Structure and fracture resistance of alligator gar (Atractosteus spatula) armored fish scales

The alligator gar is a large fish with flexible armor consisting of ganoid scales. These scales contain a thin layer of ganoine (microhardness ～2.5 GPa) and a bony body (microhardness ～400 MPa), with jagged edges that provide effective protection against predators. We describe here the structure of both ganoine and bony foundation and characterize the mechanical properties and fracture mechanisms. The bony foundation is characterized by two components: a mineralized matrix and parallel arrays of tubules, most of which contain collagen fibers. The spacing of the empty tubules is ～60 μm; the spacing of those filled with collagen fibers is ～7 μm. Using micromechanical testing of such scales in a variable-pressure scanning electron microscope, we identify interactions between propagating cracks and the microstructure, and show that the toughness of the scales increases with crack extension in a classical resistance-curve response from the activation of extrinsic toughening mechanisms. We demonstrate how mechanical damage evolves in these structures, and further identify that the reinforcement of the mineral by the network of collagen fibers is the principal toughening mechanism resisting such damage. Additionally, we define the anisotropy of the toughness of the scales and relate this to the collagen fiber orientation.     

Mechanical properties and the laminate structure of Arapaima gigas scales

The Arapaima gigas scales play an important role in protecting this large Amazon basin fish against predators such as the piranha. They have a laminate composite structure composed of an external mineralized layer and internal lamellae with thickness of 50–60 μm each and composed of collagen fibers with ∼1 μm diameter. The alignment of collagen fibers is consistent in each individual layer but varies from layer to layer, forming a non-orthogonal plywood structure, known as Bouligand stacking. X-ray diffraction revealed that the external surface of the scale contains calcium-deficient hydroxyapatite. EDS results confirm that the percentage of calcium is higher in the external layer. The micro-indentation hardness of the external layer (550 MPa) is considerably higher than that of the internal layer (200 MPa), consistent with its higher degree of mineralization. Tensile testing of the scales carried out in the dry and wet conditions shows that the strength and stiffness are hydration dependent. As is the case of most biological materials, the elastic modulus of the scale is strain-rate dependent. The strain-rate dependence of the elastic modulus, as expressed by the Ramberg–Osgood equation, is equal to 0.26, approximately ten times higher than that of bone. This is attributed to the higher fraction of collagen in the scales and to the high degree of hydration (30% H₂O). Deproteinization of the scale reveals the structure of the mineral component consisting of an interconnected network of platelets with a thickness of ∼50 nm and diameter of ∼500 nm.     

Mechanical and biological properties of keratose biomaterials

The oxidized form of extractable human hair keratin proteins, commonly referred to as keratose, is gaining interest as a biomaterial for multiple tissue engineering studies including those directed toward peripheral nerve, spinal cord, skin, and bone regeneration. Unlike its disulfide cross-linked counterpart, kerateine, keratose does not possess a covalently cross-linked network structure and consequently displays substantially different characteristics. In order to understand its mode(s) of action and potential for clinical translatability, detailed characterization of the composition, physical properties, and biological responses of keratose biomaterials are needed. Keratose was obtained from end-cut human hair fibers by peracetic acid treatment, followed by base extraction, and subsequent dialysis. Analysis of lyophilized keratose powder determined that it contains 99% proteins by mass with amino acid content similar to human hair cortex. Metallic elements were also found in minute quantities. Protein oxidation led to disulfide bond cleavage and drastic reduction of free thiols due to conversion of sulfhydryl to sulfonic acid, chain fragmentation, and amino acid modifications. Mass spectrometry identified the major protein constituents as a heterogeneous mixture of 15 hair keratins (type I: K31-35 and K37-39, and type II: K81-86) with small amounts of epithelial keratins which exist in monomeric, dimeric, multimeric, and even degraded forms. Re-hydration with PBS enabled molecular assembly into an elastic solid-like hydrogel. Highly-porous scaffolds formed by lyophilization of the gel had the compression behavior of a cellular foam material and reverted back to gel upon wetting. Cytotoxicity assays showed that the EC50 for various cell lines were attained at 8-10?mg/mL keratose, indicating the non-toxic nature of the material. Implantation in mouse subcutaneous tissue pockets demonstrated that keratose resorption follows a rectangular hyperbolic regression with 92% degradation by an 8-week time point. Keratose was shown to integrate with the host tissue as evidenced by infiltration of leukocytes and fibroblasts, bulk material angiogenesis, and minimal fibrous encapsulation. Tissue response benchmarks were superior in keratose compared to the control PLGA 90:10 mesh. Finally, the degraded keratose was observed to remodel with the natural collagen extracellular matrix, verifying the benefit of using keratose as a temporary matrix for regenerative medicine applications.     

