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1.  Controlled release of vascular endothelial growth factor using poly-lactic-co-glycolic acid microspheres: In vitro characterization and application in polycaprolactone fumarate nerve conduits 
Acta biomaterialia  2011;8(2):511-518.
Vascular endothelial growth factor (VEGF) is a potent angiogenic stimulator. Controlled release of such stimulators may enhance and guide the vascularization process, and when applied in a nerve conduit may play a role in nerve regeneration. We report the fabrication and in vitro characterization of VEGF encapsulating poly-lactic-co-glycolic acid (PLGA) microspheres and the in vivo application of nerve conduits supplemented with VEGF-containing microspheres. PLGA microspheres containing VEGF were prepared by the double emulsion-solvent evaporation technique. This yielded 83.16% of the microspheres with a diameter < 53 µm. VEGF content measured by ELISA indicated 93.79 ±10.64% encapsulation efficiency. Release kinetics were characterized by an initial burst release of 67.6±8.25% within the first 24 hours, followed by consistent release of approximately 0.34% per day for 4 weeks. Bioactivity of the released VEGF was tested by human umbilical vein endothelial cell (HUVEC) proliferation assay. VEGF released at all time points enhanced HUVEC proliferation confirming that VEGF retained its bioactivity through the 4-week time period. When the microsphere delivery system was placed in a biosynthetic nerve scaffold, robust nerve regeneration was observed. This study established a novel system for controlled release of growth factors and enables in vivo studies of nerve conduits conditioned with this system.
doi:10.1016/j.actbio.2011.10.001
PMCID: PMC3972821  PMID: 22019759
microsphere; poly-lactic co-glycolic acid; vascular endothelial growth factor; bioactivity; biodegradation; nerve guide
2.  Incorporation of phosphate group modulates bone cell attachment and differentiation on oligo(polyethylene glycol) fumarate hydrogel 
Acta biomaterialia  2012;8(4):1430-1439.
In this work, we have investigated the development of a synthetic hydrogel that contains a negatively charged phosphate group for use as a substrate for bone cell attachment and differentiation in culture. The photoreactive, phosphate-containing molecule, bis(2-(methacryloyloxy)ethyl)phosphate (BP), was incorporated into oligo(polyethylene glycol) fumarate hydrogel and the mechanical, rheological and thermal properties of the resulting hydrogels were characterized. Our results showed changes in hydrogel compression and storage moduli with incorporation of BP. The modification also resulted in decreased crystallinity as recorded by differential scanning calorimetry. Our data revealed that incorporation of BP improved attachment and differentiation of human fetal osteoblast (hFOB) cells in a dose-dependent manner. A change in surface chemistry and mineralization of the phosphate-containing surfaces verified by scanning electron microscopy and energy dispersive X-ray analysis was found to be important for hFOB cell attachment and differentiation. We also demonstrated that phosphate-containing hydrogels support attachment and differentiation of primary bone marrow stromal cells. These findings suggest that BP-modified hydrogels are capable of sustaining attachment and differentiation of both bone marrow stromal cells and osteoblasts that are critical for bone regeneration.
doi:10.1016/j.actbio.2011.12.031
PMCID: PMC3970912  PMID: 22277774
Hydrogel; Bone regeneration; Osteoblast; Rabbit marrow stromal cells
3.  Controlled release of doxorubicin from pH-responsive microgels 
Acta biomaterialia  2012;9(3):5438-5446.
