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Roberts CT, Beck SK, Prejean CM, Graul LM, Maitland DJ, Grunlan MA. Star-PCL shape memory polymer (SMP) scaffolds with tunable transition temperatures for enhanced utility. J Mater Chem B 2024; 12:3694-3702. [PMID: 38529581 PMCID: PMC11022546 DOI: 10.1039/d4tb00050a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2024] [Accepted: 03/13/2024] [Indexed: 03/27/2024]
Abstract
Thermoresponsive shape memory polymers (SMPs) prepared from UV-curable poly(ε-caprolactone) (PCL) macromers have the potential to create self-fitting bone scaffolds, self-expanding vaginal stents, and other shape-shifting devices. To ensure tissue safety during deployment, the shape actuation temperature (i.e., the melt transition temperature or Tm of PCL) must be reduced from ∼55 °C that is observed for scaffolds prepared from linear-PCL-DA (Mn ∼ 10 kg mol-1). Moreover, increasing the rate of biodegradation would be advantageous, facilitating bone tissue healing and potentially eliminating the need for stent retrieval. Herein, a series of six UV-curable PCL macromers were prepared with linear or 4-arm star architectures and with Mns of 10, 7.5, and 5 kg mol-1, and subsequently fabricated into six porous scaffold compositions (10k, 7.5k, 5k, 10k★, 7.5k★, and 5k★) via solvent casting particulate leaching (SCPL). Scaffolds produced from star-PCL-tetraacrylate (star-PCL-TA) macromers produced pronounced reductions in Tm with decreased Mnversus those formed with the corresponding linear-PCL-diacrylate (linear-PCL-DA) macromers. Scaffolds were produced with the desired reduced Tm profiles: 37 °C < Tm < 55 °C (self-fitting bone scaffold), and Tm ≤ 37 °C (self-expanding stent). As macromer Mn decreased, crosslink density increased while % crystallinity decreased, particularly for scaffolds prepared from star-PCL-TA macromers. While shape memory behavior was retained and radial expansion pressure increased, this imparted a reduction in modulus but with an increase in the rate of degradation.
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Affiliation(s)
- Courteney T Roberts
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas 77843, USA.
| | - Sarah K Beck
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas 77843, USA.
| | - C Mabel Prejean
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas 77843, USA.
| | - Lance M Graul
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas 77843, USA.
| | - Duncan J Maitland
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas 77843, USA.
| | - Melissa A Grunlan
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas 77843, USA.
- Department of Materials Science and Engineering, Texas A&M University, College Station, Texas 77843, USA
- Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA
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Graul LM, Horn SJ, Nash LD, Cheung TB, Clubb FJ, Maitland DJ. Image-Based Evaluation of In Vivo Degradation for Shape-Memory Polymer Polyurethane Foam. Polymers (Basel) 2022; 14:4122. [PMID: 36236069 PMCID: PMC9571375 DOI: 10.3390/polym14194122] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2022] [Revised: 09/09/2022] [Accepted: 09/12/2022] [Indexed: 11/06/2022] Open
Abstract
Shape-memory polymer (SMP) polyurethane foams have been applied as embolic devices and implanted in multiple animal models. These materials are oxidatively degradable and it is critical to quantify and characterize the degradation for biocompatibility assessments. An image-based method using high-resolution and magnification scans of histology sections was used to estimate the mass loss of the peripheral and neurovascular embolization devices (PED, NED). Detailed analysis of foam microarchitecture (i.e., struts and membranes) was used to estimate total relative mass loss over time. PED foams implanted in porcine arteries showed a degradation rate of ~0.11% per day as evaluated at 30-, 60-, and 90-day explant timepoints. NED foams implanted in rabbit carotid elastase aneurysms showed a markedly faster rate of degradation at ~1.01% per day, with a clear difference in overall degradation between 30- and 90-day explants. Overall, membranes degraded faster than the struts. NEDs use more hydrophobic foam with a smaller pore size (~150-400 μm) compared to PED foams (~800-1200 μm). Previous in vitro studies indicated differences in the degradation of the two polymer systems, but not to the magnitude seen in vivo. Implant location, animal species, and local tissue health are among the hypothesized reasons for different degradation rates.
