In Situ Synthesis and Self-Assembly of Peptide-PEG Conjugates: A Facile Method for the Construction of Fibrous Hydrogels.

Peptide-based hydrogels have gained considerable attention as a compelling platform for various biomedical applications in recent years. Their attractiveness stems from their ability to seamlessly integrate diverse properties, such as biocompatibility, biodegradability, easily adjustable hydrophilicity/hydrophobicity, and other functionalities. However, a significant drawback is that most of the functional self-assembling peptides cannot form robust hydrogels suitable for biological applications. In this study, we present the synthesis of novel peptide-PEG conjugates and explore their comprehensive hydrogel properties. The hydrogel comprises double networks, with the first network formed through the self-assembly of peptides to create a ß-sheet secondary structure. The second network is established through covalent bond formation via N-hydroxysuccinimide chemistry between peptides and a 4-arm PEG to form a covalently linked network. Importantly, our findings reveal that this hydrogel formation method can be applied to other peptides containing lysine-rich sequences. Upon encapsulation of the hydrogel with antimicrobial peptides, the hydrogel retained high bacterial killing efficiency while showing minimum cytotoxicity toward mammalian cells. We hope that this method opens new avenues for the development of a novel class of peptide-polymer hydrogel materials with enhanced performance in biomedical contexts, particularly in reducing the potential for infection in applications of tissue regeneration and drug delivery.

Biodegradable and Inherently Fluorescent pH-Responsive Nanoparticles for Cancer Drug Delivery.

PURPOSE: The development of two novel pH-only and pH- and thermo-responsive theranostic nanoparticle (NP) formulations to deliver an anticancer drug and track the accumulation and therapeutic efficacy of the formulations through inherent fluorescence. METHODS: A pH-responsive formulation was synthesized from biodegradable photoluminescent polymer (BPLP) and sodium bicarbonate (SBC) via an emulsion technique, while a thermoresponsive BPLP copolymer (TFP) and SBC were used to synthesize a dual-stimuli responsive formulation via free radical co-polymerization. Cisplatin was employed as a model drug and encapsulated during synthesis. Size, surface charge, morphology, pH-dependent fluorescence, lower critical solution temperature (LCST; TFP NPs only), cytocompatibility and in vitro uptake, drug release kinetics and anticancer efficacy were assessed. RESULTS: While all BPLP-SBC and TFP-SBC combinations produced spherical nanoparticles of a size between 200-300 nm, optimal polymer-SBC ratios were selected for further study. Of these, the optimal BPLP-SBC formulation was found to be cytocompatible against primary Type-1 alveolar epithelial cells (AT1) up to 100 µg/mL, and demonstrated sustained drug release over 14 days, dose-dependent uptake, and marked pH-dependent A549 cancer cell killing (72 vs. 24% cell viability, at pH 7.4 vs. 6.0). The optimal TFP-SBC formulation showed excellent cytocompatibility against AT1 cells up to 500 µg/mL, sustained release characteristics, dose-dependent uptake, pH-dependent (78% at pH 7.4 vs. 64% at pH 6.0 at 37°C) and marked temperature-dependent A549 cancer cell killing (64% at 37°C vs. 37% viability at pH 6.0, 41°C). CONCLUSIONS: In all, both formulations hold promise as inherently fluorescent, stimuli-responsive theranostic platforms for passively targeted anti-cancer therapy.

Study of siRNA Delivery via Polymeric Nanoparticles in Combination with Angiogenesis Inhibitor for The Treatment of AFP-Related Liver Cancer.