Stimuli-responsive hydrogels have enormous potential in drug delivery applications. They can be used for site-specific drug delivery due to environmental variables in the body such as pH and temperature. In this study, we have developed pH-responsive microgels for the delivery of doxorubicin (DOX) in order to optimize its anti-tumor activity while minimizing its systemic toxicity. We used a copolymer of oligo(polyethylene glycol) fumarate (OPF) and sodium methacrylate (SMA) to fabricate the pH-responsive microgels. We demonstrated that the microgels were negatively charged, and the amounts of charge on the microgels were correlated with the SMA concentration in their formulation. The resulting microgels exhibited sensitivity to the pH and ionic strength of the surrounding environment. We demonstrated that DOX was efficiently loaded into the microgels and released in a controlled fashion via an ion-exchange mechanism. Our data revealed that the DOX release was influenced by the pH and ionic strength of the solution. Moreover, we designed a phenomenological mathematical model, based on a stretched exponential function, to quantitatively analyze the cumulative release of DOX. We found a linear correlation between the maximum release of DOX calculated from the model and the SMA concentration in the microgel formulation. The anti-tumor activity of the released DOX was assessed using a human chordoma cell line. Our data revealed that OPF–SMA microgels prolonged the cell killing effect of DOX.
doi:10.1016/j.actbio.2012.09.019
PMCID: PMC3970914  PMID: 23022545
pH-responsive; Doxorubicin; Microgels; Chordoma; Oligo(polyethylene glycol) fumarate
4.  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.
doi:10.1021/bm100526a
PMCID: PMC3947846  PMID: 20942380
hydrogel; electrical; conductive; nerve; tissue regeneration
5.  Evaluation of Osteoconductive Scaffolds in the Canine Femoral Multi-Defect Model 
Tissue Engineering. Part A  2013;19(5-6):634-648.
Treatment of large segmental bone defects remains an unsolved clinical challenge, despite a wide array of existing bone graft materials. This project was designed to rapidly assess and compare promising biodegradable osteoconductive scaffolds for use in the systematic development of new bone regeneration methodologies that combine scaffolds, sources of osteogenic cells, and bioactive scaffold modifications. Promising biomaterials and scaffold fabrication methods were identified in laboratories at Rutgers, MIT, Integra Life Sciences, and Mayo Clinic. Scaffolds were fabricated from various materials, including poly(L-lactide-co-glycolide) (PLGA), poly(L-lactide-co-ɛ-caprolactone) (PLCL), tyrosine-derived polycarbonate (TyrPC), and poly(propylene fumarate) (PPF). Highly porous three-dimensional (3D) scaffolds were fabricated by 3D printing, laser stereolithography, or solvent casting followed by porogen leaching. The canine femoral multi-defect model was used to systematically compare scaffold performance and enable selection of the most promising substrate(s) on which to add cell sourcing options and bioactive surface modifications. Mineralized cancellous allograft (MCA) was used to provide a comparative reference to the current clinical standard for osteoconductive scaffolds. Percent bone volume within the defect was assessed 4 weeks after implantation using both MicroCT and limited histomorphometry. Bone formed at the periphery of all scaffolds with varying levels of radial ingrowth. MCA produced a rapid and advanced stage of bone formation and remodeling throughout the defect in 4 weeks, greatly exceeding the performance of all polymer scaffolds. Two scaffold constructs, TyrPCPL/TCP and PPF4SLA/HAPLGA Dip, proved to be significantly better than alternative PLGA and PLCL scaffolds, justifying further development. MCA remains the current standard for osteoconductive scaffolds.
doi:10.1089/ten.tea.2012.0289
PMCID: PMC3568967  PMID: 23215980
6.  Histone deacetylase 3 is required for maintenance of bone mass during aging 
Bone  2012;52(1):296-307.
