Aggregation and Gelation Behavior of Stereocomplexed Four-Arm PLA-PEG Copolymers Containing Neutral or Cationic Linkers

Poly(lactide) (PLA) and poly(ethylene glycol) (PEG)-based hydrogels were prepared by mixing phosphate buffer saline (PBS, pH 7.4) solutions of four-arm (PEG-PLA)₂-R-(PLA-PEG)₂ enantiomerically pure copolymers having the opposite chirality of the poly(lactide) blocks. Dynamic Light Scattering, rheology measurements, and fluorescence spectroscopy suggested that, depending on the nature of the linker R, the gelation process followed rather different mechanisms. In all cases, mixing of equimolar amounts of the enantiomeric copolymers led to micellar aggregates with a stereocomplexed PLA core and a hydrophilic PEG corona. Yet, when R was an aliphatic heptamethylene unit, temperature-dependent reversible gelation was mainly induced by entanglements of PEG chains at concentrations higher than 5 wt.%. When R was a linker containing cationic amine groups, thermo-irreversible hydrogels were promptly generated at concentrations higher than 20 wt.%. In the latter case, stereocomplexation of the PLA blocks randomly distributed in micellar aggregates is proposed as the major determinant of the gelation process.

Multi-functional polymeric micelles for chemotherapy-based combined cancer therapy

Currently, the therapeutic performance of traditional mono-chemotherapy on cancers remains unsatisfactory because of the tumor heterogeneity and multidrug resistance. In light of intricate tumor structures and distinct tumor microenvironments (TMEs), combinational therapeutic strategies with multiple anticancer drugs from different mechanisms can synergistically optimize the outcomes and concomitantly minimize the adverse effects during the therapy process. Extensive research on polymeric micelles (PMs) for biomedical applications has revealed the growing importance of nanomedicines for cancer therapy in the recent decade. Starting from traditional simple delivery systems, PMs have been extended to multi-faceted therapeutic strategies. Here we review and summarize the most recent advances in combinational therapy based on multifunctional PMs including a combination of multiple anticancer drugs, chemo-gene therapy, chemo-phototherapy and chemo-immunotherapy. The design approaches, action mechanisms and therapeutic applications of these nanodrugs are summarized. In addition, we highlight the opportunities and potential challenges associated with this promising field, which will provide new guidelines for advanced combinational cancer chemotherapy.

Folated pH-degradable nanogels for the simultaneous delivery of docetaxel and an IDO1-inhibitor in enhancing cancer chemo-immunotherapy

Floated pH-degradable PVA nanogels (FA-NGs) are developed for simultaneous delivery of DTX and IDO1-inhibitor N9 to enhance cancer chemo-immunotherapy.

Microstructured Photo-Crosslinked Poly(Trimethylene Carbonate) for Use in Soft Lithography Applications: A Biodegradable Alternative for Poly(Dimethylsiloxane)

Photo-crosslinkable poly(trimethylene carbonate) (PTMC) macromers were used to fabricate microstructured surfaces. Microstructured PTMC surfaces were obtained by hot embossing the macromer against structured silicon masters and subsequent photo-crosslinking, resulting in network formation. The microstructures of the master could be precisely replicated, limiting the shrinkage. Microstructured PTMC was investigated for use in two different applications: as stamping material to transfer a model protein to another surface and as structured substrate for cell culture. Using the flexible and elastic materials as stamps, bovine serum albumin labelled with fluorescein isothiocyanate was patterned on glass surfaces. In cell culture experiments, the behavior of human mesenchymal stem cells on nonstructured and microstructured PTMC surfaces was investigated. The cells strongly adhered to the PTMC surfaces and proliferated well. Compared to poly(dimethylsiloxane) (PDMS), which is commonly used in soft lithography, the PTMC networks offer significant advantages. They show better compatibility with cells, are biodegradable, and have much better mechanical properties. Both materials are transparent, flexible, and elastic at room temperature, but the tear resistance of PTMC networks is much higher than that of PDMS. Thus, PTMC might be an alternative material to PDMS in the fields of biology, medicine, and tissue engineering, in which microfabricated devices are increasingly being applied.

