Unloaded Control Research Articles

The Transport Profile of Cytokines in Epidermal Equivalents Subjected to Mechanical Loading

Pressure ulcer risk assessment might be optimized by incorporating the soft tissue reaction to mechanical loading in the currently used risk assessment scales. Cytokines, like IL-1alpha, IL-1RA, IL-8, and TNF-alpha, might be used to determine this tissue reaction, since they are released after 24 h of mechanical loading of epidermal equivalents. In the current study, the release and transport of these cytokines with time was evaluated. Epidermal equivalents were subjected to 20 kPa for different time periods (1, 2, 4, 6, 8, 16, and 24 h). Compared to the unloaded control group, a significant increase was found for IL-1alpha (4.7-fold), IL-1RA (4.8-fold), and IL-8 (3.6-fold) release after 1 h loading. For TNF-alpha, the release was significantly increased after 4 h of loading (5.1-fold compared to the unloaded situation), coinciding with the first signs of gross structural tissue damage. These cytokine values were determined in the surrounding medium and a transport model was developed to evaluate the distribution of cytokines inside the culture. These simulations revealed that all IL-8 and TNF-alpha was released from the keratinocytes, whereas most of the IL-1alpha and IL-1RA remained inside the keratinocytes during the 24 h loading period. In conclusion, IL-1alpha, IL-1RA, and IL-8 appear promising biochemical markers for pressure ulcer risk assessment, since their release is increased after 1 h of epidermal loading and before the onset of structural tissue damage.

Measurement of glucose metabolism in rat spinal cord slices with dynamic positron autoradiography

We attempted to measure the regional metabolic rate of glucose (MRglc) in sliced spinal cords in vitro. The thoracic spinal cord of a mature Wister rat was cut into 400-mum slices in oxygenated and cooled (1-4 degrees C) Krebs-Ringer solution. After at least 60 min of preincubation, the spinal cord slices were transferred into double polystyrene chambers and incubated in Krebs-Ringer solution at 36 degrees C, bubbled with 5% O(2)/5% CO(2) gas. To measure MRglc, we used the dynamic positron autoradiography technique (dPAT) with F-18-2-fluoro-2-deoxy-d-glucose ([(18)F]FDG) and the net influx constant of [(18)F]FDG as an index. Uptake curves of [(18)F]FDG were well fitted by straight lines for more than 7 h after the slicing of the spinal cord (linear regression coefficient, r=0.99), indicating a constant uptake of glucose by the spinal cord tissue. The slope (K), which denotes MRglc, is affected by tetrodotoxin, and high K(+) (50 mM) or Ca(2+)-free, high Mg(2+) solution. After 10 min of hypoxia, the K value following reoxygenation was similar to the unloaded control value, but after 45 min of hypoxia, the K value was markedly lower than the unloaded control value, and after >90 min of reoxygenation it was nearly 0. Our results indicate that the living spinal cord slices used retained an activity-dependent metabolism to some extent. This technique may provide a new approach for measuring MRglc in sliced living spinal cord tissue in vitro and for quantifying the dynamic changes in MRglc in response to various interventions such as hypoxia.

Efficacy of colistin‐impregnated beads to prevent multidrug‐resistant A. baumannii implant‐associated osteomyelitis

Osteomyelitis (OM) from multidrug-resistant (MDR) Acinetobacter has emerged in >30% of combat-related injuries in Iraq and Afghanistan. While most of these strains are sensitive to colistin, the drug is not available in bone void fillers for local high-dose delivery. To address this, we developed a mouse model with MDR strains isolated from wounded military personnel. In contrast to S. aureus OM, which is osteolytic and characterized by biofilm in necrotic bone, A. baumannii OM results in blastic lesions that do not contain apparent biofilm. We also found that mice mount a specific IgG response against three proteins (40, 47, and 56 kDa) regardless of the strain used, suggesting that these may be immuno-dominant antigens. PCR for the A. baumannii-specific parC gene confirmed a 100% infection rate with 75% of the MDR strains, and in vitro testing confirmed that all strains were sensitive to colistin. We also developed a real-time quantitative PCR (RTQ-PCR) assay that could detect as few as 10 copies of parC in a sample. To demonstrate the efficacy of colistin prophylaxis in this model, mice were treated with either parenteral colistin (0.2 mg colistinmethate i.m. for 7 days), local colistin (PMMA bead impregnated with 1.0 mg colistin sulfate), or an unloaded PMMA bead control. While the parenteral colistin failed to demonstrate any significant effects versus the placebo, the colistin PMMA bead significantly reduced the infection rate such that only 29.2% of the mice had detectable levels of parC at 19 days (p < 0.05 vs. i.m. colistin and placebo).

