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Wright J, Nguyen A, D’Souza N, Forbess JM, Nugent A, Reddy SRV, Jaquiss R, Welch TR. Bioresorbable Stent to Manage Congenital Heart Defects in Children. MATERIALIA 2021; 16:101078. [PMID: 34109305 PMCID: PMC8184019 DOI: 10.1016/j.mtla.2021.101078] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Intravascular stents for pediatric patients that degrade without inhibiting vessel growth remain a clinical challenge. Here, poly(L-lactide) fibers (DH-BDS) at two thicknesses, 250 μm and 300 μm, were assembled into large, pediatric-sized stents (Ø10 - Ø20 mm). Fibers were characterized mechanically and thermally, then stent mechanical properties were compared to metal controls, while mass loss and degradation kinetics modeling estimated total stent degradation time. Thicker fibers displayed lower stiffness (1969 ± 44 vs 2126 ± 37 MPa) and yield stress (117 ± 12 vs 137 ± 5 MPa) than thinner counterparts, but exhibited similar fail strength (478 ± 28 vs 476 ± 16 MPa) at higher strains (47 ± 2 vs 44 ± 2%). Stents all exhibited crystallinity between 51.3 - 54.4% and fiber glass transition temperatures of 88.6 ± 0.5 °C and 84.6 ± 0.5 °C were well above physiological ranges. Radial strength (0.31 ± 0.01 - 0.34 ± 0.02 N/mm) in thinner stents was similar to metal stents (0.24 - 0.41 N/mm) up to Ø14 mm with no foreshortening and thicker coils granted comparable radial strength (0.32 ± 0.02 - 0.34 ± 0.02 N/mm) in stents larger than Ø14 mm. Both 10 mm (1.17 ± 0.02 % and 0.86 ± 0.1 %) and 12 mm (1.1 ± 0.03% and 0.89 ± 0.1%) stents exhibited minimal weight loss over one year. Degradation kinetics models predicted full stent degradation within 2.8 - 4.5 years depending on thickness. DH-BDS exhibiting hoop strength similar to metal stents and demonstrating minimal degradation and strength loss over the first year before completely disappearing within 3 to 4.5 years show promise as a pediatric interventional alternative to current strategies.
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Affiliation(s)
- Jamie Wright
- Department of Cardiovascular Thoracic Surgery, University of Texas at Southwestern Medical Center of Dallas, 5323 Harry Hines Blvd, Dallas, TX 75390-8879, USA
| | - Annie Nguyen
- Department of Cardiovascular Thoracic Surgery, University of Texas at Southwestern Medical Center of Dallas, 5323 Harry Hines Blvd, Dallas, TX 75390-8879, USA
| | - Nandika D’Souza
- Department of Material Science, University of North Texas, 1155 Union Circle #310440, Denton, TX 76203-5017
| | - Joseph M. Forbess
- Department of Surgery, University of Maryland School of Medicine, 655 W. Baltimore Street, Baltimore MD 21201
| | - Alan Nugent
- Department of Pediatrics, Northwestern University, Ann & Robert H. Lurie Children’s Hospital of Chicago Box 21, 225 E Chicago Avenue, Chicago IL 60611, USA
| | - Surendranath R. Veeram Reddy
- Department of Pediatrics, University of Texas at Southwestern Medical Center of DallasAc, 5323 Harry Hines Blvd, Dallas, TX 75390-9063, USA
| | - Robert Jaquiss
- Department of Cardiovascular Thoracic Surgery, University of Texas at Southwestern Medical Center of Dallas, 5323 Harry Hines Blvd, Dallas, TX 75390-8879, USA
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Wei H, Yan S, Menary G. Modelling Stretch Blow Moulding of Poly (l-lactic acid) for the Manufacture of Bioresorbable Vascular Scaffold. Polymers (Basel) 2021; 13:polym13060967. [PMID: 33809921 PMCID: PMC8004264 DOI: 10.3390/polym13060967] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2021] [Revised: 03/09/2021] [Accepted: 03/16/2021] [Indexed: 11/25/2022] Open
Abstract
Stretch blow moulding (SBM) has been employed to manufacture bioresorbable vascular scaffold (BVS) from poly (l-lactic acid) (PLLA), whilst an experience-based method is used to develop the suitable processing conditions by trial-and-error. FEA modelling can be used to predict the forming process by the scientific understanding on the mechanical behaviour of PLLA materials above the glass transition temperature (Tg). The applicability of a constitutive model, the ‘glass-rubber’ (GR) model with material parameters from biaxial stretch was examined on PLLA sheets replicating the biaxial strain history of PLLA tubes during stretch blow moulding. The different stress–strain relationship of tubes and sheets under equivalent deformation suggested the need of re-calibration of the GR model for tubes. A FEA model was developed for PLLA tubes under different operation conditions, incorporating a virtual cap and rod to capture the suppression of axial stretch. The reliability of the FEA modelling on tube blowing was validated by comparing the shape evolution, strain history and stress–strain relationship from modelling to the results from the free stretch blow test.
