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1.  Potential of Hydrogels Based on Poly(Ethylene Glycol) and Sebacic Acid as Orthopedic Tissue Engineering Scaffolds 
Tissue Engineering. Part A  2009;15(8):2299-2307.
In this study, the bioactive effects of poly(ethylene glycol) (PEG) sebacic acid diacrylate (PEGSDA) hydrogels with or without RGD peptide modification on osteogenic differentiation and mineralization of marrow stromal cells (MSCs) were examined. In a separate experiment, the ability of PEGSDA hydrogel to serve as a delivery vehicle for bone morphogenetic protein 2 (BMP-2) was also investigated. As a scaffold, the attachment and proliferation of MSCs on PEGSDA hydrogel scaffolds with and without RGD peptide modification was similar to the control, tissue culture polystyrene. In contrast, cells were barely seen on unmodified PEG diacrylate (PEGDA) hydrogel throughout the culture period for up to 21 days. Osteogenic phenotypic expression such as alkaline phosphatase (ALP) of MSCs as well as mineralized calcium content were significantly higher on PEGSDA-based hydrogels than those on the control or PEGDA hydrogels. Potential use of PEGSDA scaffold as a delivery vehicle of osteogenic molecules such as BMP-2 was also evaluated. Initial burst release of BMP-2 from PEGSDA hydrogel scaffold (14.7%) was significantly reduced compared to PEGDA hydrogel scaffold (84.2%) during the first 3 days of a 21-day release period. ALP activity of an osteoblast was significantly higher in the presence of BMP-2 released from PEGSDA hydrogel scaffolds compared to that in the presence of BMP-2 released from PEGDA scaffolds, especially after 6 days of release. Overall, PEGSDA hydrogel scaffolds without further modification may be useful as orthopedic tissue engineering scaffolds as well as local drug carriers for prolonged sustained release of osteoinductive molecules.
doi:10.1089/ten.tea.2008.0326
PMCID: PMC2792107  PMID: 19292677
2.  In Vivo Biocompatibility of PLGA-Polyhexylthiophene Nanofiber Scaffolds in a Rat Model 
BioMed Research International  2013;2013:390518.
Electroactive polymers have applications in tissue engineering as a physical template for cell adhesion and carry electrical signals to improve tissue regeneration. Present study demonstrated the biocompatibility and biodegradability of poly(lactide-co-glycolide)-poly(3-hexylthiophene) (PLGA-PHT) blend electrospun scaffolds in a subcutaneous rat model. The biocompatibility of PLGA-undoped PHT, PLGA-doped PHT, and aligned PLGA-doped PHT nanofibers was evaluated and compared with random PLGA fibers. The animals were sacrificed at 2, 4, and 8 weeks; the surrounding tissue along with the implant was removed to evaluate biocompatibility and biodegradability by histologic analysis and GPC, respectively. Histology results demonstrated that all scaffolds except PLGA-undoped PHT showed decrease in inflammation over time. It was observed that the aligned PLGA-doped PHT fibers elicited moderate response at 2 weeks, which further reduced to a mild response over time with well-organized tissue structure and collagen deposition. The degradation of aligned nanofibers was found to be very slow when compared to random fibers. Further, there was no reduction in the molecular weight of undoped form of PHT throughout the study. These experiments revealed the biocompatibility and biodegradability of PLGA-PHT nanofibers that potentiate it to be used as a biomaterial for various applications.
doi:10.1155/2013/390518
PMCID: PMC3736537  PMID: 23971031
3.  Tunable Hydrogel-Microsphere Composites that Modulate Local Inflammation and Collagen Bulking 
Acta biomaterialia  2012;8(9):3218-3227.
Injectable biomaterials alone may alter local tissue responses, including inflammatory cascades and matrix production (e.g., stimulatory dermal fillers are used as volumizing agents that induce collagen production). To expand upon the available material compositions and timing of presentation, a tunable hyaluronic acid (HA) and poly(lactide-co-glycolide) (PLGA) microsphere composite system was formulated and assessed in subcutaneous and cardiac tissues. HA functionalized with hydroxyethyl methacrylate (HeMA) was used as a precursor to injectable and degradable hydrogels that carry PLGA microspheres (~50 m diameter) to tissues, where the HA hydrogel degradation (~20 or 70 days) and quantity of PLGA microspheres (0–300 mg/ml) are readily varied. When implanted subcutaneously, faster hydrogel degradation and more microspheres (e.g., 75mg/mL) generally induced more rapid tissue and cellular interactions and a greater macrophage response. In cardiac applications, tissue bulking may be useful to alter stress profiles and to stabilize the tissue after infarction, limiting left ventricular (LV) remodeling. When fast degrading HeMA-HA hydrogels containing 75 mg/mL microspheres were injected into infarcted tissue in sheep, LV dilation was limited and the thickness of the myocardial wall and the presence of vessels in the apical infarct region were increased ~35% and ~60%, respectively, compared to empty hydrogels. Both groups decreased volume changes and infarct areas at 8 weeks, compared to untreated controls. This work illustrates the importance of material design in expanding the application of tissue bulking composites to a range of biomedical applications.
