Page 1. PART III Biomaterials 117 Page 2. 8 Biodegradable Polyphosphazene Scaffolds for Tissue En... more Page 1. PART III Biomaterials 117 Page 2. 8 Biodegradable Polyphosphazene Scaffolds for Tissue Engineering SYAM P. NUKAVARAPU and SANGAMESH G. KUMBAR Department of Orthopaedic Surgery, University of Connecticut ...
Synthetic biodegradable polymers serve as temporary substrates that accommodate cell infiltration... more Synthetic biodegradable polymers serve as temporary substrates that accommodate cell infiltration and tissue in-growth in regenerative medicine. To allow tissue in-growth and nutrient transport, traditional three-dimensional (3D) scaffolds must be prefabricated with an interconnected porous structure. Here we demonstrated for the first time a unique polymer erosion process through which polymer matrices evolve from a solid coherent film to an assemblage of microspheres with an interconnected 3D porous structure. This polymer system was developed on the highly versatile platform of polyphosphazene-polyester blends. Co-substituting a polyphosphazene backbone with both hydrophilic glycylglycine dipeptide and hydrophobic 4-phenylphenoxy group generated a polymer with strong hydrogen bonding capacity. Rapid hydrolysis of the polyester component permitted the formation of 3D void space filled with self-assembled polyphosphazene spheres. Characterization of such self-assembled porous structures revealed macropores (10-100 μm) between spheres as well as micro- and nanopores on the sphere surface. A similar degradation pattern was confirmed in vivo using a rat subcutaneous implantation model. 12 weeks of implantation resulted in an interconnected porous structure with 82-87% porosity. Cell infiltration and collagen tissue in-growth between microspheres observed by histology confirmed the formation of an in situ 3D interconnected porous structure. It was determined that the in situ porous structure resulted from unique hydrogen bonding in the blend promoting a three-stage degradation mechanism. The robust tissue in-growth of this dynamic pore forming scaffold attests to the utility of this system as a new strategy in regenerative medicine for developing solid matrices that balance degradation with tissue formation.
Amino end-terminated poly(l-lactic acid), poly(trimethylene carbonate), and polycaprolactone were... more Amino end-terminated poly(l-lactic acid), poly(trimethylene carbonate), and polycaprolactone were synthesized via ring-opening polymerization techniques. The amino terminus was used to form a covalent link to poly(dichlorophosphazene), itself synthesized using a living cationic polymerization. The chlorine atoms in the polyphosphazene blocks were subsequently replaced by trifluoroethoxy groups. This is the first reported synthesis of block copolymers of polyphosphazenes linked to polyesters or polycarbonates. The molecular structure of each copolymer was established using multinuclear NMR techniques. Molecular weight analysis was used to provide confirmatory evidence that the two polymers chains were covalently linked. Thermal analysis results showed evidence that in the solid state the two blocks were phase-separated because the parent thermal transitions were detectable for each copolymer.
Electrospun polycaprolactone nanofiber matrices surface functionalized with poly[(ethyl alanato),... more Electrospun polycaprolactone nanofiber matrices surface functionalized with poly[(ethyl alanato), (p-methyl phenoxy),] phosphazene were fabricated for the purpose of soft skeletal tissue regeneration. This preliminary study reports the effect of fiber diameter and polyphosphazene surface functionalization on significant scaffold properties such as morphology, surface hydrophilicity, porosity, tensile properties, human mesenchymal stem cell adhesion and proliferation. Six fiber matrices comprised of average fiber diameters in the range of 400-500, 900-1000, 1400-1500, 1900-2000, 2900-3000 and 3900-4000 nm were considered for primary evaluation. After achieving the greatest proliferation while maintaining moderate tensile modulus, matrices in the diameter range of 2900-3000 nm were selected to examine the effect of coating with 1%, 2% and 3% (weight/volume) polyphosphazene solutions. Polyphosphazene functionalization resulted in rougher surfaces that correlated with coating solution concentration. Analytical techniques such as energy dispersive X-ray analysis, Fourier transform infrared spectroscopy, elemental analysis, differential scanning calorimetry, water contact angle goniometry and confocal microscopy confirmed the presence of polyphosphazene and its distribution on the functionalized fiber matrices. Functionalization achieved through 2% polymer solutions did not affect average pore diameter, tensile modulus, suture retention strength or cell proliferation compared to PCL controls. Surface polyphosphazene functionalization significantly improved the matrix hydrophilicity evidenced through decreased water contact angle of PCL matrices from 130 degrees to 97 degrees. Further, enhanced total protein synthesis by cells during in vitro culture was seen on 2% PPHOS functionalized matrices over controls. Improving PCL matrix hydrophilicity via proposed surface functionalization may be an efficient method to improve cell-PCL matrix interactions.