Mechanical and biological properties of apatite composite resins

Well-crystallized hydroxyapatite was synthesized at 80 degrees C and pH 7.4, and mixed as filler with 2.2'(4-methacryloxydiethoxyphenyl) propane. BPO and DHPT were used as polymerization initiators. The compressive strength and Knoop hardness of the apatite composite resins increased with the increase of apatite content, and approached a plateau above an apatite-resin ratio (Ap/R) of 1. The thermal expansion coefficient of the composite with apatite-resin ratio Ap/R = 1 was almost equal to that of teeth. In tooth cavities, the composites seemed to adhere well to enamel without a bonding agent. The biocompatibility of the composites implanted hypodermically into rats appeared to improve with the increase of apatite content, and implants showed no significant inflammation after 1 wk and 4 wk.     

Fabrication, characterization, and biological assessment of multilayered DNA-coatings for biomaterial purposes

This study describes the fabrication of two types of multilayered coatings onto titanium by electrostatic self-assembly (ESA), using deoxyribosenucleic acid (DNA) as the anionic polyelectrolyte and poly-d-lysine (PDL) or poly(allylamine hydrochloride) (PAH) as the cationic polyelectrolyte. Both coatings were characterized using UV-vis spectrophotometry, atomic force microscopy (AFM), X-ray photospectroscopy (XPS), contact angle measurements, Fourier transform infrared spectroscopy (FTIR), and for the amount of DNA immobilized. The mutagenicity of the constituents of the coatings was assessed. Titanium substrates with or without multilayered DNA-coatings were used in cell culture experiments to study cell proliferation, viability, and morphology. Results of UV-vis spectrophotometry, AFM, and contact angle measurements clearly indicated the progressive build-up of the multilayered coatings. Furthermore, AFM and XPS data showed a more uniform build-up and morphology of [PDL/DNA]-coatings compared to [PAH/DNA]-coatings. DNA-immobilization into both coatings was linear, and approximated 3microg/cm(2) into each double-layer. The surface morphology of both types of multilayered DNA-coatings showed elevations in the nanoscale range. No mutagenic effects of DNA, PDL, or PAH were detected, and cell viability and morphology were not affected by the presence of either type of multilayered DNA-coating. Still, the results of the proliferation assay revealed an increased proliferation of primary rat dermal fibroblasts on both types of multilayered DNA-coatings compared to non-coated controls. The biocompatibility and functionalization of the coatings produced here, will be assessed in subsequent cell culture and animal-implantation studies.     

Isolation, characterization, and biological properties of an endotoxin-like material from the gram-positive organism Listeria monocytogenes.

