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Webster VA, Young FR, Patel JM, Scariano GN, Akkus O, Gurkan UA, Chiel HJ, Quinn RD. 3D-Printed Biohybrid Robots Powered by Neuromuscular Tissue Circuits from Aplysia californica. BIOMIMETIC AND BIOHYBRID SYSTEMS 2017. [DOI: 10.1007/978-3-319-63537-8_40] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Tsai AG, Ashworth TJ, Marcus R, Akkus O. Femoral Iatrogenic Subtrochanteric Fatigue Fracture Risk is not Increased by Placing Drill Holes Below the Level of the Lesser Trochanter. THE IOWA ORTHOPAEDIC JOURNAL 2017; 37:23-28. [PMID: 28852330 PMCID: PMC5508277] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
BACKGROUND Iatrogenic subtrochanteric fractures of the femur can occur postoperatively following placement of screws in the lateral femoral cortex. Drilling holes below the lesser trochanter is generally avoided to prevent fatigue failure; however, there is little biomechanical evidence to support this recommendation. We hypothesized that hole placement below the level of the lesser trochanter will not accelerate fatigue failure compared to holes at the level of the lesser trochanter. METHODS Twelve matched-pairs of male fresh-frozen cadaveric femurs were used for biomechanical testing. A single screw hole was drilled through the lateral femoral cortex either at the level of the lesser trochanter (proximal-hole group) or below the lesser trochanter (distal-hole group). Each femur was cycled to failure using a physiologically-relevant loading model. Paired t-test was used to evaluate for a difference in cycles to failure between groups. RESULTS There was no statistical difference in cycles to failure between the groups with the hole drilled at or below the lesser trochanter. CONCLUSIONS The traditional recommendation to avoid drilling holes below the level of the lesser trochanter is based mainly on experience and case reports in the literature. The results of this study indicate that placing holes below the level of the lesser trochanter, in and of itself, may not pose any additional risk of fracture. Other important factors need to be considered, such as tapering of the lateral femoral cortex. CLINICAL RELEVANCE There are often situations where the patient's anatomy and facture pattern is more conducive to placing a screw distal to the lesser trochanter. This study may allow surgeons greater flexibility in placing screws more distally in the lateral femoral cortex by demonstrating the safety of doing so, at least in the population studied.
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Akkus A, Akkus A, Roperto R, Akkus O, Porto T, Teich S, Lang L. Evaluation of mineral content in healthy permanent human enamel by Raman spectroscopy. J Clin Exp Dent 2016; 8:e546-e549. [PMID: 27957268 PMCID: PMC5149089 DOI: 10.4317/jced.53057] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2016] [Accepted: 03/16/2016] [Indexed: 11/30/2022] Open
Abstract
Background An understanding of tooth enamel mineral content using a clinically viable method is essential since variations in mineralization may serve as an early precursor of a dental health issues, and may predict progression and architecture of decay in addition to assessing the success and effectiveness of the remineralization strategies. Material and Methods Twenty two human incisor teeth were obtained in compliance with the NIH guidelines and site specifically imaged with Raman microscope. The front portion of the teeth was divided into apical, medium and cervical regions and subsequently imaged with Raman microscope in these three locations. Results Measured mineralization levels have varied substantially depending on the regions. It was also observed that, the cervical enamel is the least mineralization as a populational average. Conclusions Enamel mineralization is affected by a many factors such as are poor oral hygiene, alcohol consumption and high intake of dietary carbohydrates, however the net effect manifests as overall mineral content of the enamel. Thus an early identification of the individual with overall low mineral content of the enamel may be a valuable screening tool in determining a group with much higher than average caries risk, allowing intervention before development of caries. Clinically applicable non-invasive techniques that can quantify mineral content, such as Raman analysis, would help answer whether or not mineralization is associated with caries risk. Key words:Enamel, Raman spectroscopy, mineral content, dental caries.
