Effect of collagen denaturation on the toughness of bone

Physiochemical effects of acid exposure on bone composition and function

Bone is primarily composed of collagen and apatite, two materials which exhibit a high sensitivity to pH dysregulation. As a result, acid exposure of bone, both clinically and in the laboratory is expected to cause compositional and mechanical changes to the tissue. Clinically, Metabolic acidosis (MA), a condition characterized by a reduced physiological pH, has been shown to have negative implications on bone health, including a decrease in bone mineral density and volume as well as increased fracture risk. The addition of bone-like apatite to ionic solutions such as phosphate buffered saline (PBS) and media has been shown to acidify the solution leading to bone acid exposure. Therefore, is it essential to understand how reduced pH physiochemically affects bone composition and in turn its mechanical properties. This study investigates the specific changes in bone due to physiochemical dissolution in acid. Excised murine bones were placed in PBS solutions at different pHs: a homeostatic pH level (pH 7.4), an acidosis equivalent (pH 7.0), and an extreme acidic solution (pH 5.5). After 5 days, the bones were removed from the solutions and characterized to determine compositional and material changes. We found that bones, without cells, were able to regulate pH via buffering, leading to a decrease in bone mineral content and an increase in collagen denaturation. Both of these compositional changes contributed to an increase in bone toughness by creating a more ductile bone surface and preventing crack propagation. Therefore, we conclude that the skeletal systems' physiochemical response to acid exposure includes multifaceted and spatially variable compositional changes that affect bone mechanics.

Causative or associative: A critical review of the role of advanced glycation end-products in bone fragility

The accumulation of advanced glycation end-products (AGEs) in the organic matrix of bone with aging and chronic disease such as diabetes is thought to increase fracture risk independently of bone mass. However, to date, there has not been a clinical trial to determine whether inhibiting the accumulation of AGEs is effective in preventing low-energy, fragility fractures. Moreover, unlike with cardiovascular or kidney disease, there are also no pre-clinical studies demonstrating that AGE inhibitors or breakers can prevent the age- or diabetes-related decrease in the ability of bone to resist fracture. In this review, we critically examine the case for a long-standing hypothesis that AGE accumulation in bone tissue degrades the toughening mechanisms by which bone resists fracture. Prior research into the role of AGEs in bone has primarily measured pentosidine, an AGE crosslink, or bulk fluorescence of hydrolysates of bone. While significant correlations exist between these measurements and mechanical properties of bone, multiple AGEs are both non-fluorescent and non-crosslinking. Since clinical studies are equivocal on whether circulating pentosidine is an indicator of elevated fracture risk, there needs to be a more complete understanding of the different types of AGEs including non-crosslinking adducts and multiple non-enzymatic crosslinks in bone extracellular matrix and their specific contributions to hindering fracture resistance (biophysical and biological). By doing so, effective strategies to target AGE accumulation in bone with minimal side effects could be investigated in pre-clinical and clinical studies that aim to prevent fragility fractures in conditions that bone mass is not the underlying culprit.

Diluted Acetic Acid Softened Intermuscular Bones from Silver Carp (Hypophthalmichthys molitrix) by Dissolving Hydroxyapatite and Collagen

Intermuscular bones (IBs) pose physical hazards that threaten consumer health and food safety. This study aimed to investigate the mechanism of softening IBs from silver carp with diluted acetic acid. IBs (separated from muscle) and fillets (without removing IBs) were treated with diluted acetic acid. Analyses of sensory attributes and the hardness of treated IBs indicated that diluted acetic acid (<10 mmol/L) could soften IBs effectively. Additionally, 0.5 mmol/L acetic acid softened IBs within fillets without significantly affecting the texture and flavor of fillets. Analyses of microstructure, minerals (calcium and phosphorus) and collagen content, and the Fourier transform infrared (FTIR) spectra of IBs indicated that acetic acid broke connections (formed by collagen that shared hydroxyl groups) between collagen molecules, and between collagen and hydroxyapatite (HAP), thus inducing the dissolution of collagen and HAP. The dissolution of HAP contributed more to IBs softening than collagen.

Environment-controlled water adsorption at hydroxyapatite/collagen interfaces

Water contributes to the structure of bone by coupling hydroxyapatite to collagen over the hierarchical levels of tissue organization. Bone water exists in two states, bound or mobile, each accomplishing different roles. Although many experimental studies show that the amount of bound water correlates with bone strength, a molecular understanding of the interactions between hydroxyapatite, collagen and water is missing. In this work, we unveil the water adsorption properties of bone tissues at the nanoscale using advanced density functional theory methods. We demonstrate that environmental factors such as collagen conformation or degree of confinement, rather than the surface itself, dictate the adsorption mode, strength and density of water on hydroxyapatite. While the results derived in this paper come from a simplified model of bone tissues, they are consistent with experimental observations and constitute a reasonable starting point for more realistic models of bone tissues. For example, we show that environmental changes expected in aging bone lead to reduced water adsorption capabilities, which is consistent with weaker bones at the macroscale. Our findings provide a new interpretation of molecular interactions in bone tissues with the potential to impact bone repair strategies.

Characterization of structural changes in modern and archaeological burnt bone: Implications for differential preservation bias

Structural and thermodynamic factors which may influence burnt bone survivorship in archaeological contexts have not been fully described. A highly controlled experimental reference collection of fresh, modern bone burned in temperature increments 100-1200˚C is presented here to document the changes to bone tissue relevant to preservation using Fourier transform infrared spectroscopy and X-ray diffraction. Specific parameters investigated here include the rate of organic loss, amount of bone mineral recrystallization, and average growth in bone mineral crystallite size. An archaeological faunal assemblage ca. 30,000 years ago from Tolbor-17 (Mongolia) is additionally considered to confirm visibility of changes seen in the modern reference sample and to relate structural changes to commonly used zooarchaeological scales of burning intensity. The timing of our results indicates that the loss of organic components in both modern and archaeological bone burnt to temperatures up to 700˚C are not accompanied by growth changes in the average crystallite size of bone mineral bioapatite, leaving the small and reactive bioapatite crystals of charred and carbonized bone exposed to diagenetic agents in depositional contexts. For bones burnt to temperatures of 700˚C and above, two major increases in average crystallite size are noted which effectively decrease the available surface area of bone mineral crystals, decreasing reactivity and offering greater thermodynamic stability despite the mechanical fragility of calcined bone. We discuss the archaeological implications of these observations within the context of Tolbor-17 and the challenges of identifying anthropogenic fire.

The association of osteochemometrics and bone mineral density in humans

OBJECTIVES

Even though much is known about bone mineral and matrix composition, studies about their relationship with several bone properties and its alterations related to bone diseases such as osteoporosis are practically non-existent in humans. Thus, the development of methods to understand the effects of bone properties at a microscopic level is paramount. This research aimed to evaluate whether Fourier transform infrared-attenuated total reflectance (FTIR-ATR) band intensity ratios correlate with femoral bone mass, bone mineral content (BMC) (total and femoral neck), bone mineral per unit area (BMD) (total, femoral neck, greater trochanter, intertrochanteric region, and Ward's area) and the area (total and femoral neck). A sample of femora from the 21st Century Identified Skeleton Collection (N = 78, 42 females and 36 males) was employed and BMC, BMD, and the femoral areas were acquired by DXA.

RESULTS

It was found that only females' BMD had a significant association with the femoral FTIR-ATR indices under study, whereas bone collagen (Am/P) and the content of carbonate Type A (API) in males correlated with the total proximal femur area of the regions of interest and the femoral neck area.

