Biomedical subjects

S J Simske

Publications and source records attributed to S J Simske.

At least 19 recordsLinked to original sources

PubMed2005

Comparison of tail-suspension and sciatic nerve crush on the musculoskeletal system in young-adult mice.

Musculoskeletal unloading and disuse result in significant muscle and bone loss. These phenomena can be modeled using sciatic nerve crush or tail-suspension. Mature animals eliminate the complication of growth superimposed on bone and muscle loss. In the current study, young-adult (12-week old male) C57BL/6J mice were subjected to sciatic nerve crush (NC; n = 9) or tail-suspension (TS; n = 9) for 14 days, with a normal ambulatory control (n = 10). The soleus, gastrocnemius, and EDL muscles were collected and weighed at sacrifice. Femurs were analyzed in three-point bending for stiffness, elastic force and maximum force. Muscle masses in tail suspended mice were reduced by 41.9% (p < 0.001), 17.5% (p < 0.001), and 9.1% (N.S.) for the soleus, gastrocnemius, and EDL, respectively. In NC mice, muscle masses were reduced by 18.6% (p = 0.004), 37.2% (p < 0.001), and 22.5% (p = 0.003). Femur stiffness, elastic and maximum forces were reduced by 20.9% (p = 0.014), 14.7% (N.S.), and 11.6% (N.S.) in TS, compared to NC where masses were reduced by 15.5% (p = 0.022), 0.2% (N.S.) and 11.2% (N.S.) in the crushed leg compared to the contralateral control. NC resulted in a greater reduction of muscle mass in the gastrocnemius and EDL muscle; whereas tail-suspension had a greater effect on the soleus. Tail-suspension had the greatest effect on bone mechanical properties. When comparing these results to actual spaceflight data, it appears as though TS most closely models muscle loss, and NC most closely models changes in bone mechanical properties. These unloading models have tissue-specific effects that impact their applications for musculoskeletal research.

Adaptation, Physiological↗

PubMed2005

A novel combination of methods to assess sarcopenia and muscle performance in mice.

A novel combination of assays was developed to assess sarcopenia and muscle performance. Three techniques were tested to assess muscle function both during and upon termination of treatments designed to induce sarcopenia. In unsuspended (US) and hindlimb suspended (HS) mice, a Hindlimb Exertion Force Test (HEFT), cage wheel running, and in vitro muscle electrophysiology were performed. Twelve-week old, mature male C57BL/6J mice were HS (n = 24) for two weeks, or served as US controls (n = 26). Both groups were subjected to a HEFT on day 13; that is, the maximum force exerted against a beam force transducer (2 lb. linear range, Transducer Techniques, Temecula CA) following applied tail shock stimulus (0.15 mA, 300 msec). This test primarily evaluated the hindlimb muscles used for an escape response (i.e., hamstrings, quadriceps and calf muscles). Mice (n = 10-11/group) were given voluntary access to running wheels for 7 days post treatment to evaluate muscle endurance. On day 13, HS mice showed a mean 18.9% (p = 0.002) decrease in the maximum force exerted compared to US mice. After 7 days of wheel running, HS running distance tended to decrease (13.2%, p = 0.084). HS mice ran an average of 2.0 km/day less than US control mice, with similar running patterns: distance declined on day 2 following completion of HS but increased steadily thereafter. With in vitro testing, the maximum soleus tetanus response decreased by 31.8% (p = 0.01) with HS, in agreement with the changes observed by the other assays. These three assays, combined, appear to provide effective and complementary ways to measure muscle performance and functional differences.

Animals↗

PubMed2002

Effect of MPC-11 myeloma and MPC-11 + IL-1 receptor antagonist treatment on mouse bone properties.