Angiogenesis inhibitor drugs have been explored as important pharmacological agents for cancer therapy, including hepatocellular carcinoma. These agents have several drawbacks, such as drug resistance, nonspecific toxicity, and systemic side effects. Therefore, combination therapy of the drug and small interfering RNA could be a promising option to achieve high therapeutic efficacy while allowing a lower systemic dose. Therefore, we studied adding an alpha-fetoprotein siRNA (AFP-siRNA) incorporated on polymeric nanoparticles (NPs) along with angiogenesis inhibitor drugs. The AFP siRNA-loaded NPs were successfully synthesized at an average size of 242.00 ± 2.54 nm. Combination treatment of AFP-siRNA NPs and a low dose of sunitinib produced a synergistic effect in decreasing cell viability in an in vitro hepatocellular carcinoma (HCC) model. AFP-siRNA NPs together with sorafenib or sunitinib greatly inhibited cell proliferation, showing only 39.29 ± 2.72 and 44.04 ± 3.05% cell viability, respectively. Moreover, quantitative reverse transcription PCR (qRT-PCR) demonstrated that AFP-siRNA incorporated with NPs could significantly silence AFP-mRNA expression compared to unloaded NPs. Interestingly, the expression level of AFP-mRNA was further decreased to 28.53 ± 5.10% when sunitinib was added. Therefore, this finding was considered a new promising candidate for HCC treatment in reducing cell proliferation and enhancing therapeutic outcomes.

PLGA nanoparticles containing α-fetoprotein siRNA induce apoptosis and enhance the cytotoxic effects of doxorubicin in human liver cancer cell line.

Hepatocellular carcinoma (HCC) is one of the most common cancers and is a leading cause of death. Delivery of therapeutic molecules, e.g., siRNA, to HCC cells could potentially be an alternative treatment for HCC. In this study, the siRNA targeting α-fetoprotein (AFP) mRNA was found to specifically induce apoptosis and significant cell death in HepG2 cells. It also enhanced the cytotoxic effects of doxorubicin by about two-fold, making it the candidate therapeutic molecule for HCC treatment. To deliver the siRNAs into HCC cells, the AFP siRNAs were loaded into the nanoparticles based on poly (lactic-co-glycolic) acid (PLGA). These nanoparticles induced apoptosis in HepG2 cells and synergistically increased the cytotoxicity of doxorubicin. In summary, the delivery of the AFP siRNA-loaded PLGA nanoparticles in combination with doxorubicin could be a very promising approach for the treatment of HCC.

Nanoparticle facilitated inhalational delivery of erythropoietin receptor cDNA protects against hyperoxic lung injury.

Our goals were to develop and establish nanoparticle (NP)-facilitated inhalational gene delivery, and to validate its biomedical application by testing the hypothesis that targeted upregulation of pulmonary erythropoietin receptor (EpoR) expression protects against lung injury. Poly-lactic-co-glycolic acid (PLGA) NPs encapsulating various tracers were characterized and nebulizated into rat lungs. Widespread NP uptake and distribution within alveolar cells were visualized by magnetic resonance imaging, and fluorescent and electron microscopy. Inhalation of nebulized NPs bearing EpoR cDNA upregulated pulmonary EpoR expression and downstream signal transduction (ERK1/2 and STAT5 phosphorylation) in rats for up to 21 days, and attenuated hyperoxia-induced damage in lung tissue based on apoptosis, oxidative damage of DNA, protein and lipid, tissue edema, and alveolar morphology compared to vector-treated control animals. These results establish the feasibility and therapeutic efficacy of NP-facilitated cDNA delivery to the lung, and demonstrate that targeted pulmonary EpoR upregulation mitigates acute oxidative lung damage. FROM THE CLINICAL EDITOR: Acute lung injury often results in significant morbidity and mortality, and current therapeutic modalities have proven to be ineffective. In this article, the authors developed nanocarrier based gene therapy in an attempt to upregulate the expression of pulmonary erythropoietin receptor in an animal model. Inhalation delivery resulted in reduction of lung damage.

Targeted biodegradable nanoparticles for drug delivery to smooth muscle cells.