Histone deacetylase 3 (Hdac3) is a nuclear enzyme that removes acetyl groups from lysine residues in histones and other proteins to epigenetically regulate gene expression. Hdac3 interacts with bone-related transcription factors and co-factors such as Runx2 and Zfp521, and thus is poised to play a key role in the skeletal system. To understand the role of Hdac3 in osteoblasts and osteocytes, Hdac3 conditional knockout (CKO) mice were created with the Osteocalcin (OCN) promoter driving Cre expression. Hdac3 CKOOCN mice were of normal size and weight, but progressively lost trabecular and cortical bone mass with age. The Hdac3 CKOOCN mice exhibited reduced cortical bone mineralization and material properties and suffered frequent fractures. Bone resorption was lower, not higher, in the Hdac3 CKOOCN mice, suggesting that primary defects in osteoblasts caused the reduced bone mass. Indeed, reductions in bone formation were observed. Osteoblasts and osteocytes from Hdac3 CKOOCN mice showed increased DNA damage and reduced functional activity in vivo and in vitro. Thus, Hdac3 expression in osteoblasts and osteocytes is essential for bone maintenance during aging.
doi:10.1016/j.bone.2012.10.015
PMCID: PMC3513670  PMID: 23085085
Histone deacetylase; Osteocalcin-Cre; Osteoblast; Osteocyte; DNA damage
7.  Osteoblast Growth and Bone Healing Response to Three Dimensional Poly(ε-caprolactone fumarate) Scaffolds 
Poly(ε-caprolactone fumarate) (PCLF) scaffold formulations were assessed as a delivery system of recombinant human bone morphogenetic protein (rhBMP-2) for bone tissue engineering. The formulations included PCLF with combinations of poly(vinyl alcohol) (PVA) and hydroxyapatite (HA). The assessments included in vitro and in vivo assays. In vitro assays validated cell attachment using a pre-osteoblast cell line (MC3T3-E1). Additionally, in vitro release profiles of rhBMP-2 from PCLF scaffolds were determined up to 21 days. Data suggested PCLF incorporated with PVA and HA accelerated rhBMP-2 release and the released protein was bioactive. For the in vivo study, a critical sized defect (CSD) model in a rabbit calvaria was used to test PCLF scaffolds. At 6 weeks post-implantation, significantly more bone formation was measured in PCLF scaffolds containing rhBMP-2 than in scaffolds without rhBMP-2. In conclusion, we demonstrated PCLF delivered biologically active rhBMP-2, promoted bone healing in a CSD and has potential as a bone tissue engineering scaffold.
doi:10.1002/term.442
PMCID: PMC3213277  PMID: 21744511
poly(ε-caprolactone fumarate); three-dimensional scaffold; rabbit calvarial critical sized defect; rhBMP-2; bone tissue engineering
8.  Comparison of polymer scaffolds in rat spinal cord: A step toward quantitative assessment of combinatorial approaches to spinal cord repair 
Biomaterials  2011;32(32):8077-8086.
The transected rat thoracic (T9/10) spinal cord model is a platform for quantitatively compa0ring biodegradable polymer scaffolds. Schwann cell-loaded scaffolds constructed from poly (lactic co-glycolic acid) (PLGA), poly(ε-caprolactone fumarate) (PCLF), oligo(polyethylene glycol) fumarate (OPF) hydrogel or positively charged OPF (OPF+) hydrogel were implanted into the model. We demonstrated that the mechanical properties (3-point bending and stiffness) of OPF and OPF+ hydrogels closely resembled rat spinal cord. After one month, tissues were harvested and analyzed by morphometry of neurofilament-stained sections at rostral, midlevel, and caudal scaffold. All polymers supported axonal growth. Significantly higher numbers of axons were found in PCLF (P < 0.01) and OPF+ (P < 0.05) groups, compared to that of the PLGA group. OPF+ polymers showed more centrally distributed axonal regeneration within the channels while other polymers (PLGA, PCLF and OPF) tended to show more evenly dispersed axons within the channels. The centralized distribution was associated with significantly more axons regenerating (P < 0.05). Volume of scar and cyst rostral and caudal to the implanted scaffold was measured and compared. There were significantly smaller cyst volumes in PLGA compared to PCLF groups. The model provides a quantitative basis for assessing individual and combined tissue engineering strategies.
doi:10.1016/j.biomaterials.2011.07.029
PMCID: PMC3163757  PMID: 21803415
OPF; PLGA; PCLF; axon regeneration; spinal cord injury; Schwann cell
9.  Sustained Delivery of Dibutyryl Cyclic Adenosine Monophosphate to the Transected Spinal Cord Via Oligo [(Polyethylene Glycol) Fumarate] Hydrogels 
Tissue Engineering. Part A  2011;17(9-10):1287-1302.