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Affiliation(s)
- Huidong Wei
- College of Health and Life Sciences, Aston University, Birmingham B4 7ET, UK;
| | - Shiyong Yan
- School of Mechanical and Aerospace Engineering, Queen’s University Belfast, Belfast BT9 5AH, UK;
| | - Gary Menary
- School of Mechanical and Aerospace Engineering, Queen’s University Belfast, Belfast BT9 5AH, UK;
- Correspondence:
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Ghosh S, Glöckler E, Wölper C, Tjaberings A, Gröschel AH, Schulz S. Active Ga-catalysts for the ring opening homo- and copolymerization of cyclic esters, and copolymerization of epoxide and anhydrides. Dalton Trans 2020; 49:13475-13486. [PMID: 32966460 DOI: 10.1039/d0dt02831b] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
A series of gallium complexes L12Ga4Me8 (1), L22Ga4Me8 (2), and L32Ga4Me8 (3) was synthesized by reaction of GaMe3 with Schiff base ligands L1-3H2 (L1H2 = 2,4-di-tert-butyl-6-{[(3-hydroxypropyl)imino]methyl}phenol; L2H2 = 2,4-dichloro-6-{[(3-hydroxypropyl)imino]methyl}phenol; L3H2 = 4-tert-butyl-2-{[(3-hydroxypropyl)imino]methyl}phenol) and characterized by 1H, 13C NMR, IR spectroscopy, elemental analysis and single crystal X-ray analysis (1, 2), proving their tetranuclear structure in the solid state. Complexes 1-3 showed good catalytic activity in the ring opening homopolymerization (ROP) and ring opening copolymerization (ROcoP) of lactide (LA) and ε-caprolactone (ε-CL) in the presence of benzyl alcohol (BnOH) in toluene at 100 °C, yielding polymers with the expected average molecular weights (Mn) and narrow molecular weight distributions (MWD), as well as a high isoselectivity for the ROP of rac-lactide (rac-LA), yielding isotactic-enriched PLAs with Pm values up to 0.78. Kinetic studies with complex 1 proved the first order dependence on monomer concentration, while mechanistic studies confirmed the coordination insertion mechanistic (CIM) pathway. Sequential addition of monomers gave well defined diblock copolymers of PCL-b-PLLA and PLLA-b-PCL, proving the living character of the polymerization reactions. The catalysts also showed perfect selectivity for the copolymerization of cyclohexene oxide (CHO) with both succinic anhydride (SA) and maleic anhydride (MA) in the presence of BnOH and produced >99% alternating block copolymers.
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Affiliation(s)
- Swarup Ghosh
- Faculty of Chemistry, University of Duisburg-Essen and Center for Nanointegration Duisburg-Essen (CENIDE), Universitätsstr. 7, S07 S03 C30, D-45141 Essen, Germany.
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Influence of Annealing and Biaxial Expansion on the Properties of Poly(l-Lactic Acid) Medical Tubing. Polymers (Basel) 2019; 11:polym11071172. [PMID: 31373323 PMCID: PMC6680782 DOI: 10.3390/polym11071172] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Revised: 07/04/2019] [Accepted: 07/05/2019] [Indexed: 01/30/2023] Open
Abstract
Poly-l-lactic acid (PLLA) is one of the most common bioabsorbable materials in the medical device field. However, its use in load-bearing applications is limited due to its inferior mechanical properties when compared to many of the competing metal-based permanent and bioabsorbable materials. The objective of this study was to directly compare the influence of both annealing and biaxial expansion processes to improve the material properties of PLLA. Results showed that both annealing and biaxial expansion led to an overall increase in crystallinity and that the crystallites formed during both processes were in the α’ and α forms. 2D-WAXS patterns showed that the preferred orientation of crystallites formed during annealing was parallel to the circumferential direction. While biaxial expansion resulted in orientation in both axial and circumferential directions, with relatively equal sized crystals in both directions, Da (112 Å) and Dc (97 Å). The expansion process had the most profound effect on mechanical performance, with a 65% increase in Young’s modulus, a 45% increase in maximum tensile stress and an 18-fold increase in strain at maximum load. These results indicate that biaxially expanding PLLA at a temperature above Tcc is possible, due to the high strain rates associated with stretch blow moulding.
