Biomedical subjects

Michael A K Liebschner

Publications and source records attributed to Michael A K Liebschner.

18 recordsLinked to original sources

PubMed2006

The accuracy of cephalometric tracing superimposition.

PURPOSE: The purpose of this study was to compare the accuracy of 4 methods for cephalometric tracing superimposition. They are the FH@Porion method, S-N@Sella method, least-squared averaged 5 landmarks (LS-5) method, and manual geometric method. MATERIALS AND METHODS: Eight lateral cephalometric radiographs were used. Cephalometric tracing was performed by 2 examiners. One had extensive experience in landmark digitization while the other had minimal experience. The radiographs were scanned and the reference landmarks ANS, Point A, Point B, and Pogonion were digitized, creating 8 master tracings. Then 6 digital copies of each master tracing were made, 3 for each examiner. Subsequently, the examiners were asked to digitize and trace predetermined cranial base landmarks and structures. Tracings occurred at 1-month intervals. As a result, 3 separate tracings of each set were obtained from each examiner. The tracings of each set were superimposed using 4 different methods in the CASSOS software (SoftEnable Technology Ltd, Hong Kong SAR, China). For each method of superimposition, the coordinates of ANS, Point A, Point B, and Pogonion were recorded. Their means and variances were calculated. The variance represents the variability of the superimposition method. A general linear model for repeated measures was computed to test whether there were statistically significant differences among the 4 superimposition methods, 2 examiners, 4 reference landmarks, and 2 directions. Because the distribution of the variances was skewed, they were transformed to log variances. Finally, the errors of the superimposition in millimeters for each given examiner, superimposition method, reference landmark, and direction (X, Y) were calculated. RESULTS: There was a statistically significant difference in measurement variability among the 4 superimposition methods (P < .001). For both examiners, the variability of the different superimposition methods from the highest to the lowest was: Frankfort Plane registered at Porion method, Sella-Nasion registered at Sella method, least-square averaged 5 landmarks method, and the manual geometric method. In addition, there was a statistically significant difference in the magnitude of superimposition errors between the 2 examiners (P < .001). The experienced examiner was consistently more precise than the inexperienced examiner across all methods. Moreover, there was a statistically significant difference among 4 reference landmarks (P < .001). For both examiners, the recorded variability of each given reference landmark from the lowest to the highest was: ANS, Point A, Point B, and Pogonion. Furthermore, the variability differences between horizontal and vertical directions did not reach a conventional level of significance (P = .123). Finally, the recorded errors in millimeters for each superimposition method were summarized. A smaller error in millimeters represented a higher accuracy in superimposition. The error of using manual geometric or LS-5 methods for both examiners was less than 0.50 mm, while the error of using the other 2 methods was up to 0.99 mm for the experienced examiner and 2.88 mm for the inexperienced examiner. CONCLUSION: The error of both manual and LS-5 methods was within 0.5 mm. The LS-5 method had its advantage because it could be automated by the computer.

Algorithms↗

PubMed2006

Cost-effectiveness analysis for computer-aided surgical simulation in complex cranio-maxillofacial surgery.

PURPOSE: The purpose of this study is to assess the costs and benefits of computer-aided surgical simulation (CASS) and to compare it with the current surgical planning methods for complex cranio-maxillofacial (CMF) surgery. MATERIALS AND METHODS: The comparison of methods applies to all CMF surgeries where the patient's condition is severe enough to undergo a computed tomography scan and a stereolithographic model is necessary for the surgical planning process. The costs for each method can be divided into time and other costs. The time was estimated based on the authors' experience as well as on a survey of a small group of 6 experienced CMF surgeons in the United States. The other costs were estimated based on the authors' experience. RESULTS: CASS has lower costs in terms of surgeon time, patient time, and material costs. Specifically, total surgeon hours spent in planning are 5.25 hours compared with 9.75 for current standard methods. Material and scanning costs are Dollars 1,900 for CASS compared with about Dollars 3,510 for standard methods. Patient time for planning is reduced from 4.75 hours to 2.25 hours with CASS. The reduction in both time and other costs remains when the fixed fee costs of CASS are added to the variable costs. Amortized across the 600 patients per year (1,800 for the assumed 3-year life of the training and software), this adds only a few dollars and a fraction of an hour per surgery. Even in the case of a small clinic when the cost is amortized for 6 patients per year (18 patients for the assumed 3-year life of the training and software), the per surgery costs (9.65 hours and Dollars 2,456) will still favor CASS. CONCLUSION: Any great new design should consist of at least 2 of the 3 following features: faster, cheaper, and better outcome. This analysis demonstrates that CASS is faster and less costly than the current standard planning methods for complex CMF surgery. Previous studies have also shown that CASS results in better surgical outcomes. Thus, in all regards, CASS appears to be at least as good as the current methods of surgical planning.