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Porto T, Roperto R, Akkus A, Akkus O, Porto-Neto S, Teich S, Lang L, Campos E. Mechanical properties and DIC analyses of CAD/CAM materials. J Clin Exp Dent 2016; 8:e512-e516. [PMID: 27957262 PMCID: PMC5149083 DOI: 10.4317/jced.53014] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2016] [Accepted: 02/17/2016] [Indexed: 11/23/2022] Open
Abstract
Background This study compared two well-known computer-aided-design/computer-aided-manufactured (CAD/CAM) blocks (Paradigm MZ100 [3M ESPE] and Vitablocs Mark II [Vita] in terms of fracture toughness (Kic), index of brittleness (BI) and stress/strain distributions. Material and Methods Three-point bending test was used to calculate the fracture toughness, and the relationship between the Kic and the Vickers hardness was used to calculate the index of brittleness. Additionally, digital image correlation (DIC) was used to analyze the stress/strain distribution on both materials. Results The values for fracture toughness obtained under three-point bending were 1.87Pa√m (±0.69) for Paradigm MZ100 and 1.18Pa√m (±0.17) for Vitablocs Mark II. For the index of brittleness, the values for Paradigm and Vitablocs were 73.13μm-1/2 (±30.72) and 550.22μm-1/2 (±82.46). One-way ANOVA was performed to find differences (α=0.05) and detected deviation between the stress/strain distributions on both materials. Conclusions Both CAD/CAM materials tested presented similar fracture toughness, but, different strain/stress distributions. Both materials may perform similarly when used in CAD/CAM restorations. Key words:Ceramic, CAD/CAM, hybrid materials, composite resin, fracture toughness.
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Webster VA, Nieto SG, Grosberg A, Akkus O, Chiel HJ, Quinn RD. Simulating muscular thin films using thermal contraction capabilities in finite element analysis tools. J Mech Behav Biomed Mater 2016; 63:326-336. [DOI: 10.1016/j.jmbbm.2016.06.027] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2016] [Revised: 06/27/2016] [Accepted: 06/28/2016] [Indexed: 10/21/2022]
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Islam A, Younesi M, Mbimba T, Akkus O. Collagen Substrate Stiffness Anisotropy Affects Cellular Elongation, Nuclear Shape, and Stem Cell Fate toward Anisotropic Tissue Lineage. Adv Healthc Mater 2016; 5:2237-47. [PMID: 27377355 PMCID: PMC5203936 DOI: 10.1002/adhm.201600284] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2016] [Revised: 06/03/2016] [Indexed: 01/01/2023]
Abstract
Rigidity of substrates plays an important role in stem cell fate. Studies are commonly carried out on isotropically stiff substrate or substrates with unidirectional stiffness gradients. However, many native tissues are anisotropically stiff and it is unknown whether controlled presentation of stiff and compliant material axes on the same substrate governs cytoskeletal and nuclear morphology, as well as stem cell differentiation. In this study, electrocompacted collagen sheets are stretched to varying degrees to tune the stiffness anisotropy (SA) in the range of 1 to 8, resulting in stiff and compliant material axes orthogonal to each other. The cytoskeletal aspect ratio increased with increasing SA by about fourfold. Such elongation was absent on cellulose acetate replicas of aligned collagen surfaces indicating that the elongation was not driven by surface topography. Mesenchymal stem cells (MSCs) seeded on varying anisotropy sheets displayed a dose-dependent upregulation of tendon-related markers such as Mohawk and Scleraxis. After 21 d of culture, highly anisotropic sheets induced greater levels of production of type-I, type-III collagen, and thrombospondin-4. Therefore, SA has direct effects on MSC differentiation. These findings may also have ramifications of stem cell fate on other anisotropically stiff tissues, such as skeletal/cardiac muscles, ligaments, and bone.
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Younesi M, Donmez BO, Islam A, Akkus O. Heparinized collagen sutures for sustained delivery of PDGF-BB: Delivery profile and effects on tendon-derived cells In-Vitro. Acta Biomater 2016; 41:100-9. [PMID: 27240725 DOI: 10.1016/j.actbio.2016.05.036] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2015] [Revised: 05/23/2016] [Accepted: 05/26/2016] [Indexed: 01/30/2023]
Abstract
UNLABELLED Suturing is the standard of repair for lacerated flexor tendons. Past studies focused on delivering growth factors to the repair site by incorporating growth factors to nylon sutures which are commonly used in the repair procedure. However, conjugation of growth factors to nylon or other synthetic sutures is not straightforward. Collagen holds promise as a suture material by way of providing chemical sites for conjugation of growth factors. On the other hand, collagen also needs to be reconstituted as a mechanically robust thread that can be sutured. In this study, we reconstituted collagen solutions as suturable collagen threads by using linear electrochemical compaction. Prolonged release of PDGF-BB (Platelet derived growth factor-BB) was achieved by covalent bonding of heparin to the collagen sutures. Tensile mechanical tests of collagen sutures before and after chemical modification indicated that the strength of