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Biomedical subjects

Jason A Burdick

Publications and source records attributed to Jason A Burdick.

At least 19 recordsLinked to original sources
PubMed2007

Photocrosslinkable hydrogel for myocyte cell culture and injection.

Conventional treatment options for myocardial infarction are limited by the inability of mature myocardium to regenerate after injury. Although functional improvements after injection of cells and growth factors have been demonstrated, the clinical utility of this procedure has been hampered by poor cell localization, low survival, and rapid clearance of injected growth factors. The main objective of this study was to evaluate the applicability of a hydrogel, based on photocrosslinkable chitosan and acryloyl-poly(ethylene glycol)-RGDS (Az-chitosan/Acr-PEG-RGD) for myocyte cell culture and myocardial injection. Chitosan was modified with photoreactive azidobenzoic acid and Acr-PEG-RGD was synthesized by reacting YRGDS with an equimolar amount of acryloyl-PEG-N-hydroxysuccinimide. For injection and encapsulation each polymer was dissolved in Di-H(2)O (pH 6.4), the solutions were mixed and crosslinked by UV application (4 mW/cm(2)). C2C12 myoblasts proliferated and differentiated on hydrogels containing 5 mM RGD but not on the pure photocrosslinked chitosan. In vitro, the crosslinked hydrogels retained 80% of encapsulated VEGF for 24 days. Live/dead staining of neonatal rat cardiomyocytes encapsulated into Az-chitosan/Acr-PEG-RGD hydrogels indicated high cell viability upon UV crosslinking. Ex vivo, we localized the hydrogel on the surface and in the ventricle wall of an adult rat heart by brief (2 min) UV light application.

Animals↗
PubMed2006

Micromolding of photocrosslinkable hyaluronic acid for cell encapsulation and entrapment.

Micropatterning of hydrogels is potentially useful for a variety of applications, including tissue engineering, fundamental biological studies, diagnostics, and high-throughput screening. Although synthetic polymers have been developed for these applications, natural polymers such as polysaccharides may have advantages for biological samples and cell-based devices because they are natural components of the in vivo microenvironment. In this study, we synthesized and used hyaluronic acid (HA) modified with photoreactive methacrylates to fabricate microstructures as functional components of microfabricated devices. To demonstrate the universality of this approach, two types of microstructures were formed. In the first approach, HA microstructures were fabricated and used as docking templates to enable the subsequent formation of cell microarrays within low shear stress regions of the patterns. Cells within these microwells remained viable, could generate spheroids, and could be retrieved using mechanical disruption. In the second approach, cells were encapsulated directly within the HA hydrogels. Arrays of viable embryonic stem (ES) cells or fibroblasts were encapsulated within HA hydrogels and could later be recovered using enzymatic digestion of the microstructures. These results demonstrate that it is possible to incorporate photocrosslinkable HA, a natural, versatile, degradable, and biocompatible biopolymer, into micro-electromechanical systems.

Animals↗
PubMed2006

Peritoneal application of chitosan and UV-cross-linkable chitosan.

The suitability of chitosan and UV-cross-linkable chitosan for intraperitoneal use, for example as a barrier device for preventing peritoneal adhesions or for drug delivery, was examined. In vitro experiments using two major cell types present in the peritoneal cavity (mesothelial cells and peritoneal macrophages) revealed neither attractive interactions between cross-linked chitosan gels and the cells nor a proliferative effect. However, the same UV-cross-linked chitosan applied in the peritoneal cavity of rabbits caused a granulomatous reaction with adhesion formation within two weeks in all animals, which persisted up to 4 weeks after exposure. Unmodified chitosan also caused adhesions, while UV irradiation did not. UV-cross-linkable chitosan induced significant elevations in MIP-2 and TNF-alpha from peritoneal macrophages, suggesting that soluble mediators could play a role in inducing adhesion formation. These results reinforce the view that the predictive value of in vitro cytotoxicity assays in matters of biocompatibility may not be sufficient, and suggest that other assays such as cytokine levels may be of value in predicting outcomes in situations involving multiple cell types (i.e. in vivo).

Animals↗
PubMed2006

Influence of gel properties on neocartilage formation by auricular chondrocytes photoencapsulated in hyaluronic acid networks.

