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1.  Development of Electrically Conductive Oligo(polyethylene Glycol) Fumarate-Polypyrrole Hydrogels for Nerve Regeneration 
Biomacromolecules  2010;11(11):2845-2853.
Electrically conductive hydrogel composites consisting of oligo(polyethylene glycol) fumarate (OPF) and polypyrrole (PPy) were developed for applications in nerve regeneration. OPF-PPy scaffolds were synthesized using three different anions: naphthalene-2-sulfonic acid sodium salt (NSA), dodecylbenzenesulfonic acid sodium salt (DBSA), and dioctyl sulfosuccinate sodium salt (DOSS). Scaffolds were characterized by ATR-FTIR, XPS, AFM, dynamic mechanical analysis, electrical resistivity measurements, and swelling experiments. OPF-PPy scaffolds were shown to consist of up to 25 mol% polypyrrole with a compressive modulus ranging from 265 to 323 kPa and a sheet resistance ranging from 6 to 30 × 103 Ohms/square. In vitro studies using PC12 cells showed OPF-PPy materials had no cytotoxicity and PC12 cells showed distinctly better cell attachment and an increase in the percent of neurite bearing cells on OPF-PPy materials compared to OPF. The neurite lengths of PC12 cells were significantly higher on OPF-PPyNSA and OPF-PPyDBSA. These results show that electrically conductive OPF-PPy hydrogels are promising candidates for future applications in nerve regeneration.
PMCID: PMC3947846  PMID: 20942380
hydrogel; electrical; conductive; nerve; tissue regeneration
2.  Enhanced Cell Ingrowth and Proliferation through Three-Dimensional Nanocomposite Scaffolds with Controlled Pore Structures 
Biomacromolecules  2010;11(3):682-689.
We present enhanced cell ingrowth and proliferation through crosslinked three-dimensional (3D) nanocomposite scaffolds fabricated using poly(propylene fumarate) (PPF) and hydroxyapatite (HA) nanoparticles. Scaffolds with controlled internal pore structures were produced from computer-aided design (CAD) models and solid freeform fabrication (SFF) technique, while those with random pore structures were fabricated by NaCl leaching technique for comparison. The morphology and mechanical properties of scaffolds were characterized using scanning electron microscopy (SEM) and mechanical testing, respectively. Pore interconnectivity of scaffolds was assessed using X-ray micro-computed tomography (micro-CT) and 3D imaging analysis. In vitro cell studies have been performed using MC3T3-E1 mouse preosteoblasts and cultured scaffolds in a rotating-wall-vessel bioreactor for 4 and 7 days to assess cell attachment, viability, ingrowth depth, and proliferation. The mechanical properties of crosslinked nanocomposite scaffolds were not significantly different after adding HA or varying pore structures. However, pore interconnectivity of PPF/HA nanocomposite scaffolds with controlled pore structures has been significantly increased, resulting in enhanced cell ingrowth depth 7 days after cell seeding. Cell attachment and proliferation are also higher in PPF/HA nanocomposite scaffolds. These results suggest that crosslinked PPF/HA nanocomposite scaffolds with controlled pore structures may lead to promising bone tissue engineering scaffolds with excellent cell proliferation and ingrowth.
PMCID: PMC2839506  PMID: 20112899
Poly(propylene fumarate) (PPF); Hydroxyapatite (HA); Nanocomposite; Solid freeform fabrication (SFF); Pre-osteoblast responses
3.  Photo-crosslinked Hybrid Polymer Networks Consisting of Poly(propylene fumarate) (PPF) and Poly(caprolactone fumarate) (PCLF): Controlled Physical Properties and Regulated Bone and Nerve Cell Responses 
Biomacromolecules  2008;9(4):1229-1241.