Computer Simulation↗

PubMed2005

Testing two predictions for fracture load using computer models of trabecular bone.

Aging induces several types of architectural changes in trabecular bone including thinning, increased levels of anisotropy, and perforation. It has been determined, on the basis of analysis of mathematical models, that reduction in fracture load caused by perforation is significantly higher than those due to equivalent levels of thinning or anisotropy. The analysis has also provided an expression which relates the fractional reduction of strength tau to the fraction of elements nu that have been removed from a network. Further, it was proposed that the ratio Gamma of the elastic constant of a sample and its linear response at resonance can be used as a surrogate for tau. Experimental validation of these predictions requires following architectural changes in a given sample of trabecular bone; techniques to study such changes using microcomputed tomography are only beginning to be available. In the present study, we use anatomically accurate computer models constructed from digitized images of bone samples for the purpose. Images of healthy bone are subjected to successive levels of synthetic degradation via surface erosion. Computer models constructed from these images are used to calculate their fracture load and other mechanical properties. Results from these computations are shown to be consistent with predictions derived from the analysis of mathematical models. Although the form of tau(nu) is known, parameters in the expression are expected to be sample-specific, and hence nu is not a reliable predictor of strength. We provide an example to demonstrate this. In contrast, analysis of model networks shows that the linear part of tau(Gamma) depends only on the structure of trabecular bone. Computations on models constructed from samples of iliac crest trabecular bone are shown to be in agreement with this assertion. Since Gamma can be computed from a vibrational assessment of bone, we argue that the latter can be used to introduce new surrogates for bone strength and hence diagnostic tools for osteoporosis.

Bone Density↗

PubMed2005

Hydraulic strengthening affects the stiffness and strength of cortical bone.

A nonlinear, interstitial fluid flow constitutive model for cortical bone was developed to study the strain-rate dependency of cortical bone apparent modulus (Ea). Nine representative volume element (RVE) structural models of cortical bone spanning an effective pore volume fraction P range of 1-40% were examined. Dynamic loading conditions were used to study the fluid flow contribution or hydraulic strengthening (HS) effect on Ea for each RVE model. The model indicated that there is an upper and lower asymptotic bound of strain-rate (10(+/-3) sec(-1)) above or below which there are no further HS effects on Ea. At certain strain-rates (10(-1) to 10(0) sec(-1)) variations in cortical bone porosity had little or no influence on Ea. At lower and higher frequencies, the loss tangent, hence the magnitude of viscoelastic effects is greater. For strain-rates less than 10(-1) sec(-1), lower porosity RVE models were always stiffer than higher porosity RVE models. A generalized power law model is proposed to account for the fact that HS in cortical bone exhibits an upper and lower asymptotic bound and is bi-modal in terms of strain-rate.

Animals↗

PubMed2005

Flow perfusion enhances the calcified matrix deposition of marrow stromal cells in biodegradable nonwoven fiber mesh scaffolds.

