Browsing by Subject "Compression"

Now showing 1 - 5 of 5
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    Compression-induced structural and mechanical changes of fibrin-collagen composites
    (Elsevier, 2017-07) Kim, O. V.; Litvinov, R. I.; Chen, J.; Chen, D. Z.; Weisel, J.W.; Alber, M. S.; Medicine, School of Medicine
    Fibrin and collagen as well as their combinations play an important biological role in tissue regeneration and are widely employed in surgery as fleeces or sealants and in bioengineering as tissue scaffolds. Earlier studies demonstrated that fibrin-collagen composite networks displayed improved tensile mechanical properties compared to the isolated protein matrices. Unlike previous studies, here unconfined compression was applied to a fibrin-collagen filamentous polymer composite matrix to study its structural and mechanical responses to compressive deformation. Combining collagen with fibrin resulted in formation of a composite hydrogel exhibiting synergistic mechanical properties compared to the isolated fibrin and collagen matrices. Specifically, the composite matrix revealed a one order of magnitude increase in the shear storage modulus at compressive strains>0.8 in response to compression compared to the mechanical features of individual components. These material enhancements were attributed to the observed structural alterations, such as network density changes, an increase in connectivity along with criss-crossing, and bundling of fibers. In addition, the compressed composite collagen/fibrin networks revealed a non-linear transformation of their viscoelastic properties with softening and stiffening regimes. These transitions were shown to depend on protein concentrations. Namely, a decrease in protein content drastically affected the mechanical response of the networks to compression by shifting the onset of stiffening to higher degrees of compression. Since both natural and artificially composed extracellular matrices experience compression in various (patho)physiological conditions, our results provide new insights into the structural biomechanics of the polymeric composite matrix that can help to create fibrin-collagen sealants, sponges, and tissue scaffolds with tunable and predictable mechanical properties.
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    Foam-like compression behavior of fibrin networks
    (Springer, 2016-02) Kim, Oleg V.; Liang, Xiaojun; Litvinov, Rustem I.; Weisel, John W.; Alber, Mark S.; Purohit, Prashant K.; Department of Medicine, IU School of Medicine
    The rheological properties of fibrin networks have been of long-standing interest. As such there is a wealth of studies of their shear and tensile responses, but their compressive behavior remains unexplored. Here, by characterization of the network structure with synchronous measurement of the fibrin storage and loss moduli at increasing degrees of compression, we show that the compressive behavior of fibrin networks is similar to that of cellular solids. A nonlinear stress-strain response of fibrin consists of three regimes: (1) an initial linear regime, in which most fibers are straight, (2) a plateau regime, in which more and more fibers buckle and collapse, and (3) a markedly nonlinear regime, in which network densification occurs by bending of buckled fibers and inter-fiber contacts. Importantly, the spatially non-uniform network deformation included formation of a moving "compression front" along the axis of strain, which segregated the fibrin network into compartments with different fiber densities and structure. The Young's modulus of the linear phase depends quadratically on the fibrin volume fraction while that in the densified phase depends cubically on it. The viscoelastic plateau regime corresponds to a mixture of these two phases in which the fractions of the two phases change during compression. We model this regime using a continuum theory of phase transitions and analytically predict the storage and loss moduli which are in good agreement with the experimental data. Our work shows that fibrin networks are a member of a broad class of natural cellular materials which includes cancellous bone, wood and cork.
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    Geometric Characterization of Local Changes in Tungsten Microneedle Tips after In-Vivo Insertion into Peripheral Nerves
    (MDPI, 2022) Sergi, Pier Nicola; Jensen, Winnie; Yoshida, Ken; Biomedical Engineering, Purdue School of Engineering and Technology
    Peripheral neural interfaces are used to connect the peripheral nervous system to high-tech robotic devices and computer interfaces. Soft materials are nowadays used to build the main structural part of these interfaces because they are able to mimic the mechanical properties of peripheral nerves. However, if on the one hand soft materials provide effective connections, reducing mechanical mismatch with nervous tissues and creating a close contact between active sites and neural fibers, on the other hand, most of them are not mechanically stable during implantation. As a consequence, tungsten (W) microneedles are used to insert soft neural interfaces, because they are able to pierce the peripheral nervous tissue because of their high stiffness. Nevertheless, this stiffness cannot prevent microneedles from local microscopic structural damage, even after successful insertions. In addition, the nature of this damage is not totally clear. Therefore, this work aimed at quantitatively investigating the phenomenological changes of the microneedles’ tip shape after insertion into the in vivo peripheral nerves. In particular, a quantification of the interactions between peripheral nerves and W microneedles was proposed through the Oliver-Pharr formula, and the interaction force was found to be directly proportional to the power < m > = 2.124 of the normalized indentation depth. Moreover, an experimental correlation between insertion force and the opening tip angle was described together with an assessment of the minimum diameter to effectively puncture the peripheral nervous tissue. Finally, a computational framework was presented to describe the local changes affecting the microneedles’ tip shape. This approach was able to detect a bulging phenomenon along with the microneedle tips with a characteristic amplitude of approximately 100 μm, and a folding phenomenon, with a characteristic mean amplitude of less than 20 μm, affecting the extreme ending sections of the microneedle tips. These geometrical changes were related to the synergistic action of interaction forces likely resulting in compression and elastic instability of the tip.