Targeted delivery of therapeutic agents to prevent smooth muscle cell (SMC) proliferation is important in averting restenosis (a narrowing of blood vessels). Since platelet derived growth factor (PDGF) receptors are over-expressed in proliferating SMCs after injury from cardiovascular interventions, such as angioplasty and stent implantation, our hypothesis is that conjugation of PDGF-BB (platelet-derived growth factor BB (homodimer)) peptides to biodegradable poly (D,L-lactic-co-glycolide) (PLGA) nanoparticles (NPs) would exhibit an increased uptake of these NPs by proliferating SMCs. In this study, poly (D,L-lactide-co-glycolide) (PLGA) nanoparticles containing dexamethasone were formulated and conjugated with PDGF-BB peptides. These NPs were stable, biocompatible, and exhibited a sustained drug release over 14 days. Various particle uptake studies using HASMCs (human aortic smooth muscle cells) demonstrated that PDGF-BB peptide-conjugated nanoparticles significantly increased cellular uptake and decreased proliferation of HASMCs compared to control nanoparticles (without conjugation of PDGF-BB peptides). These NPs were internalized primarily by clathrin-mediated endocytosis and macropinocytosis. Our in vitro results suggest that PDGF-BB peptide-conjugated NPs could represent as an effective targeted, sustained therapeutic delivery system to reduce restenosis and neointimal hyperplasia.

Polydopamine nanoparticles and hyaluronic acid hydrogels for mussel-inspired tissue adhesive nanocomposites.

Bioadhesives are intended to facilitate the fast and efficient reconnection of tissues to restore their functionality after surgery or injury. The use of mussel-inspired hydrogel systems containing pendant catechol moieties is promising for tissue attachment under wet conditions. However, the adhesion strength is not yet ideal. One way to overcome these limitations is to add polymeric nanoparticles to create nanocomposites with improved adhesion characteristics. To further enhance adhesiveness, polydopamine nanoparticles with controlled size prepared using an optimized process, were combined with a mussel-inspired hyaluronic acid (HA) hydrogel to form a nanocomposite. The effects of sizes and concentrations of polydopamine nanoparticles on the adhesive profiles of mussel-inspired HA hydrogels were investigated. Results show that the inclusion of polydopamine nanoparticles in nanocomposites increased adhesion strength, as compared to the addition of poly (lactic-co-glycolic acid) (PLGA), and PLGA-(N-hydroxysuccinimide) (PLGA-NHS) nanoparticles. A nanocomposite with demonstrated cytocompatibility and an optimal lap shear strength (47 ± 3 kPa) was achieved by combining polydopamine nanoparticles of 200 nm (12.5% w/v) with a HA hydrogel (40% w/v). This nanocomposite adhesive shows its potential as a tissue glue for biomedical applications.

Self-assembling Peptides with Internal Ionizable Unnatural Amino Acids: A General Approach to pH-responsive Peptide Materials.

Self-assembled peptides are an emerging family of biomaterials that show great promise for a range of biomedical and biotechnological applications. Introducing and tuning the pH-responsiveness of the assembly is highly desirable for improving their biological activities. Inspired by proteins with internal ionizable residues, we report a simple but effective approach to constructing pH-responsive peptide assembly containing unnatural ionic amino acids with an aliphatic tertiary amine side chain. Through a combined experimental and computational investigation, we demonstrate that these residues can be accommodated and stabilized within the internal hydrophobic compartment of the peptide assembly. The hydrophobic microenvironment shifts their pKa significantly from a basic pH typically found for free amines to a more biologically relevant pH in the weakly acidic range. The pH-induced ionization and ionization-dependent self-assembly and disassembly are thoroughly investigated and correlated with the biological activity of the assembly. This new approach has unique advantages in tuning the pH-responsiveness of self-assembled peptides across a large pH range in a complex biological environment. We anticipate the ionizable amino acids developed here can be widely applicable to the synthesis and self-assembly of many amphiphilic peptides with endowed pH-responsive properties to enhance their biological activities toward applications ranging from targeted therapeutic delivery to proton transport.

Effects of poly-(lactide-co-glycolide) nanoparticles on electrophysiological properties of enteroendocrine cells.

