Gregory R. Wohl

Effects of high-fat diet on mature bone mineral content, structure, and mechanical properties.

Abstract. Diets with a high saturated fat content can produce deleterious effects on the absorption of dietary calcium and consequently an adverse effect on bone mineralization in growing animals. Hence dietary fat may have long-term consequences for skeletal health and skeletal pathologies such as osteoporosis. Whether a diet high in saturated fat has similar negative effects on adult bone, however, remains unresolved. Thus, we investigated effects of a high-fat diet on mature bone structure and mechanics. Adult (40-week-old) roosters were maintained for 20 weeks on either a diet high in saturated fat (HF) or a low-fat (LF) diet. Cortical bone samples (tarsometatarsus) were tested mechanically in three-point bending, and cancellous bone cores from the femoral condyles and tibial plateau (four sites per knee) were tested mechanically in compression. Cortical bone cross-sectional areal data were also compared among the groups, and bone mineral content (BMC) was determined (by ashing) for both cortical bone and cancellous bone samples. There were no significant high-fat diet effects on mature cortical bone mechanical properties, geometric structure, or mineral content. Diet, however, did affect cancellous bone composition. For example, LF cancellous BMC was significantly greater than HF. Mechanical properties of the cancellous bone showed similar trends such that LF cancellous bone strength was consistently greater than HF. The potential for adverse effects of a HF diet on intestinal calcium absorption in the mature animal may be more apparent in cancellous bone, with its faster rate of turnover, than in cortical bone. Changes in cancellous bone structure and mechanical properties, related to dietary saturated fats, may have implications for understanding the role of nutrition in skeletal health and prevention of pathological bone loss (osteoporosis).

Early morphometric and anisotropic change in periarticular cancellous bone in a model of experimental knee osteoarthritis quantified using microcomputed tomography

OBJECTIVE To quantify early stage microstructural changes of periarticular cancellous bone in a canine anterior cruciate ligament transection model for experimental osteoarthritis. DESIGN Unilateral transection of the anterior cruciate ligament was performed in 10 animals. Bone structure changes were quantified in five animals at 3-week post-transection and five animals at 12-week post-transection. An additional two non-operated animals were used as controls. BACKGROUND Changes in trabecular architecture of the periarticular cancellous bone in early stage post-traumatic osteoarthritis is not well understood. Previous studies have found alterations in bone mineral density in experimental osteoarthritis suggesting adaptation of the trabecular structure. Early change of the periarticular bone following a ligament injury may contribute to the long-term development of osteoarthritis. METHODS ++. Bone cores from the medial condyles of the femoral and tibial pairs were scanned with a three-dimensional microtomographic system. Structural indices were quantified including bone volume ratio, bone surface ratio, trabecular thickness, trabecular separation, trabecular number, as well as structural anisotropy determined by the mean-intercept-length method.Results. Significant structural changes were observed at 3-week post-transection, and were more prominent at 12-week post-transection. These changes were accompanied by decreasing anisotropy. CONCLUSIONS Periarticular cancellous bone microstructure is significantly altered in experimental osteoarthritis. These changes occurred as early as 3-week post-transection, and were large at 12-week post-transection. RELEVANCE The pathogenesis of post-traumatic osteoarthritis is poorly understood, but it is clear that this disease involves the entire organ system of the joint, including the cartilages, synovium, ligaments, and bones. This study focuses on the changes that occur in the bones during the early stages following a joint injury, and contributes to a better overall understanding of the disease aetiology.

Dietary fish oil supplementation adversely affects cortical bone morphology and biomechanics in growing rabbits.