Improved Adhesion and Proliferation of Human Endothelial Cells on Polyethylene Precoated with Monoclonal Antibodies Directed against Cell Membrane Antigens and Extracellular Matrix Proteins

Endothelial cell seeding may improve the patency of synthetic vascular grafts provided that platelet reactivity of non-endothelialized sites is not increased. We have investigated if surface-adsorbed monoclonal antibodies directed against endothelial cell membrane proteins and against extracellular matrix proteins promote the adhesion and proliferation of cultured human endothelial cells, without causing platelet deposition at non-endothelialized sites. Adhesion of endothelial cells onto polyethylene coated with monoclonal antibodies directed against endothelial cell-specific membrane antigens, integrin receptors and glycoprotein CD31 was equal to or higher than adhesion onto fibronectin-coated polyethylene. Endothelial cells did not proliferate on these surface-adsorbed antibodies. However, pre-coating of polyethylene with mixtures of endothelial cell-specific monoclonal antibodies and monoclonal antibodies directed against fibronectin or von Willebrand factor, resulted in relatively high adhesion and optimal proliferation. Platelet reactivity of the polyethylene surface was found to significantly increase after adsorption of fibronectin, endothelial cell-specific monoclonal antibody or its Fc fragments. In contrast, adsorption of F(ab')2 fragments of endothelial cell-specific monoclonal antibody did not promote platelet deposition. Therefore, it is concluded that coating of vascular graft materials with mixtures of F(ab')2 fragments of monoclonal antibodies specifically directed against endothelial cells and against extracellular matrix proteins may be an effective way to both promote the growth of seeded endothelial cells and limit platelet-graft interaction.

Bioresponsive functional nanogels as an emerging platform for cancer therapy

INTRODUCTION

Bioresponsive nanogels with a crosslinked three-dimensional structure and an aqueous environment that undergo physical or chemical changes including swelling and dissociation in response to biological signals such as mild acidity, hyperthermia, enzymes, reducing agents, reactive oxygen species (ROS), and adenosine-5'-triphosphate (ATP) present in tumor microenvironments or inside cancer cells have emerged as an appealing platform for targeted drug delivery and cancer therapy.

AREAS COVERED

This review highlights recent designs and development of bioresponsive nanogels for facile loading and triggered release of chemotherapeutics and biotherapeutics. The in vitro and in vivo antitumor performances of drug-loaded nanogels are discussed.

EXPERT OPINION

Bioresponsive nanogels with an excellent stability and safety profile as well as fast response to biological signals are unique systems that mediate efficient and site-specific delivery of anticancer drugs, in particular macromolecular drugs like proteins, siRNA and DNA, leading to significantly enhanced tumor therapy compared with the non-responsive counterparts. Future research has to be directed to the development of simple, tumor-targeted and bioresponsive multifunctional nanogels, which can be either constructed from natural polymers with intrinsic targeting ability or functionalized with targeting ligands. We anticipate that rationally designed nanotherapeutics based on bioresponsive nanogels will become available for future clinical cancer treatment.