This study examines the effects of an IL-6-producing murine multiple myeloma cell line on trabecular and cortical mouse bone, and evaluates the efficacy of interleukin-1 receptor antagonist (IL-1ra) in mitigating bone destruction. Six-week-old BALB/c mice were assigned to two groups: normal controls and myeloma animals (5 x 10(7) MPC-11 cells on day 0). Myeloma animals were further assigned to three unique groups: MPC-11 only; MPC-11 treated with hyaluronic acid (HA); and MPC-11 + IL-1ra/HA (100 mg/kg). Disease development was assessed at 14 and 21 days via spleen, liver, and proximal tibia histology; histomorphometry at the femoral middiaphysis; and long bone composition and mechanical testing. Histologic analysis revealed marked myeloma infiltration into organs and bone marrow and gross bone resorption of the proximal tibia. IL-1ra tended to decrease bone resorption at the proximal tibia; however, it had no effect on quantitatively measured bone parameters. Whole femur and tibia, and tibial epiphysis, percent mineralization was decreased (3.0%, 2.9%, and 6.3%, respectively) in all MPC-11 groups. The presence of myeloma did not affect long bone stiffness, strength, or length over the 3 week study. The percent of the femoral endosteal perimeter showing excessive resorption ( approximately 60%) in the MPC-11 groups increased significantly after 21 days. MPC-11 cell presence caused no change in bone formation or morphology. Normal growth mechanisms were not impacted, as the bones lengthened and increased in size and mass despite the presence of myeloma. IL-1 does not appear to be a primary factor in in vivo bone destruction caused by the MPC-11 cell line. These findings reveal the stochastic nature of bone lesions in multiple myeloma and suggest that IL-1 is not a cytokine critical to this disease pathology.

Animals↗

PubMed2001

Osteoprotegerin ameliorates sciatic nerve crush induced bone loss.

This study examines the ability of osteoprotegerin (OPG) to prevent the local bone resorption caused by sciatic nerve damage. Sixty-five 18-week-old male mice were assigned to one of six groups (n = 10-11/group). A baseline control group was sacrificed on day zero of the 10-day study. The remaining groups were placebo sham operated, placebo nerve crush (Plac NC) operated, 0.1 mg/kg/day OPG + nerve crush (LOW), 0.3 mg/kg/day OPG + nerve crush (MED), and 1.0 mg/kg/day OPG + nerve crush (HI). Nerve crush or sham operations were performed on the right leg. The left leg served as a contralateral control to the nerve crushed (ipsilateral) leg. The difference in mass between the right and left femur and tibia was examined. Additionally, quantitative histomorphometry was performed on the right and left femur and tibia diaphyses. Nerve crush resulted in a significant loss of bone mass in the ipsilateral side compared to the contralateral side. Bone mass for the ipsilateral bones of the Plac NC group were significantly reduced by 3.8% in the femur and 3.5% in the tibia compared to the contralateral limb. The percent diminution was reduced for OPG treated mice compared to the Plac NC group for both the femur and tibia. In the femur, the percent reduction of ipsilateral bone mass was reduced to 1.0% (LOW), 1.3% (MED) and 1.6% (HI) compared to the contralateral limb. In the tibia, loss of bone mass in the ipsilateral limb was reduced to 1.4% (LOW), 1.4% (MED), and 2.4% (HI) compared to the contralateral. OPG also decreased the amount of tibial endocortical resorption compared to the Plac NC group. In summary, OPG mitigated bone loss caused by damage to the sciatic nerve.

Animals↗

PubMed2001

The effects of osteoprotegerin on the mechanical properties of rat bone.