The bacterial component responsible for the induction of transient cold agglutinin syndrome in rabbits after intravenous injection of heat-killed Listeria monocytogenes type 4B has been purified and biologically and chemically characterized. A purified immunoglobulin M cold agglutinin was prepared from high-titer sera resulting from the immunization of rabbits with heat-killed L. monocytogenes type 4B and was subsequently used to monitor the purification of the bacterial component responsible for its induction. The bacterial component was isolated from a hot phenol-water extract of lyophilized L. monocytogenes type 4B by multiple molecular sieve chromatography. Upon chemical analysis the purified material was found to be strikingly similar in chemical composition to gram-negative lipopolysaccharide endotoxins. The material contained 15% total fatty acid (of which 50% was beta-hydroxymyristic acid), 40 to 45% neutral sugar (glucose, galactose, and rhamnose), 11.5% amino sugar, 12% uronic acid, 2.5% 2-keto-3-deoxyoctonic acid, 2% heptose, 0.87% phosphorus, and 1.6% amino acid, thereby accounting for 85 to 90% of the weight of the component. Electron micrographs of the purified material were similar to those of lipopolysaccharide preparations from gram-negative organisms. The purified material exist in aqueous solutions as large aggregates, but can be dissociated into a single smaller subunit (3.1S) by dialysis against sodium dodecyl sulfate buffer. The listerial component was toxic and pyrogenic to rabbits, producing symptoms typical of gram-negative endotoxins. Activity in the limulus lysate gelation assay and in the carbocyanine dye assay provides a further link of this material with classical gram-negative endotoxins.     

Mechanical evaluation and design of a multilayered collagenous repair biomaterial

One method of fabricating implantable biomaterials is to utilize biologically derived, chemically modified tissues to form constructs that are both biocompatible and remodelable. Rigorous mechanical characterization is a necessary component in material evaluation to ensure that the constructs will withstand in vivo loading. In this study we performed an in-depth biaxial mechanical and quantitative structural analysis of GraftPatch (GP), a biomaterial constructed by assembling chemically treated layers of porcine small intestinal submucosa (SIS). The mechanical behavior of GP was compared to both native SIS and to glutaraldehyde-treated bovine pericardium (GLBP) as a reference biomaterial. Under biaxial loading, GP was found to be stiffer than native SIS and mechanically anisotropic, with the preferred fiber direction demonstrating greater stiffness. Quantitative structural analysis using small-angle light scattering indicated a uniform fiber structure similar to GLBP and SIS. To enable test-protocol-independent quantitative comparisons, the biaxial mechanical data were fit to an orthotropic constitutive model, which indicated a similar degree of mechanical anisotropy between the three groups. We also demonstrate how the constitutive model can be used to design layered biocomposite materials that can undergo large deformations.     

Mechanical and biological properties of photocurable oligolactide-HA composites investigated under accelerated degradation

The major concern related to biodegradable bone substitute materials is the loss of mechanical strength which can be undesirable when occurring too quickly before new bone formation. In this study, the multifunctional lactide oligomers having 2, 3, and 4 arms end capped with methacrylate groups were synthesized with the aim of improving the degradation properties. Their composites with hydroxyapatite (HA) were photopolymerized and subjected to accelerated degradation at 60 °C. The results showed that increasing number of arms significantly improved thermal and mechanical properties as well as biocompatibility of the composites. All composites although varying in number of arms had similar levels of bone-specific gene expression and calcification indicating their equal bioactivity in supporting bone formation. The high HA content in the composites was proposed to be responsible for enhanced osteoblast response, and this tended to suppress the effects of polymeric structure.     

多孔生物陶瓷与PVA水凝胶复合材料的制备与力学性能分析

目的将多孔生物陶瓷和聚乙烯醇(PVA)水凝胶交联成为一个仿生软骨-硬关节双层结构,并对该结构的微观形貌和力学性能进行分析。方法以羟基磷灰石(HA)为基体,采用添加碳酸氢铵(NH4HCO3)晶粒造孔的方式制备不同孔隙率的多孔羟基磷灰石生物陶瓷,以聚乙烯醇(PVA)为主要原料,环氧丙烷为交联剂,在多孔生物陶瓷表面及基体内交联制备出PVA水凝胶形成双层结构,对试样的断口形貌进行表征,对试样的拉伸强度和剪切强度等性能进行测试分析。结果交联的PVA水凝胶可以渗入到生物陶瓷基体表层以下的孔隙中,并且陶瓷基体和PVA水凝胶有很好的结合。随着多孔生物陶瓷孔隙率的增大,试样的最大拉伸和剪切负载均增大,平均孔隙率为70%试样的最大拉伸和剪切负载分别为153.61 N和64.46 N;而相应的拉伸和剪切强度略有下降,平均孔隙率为30%试样对应的最大拉伸和剪切强度分别为2.12 MPa和1.13 MPa。两者的失效形式均是因为裂纹的扩展,断口的微观形貌表明,断裂面存在明显的裂纹和内部缺陷,同时可观察出裂纹源和扩展方向。结论考虑到多孔生物陶瓷基体的强度,平均孔隙率为50%的多孔生物陶瓷的渗入效果适中,试样的拉伸强度和剪切强度、多孔生物陶瓷基体的压缩强度也有一定的保证,选择孔隙率为50%的试样较为合适。     