This study describes the use of oligo [(polyethylene glycol) fumarate] (OPF) hydrogel scaffolds as vehicles for sustained delivery of dibutyryl cyclic adenosine monophosphate (dbcAMP) to the transected spinal cord. dbcAMP was encapsulated in poly(lactic-co-glycolic acid) (PLGA) microspheres, which were embedded within the scaffolds architecture. Functionality of the released dbcAMP was assessed using neurite outgrowth assays in PC12 cells and by delivery to the transected spinal cord within OPF seven channel scaffolds, which had been loaded with Schwann cells or mesenchymal stem cells (MSCs). Our results showed that encapsulation of dbcAMP in microspheres lead to prolonged release and continued functionality in vitro. These microspheres were then successfully incorporated into OPF scaffolds and implanted in the transected thoracic spinal cord. Sustained delivery of dbcAMP inhibited axonal regeneration in the presence of Schwann cells but rescued MSC-induced inhibition of axonal regeneration. dbcAMP was also shown to reduce capillary formation in the presence of MSCs, which was coupled with significant functional improvements. Our findings demonstrate the feasibility of incorporating PLGA microsphere technology for spinal cord transection studies. It represents a novel sustained delivery mechanism within the transected spinal cord and provides a platform for potential delivery of other therapeutic agents.
doi:10.1089/ten.tea.2010.0396
PMCID: PMC3079174  PMID: 21198413
10.  The effects of fixed electrical charge on chondrocyte behavior 
Acta biomaterialia  2011;7(5):2080-2090.
In this study, we have compared the effects of negative and positive fixed charge on chondrocyte behavior in vitro. Electrical charges have been incorporated into oligo(poly(ethylene glycol) fumarate) (OPF) using small charged monomers such as sodium methacrylate (SMA) and (2-(methacryloyloxy) ethyl)-trimethyl ammonium chloride (MAETAC) to produce negatively and positively charged hydrogels, respectively. The hydrogel physical and electrical properties were characterized through measuring and calculating the swelling ratio and zeta potential, respectively. Our results revealed that the properties of these OPF modified hydrogels varied according to the concentration of charged monomers. Zeta potential measurements demonstrated that the electrical property of the OPF hydrogel surfaces changed due to incorporation of SMA and MAETAC and that this change in electrical property was dose-dependent. Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy was used to determine the hydrogel surface composition. To assess the effects of surface properties on chondrocyte behavior, primary chondrocytes isolated from rabbit ears were seeded as a monolayer on top of the hydrogels. We demonstrated that the cells remained viable over 7 days and began to proliferate while seeded on top of the hydrogels. Collagen type II staining was positive in all samples; however, the intensity of the stain was higher on negatively charged hydrogels. Similarly, GAG production was significantly higher on negatively charged hydrogels compared to neutral hydrogel. Reverse transcription polymerase chain reaction showed up-regulation of collagen type II and down-regulation of collagen type I on the negatively charged hydrogels. These findings indicate that charge plays an important role in establishing an appropriate environment for chondrocytes and hence in the engineering of cartilage. Thus, further investigation into charged hydrogels for cartilage tissue engineering is merited.