ABBREVIATIONS

AIE, aggregation-induced emission; ATP, adenosine-5'-triphosphate; ATRP, atom transfer radical polymerization; BSA, bovine serum albumin; CBA, cystamine bisacrylamide; CC, Cytochrome C; CDDP, cisplatin; CT, computed tomography; DC, dendritic cell; DiI, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate; DOX, doxorubicin; dPG, dendritic polyglycerol; DTT, dithiothreitol; EAMA, 2-(N,N-diethylamino)ethyl methacrylate; EPR, enhanced permeability and retention; GrB, granzyme B; GSH, glutathione tripeptide; HA, hyaluronic acid; HAase, hyaluronidases; HCPT, 10-Hydroxycamptothecin; HEP, heparin; HPMC, hydroxypropylmethylcellulose; LBL, layer-by-layer; MTX, methotrexate; NCA, N-carboxyanhydride; OVA, ovalbumin; PAH, poly(allyl amine hydrochloride); PBA, phenylboronic acid; PCL, polycaprolactone; PDEAEMA, poly(2-diethylaminoethyl methacrylate); PDGF, platelet derived growth factor; PDPA, poly(2-(diisopropylamino)ethyl methacrylate); PDS, pyridyldisulfide; PEG, poly(ethylene glycol); PEGMA, polyethyleneglycol methacrylate; PEI, polyethyleneimine; PHEA, poly(hydroxyethyl acrylate); PHEMA, poly(2-(hydroxyethyl) methacrylate; PNIPAM, poly(N-isopropylacrylamide); PMAA, poly(methacrylic acid); PPDSMA, poly(2-(pyridyldisulfide)ethyl methacrylate); PTX, paclitaxel; PVA, poly(vinyl alcohol); QD, quantum dot; RAFT, reversible addition-fragmentation chain transfer; RGD, Arg-Gly-Asp peptide; ROP, ring-opening polymerization; ROS, reactive oxygen species; TMZ, temozolomide; TRAIL, tumor necrosis factor-related apoptosis inducing ligand; VEGF, vascular endothelial growth factor.

Experimental Myringoplasty

Artificial eardrums made from biodegradable poly(D, L-lactic acid), poly(glycolic acid) and poly(ß-benzyl-L-aspartate-co-L-leucine) 50/50, and made from the microporous poly(tetrafluoroethylene) and bisphenol-A poly(carbonate) membranes were implanted into the ear and as a reference subcutaneously in rats.

The implants were histologically examined for periods up to one year. From the biodegradable polymers studied the poly(ß-benzyl-L-aspartate-co-L-leucine) 50/50 evoked the least tissue reaction and the newly formed tympanic membranes are the best in terms of thickness and overall integrity. The microporous poly(tetrafluoroethylene) membrane can be considered as a valuable support for the formation of a reinforced tympanic membrane.

The Effect of Radiolabeling of Human Fibrinogen on Its Adsorption Behaviour on a Polystyrene Surface

Human fibrinogen (HFB) was labeled with different radioactive labels (Technetium −99m and Iodine −125) in various ways. Characterization by chromatographic and electrophoretic methods did not show differences between the labeled and the nonlabeled proteins.

The effect of the label and the labeling method on the adsorption behaviour of 99mTc and 125l labeled HFB at a polystyrene surface was investigated.

In all cases labeled HFB showed preferential adsorption as compared to nonlabeled HFB. The preferential adsorption was expressed in terms of a factor ø (van der Scheer et al. 1978a), which will be 1, when no preferential adsorption occurs. 99mTc – and 125| – HFB showed ø values from 1.48 – 1.88. It is concluded that only meaningful adsorption experiments with labeled proteins can be performed when the possible occurrence of preferential adsorption has been investigated by appropriate methods. The results of prior work on protein adsorption at biomaterials using radiolabeled proteins have to be reconsidered.

Tissue Regenerating Capacity of Carbodiimide-Crosslinked Dermal Sheep Collagen during Repair of the Abdominal Wall

In future, the function of collagen-based biomaterials as temporary scaffolds for the generation of new tissue may be emphasized. In this study the function of dermal sheep collagen (DSC) crosslinked with carbodiimide (ENDSC) as repair material for abdominal wall defects in rats was compared with that of commercial hexamethylenediisocyanate-crosslinked HDSC. The results indicate that early after implantation both ENDSC and HDSC functioned well as a matrix for cellular ingrowth. However during further implantation HDSC soon degraded resulting in herniations, while ENDSC showed a delay in the degradation time of at least 20 weeks. ENDSC thereby enabled collagen new-formation and functioned as a guidance for muscle overgrowth. These results are very promising concerning the problem of the ongoing foreign body reaction with continuing risk of implant rejection observed in clinical practice with non-degradable materials.

