1
|
Sharma S, Buist ML. Comparing finite viscoelastic constitutive relations and variational principles in modeling gastrointestinal soft tissue deformation. J Mech Behav Biomed Mater 2024; 155:106560. [PMID: 38744120 DOI: 10.1016/j.jmbbm.2024.106560] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2023] [Revised: 04/20/2024] [Accepted: 04/23/2024] [Indexed: 05/16/2024]
Abstract
The mechanical attributes of soft tissues within the gastrointestinal (GI) tract are crucial for the effective operation of the GI system, and alterations in these properties may play a role in motility-related disorders. Various constitutive modeling approaches have been suggested to comprehend the response of soft tissues to diverse loading conditions. Among these, hyperelastic constitutive models based on finite elasticity have gained popularity. However, these models fall short in capturing rate- and time-dependent tissue properties. In contrast, finite viscoelastic models offer a solution to overcome these limitations. Nevertheless, the development of a suitable finite viscoelastic model, coupled with a variational formulation for efficient finite element (FE) implementation, remains an ongoing challenge. This study aims to address this gap by developing diverse finite viscoelastic constitutive relations and applying them to characterize soft tissue. Furthermore, the research explores the creation of compressible, nearly incompressible, and incompressible versions of viscoelastic constitutive relations, along with their variational formulation, to facilitate efficient FE implementation. The proposed model demonstrates remarkable accuracy in replicating experimental results, achieving an R2 value exceeding 0.99.
Collapse
Affiliation(s)
- Swati Sharma
- Department of Biomedical Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117583, Singapore
| | - Martin Lindsay Buist
- Department of Biomedical Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117583, Singapore.
| |
Collapse
|
2
|
The Turning Point for Morphomechanical Remodeling During Complete Intestinal Obstruction in Rats Occurs After 12–24 h. Ann Biomed Eng 2018; 46:705-716. [DOI: 10.1007/s10439-018-1992-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Accepted: 02/05/2018] [Indexed: 12/31/2022]
|
3
|
Sun D, Zhao J, Liao D, Chen P, Gregersen H. Shear Modulus of the Partially Obstructed Rat Small Intestine. Ann Biomed Eng 2016; 45:1069-1082. [DOI: 10.1007/s10439-016-1739-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Accepted: 09/17/2016] [Indexed: 12/11/2022]
|
4
|
Yang J, Zhao J, Chen P, Nakaguchi T, Grundy D, Gregersen H. Interdependency between mechanical parameters and afferent nerve discharge in hypertrophic intestine of rats. Am J Physiol Gastrointest Liver Physiol 2016; 310:G376-86. [PMID: 26585414 DOI: 10.1152/ajpgi.00192.2015] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/17/2015] [Accepted: 11/13/2015] [Indexed: 01/31/2023]
Abstract
Partial intestinal obstruction causes smooth muscle hypertrophy, enteric neuronal plasticity, motility disorders, and biomechanical remodeling. In this study we characterized the stimulus-response function of afferent fibers innervating the partially obstructed jejunum. A key question is whether changes in afferent firing arise from remodeled mechanical tissue properties or from adaptive afferent processes. Partial obstruction was created by placing a polyethylene ring for 2 wk in jejunum of seven rats. Sham obstruction was made in six rats and seven rats served as normal controls. Firing from mesenteric afferent nerve bundles was recorded during mechanical ramp, relaxation, and creep tests. Stress-strain, spike rate increase ratio (SRIR), and firing rate in single units were assessed for evaluation of interdependency of the mechanical stimulations, histomorphometry data, and afferent nerve discharge. Partial intestinal obstruction resulted in hypertrophy and jejunal stiffening proximal to the obstruction site. Low SRIR at low strains during fast distension and at high stresses during slow distension was found in the obstructed rats. Single unit analysis showed increased proportion of mechanosensitive units but absent high-threshold (HT) units during slow stimulation, decreased number of HT units during fast stimulation, and shift from HT sensitivity towards low threshold sensitivity in the obstructed jejunum. Biomechanical remodeling and altered afferent response to mechanical stimulations were found in the obstructed jejunum. Afferents from obstructed jejunum preserved their function in encoding ongoing mechanical stimulation but showed changes in their responsiveness. The findings support that mechanical factors rather than adaption are important for afferent remodeling.