Abstract. Despite substantial evidence that fish oil-derived (n-3) polyunsaturated fatty acids (PUFA) may protect against cardiovascular disease, the effects of supplements containing (n-3) PUFA on the skeletal system are unknown. Here we investigated how a diet supplemented with 10 g/100 g fish oil affected tibial cortical morphology and mechanical properties in weanling rabbits. Rabbits were subdivided into a normal control (n = 10), a fish oil (n = 20), and a pair-fed (n = 20) group. The pair-fed group was energy restricted to match average body mass of the fish oil group. At completion of the 40 day dietary intervention, control rabbits were significantly heavier than the other two groups. Comparison between control and pair-fed rabbits revealed that energy restriction alone (30%) did not induce significant changes in tibial middiaphyseal morphology, but tibial longitudinal growth was significantly impaired. Most tibial mechanical properties were significantly degraded by energy restriction. Fish oil-supplemented rabbits had significantly smaller middiaphyseal areal properties and shorter tibiae than pair-fed rabbits. Tibial structural properties were significantly reduced in fish oil-fed rabbits, but tibial stress at the proportional limit (material property) was not significantly affected. Our data suggest that 10% fish oil supplementation in the presence of modest vitamin E supplementation can have detrimental effects on the skeleton of rapidly growing rabbits.

Bone Affinity of a Bisphosphonate-Conjugated Protein in Vivo

Growth factors capable of stimulating bone formation are potential therapeutic agents for osteoporosis treatment. It is essential, however, that a targeting mechanism is incorporated into the growth factors to deposit them at osseous tissue with minimal distribution to extraskeletal sites. To this end, a strategy has been developed in which a bone‐seeking molecule, 1‐amino‐1,1‐diphosphonate methane (aminoBP), was chemically conjugated to a model protein, bovine serum albumin (BSA). This study was carried out to assess the bone affinity of the conjugates in a tibia injection model. Using ovariectomized (OVX) rats, initial (3 h) retention of BSA and aminoBP‐BSA were found to be equivalent when injected into the medullary cavity of tibia. After 1 day, an 8‐ and 12‐fold higher tibiae retention of the protein was obtained in normal and OVX rats as a result of aminoBP conjugation. A similar result (∼12‐fold difference) was also obtained in OVX rats after 3 days. We concluded that aminoBP conjugation to BSA imparted a high bone affinity and enhanced bone retention of proteins in normal and OVX rats.

Plasma enhanced bonding of polydimethylsiloxane with parylene and its optimization

Polydimethylsiloxane (PDMS) and parylene are among the most widely used polymers in biomedical and microfluidic applications due to their favorable properties. Due to differences in their chemical structure and fabrication methods, it is difficult to integrate them together on a single microfluidic device. In this paper, we have demonstrated a method to bond patterned PDMS with parylene without the use of high temperature or pressure in a two-step process. The steps include (1) the attachment of cured PDMS surface to parylene using microcontact printing to form a weak bond followed by (2) a plasma exposure of sealed assembly to SF6, N2 and O2 gases, which enhanced the quality of bond by approximately fourfold to 1.4 MPa. We systematically investigated the effect of gas flow rates, chamber pressure, plasma time and power using Taguchis design of experiment method. Composition of the bond formed in this process was evaluated to understand the mechanism of bond formation. Microfluidic channels fabricated from a PDMS replica and a flat parylene-coated surface, bonded using this method, have been able to withstand burst pressures of up to 146 kPa compared to 35 kPa for PDMS prepolymer microcontact printed assembly.

Maintenance of bone mass and architecture in denning black bears (Ursus americanus)

Bone mass is dramatically compromised during periods of weightlessness, inactivity, or bed rest. Animals that hibernate reduce their body temperature, heart rate and metabolic activity, and likewise lower bone turnover activity during their immobile state. Black bears Ursus americanus, however, do not hibernate, but rather overwinter by denning during which they maintain a nearly normal functional heart rate, cardiac output and temperature. Furthermore, markers of bone turnover in black bears are maintained during denning periods. Thus, the purpose of this work was to determine if the denning state of relative immobility in black bears results in changes in bone mass and bone architectural structure. Harvested forelimbs (ulna and radius) were compared between pre- and post-denning black bears using X-ray imaging, dual energy X-ray absorptiometry, and micro-computed tomography to quantify total distal forelimb bone mineral density, cancellous bone mineral density, bone mineral content, bone volume fraction, degree of anisotropy, structure model index, and trabecular thickness. No significant differences in any of the measured parameters were found in comparing radius and ulna from autumn and spring bears in this cross-sectional sample, suggesting that black bears did not experience a significant change in bone mass or architecture during denning. The statistical power for detecting a significant difference (P≤ 0.05) for this sample was 0.8. The specific mechanism by which the preservation of bone was attained may be related to skeletal muscle interaction or circulating systemic hormones.