Reduction-responsive core-crosslinked hyaluronic acid-b-poly(trimethylene carbonate-co-dithiolane trimethylene carbonate) micelles: synthesis and CD44-mediated potent delivery of docetaxel to triple negative breast tumor in vivo

Docetaxel-loaded core crosslinked HA-P(TMC-DTC) micelles show high targetability to CD44-overexpressing MDA-MB-231 breast tumor and effectively inhibit tumor growth.

Endothelial Cell Seeding on Crosslinked Collagen: Effects of Crosslinking on Endothelial Cell Proliferation and Functional Parameters

Endothelial cell seeding, a promising method to improve the performance of small-diameter vascular grafts, requires a suitable substrate, such as crosslinked collagen. Commonly used crosslinking agents such as glutaraldehyde and formaldehyde cause, however, cytotoxic reactions and thereby hamper endothelialization of currently available collagen-coated vascular graft materials.

The aim of this study was to investigate the effects of an alternative method for crosslinking of collagen, using N-(3-dimethylaminopropyl)-N’-ethylcarbodiimide (EDC) in combination with N-hydroxysuccinimide (NHS), on various cellular functions of human umbilical vein endothelial cells (HUVECs) in vitro. Compared to non-crosslinked type I collagen, proliferation of seeded endothelial cells was significantly increased on EDC/NHS-crosslinked collagen. Furthermore, higher cell numbers were found with increasing crosslink densities. Neither the morphology of the cells nor the secretion of prostacyclin (PGI2), von Willebrand factor (vWF), tissue plasminogen activator (t-PA) and plasminogen activator inhibitor (PAI-1) was affected by the crosslink density of the collagen substrate. Therefore, EDC/NHScrosslinked collagen is candidate substrate for in vivo application such as endothelial cell seeding of collagen-coated vascular grafts.

Endothelialization of Crosslinked Albumin-heparin Gels

Crosslinked gels of albumin as well as heparinized albumin gels, potential sealants of prosthetic vascular grafts, were studied with regard to in vitro stability, binding of basic fibroblast growth factor (bFGF) and cellular interactions. A small percentage of the heparin present in these gels, was released during storage in SDS solution. During storage in cell culture medium at 37° C, heparin release was 21-25 percent. Release of albumin did not occur.

Human umbilical vein endothelial cells (HUVECs) rapidly adhered and subsequently spread on (heparinized) albumin gels, but proliferation was only observed if heparin was present in the gel.

Binding of 125I-bFGF to heparinized albumin gel was 35 percent higher than to non-heparinized albumin gel. Growth of HUVECs occurred only on heparinized albumin gel loaded with bFGF and not on bFGF-loaded albumin gel.

The number of platelets deposited under stationary conditions onto heparinized albumin gel was about twice the number found on nonheparinized albumin gel. Seeding of HUVECs on heparinized albumin gel, significantly reduced the number of platelets adhering to this surface. Moreover, no spreading of platelets was observed on substrates seeded with HUVECs.

It can be concluded that crosslinked gels of albumin to which heparin is immobilized, are candidate sealants for prosthetic vascular grafts and suitable substrates for endothelial cell seeding.

cRGD/TAT Dual-Ligand Reversibly Cross-Linked Micelles Loaded with Docetaxel Penetrate Deeply into Tumor Tissue and Show High Antitumor Efficacy in Vivo