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Affiliation(s)
- Lance M. Graul
- Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA
| | - Staci J. Horn
- Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA
- Department of Veterinary Pathobiology, Texas A&M University, College Station, TX 77843, USA
| | | | - Thomas B. Cheung
- Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA
| | - Fred J. Clubb
- Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA
- Department of Veterinary Pathobiology, Texas A&M University, College Station, TX 77843, USA
| | - Duncan J. Maitland
- Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA
- Shape Memory Medical Inc., Santa Clara, CA 95054, USA
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Graul LM, Liu S, Maitland DJ. Theoretical error of sectional method for estimation of shape memory polyurethane foam mass loss. J Colloid Interface Sci 2022; 625:237-247. [PMID: 35716618 DOI: 10.1016/j.jcis.2022.06.045] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2021] [Revised: 06/03/2022] [Accepted: 06/09/2022] [Indexed: 11/25/2022]
Abstract
INTRODUCTION Measuring in vivo degradation for polymeric scaffolds is critical for analysis of biocompatibility. Traditionally, histology has been used to estimate mass loss in scaffolds, allowing for simultaneous evaluation of mass loss and the biologic response to the implant. Oxidatively degradable shape memory polyurethane (SMP) foams have been implemented in two vascular occlusion devices: peripheral embolization device (PED) and neurovascular embolization device (NED). This work explores the errors introduced when using histological sections to evaluate mass loss. METHODS Models of the SMP foams were created to mimic the device geometry and the tetrakaidekahedral structure of the foam pore. These models were degraded in Blender for a wide range of possible degradation amounts and the mass loss was estimated using m sections. RESULTS As the number of sections (m) used to estimate mass loss for a volume increased the sampling error decreased and beyond m = 5, the decrease in error was insignificant. NED population and sampling errors were higher than for PED scenarios. When m ≥ 5, the averaged sampling error was below 1.5% for NED and 1% for PED scenarios. DISCUSSION/CONCLUSION This study establishes a baseline sampling error for estimating randomly degraded porous scaffolds using a sectional method. Device geometry and the stage of mass loss influence the sampling error. Future studies will use non-random degradation to further investigate in vivo mass loss scenarios.
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Affiliation(s)
- Lance M Graul
- Department of Biomedical Engineering, Texas A&M University, College Station, TX, United States
| | - Shuling Liu
- Department of Statistics, Texas A&M University, College Station, TX, United States
| | - Duncan J Maitland
- Department of Biomedical Engineering, Texas A&M University, College Station, TX, United States.
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Pfau MR, McKinzey KG, Roth AA, Graul LM, Maitland DJ, Grunlan MA. Shape memory polymer (SMP) scaffolds with improved self-fitting properties. J Mater Chem B 2021; 9:3826-3837. [PMID: 33979417 DOI: 10.1039/d0tb02987d] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
"Self-fitting" shape memory polymer (SMP) scaffolds prepared as semi-interpenetrating networks (semi-IPNs) with crosslinked linear-poly(ε-caprolactone)-diacrylate (PCL-DA, Mn∼10 kg mol-1) and linear-poly(l-lactic acid) (PLLA, Mn∼15 kg mol-1) [75/25 wt%] exhibited robust mechanical properties and accelerated degradation rates versus a PCL-DA scaffold control. However, their potential to treat irregular craniomaxillofacial (CMF) bone defects is limited by their relatively high fitting temperature (Tfit∼55 °C; related to the Tm of PCL) required for shape recovery (i.e. expansion) and subsequent shape fixation during press fitting of the scaffold, which can be harmful to surrounding tissue. Additionally, the viscosity of the solvent-based precursor solutions, cast over a fused salt template during fabrication, can limit scaffold size. Thus, in this work, analogous semi-IPN SMP scaffolds were formed with a 4-arm star-PCL-tetracryalate (star-PCL-TA) (Mn∼10 kg mol-1) and star-PLLA (Mn∼15 kg mol-1). To assess the impact of a star-polymer architecture, four semi-IPN compositions were prepared: linear-PCL-DA/linear-PLLA (L/L), linear-PCL-DA/star-PLLA (L/S), star-PCL-TA/linear-PLLA (S/L) and star-PCL-TA/star-PLLA (S/S). Two PCL controls were also prepared: LPCL (i.e. 100% linear-PCL-DA) and SPCL (i.e. 100% star-PCL-TA). The S/S semi-IPN scaffold exhibited particularly desirable properties. In addition to achieving a lower, tissue-safe Tfit (∼45 °C), it exhibited the fastest rate of degradation which is anticipated to more favourably permit neotissue infiltration. The radial expansion pressure exerted by the S/S semi-IPN scaffold at Tfit was greater than that of LPCL, which is expected to enhance osseointegration and mechanical stability. The intrinsic viscosity of the S/S semi-IPN macromer solution was also reduced such that larger scaffold specimens could be prepared.