In this study, we report on the ability of resorbable poly(L-lactic acid) (PLLA) nonwoven scaffolds to support the attachment, growth, and differentiation of marrow stromal cells (MSCs) under fluid flow. Rat MSCs were isolated from young male Wistar rats and expanded using established methods. The cells were then seeded on PLLA nonwoven fiber meshes. The PLLA nonwoven fiber meshes had 99% porosity, 17 microm fiber diameter, 10 mm scaffold diameter, and 1.7-mm thickness. The nonwoven PLLA meshes were seeded with a cell suspension of 5 x 10(5) cells in 300 microl, and cultured in a flow perfusion bioreactor and under static conditions. Cell/polymer nonwoven scaffolds cultured under flow perfusion had significantly higher amounts of calcified matrix deposited on them after 16 days of culture. Microcomputed tomography revealed that the in vitro generated extracellular matrix in the scaffolds cultured under static conditions was denser at the periphery of the scaffold while in the scaffolds cultured in the perfusion bioreactor the extracellular matrix demonstrated a more homogeneous distribution. These results show that flow perfusion accelerates the proliferation and differentiation of MSCs, seeded on nonwoven PLLA scaffolds, toward the osteoblastic phenotype, and improves the distribution of the in vitro generated calcified extracellular matrix.

Animals↗

PubMed2005

In vitro degradation of porous poly(propylene fumarate)/poly(DL-lactic-co-glycolic acid) composite scaffolds.

This study investigated the in vitro degradation of porous poly(propylene fumarate) (PPF-based) composites incorporating microparticles of blends of poly(DL-lactic-co-glycolic acid) (PLGA) and poly(ethylene glycol) (PEG) during a 26-week period in pH 7.4 phosphate-buffered saline at 37 degrees C. Using a fractional factorial design, four formulations of composite scaffolds were fabricated with varying PEG content of the microparticles, microparticle mass fraction of the composite material, and initial leachable porogen content of the scaffold formulations. PPF scaffolds without microparticles were fabricated with varying leachable porogen content for use as controls. The effects of including PLGA/PEG microparticles in PPF scaffolds and the influence of alterations in the composite formulation on scaffold mass, geometry, water absorption, mechanical properties and porosity were examined for cylindrical specimens with lengths of 13 mm and diameters of 6.5 mm. The composite scaffold composition affected the extent of loss of polymer mass, scaffold length, and diameter, with the greatest loss of polymer mass equal to 15+/-5% over 26 weeks. No formulation, however, exhibited any variation in compressive modulus or peak compressive strength over time. Additionally, sample porosity, as determined by both mercury porosimetry and micro-computed tomography did not change during the period of this study. These results demonstrate that microparticle carriers can be incorporated into PPF scaffolds for localized delivery of bioactive molecules without altering scaffold mechanical or structural properties up to 26 weeks in vitro.

Biocompatible Materials↗

PubMed2005

Radiographic analysis for jaw motion normalization.

PURPOSE: This study incorporated 3 objectives: 1 ) to evaluate the physical location of the center of rotation as determined by a custom mathematical algorithm, 2 ) to identify and compare the geometric center of the condylar head in radiographs with the calculated center of rotation, and 3 ) to determine whether a correlation exists between jaw motion characteristics and the mandibular geometry of the subject. MATERIALS AND METHODS: Lateral cephalometric radiographs of 9 subjects who underwent motion path analysis were obtained. The determined center of rotation of each mandible was calculated through a custom algorithm and recorded on the radiograph. Circular templates were used to determine the geometric center of the condyle for comparisons. Finally, measurements of 4 geometric jaw parameters were made and compared with motion characteristics to investigate whether mandibular geometry can be correlated to motion parameters. RESULTS: All calculated centers of rotation were found to lie in the condylar head of the mandible. The average difference between the calculated center of rotation and geometric center of the condylar head was 2.87 mm (SD, 1.69 mm). In addition, correlations were found linking the length of the mandibular rotational arm to the rotational and translational motions. However, there was no correlation found with the other geometric mandibular parameters. CONCLUSIONS: Analysis of mandibular motion allows for an accurate determination of the center of rotation. Previously identified characteristic motion exists in terms of primary rotation, followed by translation of the mandible with rotation. The magnitude of each phase differs between subjects. This study points to a natural mechanism of mandibular opening as the amount of rotation increased for longer rotational arms and amount of translation increased for shorter ones, serving to lessen the disparity in the opening amounts among individuals.