Early cortical bone healing around loaded titanium implants: a histological study in the rabbit

To identify the role of immediate implant loading on the early phases of the bone healing responses. Implants were placed in rabbit tibial diaphyses and left to heal for 3, 7, 14, 28 or 42 days. Half of the animals received an immediate loading protocol of 2.2 N at 3 Hz for 1800 cycles and 5 days/week, whereas the others served as unloaded controls. Histological assessment was combined with histomorphometrical measurements. At early time-points, an endosteal and periosteal new bone formation was found, while the cortex itself contained damaged osteocytes. At later time-points, new bone formation was also found at the cortical level itself. Differences between groups were found mainly in this new bone formation process, with larger reactions for the endosteal and periosteal bone in the loaded group after 28 and 42 days, respectively. At the end-point of the experiment, bone formation at the cortical level was reduced in the loaded group compared with the control group. These results show that the immediate loading protocol caused no differences in the sequential events leading to osseointegration in cortical bone. However, the processes of new bone formation originating from the endosteum and the periosteum lasted longer compared with the unloaded controls.

The effect of force, timing, and location on bone-to-implant contact of miniscrew implants

This study was conducted to evaluate the effect of timing and force of loading, as well as implant location, on bone-to-implant contact (BIC) of loaded and control miniscrew implants (MSI). Using seven skeletally mature male beagle dogs, 1-2 years of age, followed over a 110 day period, a randomized split-mouth design compared immediate versus delayed loading, 50 versus 25 g loading, and 25 g loads in the maxilla versus the mandible. Mobility was evaluated using a 0-3 point scale before the MSIs were prepared for histological analysis. Histomorphometric analyses were performed under light microscopy using Metamorph software on undecalcified sections. The percentage BIC was measured at three levels (coronal, middle, and apical) of the MSI. BIC was compared statistically using pairwise Wilcoxon signed-rank tests. Mobility was detected in three of the 56 (5.4 per cent) MSIs. The mobile implants were all unloaded controls and showed no BIC. All remaining stable MSIs showed some BIC. However, variation in BIC was large, ranging from 2.2 to 100 per cent. There were no significant (P > 0.05) differences in BIC associated with timing of force application, amount of force applied, or implant location. There was a tendency for less BIC at the coronal level, but the differences between levels were not statistically significant. Within the limits of this study, it is concluded that the timing and amount of force at loading and location of implant placement do not affect BIC. Moreover, it appears that only limited amounts of osseointegration are necessary to ensure implant stability.

Pitch-based carbon-fibre-reinforced poly (ether—ether—ketone) OPTIMA® assessed as a bearing material in a mobile bearing unicondylar knee joint

The introduction of unicondylar knee prostheses has allowed the preservation of the non-diseased compartment of the knee while replacing the diseased or damaged compartment. In an attempt to reduce the likelihood of aseptic loosening, new material combinations have been investigated within the laboratory. Tribological tests (friction, lubrication, and wear) were performed on metal-on-carbon-fibre-reinforced (CFR) poly (ether-ether-ketone) (PEEK) (pitch-based) mobile unicondylar knee prostheses up to 5 x 10(6) cycles. Both a loaded soak control and an unloaded soak control (both medial and lateral components) were used to compensate for weight change due to lubricant absorption. For this material combination the loaded soak control gave slightly lower wear for both the medial and the lateral components than did the unloaded soak control. The medial components gave higher steady state wear than the lateral components (1.70 mm3 per 10(6) cycles compared with 1.02 mm3 per 10(6) cycles with the loaded soak control). The results show that the CFR PEEK unicondylar knee joints performed well in these wear tests. They gave lower volumetric wear rates than conventional metal-on-ultra-high-molecular-weight polyethylene prostheses have given in the past when tested under similar conditions. The friction tests showed that, at physiological viscosities, these joints operated in the boundary-mixed-lubrication regime. The low wear produced by these joints seems to be a function of the material combination and not of the lubrication regime.