doi:10.1016/j.actbio.2012.05.027
PMCID: PMC3408556  PMID: 22659176
hyaluronic acid; hydrogel; microspheres; remodeling; myocardial infarction
4.  Temporal progression of the host response to implanted poly(ethylene glycol)-based hydrogels 
Poly(ethylene glycol) (PEG) hydrogels hold great promise as in vivo cell carriers for tissue engineering. To ensure appropriate performance of these materials when implanted, the host response must be well understood. The objectives for this study were to characterize the temporal evolution of the foreign body reaction (FBR) to acellular PEG-based hydrogels prepared from PEG diacrylate precursors when implanted subcutaneously in immunocompentent c57bl/6 mice by (immuno)histochemical analysis and gene expression. Compared to a normal FBR elicited by silicone (SIL), PEG hydrogels without or with a cell adhesion ligand RGD elicited a strong early inflammatory response evidenced by a thick band of macrophages as early as day 2, persisting through 2 weeks, and by increased interleukin-1β expression. PEG-only hydrogels showed a slower, but more sustained progression of inflammation over PEG-RGD. Temporal changes in gene expression were observed in response to PEG-based materials and in general exhibited, elevated expression of inflammatory and wound healing genes in the tissues surrounding the implants, while the expression patterns were more stable in response to SIL. While a stabilized FBR was achieved with SIL and to a lesser degree with PEG-RGD, the PEG-only hydrogels had not yet stabilized after 4 weeks. In summary, PEG-only hydrogels elicit a strong early inflammatory reaction, which persists throughout the course of the implantation even as a collagenous capsule begins to form. However, the incorporation of RGD tethers partially attenuates this response within 2 weeks leading to an improved FBR to PEG-based hydrogels.
doi:10.1002/jbm.a.33015
PMCID: PMC3091279  PMID: 21268236
5.  Adriamycin release from poly(lactide-co-glycolide)-polyethylene glycol nanoparticles: synthesis, and in vitro characterization 
The preparation, properties, and application in adriamycin delivery of biocompatible and biodegradable poly(lactide-co-glycolide)-polyethylene glycol (PLGA-PEG) nanoparticles are discussed. PLGA-PEG copolymers were synthesized by ring opening polymerization of the dl-lactide and glycolide in the presence of PEG1000.1H-NMR and FT-IR spectrum were consistent with the structure of PLGA-PEG copolymers. The adriamycin-loaded nanoparticles could be prepared using a precipitation-solvent evaporation technique. The nanoparticles have been produced by a precipitation-solvent evaporation technique. The physical characteristics and drug loading efficiency of the PLGA-PEG nanoparticles were influenced by the composition of the PLGA-PEG copolymers used to prepare the nanoparticles. Particle sizes were between 65 and 100 nm for different compositions of PLGA-PEG copolymers. PLGA-PEG nanoparticles prepared from copolymers having relatively high PLGA/PEG ratios were smaller. Entrapment efficiency was 25%–33%. Adriamycin release from the nanoparticles at pH 7.4 showed an initial burst release and then sustained release phase. These results showed that PLGA-PEG nanoparticles could be an effective carrier for cancer therapy.
PMCID: PMC2676638  PMID: 17722284
adriamycin; PLGA-PEG copolymers; cancer therapy; drug delivery systems
6.  Biodegradable Xylitol-Based Elastomers: In Vivo Behavior and Biocompatibility 
Biodegradable elastomers based on polycondensation reactions of xylitol with sebacic acid, referred to as poly(xylitol sebacate) (PXS) elastomers have recently been developed. Herein, we describe the in vivo behavior of PXS elastomers. Four PXS elastomers were synthesized, characterized and compared to poly(L-lactic-co-glycolic acid) (PLGA). PXS elastomers displayed a high level of structural integrity and form stability during degradation. The in vivo half-life ranged from approximately 3 to 52 weeks. PXS elastomers exhibited increased biocompatibility compared to PLGA implants.
doi:10.1002/jbm.a.32733
PMCID: PMC2935807  PMID: 20540093
Biomaterial; Elastomer; Biocompatibility; Degradation; Poly(xylitol sebacate); xylitol
7.  Biocompatibility and Bone Formation of Flexible, Cotton Wool-like PLGA/Calcium Phosphate Nanocomposites in Sheep 
Background:
The purpose of this preliminary study was to assess the in vivo performance of synthetic, cotton wool-like nanocomposites consisting of a biodegradable poly(lactide-co-glycolide) fibrous matrix and containing either calcium phosphate nanoparticles (PLGA/CaP 60:40) or silver doped CaP nanoparticles (PLGA/Ag-CaP 60:40). Besides its extraordinary in vitro bioactivity the latter biomaterial (0.4 wt% total silver concentration) provides additional antimicrobial properties for treating bone defects exposed to microorganisms.
Materials and Methods:
Both flexible artificial bone substitutes were implanted into totally 16 epiphyseal and metaphyseal drill hole defects of long bone in sheep and followed for 8 weeks. Histological and histomorphological analyses were conducted to evaluate the biocompatibility and bone formation applying a score system. The influence of silver on the in vivo performance was further investigated.
Results:
Semi-quantitative evaluation of histology sections showed for both implant materials an excellent biocompatibility and bone healing with no resorption in the adjacent bone. No signs of inflammation were detectable, either macroscopically or microscopically, as was evident in 5 µm plastic sections by the minimal amount of inflammatory cells. The fibrous biomaterials enabled bone formation directly in the centre of the former defect. The area fraction of new bone formation as determined histomorphometrically after 8 weeks implantation was very similar with 20.5 ± 11.2 % and 22.5 ± 9.2 % for PLGA/CaP and PLGA/Ag-CaP, respectively.