The objective of this study was to determine how changes in the network structure and properties of hyaluronic acid (HA) hydrogels, due to variations in the macromer molecular weight (50-1,100 kDa) and macromer concentration (2-20 wt %), affect neocartilage formation by encapsulated auricular chondrocytes. To investigate tissue formation, swine auricular chondrocytes were photoencapsulated in the various networks, implanted subcutaneously in the dorsum of nude mice, and explanted after 6 and 12 weeks for biochemical and histological analysis. After 12 weeks, the various constructs were 81-93% water, contained between 0.1 x 10(6) and 0.6 x 10(6) chondrocytes per sample, and consisted of 0-0.049 microg chondroitin sulfate/mug wet weight (glycosaminoglycan (GAG) content) and 0.002-0.060 microg collagen/microg wet weight. Histological staining showed an even distribution of chondrocytes and GAGs in addition to minimal type I collagen staining and intense and uniform type II collagen staining in the constructs with greatest neocartilage production. Hydrogels fabricated from 2 wt % of the 50 kDa HA macromer most resembled the properties of native cartilage and show the greatest promise for continued development for cartilage regeneration.

Animals↗
PubMed2006

Effects of auricular chondrocyte expansion on neocartilage formation in photocrosslinked hyaluronic acid networks.

The overall objective of this study was to examine the effects of in vitro expansion on neocartilage formation by auricular chondrocytes photoencapsulated in a hyaluronic acid (HA) hydrogel as a next step toward the clinical application of tissue engineering therapies for treatment of damaged cartilage. Swine auricular chondrocytes were encapsulated either directly after isolation (p = 0), or after further in vitro expansion ( p = 1 and p = 2) in a 2 wt%, 50-kDa HA hydrogel and implanted subcutaneously in the dorsum of nude mice. After 12 weeks, constructs were explanted for mechanical testing and biochemical and immunohistochemical analysis and compared to controls of HA gels alone and native cartilage. The compressive equilibrium moduli of the p = 0 and p = 1 constructs (51.2 +/- 8.0 and 72.5 +/- 35.2 kPa, respectively) were greater than the p = 2 constructs (26.8 +/- 14.9 kPa) and the control HA gel alone (12.3 +/- 1.3 kPa) and comparable to auricular cartilage (35.1 +/- 12.2 kPa). Biochemical analysis showed a general decrease in glycosaminoglycan (GAG), collagen, and elastin content with chondrocyte passage, though no significant differences were found between the p = 0 and p = 1 constructs for any of the analyses. Histological staining showed intense and uniform staining for aggrecan, as well as greater type II collagen versus type I collagen staining in all constructs. Overall, this study illustrates that constructs with the p = 0 and p = 1 auricular chondrocytes produced neocartilage tissue that resembled native auricular cartilage after 12 weeks in vivo. However, these results indicate that further expansion of the chondrocytes (p = 2) can lead to compromised tissue properties.

Animals↗
PubMed2005

Poly(ester-anhydride):poly(beta-amino ester) micro- and nanospheres: DNA encapsulation and cellular transfection.

Poly(ester-anhydride) delivery devices allow flexibility regarding carrier dimensions (micro- versus nanospheres), degradation rate (anhydride versus ester hydrolysis), and surface labeling (through the anhydride functional unit), and were therefore tested for DNA encapsulation and transfection of a macrophage P388D1 cell line. Poly(l-lactic acid-co-sebacic anhydride) and poly(l-lactic acid-co-adipic anhydride) were synthesized through melt condensation, mixed with 25 wt.% poly(beta-amino ester), and formulated with plasmid DNA (encoding firefly luciferase) into micro- and nanospheres using a double emulsion/solvent evaporation technique. The micro- and nanospheres were then characterized (size, morphology, zeta potential, DNA release) and assayed for DNA encapsulation and cellular transfection over a range of poly(ester-anhydride) copolymer ratios. Poly(ester-anhydride):poly(beta-amino ester) composite microspheres (6-12 microm) and nanospheres (449-1031 nm), generated with copolymers containing between 0 and 25% total polyanhydride content, encapsulated plasmid DNA (>or=20% encapsulation efficiency). Within this polyanhydride range, poly(adipic anhydride) copolymers provided DNA encapsulation at an increased anhydride content (10%, microspheres; 10-25%, nanospheres) compared to poly(sebacic anhydride) copolymers (1%, microspheres and nanospheres) with cellular transfection correlating with the observed DNA encapsulation.