Osteoprotegerin (OPG) is a naturally secreted protein that decreases bone resorption by inhibiting osteoclast differentiation and activation while promoting osteoclast apoptosis [8]. In this study, the effects of osteoprotegerin injections on long bone mechanical and material properties were investigated in young male Sprague-Dawley rats. OPG increased fracture strength at the femur mid-diaphysis in three-point bending by 30%, without affecting the elastic or maximum strength. At the femoral neck, OPG significantly increased the elastic (45%), maximum (15%), and fracture (35%) strengths. There was not a difference in microhardness at the femur mid-diaphysis in comparing the placebo and OPG groups. There were, however, significant increases in whole bone dry mass (25%), mineral mass (30%), organic mass (17%), and percent mineralization (4%); percent mineralization at the mid-diaphysis (3%); and percent mineralization at the distal epiphysis (6%) due to the OPG treatment. While OPG decreased endocortical bone formation (52%), total bone area, endocortical bone area, and periosteal bone formation were maintained with OPG treatment. A 30% increase in the X-ray opacity of the bone at the proximal metaphysis of the right tibiae was observed. Overall, OPG increased mineralization and strength indices in the rat femur. Its effects on strength were more pronounced in the femoral neck than at the mid-diaphysis.

Journal Article↗

PubMed2000

Osteoprotegerin mitigates tail suspension-induced osteopenia.

Osteoprotegerin (OPG) is a recently discovered protein related to the tumor necrosis factor receptor family. It has been shown to inhibit ovariectomy (ovx)-induced resorption in rats and increase bone mineral density in young mice. Tail suspension is a procedure that inhibits bone formation in maturing rodents. This study was designed to quantify OPG's effect on cortical bone formation. Fifty-four mice were assigned to one of five groups (n = 10-11/group). A baseline control group was killed on day 0 of the 10 day study. The remaining groups were: vivarium housed (nonsuspended) control mice receiving 0.3 mg/kg per day OPG; vivarium control mice receiving daily placebo injections; tail-suspended mice receiving 0. 3 mg/kg per day OPG; and tail-suspended mice receiving placebo injections. Tetracycline was administered on days 0 and 8. OPG treatment of tail-suspended mice produced mechanical properties similar to those of placebo-treated, vivarium-housed mice: structural stiffness (8.5%, 20.7%) and elastic (13.9%, 10.1%) and maximum (4.7%, 8.1%) force were increased compared with placebo controls (vivarium, suspended groups). Percent mineral composition was highly significantly greater (p < 0.001 for all comparisons) for OPG-treated mice in the femur, tibia, and humerus, relative to placebo treatment. Matrix mass was also significantly increased in the femur, although not to the same degree as mineral mass. OPG decreased the amount of femoral endocortical resorption compared with the placebo-treated groups for both vivarium (27%) and suspended (24%) mice. Administration of OPG significantly decreased endocortical formation of the tibia. Periosteal bone formation rates were not altered by OPG. OPG-mitigated tail suspension induced osteopenia not by returning bone formation to normal levels, but by inhibiting resorption and increasing percent mineral composition.

Animals↗

PubMed2000

Spaceflight induces changes in splenocyte subpopulations: effectiveness of ground-based models.

Spaceflight produces changes in the immune system. The mechanisms for the alterations in immune function after spaceflight remain unclear due in part to the difficulties associated with conducting spaceflight research. The purpose of the following studies, therefore, was to create a ground-based protocol that can reproduce the immunological changes found after spaceflight, i.e., changes in splenic lymphocyte populations. Rats were exposed to either flight aboard the Space Shuttle Endeavor (STS-77) or ground-based simulations of various components of the spaceflight experience. The ground-based mock spaceflight was comprised of exposure to launch and landing loads and unloading of the hindlimbs. In addition, each component of this ground-based mock spaceflight was tested separately. The results were that spaceflight reduced splenic CD4(+) T (helper/inducer) cells and CD11b(+) (neutrophils/macrophages) cells. The ground-based simulations of spaceflight did not reproduce the same pattern of splenocyte changes. In fact, exposure to landing loads alone increased splenic CD4(+) T (helper/inducer) cells. These findings support the conclusion that the ground models tested did not induce similar changes in the immune system as did spaceflight. It is possible, therefore, that stressors/factors unique to the spaceflight experience impact the immune system in ways that cannot be currently, fully modeled on the ground.

Animals↗

PubMed2000

Effects of high fat or high sucrose diets on rat femora mechanical and compositional properties.