Conclusions:
The cotton wool-like bone substitute material is easily applicable, biocompatible and might be beneficial in minimal invasive surgery for treating bone defects.
doi:10.2174/1874325001105010063
PMCID: PMC3092473  PMID: 21566736
In vivo; bone regeneration; flexible; scaffold; silver.
8.  Poly(lactide-co-glycolide) porous scaffolds for tissue engineering and regenerative medicine 
Interface Focus  2012;2(3):366-377.
Porous scaffolds fabricated from biocompatible and biodegradable polymers play vital roles in tissue engineering and regenerative medicine. Among various scaffold matrix materials, poly(lactide-co-glycolide) (PLGA) is a very popular and an important biodegradable polyester owing to its tunable degradation rates, good mechanical properties and processibility, etc. This review highlights the progress on PLGA scaffolds. In the latest decade, some facile fabrication approaches at room temperature were put forward; more appropriate pore structures were designed and achieved; the mechanical properties were investigated both for dry and wet scaffolds; a long time biodegradation of the PLGA scaffold was observed and a three-stage model was established; even the effects of pore size and porosity on in vitro biodegradation were revealed; the PLGA scaffolds have also been implanted into animals, and some tissues have been regenerated in vivo after loading cells including stem cells.
doi:10.1098/rsfs.2011.0123
PMCID: PMC3363019  PMID: 23741612
poly(lactide-co-glycolide) (PLGA); porous scaffolds; tissue engineering; biodegradation; mechanical properties
9.  A Microparticle/Hydrogel Combination Drug-Delivery System for Sustained Release of Retinoids 
Purpose.
To design and develop a drug-delivery system containing a combination of poly(d,l-lactide-co-glycolide) (PLGA) microparticles and alginate hydrogel for sustained release of retinoids to treat retinal blinding diseases that result from an inadequate supply of retinol and generation of 11-cis-retinal.
Methods.
To study drug release in vivo, either the drug-loaded microparticle–hydrogel combination was injected subcutaneously or drug-loaded microparticles were injected intravitreally into Lrat−/− mice. Orally administered 9-cis-retinoids were used for comparison and drug concentrations in plasma were determined by HPLC. Electroretinography (ERG) and both chemical and histologic analyses were used to evaluate drug effects on visual function and morphology.
Results.
Lrat−/− mice demonstrated sustained drug release from the microparticle/hydrogel combination that lasted 4 weeks after subcutaneous injection. Drug concentrations in plasma of the control group treated with the same oral dose rose to higher levels for 6−7 hours but then dropped markedly by 24 hours. Significantly increased ERG responses and a markedly improved retinal pigmented epithelium (RPE)–rod outer segment (ROS) interface were observed after subcutaneous injection of the drug-loaded delivery combination. Intravitreal injection of just 2% of the systemic dose of drug-loaded microparticles provided comparable therapeutic efficacy.
Conclusions.
Sustained release of therapeutic levels of 9-cis-retinoids was achieved in Lrat−/− mice by subcutaneous injection in a microparticle/hydrogel drug-delivery system. Both subcutaneous and intravitreal injections of drug-loaded microparticles into Lrat−/− mice improved visual function and retinal structure.
A novel drug-delivery system was developed for sustained release of therapeutic levels of 9-cis-retinoids. A PLGA microsphere alginate hydrogel combination was used both in vitro and in vivo to evaluate its therapeutic efficacy in retinas of Lrat−/− mice.
doi:10.1167/iovs.12-10279
PMCID: PMC3465014  PMID: 22918645
10.  Formulation and Evaluation of PLA and PLGA In Situ Implants Containing Secnidazole and/or Doxycycline for Treatment of Periodontitis 
AAPS PharmSciTech  2008;9(3):878-884.
The purpose of this study is to formulate in situ implants containing doxycycline hydrochloride and/or secnidazole that could be used in the treatment of periodontitis by direct periodontal intrapocket administration. Biodegradable polymers [poly (lactide) (PLA) and poly (lactide-co-glycolide) (PLGA)], each polymer in two concentrations 25%w/w, 35%w/w were used to formulate the in situ implants. The rheological behavior, in vitro drug release and the antimicrobial activity of the prepared implants were evaluated. Increasing the concentration of each polymer increases the viscosity and decreases the percent of the drugs released after 24 h. PLA implants showed a slower drugs release rate than PLGA implants in which the implants composed of 25% PLGA showed the fastest drugs release. The in vitro drug release and antimicrobial activity results were compared with results of Atridox®. Results revealed that the pharmaceutical formulation based on 25% PLGA containing secnidazole and doxycycline hydrochloride has promising activity in treating periodontitis in comparison with Atridox®.
doi:10.1208/s12249-008-9126-9
PMCID: PMC2977033  PMID: 18654864
Atridox®; biodegradable polymers; doxycycline; implants; secnidazole
11.  Microsphere Degradation in Outer Hydrogel Membranes Creates Macroscopic Porosity to Counter Biofouling-Induced Sensor Degradation 
Analytical chemistry  2012;84(20):8837-8845.