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    Modeling the effect of ascites-induced compression on ovarian cancer multicellular aggregates
    (The Company of Biologists, 2018-09-25) Klymenko, Yuliya; Wates, Rebecca B.; Weiss-Bilka, Holly; Lombard, Rachel; Liu, Yueying; Campbell, Leigh; Kim, Oleg; Wagner, Diane; Ravosa, Matthew J.; Stack, M. Sharon; Mechanical and Energy Engineering, School of Engineering and Technology
    Epithelial ovarian cancer (EOC) is the most lethal gynecological malignancy. EOC dissemination is predominantly via direct extension of cells and multicellular aggregates (MCAs) into the peritoneal cavity, which adhere to and induce retraction of peritoneal mesothelium and proliferate in the submesothelial matrix to generate metastatic lesions. Metastasis is facilitated by the accumulation of malignant ascites (500 ml to >2 l), resulting in physical discomfort and abdominal distension, and leading to poor prognosis. Although intraperitoneal fluid pressure is normally subatmospheric, an average intraperitoneal pressure of 30 cmH2O (22.1 mmHg) has been reported in women with EOC. In this study, to enable experimental evaluation of the impact of high intraperitoneal pressure on EOC progression, two new in vitro model systems were developed. Initial experiments evaluated EOC MCAs in pressure vessels connected to an Instron to apply short-term compressive force. A Flexcell Compression Plus system was then used to enable longer-term compression of MCAs in custom-designed hydrogel carriers. Results show changes in the expression of genes related to epithelial-mesenchymal transition as well as altered dispersal of compressed MCAs on collagen gels. These new model systems have utility for future analyses of compression-induced mechanotransduction and the resulting impact on cellular responses related to intraperitoneal metastatic dissemination.This article has an associated First Person interview with the first authors of the paper.
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    Ridge Dimensional Changes: A Comparative Study of Socket Compression After Dental Extraction with No Compression
    (2013) Bennett, Duane Everett, II, 1984-; Prakasam, Sivaraman; Blanchard, Steven B.; Parks, Edwin T. (Edwin Thomas), 1955-; Ghoneima, Ahmed; John, Vanchit (Vanchit Kurien), 1965-
    Exodontia, or extraction of teeth, has been a well-documented dental treatment that forms one of the foundations of dentistry. The steps associated with extracting teeth have changed little in the last century and these steps are largely part of the dogma of dentistry. One such step is that of socket compression post-extraction. Rationale for socket compression after extraction is manifold. They include: shorter healing times, fewer dry sockets and re-approximating walls that were stretched in the elevation and delivery stages of extractions. The purpose of this study was to determine if post-extraction ridge compression negatively affected alveolar ridge dimensions when compared to sites that are not compressed post-extraction. Secondary outcome measures will identify if socket compression/re-approximation affects the rate of soft tissue closure or occurrence of alveolar osteitis. In this study, 14 subjects were recruited. Eight subjects formed the compression group, while six formed the non-compression group. The subjects in the compression group received compression of their alveolar ridges after extraction to approximate their original pre-extraction width. The subjects in the non-compression group did not receive ridge compression. Each subject had pre-extraction and post-extraction CBCT scans along with post-operative follow up visits at 1, 2, and 4 weeks post-extraction. The present investigation found that with respect to changes in ridge width, sites that were compressed did not lose significantly more dimension than those that were not. With respect to ridge height, sites that were compressed did not lose significantly more dimension than those that were not. Sites that were compressed and sites that were not, healed at approximately the same rate, with respect to soft tissue closure. While the results showed a lack of statistical significance between both groups, there appears to be a trend towards the ridge compression group having a smaller ridge width. Such a trend was not noted with soft tissue closure, thereby invalidating the rationale for socket compression after extraction. One of the limitations of this pilot study is the small sample size. Further validation of these results must be done with a larger sample size in order to provide clinical guidance to dental practitioners.