The influence of bovine serum lubricant on the wear of cross-linked polyethylene finger prostheses.

A two-piece finger prosthesis has been proposed, manufactured from silane cross-linked polyethylene. Using a finger wear simulator the prosthesis was tested in a dilute bovine serum lubricant. Five tests were undertaken, totalling over 45 million cycles of wear testing. In each test, a statically loaded control prosthesis was included. In all tests it was found that the lubricant uptake of the test components exceeded that of the control components, consequently no gravimetric wear was measured. To investigate this result further, six cross-linked polyethylene prostheses were taken and soaked in the serum lubricant at 37 degrees C. Three of the prostheses were statically loaded and the other three were unloaded. These tests lasted for over one hundred and sixty days. It was found that the lubricant uptake of the unloaded control components was greater than that of the loaded com-ponents. The test with statically loaded prostheses was repeated, firstly with distilled water and then in lubricant heated to 30 degrees C and 40 degrees C. No significant difference in weight increase due to lubricant uptake at these two temperatures was found. The weight increase due to soaking in dilute bovine serum was several times that due to soaking in distilled water. (Journal of Ap-plied Biomaterials & Biomechanics 2004; 2: 136-42).

Physiologic deformational loading does not counteract the catabolic effects of interleukin-1 in long-term culture of chondrocyte-seeded agarose constructs

An interplay of mechanical and chemical factors is integral to cartilage maintenance and/or degeneration. Interleukin-1 (IL-1) is a pro-inflammatory cytokine that is present at elevated concentrations in osteoarthritic joints and initiates the rapid degradation of cartilage when cultured in vitro. Several short-term studies have suggested that applied dynamic deformational loading may have a protective effect against the catabolic actions of IL-1. In the current study, we examine whether the long-term (42 days) application of dynamic deformational loading on chondrocyte-seeded agarose constructs can mitigate these catabolic effects. Three studies were carried out using two IL-1 isoforms (IL-1 α and IL-1 β) in chemically defined medium supplemented with a broad range of cytokine concentrations and durations. Physiologic loading was unable to counteract the long-term catabolic effects of IL-1 under any of the conditions tested, and in some cases led to further degeneration over unloaded controls.

Light‐Microscopic Evaluation of the Dimensions of Peri‐Implant Mucosa Around Immediately Loaded and Submerged Titanium Implants in Monkeys

Immediate loading of dental implants is a successful treatment concept. The importance of healthy peri-implant soft tissues for the long-term success of dental implants has been widely recognized. The aim of this study was to evaluate the peri-implant soft tissues around immediately loaded and submerged implants in monkeys. A total of 48 implants were inserted in six Macaca fascicularis monkeys. For 24 implants (test implants), the prosthetic abutments were inserted immediately, and a custom-made metal superstructure was cemented after 3 days; the other 24 implants were left unloaded (control implants). Block sections of bone segments containing the implants were retrieved 9 months after surgical placement. A histomorphometric measurement of sulcular epithelium (SE), junctional epithelium (JE), and connective tissue (CT) contact percentage of the soft tissues around test and control implants was carried out. In some specimens, the peri-implant epithelium was very similar to a pocket epithelium, whereas in others it was possible to observe an SE and a long junctional-like epithelium with a moderate amount of inflammatory cells. The supracrestal peri-implant CT was dense and organized in collagen fibrous bundles in an annular pattern around the implant. No statistically significant differences were present in the dimensions of SE, JE, and CT in test and control implants (P >0.05). Immediate loading did not produce changes in the dimensions of the peri-implant soft tissues.