Biofouling and tissue inflammation present major challenges toward the realization of long-term implantable glucose sensors. Following sensor implantation, proteins and cells adsorb on sensor surfaces to not only inhibit glucose flux but also signal a cascade of inflammatory events that eventually lead to permeability-reducing fibrotic encapsulation. The use of drug-eluting hydrogels as outer sensor coatings has shown considerable promise to mitigate these problems via the localized delivery of tissue response modifiers to suppress inflammation and fibrosis, along with reducing protein and cell absorption. Biodegradable poly (lactic-co-glycolic) acid (PLGA) microspheres encapsulated within a poly (vinyl alcohol) (PVA) hydrogel matrix, presents a model coating where the localized delivery of the potent anti-inflammatory drug dexamethasone has been shown to suppress inflammation over a period of 1-3 months. Here it is shown that the degradation of the PLGA microspheres provides an auxiliary venue to offset the negative effects of protein adsorption. This was realized by: 1) the creation of fresh porosity within the PVA hydrogel following microsphere degradation (which is sustained until the complete microsphere degradation); and 2) rigidification of the PVA hydrogel to prevent its complete collapse onto the newly created void space. Incubation of the coated sensors in PBS buffer led to a monotonic increase in glucose permeability (50%), with a corresponding enhancement in sensor sensitivity over a one-month period. Incubation in serum resulted in biofouling and consequent clogging of the hydrogel microporosity. This however, was partially offset by the generated macroscopic porosity following microsphere degradation. As a result of this, a two-fold recovery in sensor sensitivity for devices with microsphere/hydrogel composite coatings was observed as opposed to similar devices with blank hydrogel coatings. These findings suggest that the use of macroscopic porosity can reduce sensitivity drifts resulting from biofouling and this can be achieved synergistically with current efforts to mitigate negative tissue responses through localized and sustained drug delivery.
doi:10.1021/ac3022423
PMCID: PMC3791326  PMID: 23039161
12.  In Vivo Cytokine-Associated Responses to Biomaterials 
Biomaterials  2008;30(2):160-168.
Cytokines, chemokines, and growth factors were analyzed periodically over eight weeks from the wound exudate fluid surrounding biomaterials implanted subcutaneously within stainless steel mesh cages. TNF-α, MCP-1, MIP-1α, IL-2, IL-6, IL-1β, VEGF, IL-4, and IL-10 were measured from exudate samples collected from cages containing specimens of polyethylene (PE), polyurethane (PU), or organo-tin polyvinyl chloride (ot-PVC). Empty cages served as negative controls, and lipopolysaccharide (LPS) served as a positive control. Cytokine, chemokine, and growth factor concentrations decreased from the time of implantation to eight weeks post-implantation, and there was an overall increase in cytokine, chemokine, and growth factor production for material-containing cages compared to empty cages. However, cytokine production was only modestly affected by the different surface chemistries of the three implanted polymeric materials.
doi:10.1016/j.biomaterials.2008.09.026
PMCID: PMC2621303  PMID: 18849070
13.  Suitable carriers for encapsulation and distribution of endostar: comparison of endostar-loaded particulate carriers 
Background
Particulate carriers are necessary to control the release of endostar and prolong its circulation in vivo. The purpose of this study was to identify a suitable carrier for the capsulation and delivery of endostar.
Methods
We prepared a series of poly (DL-lactide-co-glycolide) (PLGA) and poly (ethylene glycol) (PEG)-modified PLGA (PEG-PLGA) particulate carriers, and then characterized them according to their ability to prolong the circulation of endostar, their physicochemical properties, endostar-loading content, and in vitro and in vivo particulate carrier release profiles.
Results
All the particulate carriers had spherical core shell structures. The PEG-PLGA material and nanosize range appeared to enable the carriers to encapsulate more endostar, release endostar faster in vitro, and accumulate more endostar in vivo. The drug loading capacity of PEG-PLGA and PLGA nanoparticles was 8.03% ± 3.41% and 3.27% ± 5.26%, respectively, and for PEG-PLGA and PLGA microspheres was 15.32% ± 5.61% and 9.21% ± 4.73%. The cumulative amount of endostar released from the carriers in phosphate-buffered saline over 21 days was 23.79%, 20.45%, 15.13%, and 10.41%, respectively. Moreover, the terminal elimination half-life of endostar in the rabbit was 26.91 ± 7.93 hours and 9.32 ± 5.53 hours in the PEG-PLGA group and the PLGA nanoparticle group. Peak endostar concentration was reached at day 7 in the group treated with subcutaneous injection of PEG-PLGA microspheres and at day 14 in the group receiving subcutaneous injection of PLGA microspheres. Endostar was detectable in vivo in both groups after injection of the particulate carriers.
Conclusion
PEG-PLGA nanoparticles might be better than other nanoparticulate carriers for encapsulation and distribution of endostar.
doi:10.2147/IJN.S21881
PMCID: PMC3152471  PMID: 21845043
poly(DL-lactide-co-glycolide); nanoparticle; microsphere; endostar; peptide delivery
14.  Retention of in vitro and in vivo BMP-2 bioactivity in sustained delivery vehicles for bone tissue engineering 
Biomaterials  2008;29(22):3245-3252.
