An alkyne-functionalized elastomer derived from sebacic acid, 1,3propanediol, and alkyne-function... more An alkyne-functionalized elastomer derived from sebacic acid, 1,3propanediol, and alkyne-functionalized serinol is synthesized via melt condensation. A low-power UV lamp triggers the cross-linking rapidly via thiol−yne click chemistry. The cross-linking behavior is studied by photorheology and NMR spectroscopy. The resultant elastomer possesses mechanical properties similar to those of human soft tissues and exhibits in vitro degradability and good cytocompatibility.
A facile solid-phase conversion route is proposed to fabricate a micro-framework of α-MnO2 with a... more A facile solid-phase conversion route is proposed to fabricate a micro-framework of α-MnO2 with a nanofibrous structure and high porosity. The fabrication is achieved by a three-step process using a preformed manganese tartrate with a rectangular framework as the precursor followed by thermal annealing and hydrothermal oxidation to form the final nanofibrous structure. Evolution of the phase and the morphology are characterized by FESEM, XRD, TG–DTA, and TEM measurements. The electrochemically active material α-MnO2 exhibits both attractive stability of the Coulombic efficiency after long-term cyclic charging/discharging and acceptable specific capacitance.
Multiple additive manufacturing techniques have been developed in recent years to produce structu... more Multiple additive manufacturing techniques have been developed in recent years to produce structures with tunable physical, chemical, and mechanical properties and defined architecture. Solution electrospinning, although an older and more established technique, normally cannot achieve the pattern resolution and tunability of these newer manufacturing techniques. In this study, we present solution electrowriting as a method to produce fibrous conduits from various polymers with tunable patterns, dimensions, and scaffold porosity. We demonstrate the importance of solvent selection during solution electrowriting and discuss how solvent polarity and volatility can be exploited to controllably alter the structure of the resulting scaffolds. The technique can be readily implemented with equipment for conventional electrospinning and offers versatility, control, and customization that is uncommon in the solution electrospinning field.
The initial ideas for the research projects in these articles were conceived by Prof. P. A. Heide... more The initial ideas for the research projects in these articles were conceived by Prof. P. A. Heiden, but the synthetic designs and characterizations, and decisions made on how to advance the project to achieve the objectives were those of Xiaochu Ding, Ph.D. Candidate. In chapter 2, the biocompatibility tests on SW-620 cell lines were contributed by Dr. Jagadeesh Janjanam (Dr. Ashutosh Tiwari's group, Department of Chemistry). In chapter 3, the biocompatibility tests on NIH3T3 cell lines were contributed by Mr. Trevor Moser (Dr. Tolou Shokuhfar's group, Department of Mechanical Engineering and Engineering Mechanics). FESEM and TEM characterization was conducted by Mr. Qi Gao (Dr. Raze ShahbazianYassar's group,
Poly(glycerol-sebacate) (PGS) is a biodegradable elastomer known for its mechanical properties an... more Poly(glycerol-sebacate) (PGS) is a biodegradable elastomer known for its mechanical properties and biocompatibility for soft tissue engineering. However, harsh thermal crosslinking conditions are needed to make PGS devices. To facilitate the thermal crosslinking, citric acid is explored as a crosslinker to form poly(glycerol sebacate citrate) (PGSC) elastomers. The effects of varying citrate contents and curing times are investigated on the mechanical properties, elasticity, degradation, and hydrophilicity. To examine the potential presence of unreacted citric acid, material acidity is monitored in relation to the citrate content and curing times. It is discovered that a low citrate content and a short curing time produce PGSC with tunable mechanical characteristics similar to PGS with enhanced elasticity. The materials demonstrate good cytocompatibility with human umbilical vein endothelial cells similar to the PGS control. The research study suggests that PGSC is a potential candi...