sutures following chemical conjugation stages was not compromised. Strength of lacerated tendons sutured with epitendinous collagen sutures (11.2±0.7N) converged to that of the standard nylon suture (14.9±2.9N). Heparin conjugation of collagen sutures didn't affect viability and proliferation of tendon-derived cells and prolonged the PDGF-BB release up to 15days. Proliferation of cells seeded on PDGF-BB incorporated collagen sutures was about 50% greater than those seeded on plain collagen sutures. Collagen that is released to the media by the cells increased by 120% under the effects of PDGF-BB and collagen production by cells was detectable by histology as of day 21. Addition of PDGF-BB to collagen sutures resulted in a moderate decline in the expression of the tendon-associated markers scleraxis, collagen I, tenomodulin, and COMP; however, expression levels were still greater than the cells seeded on collagen gel. The data indicate that the effects of PDGF-BB on tendon-derived cells mainly occur through increased cell proliferation and that longer term studies are needed to confirm whether this proliferation is outweighs the moderate reduction in the expression of tendon-associated genes. STATEMENT OF SIGNIFICANCE A mechanically robust pure collagen suture was fabricated via linear electrocompaction and conjugated with heparin for prolonged delivery of PDFG-BB. Sustained delivery of the PDGF-BB improved the proliferation of tendon derived cells substantially at the expense of a moderate downregulation of tenogenic markers. The collagen threads were functionally applicable as epitendinous sutures when applied to chicken flexor tendons in vitro. Overall, electrocompacted collagen sutures holds potential to improve repair outcome in flexor tendon surgeries by improving cellularity and collagen production through delivery of the PDGF-BB. The bioinductive suture concept can be applied to deliver other growth factors for a wide-array of applications.
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Shantavasinkul P, Akkus O, Palomo JM, Baumgaertel S. Surface strain distribution of orthodontic miniscrews under load. Am J Orthod Dentofacial Orthop 2016; 150:444-50. [DOI: 10.1016/j.ajodo.2016.02.019] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2015] [Revised: 02/01/2016] [Accepted: 02/01/2016] [Indexed: 11/16/2022]
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Alapan Y, Younesi M, Akkus O, Gurkan UA. Cell-Aligning Substrates: Anisotropically Stiff 3D Micropillar Niche Induces Extraordinary Cell Alignment and Elongation (Adv. Healthcare Mater. 15/2016). Adv Healthc Mater 2016. [DOI: 10.1002/adhm.201670075] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Alapan Y, Younesi M, Akkus O, Gurkan UA. Anisotropically Stiff 3D Micropillar Niche Induces Extraordinary Cell Alignment and Elongation. Adv Healthc Mater 2016; 5:1884-92. [PMID: 27191679 PMCID: PMC4982772 DOI: 10.1002/adhm.201600096] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Revised: 03/10/2016] [Indexed: 12/30/2022]
Abstract
A microfabricated pillar substrate is developed to confine, align, and elongate cells, allowing decoupled analysis of stiffness and directionality in 3D. Mesenchymal stem cells and cardiomyocytes are successfully confined in a 3D environment with precisely tunable stiffness anisotropy. It is discovered that anisotropically stiff micropillar substrates provide cellular confinement in 3D, aligning cells in the stiffer direction with extraordinary elongation.
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Akkus A, Akkus O, Roperto R, Lang L. Investigation of Intra- and Inter-individual Variations of Mineralisation in Healthy Permanent Human Enamel by Raman Spectroscopy. ORAL HEALTH & PREVENTIVE DENTISTRY 2016; 14:321-7. [PMID: 27175446 DOI: 10.3290/j.ohpd.a36098] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
PURPOSE To systematically examine mineralisation of healthy human enamel using Raman spectroscopy and provide an understanding of baseline variations that may be inherent in the healthy enamel from individual to individual as well as variations within a tooth. MATERIALS AND METHODS Human teeth were obtained in compliance with the NIH guidelines. The teeth were collected fresh within the date of the extraction and kept moist at all times with wet tissue paper without any additional disinfecting treatment. The samples were individually wrapped in wet tissue paper and stored in a -20°C freezer. Prior to Raman analysis, the specimens were thawed at room temperature for 30 min. A Raman microscope was employed with a 10X objective used to focus the laser light (785 nm). Raman spectroscopy scores were validated by microcomputed tomography (μCT) on the two teeth which had the highest and lowest mineralisation found in the Raman scans. RESULTS Mineralisation levels varied substantially between individuals. The highest Raman-based mineralisation intensity was about 5-fold greater than the lowest mineralisation score. Incisor mineralisation also varied dramatically depending on different sites on the tooth. CONCLUSIONS Clinically applicable non-invasive techniques such as Raman spectroscopy that can quantify mineral content, such as Raman spectroscopy, may help answer whether or not mineralisation is associated with caries risk.