The application of cell-penetrating peptides like TAT for in vivo targeted delivery is limited because the penetration behavior is not cell-specific. Herein, we designed cRGD and TAT comodified cross-linkable micelles (cRGD/TAT CMs), in which the TAT peptide was shielded by relatively long poly(ethylene glycol) (PEG) chains. Docetaxel (DTX)-loaded cRGD/TAT CMs were very stable with minimal drug leakage under physiological conditions, whereas rapid DTX release took place in a reductive environment. Flow cytometry showed that the cRGD/TAT CMs with molar ratios of 20% cRGD and 10% TAT (cRGD20/TAT10 CMs) were selectively and efficiently taken up by α_νβ₃-overexpressing U87MG glioma cells, with 8.3-fold and 18.3-fold higher uptake than cRGD20 CMs and PEG CMs, respectively. DTX-loaded cRGD20/TAT10 CMs exhibited a high cytotoxicity in U87MG cells, leading to rapid apoptosis of the tumor cells. Uptake mechanism studies revealed that cRGD20/TAT10 CMs mainly employed the caveolae-mediated endocytotic pathway and efficiently escaped from the lysosomes. Notably, cRGD20/TAT10 CMs had a long circulating time of 6.25 h in vivo, due to cross-linking of the micelles and shielding of the TAT peptide. Moreover, DTX-loaded cRGD20/TAT10 CMs exhibited a significantly higher accumulation and deeper penetration in subcutaneous U87MG glioma tissue compared to cRGD20 CMs and PEG CMs, leading to superior antitumor efficacy in vivo. Therefore, this dual-ligand strategy provides an effective way to realize tumor-specific penetration and inhibition.

Drug-Coupled Poly(Amino Acids) as Polymeric Prodrugs

Biodegradable poly(α-amino acids) can serve as chemical carriers of active agents. The narcotic antagonist naltrexone and the anti-hypertensive minox idil were covalently coupled to polymer backbones based upon L-glutamic acid to give polymeric prodrugs. The synthesis and release characteristics of these two systems are reviewed. The rate of hydrolytic cleavage of the polymer-drug linkage should be much slower than the rate of diffusion through the polymer matrix; thus release rates approaching zero order can be achieved. In vitro and in vivo release studies demonstrate the potential for these types of polymeric delivery systems.

Poly(Amido Amine)s Containing Agmatine and Butanol Side Chains as Efficient Gene Carriers

A new type of bioreducible poly(amido amine) copolymer is synthesized by the Michael addition polymerization of cystamine bisacrylamide (CBA) with 4-aminobutylguanidine (agmatine, AGM) and 4-aminobutanol (ABOL). Since the positively charged guanidinium groups of AGM and the hydroxybutyl groups of ABOL in the side chains have shown to improve the overall transfection efficiency of poly(amido amine)s, it is hypothesized that poly(CBA-ABOL/AGM) synthesized at the optimal ratio of both components would result in high transfection efficiency and minimal toxicity. In this study, a series of the poly(CBA-ABOL/AGM) copolymers is synthesized as gene carriers. The polymers are characterized and luciferase transfection efficiencies of the polymers in various cell lines are investigated to select the ideal ratio between AGM and ABOL. The poly(CBA-ABOL/AGM) containing 80% AGM and 20% ABOL has shown the best transfection efficiency with the lowest cytotoxicity, indicating that this polymer is very promising as a potent and nontoxic gene carrier.

Biodegradable glycopolymer-b-poly(ε-caprolactone) block copolymer micelles: versatile construction, tailored lactose functionality, and hepatoma-targeted drug delivery

An illustration of versatile construction of biodegradable glycopolymer-PCL micelles with tailored LBA-functionality for hepatoma-targeted drug delivery.

Reductively degradable α-amino acid-based poly(ester amide)-graft-galactose copolymers: facile synthesis, self-assembly, and hepatoma-targeting doxorubicin delivery

Multifunctional nanoparticles mediate specific and efficient intracellular doxorubicin delivery to asialoglycoprotein receptor-overexpressing hepatoma cells.