Linear polyacrylamide (PAAm) is modified with dopamine or nitrodopamine (PAAm-D and PAAm-ND, resp... more Linear polyacrylamide (PAAm) is modified with dopamine or nitrodopamine (PAAm-D and PAAm-ND, respectively) to evaluate the effect of nitro-group modification on the interfacial binding properties of polymer-bound catechol. Nanocomposite hydrogels are prepared by mixing PAAm-based polymers with Laponite and the viscoelastic properties of these materials are determined using oscillatory rheometry. The incorporation of a small amount of catechol (≈0.1 wt% in swollen hydrogel) drastically increases the shear moduli by 1-2 orders of magnitude over those of the catechol-free control. Additionally, PAAm-ND exhibits higher shear moduli values than PAAm-D across the whole pH range tested (pH 3.0-9.0). Based on the calculated effective crosslinking density, effective functionality, and molecular weight between crosslinks, nitro-group functionalization of dopamine results in a polymer network with increased crosslinking density and crosslinking points with higher functionality. Nitro-functiona...
The concept of self-healing synthetic materials emerged a couple of decades ago and continues to ... more The concept of self-healing synthetic materials emerged a couple of decades ago and continues to attract scientific community. Driven primarily by an opportunity to develop lifelike materials on one hand, and sustainable technologies on the other, several successful approaches to repair mechanically damaged materials have been explored. This review examines chemical and physical processes occurring during self-healing of polymers as well as examines the role of interfaces in rigid nano-objects in multicomponent composites. The complex nature of processes involved in self-healing demands understanding of multi-level molecular and macroscopic events. Two aspects of self-healing are particularly intriguing: physical flow (macro) of matter at or near a wound and chemical re-bonding (molecular)of cleaved bonds. These events usually occur concurrently, and depending upon interplay between kinetics and thermodynamics of the processes involved, these transient relations as well as efficiency are critical in designing self-healing materials. This review examines covalent bonding and supramolecular chemistry in the context of molecular heterogeneities in repair processes. Interfacial regions in nanocomposites also facilitate an opportunity for supramolecular assemblies or covalent bonding which, if designed properly, are capable of self-repairs.
Molecularly imprinted polymer nanoparticles (MIPNPs) are an increasingly important area of resear... more Molecularly imprinted polymer nanoparticles (MIPNPs) are an increasingly important area of research with potential in applications such as biosensors, solid phase extractions and bioassays. Advantages over the traditional molecularly imprinted polymers typically include a higher binding capacity, greater selectivity and affinity for target species, and aqueous compatibility. Recent research efforts have sought to impart MIPNPs with additional capabilities by introducing nanoparticle size-control, stimuli-responsiveness, biocompatibility, and optoelectronic properties. This short review describes the molecular imprinting principle and then discusses recent advances in the field of MIPNPs with particular focus on surface polymerization techniques to imprint both small and macro molecules.
Copper-based nanoparticle wood preservatives typically contain a mixture of nanoparticles. We tes... more Copper-based nanoparticle wood preservatives typically contain a mixture of nanoparticles. We test the effect of nanoparticle size on copper leaching, and if the leachate contains nanoparticles, by treating southern pine sapwood with copper oxide nanoparticles with uniform diameters of 10 and 50 nm. Significant numbers of nanoparticles are found in the leachate from the treated wood, and trends show that size is a major factor. The 50 nm nanoparticles leach slightly less than the control (ammonium copper salt), whereas 10 nm nanoparticles leach more. Effects of polymer stabilizers are also tested and they increase nanoparticle leaching compared to unstabilized nanoparticles.
A robust self-assembly of nanoparticles into fibers and 3D scaffolds is designed and fabricated b... more A robust self-assembly of nanoparticles into fibers and 3D scaffolds is designed and fabricated by functionalizing a RAFT-polymerized amphiphilic triblock copolymer with designer ionic complementary peptides so that the assembled core-shell polymeric nanoparticles are directed by peptide assembly into continuous ''nanoparticle fibers,'' ultimately leading to 3D fiber scaffolds. The assembled nanostructure is confirmed by FESEM and optical microscopy. The assembly is not hindered when a protein (insulin) is incorporated within the nanoparticles as an active ingredient. MTS cytotoxicity tests on SW-620 cell lines show that the peptides, copolymers, and peptide-copolymer conjugates are biocompatible. The methodology of self-assembled nanoparticle fibers and 3D scaffolds is intended to combine the advantages of a flexible hydrogel scaffold with the versatility of controlled release nanoparticles to offer unprecedented ability to incorporate desired drug(s) within a self-assembled scaffold system with individual control over the release of each drug.