Collapse
Affiliation(s)
- Jian Yang
- GIOME and the Key Laboratory for Biorheological Science and Technology of Ministry of Education; Bioengineering College of Chongqing University, Chongqing, China
| | - Jingbo Zhao
- Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | | | - Toshiya Nakaguchi
- Graduate School of Advanced Integrated Science, Chiba University, Chiba, Japan; and
| | - David Grundy
- Department of Biomedical Science, University of Sheffield, Sheffield, United Kingdom
| | - Hans Gregersen
- GIOME and the Key Laboratory for Biorheological Science and Technology of Ministry of Education; Bioengineering College of Chongqing University, Chongqing, China;
| |
Collapse
|
5
|
Morphometric and biomechanical remodeling of the small intestine during aging in rats. J Biomech 2015; 48:4271-8. [DOI: 10.1016/j.jbiomech.2015.10.034] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2015] [Revised: 10/22/2015] [Accepted: 10/23/2015] [Indexed: 01/27/2023]
|
6
|
Chen J, Qin Z, Shan H, Xiao Y, Cai W. Early Adaptation of Small Intestine After Massive Small Bowel Resection in Rats. IRANIAN JOURNAL OF PEDIATRICS 2015; 25:e530. [PMID: 26396708 PMCID: PMC4575806 DOI: 10.5812/ijp.530] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/30/2014] [Accepted: 12/22/2014] [Indexed: 02/08/2023]
Abstract
BACKGROUND It is important that the residual bowel adapts after massive resection. The necessary intestinal adaptation is a progressive recovery from intestinal failure through increase in absorptive surface area and functional capacity and includes both morphological and functional adaptations. OBJECTIVES The aim of this study was to investigate intestinal morphological and functional adaptations of small bowel syndrome (SBS) model rats (SBS1W) 7 days after bowel resection. MATERIALS AND METHODS Male sprague-dawley rats (n = 20/group) underwent either a 75% proximal small bowel resection (SBS1W group) or a control operation (control group). Markers of morphological adaptation were revealed by TEM analysis of H&E-stained tissue samples. The intestinal barrier condition was assessed by BT, and sIgA concentration in intestinal mucus was measured by ELISA. Contractility and the slow wave rhythm of the entire intestinal remnant were measured and recorded. RESULTS The SBS1W group experienced more weight loss than control group and had a clearly different intestinal morphology as revealed in TEM images. Compared with control rats, the SBS1W group had a lower sIgA concentration in intestinal mucus and higher BT to lymph nodes (70% vs 40%; level I), portal blood (40% vs 10%; level II), and peripheral blood (60% vs 30%; level III). Disorder of spontaneous rhythmic contraction, irregular amplitude, and slow frequency were detected in the SBS1W group by a muscle strips test. Similarly, the slow wave of the entire intestinal remnant in the SBS1W group was irregular and uncoordinated. CONCLUSIONS The finding of intestinal adaptation following massive SBR in SBS1W rats provides more understanding of the mechanisms of progressive recovery from the intestinal failure that underlies SBS. The mechanical, chemical, immunological, and biological barriers were all impaired at 7 days following bowel resection, indicating that the SBS model rats were still in the intestinal adaptation phase.
Collapse
Affiliation(s)
- Jie Chen
- Department of Pediatric Surgery, Xin Hua Hospital, Shanghai Jiao Tong University, Shanghai, China
| | - Zhen Qin
- Department of Pediatric Surgery, Xin Hua Hospital, Shanghai Jiao Tong University, Shanghai, China
| | - Hongmei Shan
- Shanghai Key Laboratory of Pediatric Gastroenterology and Nutrition, Shanghai Institute of Pediatric Research, Shanghai Jiao Tong University, Shanghai, China
| | - Yongtao Xiao
- Shanghai Key Laboratory of Pediatric Gastroenterology and Nutrition, Shanghai Institute of Pediatric Research, Shanghai Jiao Tong University, Shanghai, China
| | - Wei Cai
- Department of Pediatric Surgery, Xin Hua Hospital, Shanghai Jiao Tong University, Shanghai, China
- Shanghai Key Laboratory of Pediatric Gastroenterology and Nutrition, Shanghai Institute of Pediatric Research, Shanghai Jiao Tong University, Shanghai, China
- Corresponding author: Wei Cai, Shanghai Key Laboratory of Pediatric Gastroenterology and Nutrition, Shanghai Institute of Pediatric Research, Shanghai Jiao Tong University, Shanghai, China. Tel: +86-2125078425, E-mail:
| |
Collapse
|
7
|
Krarup PM, Rehn M, Sand-Dejmek J, Ehrnström R, Ågren MS, Syk I. Rapid morphological changes and loss of collagen following experimental acute colonic obstruction. Int J Colorectal Dis 2013; 28:341-7. [PMID: 22903297 DOI: 10.1007/s00384-012-1548-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 07/25/2012] [Indexed: 02/04/2023]
Abstract
PURPOSE Anastomosis of an acutely obstructed colon is associated with an increased risk of dehiscence. In experimental models, acute obstruction decreases collagen in the colonic wall, but the time course and propagation along the colon of the biochemical changes are unknown. Furthermore, there is a paucity of information on the correlation between these biochemical changes and histological features. METHODS Forty male Sprague Dawley rats were subjected to partial obstruction by placing a silicone ring around the left colon 30 mm above the reflection. Obstruction was maintained for 0, 1, 2, 3 or 4 days. Samples from five different locations along the colon were analysed on circumference, tissue water content, collagen concentration and histomorphology. Neutrophil and macrophage infiltration was characterized immunohistochemically. RESULTS The colonic circumference and water content increased (p < 0.001), while the collagen concentration decreased by 48 % (p < 0.01) proximal to the obstruction already after 1 day. The degree of dilation and collagen reduction did not change significantly over the subsequent 3 days of obstruction, whereas the water content normalized by day 3. Mucosal and submucosal oedema and the relative neutrophil infiltration were highest after 1 day in the colonic segment proximal to the stenosis while the macrophage population continued to increase to day 4. Muscular necrosis in addition to ganglionitis and neuritis in the nervous plexus increased with duration of obstruction. CONCLUSIONS The pronounced and rapid changes of the composition of cells and the extracellular matrix of the colonic wall following acute obstruction may be of guidance for present surgical treatments and future pharmacological interventions.
Collapse
Affiliation(s)
- Peter-Martin Krarup
- Department of Surgery K, Bispebjerg University Hospital, Bispebjerg Bakke 23, 2400 Copenhagen, Denmark.
| | | | | | | | | | | |
Collapse
|
8
|
Bertoni S, Saccani F, Gatti R, Rapalli A, Flammini L, Ballabeni V, Barocelli E. Accommodation and peristalsis are functional responses to obstruction in rat hypertrophic ileum. World J Gastroenterol 2013; 19:846-54. [PMID: 23430377 PMCID: PMC3574881 DOI: 10.3748/wjg.v19.i6.846] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/04/2012] [Revised: 09/13/2012] [Accepted: 09/22/2012] [Indexed: 02/06/2023] Open
Abstract
AIM: To investigate the effects of chronic obstruction on enteric reflexes evoked by electrical stimulation (EFS) or intraluminal distension of the rat hypertrophic ileum.