In this study, we investigated the in vitro and in vivo biologic activity of bone morphogenetic protein 2 (BMP-2) released from four sustained delivery vehicles for bone regeneration. BMP-2 was incorporated in 1) a gelatin hydrogel, 2) poly(lactic-co-glycolic acid) (PLGA) microspheres embedded in a gelatin hydrogel, 3) microspheres embedded in a poly(propylene fumarate) (PPF) scaffold and 4) microspheres embedded in a PPF scaffold surrounded by a gelatin hydrogel. A fraction of the incorporated BMP-2 was radiolabeled with 125I to determine its in vitro and in vivo release profiles. The release and bioactivity of BMP-2 were tested weekly over a period of 12 weeks in preosteoblast W20-17 cell line culture and in a rat subcutaneous implantation model. Outcome parameters for in vitro and in vivo bioactivity of the released BMP-2 were alkaline phosphatase (AP) induction and bone formation, respectively. The four implant types showed different in vitro release profiles over the 12-week period, which changed significantly upon implantation. The AP induction by BMP-2 released from gelatin implants showed a loss in bioactivity after 6 weeks in culture, while the BMP-2 released from the other implants continued to show bioactivity over the full 12-week period. Micro-CT and histological analysis of the delivery vehicles after 6 weeks of implantation showed significantly more bone in the microsphere/PPF scaffold composites (implant 3, p < 0.02). After 12 weeks, the amount of newly formed bone in the microsphere/PPF scaffolds remained significantly higher than in the gelatin and microsphere/gelatin hydrogels (p < 0.001), however there was no statistical difference compared to the microsphere/PPF/gelatin composite. Overall, the results from this study show that BMP-2 could be incorporated into various bone tissue engineering composites for sustained release over a prolonged period of time with retention of bioactivity.
doi:10.1016/j.biomaterials.2008.04.031
PMCID: PMC2577841  PMID: 18472153
15.  Biocompatibility and Biodegradation Studies of Subconjunctival Implants in Rabbit Eyes 
PLoS ONE  2011;6(7):e22507.
Sustained ocular drug delivery is difficult to achieve. Most drugs have poor penetration due to the multiple physiological barriers of the eye and are rapidly cleared if applied topically. Biodegradable subconjunctival implants with controlled drug release may circumvent these two problems. In our study, two microfilms (poly [d,l-lactide-co-glycolide] PLGA and poly[d,l-lactide-co-caprolactone] PLC were developed and evaluated for their degradation behavior in vitro and in vivo. We also evaluated the biocompatibility of both microfilms. Eighteen eyes (9 rabbits) were surgically implanted with one type of microfilm in each eye. Serial anterior-segment optical coherence tomography (AS-OCT) scans together with serial slit-lamp microscopy allowed us to measure thickness and cross-sectional area of the microfilms. In vitro studies revealed bulk degradation kinetics for both microfilms, while in vivo studies demonstrated surface erosion kinetics. Serial slit-lamp microscopy revealed no significant inflammation or vascularization in both types of implants (mean increase in vascularity grade PLGA50/50 12±0.5% vs. PLC70/30 15±0.6%; P = 0.91) over a period of 6 months. Histology, immunohistochemistry and immuno-fluorescence also revealed no significant inflammatory reaction from either of the microfilms, which confirmed that both microfilms are biocompatible. The duration of the drug delivery can be tailored by selecting the materials, which have different degradation kinetics, to suit the desired clinical therapeutic application.
doi:10.1371/journal.pone.0022507
PMCID: PMC3142149  PMID: 21799878
16.  Intracerebral Implantation of Hydrogel-Coupled Adhesion Peptides: Tissue Reaction 
Arg-Gly-Asp peptides (RGD) were synthesized and chemically coupled to the bulk of N-(2-hydroxypropyl) methacrylamide-based polymer hydrogels. Fourier Transform Infrared Spectroscopy (FFIR) and amino acid analysis confirmed the peptide coupling to the polymer. Activated and control (unmodified) polymer matrices were stereotaxically implanted in the striata of rat brains, and two months later the brains were processed for immunohistochemistry using antibodies for glial acidic fibrillary protein (GFAP), laminin and neurofilaments. RGD-containing polymer matrices promoted stronger adhesion to the host tissue than the unmodified polymer matrices. In addition, the RGD-grafted polymer implants promoted and supported the growth and spread of GFAP-positive glial tissue onto and into the hydrogels. Neurofilament-positive fibers were also seen running along the surface of the polymer and, in some instances, penetrating the matrix. These findings are discussed in the context of using bioactive polymers as a new approach for promoting tissue repair and axonal regeneration of damaged structures of the central nervous system.
doi:10.1155/NP.1994.245
PMCID: PMC2565294  PMID: 7578440
17.  Effect of Dexamethasone-Loaded Poly(Lactic-Co-Glycolic Acid) Microsphere/Poly(Vinyl Alcohol) Hydrogel Composite Coatings on the Basic Characteristics of Implantable Glucose Sensors 
Background
Hydrogels alone and in combination with microsphere drug delivery systems are being considered as biocompatible coatings for implantable glucose biosensors to prevent/minimize the foreign body response. Previously, our group has demonstrated that continuous release of dexamethasone from poly(lactic-co-glycolic acid) (PLGA) microsphere/poly(vinyl alcohol) (PVA) hydrogel composites can successfully prevent foreign body response at the implantation site. The objective of this study was to investigate the effect of this composite coating on sensor functionality.