A simple, one-step and one-pot method was used to synthesize amphiphilic self-assembling chitosan... more A simple, one-step and one-pot method was used to synthesize amphiphilic self-assembling chitosang-PMMA nanoparticles (∼100 nm diameter by SEM, but ∼150-200 nm in water by DLS), containing ∼25-28 wt.% (∼82-93% capture efficiency) of the fungicide tebuconazole. The matrix composition was selected to be environmentally low impact, while the nanoparticle preparation conditions were designed to ensure the nanoparticles were sufficiently small to be able to penetrate the pit pairs of solid wood. These nanoparticles were delivered into southern pine sapwood blocks at target fungicide retentions of 0.2, 0.4 and 0.8 kg tebuconazole/m 3 wood. SEM analysis of a 19 mm × 19 mm × 455 mm nanoparticletreated wooden stake confirmed penetration throughout the interior of the treated stake. Leaching studies confirmed that biocide introduced into sapwood via nanoparticle carriers leached only about 9% as much fungicide as solution-treated controls, while soil jar tests showed the nanoparticle-treated wood blocks effectively protected the wood from biological decay when tested against G. trabeum, a brown rot fungus.
Heparin-binding growth factors are incorporated in a new shear thinning hydrogel for sustained re... more Heparin-binding growth factors are incorporated in a new shear thinning hydrogel for sustained release with prolonged bioactivity for tissue regeneration.
The aqueous nature of complex coacervates provides a biologically-relevant context for various th... more The aqueous nature of complex coacervates provides a biologically-relevant context for various therapeutic applications. In this sense, biological applications demand a corresponding level of biocompatibility from the polyelectrolytes that participate in complex coacervation. Continued development with naturally-occurring polyelectrolytes such as heparin and chitosan underscore such aims. Herein, we design a synthetic polycation, in which betaine is conjugated to a biodegradable polyester backbone. Betaine is a naturally-occurring methylated amino acid that is ubiquitously present in human plasma. Inspired by its vast range of benefits - including but not limited to anti-inflammation, anti-cancer, anti-bacterial, anti-oxidant, protein stabilization, and cardiovascular health - we aim to impart additional functionality to a polycation for eventual use in a complex coacervate with heparin. We report on its in vitro and in vivo biocompatibility, in vitro and in vivo effect on angiogene...
Autologous veins are the most widely used grafts for bypassing small arteries in coronary and per... more Autologous veins are the most widely used grafts for bypassing small arteries in coronary and peripheral arterial occlusive diseases. However, they have limited availability and cause donor-site morbidity. Here, we report a direct comparison of acellular biodegradable synthetic grafts and autologous veins as interposition grafts of rat carotid arteries, which is a good model for clinically relevant small arteries. Notably, extensive but transient infiltration of circulating monocytes at day 14 in synthetic grafts leads to a quickly-resolved inflammation and arterial-like tissue remodeling. The vein graft exhibits a similar inflammation phase except the prolonged presence of inflammatory monocytes. The walls of the remodeled synthetic graft contain many circumferentially aligned contractile non-proliferative smooth muscle cells (SMCs), collagen and elastin. In contrast, the walls of the vein grafts contain disorganized proliferating SMCs and thicken over time, suggesting the onset of stenosis. At 3 months, both grafts have a similar patency, extracellular matrix composition, and mechanical properties. Furthermore, synthetic grafts exhibit recruitment and re-orientation of newly synthesized collagen fibers upon mechanical loading. To our knowledge, this is the first demonstration of a biodegradable synthetic vascular graft with a performance similar to an autologous vein in small artery grafting.