METHODS: Motor responses to EFS and to intraluminal distension were studied in the absence and in the presence of various inhibitors of enteric mediators. Ileum segments from operated (chronic ileal obstruction), sham-operated (control) and normal rats were horizontally mounted, connected to a pressure transducer and intraluminally perfused. The effects of selective serotonin receptor (5-HTR) blockers were investigated on distension-induced responses. The cellular localization of 5-HT3Rs was also examined in control and hypertrophic tissues through confocal microscopy.
RESULTS: In non-obstructed segments, EFS elicited tetrodotoxin (TTX)-sensitive responses with high amplitude contraction followed by weak relaxation. In hypertrophic tissues, EFS lowered the baseline pressure and evoked TTX-sensitive contractions significantly larger than normal (P < 0.01) or control (P < 0.05), and devoid of any relaxation phase (P < 0.01 vs normal). Incubation with atropine and guanethidine [non-adrenergic non-cholinergic (NANC) conditions] did not modify intestinal tone in normal and control preparations, but reversed the accommodation produced by EFS in hypertrophic tissues, and depressed the amplitude of contractions in all types of tissues. L-NAME and α-chymotrypsin blocked residual NANC motility in all tissues and augmented intraluminal pressure in hypertrophic segments (P < 0.05 vs NANC conditions). Intraluminal distension of the intestinal wall evoked non-propulsive cycles of contractions and relaxations in non-obstructed tissues. In all hypertrophic segments, strong propulsive strokes, markedly wider (P < 0.001), and larger than normal (P < 0.001) or control (P < 0.05) were elicited. Both motor patterns were blocked under NANC conditions and with simultaneous incubation with L-NAME and α-chymotrypsin. In all types of tissues, incubation with ketanserin or GR125487 did not modify distension-induced motility. In contrast, blockade of 5-HT3Rs by ondansetron concentration-dependently inhibited motor responses in normal and control tissues, but only slightly impaired enteric reflexes in the hypertrophic preparations. Finally, confocal microscopy did not reveal a different cellular distribution of 5-HT3Rs in control and hypertrophic ileum.
CONCLUSION: Accommodation and distension-induced peristalsis of rat hypertrophic ileum are controlled by cholinergic and peptidergic transmission and are negligibly affected by 5-HT3Rs, which modulate distension-induced motility in non-obstructed tissues.
Collapse
|
9
|
|
10
|
Guo X, Huang X, Wu YS, Liu DH, Lu HL, Kim YC, Xu WX. Down-regulation of hydrogen sulfide biosynthesis accompanies murine interstitial cells of Cajal dysfunction in partial ileal obstruction. PLoS One 2012; 7:e48249. [PMID: 23133623 PMCID: PMC3486862 DOI: 10.1371/journal.pone.0048249] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2012] [Accepted: 09/21/2012] [Indexed: 12/14/2022] Open
Abstract
Purpose To investigate the role of endogenous hydrogen sulfide (H2S) in partial obstruction-induced dysfunction of the interstitial cells of Cajal (ICC) in mice ileum. Materials and Methods Partial intestinal obstruction was induced surgically in male imprinting control region (ICR) mice. ICC networks were studied by Immunohistochemistry. Electrical activity was recorded by intracellular recording techniques. The expression of ICC phenotype marker c-kit receptor tyrosine kinase (c-kit), membrane binding stem cell factor (mSCF), the endogenous H2S biosynthesis enzymes cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) was studied by Western blotting. The expression of tumor necrosis factor-α (TNF-α) mRNA was observed by using real-time polymerase chain reaction. Results Partial intestinal obstruction resulted in ICC networks were disrupted above obstruction 14 days after the operation. The slow waves of intestinal smooth muscles in the dilated region were significantly suppressed and their amplitude and frequency were reduced, whilst the resting membrane potentials were depolarized. The expression of c-kit and mSCF was significantly decreased, also suggesting the disruption of the ICC network. The expression of TNF-α was significantly increased in the tunica muscularis of the obstructed intestine. Treatment of cultured intestinal smooth muscle cells with TNF-α caused dramatic down regulation of mSCF. The expression of CBS and CSE was significantly decreased in the tunica muscularis of the obstructed intestine. Intraperitoneal injection (i.p) of DL-propargylglycine, an irreversible inhibitor of CSE, and aminooxyacetic acid, an inhibitor of CBS, elevated the expression of TNF-α mRNA in the tunica muscularis of the ileum. Obstruction-induced over expression of TNF-α was significantly improved by supplementation of NaHS, but not the expressions of mSCF and c-kit. Conclusions The down regulation of endogenous H2S biosynthesis is related to over expression of TNF-α in obstructed small intestine. TNF-α-mediated mSCF down-regulation is not the only reason of partial intestinal obstruction-induced loss of ICC.
