Sourav S. Patnaik

Cardiac differentiation of cardiosphere-derived cells in scaffolds mimicking morphology of the cardiac extracellular matrix

Stem cell therapy has the potential to regenerate heart tissue after myocardial infarction (MI). The regeneration is dependent upon cardiac differentiation of the delivered stem cells. We hypothesized that timing of the stem cell delivery determines the extent of cardiac differentiation as cell differentiation is dependent on matrix properties such as biomechanics, structure and morphology, and these properties in cardiac extracellular matrix (ECM) continuously vary with time after MI. In order to elucidate the relationship between ECM properties and cardiac differentiation, we created an in vitro model based on ECM-mimicking fibers and a type of cardiac progenitor cell, cardiosphere-derived cells (CDCs). A simultaneous fiber electrospinning and cell electrospraying technique was utilized to fabricate constructs. By blending a highly soft hydrogel with a relatively stiff polyurethane and modulating fabrication parameters, tissue constructs with similar cell adhesion property but different global modulus, single fiber modulus, fiber density and fiber alignment were achieved. The CDCs remained alive within the constructs during a 1week culture period. CDC cardiac differentiation was dependent on the scaffold modulus, fiber volume fraction and fiber alignment. Two constructs with relatively low scaffold modulus, ∼50-60kPa, most significantly directed the CDC differentiation into mature cardiomyocytes as evidenced by gene expressions of cardiac troponin T (cTnT), calcium channel (CACNA1c) and cardiac myosin heavy chain (MYH6), and protein expressions of cardiac troponin I (cTnI) and connexin 43 (CX43). Of these two low-modulus constructs, the extent of differentiation was greater for lower fiber alignment and higher fiber volume fraction. These results suggest that cardiac ECM properties may have an effect on cardiac differentiation of delivered stem cells.

Mayer–Rokitansky–Küster–Hauser (MRKH) syndrome: A historical perspective

Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome is a congenital defect of the Müllerian ducts characterized by uterovaginal agenesis and underdeveloped female genital organs. This paper is a tribute to the contributors of this condition - August Franz Joseph Karl Mayer, Karl Freiherr von Rokitansky, Hermann Küster and Georges André Hauser. In addition to their contributions, we have discussed findings and reports of similar defects from other important scientists (Hippocrates, Albucasis, etc.) dating as far back as 460B.C. We have also discussed the disease types and different classification systems including VCUAM and AFS/ASRM among others. Even with several surgical and non-surgical treatment options, there are still many questions that remain unanswered and very little is known about the etiology or genetic predisposition of this condition.

Characterisation of the mechanical properties of infarcted myocardium in the rat under biaxial tension and uniaxial compression

Understanding the passive mechanical properties of infarcted tissue at different healing stages is essential to explore the emerging biomaterial injection-based therapy for myocardial infarction (MI). Although rats have been widely used as animal models in such investigations, the data in literature that quantify the passive mechanical properties of rat heart infarcts is very limited. MI was induced in rats and hearts were harvested immediately (0 day), 7, 14 and 28 days after infarction onset. Left ventricle anterioapical samples were cut and underwent equibiaxial and non equibiaxial tension followed by uniaxial compression mechanical tests. Histological analysis was conducted to confirm MI and to quantify the size of the induced infarcts. Infarcts maintained anisotropy and the nonlinear biaxial and compressive mechanical behaviour throughout the healing phases with the circumferential direction being stiffer than the longitudinal direction. Mechanical coupling was observed between the two axes in all infarct groups. The 0, 7, 14 and 28 days infarcts showed 438, 693, 1048 and 1218kPa circumferential tensile moduli. The 28 day infarct group showed a significantly higher compressive modulus compared to the other infarct groups (p=0.0060, 0.0293, and 0.0268 for 0, 7 and 14 days groups). Collagen fibres were found to align in a preferred direction for all infarct groups supporting the observed mechanical anisotropy. The presented data are useful for developing material models for healing infarcts and for setting a baseline for future assessment of emerging mechanical-based MI therapies.

