Browsing by Author "Department of Biomedical Engineering, School of Engineering and Technology"

Now showing 1 - 10 of 34
  • Thumbnail Image
    Item
    Accurate and representative decoding of the neural drive to muscles in humans with multi-channel intramuscular thin-film electrodes
    (Wiley, 2015-09-01) Muceli, Silvia; Poppendieck, Wigand; Negro, Francesco; Yoshida, Ken; Hoffmann, Klaus P.; Butler, Jane E.; Gandevia, Simon C.; Farina, Dario; Department of Biomedical Engineering, School of Engineering and Technology
    Intramuscular electrodes developed over the past 80 years can record the concurrent activity of only a few motor units active during a muscle contraction. We designed, produced and tested a novel multi-channel intramuscular wire electrode that allows in vivo concurrent recordings of a substantially greater number of motor units than with conventional methods. The electrode has been extensively tested in deep and superficial human muscles. The performed tests indicate the applicability of the proposed technology in a variety of conditions. The electrode represents an important novel technology that opens new avenues in the study of the neural control of muscles in humans. We describe the design, fabrication and testing of a novel multi-channel thin-film electrode for detection of the output of motoneurones in vivo and in humans, through muscle signals. The structure includes a linear array of 16 detection sites that can sample intramuscular electromyographic activity from the entire muscle cross-section. The structure was tested in two superficial muscles (the abductor digiti minimi (ADM) and the tibialis anterior (TA)) and a deep muscle (the genioglossus (GG)) during contractions at various forces. Moreover, surface electromyogram (EMG) signals were concurrently detected from the TA muscle with a grid of 64 electrodes. Surface and intramuscular signals were decomposed into the constituent motor unit (MU) action potential trains. With the intramuscular electrode, up to 31 MUs were identified from the ADM muscle during an isometric contraction at 15% of the maximal force (MVC) and 50 MUs were identified for a 30% MVC contraction of TA. The new electrode detects different sources from a surface EMG system, as only one MU spike train was found to be common in the decomposition of the intramuscular and surface signals acquired from the TA. The system also allowed access to the GG muscle, which cannot be analysed with surface EMG, with successful identification of MU activity. With respect to classic detection systems, the presented thin-film structure enables recording from large populations of active MUs of deep and superficial muscles and thus can provide a faithful representation of the neural drive sent to a muscle.
  • Thumbnail Image
    Item
    A Brief Review of Bone Adaptation to Unloading.
    (Elsevier, 2008) Zhang, Ping; Hamamura, Kazunori; Yokota, Hiroki; Department of Biomedical Engineering, School of Engineering and Technology
    Weight-bearing bone is constantly adapting its structure and function to mechanical environments. Loading through routine exercises stimulates bone formation and prevents bone loss, but unloading through bed rest and cast immobilization as well as exposure to weightlessness during spaceflight reduces its mass and strength. In order to elucidate the mechanism underlying unloading-driven bone adaptation, ground-based in vitro and in vivo analyses have been conducted using rotating cell culturing and hindlimb suspension. Focusing on gene expression studies in osteoblasts and hindlimb suspension studies, this minireview introduces our recent understanding on bone homeostasis under weightlessness in space. Most of the existing data indicate that unloading has the opposite effects to loading through common signaling pathways. However, a question remains as to whether any pathway unique to unloading (and not to loading) may exist.
