neck or within the neck itself, depending on the type of loád applied. Under lateral hip implant tensile loads, a maximum stress concentration factor of 1.97 was obtained for a single bead sinter‐bonded onto a implant surface. Addition of a single layer of beads onto the implant surface resulted in a significant increase in stress at the most proximal and distal ends of the porous layer, with a maximum stress concentration factor of 4.3. Addition of a second layer of beads did not significantly increase the magnitude of the stress concentration occurring at the ends of the porous layer. The results of this study provide stress concentration factors for porous coatings with sinter necks of known dimensions under loading conditions similar to those present along the lateral surface of a hip prosthesis.
Cellular interactions with biomaterials: In vivo cracking of pre‐stressed pellethane 2363‐80A
Authors: Zhao Q. , Agger M. P. , Fitzpatrick M. , Anderson J. M. , Hiltner A. , Stokes K. , Urbanski P.
Published: December 2004

The phenomenon of stress cracking of Pellethane 2363‐80A (PEU) was investigated using the cage implant system. A cytotoxic polyvinylchloride (PVC) and a silicone rubber containing an anti‐inflammatory steroid were used to create inflammatory environments in which the biostability of the pre‐stressed PEU was tested. These coimplants provided alternative in vivo environments to study in vivo polymer interactions. The inflammatory responses to the implanted cages were monitored by analyzing the exudates aspirated from the cages at different implantation times over 21 days. The pre‐stressed PEU specimens were retrieved after 5, 10, and 15 weeks postimplantation and examined by optical microscopy (OM) and scanning electron microscopy (SEM). The results support the conclusion that in vivo cracking of stressed (strained) Pellethane 80A is related to cell–polymer interactions. Severe cracking or rupture of the implanted PEU specimens was observed as early as 5 weeks postimplantation. Molecular chain degradation of the implanted specimens was evident from molecular weight measurements. Neither surface cracking nor degradation of macromolecules was found on the pre‐stressed PEU specimens with the added cytotoxic PVC implanted over 15 weeks. No cracking was observed on the pre‐stressed specimens in the presence of steroid silicone rubber, even after 10 weeks implantation.
Evaluation of metallic personalized hemiarthroplasty: A canine patellofemoral model
Authors: Laberge Martine , Dennis Bobyn J. , Drouin G. , Rivard Charles H.
Published: December 2004

The purpose of this study was to characterize the response of articular cartilage to weight bearing against a metallic personalized hemiarthroplasty prosthesis. Ten dogs each underwent surgery in which an elastomeric replica of the left femoral patellar groove was made. Using this replica, a 0.5‐mm‐thick prosthesis was cast in Co‐Cr alloy and subsequently the surface was polished to a mirror finish which had a center line average roughness value in the range of human hemiarthroplasty implants. A second surgery was performed to resurface the left trochlea with this prosthesis. Five animals were sacrificed at 3 months and 5 at 6 months. Cartilage damage occurred primarily in the distal region of the patella, and was especially evident at 6 months. Mechanical indentation tests conducted on patellar cartilage in a saline bath at 37°C indicated both increased deformation and residual deformation in the affected areas, indicative of degenerative change. Areas of fibrillation with a depletion of proteoglycans were identified histologically. These areas were only superficial at 3 months but became more extensive at 6 months. Rheological analysis of the synovial fluid of tests joints indicated that a decrease in viscosity occurred from 3 to 6 months, an additional indicator of progressive degeneration. This novel implant model showed that even if a metallic hemiarthroplasty implant had an identical geometry as the joint surface being replaced and had a reasonably smooth surface, cartilage degeneration inevitably resulted.
Evaluation of hydroxylapatite/poly(l‐lactide) composites: Mechanical behavior
Authors: Verheyen C. C. P. M. , De Wijn J. R. , Van Blitterswijk C. A. , De Groot K.
Published: December 2004