Preparation of a designed poly(trimethylene carbonate) microvascular network by stereolithography

Designed flexible and elastic network structures are prepared by stereolithography using a photo-crosslinkable resin based on a poly(trimethylene carbonate) (PTMC) macromer with a molecular weight of 3150 g/mol. Physical properties and the compatibility with human umbilical vein endothelial cells (HUVECs) are evaluated. The hydrophobic networks are found to be flexible and elastic, with an E modulus of 7.9 ± 0.1 MPa, a tensile strength of 3.5 ± 0.1 MPa and an elongation at break of 76.7 ± 0.7%. HUVECs attach and proliferate well on the surfaces of the built structures. A three-dimensional microvascular network is designed to serve as a perfusable scaffold for tissue engineering. In the design, 5 generations of open channels each branch into 4 smaller channels yielding a microvascular region with a high density of capillaries. The overall cross-sectional area through which medium or blood can be perfused remains constant. These structures would ensure efficient nourishment of cells in a large volume of tissue. Built by stereolithography using the PTMC resin, the smallest channels of these structures have square cross-sectional areas, with inner widths of approximately 224 μm and wall thicknesses of approximately 152 μm. The channels are open, allowing water to perfuse the scaffold at 0.279 ± 0.006 mL/s at 80 mmHg and 0.335 ± 0.009 mL/s at 120 mmHg.

Biodegradable elastomers for biomedical applications and regenerative medicine

Synthetic biodegradable polymers are of great value for the preparation of implants that are required to reside only temporarily in the body. The use of biodegradable polymers obviates the need for a second surgery to remove the implant, which is the case when a nondegradable implant is used. After implantation in the body, biomedical devices may be subjected to degradation and erosion. Understanding the mechanisms of these processes is essential for the development of biomedical devices or implants with a specific function, for example, scaffolds for tissue-engineering applications. For the engineering and regeneration of soft tissues (e.g., blood vessels, cardiac muscle and peripheral nerves), biodegradable polymers are needed that are flexible and elastic. The scaffolds prepared from these polymers should have tuneable degradation properties and should perform well under long-term cyclic deformation conditions. The required polymers, which are either physically or chemically crosslinked biodegradable elastomers, are reviewed in this article.

WITHDRAWN: Vision, launch and early days of Journal of Controlled Release

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/10.1016/j.jconrel.2014.03.010. The duplicate article has therefore been withdrawn.

Glyco-nanoparticles with sheddable saccharide shells: a unique and potent platform for hepatoma-targeting delivery of anticancer drugs

Reduction-sensitive shell-sheddable glyco-nanoparticles were designed and developed based on poly(ε-caprolactone)-graft-SS-lactobionic acid (PCL-g-SS-LBA) copolymer for efficient hepatoma-targeting delivery of doxorubicin (DOX). PCL-g-SS-LBA was prepared by ring-opening copolymerization of ε-caprolactone and pyridyl disulfide carbonate followed by postpolymerization modification with thiolated lactobionic acid (LBA-SH) via thiol-disulfide exchange reaction. The dynamic light scattering (DLS) and transmission electron microscopy (TEM) showed that PCL-g-SS-LBA was self-assembled into monodisperse nanoparticles (SS-GNs) with a mean diameter of about 80 nm. SS-GNs while remaining stable under physiological conditions (37 °C, pH 7.4) were prone to rapid shell-shedding and aggregation in the presence of 10 mM dithiothreitol (DTT). DOX was loaded into SS-GNs with a decent loading content of 12.0 wt %. Notably, in vitro release studies revealed that about 80.3% DOX was released from DOX-loaded SS-GNs in 24 h under a reductive condition while low drug release (<21%) was observed for DOX-loaded PCL-g-LBA nanoparticles (reduction-insensitive control) under otherwise the same condition and for DOX-loaded SS-GNs under a nonreductive condition. The flow cytometry and confocal microscopy observations indicated that SS-GNs were efficiently taken up by asialoglycoprotein receptor (ASGP-R)-overexpressing HepG2 cells likely via a receptor-mediated endocytosis mechanism and DOX was released into the nuclei of cells following 4 h incubation. MTT assays showed that DOX-loaded SS-GNs exhibited a high antitumor activity toward HepG2 cells, which was comparable to free DOX and about 18-fold higher than their reduction-insensitive counterparts, while blank SS-GNs were nontoxic up to a tested concentration of 1.0 mg/mL. These shell-sheddable glyco-nanoparticles are promising for hepatoma-targeting chemotherapy.