Adult↗

PubMed2004

A study of age-related architectural changes that are most damaging to bones.

Osteoporosis-related bone damage causes major socioeconomic problems. For efficient use of therapeutic agents, it is necessary to be able to reliably identify patients with high propensity for nontraumatic fracture. Age-related bone loss imposes several architectural changes in bone; one of the few ways to estimate damage due to individual changes, and hence determine the most serious types of damage, is via the analysis of suitable mathematical models. Anatomical sites such as the vertebral body, proximal femur, and distal radius are locations where most age-related fractures occur. The inner porous (or trabecular) bone from these sites, which resemble disordered cubic networks, play a significant role in load transmission at these sites. Analysis of a mathematical model of porous bone is used to show that perforation of elements of the network is the most damaging architectural change to a bone. We also show that an expression for bone strength, derived on this basis, can capture changes in strength caused by the inclusion of other features like thinning of trabecular bone and the anisotropy of the network. We finally argue that bone density, which is currently the most routinely used diagnostic, cannot be a reliable surrogate for bone strength.

Aging↗

PubMed2004

Biomechanics of prophylactic vertebral reinforcement.

STUDY DESIGN: The effects of bone cement placement, volume, and bone density on the degree of biomechanical reinforcement on cadaveric vertebral bodies were studied using experimentally calibrated detailed finite element models. OBJECTIVES: To investigate the efficacy of prophylactic vertebroplasty on intact vertebral bodies with respect to biomechanical recovery and fracture risk reduction. SUMMARY OF BACKGROUND DATA: Vertebroplasty is a potentially effective fracture prevention treatment, but the risk of complications due to cement leakage must be minimized. Therefore, the least amount of bone cement required to improve vertebral strengths to low fracture risk levels need to be determined. METHODS: Six different polymethyl methacrylate volumes--1, 2.5, 3.5, 5, 7.5 and 9 cm--were virtually implanted into previously validated vertebral body finite element models, following bipedicular and posterolateral vertebroplasty approaches. Stiffness and fracture load of the treated and untreated vertebral body models under uniaxial compression were determined. RESULTS: Greater augmentation effects were observed for vertebral bodies with average quantitative computed tomography densities below 0.1 g/cm injected with polymethyl methacrylate volumes higher than 20% compared to lower injection volumes and higher bone densities, as well as for the bipedicular approach versus posterolateral. Vertebral bodies at high risk of fracture required at least 20% fill of polymethyl methacrylate to improve the mechanical integrity of vertebral bodies to low fracture risk levels, whereas 5% to 15% polymethyl methacrylate volumes were needed for the medium-risk vertebral bodies. CONCLUSION: Prophylactic vertebroplasty can be effective in reducing fracture risk. However, for the polymethyl methacrylate volume (20%) required for the successful reinforcement of high-risk vertebral bodies, the risk of complications will be as high as that for current vertebroplasty procedure for fracture repair. Therefore, alternative materials have to be investigated for prophylactic vertebroplasty. Furthermore, bipedicular vertebroplasty is the recommended approach due to its higher strengthening effect and easier surgical access than the posterolateral case.

Adult↗

PubMed2004

The effect of compressive axial preload on the flexibility of the thoracolumbar spine.

STUDY DESIGN: An in vitro flexibility study of the human thoracolumbar spine under compressive preload. OBJECTIVE: To attain kinematics descriptive of the thoracolumbar spine in vitro by applying a pure bending moment under a range of physiologic compressive preloads. SUMMARY OF BACKGROUND DATA: Many studies on the mechanical behavior of the spine under pure moment have been conducted; however, little is known regarding variations in the range of motion of the thoracolumbar spine attributable to simulated body weight and other physiologic load conditions. METHODS: Five fresh human cadaveric thoracolumbar spine specimens (T9-L3) were used. Five compressive axial preloads ranging from 75 to 975 N were applied to each specimen along the spinal curvature through four adjustable brackets attached to each vertebral body. Flexibility measurements were taken by applying a maximum of 5 Nm pure bending moment to the specimen in flexion and extension. The flexibilities in flexion and extension for each loading case were compared. RESULTS: The thoracolumbar spine supported compressive preloads as much as 975 N without damage or instability in the sagittal plane when the preload was applied along the natural curvature of the spine through estimated centers of rotation. The flexibility in bending (flexion/extension) of the ligamentous thoracolumbar spine decreased with increasing compressive preload. CONCLUSION: A higher bending stiffness was reached after the compressive load exceeded 500 N. Such knowledge could be used to establish better testing guidelines for implant evaluation and more realistic loading conditions.

