Vascular grafting strategies in coronary intervention

© 2014 Knight, Gillies and Mequanint. With the growing need for coronary revascularizations globally, several strategies to restore blood flow to the heart have been explored. Bypassing the atherosclerotic coronary arteries with autologous grafts, synthetic prostheses, and tissue-engineered vascular grafts continue to be evaluated in search of a readily available vascular graft with clinically acceptable outcomes. The development of such a vascular graft including tissue engineering approaches both in situ and in vitro is herein reviewed, facilitating a detailed comparison on the role of seeded cells in vascular graft patency

Bone repair and regenerative biomaterials: Towards recapitulating the microenvironment

© 2019 by the authors. Biomaterials and tissue engineering scaffolds play a central role to repair bone defects. Although ceramic derivatives have been historically used to repair bone, hybrid materials have emerged as viable alternatives. The rationale for hybrid bone biomaterials is to recapitulate the native bone composition to which these materials are intended to replace. In addition to the mechanical and dimensional stability, bone repair scaffolds are needed to provide suitable microenvironments for cells. Therefore, scaffolds serve more than a mere structural template suggesting a need for better and interactive biomaterials. In this review article, we aim to provide a summary of the current materials used in bone tissue engineering. Due to the ever-increasing scientific publications on this topic, this review cannot be exhaustive; however, we attempted to provide readers with the latest advance without being redundant. Furthermore, every attempt is made to ensure that seminal works and significant research findings are included, with minimal bias. After a concise review of crystalline calcium phosphates and non-crystalline bioactive glasses, the remaining sections of the manuscript are focused on organic-inorganic hybrid materials

Sol-gel derived tertiary bioactive glass–ceramic nanorods prepared via hydrothermal process and their composites with poly(Vinylpyrrolidone-Co-Vinylsilane)

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Bioactive glass (BG) nanoparticles have wide applications in bone repair due to their bone-bonding and biodegradable nature. In this work, nanometric rod-shaped ternary SiO2-CaO-P2O5 bioactive glass particles were prepared through sol-gel chemistry followed by a base-induced hydrothermal process at 130 ◦C and 170 ◦C for various times up to 36 h. This facile, low-temperature and surfactant-free hydrothermal process has shown to be capable of producing uniform nanorods and nanowires. One-dimensional growth of nanorods and the characteristics of siloxane bridging networks were dependent on the hydrothermal temperature and time. Hardened bioactive composites were prepared from BG nanorods and cryo-milled poly(vinylpyrrolidone-co-triethoxyvinylsilane) in the presence of ammonium phosphate as potential bone graft biomaterials. Covalent crosslinking has been observed between the organic and inorganic components within these composites. The ultimate compressive strength and modulus values increased with increasing co-polymer content, reaching 27 MPa and 500 MPa respectively with 30% co-polymer incorporation. The materials degraded in a controlled non-linear manner when incubated in phosphate-buffered saline from 6 h to 14 days. Fibroblast cell attachment and spreading on the composite were not as good as the positive control surfaces and suggested that they may require protein coating in order to promote favorable cell interactions

Fabrication and In-Situ Cross-linking of Carboxylic Acid-Functionalized Poly(ester amide) Scaffolds for Tissue Engineering

Three-dimensional (3D) scaffolds are important tools for tissue engineering, and should ideally provide both biochemical cues and biomechanical support for cells. Poly(ester amide)s (PEAs) have emerged as promising materials for the preparation of tissue engineering scaffolds and the pendant side chains of residues such as ʟ-lysine and ʟ-aspartic acid can provide sites for the conjugation of biochemical signals. However, it has been challenging to combine scaffold morphological stability with the presentation of reactive groups on PEA scaffolds. We describe here a new approach involving the functionalization of a ʟ-lysine-containing PEA with maleic anhydride to simultaneously introduce cross-linkable alkenes and carboxylic acid conjugation sites. Maleic-acid-functionalized PEA was processed to form 3D scaffolds using a salt leaching method and the scaffolds were cross-linked in situ using a poly(ethylene glycol) dimethacrylate cross-linking agent by thermal free radical curing. Micro-computed tomography analysis indicated that the cross-linked scaffolds had higher polymer volume fraction, lower porosity, and smaller pore size than the non-cross-linked scaffolds, but both scaffolds exhibited high morphological stability and negligible mass loss upon incubation in phosphate buffered saline for 5 days. The Young’s moduli of the cross-linked and non-cross-linked scaffolds were 28 and 9 kPa respectively. Fluorescein-labeled bovine serum albumin was successfully conjugated to the scaffolds using a carbodiimide-based coupling. Finally, it was shown that the scaffolds supported the attachment and proliferation of mouse embryonic mesenchymal multipotent cells, showing their promise as platforms for tissue engineering applications

Type i collagen cleavage is essential for effective fibrotic repair after myocardial infarction