PLGA nanoparticles are widely used to deliver pharmacological compounds and genes to a variety of cell types. Despite the fact that many of these cells types depend critically on ion channel activity to function normally, there have been no studies on the effect of nanoparticles on the ion channel activity. To this end, we have investigated the effect of nanoparticles on cholecystokinin (CCK)-releasing enteroendocrine cell (EEC) line STC-1. It has been shown that regulation of CCK release from STC-1 cells in response to food depends on the normal electrogenic properties of these cells, including the activity of voltage-gated calcium and potassium channels. Due to the importance of voltage-gated ion channels in the normal physiological responses of STC-1 cells, we performed electrophysiological (patch clamp) experiments to assess the effects of PLGA nanoparticles on the voltage-gated calcium and potassium channels. Whole-cell patch clamp recordings on STC-1 cells containing 100 nm nanoparticles show no macroscopic differences in calcium and potassium channel activity. Additional experiments determined that the activation, inactivation, and use-dependent inactivation of these voltage-gated ion channels did not have any significant effect of nanoparticles on these basic biophysical properties. Lastly, we have examined the effects of PLGA nanoparticles on stimulus-induced rise in intracellular calcium concentration in STC-1 cells, which is necessary for release of CCK. Our data demonstrate that the use of PLGA nanoparticles did not alter the electrophysiological properties of STC-1 cells and supports the use of PLGA nanoparticles as an attractive option for delivering pharmaceuticals/genes to cells of the digestive system that might eventually prove useful for reducing appetite/food intake and in treatment of various gastrointestinal illnesses.

Synthesis and characterization of a novel pH-responsive drug-releasing nanocomposite hydrogel for skin cancer therapy and wound healing.

Local skin cancer recurrence occurs in ∼12% of the patients post-surgery due to persistent growth of residual cancer cells. Wound infection is another significant complication following surgery. We report a novel in situ-forming nanocomposite hydrogel (NCH) containing PLGA-carboxymethyl chitosan nanoparticles (186 nm) for localized pH-responsive skin cancer therapy and wound healing. This injectable hydrogel, comprising of a citric acid-derived polymer backbone, gelled within 5 minutes, and demonstrated excellent swelling (283% of dry weight) and compressive strengths (∼5.34 MPa). Nanoparticle incorporation did not significantly affect hydrogel properties. The NCH effluents were cytocompatible with human dermal fibroblasts at 500 µg ml-1 concentration and demonstrated pH-dependent drug release and promising therapeutic efficacy against A431 and G361 skin cancer cells in vitro. Significant zones of inhibition were observed in S. aureus and E. coli cultures on NCH treatment, confirming its antibacterial properties. Our studies show that the pH-responsive NCH can be potentially used for adjuvant skin cancer treatment and wound healing.

Mussel-inspired bioadhesives in healthcare: design parameters, current trends, and future perspectives.

Mussels are well-known for their extraordinary capacity to adhere onto different surfaces in various hydrophillic conditions. Their unique adhesion ability under water or in wet conditions has generated considerable interest towards developing mussel inspired polymeric systems that can mimic the chemical mechanisms used by mussels for their adhesive properties. Catechols like 3,4-dihydroxy phenylalanine (DOPA) and their biochemical interactions have been largely implicated in mussels' strong adhesion to various substrates and have been the centerpoint of research and development efforts towards creating superior tissue adhesives for surgical and tissue engineering applications. In this article, we review bioadhesion and adhesives from an engineering standpoint, specifically the requirements of a good tissue glue, the relevance that DOPA and other catechols have in tissue adhesion, current trends in mussel-inspired bioadhesives, strategies to develop mussel-inspired tissue glues, and perspectives for future development of these materials.

Glutathione-responsive biodegradable polyurethane nanoparticles for lung cancer treatment.

Lung cancer is one of the major causes of cancer-related deaths worldwide. Stimuli-responsive polymers and nanoparticles, which respond to exogenous or endogenous stimuli in the tumor microenvironment, have been widely investigated for spatiotemporal chemotherapeutic drug release applications for cancer chemotherapy. We developed glutathione (GSH)-responsive polyurethane nanoparticles (GPUs) using a GSH-cleavable disulfide bond containing polyurethane that responds to elevated levels of GSH within lung cancer cells. The polyurethane nanoparticles were fabricated using a single emulsion and mixed organic solvent method. Cisplatin-loaded GSH-sensitive nanoparticles (CGPU) displayed a GSH-dose dependent release of cisplatin. In addition, a significant reduction in in vitro survival fraction of A549 lung cancer cells was observed compared to free cisplatin of equivalent concentration (survival fraction of ~0.5 and ~0.7, respectively). The in vivo biodistribution studies showed localization of fluorescently labeled GPUs (~7% of total injected dose per gram tissue) in the lung tumor regions after mouse-tail IV injections in xenograft A549 lung tumor models. The animals exposed to CGPUs also exhibited the inhibition of lung tumor growth compared to animals administered with saline (tumor growth rate of 1.5 vs. 13 in saline) and free cisplatin (tumor growth rate of 5.9) in mouse xenograft A549 lung tumor models within 14 days. These nanoparticles have potential to be used for on-demand drug release for an enhanced chemotherapy to effectively treat lung cancer.