An alkyne-functionalized elastomer derived from sebacic acid, 1,3propanediol, and alkyne-function... more An alkyne-functionalized elastomer derived from sebacic acid, 1,3propanediol, and alkyne-functionalized serinol is synthesized via melt condensation. A low-power UV lamp triggers the cross-linking rapidly via thiol−yne click chemistry. The cross-linking behavior is studied by photorheology and NMR spectroscopy. The resultant elastomer possesses mechanical properties similar to those of human soft tissues and exhibits in vitro degradability and good cytocompatibility.
A facile solid-phase conversion route is proposed to fabricate a micro-framework of α-MnO2 with a... more A facile solid-phase conversion route is proposed to fabricate a micro-framework of α-MnO2 with a nanofibrous structure and high porosity. The fabrication is achieved by a three-step process using a preformed manganese tartrate with a rectangular framework as the precursor followed by thermal annealing and hydrothermal oxidation to form the final nanofibrous structure. Evolution of the phase and the morphology are characterized by FESEM, XRD, TG–DTA, and TEM measurements. The electrochemically active material α-MnO2 exhibits both attractive stability of the Coulombic efficiency after long-term cyclic charging/discharging and acceptable specific capacitance.
Multiple additive manufacturing techniques have been developed in recent years to produce structu... more Multiple additive manufacturing techniques have been developed in recent years to produce structures with tunable physical, chemical, and mechanical properties and defined architecture. Solution electrospinning, although an older and more established technique, normally cannot achieve the pattern resolution and tunability of these newer manufacturing techniques. In this study, we present solution electrowriting as a method to produce fibrous conduits from various polymers with tunable patterns, dimensions, and scaffold porosity. We demonstrate the importance of solvent selection during solution electrowriting and discuss how solvent polarity and volatility can be exploited to controllably alter the structure of the resulting scaffolds. The technique can be readily implemented with equipment for conventional electrospinning and offers versatility, control, and customization that is uncommon in the solution electrospinning field.
The initial ideas for the research projects in these articles were conceived by Prof. P. A. Heide... more The initial ideas for the research projects in these articles were conceived by Prof. P. A. Heiden, but the synthetic designs and characterizations, and decisions made on how to advance the project to achieve the objectives were those of Xiaochu Ding, Ph.D. Candidate. In chapter 2, the biocompatibility tests on SW-620 cell lines were contributed by Dr. Jagadeesh Janjanam (Dr. Ashutosh Tiwari's group, Department of Chemistry). In chapter 3, the biocompatibility tests on NIH3T3 cell lines were contributed by Mr. Trevor Moser (Dr. Tolou Shokuhfar's group, Department of Mechanical Engineering and Engineering Mechanics). FESEM and TEM characterization was conducted by Mr. Qi Gao (Dr. Raze ShahbazianYassar's group,
Poly(glycerol-sebacate) (PGS) is a biodegradable elastomer known for its mechanical properties an... more Poly(glycerol-sebacate) (PGS) is a biodegradable elastomer known for its mechanical properties and biocompatibility for soft tissue engineering. However, harsh thermal crosslinking conditions are needed to make PGS devices. To facilitate the thermal crosslinking, citric acid is explored as a crosslinker to form poly(glycerol sebacate citrate) (PGSC) elastomers. The effects of varying citrate contents and curing times are investigated on the mechanical properties, elasticity, degradation, and hydrophilicity. To examine the potential presence of unreacted citric acid, material acidity is monitored in relation to the citrate content and curing times. It is discovered that a low citrate content and a short curing time produce PGSC with tunable mechanical characteristics similar to PGS with enhanced elasticity. The materials demonstrate good cytocompatibility with human umbilical vein endothelial cells similar to the PGS control. The research study suggests that PGSC is a potential candi...
