Yen-Chih Huang

Poly(glycerol-dodecanoate), a biodegradable polyester for medical devices and tissue engineering scaffolds

In this paper we describe the mechanical and biological features of a thermosetting polyester synthesized from glycerol and dodecanedioic acid named Poly-Glycerol-Dodecanoate (PGD). This polymer shows a glass transition temperature (T(g)) around 32 degrees C, and this accounts for its mechanical properties. At room temperature (21 degrees ) PGD behaves like a stiff elastic-plastic material, while at body temperature (37 degrees C), it shows a compliant non-linear elastic behavior. Together with biodegradability and biocompatibility PGD has distinct shape memory features. After the polymer is cured, no matter what the final configuration is, we can recover the original shape by heating PGD to temperatures of 32 degrees C and higher. The mechanical properties together with biocompatibility/biodegradability and shape memory features make PGD an attractive polymer for biomedical applications.

Thermal and pH Sensitive Multifunctional Polymer Nanoparticles for Cancer Imaging and Therapy.

In this study, we prepared novel poly(Glycerol malate co-dodecanedioate) (PGMD) NPs containing an imaging/hyperthermia agent (IR820) and a chemotherapeutic agent (doxorubicin, DOX). The PGMD polymer was prepared by thermal condensation. IR820 and DOX loaded PGMD NPs were prepared using the single oil emulsion technique. The size of the NPs measured was around 150 nm. Drug loading efficiency of DOX and IR820 was around 4% and 8%, respectively. An acidic environment (pH=5.0) induced higher DOX release as compared to pH=7.4. DOX release was also enhanced by exposure to laser, which increased the temperature to 42°C. Cytotoxicity of the drug loaded NPs was comparable in MES-SA but was higher in Dx5 cells compared to free drug (p<0.05). The combination of hyperthermia and chemotherapy improved cytotoxicity in both cell lines. The NP formulation significantly improved the plasma half-life of IR820 in mice after tail vein injection.

Near-infrared dye loaded polymeric nanoparticles for cancer imaging and therapy and cellular response after laser-induced heating

Summary Background: In the past decade, researchers have focused on developing new biomaterials for cancer therapy that combine imaging and therapeutic agents. In our study, we use a new biocompatible and biodegradable polymer, termed poly(glycerol malate co-dodecanedioate) (PGMD), for the synthesis of nanoparticles (NPs) and loading of near-infrared (NIR) dyes. IR820 was chosen for the purpose of imaging and hyperthermia (HT). HT is currently used in clinical trials for cancer therapy in combination with radiotherapy and chemotherapy. One of the potential problems of HT is that it can up-regulate hypoxia-inducible factor-1 (HIF-1) expression and enhance vascular endothelial growth factor (VEGF) secretion. Results: We explored cellular response after rapid, short-term and low thermal dose laser-IR820-PGMD NPs (laser/NPs) induced-heating, and compared it to slow, long-term and high thermal dose heating by a cell incubator. The expression levels of the reactive oxygen species (ROS), HIF-1 and VEGF following the two different modes of heating. The cytotoxicity of NPs after laser/NP HT resulted in higher cell killing compared to incubator HT. The ROS level was highly elevated under incubator HT, but remained at the baseline level under the laser/NP HT. Our results show that elevated ROS expression inside the cells could result in the promotion of HIF-1 expression after incubator induced-HT. The VEGF secretion was also significantly enhanced compared to laser/NP HT, possibly due to the promotion of HIF-1. In vitro cell imaging and in vivo healthy mice imaging showed that IR820-PGMD NPs can be used for optical imaging. Conclusion: IR820-PGMD NPs were developed and used for both imaging and therapy purposes. Rapid and short-term laser/NP HT, with a low thermal dose, does not up-regulate HIF-1 and VEGF expression, whereas slow and long term incubator HT, with a high thermal dose, enhances the expression of both transcription factors.

Force Characteristics of In Vivo Tissue-engineered Myocardial Constructs Using Varying Cell Seeding Densities

Experiments have been successfully performed culminating in functional, vascularized, three-dimensional cardiac muscle tissue. Past experience in tissue engineering has led us to the understanding that cell seeding density plays a critical role in the formation and function of both in vitro and in vivo engineered tissues. Therefore, to improve upon the mechanics of this model and to facilitate the formation of myocardial tissue with improved functional performance, we sought to optimize the seeding density of cardiomyocytes in these constructs. Neonatal cardiac myocytes were isolated from 2-day-old Fischer 344 rat hearts. Silicone chambers containing fibrin gel were seeded with varying numbers of cardiac cells (1, 5, 10, and 20 million). Control chambers were prepared using fibrin gel alone. All of the chambers were then implanted around the femoral vessels of isogenic rats. Six constructs per cell seeding density group were implanted. Histological and immunohistochemical evaluation was performed via hematoxylin and eosin, von Gieson, and alpha-sarcomeric actin staining protocols. Linear contractile force measurements were obtained for each construct following 4 weeks of in vivo implantation. After an implantation period of 4 weeks, the newly formed cardiac constructs contained within the chambers were harvested. The femoral vessels within the constructs were found to be patent in all cases. With direct electrical stimulation, the constructs were able to generate an average active force that varied depending on their seeding density. Constructs with seeding densities of 1, 5, 10, and 20 million cells produced an average active force of 208, 241, 151, and 108 microN, respectively. The control constructs did not generate any active force on electrical stimulation. This study demonstrates the in vivo survival, vascularization, organization, and function of transplanted myocardial cells. It is also apparent that cell seeding density plays a direct role in the force generation and mechanical properties of these engineered constructs. Among different groups using varying cell seeding densities, we found that the group with 5 million cells generated maximum active force.