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Morris VB, Nimbalkar S, Younesi M, McClellan P, Akkus O. Mechanical Properties, Cytocompatibility and Manufacturability of Chitosan:PEGDA Hybrid-Gel Scaffolds by Stereolithography. Ann Biomed Eng 2016; 45:286-296. [PMID: 27164837 DOI: 10.1007/s10439-016-1643-1] [Citation(s) in RCA: 90] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Accepted: 05/05/2016] [Indexed: 01/23/2023]
Abstract
Extracellular matrix mimetic hydrogels which hybridize synthetic and natural polymers offer molecularly-tailored, bioactive properties and tunable mechanical strength. In addition, 3D bioprinting by stereolithography allows fabrication of internal pores and defined macroscopic shapes. In this study, we formulated a hybrid biocompatible resin using natural and synthetic polymers (chitosan and polyethylene glycol diacrylate (PEGDA), respectively) by controlling molecular weight of chitosan, feed-ratios, and photo-initiator concentration. Ear-shaped, hybrid scaffolds were fabricated by a stereolithographic method using a 405 nm laser. Hybrid hydrogel scaffolds of chitosan (50-190 kDa) and PEGDA (575 Da) were mixed at varying feed-ratios. Some of the cationic, amino groups of chitosan were neutralized by dialysis in acidic solution containing chitosan in excess of sodium acetate solution to inhibit quenching of newly formed photoradicals. A feed-ratio of 1:7.5 was found to be the most appropriate of the formulations considered in this study in terms of mechanical properties, cell adhesion, and printability. The biofabricated hybrid scaffold showed interconnected, homogeneous pores with a nominal pore size of 50 µm and an elastic modulus of ~400 kPa. Moreover, long-term cell viability and cell spreading was observed via actin filament staining. Printability of the biocompatible resin was confirmed by printing thresholded MR images of an ear and the feed ratio of 1:7.5 provided the most faithful reproduction of the shape. To the best of our knowledge, this is the first report of stereolithographic printing hybridizing cell-adhesive properties of chitosan with mechanical robustness of PEG in scaffolds suitable for repair of complex tissue geometries, such as those of the human ear.
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Webster VA, Hawley EL, Akkus O, Chiel HJ, Quinn RD. Effect of actuating cell source on locomotion of organic living machines with electrocompacted collagen skeleton. BIOINSPIRATION & BIOMIMETICS 2016; 11:036012. [PMID: 27159923 DOI: 10.1088/1748-3190/11/3/036012] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
In robotics, there is a need for small scale, compliant actuators for use in medical applications or minimally invasive environmental monitoring. Biohybrid devices offer one solution to this need by using muscle cells to actuate compliant scaffolds. Such devices typically use biocompatible synthetic polymers as compliant scaffolds, which require additional processing steps to promote cellular alignment and attachment. Instead, electrocompacted and aligned collagen (ELAC) can be used as a completely organic scaffold, requiring no additional processing steps, with alignment being innately promoted by the topography. Locomotive living machines have been fabricated in this study using ELAC scaffolds. Devices have been produced using either primary cardiomyocytes or primary skeletal muscle cells isolated from chick embryos as actuators. When tested under the same conditions, skeletal muscle cell powered devices were approximately an order of magnitude faster, having a mean velocity of 77.6 ± 86.4 μm min(-1), compared to 9.34 ± 6.69 μm min(-1) for cardiomyocyte powered devices. In conclusion, completely organic living machines have been fabricated using electrocompacted collagen skeletons, and it was found that skeletal muscle powered devices were significantly faster than cardiomyocyte powered devices.