DISCUSSION

Men and women showed different changes related to their chemical composition in BMD, BMC, and probed area, most likely due to differences in structure and physiology, as well as mechanical strength in the proximal femoral sites where BMD was analyzed.

Raman spectroscopic determination of bone matrix quantity and quality augments prediction of human cortical bone mechanical properties

Being independent contributors to bone mechanical resistance at the apparent level, quality and quantity of bone primary constituents are essential factors in better fracture risk assessment. Raman spectroscopy (RS) holds great potential for being a clinical tool with providing quality and quantity measurements of the bone mineralized matrix. Beyond mineral quality and quantity, recent years have revealed newly developed RS-derived bone compositional measurements focusing on organic matrix and water though their associations with bone mechanics have not been fully established yet. Herein, the author reported first thorough characterization study investigating associations between twenty different RS-derived measurements and mechanical properties of human cortical bone (i.e., yield and ultimate strength, elastic modulus, toughness, post-yield toughness, and post-yield strain). Forty-five rectangular human cortical beams harvested from all four anatomical quadrants of two male donors were tested under three-point bending. Raman spectra of each specimen were collected at the spectral range of 800 to 4000 cm^-1. While correlations were tested among RS-derived measurements via Spearman's rank correlations, multivariate linear regression using mixed effects were used to determine the best RS-derived measurement or the combination of RS-derived measurements in predicting various mechanical properties of human cortical bone. Most of the RS-derived measurements were associated with the mechanical properties (Rm² ranges from 8.9 to 68.3%, p < 0.05). The various linear combinations of six RS-derived measurements focusing on different aspects of bone matrix (i.e., ν₁PO₄/Amide I, ν₁PO₄/Amide III, Carbonate/ν₁PO₄, ~I₁₆₇₀/I₁₆₄₀, ~I₃₄₅₃/I₂₉₄₉, ~I₃₅₈₄/I₂₉₄₉) improved the prediction (Rm² = 43.5 to 70.2%, p < 0.05). While a causal relationship still needs to be investigated, RS has a great potential to establish a robust patient-specific fracture risk prediction with the latest advances in technologies.

Relation between cross-sectional bone geometry and double zonal osteon frequency and morphology

OBJECTIVES

While double-zonal osteons (DZ) are characterized by a hyper-mineralized ring inside their lamellae, recent findings suggest that this ring is also defined by a change in the collagen fibers' orientation. Collagen and minerals are essential components to the maintenance of adequate bone strength and their alteration can modify the mechanical properties of the bone tissue. Consequently, the aim of this study is to explore the effect of past loads, as estimated from cross-sectional geometric properties, on the formation of DZ osteons compared to type I (common) osteons.

MATERIALS AND METHODS

The sample consists of paired humerus and femur midshaft sections (n = 23) of Eurocanadian settlers from the historical St. Matthew cemetery, Quebec City (1771-1860). Histomorphometric variables included in this study are osteon density for DZ and type I osteons (DZD; OPD), osteon area (DZOn.Ar; On. Ar), Haversian canal area (DZH.Ar; H.Ar), and the area within the hypermineralized ring (HR. Ar). Loading history is estimated from cross-sectional properties including the following variable: cortical and total area (CA, TA), maximum and minimum second moment of area (I_max , I_min ) and polar moment of area (J).

RESULTS

When the humerus and femur of the same individuals are compared, the femur has a higher OPD, DZD, and relative DZD (DZD/OPD). DZ osteons have a smaller area and Haversian canal area compared to type I osteons. The area within the hypermineralized ring in DZ is higher than the Haversian canal area of the type I osteons. Correlations between the residual scores of the regression of histomorphometric variables and cross-sectional properties of the humerus on the femur were not significant.

DISCUSSION

Based on the analysis of the entire cross-section, the lack of correlation between variations in cross-sectional properties and remodeling combined with the significant differences between humeri and femura suggests that the creation of DZ or type I osteons in the bone tissue might be due to a bone specific response, possibly related to differences in bone tissue age that needs to be further investigated. Definitive conclusion regarding biomechanical loads still seem to be premature as regional variations associated with mechanical properties remain to be explored.

Assessing matrix quality by Raman spectroscopy helps predict fracture toughness of human cortical bone

Developing clinical tools that assess bone matrix quality could improve the assessment of a person's fracture risk. To determine whether Raman spectroscopy (RS) has such potential, we acquired Raman spectra from human cortical bone using microscope- and fiber optic probe-based Raman systems and tested whether correlations between RS and fracture toughness properties were statistically significant. Calculated directly from intensities at wavenumbers identified by second derivative analysis, Amide I sub-peak ratio I₁₆₇₀/I₁₆₄₀, not I₁₆₇₀/I₁₆₉₀, was negatively correlated with K_init (N = 58; R² = 32.4%) and J-integral (R² = 47.4%) when assessed by Raman micro-spectroscopy. Area ratios (A₁₆₇₀/A₁₆₉₀) determined from sub-band fitting did not correlate with fracture toughness. There were fewer correlations between RS and fracture toughness when spectra were acquired by probe RS. Nonetheless, the I₁₆₇₀/I₁₆₄₀ sub-peak ratio again negatively correlated with K_init (N = 56; R² = 25.6%) and J-integral (R² = 39.0%). In best-fit general linear models, I₁₆₇₀/I_1640, age, and volumetric bone mineral density explained 50.2% (microscope) and 49.4% (probe) of the variance in K_init. I₁₆₇₀/I₁₆₄₀ and v₁PO₄/Amide I (microscope) or just I₁₆₇₀/I₁₆₄₀ (probe) were negative predictors of J-integral (adjusted-R² = 54.9% or 37.9%, respectively). While Raman-derived matrix properties appear useful to the assessment of fracture resistance of bone, the acquisition strategy to resolve the Amide I band needs to be identified.

Ribose pre-treatment can protect the fatigue life of γ-irradiation sterilized bone

Structural bone allografts are often sterilized with γ-irradiation to decrease infection risk, which unfortunately degrades the bone collagen connectivity, making the bone weak and brittle. In previous studies, we successfully protected the quasi-static mechanical properties of human cortical bone by pre-treating with ribose, prior to irradiation. This study focused on the quasi-static and fatigue tensile properties of ribose treated irradiated sterilized bone allografts. Seventy-five samples were cut from the mid-shaft diaphysis of human femurs into standardized dog-bone shape geometries for quasi-static and fatigue tensile testing. Specimens were prepared in sets of three adjacent specimens. Each set was made of a normal (N), irradiated (I) and ribose pre-treated + irradiation (R) group. The R group was incubated in a 1.2 M ribose solution before γ-irradiation. The quasi-static tensile and decalcified tests were conducted to failure under displacement control. The fatigue samples were tested under cyclic loading (10 Hz, peak stress of 45MP, minimum-to-maximum stress ratio of 0.1) until failure or reaching 10 million cycles. Ribose pre-treatment significantly improved significantly the mechanical properties of irradiation sterilized human bone in the quasi-static tensile and decalcified tests. The fatigue life of the irradiated group was impaired by 99% in comparison to the normal control. Surprisingly, the R-group has significantly superior properties over the I-group and N-group (p < 0.01, p < 0.05) (> 100%). This study shows that incubating human cortical bone in a ribose solution prior to irradiation can indeed improve the fatigue life of irradiation-sterilized cortical bone allografts.