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Affiliation(s)
- Michaela R Pfau
- Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA.
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Fletcher GK, Nash LD, Graul LM, Jang LK, Herting SM, Wilcox MD, Touchet TJ, Sweatt AK, McDougall MP, Wright SM, Maitland DJ. Chemical Modifications of Porous Shape Memory Polymers for Enhanced X-ray and MRI Visibility. Molecules 2020; 25:E4660. [PMID: 33066091 PMCID: PMC7587375 DOI: 10.3390/molecules25204660] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Revised: 10/07/2020] [Accepted: 10/12/2020] [Indexed: 12/02/2022] Open
Abstract
The goal of this work was to develop a shape memory polymer (SMP) foam with visibility under both X-ray and magnetic resonance imaging (MRI) modalities. A porous polymeric material with these properties is desirable in medical device development for applications requiring thermoresponsive tissue scaffolds with clinical imaging capabilities. Dual modality visibility was achieved by chemically incorporating monomers with X-ray visible iodine-motifs and MRI visible monomers with gadolinium content. Physical and thermomechanical characterization showed the effect of increased gadopentetic acid (GPA) on shape memory behavior. Multiple compositions showed brightening effects in pilot, T1-weighted MR imaging. There was a correlation between the polymeric density and X-ray visibility on expanded and compressed SMP foams. Additionally, extractions and indirect cytocompatibility studies were performed to address toxicity concerns of gadolinium-based contrast agents (GBCAs). This material platform has the potential to be used in a variety of medical devices.
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Affiliation(s)
- Grace K. Fletcher
- Texas A&M University Biomedical Engineering, Bizzell St, College Station, TX 77843, USA; (G.K.F.); (L.M.G.); (L.K.J.); (S.M.H.); (M.D.W.); (T.J.T.); (A.K.S.); (M.P.M.); (S.M.W.)
| | | | - Lance M. Graul
- Texas A&M University Biomedical Engineering, Bizzell St, College Station, TX 77843, USA; (G.K.F.); (L.M.G.); (L.K.J.); (S.M.H.); (M.D.W.); (T.J.T.); (A.K.S.); (M.P.M.); (S.M.W.)
| | - Lindy K. Jang
- Texas A&M University Biomedical Engineering, Bizzell St, College Station, TX 77843, USA; (G.K.F.); (L.M.G.); (L.K.J.); (S.M.H.); (M.D.W.); (T.J.T.); (A.K.S.); (M.P.M.); (S.M.W.)
| | - Scott M. Herting
- Texas A&M University Biomedical Engineering, Bizzell St, College Station, TX 77843, USA; (G.K.F.); (L.M.G.); (L.K.J.); (S.M.H.); (M.D.W.); (T.J.T.); (A.K.S.); (M.P.M.); (S.M.W.)
| | - Matthew D. Wilcox
- Texas A&M University Biomedical Engineering, Bizzell St, College Station, TX 77843, USA; (G.K.F.); (L.M.G.); (L.K.J.); (S.M.H.); (M.D.W.); (T.J.T.); (A.K.S.); (M.P.M.); (S.M.W.)
| | - Tyler J. Touchet
- Texas A&M University Biomedical Engineering, Bizzell St, College Station, TX 77843, USA; (G.K.F.); (L.M.G.); (L.K.J.); (S.M.H.); (M.D.W.); (T.J.T.); (A.K.S.); (M.P.M.); (S.M.W.)
| | - Ana Katarina Sweatt
- Texas A&M University Biomedical Engineering, Bizzell St, College Station, TX 77843, USA; (G.K.F.); (L.M.G.); (L.K.J.); (S.M.H.); (M.D.W.); (T.J.T.); (A.K.S.); (M.P.M.); (S.M.W.)
| | - Mary P. McDougall
- Texas A&M University Biomedical Engineering, Bizzell St, College Station, TX 77843, USA; (G.K.F.); (L.M.G.); (L.K.J.); (S.M.H.); (M.D.W.); (T.J.T.); (A.K.S.); (M.P.M.); (S.M.W.)
