Past, present and future of biomedical applications of dextran-based hydrogels: A review

This review extensively surveys the biomedical applications of hydrogels containing dextran. Dextran has gained much attention as a biomaterial due to its distinctive properties such as biocompatibility, non-toxicity, water solubility and biodegradability. It has emerged as a critical constituent of hydrogels for biomedical applications including drug delivery devices, tissue engineering scaffolds and biosensor materials. The benefits, challenges and potential prospects of dextran-based hydrogels as biomaterials are highlighted in this review.

Vitamin-H Channeled Self-Therapeutic P-gp Inhibitor Curcumin-Derived Nanomicelles for Targeting the Tumor Milieu by pH- and Enzyme-Triggered Hierarchical Disassembly

An effective nanocarrier-mediated drug delivery to cancer cells primarily faces limitations like the presence of successive drug delivery barriers, insufficient circulation time, drug leakage, and decreased tumor penetration capacity. With the aim of addressing this paradox, a self-therapeutic, curcumin-derived copolymer was synthesized by conjugation with PEGylated biotin via enzyme- and acid-labile ester and acetal linkages. This copolymer is a prodrug of curcumin and self-assembles into ∼150-200 nm-sized nanomicelles; it is capable of encapsulating doxorubicin (DOX) and hence can be designated as self-therapeutic. pH- and enzyme-responsive linkages in the polymer skeleton assist in its hierarchical disassembly only in the tumor microenvironment. Further, the conjugation of biotin and poly(ethylene glycol) (PEG) imparts features of tumor specificity and improved circulation times to the nanocarrier. The dynamic light scattering (DLS) analysis supports this claim and demonstrates rapid swelling and disruption of micelles under acidic pH. UV-vis spectroscopy provided evidence of an accelerated acetal degradation at pH 4.0 and 5.0. The in vitro release studies revealed a controlled release of DOX under acidic conditions and curcumin release in response to the enzyme. The value of the combination index calculated on HepG2 cells was found to be <1, and hence, the drug pair curcumin and DOX acts synergistically for tumor regression. To prove the efficiency of acid-labile linkages and the prodrug strategy for effective cancer therapy, curcumin-derived polymers devoid of sensitive linkages were also prepared. The prodrug stimuli-responsive nanomicelles showed enhanced cell cytotoxicity and tumor penetration capability on HepG2 cells as well as drug-resistant MCF-7 cell lines and no effect on normal NIH/3T3 fibroblasts as compared to the nonresponsive micelles. The results were also supported by in vivo evidence on a hepatocellular carcinoma (HCC)-induced nude mice model. An evident decrease in MMP-2, MMP-9, and α-fetoprotein (AFP), the biomarkers specific to tumor progression, was observed along with metastasis upon treatment with the drug-loaded dual-responsive nanomicelles. These observations corroborated with the SGOT and SGPT data as well as the histoarchitecture of the liver tissue in mice.

Prospects of Delivering Natural Compounds by Polymer-Drug Conjugates in Cancer Therapeutics

Synthetic chemotherapeutics have played a crucial role in minimizing mostly palliative symptoms associated with cancer; however, they have also created other problems such as system toxicity due to a lack of specificity. This has led to the development of polymer-drug conjugates amongst other novel drug delivery systems. Most of the formulations designed using delivery systems consist of synthetic drugs and face issues such as drug resistance, which has already rendered drugs such as antibiotics ineffective. This is further exacerbated by toxicity due to long term use. Given these problems and the fact that conjugation of synthetic compounds to polymers has been relatively slow with no formulation on the market after a decade of extensive studies, the focus has shifted to using this platform with medicinal plant extracts to improve solubility, specificity and increase drug release of medicinal and herbal bioactives. In recent years, various plant extracts such as flavonoids, tannins and terpenoids have been studied extensively using this approach. The success of formulations developed using novel drug-delivery systems is highly dependent on the tumour microenvironment especially on the enhanced permeability and retention effect. As a result, the compromised lymphatic network and 'leaky' vasculature exhibited by tumour cells act as a guiding principle in the delivering of these formulations. This review focuses on the state of the polymer-drug conjugates and their exploration with natural compounds, the progress and difficulties thus far, and future directions concerning cancer treatment.

Self-assembly of amphiphilic copolymers containing polysaccharide: PISA versus nanoprecipitation, and the temperature effect

The self-assembly methods and the temperature have a considerable impact on the morphology of the resulting nanoobjects in the case of amphiphilic glycopolymers.

Preparation and application of dextran and its derivatives as carriers

As a natural and renewable biological macromolecule, dextran not only has excellent biodegradability, but also has good biocompatibility. Dextran and its derivatives are functional polymers for the construction of targeted drug delivery systems. Herein, the application of dextran as prodrug and nanoparticle/nanogel/microsphere/micelle carrier for targeting drug delivery system was summarized. It is clarified that dextran is an important biomaterial with application value.