Manipulating the Amount and Structure of the Organic Matrix Affects the Water Compartments of Human Cortical Bone

Being predictors of the mechanical properties of human cortical bone, bound and pore water measurements by magnetic resonance (MR) imaging are being developed for the clinical assessment of fracture risk. While pore water is a surrogate of cortical bone porosity, the determinants of bound water are unknown. Manipulation of organic matrix properties by oxidative deproteinization, thermal denaturation, or nonenzymatic glycation lowers bone toughness. Because bound water contributes to bone toughness, we hypothesized that each of these matrix manipulations affect bound water fraction (V_bw/V_bone). Immersing cadaveric bone samples in sodium hypochlorite (NaClO) for 96 hours did not affect tissue mineral density or cortical porosity, but rather decreased V_bw/V_bone and increased short‐T₂ pore water signals as determined by ¹H nuclear MR relaxometry (¹H NMR). Moreover, the post treatment V_bw/V_bone linearly correlated with the remaining weight fraction of the organic matrix. Heating bone samples at 110°C, 120°C, 130°C, and then 140°C (∼24 hours per temperature and rehydration for ∼24 hours before ¹H NMR analysis) did not affect V_bw/V_bone. After subsequently heating them at 200°C, V_bw/V_bone increased. Boiling bone samples followed by heating at 110°C, 120°C, and then 130°C in water under pressure (8 hours per temperature) had a similar effect on V_bw/V_bone. Raman spectroscopy analysis confirmed that the increase in V_bw/V_bone coincided with an increase in an Amide I subpeak ratio that is sensitive to changes in the helical structure of collagen I. Glycation of bone by ribose for 4 weeks, but not in glucose for 16 weeks, decreased V_bw/V_bone, although the effect was less pronounced than that of oxidative deproteinization or thermal denaturation. We propose that MR measurements of bound water reflect the amount of bone organic matrix and can be modulated by collagen I helicity and by sugar‐derived post translational modifications of the matrix. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Mechanical-chemical analyses and sub-chronic systemic toxicity of chemical treated organic bovine bone

Sequentially chemical-treated bovine bone was not only evaluated by mechanical and chemical analyses but also implanted into the gluteal muscles of rats for 12 weeks to investigate potential local pathological effects and systemic toxicities. The test (chemical treated bone) and control (heat treated bone) materials were compared using scanning electron microscope (SEM), x-ray diffraction pattern, inductively coupled plasma analysis, and bending strength test. In the SEM images, the micro-porous structure of heat-treated bone was changed to sintered ceramic-like structure. The structure of bone mineral from test and control materials was analyzed as100% hydroxyapatite. The ratio of calcium (Ca) to potassium (P), the main inorganic elements, was same even though the Ca and P percentages of the control material was relatively higher than the test material. No death or critical symptoms arose from implantation of the test (chemical treated bone) and control (physiological saline) materials during 12 weeks. The implanted sites were macroscopically examined, with all the groups showing non-irritant results. Our results indicate that chemical processed bovine bone has a better mechanical property than the heat treated bone and the implantation of this material does not produce systemic or pathological toxicity.

Dynamic Analysis of New Bone Obtained by Nonvascular Transport Distraction Osteogenesis in Canines

PURPOSE

The aim of the present study was to construct a nonvascular transport disc to repair the canine mandibular defects model and to perform a dynamic analysis of the new bone obtained by nonvascular transport distraction osteogenesis (NTDO) in canines.

MATERIALS AND METHODS

Thirty adult dogs were randomly divided into 3 groups, with 10 dogs in each group. Canine mandibular defect models of NTDO were constructed. All the dogs were marked by tetracycline hydrochloride at a different distraction stage. The dogs were euthanized at 2, 4, and 12 weeks after distraction, and the quality ratio of calcium and phosphate for the new bone was measured using electron dispersive spectroscopy.

RESULTS

The canine mandibular defects were successfully repaired. Using tetracycline hydrochloride, we successfully observed the quality and speed of new bone formation. The quality ratio of calcium and phosphate was similar between the new bone formation and the original bone. The time spent using a nonvascular transport disc to repair mandibular defects was consistent with using a vascularized transport disc, and the quality of the new bone and the original bone was exactly the same.

CONCLUSION

When the bone mass is insufficient or the conditions are not suitable for a vascularized transport disc, the nonvascular transport disc can be used as an alternative.

Collagen modifications in postmenopausal osteoporosis: advanced glycation endproducts may affect bone volume, structure and quality

The classic model of postmenopausal osteoporosis (PM-OP) starts with the depletion of estrogen, which in turn stimulates imbalanced bone remodeling, resulting in loss of bone mass/volume. Clinically, this leads to fractures because of structural weakness. Recent work has begun to provide a more complete picture of the mechanisms of PM-OP involving oxidative stress and collagen modifications known as advanced glycation endproducts (AGEs). On one hand, AGEs may drive imbalanced bone remodeling through signaling mediated by the receptor for AGEs (RAGE), stimulating resorption and inhibiting formation. On the other hand, AGEs are associated with degraded bone material quality. Oxidative stress promotes the formation of AGEs, inhibits normal enzymatically derived crosslinking and can degrade collagen structure, thereby reducing fracture resistance. Notably, there are multiple positive feedback loops that can exacerbate the mechanisms of PM-OP associated with oxidative stress and AGEs. Anti-oxidant therapies may have the potential to inhibit the oxidative stress based mechanisms of this disease.

Influence of thermodisinfection and duration of cryopreservation at different temperatures on pull out strength of cancellous bone

Thermodisinfection of human femoral heads from living donors harvested during hip joint replacement is an established processing procedure. This study was designed to examine the influence of heat sterilization on pull out strength of cancellous bone and storage at different temperatures up to 2 years since we had previously studied the storage of unprocessed cancellous bone. Porcine cancellous bone resembling human bone structure was obtained from 140 proximal humerus of 6-8 months old piglets. Pull out strength of screws after thermodisinfection was compared with unprocessed cancellous bone and tested immediately and after 6, 12 and 24 months of storage at -20 and -80 °C. A three-way ANOVA was performed and significance level was 5 %. The thermodisinfected bone showed a pull out force of 2729 N (1657-3568 N). The reduction of pull out strength compared with unprocessed bone over all periods of storage was 276 N on average with 95 % confidence interval ranging from 166 N to 389 N (p < 0.0001). Different freezing temperatures did not influence this mechanic property within 24 months storage and showed no difference compared with fresh frozen bone. Thermodisinfection of cancellous bone preserves tensile strength necessary for clinical purposes. The storage at -20 °C for at least 2 years did not show relevant decrease of pull out strength compared with -80 °C without difference between thermodisinfected and fresh frozen bone. The increase of the storage temperature to -20 °C for at least 2 years should be considered.

The microstructural and biomechanical development of the condylar bone: a review

BACKGROUND

Bone constantly strives for optimal architecture. Mandibular condyle, which is subjected to various mechanical loads forcing it to be highly adaptive, has a unique structure and a relatively high remodelling rate. Despite the eminent clinical relevance of mandibular condyle, literature on its structural and biomechanical development and on the mechanical role of its mineralized and non-mineralized bone components is scarce.

OBJECTIVE

The aim of the present review is to provide a brief introduction to basic bone mechanics and a synopsis of the growth and development of human mandibular condyle. Subsequently, the current ideas on the relationship between the structural and biomechanical properties of bone in general and of mandibular condyle in particular are reviewed. Finally, up-to-date knowledge from fundamental bone research will be blended with the current knowledge relevant to clinical dentistry, above all orthodontics.

METHODS

A comprehensive literature study was performed with an emphasis on recent and innovative work focusing on the interaction between microarchitectural and micromechanical properties of bone.