Journal of Biomaterials Science-polymer Edition, 2011
Self-setting hydroxyapatite-biodegradable injectable composites are excellent candidates for appl... more Self-setting hydroxyapatite-biodegradable injectable composites are excellent candidates for applications in orthopaedics. We have previously demonstrated the feasibility of development of self-setting calcium-deficient nanocrystalline hydroxyapatite-polymer composites using different calcium phosphate precursors and biodegradable polyphosphazenes. This study aimed to evaluate these novel injectable composites as suitable materials for orthopaedic applications through evaluating their biomechanical properties, osteoblast cellular attachment and gene expression over time. Our studies demonstrated that the morphology of the composite groups (PNEA-CDHA, PNEA-CDSHA, PNEA(50)mPh(50)-CDHA, PNEA(50)mPh(50)-CDSHA, PNEA(50)PhPh(50)-CDHA, and PNEA(50)PhPh(50)-CDSHA) formed was similar and found to have micro- and nanoporous structures resembling trabecular bone. The osteoblast phenotypic marker of bone, alkaline phosphatase, was expressed by the cells on the surface of the composites throughout the study and was comparable to tissue-culture polystyrene (control). Furthermore, the cells seeded on the composites expressed the characteristic osteoblastic genes, such as type-I collagen, alkaline phosphatase, osteocalcin, osteopontin and bone sialoprotein, indicating osteoblast differentiation, maturation and mineralization. Within our injectable composite groups, significant gene expression levels were displayed (P < 0.05). These novel injectable biodegradable polyphosphazenes-calcium-deficient hydroxyapatites materials are promising candidates for orthopaedic applications.
IEEE Engineering in Medicine and Biology Magazine, Sep 1, 2003
... AMA AMBROSIO, JS SAHOTA, C. RUNGE, SM KURTZ, S. LAKSHMI, HR ALLCOCK, AND CT LAURENCIN ... mat... more ... AMA AMBROSIO, JS SAHOTA, C. RUNGE, SM KURTZ, S. LAKSHMI, HR ALLCOCK, AND CT LAURENCIN ... matrices at a seeding density of 50,000 cells/well and the cells were grown in alpha modification of Eagles minimal essential media (ICN, Irvine, Virginia) supplemented ...
Encyclopedia of Polymer Science and Technology, 2019
Polyphosphazenes are a unique class of inorganic-organic hybrid polymers with a backbone composed... more Polyphosphazenes are a unique class of inorganic-organic hybrid polymers with a backbone composed of alternating phosphorus and nitrogen atoms. The ease with which the precursor prepolymer poly(dichlorophosphazene) can be modified has resulted in a versatile polymer system. The labile nature of the P−Cl bonds has allowed the substitution of chlorine atoms with groups like alkoxy‐, aryloxy, alkyl ether, fluoroalkoxy, amino acid/peptide esters, drug molecules, transition metal groups, and many more. Careful selection of the side groups offers efficient control of material properties such as bioactivity, crystallinity, solubility, and surface characteristics. Hence, these properties have led to the use of this exceptional class of polymers in a broad range of applications such as biomaterials for regenerative engineering and drug delivery, elastomers, solid membranes for gas/liquid separation, optical materials, flame retardants, and electrolytes for energy storage cells. This article gives an overview of the synthetic routes of polyphosphazene polymers and their composition–structure–properties relationships and highlights their applications in various fields.