Methods
The PLGA microsphere/PVA hydrogel coatings were prepared and applied to glucose biosensors. The swelling properties of the composite coatings and their diffusivity to glucose were evaluated as a function of microsphere loading. Sensor linearity, response time, and sensitivity were also evaluated as a function of coating composition.
Results
The PLGA microsphere/PVA hydrogel composite coating did not compromise sensor linearity (sensors were linear up to 30 mM), which is well beyond the physiological glucose range (2 to 22 mM). The sensor response time did increase in the presence of the coating (from 10 to 19 s); however, this response time was still less than the average reported values. Although the sensitivity of the sensors decreased from 73 to 62 nA/mM glucose when the PLGA microsphere loading in the PVA hydrogel changed from 0 to 100 mg/ml, this reduced sensitivity is acceptable for sensor functionality. The changes in sensor response time and sensitivity were due to changes in glucose permeability as a result of the coatings. The embedded PLGA microspheres reduced the fraction of bulk water present in the hydrogel matrix and consequently reduced glucose diffusion.
Conclusions
This study demonstrates that the PLGA microsphere/PVA hydrogel composite coatings allow sufficient glucose diffusion and sensor functionality and therefore may be utilized as a smart coating for implantable glucose biosensors to enhance their in vivo functionality.
PMCID: PMC3570887  PMID: 23294792
glucose biosensor; hydrogel; linearity; microsphere; response time; sensitivity
18.  RGDS-functionalized polyethylene glycol hydrogel-coated magnetic iron oxide nanoparticles enhance specific intracellular uptake by HeLa cells 
The objective of this study was to develop thin, biocompatible, and biofunctional hydrogel-coated small-sized nanoparticles that exhibit favorable stability, viability, and specific cellular uptake. This article reports the coating of magnetic iron oxide nanoparticles (MIONPs) with covalently cross-linked biofunctional polyethylene glycol (PEG) hydrogel. Silanized MIONPs were derivatized with eosin Y, and the covalently cross-linked biofunctional PEG hydrogel coating was achieved via surface-initiated photopolymerization of PEG diacrylate in aqueous solution. The thickness of the PEG hydrogel coating, between 23 and 126 nm, was tuned with laser exposure time. PEG hydrogel-coated MIONPs were further functionalized with the fibronectin-derived arginine-glycine-aspartic acid-serine (RGDS) sequence, in order to achieve a biofunctional PEG hydrogel layer around the nanoparticles. RGDS-bound PEG hydrogel-coated MIONPs showed a 17-fold higher uptake by the human cervical cancer HeLa cell line than that of amine-coated MIONPs. This novel method allows for the coating of MIONPs with nano-thin biofunctional hydrogel layers that may prevent undesirable cell and protein adhesion and may allow for cellular uptake in target tissues in a specific manner. These findings indicate that the further biofunctional PEG hydrogel coating of MIONPs is a promising platform for enhanced specific cell targeting in biomedical imaging and cancer therapy.
doi:10.2147/IJN.S29442
PMCID: PMC3356191  PMID: 22619531
PEG hydrogel; surface-initiated photopolymerization; nanoparticle encapsulation; agglomeration
19.  Controlled Gelation and Degradation Rates of Injectable Hyaluronic Acid-based Hydrogels through a Double Crosslinking Strategy 
Various biodegradable hydrogels have been employed as injectable scaffolds for tissue engineering and drug delivery. We report a double crosslinking strategy of biocompatible and biodegradable hydrogels derived from aminated and oxidized hyaluronic acid (HA) with genipin (GP), a compound naturally derived from the gardenia fruit. Fast gelation is attributed to the Schiff-base reaction between amino and aldehyde groups of polysaccharide derivatives, and the subsequent crosslinking with GP results is ideal biodegradability and mechanical properties. The gelation time, morphology, equilibrium swelling, compressive modulus and degradation of double crosslinked hydrogels were examined. The double crosslinked hydrogels were examined in vivo via subcutaneous injection into mouse model. Histological results indicated favorable biocompatility as revealed by an absence of neutrophils and macrophages. These studies demonstrate that double crosslinked HA hydrogels are potentially useful as injectable, biodegradable hydrogels in tissue engineering applications.
doi:10.1002/term.378
PMCID: PMC3111820  PMID: 22002922
hyaluronic acid; Schiff-base; genipin; injectable hydrogel; soft tissue engineering
20.  Extended and Sequential Delivery of Protein from Injectable Thermoresponsive Hydrogels 
Thermoresponsive hydrogels are attractive for their injectability and retention in tissue sites where they may serve as a mechanical support and as a scaffold to guide tissue remodeling. Our objective in this report was to develop a thermoresponsive, biodegradable hydrogel system that would be capable of protein release from two distinct reservoirs – one where protein was attached to the hydrogel backbone, and one where protein was loaded into biodegradable microparticles mixed into the network. Thermoresponsive hydrogels consisting of N-isopropylacrylamide (NIPAAm), 2-hydroxyethyl methacrylate (HEMA), and biodegradable methacrylate polylactide (MAPLA) were synthesized along with modified copolymers incorporating 1 mol% protein-reactive methacryloxy N,hydroxysuccinimide (MANHS), hydrophilic acrylic acid (AAc), or both. In vitro, bovine serum albumin (BSA) release was studied from hydrogels, poly(lactide-co-glycolide) microparticles, or microparticles mixed into the hydrogels. The synthesized copolymers were able to gel below 37°C and release protein in excess of 3 months. The presence of MANHS and AAc in the copolymers was associated with higher loaded protein retention during thermal transition (45% vs 22%) and faster release (2 months), respectively. Microspheres entrapped in the hydrogel released protein in a delayed fashion relative to microspheres in saline. The combination of a protein-reactive hydrogel mixed with protein-loaded microspheres demonstrated a sequential release of specific BSA populations. Overall, the described drug delivery system combines the advantages of injectability, degradability, extended release, and sequential release which may be useful in tissue engineering applications.