CONCLUSIONS

Mandibular condyle is a bone structure with a high bone turnover rate. Mechanical properties of mandibular condyle improve during adolescence and are optimal during adulthood. Local mineralization degree might not be a decisive determinant of the local bone tissue stiffness as was believed hitherto. Bone collagen and its cross links play a role in toughness and tensile strength of bone but not in its compressive properties. Clinical procedures might affect mandibular condyle, which is highly reactive to changes in its mechanical environment.

The relationships between femoral cortex geometry and tissue mechanical properties

Bone tissue and geometry are constantly modified through modeling and remodeling at the periosteal, endosteal and intracortical envelopes. Results from several studies indicate that femoral bone geometry is a predictor of whole bone strength (e.g. femoral neck strength), however, it is not known whether there is a relationship between bone structural and material properties. Bone geometry can be determined from parameters based on plane X-ray radiogrammetry which are used to evaluate femoral bone quality for implant success. If there is a relationship between these parameters and tissue mechanical properties, this would have implications in the interpretation of such parameters for assessment of fracture risk and in further understanding of bone biology. Following measurement of radiogrammetric parameters from antero-posterior and medio-lateral X-rays (cortical thickness, bone diameter, bone area, moment of inertia, cortical index, Singh index), human femurs were machined into standard test specimens for assessment of tensile fracture toughness (GIc) of the tissue. Results indicated that tensile fracture toughness generally increased with increasing bone size. We also found that fracture toughness of the tissue was significantly related to radiogrammetric indices and that some of these indices explained a greater variability in toughness than porosity, age or gender.

In vitro non-enzymatic ribation reduces post-yield strain accommodation in cortical bone

Non-enzymatic glycation (NEG) and advanced glycation endproducts (AGEs) may contribute to bone fragility in various diseases, ageing, and other conditions by modifying bone collagen and causing degraded mechanical properties. In this study, we sought to further understand how collagen modification in an in vitro non-enzymatic ribation model leads to loss of cortical bone toughness. Previous in vitro studies using non-enzymatic ribation reported loss of ductility in the cortical bone. Increased crosslinking is most commonly blamed for these changes; however, some studies report positive correlations between measures of total collagen crosslinking and work-to-fracture/toughness measurements whilst correlations between general NEG and measures of ductility are often negative. Fifteen bone beam triplets were cut from bovine metatarsi. Each provided one native non-incubated control, one incubated control and one ribated specimen. Incubation involved simulated body fluid±ribose for fourteen days at 37°C. Pentosidine and pyridinoline crosslinks were measured using HPLC. Three-point bending tests quantified mechanical properties. Fracture surfaces were examined using scanning electron microscopy. The effects of ribation on bone collagen molecular stability and intermolecular connectivity were investigated using differential scanning calorimetry and hydrothermal isometric tension testing. Ribation caused increased non-enzymatic collagen modification and pentosidine content (16mmol/mol collagen) and inferior post-yield mechanical behaviour, especially post-yield strain and flexural toughness. Fracture surfaces were smoother with less collagen fibril deformation or tearing than observed in controls. In the ribated group only, pentosidine content and thermomechanical measures of crosslinking were positively correlated with measures of strain accommodation and energy absorption before failure. Non-enzymatic ribation and the resulting modifications reduce cortical bone pseudo-plasticity through a reduced capacity for post-yield strain accommodation. However, the positive correlations we have found suggest that increased crosslinking may not provide a complete explanation for this embrittlement.

Effects of low-intensity electromagnetic fields on the proliferation and differentiation of cultured mouse bone marrow stromal cells

BACKGROUND

Electromagnetic fields (EMFs) used in stem-cell tissue engineering can help elucidate their biological principles.

OBJECTIVE

The aim of this study was to investigate the effects of low-intensity EMFs on cell proliferation, differentiation, and cycle in mouse bone marrow stromal cells (BMSCs) and the in vivo effects of EMFs on BMSC.

METHODS

Harvested BMSCs were cultured for 3 generations and divided into 4 groups. The methylthiotetrazole (MTT) assay was used to evaluate cell proliferation, and alkaline phosphatase activity was measured via a colorimetric assay on the 3rd, 7th, and 10th days. Changes in cell cycle also were analyzed on the 7th day, and bone nodule formation was analyzed on the 12th day. Additionally, the expression of the collagen I gene was examined by reverse transcription-polymerase chain reaction (RT-PCR) on the 10th day. The BMSCs of the irradiated group and the control group were transplanted into cortical bone of different mice femurs separately, with poly(lactic-co-glycolic acid) (PLGA) serving as a scaffold. After 4 and 8 weeks, bone the bone specimens of mice were sliced and stained by hematoxylin and eosin separately.

RESULTS

The results showed that EMFs (0.5 mT, 50 Hz) accelerated cellular proliferation, enhanced cellular differentiation, and increased the percentage of cells in the G(2)/M+S (postsynthetic gap 2 period/mitotic phase + S phase) of the stimulation. The EMF-exposed groups had significantly higher collagen I messenger RNA levels than the control group. The EMF + osteogenic medium-treated group readily formed bone nodules. Hematoxylin and eosin staining showed a clear flaking of bone tissue in the irradiated group.

CONCLUSION

Irradiation of BMSCs with low-intensity EMFs (0.5 mT, 50 Hz) increased cell proliferation and induced cell differentiation. The results of this study did not establish a stricter animal model for studying osteogenesis, and only short-term results were investigated. Further study of the mechanism of EMF is needed.

Differential effects of PPAR-{gamma} activation versus chemical or genetic reduction of DPP-4 activity on bone quality in mice

Patients with type 2 diabetes mellitus have an increased risk of fracture that can be further exacerbated by thiazolidinediones. A new class of antidiabetic agents control glucose through reduction of dipeptidyl peptidase-4 (DPP-4) activity; however the importance of DPP-4 for the control of bone quality has not been extensively characterized. We compared the effects of the thiazolidinedione pioglitazone and the DPP-4 inhibitor sitagliptin on bone quality in high-fat diet (HFD)-fed wild-type mice. In complementary studies, we examined bone quality in Dpp4(+/+) vs. Dpp4(-/-) mice. Pioglitazone produced yellow bones with greater bone marrow adiposity and significantly reduced vertebral bone mechanics in male, female, and ovariectomized (OVX) HFD fed female mice. Pioglitazone negatively affected vertebral volumetric bone mineral density, trabecular architecture, and mineral apposition rate in male mice. Sitagliptin treatment of HFD-fed wild-type mice significantly improved vertebral volumetric bone mineral density and trabecular architecture in female mice, but these improvements were lost in females after OVX. Genetic inactivation of Dpp4 did not produce a major bone phenotype in male and female Dpp4(-/-) mice; however, OVX Dpp4(-/-) mice exhibited significantly reduced femoral size and mechanics. These findings delineate the skeletal consequences of pharmacological and genetic reduction of DPP-4 activity and reveal significant differences in the effects of pioglitazone vs. sitagliptin vs. genetic Dpp4 inactivation on bone mechanics in mice.

The critical barrier to progress in dentine bonding with the etch-and-rinse technique

OBJECTIVES

The lack of durability in resin-dentine bonds led to the use of chlorhexidine as MMP-inhibitor to prevent the degradation of hybrid layers. Biomimetic remineralisation is a concept-proven approach in preventing the degradation of resin-dentine bonds. The purpose of this study is to examine the integrity of aged resin-dentine interfaces created with a nanofiller-containing etch-and-rinse adhesive after the application of these two approaches.

METHODS

The more established MMP-inhibition approach was examined using a parallel in vivo and in vitro ageing design to facilitate comparison with the biomimetic remineralisation approach using an in vitro ageing design. Specimens bonded without chlorhexidine exhibited extensive degradation of the hybrid layer after 12 months of in vivo ageing.