Effect of strain at low‐frequency loading on peri‐implant bone (re)modelling: a guinea‐pig experimental study

AbstractObjectives: To investigate whether controlled early loading enhances peri‐implant bone mass and bone‐to‐implant contact. Low‐frequency stimulation (3 Hz) and varying force amplitudes, causing varying strains, were applied in three guinea‐pig series.Material and methods: Three series of guinea‐pigs received percutaneous TiO2‐blasted implants in both tibiae. One week after implant installation, one implant was stimulated with a sinusoidally varying bending moment while the contra‐lateral implant served as an unloaded control. Force amplitudes of 0.5, 1 and 2 N were applied on a 20‐mm‐long cantilever, resulting in strains of 133, 267 and 533 μɛ, respectively, measured by a strain gauge bonded on the surface of the tibial bone at 1.3 mm from the implant's distal surface. Implant stability was followed by means of resonance frequency analysis. Bone‐to‐implant contact and bone mass [BM (%) bone occupied area fraction] were analysed histomorphometrically.Results: A significant positive effect on the difference in bone mass at the stimulated vs. at the control side was observed in the distal half peri‐implant marrow cavity for early mechanical stimulation at a frequency of 3 Hz (P&lt;0.0001). An optimum was reached for the applied load, which causes a strain of approximately 267 μɛ 1.3 mm from the implant. Implant stability gradually increased in time; no significant effect of early stimulation could be measured.Conclusions: The effect of early controlled mechanical stimulation on the peri‐implant bone, in this cortical bone model, is strongly dependent on force amplitude/strain at low‐frequency stimulation.

Fretting crevice corrosion of stainless steel stem–CoCr femoral head connections: Comparisons of materials, initial moisture, and offset length

Modular tapers continue to be used in a wide variety of orthopedic implants. In this study, stainless steel (ASTM F-1568) femoral hip stems combined with Co-Cr-Mo alloy heads (SS/CoCr) were tested in an in vitro fretting corrosion test set-up to assess the propensity for mechanically assisted corrosion. Three different aspects of the modular design were evaluated in this study: (1) material combination compared to CoCr/CoCr, (2) wet versus dry assembly for SS/CoCr couples, and (3) 0- and 6-mm head offset for SS/CoCr couples. Fretting corrosion tests over a range of cyclic loads up to 3300 N were performed, and continuous cyclic loading at 3300 N for 1 M cycles were performed on each group (n = 5). Fretting micromotion was measured as a function of cyclic load on select couples to detect the nature and extent of motion present. The results showed that SS/CoCr couples were more susceptible to fretting corrosion than CoCr/CoCr couples, that dry assembly does not prevent fretting corrosion from taking place but raises the onset load, and that 6-mm offset heads had higher visual evidence of fretting damage but showed mixed statistical results in terms of onset loads and OCP shifts and currents compared to the 0-mm offset samples. Current and voltage excursions over 1 million cycles tended to diminish towards their unloaded control levels but did not fully recover until cyclic loading ceased. Micromotion measurements indicated fretting motions in the range of 10-25 microm where 0-mm heads tended to piston on the trunion, while 6 mm heads tended to rock.

The Effects of Laser Microtextured Collars Upon Crestal Bone Levels of Dental Implants

The purpose of this study was to examine the crestal bone, connective tissue, and epithelial cell response to a laser microtextured collar compared with a machined collar, in the dog model. Six mongrel dogs had mandibular premolars and first molars extracted and after healing replaced with BioLok implants 4 x 8 mm. Each dog had 3 control implants placed on one side of the mandible and 3 experimental, laser microtextured, implants placed contralaterally. After 3 months, 1 dog was killed. Bridges were placed on the implants of 4 of the dogs. The sixth dog served as a negative control for the duration of the experiment. Two of the dogs were killed 3 months after loading, of the dogs were killed 6 months after loading as was the negative (unloaded) control. Histology, electron microscopy, and histomorpho-metric analysis was done on histologic sections obtained from block sections of the mandible containing the implants. Initially the experimental implants showed greater bone attachment along the collar. With time the bone heights along the control and experimental collars were equivalent. However, the controls had more soft tissue downgrowth, greater osteoclastic activity, and increased saucerization compared with sites adjacent to experimental implants. There was closer adaptation of the bone to the laser microtextured collars. Use of tissue-engineered collars with microgrooving seems to promote bone and soft tissue attachment along the collar and facilitate development of a biological width.