Diets high in fat and/or sucrose decrease whole bone mechanical properties and mineralization. This study examines the impact on rat bone mechanical properties and composition of age and diets (a) low in fat, (b) high in sucrose, and (c) high in fat. Sprague-Dawley rats aged 3 weeks (weanling [W]; n = 42), 8 weeks (young [Y]; n = 42), 16 weeks (teenage [T]; n = 39) and 56 weeks (old [O]; n = 40) were randomly assigned to groups: low fat, high sucrose and high fat with n = 12-16 per group. All animals were fed a purified low-fat, high starch diet for two weeks, and fed a low fat (STD), high sucrose (HSD), or high-fat (HFD) for five additional weeks. After sacrifice, the femurs were harvested and non-osseous tissue was removed. The bones were dried at 25 degrees C for 48 hours. Length and the periosteal minimum and maximum diameter (D-min and D-max) at the mid-diaphysis of the femurs were measured with Vernier calipers. The femurs were rehydrated and tested via three-point flexure. Bones were weighed after drying at 105 degrees C (48 hours; Dry-M) and 800 degrees C (24 hours; Ash-M). Percent mineralization (%Min) was calculated as Ash-M/Dry-M X 100%. Length, D-min and D-max, Dry-M and Ash-M all significantly (p < 0.05) increased with age (W < Y < T < O) within each group. %Min and stiffness were significantly greater in [O] than in the younger femurs. No significant results were seen in any age group due to varying diet. These results indicate that five weeks of high fat or high sucrose diet feeding does not affect whole bone size, composition or mechanical properties. Whether a longer dietary period or different diet composition would elicit changes requires further study.

Animals↗

PubMed1999

Effect of nitinol implant porosity on cranial bone ingrowth and apposition after 6 weeks.

The present study addresses two aspects of the use of nitinol in cranial bone defect repair. The first is to verify that there is substantial bone ingrowth into the implant after 6 weeks; the second is to determine the effect of pore size on the ability of bone to grow into the implant during the early (6-week) postoperative period. Porous equiatomic (equal atomic masses of titanium and nickel) nickel-titanium (nitinol) implants with three different morphologies (differing in pore size and percent porosity) were implanted for 6 weeks in the parietal bones of New Zealand White rabbits. Ingrowth of bone into the implants and apposition of bone along the exterior and interior implant surfaces were calculated. The mean pore size (MPS) of implant type #1 (353 +/- 74 microm) differed considerably from implant types #2 (218 +/- 28 microm) and #3 (178 +/- 31 microm). There was no significant difference among implant types in the percentages of bone and void/soft tissue composition of the aggregate implants. The amount of bone ingrowth also was not significantly different among the implant types. Implant #1 was significantly higher in pore volume and thus had a significantly higher volume of ingrown bone (2.59 +/- 0.60 mm3) than implant #3 (1. 52 +/- 0.66 mm3) and a greater amount, but not significantly greater, than implant #2 (1.76 +/- 0.47 mm3). Pore size does not appear to affect bone ingrowth during the cartilaginous period of bone growth in the implant. This implies that within the commonly accepted range of implant porosities (150-400 microm), at 6 weeks bone ingrowth near the interface of nitinol implants is similar.

Alloys↗

PubMed1999

Quantification of bone ingrowth into porous block hydroxyapatite in humans.