Controlling the kinetic chain length of the crosslinks in photo-polymerized biodegradable networks

Biodegradable polymer networks were prepared by photo-initiated radical polymerization of methacrylate functionalized poly(D,L-lactide) oligomers. The kinetic chains formed in this radical polymerization are the multifunctional crosslinks of the networks. These chains are carbon-carbon chains that remain after degradation. If their molecular weight is too high these poly(methacrylic acid) chains can not be excreted by the kidneys. The effect of the photo-initiator concentration and the addition of 2-mercaptoethanol as a chain transfer agent on the molecular weight of the kinetic chains was investigated. It was found that both increasing the initiator concentration and adding 2-mercaptoethanol decrease the kinetic chain length. However, the effect of adding 2-mercaptoethanol was much larger. Some network properties such as the glass transition temperature and the swelling ratio in acetone are affected when the kinetic chain length is decreased.

Structure formation and hydrogen bonding in all-aliphatic segmented copolymers with uniform hard segments

Fully aliphatic segmented poly(ether ester amide) copolymers with uniform hard segments prepared by melt polycondensation of α,ω-hydroxyl end-functionalized polytetrahydrofuran and short glycine or β-alanine bisester-bisoxalamide units hold promise for biomedical applications. For polymers with the hard block contents varying from 10% to 27%, differential scanning calorimetry and atomic force microscopy reveal a highly phase-separated morphology, with ribbon-like nanocrystals dispersed in the soft segment matrix. To relate the polymer properties to the structure of the hard segment, the monomers were prepared and studied by optical and X-ray diffraction measurements. It was shown that the glycine and β-alanine carbonyl ester groups are tilted away from the oxalamide plane, which can affect the degradation rate via hydrolysis of the ester bond.

In situ forming reduction-sensitive degradable nanogels for facile loading and triggered intracellular release of proteins

In situ forming reduction-sensitive degradable nanogels were designed and developed based on poly(ethylene glycol)-b-poly(2-(hydroxyethyl) methacrylate-co-acryloyl carbonate) (PEG-P(HEMA-co-AC)) block copolymers for efficient loading as well as triggered intracellular release of proteins. PEG-P(HEMA-co-AC) copolymers were prepared with controlled Mn of 9.1, 9.5, and 9.9 kg/mol and varying numbers of AC units per molecule of 7, 9 and 11, respectively (denoted as copolymer 1, 2, and 3) by reversible addition-fragmentation chain transfer copolymerization. These copolymers were freely soluble in phosphate buffer but formed disulfide-cross-linked nanogels with defined sizes ranging from 72.5 to 124.1 nm in the presence of cystamine via ring-opening reaction with cyclic carbonate groups. The sizes of nanogels decreased with increasing AC units as a result of increased cross-linking density. Dynamic light scattering studies showed that these nanogels though stable at physiological conditions were rapidly dissociated in response to 10 mM dithiothreitol (DTT). Interestingly, FITC-labeled cytochrome C (FITC-CC) could be readily loaded into nanogels with remarkable loading efficiencies (up to 98.2%) and loading contents (up to 48.2 wt.%). The in vitro release studies showed that release of FITC-CC was minimal under physiological conditions but significantly enhanced under reductive conditions in the presence of 10 mM DTT with about 96.8% of FITC-CC released in 22 h from nanogel 1. In contrast, protein release from 1,4-butanediamine cross-linked nanogels (reduction-insensitive control) remained low under otherwise the same conditions. MTT assays showed that these nanogels were nontoxic to HeLa cells up to a tested concentration of 2 mg/mL. Confocal microscopy results showed that nanogel 1 delivered and released FITC-CC into the perinuclei region of HeLa cells following 8 h incubation. CC-loaded reductively degradable nanogels demonstrated apparently better apoptotic activity than free CC as well as reduction-insensitive controls. These in situ forming, surfactant and oil-free, and reduction-sensitive degradable nanogels are highly promising for targeted protein therapy.