Mechanical properties and biological behavior of carbon nanotube/polycarbosilane composites for implant materials

Multiwalled carbon nanotube/polycarbosilane (MWCNT/PCS) composites were fabricated by the spark plasma sintering (SPS) method. The MWCNT/PCS composites consisted of MWCNTs and nanosized SiC particles pyrolyzed from PCS and possessing good mechanical properties for bone tissue repair or dental implantation. The MWCNT/PCS composites were implanted in the subcutaneous tissue and femur of rats at 1 and 4 weeks after implantation. Histological investigations showed that there was little inflammatory response in the subcutaneous tissue, and newly formed bone tissue was observed in the femur. These results indicated that the MWCNT/PCS composite had little prophlogistic effect and good osteoconductivity. The study suggested the possibility that the MWCNT/PCS composite could be a candidate bone-substitute and dental-implant material in the future.     

Factor structure of the McCarthy scales for males and females

Determined the factor structure of the McCarthy Scales (1972) for a referred group of male and female children, ages 6 to 81/2, from rural eastern North Carolina and compared their factor structure to that of the standardization sample. Three hundred and one males and 177 females were separated into two groups and examined independently. The 21 individual test scores of the McCarthy were correlated and then subjected to a principal factor analysis followed by Varimax rotation. Three meaningful factors emerged for males and females: Verbal, Perceptual, and Motor factors for males and General-Cognitive, Verbal, and Memory factors for females. The factor analyses for males and females agreed with previous factor analytic studies conducted with referred samples on the absence of a Quantitative factor and inconsistencies in the emergence of General-Cognitive and Memory factors. Coefficients of congruence with Kaufman's (1975) standardization analysis suggest that the McCarthy Scales reflect a general dimension of cognitive ability rather than a measure of distinct abilities for a referred sample of males and females.     

生物型人工韧带的体外检测和体内组织相容性的实验研究

目的:应用最新生化处理技术研制了一种以动物组织为原料的去抗原生物型人工韧带,检测其结构、力学性能及组织相容性,探讨应用去抗原生物型人工韧带重建膝关节叉韧带的可行性。方法:对动物肌腱/韧带组织进行环氧交联固定、多方位去抗原、力学增强改性以及表面活性修饰处理制得生物型人工韧带,应用组织学检查、扫描电镜、细胞培养及力学测试等多种方法分析生物型人工韧带的组织结构、生物力学特性和体内/体外组织相容性。结果:生物型人工韧带的外观与正常肌腱外观相似。组织学检查显示韧带为无细胞的胶原纤维。电镜检查显示韧带为走向一致的发状纤维样物紧密平行排列。异种骨髓基质细胞于韧带表面培养3周,可见细胞黏附并可见细胞分泌的基质沉积于细胞周围,韧带内部未见细胞。人工韧带平均直径约5 mm。在速度100 mm/m in条件下进行力学测试,平均最大拉力为927.19 N,抗拉强度47.22 N/mm2,与正常山羊的前交叉韧带(ACL)相应参数相近。人工韧带置换羊ACL术后12周,韧带表面可见滑膜组织覆盖并有小血管长入,术后52周人工韧带材料被新生的韧带替代,近关节面骨隧道内的人工韧带材料纤维周边可见韧带-纤维软骨-钙化软骨-骨的直接连接模式。结论:应用新的生化处理技术研制的生物型人工韧带有效地去除了猪肌腱的异种蛋白的免疫原性,具有良好的生物力学特性和组织相容性,作为膝关节叉韧带重建的韧带替换材料具有良好的应用前景。     