Adipates↗
PubMed2005

Stimulation of neurite outgrowth by neurotrophins delivered from degradable hydrogels.

Degradable hydrogels are useful vehicles for the delivery of growth factors to promote the regeneration of diseased or damaged tissue. In the central nervous system, there are many instances where the delivery of neurotrophins has great potential in tissue repair, especially for treatment of spinal cord injury. In this work, hydrogels based on poly(ethylene glycol) that form via a photoinitiated polymerization were investigated for the delivery of neurotrophins. The release kinetics of these factors are controlled by changes in the network crosslinking density, which influences neurotrophin diffusion and subsequent release from the gels with total release times ranging from weeks to several months. The release and activity of one neurotrophic factor, ciliary-neurotrophic factor (CNTF), was assessed with a cell-based proliferation assay and an assay for neurite outgrowth from retinal explants. CNTF released from a degradable hydrogel above an explanted retina was able to stimulate outgrowth of a significantly higher number of neurites than controls without CNTF. Finally, unique microsphere/hydrogel composites were developed to simultaneously deliver multiple neurotrophins with individual release rates.

Animals↗
PubMed2005

Formulation and surface modification of poly(ester-anhydride) micro- and nanospheres.

This report presents the formulation and surface modification of poly(ester-anhydride) copolymers. Two synthetic schemes were used to generate a variety of copolymers with varying compositions and molecular weights. These polymers were formulated into both micro- and nanospheres using a water-in-oil-in-water double emulsion technique. Microspheres were between 3 and 10 microm in diameter; whereas, nanospheres were between 300 and 500 nm. Finally, both micro- and nanospheres were surface modified using cystamine and quantified, following cystamine reduction, with DTNB (Ellman's reagent). Surface labeling was observed at 0.20-35 micromol/g for microspheres and 0.6-100 micromol/g for nanospheres and followed the expected trend of increased labeling with increased polyanhydride content.

Absorbable Implants↗
PubMed2004

Molded polyethylene glycol microstructures for capturing cells within microfluidic channels.

The ability to control the deposition and location of adherent and non-adherent cells within microfluidic devices is beneficial for the development of micro-scale bioanalytical tools and high-throughput screening systems. Here, we introduce a simple technique to fabricate poly(ethylene glycol)(PEG) microstructures within microfluidic channels that can be used to dock cells within pre-defined locations. Microstructures of various shapes were used to capture and shear-protect cells despite medium flow in the channel. Using this approach, PEG microwells were fabricated either with exposed or non-exposed substrates. Proteins and cells adhered within microwells with exposed substrates, while non-exposed substrates prevented protein and cell adhesion (although the cells were captured inside the features). Furthermore, immobilized cells remained viable and were stained for cell surface receptors by sequential flow of antibodies and secondary fluorescent probes. With its unique strengths in utility and control, this approach is potentially beneficial for the development of cell-based analytical devices and microreactors that enable the capture and real-time analysis of cells within microchannels, irrespective of cell anchorage properties.

Animals↗
PubMed2004

Fabrication of gradient hydrogels using a microfluidics/photopolymerization process.

A method of fabricating photo-cross-linked hydrogels with gradients of immobilized molecules and crosslinking densities is introduced. Two macromer/initiator solutions are injected into a unique poly(dimethylsiloxane) channel system that produces a prepolymer gradient that is subsequently polymerized into a water-swollen hydrogel with ultraviolet light exposure. The gradient is controlled by the injection flow rate (optimized to 0.3 microL/min per inlet to produce a linear gradient). The technique is investigated both through fabrication of adhesive ligand gradients that modulate spatial distribution of attached endothelial cells and gradients of cross-linking densities that led to unique hydrogel architectures and spatially dependent swelling.

Cell Adhesion↗
PubMed2003

Histocompatibility of photocrosslinked polyanhydrides: a novel in situ forming orthopaedic biomaterial.