Linear polyacrylamide (PAAm) is modified with dopamine or nitrodopamine (PAAm-D and PAAm-ND, resp... more Linear polyacrylamide (PAAm) is modified with dopamine or nitrodopamine (PAAm-D and PAAm-ND, respectively) to evaluate the effect of nitro-group modification on the interfacial binding properties of polymer-bound catechol. Nanocomposite hydrogels are prepared by mixing PAAm-based polymers with Laponite and the viscoelastic properties of these materials are determined using oscillatory rheometry. The incorporation of a small amount of catechol (≈0.1 wt% in swollen hydrogel) drastically increases the shear moduli by 1-2 orders of magnitude over those of the catechol-free control. Additionally, PAAm-ND exhibits higher shear moduli values than PAAm-D across the whole pH range tested (pH 3.0-9.0). Based on the calculated effective crosslinking density, effective functionality, and molecular weight between crosslinks, nitro-group functionalization of dopamine results in a polymer network with increased crosslinking density and crosslinking points with higher functionality. Nitro-functiona...
The concept of self-healing synthetic materials emerged a couple of decades ago and continues to ... more The concept of self-healing synthetic materials emerged a couple of decades ago and continues to attract scientific community. Driven primarily by an opportunity to develop lifelike materials on one hand, and sustainable technologies on the other, several successful approaches to repair mechanically damaged materials have been explored. This review examines chemical and physical processes occurring during self-healing of polymers as well as examines the role of interfaces in rigid nano-objects in multicomponent composites. The complex nature of processes involved in self-healing demands understanding of multi-level molecular and macroscopic events. Two aspects of self-healing are particularly intriguing: physical flow (macro) of matter at or near a wound and chemical re-bonding (molecular)of cleaved bonds. These events usually occur concurrently, and depending upon interplay between kinetics and thermodynamics of the processes involved, these transient relations as well as efficiency are critical in designing self-healing materials. This review examines covalent bonding and supramolecular chemistry in the context of molecular heterogeneities in repair processes. Interfacial regions in nanocomposites also facilitate an opportunity for supramolecular assemblies or covalent bonding which, if designed properly, are capable of self-repairs.
Molecularly imprinted polymer nanoparticles (MIPNPs) are an increasingly important area of resear... more Molecularly imprinted polymer nanoparticles (MIPNPs) are an increasingly important area of research with potential in applications such as biosensors, solid phase extractions and bioassays. Advantages over the traditional molecularly imprinted polymers typically include a higher binding capacity, greater selectivity and affinity for target species, and aqueous compatibility. Recent research efforts have sought to impart MIPNPs with additional capabilities by introducing nanoparticle size-control, stimuli-responsiveness, biocompatibility, and optoelectronic properties. This short review describes the molecular imprinting principle and then discusses recent advances in the field of MIPNPs with particular focus on surface polymerization techniques to imprint both small and macro molecules.
Copper-based nanoparticle wood preservatives typically contain a mixture of nanoparticles. We tes... more Copper-based nanoparticle wood preservatives typically contain a mixture of nanoparticles. We test the effect of nanoparticle size on copper leaching, and if the leachate contains nanoparticles, by treating southern pine sapwood with copper oxide nanoparticles with uniform diameters of 10 and 50 nm. Significant numbers of nanoparticles are found in the leachate from the treated wood, and trends show that size is a major factor. The 50 nm nanoparticles leach slightly less than the control (ammonium copper salt), whereas 10 nm nanoparticles leach more. Effects of polymer stabilizers are also tested and they increase nanoparticle leaching compared to unstabilized nanoparticles.
A robust self-assembly of nanoparticles into fibers and 3D scaffolds is designed and fabricated b... more A robust self-assembly of nanoparticles into fibers and 3D scaffolds is designed and fabricated by functionalizing a RAFT-polymerized amphiphilic triblock copolymer with designer ionic complementary peptides so that the assembled core-shell polymeric nanoparticles are directed by peptide assembly into continuous ''nanoparticle fibers,'' ultimately leading to 3D fiber scaffolds. The assembled nanostructure is confirmed by FESEM and optical microscopy. The assembly is not hindered when a protein (insulin) is incorporated within the nanoparticles as an active ingredient. MTS cytotoxicity tests on SW-620 cell lines show that the peptides, copolymers, and peptide-copolymer conjugates are biocompatible. The methodology of self-assembled nanoparticle fibers and 3D scaffolds is intended to combine the advantages of a flexible hydrogel scaffold with the versatility of controlled release nanoparticles to offer unprecedented ability to incorporate desired drug(s) within a self-assembled scaffold system with individual control over the release of each drug.