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Unal M, Jung H, Akkus O. Novel Raman Spectroscopic Biomarkers Indicate That Postyield Damage Denatures Bone's Collagen. J Bone Miner Res 2016; 31:1015-25. [PMID: 26678707 DOI: 10.1002/jbmr.2768] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/03/2015] [Revised: 12/10/2015] [Accepted: 12/14/2015] [Indexed: 01/12/2023]
Abstract
Raman spectroscopy has become a powerful tool in the assessment of bone quality. However, the use of Raman spectroscopy to assess collagen quality in bone is less established than mineral quality. Because postyield mechanical properties of bone are mostly determined by collagen rather than the mineral phase, it is essential to identify new spectroscopic biomarkers that help infer the status of collagen quality. Amide I and amide III bands are uniquely useful for collagen conformational analysis. Thus, the first aim of this work was to identify the regions of amide bands that are sensitive to thermally induced denaturation. Collagen sheets and bone were thermally denatured to identify spectral measures that change significantly following denaturation. The second aim was to assess whether mechanical damage denatures the collagen phase of bone, as reflected by the molecular spectroscopic biomarkers identified in the first aim. The third aim was to assess the correlation between these new spectroscopic biomarkers and postyield mechanical properties of cortical bone. Our results revealed five peaks whose intensities were sensitive to thermal and mechanical denaturation: ∼1245, ∼1270, and ∼1320 cm(-1) in the amide III band, and ∼1640 and ∼1670 cm(-1) in the amide I band. Four peak intensity ratios derived from these peaks were found to be sensitive to denaturation: 1670/1640, 1320/1454, 1245/1270, and 1245/1454. Among these four spectral biomarkers, only 1670/1640 displayed significant correlation with all postyield mechanical properties. The overall results showed that these peak intensity ratios can be used as novel spectroscopic biomarkers to assess collagen quality and integrity. The changes in these ratios with denaturation may reflect alterations in the collagen secondary structure, specifically a transition from ordered to less-ordered structure. The overall results clearly demonstrate that this new spectral information, specifically the ratio of 1670/1640, can be used to understand the involvement of collagen quality in the fragility of bone. © 2015 American Society for Bone and Mineral Research.
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Roperto R, Akkus A, Akkus O, Lang L, Sousa-Neto MD, Teich S, Porto TS. Effect of different adhesive strategies on microtensile bond strength of computer aided design/computer aided manufacturing blocks bonded to dentin. Dent Res J (Isfahan) 2016; 13:117-23. [PMID: 27076825 PMCID: PMC4810908 DOI: 10.4103/1735-3327.178196] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Background: The aim of this study was to determine the microtensile bond strength (μTBS) of ceramic and composite computer aided design-computer aided manufacturing (CAD-CAM) blocks bonded to dentin using different adhesive strategies. Materials and Methods: In this in vitro study, 30 crowns of sound freshly extracted human molars were sectioned horizontally 3 mm above the cementoenamel junction to produce flat dentin surfaces. Ceramic and composite CAD/CAM blocks, size 14, were sectioned into slices of 3 mm thick. Before bonding, CAD/CAM block surfaces were treated according to the manufacturer's instructions. Groups were created based on the adhesive strategy used: Group 1 (GI) - conventional resin cement + total-etch adhesive system, Group 2 (GII) - conventional resin cement + self-etch adhesive system, and Group 3 (GIII) - self-adhesive resin cement with no adhesive. Bonded specimens were stored in 100% humidity for 24h at 37C, and then sectioned with a slow-speed diamond saw to obtain 1 mm × 1 mm × 6 mm microsticks. Microtensile testing was then conducted using a microtensile tester. μTBS values were expressed in MPa and analyzed by one-way ANOVA with post hoc (Tukey) test at the 5% significance level. Results: Mean values and standard deviations of μTBS (MPa) were 17.68 (±2.71) for GI/ceramic; 17.62 (±3.99) for GI/composite; 13.61 (±6.92) for GII/composite; 12.22 (±4.24) for GII/ceramic; 7.47 (±2.29) for GIII/composite; and 6.48 (±3.10) for GIII/ceramic; ANOVA indicated significant differences among the adhesive modality and block interaction (P < 0.05), and no significant differences among blocks only, except between GI and GII/ceramic. Bond strength of GIII was consistently lower (P < 0.05) than GI and GII groups, regardless the block used. Conclusion: Cementation of CAD/CAM restorations, either composite or ceramic, can be significantly affected by different adhesive strategies used.
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Khalifa A, Chapin K, Abdelgawad O, Anderson J, Akkus O, Hijaz A. PD36-11 BIOCOMPATIBILITY OF WOVEN COLLAGEN MESH AS A NOVEL BIOMATERIAL FOR FUTURE SLINGS. J Urol 2016. [DOI: 10.1016/j.juro.2016.02.1116] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Jung H, Akkus O. Activation of intracellular calcium signaling in osteoblasts colocalizes with the formation of post-yield diffuse microdamage in bone matrix. BONEKEY REPORTS 2016; 5:778. [PMID: 26962448 DOI: 10.1038/bonekey.2016.5] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Accepted: 01/06/2016] [Indexed: 01/09/2023]
Abstract
Previous studies demonstrated that extracellular calcium efflux ([Ca(2+)]E) originates from the regions of bone extracellular matrix that are undergoing microdamage. Such [Ca(2+)]E is reported to induce the activation of intracellular calcium signaling ([Ca(2+)]I) in MC3T3-E1 cells. The current study investigated the association between microdamage and local activation of intracellular calcium signaling quantifiably in MC3T3-E1 cells. Cells were seeded on devitalized notched bovine bone samples to induce damage controllably within the field of observation. A sequential staining procedure was implemented to stain for intracellular calcium activation followed by staining for microdamage on the same sample. The increase in [Ca(2+)]I fluorescence in cells of mechanically loaded samples was greater than that of unloaded negative control cells. The results showed that more than 80% of the cells with increased [Ca(2+)]I fluorescence were located within the damage zone. In conclusion, the findings demonstrate that there are spatial proximity between diffuse microdamage induction and the activation of intracellular calcium ([Ca(2+)]I) signaling in MC3T3-E1 cells. The downstream responses to the observed activation in future research may help understand how bone cells repair microdamage.