A Biocompatible and Near-Infrared Liposome for In Vivo Ultrasound-Switchable Fluorescence Imaging.

Fluorescence imaging is a remarkable tool for molecular targeting and multicolor imaging, but it suffers from low resolution in centimeter-deep tissues. The recently developed ultrasound-switchable fluorescence (USF) imaging has overcome this challenge and achieved in vivo imaging in a mouse with help from the indocyanine green (ICG) dye encapsulated poly(N-isopropylacrylamide) (ICG-PNIPAM) contrast agent. However, the ICG-PNIPAM has shortcomings, such as concerns about cytotoxicity and blueshifted excitation and emission spectra. This study introduces a newly developed ICG-encapsulated liposome to broaden the contrast agent selection for USF imaging and resolve the issues mentioned above. The emission peak of the ICG-liposome is 836 nm with excellent biostability and USF imaging capability. Furthermore, the cell viability test verifies the low cytotoxicity feature. Eventually, both ex vivo and in vivo USF imaging are successfully achieved and 3D USF images are acquired. The ex vivo result confirms that the ICG-liposome maintains the thermoresponsive characteristic at the right lobe of the liver and is able to conduct the USF imaging. The further in vivo USF imaging demonstrates that although the whole liver emitted fluorescence, only the right lobe of the liver contains the working ICG-liposome.

Factorial analyses of photopolymerizable thermoresponsive composite hydrogels for protein delivery.

A smart protein delivery system for wound healing applications was developed using composite nanoparticle hydrogels that can release protein in a temperature-responsive manner. This system can also be formed in situ in the presence of ultraviolet light and Irgacure 2959 photoinitiator. The system consists of temperature-sensitive poly(N-isopropylacrylamide-co-acrylamide) (PNIPAM-AAm) nanoparticles embedded in a poly(ethylene glycol) diacrylate (PEGDA) matrix. A factorial analysis was performed to evaluate the effects of PEGDA concentration (10% and 15% w/v) and PEGDA molecular weight (MW; 3.4 kDa and 8 kDa), as well as PNIPAM-AAm nanoparticle concentration (2% and 4% w/v) and temperature (23 degrees C and 40 degrees C) on the protein release profiles and swelling ratios of the hydrogels. Results indicate that PNIPAM-AAm nanoparticle concentration and temperature were the most important factors affecting the protein release during the burst release phase. Additionally, PEGDA MW was the most important factor affecting the protein release in the plateau region. It was also important in controlling the hydrogel swelling ratio. A dual-layered hydrogel was further developed to produce a protein delivery system with a better sustained release. These findings have improved our understanding of the composite hydrogel systems and will help in tailoring future systems with desired release profiles. FROM THE CLINICAL EDITOR: A smart protein delivery system for wound healing applications using composite nanoparticle hydrogels that can release protein in a temperature-responsive manner is reported in this paper. Systems like this may aid in optimal would healing in the surgical and trauma-related settings.

Scaffold-based lung tumor culture on porous PLGA microparticle substrates.