Collapse
Affiliation(s)
- Xin Guo
- Department of Physiology, Shanghai Jiaotong University School of Medicine, Shanghai, China
- Department of Urology, Affiliated Hospital of Nantong University, Nantong, China
| | - Xu Huang
- Department of Physiology, Shanghai Jiaotong University School of Medicine, Shanghai, China
| | - Yi-song Wu
- Department of Physiology, Shanghai Jiaotong University School of Medicine, Shanghai, China
| | - Dong-hai Liu
- Department of Physiology, Shanghai Jiaotong University School of Medicine, Shanghai, China
| | - Hong-li Lu
- Department of Physiology, Shanghai Jiaotong University School of Medicine, Shanghai, China
| | - Yong-chul Kim
- Department of Physiology, Chungbuk National University College of Medicine, Cheongju, Republic of Korea
| | - Wen-xie Xu
- Department of Physiology, Shanghai Jiaotong University School of Medicine, Shanghai, China
- * E-mail:
| |
Collapse
|
11
|
Chen J, Wen J, Cai W. Smooth muscle adaptation and recovery of contractility after massive small bowel resection in rats. Exp Biol Med (Maywood) 2012; 237:578-84. [PMID: 22581812 DOI: 10.1258/ebm.2012.011338] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Previous studies have suggested that massive small bowel resection (mSBR) compromises the normal intestinal processes of digestion and absorption, and requires an adaptive response to regain full function and reinstate coordinated contractile activity of the circular smooth muscle. This study was designed to investigate spontaneous contractile activity of circular smooth muscle using the mSBR rat model and to determine the functional role of M(2) and M(3) muscarinic acetylcholine receptors (mAChR) in this process. Male Sprague-Dawley rats underwent an 80% proximal SBR or sham operation. Markers of adaptation, including villus and microvillus height, were analyzed by hematoxylin and eosin staining and transmission electron microscopy. Contractility was measured by attaching the distal ileum strips to strain gauge transducers and exposing the tissue to varying doses of the cholinergic agonist carbachol. Protein expressions of M(2)- and M(3)-mAChR in intestinal smooth muscle (ISM) were detected by Western blot. Following mSBR, the ISM showed perturbed spontaneous rhythmic contraction, irregular amplitude and slow frequency by muscle strip test. However, by two weeks after mSBR, the contractile function of circular smooth muscle was found to have returned to normal levels. Protein expression of M(2)-mAChR was down-regulated following mSBR but up-regulated during the adaptive process when contractile activity of circular smooth muscle was regained. These results indicate that smooth muscle contractility was spontaneously restored in rats following mSBR, and involved the acetylcholine receptors M(2) and M(3). Thus, the disrupted contractile response of smooth muscle in short bowel syndrome may be corrected by therapeutic intervention to restore the expressions of M(2)- and M(3)-mAChR to pre-mSBR levels.
Collapse
Affiliation(s)
- Jie Chen
- Department of Pediatric Surgery, School of Medicine, Xin Hua Hospital, Shanghai Institute of Pediatric Research, Shanghai Jiao Tong University, 1665 Kong Jiang Road 200092, Shanghai, China
| | | | | |
Collapse
|
12
|
Phasic and tonic smooth muscle function of the partially obstructed guinea pig intestine. J Biomed Biotechnol 2011; 2011:489720. [PMID: 22162636 PMCID: PMC3228609 DOI: 10.1155/2011/489720] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2011] [Accepted: 08/29/2011] [Indexed: 12/19/2022] Open
Abstract
This study was to generate phasic and tonic stress-strain curves for evaluation of smooth muscle function in the obstructed guinea pig jejunum. Partial and sham obstruction of the jejunum in guinea pigs was created surgically, with guinea pigs not being operated on served as normal controls. The animals survived 2, 4, 7, and 14 days, respectively. The jejunal segment was distended to 10 cm H2O. The pressure and outer diameter changes were recorded. Passive conditions were obtained by using papaverine. Total phasic, tonic, and passive circumferential stress and strain were computed from the diameter and pressure data with reference to the zero-stress-state geometry. The active phasic and tonic stresses were defined as the total phasic and tonic stress minus the passive stress. The thickness of intestinal muscle layers increased in a time-dependent manner after obstruction. The amplitude of passive, total phasic, total tonic, active phasic, and active tonic circumferential stresses increased as function of strain 7 days after obstruction. However, when normalized to muscle layer thickness, the amplitude of active stresses did not differ among the groups. In conclusion, the long-term-obstructed intestine exhibits increased total smooth muscle contraction force. However, the contraction force per smooth muscle unit did not increase.
Collapse
|
13
|
Zhao J, Liao D, Yang J, Gregersen H. Stress and strain analysis of contractions during ramp distension in partially obstructed guinea pig jejunal segments. J Biomech 2011; 44:2077-82. [PMID: 21632056 PMCID: PMC3150803 DOI: 10.1016/j.jbiomech.2011.05.017] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2010] [Revised: 04/15/2011] [Accepted: 05/11/2011] [Indexed: 12/21/2022]
Abstract
Previous studies have demonstrated morphological and biomechanical remodeling in the intestine proximal to an obstruction. The present study aimed to obtain stress and strain thresholds to initiate contraction and the maximal contraction stress and strain in partially obstructed guinea pig jejunal segments. Partial obstruction and sham operations were surgically created in mid-jejunum of male guinea pigs. The animals survived 2, 4, 7 and 14 days. Animals not being operated on served as normal controls. The segments were used for no-load state, zero-stress state and distension analyses. The segment was inflated to 10 cmH(2)O pressure in an organ bath containing 37°C Krebs solution and the outer diameter change was monitored. The stress and strain at the contraction threshold and at maximum contraction were computed from the diameter, pressure and the zero-stress state data. Young's modulus was determined at the contraction threshold. The muscle layer thickness in obstructed intestinal segments increased up to 300%. Compared with sham-obstructed and normal groups, the contraction stress threshold, the maximum contraction stress and the Young's modulus at the contraction threshold increased whereas the strain threshold and maximum contraction strain decreased after 7 days obstruction (P<0.05 and 0.01). In conclusion, in the partially obstructed intestinal segments, a larger distension force was needed to evoke contraction likely due to tissue remodeling. Higher contraction stresses were produced and the contraction deformation (strain) became smaller.