By mixing hydroxylapatite (HA) into L(‐) dilactide monomer, prior to polymerization to poly(L‐lactide) (PLLA), hydroxylapatite filled poly(L‐lactide) composites were obtained. This study reports about the mechanical properties of these composites compared with unfilled PLLA. It was concluded that a 30 wt% HA/PLLA composite has better compressive and tensile strengths, higher stiffness and Vickers hardness number than unfilled PLLA (Mv: 125‐150,000). Gas sterilization (ethylene oxide) affects molecular weight and flexural strength significantly. Implantation studies revealed loss of 50% of initial flexural strength within 3 weeks, and a faster decline of flexural strength was observed in phosphate buffered saline than in the subcutis of goats. From a mechanical point of view storage at −20°C proved to be a safe method. In its current state HA/PLLA composites can not be used as implant materials that have to resist major forces. However, such composites might be useful in nonloadbearing applications in orthopedic or maxillofacial surgery. © 1992 John Wiley & Sons, Inc.
Cell‐Type‐Specific adhesion mechanisms mediated by fibronectin adsorbed to chemically derivatized substrata
Authors: Lewandowska Kristine , Pergament Edward , Sukenik Chaim N. , Culp Lloyd A.
Published: December 2004

Plasma fibronectin (pFN) adhesion mechanisms on inert substrata were evaluated for murine fibroblasts (3T3) and human neuroblastoma (Platt) cells using glass coverslips Chemically derivatized with a self‐assembled monolayer of aliphatic chains terminated with a specific endgroup to interact with adsorbed pFN: [CH3], [SH], [SCOCH3], NH2 [S03H] or underivatized glass [SiOH]. All surfaces bound similar amounts of pFN and facilitated attachment of both cell types within narrow ranges. However, spreading/differentiation responses of cells differed considerably among the surfaces. While 3T3 cells spread and developed microfilament stress fibers comparably on all surfaces, inclusion of an RGDScontaining synthetic peptide i n t h e medium revealed variation in resistance to stress fiber formation mediated by an RGDS‐recognizing integrin: [NH3] > [CH3] >> [SiOH],[SH],[SCOCH3]. Different patterns of neurite formation were observed for neuroblastoma cells: [SiOH], [NH3]. Similarity in cell responses to both [CH3] and [NH2] surfaces argues against pattern dependent upon the hydrophobicity of substrata. When pFN was diluted to a subsaturable concentration with albumin for adsorption, neuroblastoma responses changed significantly from those observed on pFN‐saturated surfaces, for both spreading and neurite generation: [NH2],[S03H] >> [SH], [SCOCH3] > [SiOH],[CH3]. Responses to the pFN :albumin mixture were markedly improved from responses after sequential adsorptions, demonstrating optimization of pFN conformation (not merely binding) by coadsorption of albumin molecules. In most cases, the [NH2] surface yielded responses distinctively different from the other surfaces. Overall, these data suggest many variations in the conformation of pFN molecules adsorbed to specific inert surfaces, as well as variations in the responses of cell surface receptors to conformationally specific pFNs. They also reveal cell‐type‐specific changes in differentiated cell responses on derivatized substrata, mediated by different classes of cell surface receptors for the two cell types, and provide optimism for regulating FN‐dependent adhesion mechanisms in either positive or negative contexts on biomaterial surfaces derivatized with one or more of these chemical end‐groups. © John Wiley & Sons, Inc.
The ultrastructure of the bone‐hydroxyapatite interface in vitro
Authors: de Bruijn J. D. , Klein C. P. A. T. , de Groot K. , van Blitterswijk C. A.
Published: December 2004

Rat bone marrow cells were cultured on plasma‐sprayed hydroxyapatite (HA). The cells formed a mineralized extracellular matrix (ECM) that exhibited several characteristics of bone tissue. The interface between this mineralized ECM and the HA was studied at the ultrastructural level with scanning and transmission electron microscopy and x‐ray microanalysis. Initially, the deposition of a globular, afibrillar matrix was observed on HA. This was followed by the integration of collagen fibers in this matrix and their subsequent mineralization. At the bone‐HA interface two distinctly different interfacial structures were observed. An electron‐dense layer with a thickness of 20‐60 nm was regularly present, which contained both organic and inorganic material and was rich in glycosaminoglycans. The interfaces differed however, in the presence or absence of an amorphous zone which was free of collagen fibers and had an average thickness of 0.7‐0.8 μm. It was frequently seen interposed between the electron‐dense layer and the hydroxyapatite. Similar interfacial structures have also been described in the in vivo environment, where they were referred to as lamina limitans‐like or cement linelike. From the results of this study, it can be concluded that the described in vitro system is a suitable model to study bonebiomaterial interactions. © 1992 John Wiley & Sons, Inc.
Storage and elimination of titanium, aluminum, and vanadium salts, in vivo
Authors: Merritt K. , Margevicius R. W. , Brown S. A.
Published: December 2004