Scaffold-based cancer cell culture techniques have been gaining prominence especially in the last two decades. These techniques can potentially overcome some of the limitations of current three-dimensional cell culture methods, such as uneven cell distribution, inadequate nutrient diffusion, and uncontrollable size of cell aggregates. Porous scaffolds can provide a convenient support for cell attachment, proliferation and migration, and also allows diffusion of oxygen, nutrients and waste. In this paper, a comparative study was done on porous poly (lactic-co-glycolic acid) (PLGA) microparticles prepared using three porogens-gelatin, sodium bicarbonate (SBC) or novel poly N-isopropylacrylamide [PNIPAAm] particles, as substrates for lung cancer cell culture. These fibronectin-coated, stable particles (19-42 µm) supported A549 cell attachment at an optimal cell seeding density of 250,000 cells/ mg of particles. PLGA-SBC porous particles had comparatively larger, more interconnected pores, and favored greater cell proliferation up to 9 days than their counterparts. This indicates that pore diameters and interconnectivity have direct implications on scaffold-based cell culture compared to substrates with minimally interconnected pores (PLGA-gelatin) or pores of uniform sizes (PLGA-PMPs). Therefore, PLGA-SBC-based tumor models were chosen for preliminary drug screening studies. The greater drug resistance observed in the lung cancer cells grown on porous particles compared to conventional cell monolayers agrees with previous literature, and indicates that the PLGA-SBC porous microparticle substrates are promising for in vitro tumor or tissue development.

Nanoparticle eluting-angioplasty balloons to treat cardiovascular diseases.

Nanoparticles (NPs) can be used to locally deliver anti-restenosis drugs when they are infused directly to the injured arteries after intervention procedures such as angioplasty. However, the efficacy of transferring NPs via infusion to the arterial wall is limited, at least partially, due to poor NP retention on the inner artery wall. To improve NP retention, angioplasty balloons coated with drug-loaded NPs were fabricated via either layer-by-layer (LbL) electrostatic coating or acrylic-based hydrogel (AAH) coating techniques. Three types of NPs, namely poly (lactide-co-glycolide) (PLGA), biodegradable photo-luminescent PLGA and urethane doped polyester were studied. The transfer efficacy of NPs from various coatings to the arterial wall were further evaluated to find the optimal coating conditions. The ex vivo NP transfer studies showed significantly more NPs being transferred to the rat arterial wall after the angioplasty procedure by the AAH coating (95% transfer efficiency) compared to that of the LbL technique (60%) and dip coating (20%) under flow conditions (10 dyn/cm2). Our results suggest that the AAH coating of drug-loaded NPs on the angioplasty balloon could potentially provide superior retention of drug-loaded NPs onto the arterial wall for a better local delivery of drug-loaded NPs to effectively treat arterial diseases.

Biodegradable Nanoparticles Enhanced Adhesiveness of Mussel-Like Hydrogels at Tissue Interface.

Popular bioadhesives, such as fibrin, cyanoacrylate, and albumin-glutaraldehyde based materials, have been applied for clinical applications in wound healing, drug delivery, and bone and soft tissue engineering; however, their performances are limited by weak adhesion strength and rapid degradation. In this study a mussel-inspired, nanocomposite-based, biodegradable tissue adhesive is developed by blending poly(lactic-co-glycolic acid) (PLGA) or N-hydroxysuccinimide modified PLGA nanoparticles (PLGA-NHS) with mussel-inspired alginate-dopamine polymer (Alg-Dopa). Adhesive strength measurement of the nanocomposites on porcine skin-muscle constructs reveals that the incorporation of nanoparticles in Alg-Dopa significantly enhances the tissue adhesive strength compared to the mussel-inspired adhesive alone. The nanocomposite formed by PLGA-NHS nanoparticles shows higher lap shear strength of 33 ± 3 kPa, compared to that of Alg-Dopa hydrogel alone (14 ± 2 kPa). In addition, these nanocomposites are degradable and cytocompatible in vitro, and elicit in vivo minimal inflammatory responses in a rat model, suggesting clinical potential of these nanocomposites as bioadhesives.

Bacterial sensitivity assessment of multifunctional polymeric coatings for airway stents.