Experimental Evidence of Mechanical Isotropy in Porcine Lung Parenchyma

Pulmonary injuries are a major source of morbidity and mortality associated with trauma. Trauma includes injuries associated with accidents and falls as well as blast injuries caused by explosives. The prevalence and mortality of these injuries has made research of pulmonary injury a major priority. Lungs have a complex structure, with multiple types of tissues necessary to allow successful respiration. The soft, porous parenchyma is the component of the lung which contains the alveoli responsible for gas exchange. Parenchyma is also the portion which is most susceptible to traumatic injury. Finite element simulations are an important tool for studying traumatic injury to the human body. These simulations rely on material properties to accurately recreate real world mechanical behaviors. Previous studies have explored the mechanical properties of lung tissues, specifically parenchyma. These studies have assumed material isotropy but, to our knowledge, no study has thoroughly tested and quantified this assumption. This study presents a novel methodology for assessing isotropy in a tissue, and applies these methods to porcine lung parenchyma. Briefly, lung parenchyma samples were dissected so as to be aligned with one of the three anatomical planes, sagittal, frontal, and transverse, and then subjected to compressive mechanical testing. Stress-strain curves from these tests were statistically compared by a novel method for differences in stresses and strains at percentages of the curve. Histological samples aligned with the anatomical planes were also examined by qualitative and quantitative methods to determine any differences in the microstructural morphology. Our study showed significant evidence to support the hypothesis that lung parenchyma behaves isotropically.

Establishing Early Functional Perfusion and Structure in Tissue Engineered Cardiac Constructs.

Myocardial infarction (MI) causes massive heart muscle death and remains a leading cause of death in the world. Cardiac tissue engineering aims to replace the infarcted tissues with functional engineered heart muscles or revitalize the infarcted heart by delivering cells, bioactive factors, and/or biomaterials. One major challenge of cardiac tissue engineering and regeneration is the establishment of functional perfusion and structure to achieve timely angiogenesis and effective vascularization, which are essential to the survival of thick implants and the integration of repaired tissue with host heart. In this paper, we review four major approaches to promoting angiogenesis and vascularization in cardiac tissue engineering and regeneration: delivery of pro-angiogenic factors/molecules, direct cell implantation/cell sheet grafting, fabrication of prevascularized cardiac constructs, and the use of bioreactors to promote angiogenesis and vascularization. We further provide a detailed review and discussion on the early perfusion design in nature-derived biomaterials, synthetic biodegradable polymers, tissue-derived acellular scaffolds/whole hearts, and hydrogel derived from extracellular matrix. A better understanding of the current approaches and their advantages, limitations, and hurdles could be useful for developing better materials for future clinical applications.

Biomechanical Testing and Histologic Examination of Intradermal Skin Closure in Dogs Using Barbed Suture Device and Non‐Barbed Monofilament Suture

OBJECTIVE To compare the biomechanical strength and histologic features of 3-0 Glycomer™ 631 barbed suture (V-LOC™ 90 Absorbable Wound Closure Device, Covidien, Mansfield, MA) to non-barbed 3-0 Glycomer™ 631 suture (Biosyn™, Covidien) for intradermal skin wound closure in the dog. STUDY DESIGN Randomized, factorial, in vivo. ANIMALS Eighteen purpose-bred, mature male, and female hound dogs. METHODS Eighteen adult hound dogs were randomly assigned to 1 of 3 groups designated by postoperative day of assessment. Six skin incisions were made along the dorsum in the thoracolumbar region of each dog with an equal number (n=3) randomly assigned to closure with barbed or non-barbed suture. Six dogs were euthanatized on postoperative days 3, 10, and 14, respectively. Two additional incisions were made on each dog after euthanasia for baseline data (Day 0). The skin incision specimens were harvested for biomechanical testing and histologic evaluation. RESULTS Non-barbed closure had significantly higher maximum load at failure (P<.001) and stiffness (P<.001) than barbed closure regardless of day. The average tissue reaction score was significantly higher for barbed closure (P=.008), regardless of day. Suturing time for barbed closures was significantly shorter. There was no significant difference in frequency of complications between closures. CONCLUSION Barbed Glycomer™ 631 closures had a significantly lower maximum load at failure and stiffness, and higher average tissue reaction scores, but showed no difference in short term outcome for intradermal closure of dorsally located skin incisions in dogs.