Hamsters were injected with titanium, aluminum, and vanadium salts either intraperitoneally or intramuscularly to study the transport, storage, and elimination of these metals. Blood samples were taken at 4 h or 24 h, and urine samples were taken a t 24, 48, and 72 h. The hamsters were then injected weekly for 5 weeks after the initial injection. Blood and portions of the kidneys, liver, lung, and spleen were taken at sacrifice. All samples were analyzed for titanium, aluminum, and vanadium concentrations using graphite furnace atomic absorption spectroscopy (GFAAS). Titanium was found not to be excreted in the urine, was found in low levels in the blood, and was elevated over control in the kidney, liver, and spleen. Aluminum detection via GFAAS showed wide standard deviations and high levels in controls; however, aluminum was found to be excreted in the urine, and to be transported by the blood in the experimental animals. A small amount accumulated in the liver and spleen. Vanadium was excreted in high levels in the urine. A small amount was found in the blood, and the level in the organs was below the reliable detection limits. The rapid excretion of vanadium might be related to its solubility in physiological conditions, while the limited excretion of titanium may be related to its being insoluble in the physiologic environment. © 1992 John Wiley & Sons, Inc.
In vivo versus in vitro degradation of controlled release polymers for intracranial surgical therapy
Authors: Wu Mary P. , Tamada Janet A. , Brem Henry , Langer Robert
Published: December 2004

Intracranial studies to analyze the degradation kinetics of the bioerodible polymer poly[bis(p‐carboxyphenoxy)propane‐sebacic acid] [p(CPP‐SA) 20:80] copolymer wafers were conducted in a rat model. Rats were separated into four groups: those receiving (1) polymer, (2) polymer loaded with the chemotherapeutic agent BCNU,(3) drugloaded polymer with previous tumor implantation, and (4) polymer and an absorbable hemostatic material. A polymer wafer was surgically implanted into the brain of each animal. Residual polymer was harvested at varying times for chromatographic analysis. In vitro effects of pH, mixing, and water availability on degradation were also studied. The results of in vitro and in vivo studies were compared to understand the behavior of polymers in a clinical setting. We found that degradation of p(CPP‐SA) initially occurred more slowly in vivo than in vitro. The presence of BCNU, tumor, and absorbable hemostatic material did not affect the ultimate time of polymer degradation in vivo, and the intrinsic polymer degradation time of 1 mm thick p(CPP‐SA) 20:80 disks in vivo was 6–8 weeks. © 1994 John Wiley & Sons, Inc.
Evaluation of magnetic alginate beads as a solid support for positive selection of CD34+ cells
Authors: Pope Niedre M. , Alsop Roger C. , Chang Yu‐An , Smith Alan K.
Published: December 2004

Paramagnetic alginate beads with a 10–100 μm size range have been developed. These beads, when activated with chloroacetic anhydride and covalently coupled to avidin (30 μg/mg beads), were able to bind biotinylated goat anti‐mouse (B‐GAM) antibody (Ab). The beads with immobilized antibody were then used as a model system for the capture and non‐enzymatic release of CD34+ (KG1a) cells. A maximum of 82% KG1a (average = 65 ± 16.1%) cell capture, and 57% (average = 51 ± 5.9%) cell release has been attained using this model system. Optimization of the system in terms of further bead size reduction, and in terms of developing a system to recover released cells with high purity, will make an excellent system for cell capture and nonenzymatic release. © 1994 John Wiley & Sons, Inc.
Cell growth on poly(vinyl alcohol) hydrogel membranes containing biguanido groups
Authors: Iio Kokoro , Minoura Norihiko , Aiba Seiichi , Nagura Masanobu , Kodama Makoto
Published: December 2004