doi:10.1016/j.actbio.2011.01.012
PMCID: PMC3103083  PMID: 21262395
hydrogel; cartilage tissue engineering; OPF; scaffold
11.  Crosslinking Characteristics and Mechanical Properties of an Injectable Biomaterial Composed of Polypropylene fumarate and Polycaprolactone Copolymer 
In this work, a series of copolymers of polypropylene fumarate-co-polycaprolactone (PPF-co-PCL) were synthesized via a three-step polycondensation reaction of oligomeric polypropylene fumarate (PPF) with polycaprolactone (PCL). The effects of PPF precursor molecular weight, PCL precursor molecular weight, and PCL fraction in the copolymer (PCL feed ratio) on the maximum crosslinking temperature, gelation time, and mechanical properties of the crosslinked copolymers were investigated. The maximum crosslinking temperature fell between 38.2±0.3 and 47.2±0.4 °C, which increased with increasing PCL precursor molecular weight. The gelation time was between 4.2±0.2 and 8.5±0.7 min, and decreased with increasing PCL precursor molecular weight. The compressive moduli ranged from 44±1.8 to 142±7.4 MPa, with enhanced moduli at higher PPF precursor molecular weight and lower PCL feed ratio. The compressive toughness was in the range of 4.1±0.3 and 17.1±1.3 KJ/m3. Our data suggest that the crosslinking and mechanical properties of PPF-co-PCL can be modulated by varying the composition. Therefore the PPF-co-PCL copolymers may offer increased versatility as an injectable, in situ polymerizable biomaterial than the individual polymers of PPF and PCL.
doi:10.1163/092050610X487765
PMCID: PMC3062160  PMID: 20566042
Polypropylene fumarate; polycaprolactone; injectable biomaterials; in situ polymerizable
12.  A Stimuli-Responsive Hydrogel for Doxorubicin Delivery 
Biomaterials  2010;31(31):8051-8062.
The goal of this study was to develop a polymeric carrier for delivery of anti-tumor drugs and sustained release of these agents in order to optimize anti-tumor activity while minimizing systemic effects. We used oligo(poly(ethylene glycol) fumarate) (OPF) hydrogels modified with small negatively charged molecules, sodium methacrylate (SMA), for delivery of doxorubicin (DOX). SMA at different concentrations was incorporated into the OPF hydrogel with a photo-crosslinking method. The resulting hydrogels exhibited sensitivity to the pH and ionic strength of the surrounding environment. Our results revealed that DOX was bound to the negatively charged hydrogel through electrostatic interaction and was released in a timely fashion with an ion exchange mechanism. Release kinetics of DOX was directly correlated to the concentration of SMA in the hydrogel formulations. Anti-tumor activity of the released DOX was assessed using a human osteosarcoma cell line. Our data revealed that DOX released from the modified, charged hydrogels remained biologically active and had the capability to kill cancer cells. In contrast, control groups of unmodified OPF hydrogels with or without DOX did not exhibit any cytotoxicity. This study demonstrates the feasibility of using SMA-modified OPF hydrogels as a potential carrier for chemotherapeutic drugs for cancer treatments.
doi:10.1016/j.biomaterials.2010.06.054
PMCID: PMC2936247  PMID: 20696470
13.  The Development of Electrically Conductive Polycaprolactone Fumarate-Polypyrrole Composite Materials for Nerve Regeneration 
Biomaterials  2010;31(23):5916-5926.
Electrically conductive polymer composites composed of polycaprolactone fumarate and polypyrrole (PCLF-PPy) have been developed for nerve regeneration applications. Here we report the synthesis and characterization of PCLF-PPy and in vitro studies showing PCLF-PPy materials support both PC12 cell and dorsal root ganglia (DRG) neurite extension. PCLF-PPy composite materials were synthesized by polymerizing pyrrole in pre-formed PCLF scaffolds (Mn 7,000 or 18,000 g mol−1) resulting in interpenetrating networks of PCLF-PPy. Chemical compositions and thermal properties were characterized by ATR-FTIR, XPS, DSC, and TGA. PCLF-PPy materials were synthesized with five different anions (naphthalene-2-sulfonic acid sodium salt (NSA), dodecylbenzenesulfonic acid sodium salt (DBSA), dioctyl sulfosuccinate sodium salt (DOSS), potassium iodide (I), and lysine) to investigate effects on electrical conductivity and to optimize chemical composition for cellular compatibility. PCLF-PPy materials have variable electrical conductivity up to 6 mS cm−1 with bulk compositions ranging from 5 to 13.5 percent polypyrrole. AFM and SEM characterization show microstructures with a root mean squared (RMS) roughness of 1195 nm and nanostructures with RMS roughness of 8 nm. In vitro studies using PC12 cells and DRG show PCLF-PPy materials synthesized with NSA or DBSA support cell attachment, proliferation, neurite extension, and are promising materials for future studies involving electrical stimulation.