- Texas A&M University Electrical and Computer Engineering, Bizzell St, College Station, TX 77843, USA
| | - Steven M. Wright
- Texas A&M University Biomedical Engineering, Bizzell St, College Station, TX 77843, USA; (G.K.F.); (L.M.G.); (L.K.J.); (S.M.H.); (M.D.W.); (T.J.T.); (A.K.S.); (M.P.M.); (S.M.W.)
- Texas A&M University Electrical and Computer Engineering, Bizzell St, College Station, TX 77843, USA
| | - Duncan J. Maitland
- Texas A&M University Biomedical Engineering, Bizzell St, College Station, TX 77843, USA; (G.K.F.); (L.M.G.); (L.K.J.); (S.M.H.); (M.D.W.); (T.J.T.); (A.K.S.); (M.P.M.); (S.M.W.)
- Shape Memory Medical Inc., Santa Clara, CA 95054, USA;
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Jessen SL, Friedemann MC, Ginn-Hedman AM, Graul LM, Jokerst S, Robinson CB, Landsman TL, Clubb FJ, Maitland DJ. Microscopic Assessment of Healing and Effectiveness of a Foam-Based Peripheral Occlusion Device. ACS Biomater Sci Eng 2019; 6:2588-2599. [PMID: 32715083 DOI: 10.1021/acsbiomaterials.9b00895] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The IMPEDE Embolization Plug is a catheter-delivered vascular occlusion device that utilizes a porous shape memory polymer foam as a scaffold for thrombus formation and distal coils to anchor the device within the vessel. In this study, we investigated the biological response of porcine arteries to the IMPEDE device by assessing the extent of healing and overall effectiveness in occluding the vessel at 30, 60, and 90 days. Compared to control devices (Amplatzer Vascular Plug and Nester Embolization Coils), the host response to IMPEDE showed increased cellular infiltration (accommodated by the foam scaffold), which led to advanced healing of the initial thrombus to mature collagenous connective tissue (confirmed by transmission electron microscopy (TEM)). Over time, the host response to the IMPEDE device included degradation of the foam by multinucleated giant cells, which promoted fibrin and polymer degradation and advanced the healing response. Device effectiveness, in terms of vessel occlusion, was evaluated histologically by assessing the degree of recanalization. Although instances of recanalization were often observed at all time points for both control and test articles, the mature connective tissue within the foam scaffold of the IMPEDE devices improved percent vessel occlusion; when recanalization was observed in IMPEDE-treated vessels, channels were exclusively peri-device rather than intradevice, as often observed in the controls, and the vessels mostly remained >75% occluded. Although total vessel occlusion provides the optimal ischemic effect, in cardiovascular pathology, there is a progressive ischemic effect on the downstream vasculature as a vessel narrows. As such, we expect a sustained ischemic therapeutic effect to be observed in vessels greater than 75% occluded. Overall, the current study suggests the IMPEDE device presents advantages over controls by promoting an enhanced degree of healing within the foam scaffold, which decreases the likelihood of intradevice recanalization and ultimately may lead to a sustained ischemic therapeutic effect.