  • Thumbnail Image
    Item
    Comparative study of visible light polymerized gelatin hydrogels for 3D culture of hepatic progenitor cells
    (Wiley, 2017-03) Greene, Tanja; Lin, Tsai-Yu; Andrisani, Oaurania M.; Lin, Chien-Chi; Department of Biomedical Engineering, School of Engineering and Technology
    Photopolymerization techniques have been widely used to create hydrogels for biomedical applications. Visible light-based photopolymerizations are commonly initiated by type II (i.e., noncleavage-type) photoinitiator in conjunction with a coinitiator. On the other hand, type I photoinitiators (i.e., cleavage type) are rarely compatible with visible light-based initiation due to their limited molar absorbability in the visible light wavelengths. Here, we report visible light initiated orthogonal photoclick crosslinking to fabricate gelatin-norbornene and poly(ethylene glycol)-tetra-thiol hydrogels using either cleavage-type (i.e., lithium acylphosphinate, LAP) or noncleavage-type photoinitiator (i.e., eosin-Y, EY) without the use of a coinitiator. Regardless of the initiator type, the step-growth gelatin-PEG hybrid hydrogels crosslinked and degraded similarly. While both systems exhibited similar cytocompatibility for hepatic progenitor HepaRG cells, gelation initiated by noncleavage-type initiator EY afforded slightly higher degree of hepatic gene expression.
  • Thumbnail Image
    Item
    Comparison of Biomaterial-Dependent and -Independent Bioprinting Methods for Cardiovascular Medicine
    (Elsevier, 2017) Moldovan, Leni; Babbey, Clifford; Murphy, Michael; Moldovan, Nicanor I.; Department of Biomedical Engineering, School of Engineering and Technology
    There is an increasing need of human organs for transplantation, of alternatives to animal experimentation, and of better in vitro tissue models for drug testing. All these needs create unique opportunities for the development of novel and powerful tissue engineering methods, among which the 3D bioprinting is one of the most promising. However, after decades of incubation, ingenuous efforts, early success and much anticipation, biomaterial-dependent 3D bioprinting, although shows steady progress, is slow to deliver the expected clinical results. For this reason, alternative ‘scaffold-free’ 3D bioprinting methods are developing in parallel at an accelerated pace. In this opinion paper we discuss comparatively the two approaches, with specific examples drawn from the cardiovascular field. Moving the emphasis away from competition, we show that the two platforms have similar goals but evolve in complementary technological niches. We conclude that the biomaterial-dependent bioprinting is better suited for tasks requiring faster, larger, anatomically-true, cell-homogenous and matrix-rich constructs, while the scaffold-free biofabrication is more adequate for cell-heterogeneous, matrix-poor, complex and smaller constructs, but requiring longer preparation time.
  • Thumbnail Image
    Item
    Compensatory enlargement of Ossabaw miniature swine coronary arteries in diffuse atherosclerosis
    (Elsevier, 2015-03) Choy, Jenny S.; Luo, Tong; Huo, Yunlong; Wischgoll, Thomas; Schultz, Kyle; Teague, Shawn D.; Sturek, Michael; Kassab, Ghassan S.; Department of Biomedical Engineering, School of Engineering and Technology
    Studies in human and non-human primates have confirmed the compensatory enlargement or positive remodeling (Glagov phenomenon) of coronary vessels in the presence of focal stenosis. To our knowledge, this is the first study to document arterial enlargement in a metabolic syndrome animal model with diffuse coronary artery disease (DCAD) in the absence of severe focal stenosis. Two different groups of Ossabaw miniature pigs were fed a high fat atherogenic diet for 4 months (Group I) and 12 months (Group II), respectively. Group I (6 pigs) underwent contrast enhanced computed tomographic angiography (CCTA) and intravascular ultrasound (IVUS) at baseline and after 4 months of high fat diet, whereas Group II (7 pigs) underwent only IVUS at 12 months of high fat diet. IVUS measurements of the left anterior descending (LAD), left circumflex (LCX) and right coronary (RCA) arteries in Group I showed an average increase in their lumen cross-sectional areas (CSA) of 25.8%, 11.4%, and 43.4%, respectively, as compared to baseline. The lumen CSA values of LAD in Group II were found to be between the baseline and 4 month values in Group I. IVUS and CCTA measurements showed a similar trend and positive correlation. Fractional flow reserve (FFR) was 0.91 ± 0.07 at baseline and 0.93 ± 0.05 at 4 months with only 2.2%, 1.6% and 1% stenosis in the LAD, LCX and RCA, respectively. The relation between percent stenosis and lumen CSA shows a classical Glagov phenomenon in this animal model of DCAD.