This study sought to quantify bone ingrowth from a single bone-implant surface into porous block hydroxyapatite used in maxillofacial applications. Seventeen maxillary hydroxyapatite implants (implant time of 4-138 months, 39-month mean) were harvested for analysis from 14 patients. The implants had been placed into the lateral maxillary wall during orthognathic surgery, juxtapositioned to the maxillary sinus. Ingrowth was measured in 100-microm increments from a bone-implant interface to a depth of 1500 microm. Bone ingrowth averaged over the 14 patients (0-1100 microm depth) is described by the equation % ingrowth - 20% * (depth in millimeters) + 41.25% (R2 = 0.98, n = 10 incremental depths). Beyond 1100 microm, the average ingrowth remained constant at 15.0 +/- 0.7%. The duration of implantation also showed as affect on the percent ingrowth into the implants at the incremental depths, and the percent ingrowth asymptotically approached a maximum. Overall, the composite average data from all depths is best described by the logarithmic function % ingrowth = 15% * ln(implantation time in months) - 24.0% (R2 = 0.71, n = 14 patients). Several factors may come into play in determining bone ingrowth including the mechanical environment, the osteoconductivity of the implant material, and the osteogenic capability of the tissues in the pore spaces. Measurements of bone ingrowth are most influenced by the depth into the implant and the time the implant was in the body; the age of the patient had little affect on bone ingrowth.

Adolescent↗

PubMed1999

Effects of space flight and IGF-1 on immune function.

We tested the hypothesis that insulin-like growth factor-1 (IGF-1) would ameliorate space flight-induced effects on the immune system. Twelve male, Sprague-Dawley rats, surgically implanted with mini osmotic pumps, were subjected to space flight for 10 days on STS-77. Six rats received 10 mg/kg/day of IGF-1 and 6 rats received saline. Flight animals had a lymphocytopenia and granulocytosis which were reversed by IGF-1. Flight animals had significantly higher corticosterone levels than ground controls but IGF-1 did not impact this stress hormone. Therefore, the reversed granulocytosis did not correlate with serum corticosterone. Space flight and IGF-1 also combined to induce a monocytopenia that was not evident in ground control animals treated with IGF-1 or in animals subjected to space flight but given physiological saline. There was a significant increase in spleen weights in vivarium animals treated with IGF-1, however, this change did not occur in flight animals. We observed reduced agonist-induced lymph node cell proliferation by cells from flight animals compared to ground controls. The reduced proliferation was not augmented by IGF-1 treatment. There was enhanced secretion of TNF, IL-6 and NO by flight-animal peritoneal macrophages compared to vivarium controls, however, O2(-) secretion was not affected. These data suggest that IGF-1 can ameliorate some of the effects of space flight but that space flight can also impact the normal response to IGF-1. Grant Numbers: NAGW-1197, NAGW-2328.

Animals↗

PubMed1999

Effects of spaceflight and PEG-IL-2 on rat physiological and immunological responses.

Sprague-Dawley rats were subjected to two 8-day spaceflights on the space shuttle. Rats housed in the National Aeronautics and Space Administration's animal enclosure were injected (iv or sc) with pegylated interleukin-2 (PEG-IL-2) or a placebo. We tested the hypothesis that PEG-IL-2 would ameliorate some of the effects of spaceflight. We measured body and organ weights; blood cell differentials; plasma corticosterone; colony-forming units (macrophage and granulocyte macrophage); lymphocyte mitogenic, superantigenic, and interferon-gamma responses; bone marrow cell and peritoneal macrophage cytokine secretion; and bone strength and mass. Few immunological parameters were affected by spaceflight. However, some spaceflight effects were observed in each flight. Specifically, peritoneal macrophage spontaneous secretion of tumor necrosis factor-alpha occurred in the first but not in the second flight. A significant monocytopenia and lymphocytopenia were detected in the second but not in the first flight. The second mission produced bone changes more consistent with past spaceflight investigations. PEG-IL-2 did not appear to be beneficial; however, this was mostly due to the lack of spaceflight effects. These studies reflect the difficulty in reproducing experimental models by using current space shuttle conditions.

Animals↗

PubMed1999

The effects of age and dietary restriction without nutritional supplementation on whole bone structural properties in C57BL/6J mice.