Peptide modified polymer poly (glycerol- dodecanedioate co-fumarate) for efficient control of motor neuron differentiation

Neural tissue engineering is one of the most promising approaches for healing nerve damage, which bypasses the limits of contemporary conventional treatments. In a previous study, we developed a fibrous scaffold via electrospinning poly (glycerol dodecanedioate) (PGD) and gelatin that mimics the structure of a native extracellular matrix (ECM) for soft tissue engineering application. In this study, fumaric acid (FA) was incorporated into the PGD synthesis process, which produced a PGD derivative referred to as poly (glycerol dodecanedioate co-fumarate) (PGDF). This introduced a new functional group, a double bond, into the polymer thus providing new modification possibilities. Arg-Gly-Asp-Cys (RGDC) and laminin peptides were chosen as biomolecules to modify the fiber and facilitate cell attachment and differentiation efficiency. The release of FA into the medium was quantified to investigate the bioreactivity of the derived scaffolds. In combination with UV crosslinking, the developed PGDF fiber mats were able to withstand degradation processes for up to 2 months, which ensures that neural tissue engineering applications are viable. Cell viability and motor neuron differentiation efficiency were demonstrated to be significantly improved with the addition of FA, RGDC and laminin peptides.

Near-infrared imaging loaded polymeric nanoparticles: in vitro and in vivo studies

Introduction: Recent research has focused on developing new biomaterials for delivery of imaging agents and drugs. In our study, we report a new biocompatible and biodegradable polymer, termed poly(glycerol-co-malic-dodecanoate) (PGMD), which was then used for synthesis of nanoparticles (NPs) and loading of NIR dyes. Methods: The PGMD polymer was synthesized via thermal condensation method and was characterized by FTIR. The NPs were synthesized via o/w single emulsion technique. IR820 was chosen as the NIR dye. The loading efficiency of IR820 in PGMD NPs was measured by spectrophotometer. The release of IR820 was estimated with a spectrofluorometer in different pH phosphate buffered saline. The cytotoxicity of NPs was estimated through a Sulforhodamine B colorimetric assay. A biodistribution and pharmacokinetics study of the NPs versus free IR820 was performed in a murine model (n=12) after i.v. injection. Plasma samples were collected at time points 15-30-60 minutes and 24 hours. Organ samples were also collected and measured at the 24-hour time point. Results and Discussion: Void PGMD NPs and IR820-PGMD NPs had mean sizes around 90 nm and 110 nm, respectively. FTIR showed that polyester bonds were forming in the PGMD polymer. The release of IR820 was increased in acidic buffer (pH=5.0) as compared to neutral buffer (pH=7.4), indicating that the release of IR820 is controllable. Cellular uptake studies showed comparable fluorescence of IR820-PGMD NPs to free IR820 (5 μM) after 24-hour exposure. IR820-PGMD NPs induced significant cancer cell killing after laser exposure due to the photothermal effect of the dye. In vivo studies showed that the IR820 in NPs formulation has a longer plasma half-life than free IR820, providing longer imaging collection times for cancer diagnostics, and potentially widening the window for hyperthermia applications. Conclusion: We expect that ease of synthesis and good biocompatibility make PGMD a good candidate for numerous imaging agent and drug delivery applications. The IR820-PGMD NPs have the ability to be used for both imaging and hyperthermia purposes.

Theranostic Nanoparticles for Imaging and Therapy and Cellular Response after Laser-induced Heating

In our study, we use a new biocompatible and biodegradable polymer, which is termed poly(glycerol-co-malic-dodecanoate) (PGMD), for the synthesis of nanoparticles (NPs) and loading of Near-Infrared (NIR) dyes. IR820 was chosen for the purpose of imaging and hyperthermia (HT). One of the potential problems of hyperthermia (HT) is that HT can up-regulate hypoxia-inducible factor-1 (HIF-1) expression and enhance vascular endothelial growth factor (VEGF) secretion. We explored the cellular response after rapid, short-term and low thermal dose laser-IR820-PGMD NPs (laser/NP) induced-heating, and compared it to slow, long-term and high thermal dose heating using a cell incubator. The cytotoxicity of NPs after laser/NP HT resulted in higher cell killing compared to incubator HT. Reactive oxygen species (ROS), HIF-1, and VEGF level were highly elevated under incubator HT, but remained at the baseline level under the laser/NP HT. In vitro cell imaging and in vivo healthy mice imaging showed that IR820-PGMD NPs can be used for optical imaging. In conclusion, IR820-PGMD NPs were developed and used for both imaging and therapy purposes. Rapid and short-term laser/NP HT, with a low thermal dose, does not up-regulate HIF-1 and VEGF expression, whereas slow and long-term incubator HT, with a high thermal dose, enhances the expression of both transcription factors.