Aged↗

PubMed2004

A comparative assessment of mandibular condylar position in patients with anterior disc displacement of the temporomandibular joint.

PURPOSE: The purpose of this study was to determine whether the position of the mandibular condyle in patients with anterior disc displacement (ADD) is different from that of a control group with normal joints using a novel method to quantify the irregular shape of the temporomandibular joint (TMJ). MATERIALS AND METHODS: Twenty-six magnetic resonance images of TMJs with ADD were evaluated and compared with 14 normal joints. The position of the condyle was determined by using 2 different methods: 1) measuring the horizontal and vertical normalized distances in millimeters between the geometric centers of the glenoid fossa and the condyle and 2) calculating the anteroposterior joint space ratio. RESULTS: Using the first method, the horizontal distance between the centers of the condyle and the glenoid fossa was 14.0 +/- 11.1 in the ADD group and 5.3 +/- 10.9 in the control group (P <.001). The vertical distance was 64.7 +/- 22.7 in the ADD group and 68.3 +/- 32.9 in the control group (P =.015). The ratio of the horizontal and the vertical condylar displacement in the ADD group was 2.4. Using the second method, the anteroposterior joint space ratios in the ADD group and in the control group were 1.7 +/- 0.5 and 1.2 +/- 0.4, respectively (P =.001). CONCLUSION: This study found that condyles of patients with ADD were situated more posterior and superior in the fossa than those in the control group. Moreover, in the ADD group, the posterior condylar displacement was noted to be 2.4 times greater than the superior condylar displacement.

Adolescent↗

PubMed2004

Biomechanical evaluation of the pins of a mandibular external distractor.

PURPOSE: Our goal was to establish whether the pins of an external distractor were capable of overcoming tissue resistance to distraction. MATERIALS AND METHODS: The study was carried out in 2 parts. The first part of the study determined the bending rigidity of the distractors pins. To accomplish this, the distractor was installed on the mandible of a stereolithographic model using 4 regular 2.0-mm steel pins. An osteotomy was not performed. The distractor was activated using a torque gauge, and the bending rigidity of the pins was recorded. The second part of the study determined the tissue resistance to mandibular distraction using fresh cadavers. Six cadavers were divided into 2 groups to determine tissue resistance to angular and linear distraction, respectively. The devices used to measure tissue resistance were a modified external multiplanar distractor and a torque gauge. RESULTS: In the anteroposterior direction, the tissue resistance to linear distraction clearly exceeded the bending rigidity of the pins for the first 7.5 mm of activation. After this, the opposite was true. In the vertical direction, the tissue resistance clearly exceeded the bending rigidity of the pins for the first 8.0 mm of activation. After this, the opposite was true. For the first 15.0 degrees of angular distraction in the sagittal plane, the tissue resistance was almost identical to the bending rigidity of the pins. After this, the tissue resistance significantly exceeded the bending rigidity of the pins. For the first 7.0 degrees of angular distraction in the transverse plane, the tissue resistance was marginally greater than the bending rigidity of the pins. After this, the bending rigidity of the pins increased significantly. CONCLUSION: The 2.0-mm steel pins used in most external multiplanar distractors are not capable of overcoming the tissue resistance to linear or angular distraction.

Biomechanical Phenomena↗

PubMed2004

Biomechanical considerations of animal models used in tissue engineering of bone.