While caloric restriction is a proven means to extend longevity, its effects on bone are not well understood. This study examined the effects of dietary restriction without vitamin or mineral supplementation on bone in female 60- and 120-day-old C57BL/6J mice. Baseline controls were sacrificed at 60 or 120 days, while diet-restricted animals ate approximately 72.9-78.6% of the ad libitum fed animals for thirty days. 60-day-old ad libitum animals experienced normal growth with average increases of 6.4% in bone length, 23.5% in bone mass, 9.4% in %mineralization, 36.4% in maximum strength, 59.2% in stiffness, 22.3% in cortical thickness, 12.9% in %cortical area, and 11.3% in microhardness. Growth in 120-day-old ad libitum animals followed a trend but with more modest increases. Diet-restricted mice matured very little from baseline levels in 60-day-old animals. There were no significant changes from baseline levels in the parameters indicated above, except for a 8.3% decrease in %cortical area attributable to increased resorption. 120-day-old diet-restricted animals also evidenced little deviation from baseline levels except for significant decreases in %mineralization (2.1%) and %cortical area (6.7%). The effects of diet restriction on bone properties decreased with age. Bone from 60-day-old diet-restricted mice showed diminished mechanical and compositional properties, resulting from little growth and excess resorption. Bone from 120-day-old diet-restricted mice showed little growth and some resorption. Increased resorption, localized on the endosteal surfaces, likely minimized the negative impact of structural degradation of the long bones. Resorption may have also provided minerals to compensate for nutritional deficiencies.

Aging↗

PubMed1998

Long-term bone ingrowth and residual microhardness of porous block hydroxyapatite implants in humans.

PURPOSE: This study examined the ingrowth of bone into coralline, porous hydroxyapatite (HA) block (Interpore 200) over long periods after orthognathic surgery and analyzed their microhardness as a measure of the structural integrity of the ingrown bone as well as of the HA. MATERIALS AND METHODS: Twenty-five maxillary HA implants (4 to 138 months of implantation; mean, 32 months) were removed from 17 patients. These implants had been placed into the lateral maxillary wall, juxtapositioned to the maxillary sinus during orthognathic surgery, and were harvested for analysis after voluntary consent. RESULTS: Microscopic examination showed normal bone morphology in all implants; no inflammatory response was observed. Histomorphometric measurements indicated that there was significant bone ingrowth in all implants, with an overall mean of 23+/-7% bone (range, 7% to 31%), 51%+/-7% HA matrix (range, 39% to 65%), and the remainder being soft tissue or void at 26%+/-9% (range, 10% to 40%). No significant difference in microhardness values between the bone in the implant and the bone surrounding the implant was noted, indicating that the structural integrity of the porous block HA/bone aggregate had been maintained. Bone ingrowth appeared to plateau around 20 months, reaching an equilibrium in which the relative amount of osseous tissue remained constant. CONCLUSION: Based on the findings in this study, porous block HA is a viable material for long-term implantation in the maxilla during orthognathic surgery.

Analysis of Variance↗

PubMed1998

Histomorphometric, physical, and mechanical effects of spaceflight and insulin-like growth factor-I on rat long bones.

Previous experiments have shown that skeletal unloading resulting from exposure to microgravity induces osteopenia in rats. In maturing rats, this is primarily a function of reduced formation, rather than increased resorption. Insulin-like growth factor-I (IGF-I) stimulates bone formation by increasing collagen synthesis by osteoblasts. The ability of IGF-I to prevent osteopenia otherwise caused by spaceflight was investigated in 12 rats flown for 10 days aboard the Space Shuttle, STS-77. The effect IGF-I had on cortical bone metabolism was generally anabolic. For example, humerus periosteal bone formation increased a significant 37.6% for the spaceflight animals treated with IGF-I, whereas the ground controls increased 24.7%. This increase in humeral bone formation at the periosteum is a result of an increased percent mineralizing perimeter (%Min.Pm), rather than mineral apposition rate (MAR), for both spaceflight and ground control rats. However, IGF-I did inhibit humerus endocortical bone formation in both the spaceflight and ground control rats (38.1% and 39.2%, respectively) by limiting MAR. This effect was verified in a separate ground-based study. Similar histomorphometric results for spaceflight and ground control rats suggest that IGF-I effects occur during normal weight bearing and during spaceflight. Microhardness measurements of the newly formed bone indicate that the quality of the bone formed during IGF-I treatment or spaceflight was not adversely altered. Spaceflight did not consistently change the structural (force-deflection) properties of the femur or humerus when tested in three-point bending. IGF-I significantly increased femoral maximum and fracture strength.