Collapse
Affiliation(s)
- Jingbo Zhao
- Institute of Clinical Medicine, Aarhus University, Aarhus, Denmark.
| | | | | | | |
Collapse
|
14
|
Guo X, Liu DH, Huang X, Lu HL, Wu YS, Han YF, Xu WX. Phenotype alterations of interstitial cells of Cajal in mice with partial intestinal obstruction. Shijie Huaren Xiaohua Zazhi 2011; 19:1886-1891. [DOI: 10.11569/wcjd.v19.i18.1886] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
AIM: To investigate changes in mechanic and electrical activities in intestinal smooth muscle and the phenotypes of interstitial cells of Cajal (ICC) in mice with partial intestinal obstruction.
METHODS: A mouse model of partial mechanical ileal obstruction was induced by surgery. The histochemical technique was used to investigate morphological changes in the distended intestinal regions of model mice 14 d after surgical induction. Mechanic and electric activities were recorded in normal and distended intestinal circular muscle using conventional physiological and intracellular recording techniques. The expression of c-kit, an ICC phenotype marker, was examined by fluorescent immunohistochemistry.
RESULTS: Fourteen days after surgical induction, there was an increase in intestinal diameter and hypertrophy of the tunica muscularis. Decreased frequency and altered rhythm of spontaneous contractions of intestinal smooth muscle were noted. The amplitude and frequency of slow waves and resting membrane potential decreased significantly. The expression of ICC was significantly down-regulated.
CONCLUSION: The changes in spontaneous rhythmic contractions and the slow waves are associated with the phenotype alterations of ICC in mice with partial intestinal obstruction.
Collapse
|
15
|
3d Mechanical properties of the partially obstructed guinea pig small intestine. J Biomech 2011; 43:2079-86. [PMID: 20435312 DOI: 10.1016/j.jbiomech.2010.04.008] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2009] [Revised: 04/09/2010] [Accepted: 04/09/2010] [Indexed: 12/16/2022]
Abstract
BACKGROUND AND AIMS Partial obstruction of the small intestine results in severe hypertrophy of smooth muscle cells, dilatation and functional denervation. Hypertrophy of the small intestine is associated with alteration of the wall structure and the mechanical properties. The aims of this study were to determine three dimensional material properties of the obstructed small intestine in guinea pigs and to obtain the 3D stress-strain distributions in the small intestinal wall. METHODS Partial obstruction of mid-jejunum was created surgically in five guinea pigs that were euthanized 2 weeks after the surgery. Ten-cm-long segments proximal to the obstruction site were used for the stretch-inflation mechanical test using a tri-axial test machine. The outer diameter, longitudinal force and the luminal pressure during the test were recorded simultaneously. An anisotropic exponential pseudo-strain energy density function was used as the constitutive equation to fit the experimental loading curve and for computation of the stress-strain distribution. RESULTS The wall thickness and the wall area increased significantly in the obstructed jejunum (P<0.001). The pressure-outer radius curves in the obstructed segments were translated to the left of the normal segments, indicating wall stiffening after the obstruction. The circumferential stress and the longitudinal stress through the wall were higher in the obstructed segments (P<0.02). This was independent of whether the zero-stress state or the no-load states were used as the reference state. CONCLUSION The mechanical behaviour of the obstructed small intestine can be described using a 3D constitutive model. The obstruction-induced biomechanical properties change was characterized by higher circumferential and longitudinal stresses in the wall and altered material constants in the 3D constitutive model.
Collapse
|
16
|
Oliveira-Barros LM, Costa-Casagrande TA, Cogliati B, Sá LRM, Matera JM. Histologic and immunohistochemical evaluation of intestinal innervation in dogs with and without intussusception. Am J Vet Res 2010; 71:636-42. [PMID: 20513178 DOI: 10.2460/ajvr.71.6.636] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVE To assess viability of innervation in bowel segments appearing macroscopically viable from dogs with intussusception. ANIMALS 7 dogs without gastrointestinal dysfunction that had been euthanized for reasons unrelated to the study (control dogs) and 13 dogs with intussusception that underwent enterectomy and intestinal anastomosis (affected dogs). PROCEDURES A total of 31 samples of intestinal tissue were obtained from the control dogs; 28 samples were obtained from affected dogs during surgery. Samples were histologically and immunohistochemically prepared and subjectively scored for degree of vacuolization and staining, respectively. Other data collected included mean muscle cell density of circular and longitudinal muscular layers, ratio between areas of muscular layers, mean number of myenteric plexuses, mean ganglion cell density of myenteric plexuses, and degree of degeneration in neuronal plexuses as estimated through synaptophysin and neuron-specific enolase (NSE) immunoreactivity. RESULTS Mean muscle cell density of longitudinal muscular layers, ratio between areas of muscular layers, and synaptophysin immunoreactivity did not differ significantly between affected and control dogs; values of all other variables did. Correlations were evident between mean ganglion cell density in myenteric plexuses and mean muscle cell density in circular muscular layers, degree of neuronal degeneration in myenteric plexuses and NSE immunoreactivity, and degree of neuronal degeneration in myenteric plexuses and mean ganglion cell density of myenteric plexuses. CONCLUSIONS AND CLINICAL RELEVANCE Innervation may be impaired in bowel segments that appear macroscopically viable. Therefore, careful evaluation of preserved surgical margins during enterectomy and enteroanastomosis and monitoring of digestive function after surgery are important.