Cell-polymer interactions in subcutaneous and bony tissue were examined for a novel class of in situ forming and surface eroding polyanhydride networks. Specifically, photopolymerized disks of several polyanhydride compositions were implanted subcutaneously in rats, and the tissue was analyzed for an inflammatory response. The compositions elicited varied histological responses, ranging from highly active cell layers to moderate fibrous capsules, depending on the degrading polymer composition. Furthermore, one composition was photopolymerized in a model orthopaedic defect in the proximal tibia. The feasibility of photopolymerizing the methacrylated monomers in situ and the adherence of the photocrosslinked polyanhydride to the medullary canal were examined.

Anhydrides↗
PubMed2003

An initial investigation of photocurable three-dimensional lactic acid based scaffolds in a critical-sized cranial defect.

Degradable polymer networks formed by the photoinitiated polymerization of multifunctional monomers have great potential as in situ forming materials, especially for bone tissue engineering. In this study, one specific chemistry was analyzed with respect to bone formation in a critical-sized defect model with and without adsorbed osteoinductive growth factors present. The scaffolds degraded in approximately 8 months and possessed an elastic modulus similar to that of trabecular bone. A porous scaffold fabricated with approximately 80% porosity and pore diameters ranging from 45 to 150 mm was implanted in a critical-sized cranial defect in rats. When implanted alone, the scaffolds were filled primarily with fibrous tissue after 9 weeks with only mild inflammation at the defect site. When the scaffolds released osteoinductive growth factors, statistically more bone filled the scaffold. For instance, 65.8+/-9.4% (n=5) of the defects were filled with radiopaque tissue in the osteoinductive releasing scaffolds, whereas only 24.2+/-7.4% (n=5) of the defects were filled in the untreated defects 9 weeks after implantation. These results illustrate not only the benefits of delivering osteoinductive factors when developing synthetic bone grafts, but the potential of these materials for supporting the infiltration and development of bone in large defects.

Animals↗
PubMed2003

Photoinitiated crosslinked degradable copolymer networks for tissue engineering applications.

Diethylene glycol was used to initiate the ring opening polymerization of D,L-lactide and epsilon -caprolactone, as well as combinations of the two monomers. Esterification of the oligomer end groups with methacryloyl chloride led to divinyl terminated macromers that were reacted via photoinitiated polymerizations to produce crosslinked networks. The lactic and/or caproic acid repeat units can be hydrolyzed under physiological conditions, leading to degradable networks that may be useful for tissue engineering applications. Specifically, methacryloyl terminated poly(lactic acid-co-caproic acid) diethylene glycol based oligomers were prepared and characterized by 1H NMR. The number of ester linkages was kept constant while the ratio of lactic:caproic acid segments was varied. These macromers were then photopolymerized at 450 nm using a visible light initiating system to produce crosslinked degradable networks. The kinetics of the polymerizations were followed by DSC, and the dynamic mechanical behavior was monitored as a function of temperature to obtain the T(g) for each network composition. 1mm thick disks were subjected to hydrolytic degradation in an aqueous phosphate buffer solution at a pH=7.4 and 37 degrees C. The changes in the compressive modulus, as well as the % mass loss as a function of time, were recorded. Cellular compatibility was determined by seeding primary rat calverial osteoblast cells onto the disks and characterizing the cell morphology using scanning electron microscopy.

Animals↗
PubMed2002

Delivery of osteoinductive growth factors from degradable PEG hydrogels influences osteoblast differentiation and mineralization.

Degradable poly(ethylene glycol) (PEG) hydrogels with varying mass loss profiles were investigated to assess their applicability as delivery vehicles for osteoinductive growth factors in bone tissue engineering. Protein release is readily controlled by changes in both the structure (i.e., macromer concentration) and chemistry (i.e., number of degradable units) of the starting macromer. In vitro studies indicate an increase in total protein levels, alkaline phosphatase, and mineralization by osteoblasts cultured in the presence of osteoinductive growth factors compared to cells cultured with standard media. When growth factors are delivered from a 25 wt% hydrogel, a significant increase in both alkaline phosphatase and mineralization was seen after 3 weeks of culture over growth factor delivery in a bolus fashion. Additionally, gene expression levels of both osteocalcin and type I collagen were higher at early timepoints when growth factors were released from hydrogels. These results indicate that growth factors remain active after photoencapsulation, that the sustained delivery of growth factors alters various markers of osteoblastic differentiation, and that these networks could be useful as delivery vehicles for growth factors in bone tissue engineering. Finally, ectopic bone formation was present in subcutaneous rat tissue after implantation of hydrogel networks loaded with osteoinductive growth factors.