RESULTS

Dissolution of nanofillers could be seen within a water-rich zone within the adhesive layer. Although specimens bonded with chlorhexidine exhibited intact hybrid layers, water-rich regions remained in those hybrid layers and degradation of nanofillers occurred within the adhesive layer. Specimens subjected to in vitro biomimetic remineralisation followed by in vitro ageing demonstrated intrafibrillar collagen remineralisation within hybrid layers and deposition of mineral nanocrystals in nanovoids within the adhesive.

CONCLUSIONS

The impact was realized by understanding the lack of an inherent mechanism to remove water from resin-dentine interfaces as the critical barrier to progress in bonding with the etch-and-rinse technique. The experimental biomimetic remineralisation strategy offers a creative solution for incorporating a progressive hydration mechanism to achieve this goal, which warrants its translation into a clinically applicable technique.

Effect of outer mandibular cortex osteotomy on local morphology and biomechanics in young miniature pigs

AIM

The purpose of this study was to research the effect of outer mandibular cortex osteotomy on local morphology and biomechanics in young miniature pigs.

METHODS

Eight 3-month-old miniature pigs were used as experimental animals to establish an animal model for removing the outer cortex of the mandibular body, and the changes in local morphology, fine structure, and biomechanics of the mandible after the operation were evaluated.

RESULTS

The thickness of the operated side decreased to a greater extent than that of the control side. Further, local histologic structure and biomechanics characteristics could be recovered under stress conditions and were close to those of the normal side after the operation. However, some animals (37.5%) exhibited mandible deviation after operation.

CONCLUSION

Under normal conditions, mandibular outer cortex osteotomy should not be performed in the case of children.

Effect of marine collagen peptides on long bone development in growing rats

BACKGROUND

Nutritional factors play an important role in skeletal development during growth. However, the absorption rates of many bone-related minerals are relatively low from traditional diets, especially for people in Asia and Africa. In the present study, the effect of marine collagen peptides (MCP) derived from chum salmon (Oncorhynchus keta) skin on the development of femurs in growing rats of both sexes was investigated.

RESULTS

MCP supplementation could increase the size, mineral density, dry weight, ash weight, content of most minerals and both stiffness and toughness of femurs in male growing rats. However, such effects were milder in female rats. The reported increase in mineral density was likely to be related to increased osteoblast activity rather than a decreased rate of bone resorption, as an increase in serum osteocalcin and bone-specific alkaline phosphatase content was observed, but no significant difference in serum N-terminal telopeptide of type I collagen compared with control was found.

CONCLUSION

MCP supplementation could promote the development of long bones in growing male rats.

Fluoride effects on bone formation and mineralization are influenced by genetics

INTRODUCTION

A variation in bone response to fluoride (F(-)) exposure has been attributed to genetic factors. Increasing fluoride doses (0 ppm, 25 ppm, 50 ppm, 100 ppm) for three inbred mouse strains with different susceptibilities to developing dental enamel fluorosis (A/J, a "susceptible" strain; SWR/J, an "intermediate" strain; 129P3/J, a "resistant" strain) had different effects on their cortical and trabecular bone mechanical properties. In this paper, the structural and material properties of the bone were evaluated to explain the previously observed changes in mechanical properties.

MATERIALS AND METHODS

This study assessed the effect of increasing fluoride doses on the bone formation, microarchitecture, mineralization and microhardness of the A/J, SWR/J and 129P3/J mouse strains. Bone microarchitecture was quantified with microcomputed tomography and strut analysis. Bone formation was evaluated by static histomorphometry. Bone mineralization was quantified with backscattered electron (BSE) imaging and powder X-ray diffraction. Microhardness measurements were taken from the vertebral bodies (cortical and trabecular bones) and the cortex of the distal femur.

RESULTS

Fluoride treatment had no significant effect on bone microarchitecture for any of the strains. All three strains demonstrated a significant increase in osteoid formation at the largest fluoride dose. Vertebral body trabecular bone BSE imaging revealed significantly decreased mineralization heterogeneity in the SWR/J strain at 50 ppm and 100 ppm F(-). The trabecular and cortical bone mineralization profiles showed a non-significant shift towards higher mineralization with increasing F(-) dose in the three strains. Powder X-ray diffraction showed significantly smaller crystals for the 129P3/J strain, and increased crystal width with increasing F(-) dose for all strains. There was no effect of F(-) on trabecular and cortical bone microhardness.

CONCLUSION

Fluoride treatment had no significant effect on bone microarchitecture in these three strains. The increased osteoid formation and decreased mineralization heterogeneity support the theory that F(-) delays mineralization of new bone. The increasing crystal width with increasing F(-) dose confirms earlier results and correlates with most of the decreased mechanical properties. An increase in bone F(-) may affect the mineral-organic interfacial bonding and/or bone matrix proteins, interfering with bone crystal growth inhibition on the crystallite faces as well as bonding between the mineral and organic interface. The smaller bone crystallites of the 129P3/J (resistant) strain may indicate a stronger organic/inorganic interface, reducing crystallite growth rate and increasing interfacial mechanical strength.

Bisphosphonate treatment in the oim mouse model alters bone modeling during growth

Osteogenesis imperfecta (OI) is a heritable disease, which results from an abnormal amount or structure of Type I collagen. Bisphosphonates, a class of synthetic antiresorptive drugs, used in osteoporosis management, are also used to decrease fracture incidence and improve quality of life in children with OI. In this study, we used the oim mouse to test the hypotheses that pamidronate treatment during active growth (1) produces larger, stronger, stiffer long bone diaphyses without altering bone material properties, and (2) negatively impacts longitudinal bone growth. Our results indicate that femoral cross-sectional moment of inertia in the distal metaphysis tended to increase with pamidronate treatment and that the treated bones are thicker and structurally stiffer, but shorter than their control-dose counterparts.

Osteopenia and osteoporosis in adult baboons (Papio hamadryas)

BACKGROUND

Little is known about the degree to which baboons, an important animal model in skeletal research, spontaneously experience age-related osteopenia and osteoporosis.

METHODS

We measured bone mineral density (BMD) in 667 baboons, assigned T-scores to older animals based on sex-specific young adult reference groups, and compared reproductive history in older females with low BMD to those with normal BMD.

RESULTS

Approximately 25% of older baboon females were osteopenic. No females or males were osteoporotic. Neither parity nor interbirth interval spine clearly distinguished low vs. normal BMD groups. Intersite correspondence in low BMD was highest between sites in the same region rather than sites of the same bone type.

CONCLUSION

As with humans, osteopenia is common among older females. The absence of osteoporotic animals may be due to colony maintenance resulting in truncation of the aged population and selection for healthier animals in the oldest ranges.