Effect of expansile paclitaxel-loaded nanoparticles on growth of lung cancer in vivo

7593 Background: Surgical resection remains the most effective treatment for patients with non-small cell lung cancer; however, even in early stage diagnoses the presence of occult microscopic disease at the surgical resection margin significantly impacts long-term patient survival. Thus, the focus of this study is to establish proof of concept that locoregional growth of microscopic tumor burden can be prevented through the application of a novel “expansile” nanoparticle drug delivery system. Methods: Biocompatible polymer nanoparticles that enter tumor cells and swell 300 fold in response to pH were loaded with paclitaxel (Pax-NP) and assessed for efficacy against murine Lewis lung carcinoma (LLC) cells using cell viability assays in vitro and tumor implantation in vivo. Paclitaxel-loaded non-expansile nanoparticles (Pax-neNP) that are not sensitive to pH variation were also produced. For the in vivo studies, 7.5 x 105 LLC tumor cells were co-injected with 0.25 mg unloaded control (expansile) NP, Pax-NP, Pax-neNP or paclitaxel alone in 100μL Cremophor EL/ethanol (each equivalent to a 2.5 μg dose of paclitaxel) subcutaneously in C57Bl/6 mice. Results: In vitro assays demonstrated that co-culture of LLC cells and Pax-NP results in significant inhibition of tumor growth (p<0.01, t-test vs control). In contrast, LLC incubated with unloaded NP did not inhibit tumor growth. Moreover, Pax-NP prevented tumor growth in vivo. Whereas LLC alone (n=11) or LLC with 0.25mg unloaded NP (n=14) or Pax-neNP (n=12) resulted in the development of tumors with volumes of 388±86, 382±82 and 268±63 mm3, respectively (mean ± SE), only one mouse (n=15) developed a small tumor (2±2 mm3) following the injection of LLC and Pax-NP (p<0.05 via ANOVA). Further, injection with an equivalent dose of paclitaxel did not significantly reduce tumor growth (225±95, n=6). Conclusions: These results establish that locoregional growth of microscopic tumor burden can be inhibited by intracellular nanoparticle-mediated drug delivery. These early results suggest that Pax-NP, which undergo cellular uptake with resultant drug release, may afford enhanced local drug delivery aimed at preventing the growth of occult microscopic disease present at the resection margin following parenchyma-sparing surgery for lung cancer. No significant financial relationships to disclose.

Effect of Dynamic Loading on the Integrity of the Interface between Root Canal and Obturation Materials

The purpose of this study was to evaluate the effect of occlusal load on the integrity of root canal obturation. Maxillary anterior teeth were cleaned, shaped, and obturated with either gutta-percha (GP)/AH Plus or Resilon/Epiphany. Afterwards, teeth were placed under 100 N force at 2 Hz for 22 hours in a 37°C water bath. Teeth were sectioned and examined for disruption in the integrity of the obturation by using optical microscopy. The length of the separation between the obturation and the root canal walls was measured and compared statistically. GP and Resilon obturated canals subjected to occlusal load displayed significantly greater interface disruption compared with unloaded controls (p < .05). The results indicate that occlusal load generates separation forces on the obturation interface that might compromise the sealing ability of the obturation.

A potential application of dietary soy protein, aminoguanidine and L‐carnitine as anti‐oxidants in an animal model of simulated microgravity.