doi:10.1016/j.biomaterials.2010.04.012
PMCID: PMC2893281  PMID: 20483452
Electrically Conductive; Polypyrrole; Nerve; PCLF
14.  Stimulation of neurite outgrowth using positively charged hydrogels 
Biomaterials  2009;30(23-24):3874-3881.
Autologous nerve grafts are currently the best option for the treatment of segmental peripheral nerve defects. However, autografts have several drawbacks including size mismatch and loss of sensation in the donor nerve’s sensory distribution. In this work, we have investigated the development of a synthetic hydrogel that contains positive charge for use as a substrate for nerve cell attachment and neurite outgrowth in culture. We have demonstrated that modification of oligo-(polyethylene glycol) fumarate (OPF) with a positively charged monomer improves primary sensory rat neuron attachment and differentiation in a dose-dependent manner. Positively charged hydrogels also supported attachment of dorsal root ganglion (DRG) explants that contain sensory neurons, Schwann cells and neuronal support cells. Furthermore, charged hydrogels were analyzed for the appearance of myelinated structures in a co-culture containing DRG neurons and Schwann cells. DRGs and Schwann cells remained viable on charged hydrogels for a time period of three weeks and neurites extended from the DRGs. Sudan black staining revealed that neurites emerging from DRGs were accompanied by migrating Schwann cells. These findings suggest that charged OPF hydrogels are capable of sustaining both primary nerve cells and the neural support cells that are critical for regeneration.
doi:10.1016/j.biomaterials.2009.04.018
PMCID: PMC2716054  PMID: 19427689
hydrogel; nerve regeneration; Schwann cells; scaffold
15.  Effect of Hydrogel Porosity on Marrow Stromal Cell Phenotypic Expression 
Biomaterials  2008;29(14):2193-2202.
This study describes investigation of porous photocrosslinked oligo[(polyethylene glycol) fumarate] (OPF) hydrogels as potential matrix for osteoblastic differentiation of marrow stromal cells (MSCs). The porosity and interconnectivity of porous hydrogels were assessed using magnetic resonance microscopy (MRM) as a noninvasive investigative tool that could image the water construct inside the hydrogels at a high spatial resolution. MSCs were cultured onto the porous hydrogels and cell number was assessed using PicoGreen DNA assay. Our results showed 10% of cells initially attached to the surface of scaffolds. However, cells did not show significant proliferation over a time period of 14 days. MSCs cultured on porous hydrogels had increased alkaline phosphatase activity as well as deposition of calcium, suggesting successful differentiation and maturation to the osteoblastic phenotype. Moreover, continued expression of type I collagen and osteonectin over 14 days confirmed osteoblastic differentiation of MSCs. MRM was also applied to monitor osteogenesis of MSCs on porous hydrogels. MRM images showed porous scaffolds became consolidated with osteogenic progression of cell differentiation. These findings indicate that porous OPF scaffolds enhanced MSC differentiation leading to development of bone-like mineralized tissue.
doi:10.1016/j.biomaterials.2008.01.006
PMCID: PMC2386206  PMID: 18262642
Hydrogel; oligo[(polyethylene glycol) fumarate] (OPF); Marrow stromal cells; Magnetic resonance microscopy; Osteogenesis

Results 1-15 (15)