Modeling the onset and propagation of trabecular bone microdamage during low-cycle fatigue

Relatively small amounts of microdamage have been suggested to have a major effect on the mechanical properties of bone. A significant reduction in mechanical properties (e.g. modulus) can occur even before the appearance of microcracks. This study uses a novel non-linear microdamaging finite-element (FE) algorithm to simulate the low-cycle fatigue behavior of high-density trabecular bone. We aimed to investigate if diffuse microdamage accumulation and concomitant modulus reduction, without the need for complete trabecular strut fracture, may be an underlining mechanism for low-cycle fatigue failure (defined as a 30% reduction in apparent modulus). A microCT constructed FE model was subjected to a single cycle monotonic compression test, and constant and variable amplitude loading scenarios to study the initiation and accumulation of low-cycle fatigue microdamage. Microcrack initiation was simulated using four damage criteria: 30%, 40%, 50% and 60% reduction in bone element modulus (el-MR). Evaluation of structural (apparent) damage using the four different tissue level damage criteria resulted in specimen fatigue failure at 72, 316, 969 and 1518 cycles for the 30%, 40%, 50% and 60% el-MR models, respectively. Simulations based on the 50% el-MR model were consistent with previously published experimental findings. A strong, significant non-linear, power law relationship was found between cycles to failure (N) and effective strain (Deltasigma/E(0)): N=1.394x10(-25)(Deltasigma/E(0))(-12.17), r(2)=0.97, p<0.0001. The results suggest that microdamage and microcrack propagation, without the need for complete trabecular strut fracture, are mechanisms for high-density trabecular bone failure. Furthermore, the model is consistent with previous numerical fatigue simulations indicating that microdamage to a small number of trabeculae results in relatively large specimen modulus reductions and rapid failure.

Fracture toughness and work of fracture of hydrated, dehydrated, and ashed bovine bone

Bone, a tri-phase composite, consists of nano-sized apatite minerals, an organic component, and water. Heat-treated bovine cortical bone has been proposed as a candidate for void-filling bone substitute. However, the toughness of heat-treated bone is not yet fully studied. Fracture toughness (K(c)) and work of fracture (W(f)) of hydrated, dehydrated, and ashed bovine bone were estimated using a single-edge V-notched beam method. Thermal gravimetric analysis and differential thermal analysis were used to determine the temperature at which the organics and water were removed. Dehydrated specimens were obtained by placing the samples in a 60 degrees C vacuum oven for 24h or a 110 degrees C furnace for 2h. Ashed specimens were obtained by heat-treating samples at 600 degrees C for 24h. K(c) of bovine specimens decreased from 5.5MPa.m(1/2) for hydrated bone, to 3.8MPa.m(1/2) for dehydrated specimens, and to 0.36MPa.m(1/2) for ashed specimens. W(f) decreased from 7.1 to 1.1kJ/m(2) for dehydrated specimens, and to 0.04kJ/m(2) for ashed specimens. The main reasons for the significant decreases in K(c) and W(f) may be attributed to water's ability in stabilizing collagen structure and to the organics' ability in making bone more ductile. Because of the large decrease in fracture toughness and work of fracture, we suggest that ashed bone is not appropriate for load-bearing bone substitute in areas where bone experiences loadings in flexure.

Influence of interimplant distance on bone microstructure: a histomorphometric study in dogs

The microstructure of the crestal alveolar bone is important for both the maintenance of osseointegration and the location of the gingival soft tissues. The aim of this study was to evaluate and compare the bone microstructure of the alveolar bone and of the interimplant bone in implants inserted at different interimplant distances. The mandibular bilateral premolars of six dogs were extracted, and after 12 weeks, each dog received eight implants, for a total of 48 implants. Two pairs of implants, one for each hemiarch, were separated by 2 mm (group 1) and by 3 mm (group 2). After 12 weeks, the implants received temporary acrylic prostheses. After four more weeks, metallic crowns substituted the temporary prostheses. After an additional 8 weeks the animals were sacrificed and the hemimandibles were removed, dissected, and processed. The longitudinal collagen fiber orientation was 43.2% for the alveolar bone; it was 30.3% for the 2-mm group and 43.9% for the 3-mm group. There was a statistically significant difference between the 2-mm and 3-mm groups (p < .05). The orientation of transverse collagen fibers was 47.8% for the alveolar bone; it was 37.3% for the 2-mm group and 56.3% for the 3-mm group. There was a statistically significant difference between the 2-mm and 3-mm groups (p < .05). The marrow spaces were 34.87% for the alveolar bone, 52.3% for the 2-mm group, and 59.9% for the 3-mm group. There was a statistically significant difference between the alveolar bone and the 3-mm group (p < .05). The low mineral density index was 36.29 for the alveolar bone, 46.76 for the 2-mm group, and 17.91 for the 3-mm group. There was a statistically significant difference between the 2-mm and 3-mm groups (p < .05). The high mineral density was 87.57 for the alveolar bone, 72.58 for the 2-mm group, and 84.91 for the 3-mm group. There was a statistically significant difference between the alveolar bone and the 2-mm group (p < .05). The collagen fiber orientation resulted in statistically significant differences in both the 2-mm and 3-mm groups compared with the alveolar bone. The marrow spaces appeared significantly increased in the 3-mm group compared with the alveolar bone. The low mineral density index was significantly higher in the 2-mm group, while the high mineral density index was significantly higher in the alveolar bone. In conclusion, the interimplant distance should not be less than 3 mm.

Age-related factors affecting the postyield energy dissipation of human cortical bone

The risk of bone fracture depends in part on tissue quality, not just the size and mass. This study assessed the postyield energy dissipation of cortical bone in tension as a function of age and composition. Specimens were prepared from tibiae of human cadavers in which male and female donors were divided into two age groups: middle aged (51 to 56 years, n = 9) and elderly (72 to 90 years, n = 8). By loading, unloading, and reloading a specimen with rest periods inserted in between, tensile properties at incremental strain levels were assessed. In addition, postyield toughness was estimated and partitioned as plastic strain energy related to permanent deformation, released elastic strain energy related to stiffness loss, and hysteresis energy related to viscous behavior. Porosity, mineral and collagen content, and collagen crosslinks of each specimen were also measured to determine the micro- and ultrastructural properties of the tissue. Age affected all the energy terms plus strength but not elastic stiffness. The postyield energy terms were correlated with porosity, pentosidine (a marker of nonenzymatic crosslinks), and collagen content, all of which varied significantly with age. General linear models suggested that pentosidine concentration and collagen content provided the best explanation of the age-related decrease in the postyield energy dissipation. Among them, pentosidine concentration had the greatest contribution to plastic strain energy and was the best explanatory variable of damage accumulation.

Effects of non-enzymatic glycation on cancellous bone fragility

Post-translational modifications of collagen, such as non-enzymatic glycation (NEG), occur through the presence of extracellular sugars and cause the formation of advanced glycation end-products (AGEs). While AGEs have been shown to accumulate in a variety of collagenous human tissues and alter the tissues' functional behavior, the role of AGEs in modifying the mechanical properties of cancellous bone is not well understood. In this study, an in vitro ribosylation model was used to examine the effect of NEG on the mechanical behavior of cancellous bone. Cancellous bone cores and individual trabeculae were harvested from the femoral heads of eight fresh human cadavers and paired for ribosylation and control treatments. The cores were subjected to either unconfined compression tests or were demineralized and subjected to stress relaxation tests. The trabeculae were loaded to fracture in four-point bending. In vitro NEG significantly reduced the energy dissipation characteristics of the organic matrix as well as the post-yield properties including the stiffness loss of the individual trabeculae (p<0.05) and the damage fraction of cancellous bone (p<0.001). AGEs in cancellous bone cores from both treatment groups correlated with damage fraction (r(2)=0.36, p<0.05) and post-yield strain energy (r(2)=0.21, p<0.05); and with energy dissipation characteristics of the organic matrix (r(2)=0.35, p<0.05). In the control group, AGEs content increased up to six-fold with age (r(2)=0.95, p<0.008). This study shows that cancellous bone is susceptible to NEG that increases its propensity to fracture. Moreover, despite tissue turnover, cancellous bone may be susceptible to an age-related accumulation of AGEs.