The objective of the current study was to determine the effect of antioxidants in rats under simulated microgravity induced by hind‐limb suspension (HLS). Methods: A NASA validated model was used with five groups of rats. L‐carnitine and aminoguanidine were used in the drinking water in rats on Purina chow. A separate group was maintained on a soybean diet. Group 1 was hindlimb loaded control; Group 2 was hindlimb unloaded control, Group 3 was hindlimb unloaded on L‐carnitine (LC), Group 4 was hindlimb unloaded on aminoguanidine (AG), and Group 5 was hindlimb unloaded on 9.6% soybean protein diet. The animals were primed and suspended for fourteen days (total 21 days). At term, the animals were sacrificed. Tissues from brain, heart, lung, liver, stomach, pancreas, small intestine, kidney and testes were harvested. Harvested tissues were extracted for measurements of malondialdehyde (MDA) and glutathione levels. Results: MDA levels in tissues were elevated by suspension (p &lt; 0.05). MDA levels were lower (p&lt; 0.05) in the animals on LC, AG, and the soybean diet, when compared to the hindlimb unloaded control group. Glutathione levels varied between the tissues. Conclusions: Results suggest that LC, AG, and a soybean diet decrease peroxide formation, while tail suspension increases it. Data indicate that LC, AG, and a soybean diet may have a protective role in the reduction of lipid peroxidation damage produced by stress.

In vitro interface and cement mantle analysis of different femur stem designs

The aim of this study is to define stem design related factors causing both gaps in the metal–bone cement interface and cracks within the cement mantle. Six different stem designs (Exeter; Lubinus SP II; Ceraver Osteal; Mueller-straight stem; Centega; Spectron EF) ( n=15 of each design) were cemented into artificial femur bones. Ten stems of each design were loaded, while five stems served as an unloaded control. Physiologically adapted cyclical loading (DIN ISO 7206-4) was performed with a hip simulator. After loading both interfaces and the bone cement itself were analysed regarding gaps and cracks in the cement mantle. Significant differences between the stem designs concerning gaps in the metal–bone cement interface and cracks in the cement mantle became apparent. Additionally, a high correlation between gaps in the metal–bone cement interface and cracks within the cement mantle could be proven. Gaps in the metal–bone cement interface but no cracks within the cement mantle were seen in the unloaded specimens. Differences between the unloaded control groups and the cyclical loaded stems regarding the longitudinal extension and width of gaps in the metal–bone cement interface were obvious. The designs of cemented femoral stems have an influence on both the quality of the metal–bone cement contact and the failure rate of the cement mantle. Less interface gaps and less cement defects were found with anatomically formed, collared, well-rounded stem designs without undercuttings.

Dynamic and static mechanical compression affects akt phosphorylation in porcine patellofemoral joint cartilage

Protein kinase B (Akt)-dependent signaling pathways induced by mechanical loading have been identified in a variety of tissue. However, there is no evidence for a potential regulation of Akt in cartilage mechanotransduction. This study was conducted in order to determine whether or not the Akt in chondrocytes is regulated by mechanical loading. Porcine patellofemoral joints were loaded in compression at 500 N for 150 s either dynamically at 12 Hz or 1 Hz or statically using a custom-designed loading frame. Left-sided knees served as intervention, right-sided as unloaded control. Cartilage samples were harvested at different time points after mechanical loading and the phosphorylation of Akt was analyzed immunohistochemically. A downregulation of Akt phosphorylation was seen in cartilage 300 s after mechanical loading whereas Akt phosphorylation remained unchanged in unloaded specimens. In addition, regulation of Akt appeared to change with the frequency of loading, presenting different patterns in Akt phosphorylation with static and dynamic loading. Variations in Akt phosphorylation were detected through different zones of cartilage. Overall, our findings indicate that Akt signaling in porcine patellofemoral joint cartilage is dependent upon frequency of loading, cartilage zone, and the time interval between loading and cartilage harvest. It may be concluded that Akt plays a role in cartilage mechanotransduction.