Accumulation of bone strontium measured by in vivo XRF in rats supplemented with strontium citrate and strontium ranelate

Strontium ranelate is an approved pharmacotherapy for osteoporosis in Europe and Australia, but not in Canada or the United States. Strontium citrate, an alternative strontium salt, however, is available for purchase over-the-counter as a nutritional supplement. The effects of strontium citrate on bone are largely unknown. The studys objectives were 1) to quantify bone strontium accumulation in female Sprague Dawley rats administered strontium citrate (N=7) and compare these levels to rats administered strontium ranelate (N=6) and vehicle (N=6) over 8 weeks, and 2) to verify an in vivo X-ray fluorescence spectroscopy (XRF) system for measurement of bone strontium in the rat. Daily doses of strontium citrate and strontium ranelate were determined with the intention to achieve equivalent amounts of elemental strontium. However, post-hoc analyses of each strontium compound conducted using energy dispersive spectrometry microanalysis revealed a higher elemental strontium concentration in strontium citrate than strontium ranelate. Bone strontium levels were measured at baseline and 8 weeks follow-up using a unique in vivo XRF technique previously used in humans. XRF measurements were validated against ex vivo measurements of bone strontium using inductively coupled plasma mass spectrometry. Weight gain in rats in all three groups was equivalent over the study duration. A two-way ANOVA was conducted to compare bone strontium levels amongst the three groups. Bone strontium levels in rats administered strontium citrate were significantly greater (p<0.05) than rats administered strontium ranelate and vehicle. ANCOVA analyses were performed with Sr dose as a covariate to account for differences in strontium dosing. The ANCOVA revealed differences in bone strontium levels between the strontium groups were not significant, but that bone strontium levels were still very significantly greater than vehicle.

Porcine cortical bone ablation by ultrashort pulsed laser irradiation.

Ultrashort pulsed lasers in bone ablation show promise for many orthopedic applications. To minimize collateral tissue damage and control the ablation process, the ablation threshold fluence must be well characterized. Using an amplified femtosecond laser (170 fs, 800 nm, 1 kHz), the ablation threshold on unaltered porcine cortical bone was measured using the D(2) method at multiple incident pulse numbers ranging from 25 to 1000 pulses per spot. The lowered threshold at greater pulse numbers indicated an incubation effect. Using a power law model, the incubation coefficient of unaltered porcine cortical bone was found to be 0.89 ± 0.03. Through extrapolation, the single-pulse ablation threshold was found to be 3.29 ± 0.14 J/cm(2).

Functional adaptation of bone to exercise and injury

Bone adapts to altered physical stimuli, dietary changes, or injury. Dietary calcium and vitamins play important roles in maintaining skeletal health, but high-fat diets are pervasive in western cultures and may contribute to the increasing prevalence of osteoporosis and incidence of related hip fractures. Exercise helps maintain bone mass and counter osteoporosis, but exercise can also have detrimental effects-particularly for immature bone. Some negative exercise effects may also be linked to diet. For example, insufficient dietary protein during exercise can impair bone development and remodeling. Bone remodeling is a potent example of tissue repair. Chronically altered loading after a joint injury, however, can result in remodeling processes that can be detrimental to the joint. Anterior cruciate ligament injury, for example, commonly leads to osteoarthritis. Early changes in the periarticular cancellous bone may play a role in the development of knee osteoarthritis. Although these factors influence skeletal health, the mechanisms remain unclear by which bone interprets its environment and responds to mechanical stimuli or injury. To understand why different levels of exercise are beneficial or detrimental or why altered joint loading leads to changes in periarticular bone structure, underlying mechanisms must be understood by which bone interprets its mechanical environment.

Ultrafast laser ablation and machining large-size structures on porcine bone

Abstract. When using ultrafast laser ablation in some orthopedic applications where precise cutting/drilling is required with minimal damage to collateral tissue, it is challenging to produce large-sized and deep holes using a tightly focused laser beam. The feasibility of producing deep, millimeter-size structures under different ablation strategies is investigated. X-ray computed microtomography was employed to analyze the morphology of these structures. Our results demonstrated the feasibility of producing holes with sizes required in clinical applications using concentric and helical ablation protocols.