A novel scratching approach for measuring age-related changes in the in situ toughness of bone

A scratch test using a nanoindentation system was proposed in this study to assess the age-related changes in the in situ toughness of bone matrix at ultrastructural levels. A tissue removal energy density (u(r)) was defined and estimated as the work done by the scratch (U(T)) divided by the total volume of the scratch groove (u(s)). The value of u(s) was used as a relative measure of the in situ toughness of the tissue. Human cortical bone specimens obtained from middle-aged (between 49 and 59 years old) and elderly groups (over 69 years old) were tested using this technique. A significant difference in the estimated removal energy density (u(s)) in the secondary osteons was found between the middle-aged and elderly groups (5.49+/-0.696 vs. 4.09+/-1.30 N/mm(2), respectively).

Bone Strength: The Whole Is Greater Than the Sum of Its Parts

OBJECTIVE

To summarize the current knowledge regarding the various determinants of bone strength.

METHODS

Relevant English-language articles acquired from Medline from 1966 up to January 2005 were reviewed. Searches included the keywords bone AND 1 of the following: strength, remodeling, microcrack, structur*, mineralization, collagen, organic, crystallinity, osteocyte, porosity, diameter, anisotropy, stress risers, or connectivity. Abstracts from applicable conference proceedings were also reviewed for pertinent information.

RESULTS

Bone strength is determined from both its material and its structural properties. Material properties such as its degree of mineralization, crystallinity, collagen characteristics, and osteocyte viability have substantial impacts on bone strength. Structural properties such as the diameter and thickness of the cortices, the porosity of the cortical shell, the connectivity and anisotropy of the trabecular network, the thickness of trabeculae, and the presence of trabecular stress risers and microcracks impact bone strength in diverse manners. Remodeling activity either directly or indirectly impacts all of these processes.

CONCLUSIONS

Bone strength is dependent on numerous, interrelated factors. Remodeling activity has a direct impact on almost all of the components of bone strength and requires further investigation as to its impact on these factors in isolation and in unison.

Do sacrificial bonds affect the viscoelastic and fracture properties of bone?

Sacrificial bonds have been suggested as a toughening mechanism for bone tissue. Ionic bridges formed by divalent calcium ions between collagen molecules have been proposed as candidates for sacrificial bonds. If this mechanism is active at the macroscopic level, we should observe changes in mechanical properties of bone when calcium ions are maintained or removed from the tissue. To test this hypothesis, we measured viscoelastic and monotonic mechanical properties of cortical bone subjected to differing ionic environments. Storage modulus of bone could be changed up to 3.8% by the presence or absence of Na+ or Ca++ in the environment in a reversible fashion when bones were monitored continuously during treatments. A long-term one-time treatment increased the viscoelastic properties of bone soaked in Na+ solutions whereas the viscoelastic properties of bones soaked in Ca++ solutions were maintained. However, the strength and toughness of bone specimens soaked and fractured in treatment solutions were not improved. The presence of Ca++ affected the mechanical behavior of mineralized bone tissue at the macro scale. These effects were reversible, consistent with the original proposal. However, these effects may not necessarily indicate an increase in strength or toughness of the tissue at the macro scale.

Age, dehydration and fatigue crack growth in dentin

A preliminary study of the effects from age and dehydration on fatigue crack growth in human dentin was conducted. Compact tension (CT) fatigue specimens of coronal dentin were prepared from extracted molars and subjected to high cycle fatigue (10(5)<N<10(6)) under Mode I loading. Young hydrated dentin (mean age=25+/-7 years), old hydrated dentin (mean age=55+/-14 years) and young dehydrated dentin (mean age=20+/-2 years) were examined. Fatigue crack growth rates were quantified according to the Paris Law in terms of the crack growth exponent (m) and coefficient (C). The average fatigue crack growth exponent for the young hydrated dentin (m=13.3+/-1.1) was significantly less than that for the hydrated old (m=21.6+/-5.2; p<0.003) and dehydrated young dentin (m=18.8+/-2.8; p<0.01). Fatigue cracks in the old dentin underwent initiation at a lower stress intensity range than in young dentin and propagated at as significantly faster rate (over 100x). Differences in the microscopic features of the fracture surfaces from the old and young dentin suggested that particular mechanisms contributing to energy dissipation and crack growth resistance in the young hydrated dentin were not present in the old dentin. Based on results of this study, the fatigue crack growth resistance of human dentin decreases with both age of the tissue and dehydration.

Biochemical analysis of the articular cartilage and subchondral and trabecular bone of the metacarpophalangeal joint of horses with early osteoarthritis

OBJECTIVE

To assess whether site-related changes in biochemical composition are present in the cartilage and subchondral and trabecular bone of the metacarpophalangeal joint of horses with early osteoarthritis.

SAMPLE POPULATION

Right metacarpophalangeal joints from 59 mature warmblood horses.

PROCEDURE

Biochemical data (cross-link, amino acid, DNA, and ash contents; denatured collagen and glycosaminoglycan [GAG] concentrations; bone mineral density; and mineral composition) were obtained from 2 differently loaded sites of phalanx I cartilage and subchondral and trabecular bone samples; data were compared with previously published values from nonosteoarthritic equine joints.

RESULTS

Compared with findings in nonosteoarthritic joints, GAG concentration was lower in cartilage from osteoarthritic joints and there was a loss of site differences in cellularity and lysylpyridinoline (LP) cross-link content. In subchondral bone, LP cross-link content was decreased overall and there was a loss of site differences in osteoarthritic joints; ash content was higher in the osteoarthritic joints. Hydroxyproline content in trabecular bone from osteoarthritic joints was greater than that in nonosteoarthritic trabecular bone. In all 3 layers and at both sites, the linear increase of the pentosidine cross-link content with age had diminished or was not apparent in the horses with osteoarthritic joints.

CONCLUSIONS AND CLINICAL RELEVANCE

In equine metacarpophalangeal joints with early osteoarthritis, distinct biochemical changes were detected in the cartilage and subchondral and trabecular bone. The dissimilarity in response of the different tissues and differences between the sites that are affected may be related to differences in biomechanical loading and transmission and dissipation of force.

Evaluation of Young's modulus in Achilles tendons with diabetic neuroarthropathy

The Achilles tendon of the patient with Charcot's foot neuroarthropathy has significantly altered physical properties compared with a normal tendon. Twenty-nine Achilles tendons from patients with Charcot's foot (n = 20) and non-Charcot's foot controls (n = 9) were loaded onto a biomechanical testing instrument. The biomechanical properties of the Charcot and control tendons were determined and the tendons were evaluated for differences in ultimate tensile strength and elasticity (Young's modulus). Biomechanical test data show that there is a significant difference in ultimate tensile strength and elasticity between tendons of patients with Charcot's foot and those of non-Charcot's controls. The term diabetic tendo Achillis equinus is introduced as a new finding in diabetic neuroarthropathy.

Collagen fiber orientation in human peri-implant bone around immediately loaded and unloaded titanium dental implants

BACKGROUND

The main factor in determining the mechanical properties of bone is the collagen configuration.

METHODS

This study investigated the birefringence in human bone around loaded and unloaded titanium dental implants to evaluate the collagen fiber orientation using circularly polarized light (CPL) and scanning electron microscopy (SEM). A total of 10 titanium dental implants, five immediately loaded and five unloaded, were used. The birefringence measurements were performed on digitized images of both loaded and unloaded implants. All images detected at 50x were measured using a software image analysis.