Physical properties and erosion behavior of poly(trimethylene carbonate-co-ε-caprolactone) networks

Form-stable resorbable networks are prepared by gamma irradiating trimethylene carbonate (TMC)- and ε-caprolactone (CL)-based (co)polymer films. To evaluate their suitability for biomedical applications, their physical properties and erosion behavior are investigated. Homopolymer and copolymer networks that are amorphous at room temperature are flexible and rubbery with elastic moduli ranging from 1.8 ± 0.3 to 5.2 ± 0.4 MPa and permanent set values as low as 0.9% strain. The elastic moduli of the semicrystalline networks are higher and range from 61 ± 3 to 484 ± 34 MPa. The erosion behavior of (co)polymer networks is investigated in vitro using macrophage cultures, and in vivo by subcutaneous implantation in rats. In macrophage cultures, as well as upon implantation, a surface erosion process is observed for the amorphous (co)polymer networks, while an abrupt decrease in the rate and a change in the nature of the erosion process are observed with increasing crystallinity. These resorbable and form-stable networks with tuneable properties may find application in a broad range of biomedical applications.

Conference Scene: From innovative polymers to advanced nanomedicine: key challenges, recent progress and future perspectives

Recent developments in polymer-based controlled delivery systems have made a significant clinical impact. The second Symposium on Innovative Polymers for Controlled Delivery (SIPCD) was held in Suzhou, China to address the key challenges and provide up-to-date progress and future perspectives in the innovation of polymer-based therapeutics. At SIPCD, a stimulating panel discussion was introduced for the first time on “What is the future of nanomedicine?” This report highlights the most recent research and developments in biomedical polymers and nanomedicine made by 29 invited scientists from around the world, as well as important issues regarding clinical advancements of nanomedicine conferred during the panel discussion.

Redox and pH-responsive degradable micelles for dually activated intracellular anticancer drug release

Redox and pH dual-responsive biodegradable micelles were developed based on poly(ethylene glycol)-SS-poly(2,4,6-trimethoxybenzylidene-pentaerythritol carbonate) (PEG-SS-PTMBPEC) copolymer and investigated for intracellular doxorubicin (DOX) release. PEG-SS-PTMBPEC copolymer with an Mn of 5.0-4.1kg/mol formed micellar particles with an average diameter of 140nm and a low polydispersity of 0.12. DOX was loaded into PEG-SS-PTMBPEC micelles with a decent drug loading content of 11.3wt.%. The in vitro release studies showed that under physiological conditions only ca. 24.5% DOX was released from DOX-loaded micelles in 21h. The release of DOX was significantly accelerated at pH5.0 or in the presence of 10mM glutathione (GSH) at pH7.4, in which 62.8% and 74.3% of DOX was released, respectively, in 21h. The drug release was further boosted under 10mM GSH and pH 5.0 conditions, with 94.2% of DOX released in 10h. Notably, DOX release was also facilitated by 2 or 4h incubation at pH 5.0 and then at pH 7.4 with 10mM GSH, which mimics the intracellular pathways of endocytosed micellar drugs. Confocal microscopy observation indicated that DOX was delivered and released into the nuclei of HeLa cells following 8h incubation with DOX-loaded PEG-SS-PTMBPEC micelles, while DOX was mainly located in the cytoplasm for reduction-insensitive PEG-PTMBPEC controls. MTT assays revealed that DOX-loaded PEG-SS-PTMBPEC micelles had higher anti-tumor activity than reduction-insensitive controls, with low IC50 of 0.75 and 0.60μg/mL for HeLa and RAW 264.7 cells, respectively, following 48h incubation. PEG-SS-PTMBPEC micelles displayed low cytotoxicity up to a concentration of 1.0mg/mL. These redox and pH dual-bioresponsive degradable micelles have appeared as a promising platform for targeted intracellular anticancer drug release.