In an effort to understand the biological capability of polyphosphazene-based polymers, three-dim... more In an effort to understand the biological capability of polyphosphazene-based polymers, three-dimensional biomimetic bone scaffolds were fabricated using the blends of poly[(glycine ethylglycinato)75(phenylphenoxy)25]phosphazene (PNGEGPhPh) and poly(lactic-co-glycolic acid) (PLGA), and an in vivo evaluation was performed in a rabbit critical-sized bone defect model. The matrices constructed from PNGEGPhPh-PLGA blends were surgically implanted into 15 mm critical-sized radial defects of the rabbits as structural templates for bone tissue regeneration. PLGA, which is the most commonly used synthetic bone graft substitute, was used as a control in this study. Radiological and histological analyses demonstrated that PNGEGPhPh-PLGA blends exhibited favorable in vivo biocompatibility and osteoconductivity, as the newly designed matrices allowed new bone formation to occur without adverse immunoreactions. The X-ray images of the blends showed higher levels of radiodensity than that of the pristine PLGA, indicating higher rates of new bone formation and regeneration. Micro-computed tomography quantification revealed that new bone volume fractions were significantly higher for the PNGEGPhPh-PLGA blends than for the PLGA controls after 4 weeks. The new bone volume increased linearly with increasing time points, with the new tissues observed throughout the defect area for the blend and only at the implant site's extremes for the PLGA control. Histologically, the polyphosphazene system appeared to show tissue responses and bone ingrowths superior to PLGA. By the end of the study, the defects with PNGEGPhPh-PLGA scaffolds exhibited evidence of effective bone tissue ingrowth and minimal inflammatory responses. Thus, polyphosphazene-containing biomaterials have excellent translational potential for use in bone regenerative engineering applications.
The polyphosphazene backbone provides a versatile platform to explore numerous synthesis and stru... more The polyphosphazene backbone provides a versatile platform to explore numerous synthesis and structure–property relationships for many technological applications. In this study, a new class of polyphosphazene semiconducting materials was synthesized via macromolecular substitution, which integrates a PN backbone with thiophene‐based side groups. The synthesized thiophene‐based polymers were subjected to chemical oxidation (oxidative coupling) to optimize their optoelectronic properties through side‐chain chemistry. Both the spectroscopic and electronic analyses revealed that optical and electronic properties, as well as glass transition temperatures could be modulated by chemical oxidation of the polymers. The suitability of the polymers as potential semiconductors was further evaluated using their steady‐state fluorescence quenching behavior in the presence of four different dopants (PC70BM, PC60BM, F4TCNQ, and TCNQ). It was found that the addition of dopant as a quencher to the...
Page 1. PART III Biomaterials 117 Page 2. 8 Biodegradable Polyphosphazene Scaffolds for Tissue En... more Page 1. PART III Biomaterials 117 Page 2. 8 Biodegradable Polyphosphazene Scaffolds for Tissue Engineering SYAM P. NUKAVARAPU and SANGAMESH G. KUMBAR Department of Orthopaedic Surgery, University of Connecticut ...
Synthetic biodegradable polymers serve as temporary substrates that accommodate cell infiltration... more Synthetic biodegradable polymers serve as temporary substrates that accommodate cell infiltration and tissue in-growth in regenerative medicine. To allow tissue in-growth and nutrient transport, traditional three-dimensional (3D) scaffolds must be prefabricated with an interconnected porous structure. Here we demonstrated for the first time a unique polymer erosion process through which polymer matrices evolve from a solid coherent film to an assemblage of microspheres with an interconnected 3D porous structure. This polymer system was developed on the highly versatile platform of polyphosphazene-polyester blends. Co-substituting a polyphosphazene backbone with both hydrophilic glycylglycine dipeptide and hydrophobic 4-phenylphenoxy group generated a polymer with strong hydrogen bonding capacity. Rapid hydrolysis of the polyester component permitted the formation of 3D void space filled with self-assembled polyphosphazene spheres. Characterization of such self-assembled porous structures revealed macropores (10-100 μm) between spheres as well as micro- and nanopores on the sphere surface. A similar degradation pattern was confirmed in vivo using a rat subcutaneous implantation model. 12 weeks of implantation resulted in an interconnected porous structure with 82-87% porosity. Cell infiltration and collagen tissue in-growth between microspheres observed by histology confirmed the formation of an in situ 3D interconnected porous structure. It was determined that the in situ porous structure resulted from unique hydrogen bonding in the blend promoting a three-stage degradation mechanism. The robust tissue in-growth of this dynamic pore forming scaffold attests to the utility of this system as a new strategy in regenerative medicine for developing solid matrices that balance degradation with tissue formation.