RESULTS

In the bone around loaded implants, the transverse collagen fiber area was 45,481+/-3,037 pixel2 (mean+/-SD), while the area of longitudinal collagen fibers was 13,676+/-2,232 pixel2 (mean+/-SD). In the unloaded implants, the transverse collagen fiber area was 32,174+/-2,554 pixel2 (mean+/-SD), while the area of longitudinal collagen fibers was 89,073+/-1,960 pixel2 (mean+/-SD). The CPL measurements of the birefringence for transverse collagen fibers of loaded versus unloaded implants indicated that the differences were statistically significant (P <0.05). The results for the longitudinal collagen fibers of loaded versus unloaded implants were also statistically significant (P <0.05).

CONCLUSIONS

In the bone around loaded dental implants, transverse collagen fibers were more abundant, while in the unloaded implants, collagen fibers run more longitudinally. The load seemed to determine the collagen fiber orientation.

The effect of gamma radiation sterilization on the fatigue crack propagation resistance of human cortical bone

BACKGROUND

Clinical evidence has suggested that the rate of fracture in allografts sterilized with gamma radiation may be higher than that in controls. Gamma radiation sterilization has been shown to affect the post-yield properties of bone but not the elastic modulus. Since most allograft fractures occur with subcritical loads during activities of daily living, it may be that the fatigue properties of irradiated allografts are diminished. In this study, the fatigue crack propagation behavior of cortical bone sterilized with gamma radiation was compared with that of gender and age-matched controls. We hypothesized that gamma radiation significantly reduces the resistance of cortical bone to fatigue crack growth.

METHODS

Specimens for fatigue crack propagation testing were machined from four pairs of fresh-frozen human femora obtained from four individuals (a younger male, younger female, older male, and older female donor). Half of the specimens were sterilized with 31.7 kGy of gamma radiation. The specimens were cyclically loaded to failure in a servohydraulic testing system, and crack growth was monitored. The cyclic stress intensity factor and the fatigue crack growth rate were calculated to examine the kinetics of fatigue crack growth. Following testing, the damage zone around the fracture plane was analyzed histologically.

RESULTS

The morphology and kinetics of crack growth in irradiated specimens differed from the control data. Overall, the irradiated bone was significantly less resistant to fatigue crack growth than was control tissue (p < 0.05). There was less microdamage associated with fracture in the irradiated specimens than in the control specimens, with the exception of the bone from the older female donor.

CONCLUSIONS

Gamma radiation sterilization significantly reduces the fatigue crack propagation resistance of cortical bone. Irradiated specimens also demonstrate a smaller amount of microdamage along the fracture plane. These findings may be due to ultrastructural alterations in the collagen matrix caused by radiation.

CLINICAL RELEVANCE

This study suggests that, despite having pre-yield mechanical properties that are similar to those of nonirradiated bone, gamma-radiation-sterilized allograft may be more predisposed to fracture even under the subcritical loads that occur during the activities of daily living.

Influence of the degradation of the organic matrix on the microscopic fracture behavior of trabecular bone

In recent years, the important role of the organic matrix for the mechanical properties of bone has become increasingly apparent. It is therefore of great interest to understand the interactions between the organic and inorganic constituents of bone and learn the mechanisms by which the organic matrix contributes to the remarkable properties of this complex biomaterial. In this paper, we present a multifaceted view of the changes of bone's properties due to heat-induced degradation of the organic matrix. We compare the microscopic fracture behavior (scanning electron microscopy; SEM), the topography of the surfaces (atomic force microscopy; AFM), the condition of bone constituents [X-ray diffraction (XRD), thermogravimetric analysis (TGA), and gel electrophoresis], and the macromechanical properties of healthy bovine trabecular bone with trabecular bone that has a heat-degraded organic matrix. We show that heat treatment changes the microfracture behavior of trabecular bone. The primary failure mode of untreated trabecular bone is fibril-guided delamination, with mineralized collagen filaments bridging the gap of the microcrack. In contrast, bone that has been baked at 200 degrees C fractures nondirectionally like a brittle material, with no fibers spanning the microcracks. Finally, bone that has been boiled for 2 h in PBS solution fractures by delamination with many small filaments spanning the microcracks, so that the edges of the microcracks become difficult to distinguish. Of the methods we used, baking most effectively weakens the mechanical strength of bone, creating the most brittle material. Boiled bone is stronger than baked bone, but weaker than untreated bone. Boiled bone is more elastic than untreated bone, which is in turn more elastic than baked bone. These studies clearly emphasize the importance of the organic matrix in affecting the fracture mechanics of bone.

An integral biochemical analysis of the main constituents of articular cartilage, subchondral and trabecular bone

OBJECTIVE

In articular joints, the forces generated by locomotion are absorbed by the whole of cartilage, subchondral bone and underlying trabecular bone. The objective of this study is to test the hypothesis that regional differences in joint loading are related to clear and interrelated differences in the composition of the extracellular matrix (ECM) of all three weight-bearing constituents.

METHOD

Cartilage, subchondral- and trabecular bone samples from two differently loaded sites (site 1, dorsal joint margin; site 2, central area) of the proximal articular surface of 30 macroscopically normal equine first phalanxes were collected. Collagen content, cross-linking (pentosidine, hydroxylysylpyridinoline (HP), lysylpyridinoline (LP)) hydroxylation, and denaturation, as well as glycosaminoglycan (GAG) and DNA content were measured in all three tissues. In addition, bone mineral density (BMD), the percentage of ash and the mineral composition (calcium, magnesium and phosphorus) were determined in the bony samples.

RESULTS

For pentosidine cross-links there was an expected correlation with age. Denatured collagen content was significantly higher in cartilage at site 1 than at site 2 and was higher in trabecular bone compared to subchondral bone, with no site differences. There were significant site differences in hydroxylysine (Hyl) concentration and HP cross-links in cartilage that were paralleled in one or both of the bony layers. In subchondral bone there was a positive correlation between total (HP+LP) cross-links and Ca content. For Ca and other minerals there were corresponding site differences in both bony layers.

CONCLUSIONS

It is concluded that there are distinct differences in distribution of the major biochemical components over both sites in all three layers. These differences show similar patterns in cartilage, subchondral bone and trabecular bone, stressing the functional unity of these tissues. Overall, differences could be interpreted as adaptations to a considerably higher cumulative loading over time at site 2, requiring stiffer tissue. Turnover is higher in trabecular bone than in subchondral bone. In cartilage, the dorsal site 1 appears to suffer more tissue damage.

Informatics challenges in tissue engineering and biomaterials

Both tissue engineering and biomaterials have made tremendous strides recently, yet major questions remain unanswered. Tissue-engineered products have come to the market; others are in development. A fundamental issue that informatics could address for tissue engineering is to describe and to predict the cascade of biochemical and cellular reactions that occur as a function of time and implant material: surface texture, microporosity; pore size, density, and connectivity; and three-dimensional configuration. Behavior of ceramics, a subset of tissue-engineering scaffold materials and a mainstay of dental restorations, has been studied extensively for very thin layers and for thicknesses greater than 2 mm. Until recently, little has been known about dentally relevant thickness of 1-2 mm. Results have been surprising and are continuing to develop. Still, at least one fundamental question remains that could be addressed by informatics techniques: Where, along the spectrum of flat-polished material to 10-year clinical in vivo study, can we test to predict clinical performance of all-ceramic crowns accurately?

External and occlusal trauma to dental implants and a case report

Dental implants subjected to traumatic forces can survive. Cortical bone seems to provide a protective energy-absorbing mechanism in the collagen polymer that helps to prevent microcracking and fracture of bone. The collagen polymer has cross-linking bonds that break and absorb the energy of a traumatic impact so as not to cause damage to the main polymer chain. A case reported demonstrates that a traumatic force damaged the implant prosthetic crown, but not the bone encasing the implant or the integration of the implant.