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Affiliation(s)
- Staci L Jessen
- Department of Veterinary Pathobiology, Texas A&M University, College Station, Texas 77845-4467, United States.,Department of Biomedical Engineering, Texas A&M University, College Station, Texas 77843-3120, United States
| | - Molly C Friedemann
- Department of Veterinary Pathobiology, Texas A&M University, College Station, Texas 77845-4467, United States
| | - Anne-Marie Ginn-Hedman
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas 77843-3120, United States
| | - Lance M Graul
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas 77843-3120, United States
| | - Steven Jokerst
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas 77843-3120, United States
| | - Cedric B Robinson
- Department of Veterinary Pathobiology, Texas A&M University, College Station, Texas 77845-4467, United States
| | - Todd L Landsman
- Shape Memory Medical Inc., Santa Clara, California 95054, United States
| | - Fred J Clubb
- Department of Veterinary Pathobiology, Texas A&M University, College Station, Texas 77845-4467, United States.,Department of Biomedical Engineering, Texas A&M University, College Station, Texas 77843-3120, United States
| | - Duncan J Maitland
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas 77843-3120, United States.,Shape Memory Medical Inc., Santa Clara, California 95054, United States
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Herting SM, Ding Y, Boyle AJ, Dai D, Nash LD, Asnafi S, Jakaitis DR, Johnson CR, Graul LM, Yeh C, Kallmes DF, Kadirvel R, Maitland DJ. In vivo comparison of shape memory polymer foam-coated and bare metal coils for aneurysm occlusion in the rabbit elastase model. J Biomed Mater Res B Appl Biomater 2019; 107:2466-2475. [PMID: 30775843 DOI: 10.1002/jbm.b.34337] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2018] [Revised: 01/17/2019] [Accepted: 01/26/2019] [Indexed: 11/09/2022]
Abstract
Shape memory polymer (SMP) foam-coated coils (FCCs) are new embolic coils coated with porous SMP designed to expand for increased volume filling and enhanced healing after implantation. The purpose of this study was to compare chronic aneurysm healing after treatment with SMP FCCs to bare platinum coil (BPC) controls in the rabbit elastase aneurysm model. BPCs or SMP FCCs were implanted in rabbit elastase-induced aneurysms for follow-up at 30 days (n = 10), 90 days (n = 5), and 180 days (n = 12 for BPCs; n = 14 for SMP FCCs). Aneurysm occlusion and histologic healing, including a qualitative healing score, neointima thickness, collagen deposition, and inflammation were compared between the two groups. The mean neointima thickness was significantly greater in groups treated with SMP FCCs for all three time points. Histologic healing scores and collagen deposition quantification suggested that aneurysms treated with SMP FCCs experience more complete healing of the dome by 90 days, but the differences were not statistically significant. More progressive occlusion and recanalization were observed in aneurysms treated with SMP FCCs, but neither difference was statistically significant. Additionally, the SMP foam used in the FCCs was found to degrade faster in the rabbit elastase model than expected based on previous studies in a porcine sidewall aneurysm model. This study suggests that SMP FCCs can promote neointima formation along the aneurysm neck, and may lead to more complete healing of the dome and neck. These findings indicate potential benefits of this device for aneurysm occlusion procedures. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B:2466-2475, 2019.
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Affiliation(s)
- Scott M Herting
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas
| | - Yonghong Ding
- Neuroradiology Research Laboratory, Department of Radiology, Mayo Clinic, Rochester, Minnesota
| | - Anthony J Boyle
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas.,Shape Memory Medical, Santa Clara, California
| | - Daying Dai
- Neuroradiology Research Laboratory, Department of Radiology, Mayo Clinic, Rochester, Minnesota
| | - Landon D Nash
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas.,Shape Memory Medical, Santa Clara, California
| | - Solmaz Asnafi
- Neuroradiology Research Laboratory, Department of Radiology, Mayo Clinic, Rochester, Minnesota
| | - Daniel R Jakaitis
- Neuroradiology Research Laboratory, Department of Radiology, Mayo Clinic, Rochester, Minnesota
| | - Collin R Johnson
- Neuroradiology Research Laboratory, Department of Radiology, Mayo Clinic, Rochester, Minnesota
| | - Lance M Graul
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas
| | - Chung Yeh
- Shape Memory Medical, Santa Clara, California
| | - David F Kallmes
- Neuroradiology Research Laboratory, Department of Radiology, Mayo Clinic, Rochester, Minnesota
| | - Ramanathan Kadirvel
- Neuroradiology Research Laboratory, Department of Radiology, Mayo Clinic, Rochester, Minnesota
| | - Duncan J Maitland
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas.,Shape Memory Medical, Santa Clara, California
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