Mechanical properties, proteolytic degradability and biological modifications affect angiogenic process extension into native and modified fibrin matrices in vitro

During initial stages of wound healing, fibrin clots provide a three-dimensional scaffold that induces cell infiltration and regeneration. Here, L1Ig6, a ligand for alphavbeta3 integrin was covalently incorporated within fibrin matrices to explore it as a matrix-immobilized angiogenic factor. Incorporation at concentrations greater than 1 microg/ml reduced the fibrin crosslink density, as reflected by measurements of elastic modulus and swelling. The influence of crosslink density on endothelial cell process extension was characterized by modulating factor XIII concentrations in the coagulation mixture. At low incorporated concentrations of L1Ig6, it was possible to compensate gel elastic modulus via increased factor XIII, but not at high concentrations of L1Ig6. Similar findings were found when matrix swelling was analyzed. Fibrin crosslink density strongly influenced endothelial cell process extension, fewer and shorter processes were observed at high crosslink density. Matrix metalloproteinases (MMPs) were required for process extension and zymography and Western blots identified MMP-2 but not MMP-9. The amount of active MMP-2 increased for endothelial cells cultured in native and L1Ig6-modified matrices or when stimulated with VEGF-A165. The data indicate that distinct matrix properties can be tailored such that they become biologically stimulating and respond to cellular proteolytic activities, being a prerequisite for potential use of such matrices in biomedical applications.     

The hierarchical factor structure of the British ability scales

Wherry and Wherry (1969) hierarchical factor solutions were obtained on scale intercorrelations for three age groups (5:0 to 7:11, 8:0 to 13:11, 14:0 to 16:11) included in the standardization sample for the British Ability Scales. The ability hierarchy consisted of a general (g) factor and five primary factors at each of the three age levels. Three primary factors were evident at all three age levels, i. e., verbal ability (v), spatial-perceptual ability (k), and visual recall (VR). A naming (N) factor was obtained at the youngest age level (5:0 to 7:11) and a perceptual speed (ks) factor was obtained for the two older age groups (8:0 to 13:11 and 14:0 to 16:11). A short-term memory (STM) factor was obtained for the 14:0 to 16:11 age group and an achievement (A) factor was evident for the two younger age groups (5:0 to 7:11 and 8:0 to 13:11). After the extraction of factors most scales retained greater reliable specific variance than typically is found in ability measures. This suggests greater confidence in the specific interpretation of the individual scales than for other test batteries.     

Chemical, biological, and immunochemical properties of the Chlamydia psittaci lipopolysaccharide.

The lipopolysaccharide (LPS) of Chlamydia psittaci was extracted from yolk sac-grown elementary bodies, purified, and characterized chemically, immunochemically, and biologically. The LPS contained D-galactosamine, D-glucosamine, phosphorus, long-chain fatty acids, and 3-deoxy-D-manno-2-octulosonic acid in the molar ratio of approximately 1:2:2:6:5. The antigenic properties of the isolated LPS were compared with those of the LPS from Chlamydia trachomatis and Salmonella minnesota Re by the passive hemolysis and passive hemolysis inhibition tests, absorption, hydrolysis kinetics, and Western blot analysis with rabbit polyclonal antisera against chlamydiae and with a mouse monoclonal antibody recognizing a genus-specific epitope of chlamydial LPS. Two antigenic determinants were identified, one of which was chlamydia specific and the other of which was cross-reactive with Re LPS. Both determinants were destroyed during acid hydrolysis, whereby a third antigen specificity was exposed which was indistinguishable from the lipid A antigenicity. In rabbit polyclonal antisera prepared against Formalin-killed elementary bodies or detergent-solubilized membranes, two antibody specificities were differentiated. One of these was chlamydia specific, and the other was cross-reactive with Re LPS. The LPS of C. psittaci was inactive within typical endotoxin parameters (lethal toxicity, pyrogenicity, local Shwartzman reactivity); it was, however, active in some in vitro assays, such as those testing for mouse B-cell mitogenicity and the induction of prostaglandin E2 in mouse peritoneal macrophages.