Efficient deposition of type I collagen is fundamental to healing after myocardial infarction. Whether there is also a role for cleavage of type I collagen in infarct healing is unknown. To test this, we undertook coronary artery occlusion in mice with a targeted mutation (Col1a1 r/r) that yields collagenase-resistant type I collagen. Eleven days after infarction, Col1a1 r/r mice had a lower mean arterial pressure and peak left ventricular systolic pressure, reduced ventricular systolic function, and worse diastolic function, compared with wild-type littermates. Infarcted Col1a1 r/r mice also had greater 30-day mortality, larger left ventricular lumens, and thinner infarct walls. Interestingly, the collagen fibril content within infarcts of mutant mice was not increased. However, circular polarization microscopy revealed impaired collagen fibril organization and mechanical testing indicated a predisposition to scar microdisruption. Three-dimensional lattices of collagenase-resistant fibrils underwent cell-mediated contraction, but the fibrils did not organize into birefringent collagen bundles. In addition, time-lapse microscopy revealed that, although cells migrated smoothly on wild-type collagen fibrils, crawling and repositioning on collagenase-resistant collagen was impaired. We conclude that type I collagen cleavage is required for efficient healing of myocardial infarcts and is critical for both dynamic positioning of collagen-producing cells and hierarchical assembly of collagen fibrils. This seemingly paradoxical requirement for collagen cleavage in fibrotic repair should be considered when designing potential strategies to inhibit matrix degradation in cardiac disease. © 2011 American Society for Investigative Pathology

Self-assembling metal coatings from phosphated and silicone-modified polyurethane dispersions

Dissertation (Ph.D.)--Stellenbosch University, 2001.ENGLISH ABSTRACT: Self-emulsifiable and self-assembling nano-particle phosphated and siloxane-modified polyurethane dispersions, for use in metal coatings, were synthesised from a new phosphate monomer, a carboxylate monomer, a polysiloxane macroglycol and a . cycloaliphatic diisocyanate, and characterised. Crosslinked nano-particles of acrylic-modified, self-assembling, phosphated polyurethane dispersions with better water swell resistance were obtained using the phosphated nanoparticles as the 'seed' to polymerise monofunctional and multifunctional acrylic monomers in the dispersed phase. This was done by reacting 2-hydroxyethyl methacrylate end-capped polyurethane with monofunctional and multifunctional acrylate monomers in the dispersed phase. Phase inversion of the polyurethane resin from an organic solvent into dispersion was accompanied by three stages, as studied by viscosity and conductivity measurements. In an attempt to modify existing synthesis procedures of the traditional polyurethane acrylic dispersions for which organic solvents are used, polymerisable acrylic monomers were used as diluents during the urethane-forming reaction. This resulted in overcoming the limitations of the existing process. Particle-size analysis indicated that the above dispersions had smaller particle sizes, narrower distributions and better hydrophobicity than any reported to date. Aqueous vinylterminated phosphated polyurethane dispersions were studied for their viscosity behaviour under shear and showed Newtonian behaviour. The polyurethane dispersions were evaluated for their hydrolytic stability with respect to the location of the ionic groups on the segments. Greater hydrolytic stability was obtained when the ionic groups were on the urethane hard segment. The polyurethane dispersionsresponded well to UV curing, a curing technique that has not received much attention to date. The surface and interface analyses of the self-assembling coatings obtained from the phosphated and siloxane-modified polyurethane dispersions showed increased silicon enrichment at the coating/air interface and phosphorus enrichment at the metal/coating interface. Results of dynamic contact angle studies proved the poor wettability of the coatings, as shown by the increase in contact angle by probe liquids. Dynamic thermogravimetry studies of the phosphate-containing polyurethanes showed a decrease in activation energy with increasing phosphate content. This is a good indication that phosphate-containing polyurethanes could be used as fire retarding coatings that comply with fire limit regulations.AFRIKAANSE OPSOMMING: Self-emulgeerbare en selfsamestellende, nanopartikel, fosfaat- en siloksaanbevattende poliuretaandispersies, vir gebruik as deklae vir metale, is gesintetiseer en gekarakteriseer. Die uitgangstowwe vir die ~ bereiding was 'n splinternuwe fosfaatmonomeer, 'n karboksilaatmonomeer, 'n polisiloksaanglikol en 'n siklo-alifatiese diisosianaat. Deur die polimerisasie van die monofunksionele en multifunksionele akriel-monomere in die dispergeerde fase in te ent met die fosfaat-bevattende nanopartikels, is kruisgebinde nanopartikels van akrielgemodifiseerde, selfsamestellende, fosfaatbevattende poliuretaandispersies met goeie waterswelweerstand berei. Dit is bewerkstellig deur poliuretaan, met reaktiewe hidroksietiel-endgroepe, te reageer met monofunksionele akrilaatmonomere in die gedispergeerde fase. Fase-omkering van die poli-uretaanhars uit die organiese oplosmiddel, tot in dispersie, het in drie stappe plaasgevind. Dit is bepaal deur viskositeit en konduktiwiteit. Bestaande metodes van sintese Vir tradisionele poli-uretaanakrieldispersies, waarvoor organiese oplosmiddels gebruik is, is gewysig om die beperkinge van die bestaande metodes te oorkom. Suskes is behaal met die gebruik van polimeriseerbare akrielmonomere as verdunningsmiddels in die uretaanvormingsreaksie. Partikelgrootte-analises het getoon dat die verkreë dispersies kleiner partikelgroottes, nouer verspreidings en beter hidrofobisiteit gehad het as enige wat tot dusver beskryf is. Die viskositeit van die wateroplosbare, vinielgetermineerde, fosfaatbevattende poliuretanandispersies is onder afskuiwing bepaal en het Newtoniese gedrag getoon. Die hidrolitiese stabiliteit van die poli-uretane, met betrekking tot die posisie van die ioniese groepe in die segmente, is bepaaL ..Die polimere met die ioniese groepe in die harde segment van die poli-uretaan het hoër hidrolitiese stabiliteit vertoon. Kruisbinding (verharding) deur middel van UV, wat tot dusver min aandag geniet het, was baie suksesvol. Analises van die oppervlakte en die tussenvlak van die selfsamestellende deklaag, wat van die fosfaat- en siloksaanbevattende dispersies berei is, het verhoogde siloksaanverryking by die deklaag/lug tussenvlak en verhoogde fosfaatverryking by die metaal/deklaag tussenvlak getoon. Resultate van dinamiese kontakhoekstudies het bewys dat die deklae swak benat is, dws daar was 'n toename in die kontakhoek deur peilvloeistowwe. Termogravimetriese studies het getoon dat daar 'n afname was in die aktiveringsenergie van die fosfaatbevattende poli-uretane met 'n toenemende fosfaatinhoud. Hierdie feit dui daarop dat hierdie poli-uretane moontlik as brandvertragende deklae gebruik kan word