Hydrostatic Pressure Differentially Regulates Outer and Inner Annulus Fibrosus Cell Matrix Production in 3D Scaffolds

Mechanical stimulation may be used to enhance the development of engineered constructs for the replacement of load bearing tissues, such as the intervertebral disc. This study examined the effects of dynamic hydrostatic pressure (HP) on outer and inner annulus (OA, IA) fibrosus cells seeded on fibrous poly(glycolic acid)-poly(L-lactic acid) scaffolds. Constructs were pressurized (5 MPa, 0.5 Hz) for 4 h/day from day 3 to day 14 of culture and analyzed using ELISAs and immunohistochemistry (IHC) to assess extracellular matrix (ECM) production. Both cell types were viable, with OA cells exhibiting more infiltration into the scaffold, which was enhanced by HP. ELISA analyses revealed that HP had no effect on type I collagen production while a significant increase in type II collagen (COL II) was measured in pressurized OA constructs compared to day 14 unloaded controls. Both OA and IA dynamically loaded scaffolds exhibited more uniform COL II elaboration as shown by IHC analyses, which was most pronounced in OA-seeded scaffolds. Overall, HP resulted in enhanced ECM elaboration and organization by OA-seeded constructs, while IA-seeded scaffolds were less responsive. As such, hydrostatic pressurization may be beneficial in annulus fibrosus tissue engineering when applied in concert with an appropriate cell source and scaffold material.

Insulin-like growth factor I releasing silk fibroin scaffolds induce chondrogenic differentiation of human mesenchymal stem cells

Growth factor releasing scaffolds are an emerging alternative to autologous or allogenous implants, providing a biologically active template for tissue (re)-generation. The goal of this study is to evaluate the feasibility of controlled insulin-like growth factor I (IGF-I) releasing silk fibroin (SF) scaffolds in the context of cartilage repair. The impact of manufacturing parameters (pH, methanol treatment and drug load) was correlated with IGF-I release kinetics using ELISA and potency tests. Methanol treatment induced water insolubility of SF scaffolds, allowed the control of bioactive IGF-I delivery and did not affect IGF-I potency. The cumulative drug release correlated linearly with the IGF-I load. To evaluate the chondrogenic potential of the scaffolds, hMSC were seeded on unloaded and IGF-I loaded scaffolds in TGF-β supplemented medium. Chondrogenic differentiation of hMSC was observed on IGF-I loaded scaffolds, starting after 2 weeks and more strongly after 3 weeks, whereas no chondrogenic responses were observed on unloaded control scaffolds. IGF-I loaded porous SF scaffolds have the potential to provide chondrogenic stimuli to hMSC. Evidence for in vivo cartilage (re)generation must be demonstrated by future, pre-clinical proof of concept studies.

Experimental evaluation of tooth movement in the beagle dog with the mini-screw implant for orthodontic anchorage

The purposes of this study were to evaluate the stability of mini-screw implants (MSIs) and tooth movements in relation to the timing, amount, and location of force application. Additionally, clinical measurements of peri-implant health were recorded to determine predictors for MSI failure. A randomized split-mouth design was used in 7 skeletally mature male beagle dogs. All third premolars were extracted to facilitate retraction of the second premolars via sectional orthodontic appliances. In the maxilla, the effect of delayed vs immediate loading was tested under constant force (25 g). In the mandible, the effect of force level (25 vs 50 g) was tested on immediately loaded MSIs. All experimental MSIs had a corresponding unloaded control. Clinical records and measurements of tooth movement were taken at specified intervals. The overall success rate of the implants was 93% with no significant effects of timing, amount, or location of force applied. Peri-implant tissue health was not predictive of MSI failure. The maxillary and the mandibular second premolars were moved 3.3 +/- 1.0 and 3.8 +/- 1.3 mm, respectively. No significant differences in tooth movement were observed between immediate and delayed loading, at either 25 or 50 g or force, or between the maxilla and the mandible. These results support the notion that immediate MSI loading with light forces (25 and 50 g) can be accomplished with high rates of success, producing clinically relevant amounts of tooth movement that are not influenced by the amount of force or the location at which they are applied.