Polymer scaffolds facilitate spinal cord injury repair

During the past decades, improving patient neurological recovery following spinal cord injury (SCI) has remained a challenge. An effective treatment for SCI would not only reduce fractured elements and isolate developing local glial scars to promote axonal regeneration but also ameliorate secondary effects, including inflammation, apoptosis, and necrosis. Three-dimensional (3D) scaffolds provide a platform in which these mechanisms can be addressed in a controlled manner. Polymer scaffolds with favorable biocompatibility and appropriate mechanical properties have been engineered to minimize cicatrization, customize drug release, and ensure an unobstructed space to promote cell growth and differentiation. These properties make polymer scaffolds an important potential therapeutic platform. This review highlights the recent developments in polymer scaffolds for SCI engineering. STATEMENT OF SIGNIFICANCE: How to improve the efficacy of neurological recovery after spinal cord injury (SCI) is always a challenge. Tissue engineering provides a promising strategy for SCI repair, and scaffolds are one of the most important elements in addition to cells and inducing factors. The review highlights recent development and future prospects in polymer scaffolds for SCI therapy. The review will guide future studies by outlining the requirements and characteristics of polymer scaffold technologies employed against SCI. Additionally, the peculiar properties of polymer materials used in the therapeutic process of SCI also have guiding significance to other tissue engineering approaches.

Double stimuli-responsive polysaccharide block copolymers as green macrosurfactants for near-infrared photodynamic therapy

The NIR absorbing photosensitizer phthalocyanine zinc (PC(Zn)) was stabilized in aqueous media as water-dispersible nanoparticles with a reduction- and pH-responsive full polysaccharide block copolymer. A cellular uptake and also photo switchable intracellular activity of the cargo upon irradiation at wavelengths in the near infrared region were shown. The block copolymer was synthesized by applying a copper-free click strategy based on a thiol exchange reaction, creating an amphiphilic double-stimuli-responsive mixed disulfide. The dual-sensitive polysaccharide micelles represent a non-toxic and biodegradable green macrosurfactant for the delivery of phthalocyanine zinc. By encapsulation into micellar nanoparticles, the bioavailability of PC(Zn) increased significantly, enabling smart photodynamic therapy for future applications in cancer-related diseases.

Polymerization induced self-assembly: an opportunity toward the self-assembly of polysaccharide-containing copolymers into high-order morphologies

Self-assembly of polysaccharide-containing amphiphilic copolymers: polymerization induced self-assembly versus traditional techniques.

Antifouling zwitterionic dextran micelles for efficient loading DOX

Polysaccharides derivatives are typical drug nanocarriers which are nontoxic and biodegradable. However, as is the case for all drug delivery systems, polysaccharides derivatives have to face the issue of protein fouling. In this paper, we present the design and synthesis of carboxybetaine-modified dextran-polycaprolactone (CB-Dex-PCL) copolymers as doxorubicin (DOX) nanocarriers. Results showed that DOX/CB-Dex-PCL micelles exhibited better cumulative release at the pH value of 5.2 than at the physiological pH of 7.4, which indicated potential applications in killing tumor cells while minimizing the toxicity to normal tissues. Additionally, antifouling properties of carboxybetaine functionalized dextran micelles were much better than that of unmodified dextran for fibrinogen and lysozyme as tested by ITC. Finally, cytotoxicity tests using Hela cells showed that CB-Dex-PCL and DOX-loaded micelles exhibited great biocompatibility. All the above observations indicated that CB-Dex-PCL micelles are potentially excellent drug carriers for the treatment of human cancerous tumors.

pH-Responsive Natural Polymeric Gene Delivery Shielding System Based on Dynamic Covalent Chemistry

A novel pH-responsive system based on aldehyde-bearing dextran derivatives (ODEX or FDEX) was designed to use as gene carrier shielding. Through pH sensitive Schiff base bonds between amino groups of PEI (in PEI/DNA polyplex) and aldehyde groups of dextran derivatives, PEI/DNA polyplex could be shielded and further condensed to obtain an effectively decreasing ζ-potential with smaller size. Schiff base bonds were pH-responsive, which were relatively stable in neutral environment but were deformed in slightly acidic and acidic environments. Through use of this characteristic, the PEI/DNA polyplex was effectively shielded during circulation in the body, and upon arrival at the tumor, the slightly acid pH triggered the breaking of Schiff base bonds to expose the positive PEI/DNA polyplex, which further interacted with tumor cell membranes, achieving efficient gene expression. Use of such characteristics could effectively address the high transfection efficiency versus stability dilemma of gene carriers. FDEX/PEI/DNA nanoparticles not only mediate higher cellular uptake and transfection efficiency in vitro but also effectively accumulate in tumors with gene expression in vivo higher than that of the ODEX analogues. As a result, this pH-responsive system is a promising strategy for cancer therapy.

Redox tunable delivery systems: sweet block copolymer micelles via thiol–(bromo)maleimide conjugation

A tunable release of encapsulated Nile Red from xyloglucan-oligosaccharides-block-polycaprolactone obtained by thiol–(bromo)maleimide click reaction was successfully achieved by mixing their Gluathione-responsiveness.

Polymeric prodrugs conjugated with reduction-sensitive dextran–camptothecin and pH-responsive dextran–doxorubicin: an effective combinatorial drug delivery platform for cancer therapy

Two types of stimuli-sensitive polymeric prodrugs for combinatorial cancer therapy have been prepared and found to exhibit favorable anticancer activity in vitro and in vivo.