Christopher M. Hobson
University of Pittsburgh
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Featured researches published by Christopher M. Hobson.
Journal of Biomechanics | 2013
Rong Fan; Ahmed S. Bayoumi; Peter Chen; Christopher M. Hobson; William R. Wagner; John E. Mayer; Michael S. Sacks
Surgical replacement of the pulmonary valve (PV) is a common treatment option for congenital pulmonary valve defects. Engineered tissue approaches to develop novel PV replacements are intrinsically complex, and will require methodical approaches for their development. Single leaflet replacement utilizing an ovine model is an attractive approach in that candidate materials can be evaluated under valve level stresses in blood contact without the confounding effects of a particular valve design. In the present study an approach for optimal leaflet shape design based on finite element (FE) simulation of a mechanically anisotropic, elastomeric scaffold for PV replacement is presented. The scaffold was modeled as an orthotropic hyperelastic material using a generalized Fung-type constitutive model. The optimal shape of the fully loaded PV replacement leaflet was systematically determined by minimizing the difference between the deformed shape obtained from FE simulation and an ex-vivo microCT scan of a native ovine PV leaflet. Effects of material anisotropy, dimensional changes of PV root, and fiber orientation on the resulting leaflet deformation were investigated. In-situ validation demonstrated that the approach could guide the design of the leaflet shape for PV replacement surgery.
Journal of The Mechanical Behavior of Biomedical Materials | 2014
Antonio D’Amore; Nicholas J. Amoroso; Riccardo Gottardi; Christopher M. Hobson; Christopher A. Carruthers; Simon C. Watkins; William R. Wagner; Michael S. Sacks
In the present work, we demonstrate that the mesoscopic in-plane mechanical behavior of membrane elastomeric scaffolds can be simulated by replication of actual quantified fibrous geometries. Elastomeric electrospun polyurethane (ES-PEUU) scaffolds, with and without particulate inclusions, were utilized. Simulations were developed from experimentally-derived fiber network geometries, based on a range of scaffold isotropic and anisotropic behaviors. These were chosen to evaluate the effects on macro-mechanics based on measurable geometric parameters such as fiber intersections, connectivity, orientation, and diameter. Simulations were conducted with only the fiber material model parameters adjusted to match the macro-level mechanical test data. Fiber model validation was performed at the microscopic level by individual fiber mechanical tests using AFM. Results demonstrated very good agreement to the experimental data, and revealed the formation of extended preferential fiber orientations spanning the entire model space. We speculate that these emergent structures may be responsible for the tissue-like macroscale behaviors observed in electrospun scaffolds. To conclude, the modeling approach has implications for (1) gaining insight on the intricate relationship between fabrication variables, structure, and mechanics to manufacture more functional devices/materials, (2) elucidating the effects of cell or particulate inclusions on global construct mechanics, and (3) fabricating better performing tissue surrogates that could recapitulate native tissue mechanics.
Journal of Biomedical Materials Research Part A | 2015
Christopher M. Hobson; Nicholas J. Amoroso; Rouzbeh Amini; Ethan N. Ungchusri; Yi Hong; Antonio D'Amore; Michael S. Sacks; William R. Wagner
Native semi-lunar heart valves are composed of a dense fibrous network that generally follows a curvilinear path along the width of the leaflet. Recent models of engineered valve leaflets have predicted that such curvilinear fiber orientations would homogenize the strain field and reduce stress concentrations at the commissure. In the present work, a method was developed to reproduce this curvilinear fiber alignment in electrospun scaffolds by varying the geometry of the collecting mandrel. Elastomeric poly(ester urethane)urea was electrospun onto rotating conical mandrels of varying angles to produce fibrous scaffolds where the angle of fiber alignment varied linearly over scaffold length. By matching the radius of the conical mandrel to the radius of curvature for the native pulmonary valve, the electrospun constructs exhibited a curvilinear fiber structure similar to the native leaflet. Moreover, the constructs had local mechanical properties comparable to conventional scaffolds and native heart valves. In agreement with prior modeling results, it was found under quasi-static loading that curvilinear fiber microstructures reduced strain concentrations compared to scaffolds generated on a conventional cylindrical mandrels. Thus, this simple technique offers an attractive means for fabricating scaffolds where key microstructural features of the native leaflet are imitated for heart valve tissue engineering.