  • Thumbnail Image
    Item
    Constructal law of vascular trees for facilitation of flow
    (PLoS, 2014-12-31) Razavi, Mohammad S.; Shirani, Ebrahim; Salimpour, Mohammad Reza; Kassab, Ghassan S.; Department of Biomedical Engineering, School of Engineering and Technology
    Diverse tree structures such as blood vessels, branches of a tree and river basins exist in nature. The constructal law states that the evolution of flow structures in nature has a tendency to facilitate flow. This study suggests a theoretical basis for evaluation of flow facilitation within vascular structure from the perspective of evolution. A novel evolution parameter (Ev) is proposed to quantify the flow capacity of vascular structures. Ev is defined as the ratio of the flow conductance of an evolving structure (configuration with imperfection) to the flow conductance of structure with least imperfection. Attaining higher Ev enables the structure to expedite flow circulation with less energy dissipation. For both Newtonian and non-Newtonian fluids, the evolution parameter was developed as a function of geometrical shape factors in laminar and turbulent fully developed flows. It was found that the non-Newtonian or Newtonian behavior of fluid as well as flow behavior such as laminar or turbulent behavior affects the evolution parameter. Using measured vascular morphometric data of various organs and species, the evolution parameter was calculated. The evolution parameter of the tree structures in biological systems was found to be in the range of 0.95 to 1. The conclusion is that various organs in various species have high capacity to facilitate flow within their respective vascular structures.
  • Thumbnail Image
    Item
    Designing Visible Light-Cured Thiol-Acrylate Hydrogels for Studying the HIPPO Pathway Activation in Hepatocellular Carcinoma Cells
    (Wiley Blackwell (John Wiley & Sons), 2016-04) Lin, Tsai-Yu; Bragg, John C.; Lin, Chien-Chi; Department of Biomedical Engineering, School of Engineering and Technology
    Various polymerization mechanisms have been developed to prepare peptide-immobilized poly(ethylene glycol) (PEG) hydrogels, a class of biomaterials suitable for studying cell biology in vitro. Here, a visible light mediated thiol-acrylate photopolymerization scheme is reported to synthesize dually degradable PEG-peptide hydrogels with controllable crosslinking and degradability. The influence of immobilized monothiol pendant peptide is systematically evaluated on the crosslinking of these hydrogels. Further, methods are proposed to modulate hydrogel crosslinking, including adjusting concentration of comonomer or altering the design of multifunctional peptide crosslinker. Due to the formation of thioether ester bonds, these hydrogels are hydrolytically degradable. If the dithiol peptide linkers used are susceptible to protease cleavage, these thiol-acrylate hydrogels can be designed to undergo partial proteolysis. The differences between linear and multiarm PEG-acrylate (i.e., PEGDA vs PEG4A) are also evaluated. Finally, the use of the mixed-mode thiol-acrylate PEG4A-peptide hydrogels is explored for in situ encapsulation of hepatocellular carcinoma cells (Huh7). The effects of matrix stiffness and integrin binding motif (e.g., RGDS) on Huh7 cell growth and HIPPO pathway activation are studied using PEG4A-peptide hydrogels. This visible light poly-merized thiol-acrylate hydrogel system represents an alternative to existing light-cured hydrogel platforms and shall be useful in many biomedical applications.
  • Thumbnail Image
    Item
    Effects of estrogen depletion and drug treatment on collagen microstructure: implications
    (SpringerNature, 2015-05-27) Wallace, Joseph M.; Bone, Henry G.; Department of Biomedical Engineering, School of Engineering and Technology
    Commentary on: Cauble MA, Rothman E, Welch K, Fang M, Duong LT, Pennypacker BL, Orr BG, Holl MMB. Alteration of Type I collagen microstructure induced by estrogen depletion can be prevented with drug treatment. BoneKEy 2015; 4: 697. doi:10.1038/ bonekey.2015.66.