A Coupled Experiment-finite Element Modeling Methodology for Assessing High Strain Rate Mechanical Response of Soft Biomaterials.

This study offers a combined experimental and finite element (FE) simulation approach for examining the mechanical behavior of soft biomaterials (e.g. brain, liver, tendon, fat, etc.) when exposed to high strain rates. This study utilized a Split-Hopkinson Pressure Bar (SHPB) to generate strain rates of 100-1,500 sec(-1). The SHPB employed a striker bar consisting of a viscoelastic material (polycarbonate). A sample of the biomaterial was obtained shortly postmortem and prepared for SHPB testing. The specimen was interposed between the incident and transmitted bars, and the pneumatic components of the SHPB were activated to drive the striker bar toward the incident bar. The resulting impact generated a compressive stress wave (i.e. incident wave) that traveled through the incident bar. When the compressive stress wave reached the end of the incident bar, a portion continued forward through the sample and transmitted bar (i.e. transmitted wave) while another portion reversed through the incident bar as a tensile wave (i.e. reflected wave). These waves were measured using strain gages mounted on the incident and transmitted bars. The true stress-strain behavior of the sample was determined from equations based on wave propagation and dynamic force equilibrium. The experimental stress-strain response was three dimensional in nature because the specimen bulged. As such, the hydrostatic stress (first invariant) was used to generate the stress-strain response. In order to extract the uniaxial (one-dimensional) mechanical response of the tissue, an iterative coupled optimization was performed using experimental results and Finite Element Analysis (FEA), which contained an Internal State Variable (ISV) material model used for the tissue. The ISV material model used in the FE simulations of the experimental setup was iteratively calibrated (i.e. optimized) to the experimental data such that the experiment and FEA strain gage values and first invariant of stresses were in good agreement.

Biomechanical Characterization of Sheep Vaginal Wall Tissue: A Potential Application in Human Pelvic Floor Disorders

Pelvic Organ Prolapse (POP) is a leading women’s health issue affecting a significant portion of the population and has been recently coined as a “silent epidemic”. POP leads to a considerable reduction in women’s quality of life and can cause chronic pelvic pain, sexual dysfunction, and social/psychological issues. The lifetime risk for having surgery for POP is approximately 11% with 200,000 POP procedures performed each year in USA, with an annual direct cost of over

Quantitative Analysis of Tissue Damage Evolution in Porcine Liver With Interrupted Mechanical Testing Under Tension, Compression, and Shear

1000 million. Exact etiology of POP is unclear, but it is understood that POP is multi-factorial in nature. Risk factors for POP include increasing age, obesity, multiple vaginal births, gravidity, history of hysterectomy, smoking, chronic cough conditions, frequent heavy lifting, and some genetic factors. POP results due to loss or damage of structural supports that support the pelvic organs (i.e. rectum, bowel, bladder, etc). Vaginal wall prolapse (anterior and posterior) is the most common presentation. This can result from weakening of the levator ani muscle and other connective tissue structures which not only control the mechanical function, but also help support neurological and anatomical function[1].Copyright

Pentagalloyl Glucose and Its Functional Role in Vascular Health: Biomechanics and Drug-Delivery Characteristics

In this study, the damage evolution of liver tissue was quantified at the microstructural level under tensile, compression, and shear loading conditions using an interrupted mechanical testing method. To capture the internal microstructural changes in response to global deformation, the tissue samples were loaded to different strain levels and chemically fixed to permanently preserve the deformed tissue geometry. Tissue microstructural alterations were analyzed to quantify the accumulated damages, with damage-related parameters such as number density, area fraction, mean area, and mean nearest neighbor distance (NND). All three loading states showed a unique pattern of damage evolution, in which the damages were found to increase in number and size, but decrease in NND as strain level increased. To validate the observed damage features as true tissue microstructural damages, more samples were loaded to the above-mentioned strain levels and then unloaded back to their reference state, followed by fixation. The most major damage-relevant features at higher strain levels remained after the release of the external loading, indicating the occurrence of permanent inelastic deformation. This study provides a foundation for future structure-based constitutive material modeling that can capture and predict the stress-state dependent damage evolution in liver tissue.