doi:10.1002/jbm.a.34015
PMCID: PMC3266437  PMID: 22237975
thermoresponsive; injectable; sequential protein delivery; hydrogel; NIPAAm
21.  Controlling Acute Inflammation with Fast Releasing Dexamethasone-PLGA Microsphere/PVA Hydrogel Composites for Implantable Devices 
Background
Continuous release of dexamethasone from PLGA microsphere/PVA hydrogel composites has been shown to suppress the inflammatory tissue reaction in response to subcutaneously implanted foreign material for a period of one month. The scope of the present work is to investigate whether suppressing the initial acute inflammatory phase with fast releasing dexamethasone-PLGA microsphere/PVA composites (that release the drug over a period of one week) would prevent the development of a foreign body reaction in response to implantation in the subcutaneous tissue using a rat model.
Methods
Dexamethasone loaded PLGA microspheres were prepared using the solvent evaporation method. In vitro release from microspheres was analyzed using USP apparatus 4 in phosphate buffered saline (PBS) at 37°C. Composites were fabricated in 18G needles by freeze-thaw cycling the PVA/microsphere dispersion. The composites were implanted in the subcutaneous tissue of anesthetized rats. The pharmacodynamic effect was evaluated by histological examination of the tissue surrounding the composites at pre-determined time points.
Results
In vitro release studies showed that most of the drug entrapped in the microspheres was released within one week. At days 3 and 8, these fast releasing dexamethasone containing composites suppressed the acute phase of inflammation but did not prevent the development of an inflammatory reaction after dexamethasone was completely released from the composites. By day 30, chronic inflammation and fibrosis were observed in the tissue surrounding the drug-containing composites. On days 3 and 8, the number of inflammatory cells in the vicinity of the dexamethasone containing composites was similar to that in normal tissue. However, the number of inflammatory cells was higher in drug-containing composites as compared to drug-free composites by day 30. This was due to the inflammation being in a more advanced stage in drug-free composites where a granulomatous reaction had already developed.
Conclusion
Fast release of dexamethasone from PLGA/PVA composites did not provide long-term protection against the foreign body reaction in response to implantation. It would appear that a sustained delivery of anti-inflammatory agents such as dexamethasone is necessary to suppress inflammation throughout the implant life-time.
PMCID: PMC2769608  PMID: 19888374
biosensor; continuous release; dexamethasone; foreign body reaction; implants; localized delivery; microspheres
22.  Preparation and characterization of gadolinium-loaded PLGA particles surface modified with RGDS for the detection of thrombus 
Thrombotic disease is a leading cause of death and disability worldwide. The development of magnetic resonance molecular imaging provides potential promise for early disease diagnosis. In this study, we explore the preparation and characterization of gadolinium (Gd)-loaded poly (lactic-co-glycolic acid) (PLGA) particles surface modified with the Arg-Gly-Asp-Ser (RGDS) peptide for the detection of thrombus. PLGA was employed as the carrier-delivery system, and a double emulsion solvent-evaporation method (water in oil in water) was used to prepare PLGA particles encapsulating the magnetic resonance contrast agent Gd diethylenetriaminepentaacetic acid (DTPA). To synthesize the Gd-PLGA/chitosan (CS)-RGDS particles, carbodiimide-mediated amide bond formation was used to graft the RGDS peptide to CS to form a CS-RGDS film that coated the surface of the PLGA particles. Blank PLGA, Gd-PLGA, and Gd-PLGA/CS particles were fabricated using the same water in oil in water method. Our results indicated that the RGDS peptide successfully coated the surface of the Gd-PLGA/CS-RGDS particles. The particles had a regular shape, smooth surface, relatively uniform size, and did not aggregate. The high electron density of the Gd-loaded particles and a translucent film around the particles coated with the CS and CS-RGDS films could be observed by transmission electron microscopy. In vitro experiments demonstrated that the Gd-PLGA/CS-RGDS particles could target thrombi and could be imaged using a clinical magnetic resonance scanner. Compared with the Gd-DTPA solution, the longitudinal relaxation time of the Gd-loaded particles was slightly longer, and as the Gd-load concentration increased, the longitudinal relaxation time values decreased. These results suggest the potential of the Gd-PLGA/CS-RGDS particles for the sensitive and specific detection of thrombus at the molecular level.
doi:10.2147/IJN.S49835
PMCID: PMC3794837  PMID: 24124363
poly (lactic-co-glycolic acid); Arg-Gly-Asp-Ser peptide; magnetic resonance imaging; thrombus; particle
23.  A Strategy for Control of “Random” Copolymerization of Lactide and Glycolide: Application to Synthesis of PEG-b-PLGA Block Polymers Having Narrow Dispersity 
Macromolecules  2011;44(18):7132-7140.