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Dillon B, Doran P, Fuenmayor E, Healy AV, Gately NM, Major I, Lyons JG. The Influence of Low Shear Microbore Extrusion on the Properties of High Molecular Weight Poly(l-Lactic Acid) for Medical Tubing Applications. Polymers (Basel) 2019; 11:polym11040710. [PMID: 31003549 PMCID: PMC6523984 DOI: 10.3390/polym11040710] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2019] [Revised: 04/08/2019] [Accepted: 04/10/2019] [Indexed: 11/21/2022] Open
Abstract
Biodegradable polymers play a crucial role in the medical device field, with a broad range of applications such as suturing, drug delivery, tissue engineering, scaffolding, orthopaedics, and fixation devices. Poly-l-lactic acid (PLLA) is one of the most commonly used and investigated biodegradable polymers. The objective of this study was to determine the influence low shear microbore extrusion exerts on the properties of high molecular weight PLLA for medical tubing applications. Results showed that even at low shear rates there was a considerable reduction in molecular weight (Mn = 7–18%) during processing, with a further loss (Mn 11%) associated with resin drying. An increase in melt residence time from ~4 mins to ~6 mins, translated into a 12% greater reduction in molecular weight. The degradation mechanism was determined to be thermal and resulted in a ~22-fold increase in residual monomer. The differences in molecular weight between both batches had no effect on the materials thermal or morphological properties. However, it did affect its mechanical properties, with a significant impact on tensile strength and modulus. Interestingly there was no effect on the elongational proprieties of the tubing. There was also an observed temperature-dependence of mechanical properties below the glass transition temperature.
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Affiliation(s)
- Brian Dillon
- Materials Research Institute, Athlone Institute of Technology, Dublin Road, Bunnavally, Athlone and Co. Westmeath, Ireland.
| | - Patrick Doran
- Materials Research Institute, Athlone Institute of Technology, Dublin Road, Bunnavally, Athlone and Co. Westmeath, Ireland.
| | - Evert Fuenmayor
- Materials Research Institute, Athlone Institute of Technology, Dublin Road, Bunnavally, Athlone and Co. Westmeath, Ireland.
| | - Andrew V Healy
- Materials Research Institute, Athlone Institute of Technology, Dublin Road, Bunnavally, Athlone and Co. Westmeath, Ireland.
| | - Noel M Gately
- Materials Research Institute, Athlone Institute of Technology, Dublin Road, Bunnavally, Athlone and Co. Westmeath, Ireland.
| | - Ian Major
- Materials Research Institute, Athlone Institute of Technology, Dublin Road, Bunnavally, Athlone and Co. Westmeath, Ireland.
| | - John G Lyons
- Faculty of Engineering and Informatics, Athlone Institute of Technology, Dublin Road, Bunnavally, Athlone, Co. Westmeath, Ireland.
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Orhan B, Tschan MJL, Wirotius AL, Dove AP, Coulembier O, Taton D. Isoselective Ring-Opening Polymerization of rac-Lactide from Chiral Takemoto's Organocatalysts: Elucidation of Stereocontrol. ACS Macro Lett 2018; 7:1413-1419. [PMID: 35651230 DOI: 10.1021/acsmacrolett.8b00852] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Despite significant advances in organocatalysis, stereoselective polymerization reactions utilizing chiral organocatalysts have received very little attention, and much about the underlying mechanisms remains unknown. Here, we report that both commercially available (R,R)- and (S,S)-enantiomers of chiral thiourea-amine Takemoto's organocatalysts promote efficient control and high isoselectivity at room temperature of the ring-opening polymerization (ROP) of racemic lactide by kinetic resolution, yielding highly isotactic, semicrystalline and metal-free polylactide (PLA). Kinetic investigations and combined analyses of the resulting PLAs have allowed the stereocontrol mechanism, which eventually involves both enantiomorphic site control and chain-end control, to be determined. Moreover, epimerization of rac-LA to meso-LA is identified as being responsible for the introduction of some stereoerrors during the ROP process.
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Affiliation(s)
- Beste Orhan
- Laboratoire de Chimie des Polymères Organiques, Université de Bordeaux IPB-ENSCPB, Pessac F-33607 Cedex, France
- Center of Innovation and Research in Materials and Polymers (CIRMAP), Laboratory of Polymeric and Composite Materials, University of Mons, B-7000 Mons, Belgium
| | - Mathieu J.-L. Tschan
- School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
| | - Anne-Laure Wirotius
- Laboratoire de Chimie des Polymères Organiques, Université de Bordeaux IPB-ENSCPB, Pessac F-33607 Cedex, France
| | - Andrew P. Dove
- School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
| | - Olivier Coulembier
- Center of Innovation and Research in Materials and Polymers (CIRMAP), Laboratory of Polymeric and Composite Materials, University of Mons, B-7000 Mons, Belgium
| | - Daniel Taton
- Laboratoire de Chimie des Polymères Organiques, Université de Bordeaux IPB-ENSCPB, Pessac F-33607 Cedex, France
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