Tissue engineering combines the aspects of cell biology, engineering, material science, and surgery to generate new functional tissue, and provides an important approach to the repair of segmental defects and in restoring biomechanical function. The development of tissue-engineering strategies into clinical therapeutic protocols requires extensive, preclinical experimentation in appropriate animal models. The ultimate success of any treatment strategy must be established in these animal models before clinical application. It is clear that the demands of the biological and mechanical environment in the clinical repair of critical size defects with tissue-engineered materials is significantly different from those existing in experimental animals. The major considerations facing any tissue-engineering testing logic include the choice of the defect, the animal, the age of the animal, the anatomic site, the size of the lesion, and most importantly, the micro-mechanical environment. With respect to biomechanical considerations when selecting animals for tissue- engineering of bone, it is evident that no common criteria have been reported. While in smaller animals due to size constraint only structural properties of whole bones can be measured, in larger animals and humans both material properties and structural properties are of interest. Based on reported results, comparison between the tissue-engineered bone across species may be of importance in establishing better model selection criteria. It has already been found that the deformation of long bones is fairly constant across species, and that stress levels during gait are dependent on the weight of the animal and the material properties of the bone tissue. Future research should therefore be geared towards developing better biomechanical testing systems and then finding the right animal model for the existing equipment.

Animals↗

PubMed2004

Evolution of vertebroplasty: a biomechanical perspective.

This paper is a collection of computational, finite element studies on vertebroplasty performed in our laboratory, which attempts to provide new biomechanical evidence and a fresh perspective into how the procedure can be implemented more effectively toward the goal of preventing osteoporosis-related fractures. The percutaneous application of a bone cement to vertebral defects associated with osteoporotic vertebral compression fracture has proven clinical successful in alleviating back pain. When the biomechanical efficacy of the procedure was examined, however, vertebroplasty was found to be limited in its ability to provide sufficient augmentation to prevent further fractures without risking complications arising from cement extravasations. The procedure may instead be more efficient biomechanically as a prophylactic treatment, to mechanically reinforce osteoporotic vertebrae at risk for fracture. Patient selection for such intervention may be reliably achieved with the more accurate fracture risk assessments based on vertebral strength, predicted using geometrically detailed, specimen-specific finite element models, rather than on bone density alone. Optimal cement volume, placement, and material properties were also recommended. The future of vertebroplasty involving biodegradable augmentation material laced with osteogenic agents that upon release will stimulate new bone growth and increase bone mass was proposed.

Animals↗

PubMed2003

Finite element modeling of the human thoracolumbar spine.

STUDY DESIGN: Biomechanical properties within cadaveric vertebral bodies were parametrically studied using finite element analysis after calibration to experimental data. OBJECTIVES: To develop and validate three-dimensional finite element models of the human thoracolumbar spine based on quantitative computed tomography scans. Specifically, combine finite element modeling together with biomechanical testing circumventing problems associated with direct measurements of shell properties. SUMMARY OF BACKGROUND DATA: Finite element methods can help to understand injury mechanisms and stress distribution patterns within vertebral bodies as an important part in clinical evaluation of spinal injuries. Because of complications in modeling the vertebral shell, it is not clear if quantitative computed tomography-based finite element models of the spine could accurately predict biomechanical properties. METHODS: We developed a novel finite element modeling technique based on quantitative computed tomography scans of 19 radiographically normal human vertebra bodies and mechanical property data from empirical studies on cylindrical trabecular bone specimens. Structural properties of the vertebral shell were recognized as parametric variables and were calibrated to provide agreement in whole vertebral body stiffness between model and experiment. The mean value of the shell properties thus obtained was used in all models to provide predictions of whole vertebral strength and stiffness. RESULTS: Calibration of n = 19 computer models to experimental stiffness yielded a mean effective modulus of the vertebral shell of 457 +/- 931 MPa ranging from 9 to 3216 MPa. No significant correlation was found between vertebral shell effective modulus and either the experimentally measured stiffness or the average trabecular modulus. Using the effective vertebral shell modulus for all 19 models, the predicted vertebral body stiffness was an excellent predictor of experimental measurements of both stiffness (r2= 0.81) and strength (r2 = 0.79). CONCLUSION: These findings indicate that modeling of the vertebral shell using a constant thickness of 0.35 mm and an effective modulus of 457 MPa, combined with quantitative computed tomography-based modeling of trabecular properties and vertebral geometry, can accurately predict whole vertebral biomechanical properties. Use of this modeling technique, therefore, should produce substantial insight into vertebral body biomechanical behavior and may ultimately improve clinical indications of fracture risk of this cohort.