A cationic, high‐water‐content hydrogel membrane composed of poly(vinyl alcohol) (PVA) and poly(allylbiguanido‐co‐allylamine) hydrochloride (PAB) with positively charged biguanido groups that resemble arginine residues was developed. The PAB was prepared by reacting poly(allylamine) hydrochloride (PAA) with guanyl‐O‐methyl isourea. PAB/PVA hydrogel membranes were prepared by repeated freezing and thawing. For comparison, hydrogel membranes composed of PAA and PVA were also prepared. The interaction between these hydrogel membranes and mouse fibroblast (L929) was studied by a cell culture method. The PAB hydrogel blend had a relatively low percentage of initial cell attachment. The cell growth on the PAB hydrogel membranes showed a maximum at 5 mol % PAB content that was as high as commercially available plastic films. However, cells on hydrogel membranes with 50 mol % PAB content and 0 mol % PAB content (only PVA) did not seem to grow; neither did the 5/95 PAA/PVA membranes. Water contact angles of hydrogel membranes did not vary with the PAB content. Morphology of the cell attachment was observed by SEM. On the PAB blend hydrogel surfaces, cells were not spindle‐shaped and monolayers, but rather cells aggregated in spherical clusters. © 1994 John Wiley & Sons, Inc.
Biocompatibility of potential wound management products: Fungal mycelia as a source of chitin/chitosan and their effect on the proliferation of human F1000 fibroblasts in culture
Authors: Chung Lip Yong , Schmidt Richard J. , Hamlyn Paul F. , Sagar Brian F. , Andrew Andrea M. , Turner Terence D.
Published: December 2004

Aspergillus oryzae, Mucor mucedo, and Phycomyces blakesleeanus cultures were examined as sources of chitin/chitosan. The nitrogen content of the alkali‐treated mycelia/sporangiophores of A. oryzae, M. mucedo, and P. blakesleeanus was 2.52, 3.61, and 6.27% w/w, which relates to an estimated chitin content of 37, 52, and 91%, respectively. The effect of these fungal materials on the rate of proliferation of human F1000 fibroblasts in culture was examined. At 0.01% w/v, all three materials exhibited significant (P<.05) proproliferant activity over a period of 13 days. However, at 0.05% w/v, P. blakesleeanus further enhanced cell proliferation, whereas A. oryzae and M. mucedo produced a significant (P<.05) antiproliferant effect. Higher concentrations of P. blakesleeanus (0.1 and 0.5%) caused marked inhibition of F1000 cell proliferation when measured on days 3 and 6. Only the proproliferant effect of these fungal materials appears to correlate to their chitin content. Furthermore, the cytomorphology of the fibroblasts indicated that P. blakesleeanus, and to a lesser extent M. mucedo, possessed cell attractant properties, again correlating with chitin content. If developed for use as wound management materials, the sporangiophores of P. blakesleeanus and the mycelium of M. mucedo could possibly promote the growth of fibroblasts and provide a matrix for their anchorage, thus contributing to the granulation phase of the healing cascade. © 1994 John Wiley & Sons, Inc.
A semianalytic method for computing the concentration distribution in enzyme–substrate fast reaction systems
Authors: Tse‐Tsai Li , Zheng‐Wen Shi , Guo‐Qiang Zhou , Kuo‐Chen Chou
Published: December 2004

A semianalytic method is presented for computing the concentration distribution in enzyme–substrate fast reaction systems. By means of this method, not only can much computation work be saved but a semianalytic expression for the concentration distribution will be obtained. This expression is very useful for analysis and discussion of the kinetic characteristics of this kind of reaction system.
Carbodications. I. The structures and energies of C4H isomers
Authors: Chandrasekhar Jayaraman , Schleyer Paul Von Ragué , Krogh‐Jespersen Karsten
Published: December 2004