Animals↗
PubMed2002

An investigation of the cytotoxicity and histocompatibility of in situ forming lactic acid based orthopedic biomaterials.

The cytotoxicity and biocompatibility of polymer networks prefabricated from multifunctional lactic acid based oligomers that are being developed for orthopedic applications were assessed through in vitro cytotoxicity analysis and subcutaneous implantation. After 7 and 14 days, no significant difference was observed in the relative viability or alkaline phosphatase activity of primary rat calvarial osteoblasts cultured in the presence or absence of degrading polymer networks, indicating that the degradation products had no detrimental effect on the function or activity of the cultured cells. The tissue response to preformed lactic acid networks implanted in rats consisted of a mild inflammatory response with an increase in fibrous capsule thickness and inflammation correlating with faster degrading polymer compositions. This relatively neutral response is indicative of a biocompatible, degradable polymer that has potential medical applications. Finally, porous scaffolds were implanted subcutaneously in rats, and vascularized fibrous tissue infiltration was highly dependent on the scaffold porosity and architecture. This finding indicates that an in situ forming porous scaffold of this composition may support the infiltration of surrounding vascularized tissue, and thus be applicable to orthopedic treatments of large bone defects.

Alkaline Phosphatase↗
PubMed2002

Photoencapsulation of osteoblasts in injectable RGD-modified PEG hydrogels for bone tissue engineering.

Poly(ethylene glycol) (PEG) hydrogels were investigated as encapsulation matrices for osteoblasts to assess their applicability in promoting bone tissue engineering. Non-adhesive hydrogels were modified with adhesive Arg-Gly-Asp (RGD) peptide sequences to facilitate the adhesion, spreading, and, consequently, cytoskeletal organization of rat calvarial osteoblasts. When attached to hydrogel surfaces, the density and area of osteoblasts attached were dramatically different between modified and unmodified hydrogels. A concentration dependence of RGD groups was observed, with increased osteoblast attachment and spreading with higher RGD concentrations, and cytoskeleton organization was seen with only the highest peptide density. A majority of the osteoblasts survived the photoencapsulation process when gels were formed with 10% macromer, but a decrease in osteoblast viability of approximately 25% and 38% was seen after 1 day of in vitro culture when the macromer concentration was increased to 20 and 30wt%, respectively. There was no statistical difference in cell viability when peptides were added to the network. Finally, mineral deposits were seen in all hydrogels after 4 weeks of in vitro culture, but a significant increase in mineralization was observed upon introduction of adhesive peptides throughout the network.

Animals↗
PubMedDate not supplied

Kinetic chain lengths in highly cross-linked networks formed by the photoinitiated polymerization of divinyl monomers: a gel permeation chromatography investigation.

Highly cross-linked networks formed by the photoinitiated polymerization of multifunctional monomers are finding application in the field of biomaterials because of their chemical versatility, reaction control, and ability to polymerize under physiological conditions. Typically, degradation is introduced into these networks via the cross-links and leads to the release of nondegradable but water-soluble kinetic chains formed during the chain polymerization process. In this study, gel permeation chromatography (GPC) was used to characterize kinetic chain length distributions in highly cross-linked systems that are being developed for orthopedic applications. By polymerizing divinyl monomers to various conversions and subsequently degrading them, we investigated the aspects of network structural evolution related to kinetic chain formation. In general, the average kinetic chain length increased with conversion until the onset of autodeceleration, when the kinetic chains decreased in length as the propagation reaction became diffusion-controlled. The distribution of kinetic chains also changed when different initiation conditions (i.e., initiator concentration and incident light intensity) were used, and a decrease in the kinetic chain lengths was observed at higher initiation rates. Finally, kinetic chain lengths were examined as a function of depth in thick samples polymerized with different light intensities and with a photobleaching initiator. Light attenuation through the sample led to different initiation rates as a function of depth and, consequently, spatial heterogeneity in the network structure as measured by the distributions of kinetic chains.

Butadienes↗