Collapse
Affiliation(s)
- Leda M Oliveira-Barros
- Department of Surgery, School of Veterinary Medicine, University of Sao Paulo, Sao Paulo, 05508-270, Brazil.
| | | | | | | | | |
Collapse
|
17
|
Biomechanical remodelling of obstructed guinea pig jejunum. J Biomech 2010; 43:1322-9. [PMID: 20189575 DOI: 10.1016/j.jbiomech.2010.01.018] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2009] [Revised: 12/18/2009] [Accepted: 01/21/2010] [Indexed: 01/19/2023]
Abstract
Data on morphological and biomechanical remodelling are needed to understand the mechanisms behind intestinal obstruction. The effect of partial obstruction on mechanical properties with reference to the zero-stress state and on the histomorphological properties of the guinea pig small intestine was determined in this study. Partial obstruction and sham operation were surgically created in mid-jejunum of guinea pigs. The animals survived 2, 4, 7, and 14 days. The age-matched guinea pigs that were not operated served as normal controls. The segment proximal to the obstruction site was used for histological analysis, no-load state and zero-stress state data, and distension test. The segment for distension was immersed in an organ bath and inflated to 10cm H(2)O. The outer diameter change during the inflation was monitored using a microscope with CCD camera. Circumferential stresses and strains were computed from the diameter, pressure and the zero-stress state data. The opening angle and absolute value of residual strain decreased (P<0.01 and P<0.001) whereas the wall thickness, wall cross-sectional area, and the wall stiffness increased after 7 days obstruction (P<0.05, P<0.01). Histologically, the muscle and submucosa layers, especially the circumferential muscle layer increased in thickness after obstruction. The opening angle and residual strain mainly depended on the thickness of the muscle layer whereas the wall stiffness mainly depended on the thickness of the submucosa layer. In conclusion, the histomorphological and biomechanical properties of small intestine (referenced for the first time to the zero-stress state) remodel proximal to the obstruction site in a time-dependent manner.
Collapse
|
18
|
Ciarletta P, Dario P, Tendick F, Micera S. Hyperelastic Model of Anisotropic Fiber Reinforcements within Intestinal Walls for Applications in Medical Robotics. Int J Rob Res 2009. [DOI: 10.1177/0278364909101190] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The development of an anatomically realistic model of intestinal tissue is essential for the progress of several clinical applications of medical robotics. A hyperelastic theory of the layered structure of the intestine is proposed in this paper to reproduce its purely elastic passive response from the structural organization of its main constituents. The hyperelastic strain energy function is decoupled into an isotropic term, describing the ground biological matrix, and an anisotropic term, describing the single contributions of the directional fiber-reinforcements. The response of the muscular coat layer has been modeled as a stiffening effect due to two longitudinal and circular muscular reinforcements. The contribution of the submucosa has been described from a uniform distribution of fibrillar collagen in a cross-ply arrangement. An experimental procedure has been proposed in order to characterize the passive response of porcine intestinal samples from planar uniaxial traction and shear tests. The experimental data have been non-linearly fitted in the least square sense with the results of the theoretical predictions. The mechanical parameters have been fitted with high accuracy (Rmin =0.9329, RMSEmax =0.01167), demonstrating the ability of the model to reproduce the mechanical coupling due to the presence of multiple directional reinforcements. The fundamental mechanical role of collagen morphology in the passive biomechanical behavior of intestinal wall is demonstrated. These results may drive a better understanding of the key factors in growth and remodeling of healthy and diseased tissue, together with numerous applications in robotic endoscopy, minimally invasive surgery, and biomedical research.
Collapse
Affiliation(s)
- P. Ciarletta
- CRIM Laboratory, Scuola Superiore Sant'Anna, Viae Rinaldo Piaggio 34, Pontedera (Pisa), Italy,
| | - P. Dario
- CRIM Laboratory, Scuola Superiore Sant'Anna, Viae Rinaldo Piaggio 34, Pontedera (Pisa), Italy,
| | - F. Tendick
- Department of Surgery, University of California, San Francisco, CA, USA,
| | - S. Micera
- ARTS Laboratory, Scuola Superiore Sant'Anna, Viae Rinaldo Piaggio 34, Pontedera (Pisa), Italy,
| |
Collapse
|
19
|
Chaturvedi LS, Saad SA, Bakshi N, Marsh HM, Basson MD. Strain matrix-dependently dissociates gut epithelial spreading and motility. J Surg Res 2009; 156:217-23. [PMID: 19691992 DOI: 10.1016/j.jss.2009.03.050] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2009] [Revised: 03/18/2009] [Accepted: 03/22/2009] [Indexed: 01/26/2023]
Abstract
BACKGROUND Repetitive deformation enhances intestinal epithelial migration across tissue fibronectin (tFN) via Src but inhibits migration across collagen. Since cell spreading generally precedes motility, we compared the effects of cyclic strain on Caco-2 spreading and migration on tFN, collagen-I, and plasma fibronectin (pFN), and investigated the role of Src in deformation-influenced spreading and migration. MATERIALS AND METHODS Human Caco-2 intestinal epithelial cells on tFN, collagen-I or pFN were subjected to an average 10% strain at 10 cycles/min for 2 h. Src was inhibited with 10muM PP2 or Src was reduced with siRNA. Parallel studies assessed deformation effects on monolayer wound closure. RESULTS Deformation, Src-inhibition or reduction each inhibited spreading on tFN but Src-inhibition or reduction prevented further inhibition of spreading by deformation without preventing further inhibition of motility. Deformation did not alter spreading on collagen-I or pFN, but inhibited wound closure. CONCLUSIONS Although cell spreading generally precedes and parallels motility, repetitive deformation regulates motility independently of spreading. Since deformation activates Src, the ability of Src blockade to mimic strain-associated inhibition of spreading on tFN suggests that this effect occurs by a separate mechanism that may also require basal Src activity. Further delineation of the mechanisms by which strain disparately modulates spreading and motility may permit acceleration of mucosal healing by targeted interventions to separately promote spreading and epithelial motility.