A simple, one-step and one-pot method was used to synthesize amphiphilic self-assembling chitosan... more A simple, one-step and one-pot method was used to synthesize amphiphilic self-assembling chitosang-PMMA nanoparticles (∼100 nm diameter by SEM, but ∼150-200 nm in water by DLS), containing ∼25-28 wt.% (∼82-93% capture efficiency) of the fungicide tebuconazole. The matrix composition was selected to be environmentally low impact, while the nanoparticle preparation conditions were designed to ensure the nanoparticles were sufficiently small to be able to penetrate the pit pairs of solid wood. These nanoparticles were delivered into southern pine sapwood blocks at target fungicide retentions of 0.2, 0.4 and 0.8 kg tebuconazole/m 3 wood. SEM analysis of a 19 mm × 19 mm × 455 mm nanoparticletreated wooden stake confirmed penetration throughout the interior of the treated stake. Leaching studies confirmed that biocide introduced into sapwood via nanoparticle carriers leached only about 9% as much fungicide as solution-treated controls, while soil jar tests showed the nanoparticle-treated wood blocks effectively protected the wood from biological decay when tested against G. trabeum, a brown rot fungus.
Heparin-binding growth factors are incorporated in a new shear thinning hydrogel for sustained re... more Heparin-binding growth factors are incorporated in a new shear thinning hydrogel for sustained release with prolonged bioactivity for tissue regeneration.
The aqueous nature of complex coacervates provides a biologically-relevant context for various th... more The aqueous nature of complex coacervates provides a biologically-relevant context for various therapeutic applications. In this sense, biological applications demand a corresponding level of biocompatibility from the polyelectrolytes that participate in complex coacervation. Continued development with naturally-occurring polyelectrolytes such as heparin and chitosan underscore such aims. Herein, we design a synthetic polycation, in which betaine is conjugated to a biodegradable polyester backbone. Betaine is a naturally-occurring methylated amino acid that is ubiquitously present in human plasma. Inspired by its vast range of benefits - including but not limited to anti-inflammation, anti-cancer, anti-bacterial, anti-oxidant, protein stabilization, and cardiovascular health - we aim to impart additional functionality to a polycation for eventual use in a complex coacervate with heparin. We report on its in vitro and in vivo biocompatibility, in vitro and in vivo effect on angiogene...
Autologous veins are the most widely used grafts for bypassing small arteries in coronary and per... more Autologous veins are the most widely used grafts for bypassing small arteries in coronary and peripheral arterial occlusive diseases. However, they have limited availability and cause donor-site morbidity. Here, we report a direct comparison of acellular biodegradable synthetic grafts and autologous veins as interposition grafts of rat carotid arteries, which is a good model for clinically relevant small arteries. Notably, extensive but transient infiltration of circulating monocytes at day 14 in synthetic grafts leads to a quickly-resolved inflammation and arterial-like tissue remodeling. The vein graft exhibits a similar inflammation phase except the prolonged presence of inflammatory monocytes. The walls of the remodeled synthetic graft contain many circumferentially aligned contractile non-proliferative smooth muscle cells (SMCs), collagen and elastin. In contrast, the walls of the vein grafts contain disorganized proliferating SMCs and thicken over time, suggesting the onset of stenosis. At 3 months, both grafts have a similar patency, extracellular matrix composition, and mechanical properties. Furthermore, synthetic grafts exhibit recruitment and re-orientation of newly synthesized collagen fibers upon mechanical loading. To our knowledge, this is the first demonstration of a biodegradable synthetic vascular graft with a performance similar to an autologous vein in small artery grafting.
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