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Islam A, Chapin K, Moore E, Ford J, Rimnac C, Akkus O. Gamma Radiation Sterilization Reduces the High-cycle Fatigue Life of Allograft Bone. Clin Orthop Relat Res 2016; 474:827-35. [PMID: 26463571 PMCID: PMC4746152 DOI: 10.1007/s11999-015-4589-y] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Accepted: 10/02/2015] [Indexed: 01/31/2023]
Abstract
BACKGROUND Sterilization by gamma radiation impairs the mechanical properties of bone allografts. Previous work related to radiation-induced embrittlement of bone tissue has been limited mostly to monotonic testing which does not necessarily predict the high-cycle fatigue life of allografts in vivo. QUESTIONS/PURPOSES We designed a custom rotating-bending fatigue device to answer the following questions: (1) Does gamma radiation sterilization affect the high-cycle fatigue behavior of cortical bone; and (2) how does the fatigue life change with cyclic stress level? METHODS The high-cycle fatigue behavior of human cortical bone specimens was examined at stress levels related to physiologic levels using a custom-designed rotating-bending fatigue device. Test specimens were distributed among two treatment groups (n = 6/group); control and irradiated. Samples were tested until failure at stress levels of 25, 35, and 45 MPa. RESULTS At 25 MPa, 83% of control samples survived 30 million cycles (run-out) whereas 83% of irradiated samples survived only 0.5 million cycles. At 35 MPa, irradiated samples showed an approximately 19-fold reduction in fatigue life compared with control samples (12.2 × 10(6) ± 12.3 × 10(6) versus 6.38 × 10(5) ± 6.81 × 10(5); p = 0.046), and in the case of 45 MPa, this reduction was approximately 17.5-fold (7.31 × 10(5) ± 6.39 × 10(5) versus 4.17 × 10(4) ± 1.91 × 10(4); p = 0.025). Equations to estimate high-cycle fatigue life of irradiated and control cortical bone allograft at a certain stress level were derived. CONCLUSIONS Gamma radiation sterilization severely impairs the high cycle fatigue life of structural allograft bone tissues, more so than the decline that has been reported for monotonic mechanical properties. Therefore, clinicians need to be conservative in the expectation of the fatigue life of structural allograft bone tissues. Methods to preserve the fatigue strength of nonirradiated allograft bone tissue are needed. CLINICAL RELEVANCE As opposed to what monotonic tests might suggest, the cyclic fatigue life of radiation-sterilized structural allografts is likely severely compromised relative to the nonirradiated condition and therefore should be taken into consideration. Methods to reduce the effect of irradiation or to recover structural allograft bone tissue fatigue strength are important to pursue.