At high levels of ab initio theory (6‐31G*//4‐31G), the most stable C4H isomer is indicated to be the nonplanar cyclobutadiene dication (1a); the planar form, 1b, is indicated to be 7.5 kcal/mol less stable. The second most stable C4H isomer, the methylenecyclopropene dication, is indicated to prefer the perpendicular (2a) over the planar (2b) arrangement by 7 kcal/mol. The “anti van't Hoff” cyclo‐(HB)2CCH2 system (4), isoelectronic with 2, also prefers the perpendicular conformation (4a), and retains the CC double bond. The linear butatriene dication (3) is the least stable C4H species investigated. The perpendicular (D2d) arrangement (3a), permitting double allyl cationlike conjugation, is preferred over the planar D2h form (3b) by 26 kcal/mol. The heat of formation of the most stable form of C4H, 1a, is estimated to be 623–640 kcal/mol. This species should be thermodynamically stable toward dissociation into smaller charged fragments.
An algorithm for the generation of nuclear spin species and nuclear spin statistical weights
Authors: Balasubramanian K.
Published: December 2004

This article develops a set of algorithms for the computer generation of nuclear spin species and nuclear spin statistical weights potentially useful in molecular spectroscopy. These algorithms generate the nuclear spin species from group structures known as generalized character cycle indices (GCCIs). Thus the required input for these algorithms is just the set of all GCCIs for the symmetry group of the molecule which can be computed easily from the character table. The algorithms are executed and illustrated with examples.
Calculation of the average properties of atoms in molecules. II
Authors: Biegler‐könig Friedrich W. , Bader Richard F. W. , Tang Ting‐Hua
Published: December 2004

This article describes an algorithm for the calculation of the average properties of an atom in a molecule. The atom is defined within the topological theory of molecular structure, a theory which defines atoms, bonds, structure, and structural stability in terms of the topological properties of a system's charge distribution. The average properties of the atom so defined are uniquely determined by quantum mechanics. Results for a number of hydrocarbon molecules, obtained by the program PROAIM (properties of atoms in molecules) which implements this algorithm, are given. In general, this program enables one to calculate the average energy of an atom in a molecule to an accuracy of ±1 kcal/mol.
Coupled calculations of vibrational frequencies and intensities. III. IR and Raman spectra of ethylene oxide and ethylene sulfide
Authors: Spiekermann M. , Bougeard D. , Schrader B.
Published: December 2004

The experimental IR and Raman spectra of ethylene oxide have been reinvestigated with particular attention to the intensities. The absolute IR intensities have been measured for the gaseous state. The spectra have been simulated by using a normal coordinate analysis coupled with a CNDO determination of the intensities. The intensity calculation using polarization functions appears to be more reliable than the standard version. Furthermore, the force field has been extended for ethylene sulfide.
On evaluation of the characteristic polynomial for large molecules
Authors: Randić Milan
Published: December 2004

Existing schemes for evaluation of the characteristic polynomial of a graph suffer from limited practicality. Their application to large molecules inordinately increases the amount of labor. Here a procedure is outlined which is useful even for large molecules. It is based on a not widely known property of the collection of characteristic polynomials for Ulam's subgraphs, which, when added, give the derivative of the characteristic polynomial of the initial graph. The characteristic polynomials for Ulam's subgraphs are, as a rule, easier to derive due to the presence of many pending bonds in graphs of chemical interest. The last step requires an integration of a polynomial (which is a straightforward step) and determining the constant of integration, which represents the determinant of the adjacency matrix. The available methods for determing the additive constant (the determinant) are combinatorially much simpler than the initial task of finding all of the coefficients of the characteristic polynomial. The approach is illustrated on selected benzenoid hydrocarbons, nonbenzenoid, and nonalternant systems. Construction of the characteristic polynomials can be accelerated by considering auxiliary fragments and irreducible subgraphs separately and combining them in the final expression. Many auxiliary fragments allow their characteristic polynomials to be expressed in a closed form using recursive relations. The results for complex molecules can thus be written in a relatively compact form. Finally, the derivative of the characteristic polynomial, expressed in terms of selected auxiliary functions and irreducible components, can be integrated directly to give the result in terms of contributions signifying various fragments rather than as an explicit function of x.
Conformational analysis by energy embedding
Authors: Crippen Gordon M.
Published: December 2004