ASME 2012 Summer Bioengineering Conference, Parts A and B | 2012
Rong Fan; Michael S. Sacks; Ahmed Bayoumi; John E. Mayer; Christopher M. Hobson; William R. Wagner
Pulmonary valve (PV) replacement surgery is a treatment option for patients with a congenitally defective pulmonary outflow track. While a tissue engineered approach offers many potential advantages, develop of such a valve involves a complex process of optimization. As an intermediate step, we have used a single leaflet replacement surgical model to further our understanding of the in-vivo remodeling process. A critical step is to determine the deformed shape of the replacement PV leaflet under transvalvular pressure. Key factors in this process are: the scaffold anisotropic mechanical properties, optimal thickness, and the exact initial leaflet shape. We have used electrospun poly (ester urethane) ureas (ES-PEUU) scaffolds since they exhibit mechanical properties very similar to the native PV. In this work we present a design framework of the optimal leaflet shape determination utilizing a single sheet of ES-PEUU for single leaflet replacement surgery via finite element (FE) simulation. The mechanical properties of ES-PEUU scaffold for leaflet replacement were obtained from biaxial in-plane tension experiments. Generalized Fung-type hyperelastic constitutive model [1] was implemented into a commercial FE software package to simulate the deformation of ES-PEUU scaffolds under pressure. By perturbing the initial shape of leaflet and simulating its quasi-static deformation under PV diastolic loading, the optimal shape of unloaded leaflet was determined by comparing the deformed shape of leaflet obtained from FE simulation of TEPV with the one from microCT scan of a native ovine PV. In-vitro test of PV after single leaflet replacement was also conducted to validate the developed method.Copyright
Journal of Medical Devices-transactions of The Asme | 2011
Rong Fan; Christopher M. Hobson; Ahmed S. Bayoumi; John E. Mayer; William R. Wagner; Michael S. Sacks
accepted method for reducing kidney temperature during minimally invasive surgery. A novel device has been designed, prototyped, and evaluated to perform effective renal cooling during minimally invasive kidney surgery to reduce damage due to extended ischemia. The device is a fluid-containing bag with foldable cooling surfaces that wrap around the organ like a taco shell. It is deployed through a 12 mm trocar, wrapped around the kidney and secured using bulldog clamps. The device then fills with an ice slurry and remains on the kidney for up to 20 min. The ice slurry is then removed from the device and the device is retracted from the body. Tests of the prototype show that the device successfully cools porcine kidneys from 37°C to 20°C in 5 minutes.
ASME 2011 Summer Bioengineering Conference, Parts A and B | 2011
Rong Fan; Christopher M. Hobson; Ahmed Bayoumi; John E. Mayer; William R. Wagner; Michael S. Sacks
Pulmonary valve (PV) replacement surgery is a treatment option for patients with a congenitally defective pulmonary outflow track. A tissue engineered pulmonary valve (TEPV) is a potential approach to serve as a replacement pediatric heart valve that has the potential for somatic growth. The single leaflet replacement surgical model can assist in assessing candidate biomaterials responses to in-vivo function. However, an empirically determined unloaded leaflet shape may result in abnormal valve function due to incomplete coaptation of leaflets and asymmetric stress distributions. Thus, to determine the final deformed shape of an engineered scaffold replacement PV leaflet under transvalvular pressure the following key factors must be determined: the scaffold anisotropic mechanical properties, optimal thickness, and the exact initial leaflet shape. We have used electrospun poly (ester urethane) ureas (ES-PEUU) scaffolds since they exhibit mechanical properties very similar to the native PV [1]. In this work we present a design framework of the optimal leaflet shape determination utilizing a single sheet of ES-PEUU for single leaflet replacement surgery via finite element (FE) simulation. The mechanical properties of ES-PEUU scaffold for leaflet replacement were obtained from biaxial in-plane tension and three-point bending flexural deformation experiments. Generalized Fung-type hyperelastic constitutive model [2] was implemented into a commercial FE software package to simulate the mechanical behavior of ES-PEUU scaffolds. By perturbing the initial shape of leaflet and simulating its quasi-static deformation under PV diastolic loading, the optimal shape of unloaded leaflet can be determined by comparing the deformed shape of leaflet obtained from FE simulation of TEPV with the one from microCT scan of a native ovine PV.Copyright
Tissue Engineering Part A | 2015
Johannes C. Kutten; David McGovern; Christopher M. Hobson; Sarah A. Luffy; Alejandro Nieponice; Kimimasa Tobita; Richard Francis; Susan D. Reynolds; Jeffrey S. Isenberg; Thomas W. Gilbert
Archive | 2013
Michael S. Sacks; Antonio D’Amore; Christopher M. Hobson
Archive | 2015
Thomas W. Gilbert; Christopher M. Hobson; Ethan N. Ungchusri
Archive | 2015
Thomas W. Gilbert; Christopher M. Hobson; Ethan N. Ungchusri