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Lopes FC, Roperto R, Akkus A, Akkus O, Souza-Gabriel AE, Sousa-Neto MD. Effects of different lasers on organic/inorganic ratio of radicular dentin. Lasers Med Sci 2016; 31:415-20. [DOI: 10.1007/s10103-015-1862-y] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2015] [Accepted: 12/28/2015] [Indexed: 10/22/2022]
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Webster VA, Chapin KJ, Hawley EL, Patel JM, Akkus O, Chiel HJ, Quinn RD. Aplysia Californica as a Novel Source of Material for Biohybrid Robots and Organic Machines. BIOMIMETIC AND BIOHYBRID SYSTEMS 2016. [DOI: 10.1007/978-3-319-42417-0_33] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Unal M, Akkus O. Raman spectral classification of mineral- and collagen-bound water's associations to elastic and post-yield mechanical properties of cortical bone. Bone 2015; 81. [PMID: 26211992 PMCID: PMC4640992 DOI: 10.1016/j.bone.2015.07.024] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Water that is bound to bone's matrix is implied as a predictor of fracture resistance; however, bound water is an elusive variable to be measured nondestructively. To date, the only nondestructive method used for studying bone hydration status is magnetic resonance variants (NMR or MRI). For the first time, bone hydration status was studied by short-wave infrared (SWIR) Raman spectroscopy to investigate associations of mineral-bound and collagen-bound water compartments with mechanical properties. Thirty cortical bone samples were used for quantitative Raman-based water analysis, gravimetric analysis, porosity measurement, and biomechanical testing. A sequential dehydration protocol was developed to replace unbound (heat drying) and bound (ethanol treatment) water in bone. Raman spectra were collected serially to track the OH-stretch band during dehydration. Four previously identified peaks were investigated: I3220/I2949, I3325/I2949 and I3453/I2949 reflect status of organic-matrix related water (mostly collagen-related water) compartments and collagen portion of bone while I3584/I2949 reflects status of mineral-related water compartments and mineral portion of bone. These spectroscopic biomarkers were correlated with elastic and post-yield mechanical properties of bone. Collagen-water related biomarkers (I3220/I2949 and I3325/I2949) correlated significantly and positively with toughness (R(2)=0.81 and R(2)=0.79; p<0.001) and post-yield toughness (R(2)=0.65 and R(2)=0.73; p<0.001). Mineral-water related biomarker correlated significantly and negatively with elastic modulus (R(2)=0.78; p<0.001) and positively with strength (R(2)=0.46; p<0.001). While MR-based techniques have been useful in measuring unbound and bound water, this is the first study which probed bound-water compartments differentially for collagen and mineral-bound water. For the first time, we showed an evidence for contributions of different bound-water compartments to mechanical properties of wet bone and the reported correlations of Raman-based water measurements to mechanical properties underline the necessity for enabling approaches to assess these new biomarkers noninvasively in vivo to improve the current diagnosis of those who may be at risk of bone fracture due to aging and diseases.
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Islam A, Bohl MS, Tsai AG, Younesi M, Gillespie R, Akkus O. Biomechanical evaluation of a novel suturing scheme for grafting load-bearing collagen scaffolds for rotator cuff repair. Clin Biomech (Bristol, Avon) 2015; 30:669-75. [PMID: 26009492 PMCID: PMC4523401 DOI: 10.1016/j.clinbiomech.2015.05.007] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/24/2014] [Revised: 03/26/2015] [Accepted: 05/11/2015] [Indexed: 02/07/2023]
Abstract
BACKGROUND Currently, there are no well-established suture protocols to attach fully load-bearing scaffolds which span tendon defects between bone and muscle for repair of critical sized tendon tears. Methods to attach load-bearing tissue repair scaffolds could enable functional repair of tendon injuries. METHODS Sixteen rabbit shoulders were dissected (New Zealand white rabbits, 1yr. old, female) to isolate the humeral-infraspinatus muscle complex. A unique suture technique was developed to allow for a 5mm segmental defect in infraspinatus tendon to be replaced with a mechanically strong bioscaffold woven from pure collagen threads. The suturing pattern resulted in a fully load-bearing scaffold. The tensile stiffness and strength of scaffold repair were compared with intact infraspinatus and regular direct repair. FINDINGS The failure load and displacement at failure of the scaffold repair group were 59.9N (standard deviation, SD=10.7) and 10.3mm (SD=2.9), respectively and matched those obtained by direct repair group which were 57.5N (SD=15.3) and 8.6mm (SD=1.5), (p>0.05). Failure load, displacement at failure and stiffness of both of the repair groups were half of the intact infraspinatus shoulder group. INTERPRETATION With the developed suture technique, scaffold repair showed similar failure load, displacement at failure and stiffness to the direct repair. This novel suturing pattern and the mechanical robustness of the scaffold at time zero indicates that the proposed model is mechanically viable for future in vivo studies which has a higher potential to translate into clinical uses.
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Islam A, Chapin K, Younesi M, Akkus O. Computer aided biomanufacturing of mechanically robust pure collagen meshes with controlled macroporosity. Biofabrication 2015. [PMID: 26200002 DOI: 10.1088/1758-5090/7/3/035005] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Reconciliation of high strength and high porosity in pure collagen based structures is a major barrier in collagen's use in load-bearing applications. The current study developed a CAD/CAM based electrocompaction method to manufacture highly porous patterned scaffolds using pure collagen. Utilization of computerized scaffold design and fabrication allows the integration of mesh-scaffolds with controlled pore size, shape and spacing. Mechanical properties of fabricated collagen meshes were investigated as a function of number of patterned layers, and with different pore geometries. The tensile stiffness, tensile strength and modulus ranges from 10-50 N cm(-1), 1-6 MPa and 5-40 MPa respectively for all the scaffold groups. These results are within the range of practical usability of different tissue engineering application such as tendon, hernia, stress urinary incontinence or thoracic wall reconstruction. Moreover, 3-fold increase in the layer number resulted in more than 5-fold increases in failure load, toughness and stiffness which suggests that by changing the number of layers and shape of the structure, mechanical properties can be modulated for the aforementioned tissue engineering application. These patterned scaffolds offer a porosity ranging from 0.8 to 1.5 mm in size, a range that is commensurate with pore sizes of repair meshes in the market. The connected macroporosity of the scaffolds facilitated cell-seeding such that cells populated the entire scaffold at the time of seeding. After 3 d of culture, cell nuclei became elongated. These results indicate that the patterned electrochemical deposition method in this study was able to develop mechanically robust, highly porous collagen scaffolds with controlled porosity which not only tries to solve one of the major tissue engineering problems at a fundamental level but also has a significant potential to be used in different tissue engineering applications.