The distance geometry approach to conformational calculation has been shown to be very effective at producing large molecular structures satisfying many given, long‐range constraints on the interatomic distances. I now present a significant extension of the method that handles strictly geometric constraints as well as before while also locating conformers of very low energy. The main feature of the algorithm is a projection of the molecule from a low energy conformation in a high dimensional space to three dimensions in such a way as to perturb the energy as little as possible. Tests of the method on very small systems with simple energy functions completely explored by independent means show that the global minimum of energy is sometimes attained. In every case the final energy is very low, and geometric constraints are completely satisfied.
Ab‐Initio studies on π‐nonbonded and through‐bonds interactions in n‐alkanes, n‐alkyl radicals, and polymethylene diradicals
Authors: Lee Ikchoon , Cheun Young Gu , Yang Kiyull
Published: December 2004

Ab‐initio studies were conducted on quantitative aspects of π‐nonbonded, σ–σ*, n–σ*, and throughbond interactions in R1CH2(CH2)N–1 CH2 R2, where R1 and R2 are H and/or nonbonding AO, n, and N = 2, 3, and 4. Geometrical preferences were found to depend both on π‐nonbonding and bond–antibonding interactions, the latter being more important. Level orderings and energy splittings involved in the through‐bond interactions of diradicals can be qualitatively predicted by examining the signs of the overlap between the n orbitals and a common vicinal σ* bond orbital, using simple orbital patterns and paying special attention to the “backside” tails of bond orbitals.
Electronic states and barriers to internal rotation in silaallenes
Authors: Krogh‐jespersen Karsten
Published: December 2004

The electronic states and barriers to internal rotation in allene (1a), 1‐silaallene (2a), and 2‐silaallene (3a) are investigated computationally using ab‐initio molecular orbital methods. Planar geometries with two‐, three‐, and four‐π‐electron configurations have been considered as possible transition states (1b–3d). Structures have been optimized at the Hartree–Fock level with a small split valence basis set (3‐21G) and higher level calculations with basis sets of split valence (6‐31G) and split valence plus polarization function (6‐31G*) quality include correlation energy estimates from Møller–Plesset second‐and third‐order perturbation theory. The electronic barrier to internal rotation in allene is estimated near 53 kcal/mol whereas the corresponding barriers in 1‐silaallene and 2‐silaallene are considerably smaller, ca. 35 and 20 kcal/mol, respectively. The transition states are predicted to possess bent geometries in all three molecules with open‐shell singlet, three‐π‐electron configurations in 1 and 2 (1c, 2c) but a closed‐shell singlet, two‐π‐electron configuration in 3 (3d).
Digital emulation of analog computer techniques for the solution of kinetic systems
Authors: Titchener M. R. , Stimpfle R. M.
Published: December 2004

A low‐cost microcomputer and package of assembly language routines has been developed to emulate the structure and performance of a large analog computer. The advantages of the analog computer, as implemented in this scheme, include (1) a significant reduction in the programming effort involved in modeling complex dynamic systems and (2) the control of the simulation and model parameters in a completely interactive and flexible manner. The symbolic nomenclature and schematic representations involving devices, such as integrators, comparators, multipliers, and function generators, offers a powerful alternative to the more conventional numerical methods, that is, to provide very simply the solutions to large systems of differential equations. This approach invariably leads the user to a more thorough understanding of the dynamic character of the system. The technique is illustrated using a chemical kinetics example involving the simulation of laser‐induced fluorescence. The results of this work have provided an assessment of a systematic error that occurs when using induced resonance fluorescence to measure OH concentrations in the troposphere of the earth.
The thioketone–enethiol tautomerism of aliphatic thiocarbonyls: An ab initio study
Authors: Bruno Alfredo E. , Steer Ronald P. , Mezey Paul G.
Published: December 2004

Approximate minimum energy reaction paths have been calculated for two thioketone–enethiol tautomeric systems using an ab initio SCF–MO method. The calculations indicate nearly equal stabil ties of the isolated tautomers in both systems and an energy barrier of ca. 85 kcal/mol for their interconversion. This barrier is expected to be significantly lower in solution as a result of solvent–solute interactions.