Collapse
Affiliation(s)
- Lakshmi S Chaturvedi
- Department of Surgery, John D. Dingell VA Medical Center, Detroit, Michigan, USA
| | | | | | | | | |
Collapse
|
20
|
Chen P, Zhao J, Nielsen VH, Clausen T, Gregersen H. Intestinal remodelling in mink fed with reduced protein content. J Biomech 2009; 42:443-8. [PMID: 19159886 DOI: 10.1016/j.jbiomech.2008.11.033] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2008] [Revised: 11/28/2008] [Accepted: 11/29/2008] [Indexed: 12/26/2022]
Abstract
Low protein intake occurs in humans in relation to diseases, starvation and post-operatively. Low-protein diets may affect the gastrointestinal structure and mechanical function. The aim was to study the passive biomechanical properties and tissue remodelling of the intestine in minks on reduced protein diets. Twenty-seven male minks were divided into three groups receiving different protein level in the diet for 6 weeks: High protein level (group H, 55% energy from protein), moderate protein level (group M, 30% energy from protein) and low protein level (group L, 15% energy from protein) (n=9 for each group). Ten centimetre long segments from duodenum, jejunum and ileum were excised at the end of the study period. The mechanical test was performed as a ramp distension experiment. The intestinal diameter and length, wall thickness, wall area and opening angle were obtained from digitized images of the intestinal segments at pre-selected pressures, no-load and zero-stress states, respectively. Circumferential and longitudinal stresses (force per area) and strains (deformation) were computed. The layer thickness was measured from intestinal histological images. No difference in body weight was found between groups at the start of the experiment. However, at the end of the experiment the body weight was smallest in group L (P=0.0003 and 0.0004 compared with groups H and M). Similarly, the wet weight per unit length, wall thickness and area were smallest in group L (P<0.05, P<0.01). The lowest wall thickness was found in the jejunum and ileum in group L (P<0.05), mainly due to decreased mucosa and submucosa thickness. The smallest opening angle and absolute values of residual strain were found in the jejunal segment in group L (P<0.05). No difference was observed for duodenal and ileal segments among the three groups. Feeding the low-protein diet shifted the stress-strain curves to the right for the circumferential direction, indicating the wall become softer in the circumferential direction. However, no significant difference was observed in the longitudinal direction for any of the intestinal segments. In conclusion, this study demonstrated that low-protein diet in minks induce histomorphometric and biomechanical remodelling of the intestine.
Collapse
Affiliation(s)
- Pengmin Chen
- Mech-Sense, Aalborg Hospital Science and Innovation Centre (AHSIC), Sdr. Skovvej 15, DK-9000 Aalborg, Denmark
| | | | | | | | | |
Collapse
|
21
|
Abstract
The gastrointestinal (GI) tract is the system of organs within multi-cellular animals that takes in food, digests it to extract energy and nutrients, and expels the remaining waste. The various patterns of GI tract function are generated by the integrated behaviour of multiple tissues and cell types. A thorough study of the GI tract requires understanding of the interactions between cells, tissues and gastrointestinal organs in health and disease. This depends on knowledge, not only of numerous cellular ionic current mechanisms and signal transduction pathways, but also of large scale GI tissue structures and the special distribution of the nervous network. A unique way of coping with this explosion in complexity is mathematical and computational modelling; providing a computational framework for the multilevel modelling and simulation of the human gastrointestinal anatomy and physiology. The aim of this review is to describe the current status of biomechanical modelling work of the GI tract in humans and animals, which can be further used to integrate the physiological, anatomical and medical knowledge of the GI system. Such modelling will aid research and ensure that medical professionals benefit, through the provision of relevant and precise information about the patient’s condition and GI remodelling in animal disease models. It will also improve the accuracy and efficiency of medical procedures, which could result in reduced cost for diagnosis and treatment.
Collapse
|
22
|
Zhao J, Liao D, Gregersen H. Phasic and tonic stress-strain data obtained in intact intestinal segment in vitro. Dig Dis Sci 2008; 53:3145-51. [PMID: 18461453 DOI: 10.1007/s10620-008-0277-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/21/2008] [Accepted: 04/02/2008] [Indexed: 12/26/2022]
Abstract
The function of the small intestine is to a large degree mechanical, and it has the capability of deforming its shape by generating phasic (short-lasting) and tonic (sustained) contraction of the smooth muscle layers. The aim of this study was to obtain phasic and tonic stress-strain (normalized force-length) curves during distension of isolated rat jejunum and ileum (somewhat similar to the isometric length-tension diagram known from in vitro studies of muscle strips). We hypothesized that the circumferential stress-strain data depend on longitudinal stretch of the intestine. Intestinal segments were isolated from ten Wistar rats and put into an organ bath containing 37 degrees C aerated Krebs solution. Ramp distension was done on active and passive intestinal segments at longitudinal stretch ratios of 0, 10, and 20%. Ramp pressures from 0 to 7.5 cmH(2)O were applied to the intestinal lumen at each longitudinal stretch ratio. Passive conditions were obtained by adding the calcium antagonist papaverine to the solution. Total and passive circumferential stress and strain were computed from the length, diameter and pressure data and from the zero-stress state geometry. The active stress was defined as the total stress minus the passive stress. The total and passive circumferential stresses increased exponentially as a function of the strain. The amplitude of both the total and passive stress was biggest in the jejunum. The total circumferential stress decreased whereas the passive circumferential stress increased when the intestine was stretched longitudinally. Consequently, longitudinal stretching caused the active circumferential stress to decrease. The passive circumferential stress during longitudinal stretching increased more in the jejunum than in the ileum. Therefore, the active circumferential stress decreased most in the jejunum. In conclusion, the circumferential active-passive stress and strain depend on the longitudinal stretch and differs between the jejunum and ileum.