Aiming to achieve suitable polymeric biomaterials with controlled physical properties for hard and soft tissue replacements, we have developed a series of blends consisting of two photo-crosslinkable polymers: polypropylene fumarate (PPF) and polycaprolactone fumarate (PCLF). Physical properties of both uncrosslinked and UV crosslinked PPF/PCLF blends with PPF composition ranging from 0% to 100% have been investigated extensively. It has been found that the physical properties such as thermal, rheological, and mechanical properties could be modulated efficiently by varying the PPF composition in the blends. Thermal properties including glass transition temperature (Tg) and melting temperature (Tm) have been correlated with their rheological and mechanical properties. Surface characteristics such as surface morphology, hydrophilicity and the capability of adsorbing serum protein from culture medium have also been examined for the crosslinked polymer and blend discs. For potential applications in bone and nerve tissue engineering, in vitro cell studies including cytotoxicity, cell adhesion, and proliferation on crosslinked discs with controlled physical properties have been performed using rat bone marrow stromal cells and SPL201 cells, respectively. In addition, the role of mechanical properties such as surface stiffness in modulating cell responses has been emphasized using this model blend system.
PMCID: PMC2888142  PMID: 18307311
Photo-crosslinking; Polymer blends; Poly(propylene fumarate) (PPF); Poly(caprolactone fumarate) (PCLF); Controlled physical properties; Cell responses
4.  Bone Tissue-Engineering Material Poly(propylene fumarate): Correlation between Molecular Weight, Chain Dimensions, and Physical Properties 
Biomacromolecules  2006;7(6):1976-1982.
Poly(propylene fumarate) (PPF) is an important biodegradable and crosslinkable polymer designed for bone tissue-engineering applications. For the first time we report the extensive characterization of this biomaterial including molecular weight dependences of physical properties such as glass transition temperature Tg, thermal degradation temperature Td, density ρ melt viscosity η0, hydrodynamic radius RH, and intrinsic viscosity [η]. The temperature dependence of η0 changes progressively with molecular weight, while it can be unified when the temperature is normalized to Tg. The plateau modulus GN0 and entanglement molecular weight Me have been obtained from the rheological master curves. A variety of chain microstructure parameters such as the Mark-Houwink-Sakurada constants K and α, characteristic ratio C∞, unperturbed chain dimension r02/M, packing length p, Kuhn length b, and tube diameter a have been deduced. Further correlation between the microstructure and macroscopic physical properties has been discussed in light of recent progress in polymer dynamics to supply a better understanding about this unsaturated polyester to advance its biomedical uses. The molecular weight dependence of Tg for six polymer species including PPF has been summarized to support that Me is irrelevant for the finite length effect on glass transition, while surprisingly these polymers can be divided into two groups when their normalized Tg is plotted simply against Mw to indicate the deciding roles of inherent chain properties such as chain fragility, intermolecular cooperativity, and chain end mobility.
PMCID: PMC2530912  PMID: 16768422
5.  Synthesis, Material Properties and Biocompatibility of a Novel Self-Crosslinkable Poly(caprolactone fumarate) as an Injectable Tissue Engineering Scaffold 
Biomacromolecules  2005;6(5):2503-2511.
A novel self-crosslinkable and biodegradable macromer poly(caprolactone fumarate) (PCLF) has been developed for guided bone regeneration. This macromer is a copolymer of fumaryl chloride, which contains double bonds for in-situ crosslinking, and poly(ε-caprolactone) that has a flexible chain to facilitate self-crosslinkability. PCLF was characterized with Fourier transform infrared (FTIR) spectroscopy, 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, and gel permeation chromatography (GPC). Porous scaffolds were fabricated with sodium chloride particles as the porogen and a chemical initiation system. The PCLF scaffolds were characterized with scanning electron microscopy (SEM) and micro-computed tomography (micro-CT). The cytotoxicity and in vivo biocompatibility of PCLF were also assessed. Our results suggest that this novel copolymer, PCLF, is an injectable, self-crosslinkable, and biocompatible macromer that may be potentially used as a scaffold for tissue engineering applications.
PMCID: PMC2530909  PMID: 16153086

Results 1-5 (5)