Animals↗

PubMed1997

Long-term ingrowth and apposition of porous hydroxylapatite implants.

Bone implant materials are often used to fill in bone gaps that frequently result from orthognathic and craniofacial reconstruction. The substrate hydroxylapatite (HA) is commonly implanted into the bone voids, resulting from these conditions due to its established biocompatibility and osteoconductive properties. The porous structure of HA provides a three-dimensional guideline for fibrovascular ingrowth, facilitating the process that ultimately results in the deposition of new bone. Porous HA (Interpore, 200) implants were implanted in the mandible or maxilla of nine humans and removed after 14-30 months (19.1-month mean). There was no evidence of an inflammatory response. The sample composition and apposition against the implant were determined using point counting and a digitizing tablet and software. Percent ingrowth in available space (%IAS) was defined as %Bone/(%Bone + %Void). A new measure of implant saturation (%IAS-%Apposition of bone) was established to help determine the fundamental manner in which long-term HA implants incorporate bone. In the mean, the samples were composed of 27% bone, 21% void, and 53% implant. The apposition percentages averaged 60% bone, 16% void, and 24% soft tissue. The %IAS averaged 58%, and implant saturation averaged -3%, indicating that a near-balance between the implant and surrounding bone has been established.

Adolescent↗

PubMed1997

Effect of gravity and diffusion interface proximity on the morphology of collagen gels.

Collagen solutions (0.25% w/v) were polymerized in microgravity (STS-77, 10 days) along with simultaneous ground controls. Assembly conditions were achieved by the passage of buffer ions across a dialysis membrane into a reaction chamber containing the dissolved collagen. The gels were analyzed macroscopically and microscopically to assess the influence of gravity and the oriented diffusion of buffer ions on the resulting product. Double-blind rankings based on visual observation of the gels established that all of the flight gels (n = 8) were more uniform in appearance than all of the ground gels (n = 6). Photography using side illumination of the gels revealed the more granular appearance of the ground gels relative to the highly uniform appearance of the flight gels. Scanning electron microscopy established this difference at the microscopic level. Proximity to the dialysis interface and the presence or absence of gravity were both found to control the porosity and uniformity of the matrix.

Buffers↗

PubMed1997

Effects of deproteinization and ashing on site-specific properties of cortical bone.

Buffered sodium hypochlorite (NaOCl) solution was used to remove selectively the collagen phase from bovine cortical bone. Changes in the mechanical behaviour and material properties were studied over a wide range of resolution (from 5 microm to 3 mm) using an integrated combination of experimental techniques. Optical microscopy indicated that timed immersion in NaOCl results in cortical bone specimens that consist of a mineralized tissue core surrounded by a layer of deproteinized or anorganic bone. With increased NaOCl treatment, the mechanical behaviour in three-point flexure of the intact specimens became increasingly characteristic of a brittle ceramic material. Localized material properties were evaluated using histology, scanning electron microscopy and microhardness testing. The site-specific properties and the mineralization of the cores were not significantly affected by the treatment; however, the interactions and structural framework of the hydroxyapatite crystallites within the anorganic material were compromised. This destruction of crystallite interlocking was not observed in samples in which the organic phase was removed by ashing at 800 degrees C. The ashed samples maintained microhardness values three times those of the bleached samples. Because of its damaging effects on cortical bone structural integrity, the NaOCl treatment did not provide a reasonable means of studying, as a function of the phasic mass fraction, incremental changes in bone mechanical behaviour or the relative roles of collagen and mineral within the structural hierarchy.

Journal Article↗