Amino end-terminated poly(l-lactic acid), poly(trimethylene carbonate), and polycaprolactone were... more Amino end-terminated poly(l-lactic acid), poly(trimethylene carbonate), and polycaprolactone were synthesized via ring-opening polymerization techniques. The amino terminus was used to form a covalent link to poly(dichlorophosphazene), itself synthesized using a living cationic polymerization. The chlorine atoms in the polyphosphazene blocks were subsequently replaced by trifluoroethoxy groups. This is the first reported synthesis of block copolymers of polyphosphazenes linked to polyesters or polycarbonates. The molecular structure of each copolymer was established using multinuclear NMR techniques. Molecular weight analysis was used to provide confirmatory evidence that the two polymers chains were covalently linked. Thermal analysis results showed evidence that in the solid state the two blocks were phase-separated because the parent thermal transitions were detectable for each copolymer.
Electrospun polycaprolactone nanofiber matrices surface functionalized with poly[(ethyl alanato),... more Electrospun polycaprolactone nanofiber matrices surface functionalized with poly[(ethyl alanato), (p-methyl phenoxy),] phosphazene were fabricated for the purpose of soft skeletal tissue regeneration. This preliminary study reports the effect of fiber diameter and polyphosphazene surface functionalization on significant scaffold properties such as morphology, surface hydrophilicity, porosity, tensile properties, human mesenchymal stem cell adhesion and proliferation. Six fiber matrices comprised of average fiber diameters in the range of 400-500, 900-1000, 1400-1500, 1900-2000, 2900-3000 and 3900-4000 nm were considered for primary evaluation. After achieving the greatest proliferation while maintaining moderate tensile modulus, matrices in the diameter range of 2900-3000 nm were selected to examine the effect of coating with 1%, 2% and 3% (weight/volume) polyphosphazene solutions. Polyphosphazene functionalization resulted in rougher surfaces that correlated with coating solution concentration. Analytical techniques such as energy dispersive X-ray analysis, Fourier transform infrared spectroscopy, elemental analysis, differential scanning calorimetry, water contact angle goniometry and confocal microscopy confirmed the presence of polyphosphazene and its distribution on the functionalized fiber matrices. Functionalization achieved through 2% polymer solutions did not affect average pore diameter, tensile modulus, suture retention strength or cell proliferation compared to PCL controls. Surface polyphosphazene functionalization significantly improved the matrix hydrophilicity evidenced through decreased water contact angle of PCL matrices from 130 degrees to 97 degrees. Further, enhanced total protein synthesis by cells during in vitro culture was seen on 2% PPHOS functionalized matrices over controls. Improving PCL matrix hydrophilicity via proposed surface functionalization may be an efficient method to improve cell-PCL matrix interactions.
Journal of Biomaterials Science-polymer Edition, 2011
Self-setting hydroxyapatite-biodegradable injectable composites are excellent candidates for appl... more Self-setting hydroxyapatite-biodegradable injectable composites are excellent candidates for applications in orthopaedics. We have previously demonstrated the feasibility of development of self-setting calcium-deficient nanocrystalline hydroxyapatite-polymer composites using different calcium phosphate precursors and biodegradable polyphosphazenes. This study aimed to evaluate these novel injectable composites as suitable materials for orthopaedic applications through evaluating their biomechanical properties, osteoblast cellular attachment and gene expression over time. Our studies demonstrated that the morphology of the composite groups (PNEA-CDHA, PNEA-CDSHA, PNEA(50)mPh(50)-CDHA, PNEA(50)mPh(50)-CDSHA, PNEA(50)PhPh(50)-CDHA, and PNEA(50)PhPh(50)-CDSHA) formed was similar and found to have micro- and nanoporous structures resembling trabecular bone. The osteoblast phenotypic marker of bone, alkaline phosphatase, was expressed by the cells on the surface of the composites throughout the study and was comparable to tissue-culture polystyrene (control). Furthermore, the cells seeded on the composites expressed the characteristic osteoblastic genes, such as type-I collagen, alkaline phosphatase, osteocalcin, osteopontin and bone sialoprotein, indicating osteoblast differentiation, maturation and mineralization. Within our injectable composite groups, significant gene expression levels were displayed (P < 0.05). These novel injectable biodegradable polyphosphazenes-calcium-deficient hydroxyapatites materials are promising candidates for orthopaedic applications.