Poly(lactic-co-glycolic acid) (PLGA) is a biodegradable copolymer that is also acceptable for use in a variety of biomedical applications. Typically, a random PLGA polymer is synthesized in a bulk batch polymerization using a tin-based catalyst at high temperatures. This methodology results in relatively broad polydispersity indexes (PDIs) due to transesterification, and the polymer product is often discolored. We report here the use of 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU), a known, effective, and convenient organocatalyst for the ring-opening polymerization of cyclic esters, to synthesize random copolymers of lactide and glycolide. The polymerization kinetics of the homo- and copolymerizations of lactide and glycolide were explored via NMR spectroscopy. A novel strategy that employs a controlled addition of the more reactive glycolide monomer to a solution containing the lactide monomer, the poly(ethylene glycol) (PEG) macroinitiator, and DBU catalyst was developed. Using this tactic (semi-batch polymerization), we synthesized a series of block copolymers that exhibited excellent correlation of the expected and observed molecular weights and possessed narrow PDIs. We also measured the thermal properties of these block copolymers and observed trends based on the composition of the block copolymer. We also explored the need for experimental rigor in several aspects of the preparations and have identified a set of convenient reaction conditions that provide polymer products that retain the aforementioned desirable characteristics. These polymerizations proceed rapidly at room temperature and without the need for tin-based catalysts to provide PEG-b-PLGAs suitable for use in biomedical investigations.
doi:10.1021/ma201169z
PMCID: PMC3266509  PMID: 22287809
24.  Pharmacokinetic properties and antitumor efficacy of the 5-fluorouracil loaded PEG-hydrogel 
BMC Cancer  2010;10:211.
Background
We have studied the in vitro and in vivo utility of polyethylene glycol (PEG)-hydrogels for the development of an anticancer drug 5-fluorouracil (5-FU) delivery system.
Methods
A 5-FU-loaded PEG-hydrogel was implanted subcutaneously to evaluate the drug retention time and the anticancer effect. For the pharmacokinetic study, two groups of male rats were administered either an aqueous solution of 5-FU (control group)/or a 5-FU-loaded PEG-hydrogel (treated group) at a dose of 100 mg/kg. For the pharmacodynamic study, a human non-small-cell lung adenocarcinoma (NSCLC) cell line, A549 was inoculated to male nude mice with a cell density of 3 × 106. Once tumors start growing, the mice were injected with 5-FU/or 5-FU-loaded PEG-hydrogel once a week for 4 weeks. The growth of the tumors was monitored by measuring the tumor volume and calculating the tumor inhibition rate (IR) over the duration of the study.
Results
In the pharmacokinetic study, the 5-FU-loaded PEG-hydrogel gave a mean residence time (MRT) of 8.0 h and the elimination half-life of 0.9 h; these values were 14- and 6-fold, respectively, longer than those for the free solution of 5-FU (p < 0.05). In the pharmacodynamic study, A549 tumor growth was significantly inhibited in the 5-FU-loaded PEG-hydrogel group in comparison to the untreated group beginning on Day 14 (p < 0.05-0.01). Moreover, the 5-FU-loaded PEG-hydrogel group had a significantly enhanced tumor IR (p < 0.05) compared to the free 5-FU drug treatment group.
Conclusion
We suggest that 5-FU-loaded PEG-hydrogels could provide a useful tool for the development of an anticancer drug delivery system.
doi:10.1186/1471-2407-10-211
PMCID: PMC2889891  PMID: 20482808
25.  The microclimate pH in poly(D,L-lactide-co-hydroxymethyl glycolide) microspheres during biodegradation 
Biomaterials  2012;33(30):10.1016/j.biomaterials.2012.06.013.
The microclimate pH (µpH) in biodegradable polymers, such as poly(D,L-lactic-coglycolic acid) (PLGA) 50/50, commonly falls to deleterious acidic levels during biodegradation, resulting in instability of encapsulated acid-labile molecules. The µpH distribution in microspheres of a more hydrophilic polyester, poly(D,L-lactide-co-hydroxymethyl glycolide) (PLHMGA), was measured and compared to that in PLGA 50/50 of similar molecular weight and degradation time scales. pH mapping in the polymers was performed after incubation under physiological conditions by using a previously validated ratiometric confocal laser scanning microscopic (CLSM) method. Confocal µpH maps revealed that PLHMGA microspheres, regardless of copolymer composition, developed a far less acidic µpH during 4 weeks of incubation compared with microspheres from PLGA. A pH-independent fluorescent probe marker of polymer matrix diffusion of µpH-controlling water-soluble acid degradation products, bodipy, was observed by CLSM to diffuse ~3–7 fold more rapidly in PLHMGA compared to PLGA microspheres, consistent with much more rapid release of acids observed from the hydrophilic polymer during bioerosion. Hence, PLHMGA microspheres are less susceptible to acidification during degradation as compared to similar PLGA formulations, and therefore, PLHMGA may be more suitable to deliver acid labile molecules such as proteins.
doi:10.1016/j.biomaterials.2012.06.013
PMCID: PMC3817572  PMID: 22819499
microclimate pH; confocal laser scanning microscopy; hydrophilic polyesters; microsphere; pH distribution; poly(lactic-co-glycolic acid)

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