  • Thumbnail Image
    Item
    Enzyme-immobilized hydrogels to create hypoxia for in vitro cancer cell culture
    (Elsevier, 2017-04) Dawes, Camron S.; Konig, Heiko; Lin, Chien-Chi; Department of Biomedical Engineering, School of Engineering and Technology
    Hypoxia is a critical condition governing many aspects of cellular fate processes. The most common practice in hypoxic cell culture is to maintain cells in an incubator with controlled gas inlet (i.e., hypoxic chamber). Here, we describe the design and characterization of enzyme-immobilized hydrogels to create solution hypoxia under ambient conditions for in vitro cancer cell culture. Specifically, glucose oxidase (GOX) was acrylated and co-polymerized with poly(ethylene glycol)-diacrylate (PEGDA) through photopolymerization to form GOX-immobilized PEG-based hydrogels. We first evaluated the effect of soluble GOX on inducing solution hypoxia (O2 < 5%) and found that both unmodified and acrylated GOX could sustain hypoxia for at least 24 h even under ambient air condition with constant oxygen diffusion from the air-liquid interface. However, soluble GOX gradually lost its ability to sustain hypoxia after 24 h due to the loss of enzyme activity over time. On the other hand, GOX-immobilized hydrogels were able to create hypoxia within the hydrogel for at least 120 h, potentially due to enhanced protein stabilization by enzyme ‘PEGylation’ and immobilization. As a proof-of-concept, this GOX-immobilized hydrogel system was used to create hypoxia for in vitro culture of Molm14 (acute myeloid leukemia (AML) cell line) and Huh7 (hepatocellular carcinoma (HCC) cell line). Cells cultured in the presence of GOX-immobilized hydrogels remained viable for at least 24 h. The expression of hypoxia associated genes, including carbonic anhydrase 9 (CA9) and lysyl oxidase (LOX), were significantly upregulated in cells cultured with GOX-immobilized hydrogels. These results have demonstrated the potential of using enzyme-immobilized hydrogels to create hypoxic environment for in vitro cancer cell culture.
  • Thumbnail Image
    Item
    Fabrication of Poly-l-lactic Acid/Dicalcium Phosphate Dihydrate Composite Scaffolds with High Mechanical Strength-Implications for Bone Tissue Engineering
    (MDPI, 2015) Tanataweethum, Nida; Liu, Wai Ching; Goebel, W. Scott; Li, Ding; Chu, Tien Min; Department of Biomedical Engineering, School of Engineering and Technology
    Scaffolds were fabricated from poly-l-lactic acid (PLLA)/dicalcium phosphate dihydrate (DCPD) composite by indirect casting. Sodium citrate and PLLA were used to improve the mechanical properties of the DCPD scaffolds. The resulting PLLA/DCPD composite scaffold had increased diametral tensile strength and fracture energy when compared to DCPD only scaffolds (1.05 vs. 2.70 MPa and 2.53 vs. 12.67 N-mm, respectively). Sodium citrate alone accelerated the degradation rate by 1.5 times independent of PLLA. Cytocompatibility of all samples were evaluated using proliferation and differentiation parameters of dog-bone marrow stromal cells (dog-BMSCs). The results showed that viable dog-BMSCs attached well on both DCPD and PLLA/DCPD composite surfaces. In both DCPD and PLLA/DCPD conditioned medium, dog-BMSCs proliferated well and expressed alkaline phosphatase (ALP) activity indicating cell differentiation. These findings indicate that incorporating both sodium citrate and PLLA could effectively improve mechanical strength and biocompatibility without increasing the degradation time of calcium phosphate cement scaffolds for bone tissue engineering purposes.