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Jung H, Best M, Akkus O. Microdamage induced calcium efflux from bone matrix activates intracellular calcium signaling in osteoblasts via L-type and T-type voltage-gated calcium channels. Bone 2015; 76:88-96. [PMID: 25819792 DOI: 10.1016/j.bone.2015.03.014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/13/2014] [Revised: 02/25/2015] [Accepted: 03/17/2015] [Indexed: 11/18/2022]
Abstract
Mechanisms by which bone microdamage triggers repair response are not completely understood. It has been shown that calcium efflux ([Ca(2+)]E) occurs from regions of bone undergoing microdamage. Such efflux has also been shown to trigger intracellular calcium signaling ([Ca(2+)]I) in MC3T3-E1 cells local to damaged regions. Voltage-gated calcium channels (VGCCs) are implicated in the entry of [Ca(2+)]E to the cytoplasm. We investigated the involvement of VGCC in the extracellular calcium induced intracellular calcium response (ECIICR). MC3T3-E1 cells were subjected to one dimensional calcium efflux from their basal aspect which results in an increase in [Ca(2+)]I. This increase was concomitant with membrane depolarization and it was significantly reduced in the presence of Bepridil, a non-selective VGCC inhibitor. To identify specific type(s) of VGCC in ECIICR, the cells were treated with selective inhibitors for different types of VGCC. Significant changes in the peak intensity and the number of [Ca(2+)]I oscillations were observed when L-type and T-type specific VGCC inhibitors (Verapamil and NNC55-0396, respectively) were used. So as to confirm the involvement of L- and T-type VGCC in the context of microdamage, cells were seeded on devitalized notched bone specimen, which were loaded to induce microdamage in the presence and absence of Verapamil and NNC55-0396. The results showed significant decrease in [Ca(2+)]I activity of cells in the microdamaged regions of bone when L- and T-type blockers were applied. This study demonstrated that extracellular calcium increase in association with damage depolarizes the cell membrane and the calcium ions enter the cell cytoplasm by L- and T-type VGCCs.
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Younesi M, Islam A, Kishore V, Panit S, Akkus O. Fabrication of compositionally and topographically complex robust tissue forms by 3D-electrochemical compaction of collagen. Biofabrication 2015; 7:035001. [PMID: 26069162 PMCID: PMC4489851 DOI: 10.1088/1758-5090/7/3/035001] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Collagen solutions are phase-transformed to mechanically robust shell structures with curviplanar topographies using electrochemically-induced pH gradients. The process enables rapid layer-by-layer deposition of collagen-rich mixtures over the entire field simultaneously to obtain compositionally diverse multilayered structures. The in-plane tensile strength and modulus of the electrocompacted collagen sheet samples were 5200-fold and 2300-fold greater than those of the uncompacted collagen samples. Out-of-plane compression tests showed a 27-fold increase in compressive stress and a 46-fold increase in compressive modulus compared to uncompacted collagen sheets. Cells proliferated 4.9 times faster, and the cellular area spread was 2.7 times greater on compacted collagen sheets. Electrocompaction also resulted in a 2.9 times greater focal adhesion area than on regular collagen hydrogel. The reported improvements in the cell-matrix interactions with electrocompaction would serve to expedite the population of electrocompacted collagen scaffolds by cells. The capacity of the method to fabricate nonlinear curved topographies with compositional heterogeneous layers is demonstrated by sequential deposition of a collagen-hydroxyapatite layer over a collagen layer. The complex curved topography of the nasal structure is replicated by the electrochemical compaction method. The presented electrochemical compaction process is an enabling modality which holds significant promise for reconstruction of a wide spectrum of topographically complex systems such as joint surfaces, craniofacial defects, ears, nose, and urogenital forms.
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