Polyurethane dispersions : synthesis, characterisation and application for primers in coil coating

Thesis (M. Sc.) -- University of Stellenbosch, 1997.One copy microfiche.Full text to be digitised and attached to bibliographic record

Systematic Studies on Surface Erosion of Photocrosslinked Polyanhydride Tablets and Data Correlation with Release Kinetic Models

Photocrosslinkable polyanhydrides that undergo surface erosion are suitable materials for controlled-release drug delivery systems. Investigating the impact of different parameters on their erosion behavior is essential before use in drug delivery systems. Although their synthesis is well-established, parameters that may substantially affect the erosion of thiol-ene polyanhydrides including temperature and pH of the media, the geometry of the polymers, and the media shaking rate (the convective force for the polymer erosion), have not yet been studied. This study explores the effects of different environmental and geometric parameters on mass loss (erosion) profiles of polyanhydrides synthesized by thiol-ene photopolymerization. A comparative study on several release kinetic models fitting is also described for a better understanding of the polymer erosion behavior. The results demonstrated that although the temperature was the only parameter that affected the induction period substantially, the mass-loss rate was influenced by the polymer composition, tablet geometry, temperature, pH, and mass transfer (shaking) rate. With regard to geometrical parameters, polymers with the same surface area to volume ratios showed similar mass loss trends despite their various volumes and surface areas. The mass loss of polyanhydride tablets with more complicated geometries than a simple slab was shown to be non-linear, and the kinetic model study indicated the dominant surface erosion mechanism. The results of this study allow for designing and manufacturing efficient delivery systems with a high-predictable drug release required in precision medicine using surface-erodible polyanhydrides

Films, Gels and Electrospun Fibers from Serum Albumin Globular Protein for Medical Device Coating, Biomolecule Delivery and Regenerative Engineering

Albumin is a natural biomaterial that is abundantly available in blood and body fluids. It is clinically used as a plasma expander, thereby increasing the plasma thiol concentration due to its cysteine residues. Albumin is a regulator of intervascular oncotic pressure, serves as an anti-inflammatory modulator, and it has a buffering role due to its histidine imidazole residues. Because of its unique biological and physical properties, albumin has also emerged as a suitable biomaterial for coating implantable devices, for cell and drug delivery, and as a scaffold for tissue engineering and regenerative medicine. As a biomaterial, albumin can be used as surface-modifying film or processed either as cross-linked protein gels or as electrospun fibers. Herein we have discussed how albumin protein can be utilized in regenerative medicine as a hydrogel and as a fibrous mat for a diverse role in successfully delivering drugs, genes, and cells to targeted tissues and organs. The review of prior studies indicated that albumin is a tunable biomaterial from which different types of scaffolds with mechanical properties adjustable for various biomedical applications can be fabricated. Based on the progress made to date, we concluded that albumin-based device coatings, delivery of drugs, genes, and cells are promising strategies in regenerative and personalized medicine