Adult↗

PubMed2002

Biomechanical evaluation of a double-threaded pedicle screw in elderly vertebrae.

We sought to test the hypothesis that a pedicle screw that has two parallel threads of different heights throughout the full length of the screw could increase both bone purchase and pull-out strength compared with a standard single-threaded screw of similar dimensions. A single-threaded pedicle screw and a double-threaded pedicle screw were respectively placed into the paired pedicles of 21 vertebral bodies. The screws were then pulled out of the pedicles, and output parameters were measured. Although insertional torque was, on average, 14.5% higher (p = 0.039) for the single-threaded screw, maximum pull-out strength (p = 0.12), energy-to-failure (p = 0.39), and stiffness (p = 0.54) were not statistically different for the two screw types. It is concluded that a second, smaller inner thread on a double-threaded pedicle screw does not translate into either increased bone purchase or higher pull-out strengths.

Aged↗

PubMedDate not supplied

Evaluation of the in vitro degradation of macroporous hydrogels using gravimetry, confined compression testing, and microcomputed tomography.

This study investigated the in vitro degradation characteristics of macroporous hydrogels based on poly(propylene fumarate-co-ethylene glycol) (P(PF-co-EG)). Four formulations were fabricated to test the effect of porosity and cross-linking density on the degradation of the resulting macroporous hydrogels. Macroporosity was introduced by the addition of sodium bicarbonate and ascorbic acid, the precursors of the carbon dioxide porogen, in the initiation system for the hydrogel cross-linking. Macroporous hydrogels with porosities of 0.80 +/- 0.03 and 0.89 +/- 0.03 were synthesized by the addition of sodium bicarbonate of concentrations 40 and 80 mg/mL and ascorbic acid of concentrations 0.05 and 0.1 mol/L, respectively. Poly(ethylene glycol) diacrylate (PEG-DA) was utilized as a cross-linker. The molecular weight between cross-links had a significant effect on weight loss after 12 weeks, where samples with M(C) of 1,880 +/- 320 synthesized with a P(PF-co-EG):PEG-DA ratio of 3:1 had a significantly greater mass loss due to degradation than those with M(C) of 1,000 +/- 100 synthesized with a P(PF-co-EG):PEG-DA ratio of 1:1. In contrast, porosity played a minimal role in determining the weight loss. Mechanical testing of the hydrogels under confined compression showed a decrease in compressive modulus over the degradation time for all formulations. In addition, an increase in hydrogel equilibrium water content and pore wall thickness was observed with degradation time, whereas the hydrogel porosity and surface area density remained invariant. The results from microcomputed tomography corroborated with the rest of the measurements and indicated a bulk degradation mechanism of the macroporous hydrogels.

Compressive Strength↗

PubMedDate not supplied

Methods: a comparative analysis of radiography, microcomputed tomography, and histology for bone tissue engineering.

This study focused on the assessment of radiography, microcomputed tomography, and histology for the evaluation of bone formation in a 15.0-mm defect in the rabbit radius after the implantation of a tissue-engineered construct. Radiography was found to be useful as a noninvasive method for obtaining images of calcified tissue throughout the time course of the experiment. With this method, however, image quality was low, making it difficult to obtain precise information about the location and quantity of the bone formed. Microcomputed tomography was used to create three-dimensional reconstructions of the bone (25-microm resolution). These reconstructions allowed for greater spatial resolution than the radiography, but did not allow for imaging of the implanted scaffold material or the surrounding, nonmineralized tissue. To visualize all materials within the defect area at the cellular level, histology was used. Histological analysis, however, is a destructive technique that did not allow for any further analysis of the samples. Each technique examined here has its own advantages and limitations, but each yields unique information regarding bone regeneration. It is only through the use of all three techniques that complete characterization of the bone growth and tissue/construct responses after implantation in vivo.

Acrylates↗