IEEE Engineering in Medicine and Biology Magazine, Sep 1, 2003
... AMA AMBROSIO, JS SAHOTA, C. RUNGE, SM KURTZ, S. LAKSHMI, HR ALLCOCK, AND CT LAURENCIN ... mat... more ... AMA AMBROSIO, JS SAHOTA, C. RUNGE, SM KURTZ, S. LAKSHMI, HR ALLCOCK, AND CT LAURENCIN ... matrices at a seeding density of 50,000 cells/well and the cells were grown in alpha modification of Eagles minimal essential media (ICN, Irvine, Virginia) supplemented ...
Encyclopedia of Polymer Science and Technology, 2019
Polyphosphazenes are a unique class of inorganic-organic hybrid polymers with a backbone composed... more Polyphosphazenes are a unique class of inorganic-organic hybrid polymers with a backbone composed of alternating phosphorus and nitrogen atoms. The ease with which the precursor prepolymer poly(dichlorophosphazene) can be modified has resulted in a versatile polymer system. The labile nature of the P−Cl bonds has allowed the substitution of chlorine atoms with groups like alkoxy‐, aryloxy, alkyl ether, fluoroalkoxy, amino acid/peptide esters, drug molecules, transition metal groups, and many more. Careful selection of the side groups offers efficient control of material properties such as bioactivity, crystallinity, solubility, and surface characteristics. Hence, these properties have led to the use of this exceptional class of polymers in a broad range of applications such as biomaterials for regenerative engineering and drug delivery, elastomers, solid membranes for gas/liquid separation, optical materials, flame retardants, and electrolytes for energy storage cells. This article gives an overview of the synthetic routes of polyphosphazene polymers and their composition–structure–properties relationships and highlights their applications in various fields.
In an effort to understand the biological capability of polyphosphazene-based polymers, three-dim... more In an effort to understand the biological capability of polyphosphazene-based polymers, three-dimensional biomimetic bone scaffolds were fabricated using the blends of poly[(glycine ethylglycinato)75(phenylphenoxy)25]phosphazene (PNGEGPhPh) and poly(lactic-co-glycolic acid) (PLGA), and an in vivo evaluation was performed in a rabbit critical-sized bone defect model. The matrices constructed from PNGEGPhPh-PLGA blends were surgically implanted into 15 mm critical-sized radial defects of the rabbits as structural templates for bone tissue regeneration. PLGA, which is the most commonly used synthetic bone graft substitute, was used as a control in this study. Radiological and histological analyses demonstrated that PNGEGPhPh-PLGA blends exhibited favorable in vivo biocompatibility and osteoconductivity, as the newly designed matrices allowed new bone formation to occur without adverse immunoreactions. The X-ray images of the blends showed higher levels of radiodensity than that of the pristine PLGA, indicating higher rates of new bone formation and regeneration. Micro-computed tomography quantification revealed that new bone volume fractions were significantly higher for the PNGEGPhPh-PLGA blends than for the PLGA controls after 4 weeks. The new bone volume increased linearly with increasing time points, with the new tissues observed throughout the defect area for the blend and only at the implant site's extremes for the PLGA control. Histologically, the polyphosphazene system appeared to show tissue responses and bone ingrowths superior to PLGA. By the end of the study, the defects with PNGEGPhPh-PLGA scaffolds exhibited evidence of effective bone tissue ingrowth and minimal inflammatory responses. Thus, polyphosphazene-containing biomaterials have excellent translational potential for use in bone regenerative engineering applications.
The polyphosphazene backbone provides a versatile platform to explore numerous synthesis and stru... more The polyphosphazene backbone provides a versatile platform to explore numerous synthesis and structure–property relationships for many technological applications. In this study, a new class of polyphosphazene semiconducting materials was synthesized via macromolecular substitution, which integrates a PN backbone with thiophene‐based side groups. The synthesized thiophene‐based polymers were subjected to chemical oxidation (oxidative coupling) to optimize their optoelectronic properties through side‐chain chemistry. Both the spectroscopic and electronic analyses revealed that optical and electronic properties, as well as glass transition temperatures could be modulated by chemical oxidation of the polymers. The suitability of the polymers as potential semiconductors was further evaluated using their steady‐state fluorescence quenching behavior in the presence of four different dopants (PC70BM, PC60BM, F4TCNQ, and TCNQ). It was found that the addition of dopant as a quencher to the...
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