Current interventional technology for pediatric airway obstruction consists of cardiovascular stents and silicon tubes. These devices are composed of permanent materials that have limitations in biocompatibility and mechanical properties that make them controversial for used in pediatrics. Bioresorbable stents offer a temporary intervention that dissolves in the body over time and can serve as a platform for local drug delivery. Here we investigate a novel approach to use an antibiotic, ciprofloxacin, as a polymerization initiator to synthesize poly(ciprofloxacin fumaric acid) (PCFA) and then a second polymer using gadodiamide as an initiator to synthesize poly(gadodiamide ciprofloxacin fumaric acid) (PGCFA). Polymer structure, degradation, thermal properties, and rheological behavior were analyzed. Ciprofloxacin released was determined and polymer degradation extracts were used in bacterial sensitivity assessments with four common airway pathogens. PCFA and PGCFA polymers and drug release properties were compared to our previously published polymer poly(fumaric acid) (PFA). These novel polymers enable new possibilities as coatings for bioresorbable biomedical applications that require antibiotic resistance and imaging capabilities. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2153-2161, 2017.

A combined strategy to reduce restenosis for vascular tissue engineering applications.

Biodegradable polymers including poly(l-lactic acid) (PLLA) have been used to develop cardiovascular prostheses such as vascular grafts and stents. However, implant-associated thrombosis, inflammation, and restenosis are still major obstacles for the utility of these devices. The lack of an endothelial cell (EC) lining (endothelialization) on the implants and the responses of the immune systems toward the implants have been associated with these complications. In our research strategy, we have combined the drug delivery principle with the strategies of tissue engineering, the controlled release of anti-inflammation drugs and enhanced endothelialization, to reduce the implant-associated adverse responses. We first integrated curcumin, an anti-inflammatory drug and anti-smooth muscle cell (SMC) proliferative drug, with PLLA. This curcumin-loaded PLLA material was then modified using adsorptive coating of adhesive proteins such as fibronectin, collagen-I, vitronectin, laminin, and matrigel to improve the endothelial cell (EC) adhesion and proliferation, and ECs were seeded on top of these modified surfaces. Our results showed steady drug release kinetics over the period of 50 days from curcumin-loaded PLLA materials. Additionally, integration of curcumin in PLLA increased the roughness of the scaffold at the nanometric scale using an atomic force microscopic analysis. Moreover, coating with fibronectin on curcumin-loaded PLLA surfaces gave the highest EC adhesion and proliferation compared to other adhesive proteins using PicoGreen DNA assays. The ability of our strategy to release the curcumin for producing anti-inflammation and anti-proliferation responses and to improve EC adhesion and growth after EC seeding suggests this strategy may reduce implant-associated adverse responses and be a better approach for vascular tissue engineering applications.

Development of a temperature-sensitive composite hydrogel for drug delivery applications.

To develop materials with improved controllability and specificity, we have investigated composite hydrogels with temperature-sensitive properties using photo cross-linking. Specifically, our novel composite materials are composed of nanoparticles made of poly(N-isopropylacrylamide) (PNIPAAm), temperature-sensitive hydrogels, and a photo cross-linker, poly(ethylene glycol) diacrylate (PEGDA). PNIPAAm particles were synthesized by emulsion polymerization and by varying concentration of four main factors: monomers (N-isopropylacrylamide), cross-linkers (N,N'-methylenebisacrylamide), surfactants (sodium dodecyl sulfate, SDS), and initiators (potassium persulfate). We found that the surfactant, SDS, was the most important factor affecting the particle size using the factorial design analysis. Additionally, both nano- and micro-PNIPAAm particles had excellent loading efficiency (>80% of the incubated bovine serum albumin (BSA)), and their release kinetics expressed an initial burst effect followed by a sustained release over time. Furthermore, BSA-loaded PNIPAAm nanoparticles were used to form three-dimensional gel networks by means of a photocuring process using a photo cross-linker, PEGDA, and a photoinitiator, Irgacure-2959 (I-2959). Results from scanning electron microscopy and in vitro BSA release studies from these hydrogels demonstrated that PNIPAAm nanoparticles were embedded inside the PEG polymeric matrix and the composite material was able to release BSA in response to changes in temperature. These PNIPAAm nanoparticle hydrogel networks may have advantages in applications of controlled drug delivery systems because of their temperature sensitivity and their ability of in situ photopolymerization to localize at the specific region in the body.