Collapse
Affiliation(s)
- Jingbo Zhao
- Center of Excellence in Visceral Biomechanics and Pain, Aalborg Hospital Science and Innovation Center (AHSIC), Sdr. Skovvej 15, 9000, Aalborg, Denmark.
| | | | | |
Collapse
|
23
|
Bertoni S, Ballabeni V, Flammini L, Gobbetti T, Impicciatore M, Barocelli E. Intestinal chronic obstruction affects motor responsiveness of rat hypertrophic longitudinal and circular muscles. Neurogastroenterol Motil 2008; 20:1234-42. [PMID: 18684211 DOI: 10.1111/j.1365-2982.2008.01174.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Extensive morphological and neurochemical changes have been experimentally and clinically documented in the hypertrophied intestine located orally to a chronic partial stenosis of the lumen. Functional studies revealed not only disruption of the interdigestive motor complex in vivo and decreased efficiency of contraction but also preservation of the peristaltic reflex in vitro. Given the critical role played in intestinal peristalsis by the coordinated activity of the longitudinal (LM) and circular muscle (CM), this work focuses on the motor responses of LM and CM isolated from rat hypertrophied ileum following mechanical obstruction. Maximal contractions to both receptor (acetylcholine and substance P) and non-receptor (K+) mediated stimuli were up to 10-fold increased in hypertrophic CM rings compared with control tissues, while a higher potency of substance P was revealed in both hypertrophied muscle layers. Relaxations to vasoactive intestinal polypeptide and 8-Br-cGMP were more intense on prostaglandin F(2alpha)-contracted hypertrophic LM strips compared with control tissues and a general tendency towards increased relaxation was shared also by hypertrophic CM basal tone. The present results collectively suggest that hypertrophic growth leads to hyperresponsiveness to contractile agents, particularly evident in the CM, and to increased sensitivity to relaxing mediators, especially exhibited by the LM. In this regard, the complementary role exerted by each muscle layer and the plasticity of the intestinal tissue could both come into play to preserve the intestinal functions in a changing environment.
Collapse
Affiliation(s)
- S Bertoni
- Department of Pharmacological, Biological and Applied Chemical Sciences, University of Parma, Parma, Italy
| | | | | | | | | | | |
Collapse
|
24
|
MacDonald JA. Smooth muscle phenotypic plasticity in mechanical obstruction of the small intestine. Neurogastroenterol Motil 2008; 20:737-40. [PMID: 18557891 DOI: 10.1111/j.1365-2982.2008.01148.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Chronic, partial obstruction of the small intestine can dramatically alter peristaltic contractile properties. Morphological studies have revealed hypertrophy of the circular smooth muscle cells in the constricted part of the intestine. In this issue of Neurogastroenterology and Motility, Chen et al. show that hyperplasia and hypertrophy of intestinal smooth muscle cells occur at distinct times in response to partial obstruction of the ileum. Furthermore, the first evidence is provided to link intestinal smooth muscle remodelling during mechanical obstruction with changes in serum response factor and two of its co-regulating factors, myocardin and Elk-1.
Collapse
Affiliation(s)
- J A MacDonald
- Department of Biochemistry and Molecular Biology, Snyder Institute of Infection, Immunity and Inflammation & Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada.
| |
Collapse
|
25
|
Chen J, Chen H, Sanders KM, Perrino BA. Regulation of SRF/CArG-dependent gene transcription during chronic partial obstruction of murine small intestine. Neurogastroenterol Motil 2008; 20:829-42. [PMID: 18557893 PMCID: PMC8320440 DOI: 10.1111/j.1365-2982.2008.01149.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Intestinal obstructions lead to a variety of motility disorders. Small intestine smooth muscles undergo dramatic phenotypic changes in response to obstruction, but the underlying molecular mechanisms are unknown. Using RT-PCR, ChIP, Re-ChIP, and Western blots, we examined the effect of small bowel mechanical obstruction on smooth muscle gene expression. Obstruction caused a transient hyperplasia, followed by a prolonged hypertrophic response of small intestine smooth muscle cells. Smooth muscle myosin heavy chain (MHC), alpha-actin, and gamma-actin expression decreased initially, and then increased as hypertrophy developed. Myocardin expression decreased initially and then increased, while kruppel-like factors (KLF)4 and KLF5 expression increased initially, and then decreased. Serum response factor (SRF) expression decreased initially, and then recovered to sham-operated levels as hypertrophy developed. SRF binding to smooth muscle MHC and alpha-actin promoters decreased initially, but then increased above sham-operated levels as hypertrophy developed. Elk-1 binding to smooth muscle myosin heavy chain and alpha-actin promoters increased initially, and then decreased to sham-operated levels as hypertrophy developed. c-fos expression increased initially, which was associated with increased SRF/Elk-1 binding to the c-fos promoter. The Elk-1 phosphorylation inhibitor U-0126 inhibited the increase in c-fos expression. These findings indicate a dynamic response of small intestine smooth muscles to bowel obstruction involving switching between differentiated, proliferative, and hypertrophic phenotypes. These results suggest that changes in the expression and interactions between SRF, myocardin, Elk-1, and c-fos play key roles in the phenotypic switching of small intestine smooth muscles in response to mechanical obstruction.
Collapse
Affiliation(s)
- J Chen
- Department of Physiology and Cell Biology, Center of Biomedical Research Excellence, University of Nevada School of Medicine, Reno, NV 89557, USA
| | | | | | | |
Collapse
|