Albumin release from biodegradable hydrogels composed of dextran and poly(ethylene glycol) macromer

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.

Pharmacokinetic Aspects of Nanoparticle-in-Matrix Drug Delivery Systems for Oral/Buccal Delivery

Oral route maintains its predominance among the ones used for drug delivery, especially when medicines are self-administered. If the dosage form is solid, therapy gains in dose precision and drug stability. Yet, some active pharmaceutical substances do not present the required solubility, permeability, or release profile for incorporation into traditional matrices. The combination of nanostructured drugs (nanoparticle [NP]) with these matrices is a new and little-explored alternative, which could bring several benefits. Therefore, this review focused on combined delivery systems based on nanostructures to administer drugs by the oral cavity, intended for buccal, sublingual, gastric, or intestinal absorption. We analyzed published NP-in-matrix systems and compared main formulation characteristics, pharmacokinetics, release profiles, and physicochemical stability improvements. The reported formulations are mainly semisolid or solid polymers, with polymeric or lipid NPs and one active pharmaceutical ingredient. Regarding drug specifics, most of them are poorly permeable or greatly metabolized. The few studies with pharmacokinetics showed increased drug bioavailability and, sometimes, a controlled release rate. From our knowledge, the gathered data make up the first focused review of these trendy systems, which we believe will help to gain scientific deepness and future advancements in the field.

Advances in thermosensitive polymer-grafted platforms for biomedical applications

Studies on "smart" polymeric material performing environmental stimuli such as temperature, pH, magnetic field, enzyme and photo-sensation have recently paid much attention to practical applications. Among of them, thermo-responsive grafted copolymers, amphiphilic steroids as well as polyester molecules have been utilized in the fabrication of several multifunctional platforms. Indeed, they performed a strikingly functional improvement comparing to some original materials and exhibited a holistic approach for biomedical applications. In case of drug delivery systems (DDS), there has been some successful proof of thermal-responsive grafted platforms on clinical trials such as ThermoDox®, BIND-014, Cynviloq IG-001, Genexol-PM, etc. This review would detail the recent progress and highlights of some temperature-responsive polymer-grafted nanomaterials or hydrogels in the 'smart' DDS that covered from synthetic polymers to nature-driven biomaterials and novel generations of some amphiphilic functional platforms. These approaches could produce several types of smart biomaterials for human health care in future.

Biocompatibility Assessment of PLCL-Sericin Copolymer Membranes Using Wharton's Jelly Mesenchymal Stem Cells

Stem cells based tissue engineering requires biocompatible materials, which allow the cells to adhere, expand, and differentiate in a large scale. An ideal biomaterial for clinical application should be free from mammalian products which cause immune reactivities and pathogen infections. We invented a novel biodegradable poly(L-lactic-co-ε-caprolactone)-sericin (PLCL-SC) copolymer membrane which was fabricated by electrospinning. Membranes with concentrations of 2.5 or 5% (w/v) SC exhibited qualified texture characteristics with a noncytotoxic release profile. The hydrophilic properties of the membranes were 35–40% higher than those of a standard PLCL and commercial polystyrene (PS). The improved characteristics of the membranes were due to an addition of new functional amide groups, C=O, N–H, and C–N, onto their surfaces. Degradation of the membranes was controllable, depending on the content proportion of SC. Results of thermogram indicated the superior stability and crystallinity of the membranes. These membranes enhanced human Wharton's jelly mesenchymal stem cells (hWJMSC) proliferation by increasing cyclin A and also promoted cell adhesion by upregulating focal adhesion kinase (FAK). On the membranes, hWJMSC differentiated into a neuronal lineage with the occurrence of nestin. These data suggest that PLCL-SC electrospun membrane represents some properties which will be useful for tissue engineering and medical applications.

Improved oral absorption of exenatide using an original nanoencapsulation and microencapsulation approach

Oral delivery is the most convenient and favorable route for chronic administration of peptides and proteins to patients. However, many obstacles are faced when developing such a delivery route. Nanoparticles (NPs) are among the leading innovative solutions for delivery of these drugs. Exenatide is a peptidic drug administered subcutaneously (SC) twice a day chronically as an add-on therapy for the worldwide pandemic disease, diabetes. Many attempts to develop oral nanocarriers for this drug have been unsuccessful due to the inability to retain this hydrophilic macromolecule under sink conditions or to find a suitable cross-linker which does not harm the chemical integrity of the peptide. In this study, we report about an original oral delivery solution based on a mixture of albumin and dextran NPs cross-linked using sodium trimetaphosphate (STMP). Moreover, we suggest a second defense line of gastro-resistant microparticles (MPs) composed of an appropriate ratio of Eudragit® L100-55 (Eudragit L) and hydroxypropylmethylcellulose (HPMC), for additional protection to these NPs presumably allowing them to be absorbed in the intestine intact. Our results demonstrate that such a system indeed improves the relative oral bioavailability of exenatide to a level of about 77% compared to subcutaneous injection due to the presence of dextran in the coating wall of the NPs which apparently promotes the lymphatic uptake in the enterocytes. This technology may be a milestone on the way to deliver other peptides and proteins orally.

Folic acid conjugated cross-linked acrylic polymer (FA-CLAP) hydrogel for site specific delivery of hydrophobic drugs to cancer cells

Background

The hydrogel based system is found to be rarely reported for the delivery of hydrophobic drug due to the incompatibility of hydrophilicity of the polymer network and the hydrophobicity of drug. This problem can be solved by preparing semi-interpenetrating network of cross-linked polymer for tuning the hydrophilicity so as to entrap the hydrophobic drugs. The current study is to develop a folic acid conjugated cross-linked pH sensitive, biocompatible polymeric hydrogel to achieve a site specific drug delivery. For that, we have synthesized a folic acid conjugated PEG cross-linked acrylic polymer (FA-CLAP) hydrogel and investigated its loading and release of curcumin. The formed polymer hydrogel was then conjugated with folic acid for the site specific delivery of curcumin to cancer cells and then further characterized and conducted the cell uptake and cytotoxicity studies on human cervical cancer cell lines (HeLa).

Results

In this study, we synthesized folic acid conjugated cross-linked acrylic hydrogel for the delivery of hydrophobic drugs to the cancer site. Poly (ethyleneglycol) (PEG) diacrylate cross-linked acrylic polymer (PAA) was prepared via inverse emulsion polymerization technique and later conjugated it with folic acid (FA-CLAP). Hydrophobic drug curcumin is entrapped into it and investigated the entrapment efficiency. Characterization of synthesized hydogel was done by using Fourier Transform-Infrared spectroscopy (FT-IR), Transmission Electron Microscopy (TEM), Differential Scanning Calorimetry (DSC). Polymerization and folate conjugation was confirmed by FT-IR spectroscopy. The release kinetics of drug from the entrapped form was studied which showed initial burst release followed by sustained release due to swelling and increased cross-linking. In vitro cytotoxicity and cell uptake studies were conducted in human cervical cancer (HeLa) cell lines.

Conclusions

Results showed that curcumin entrapped folate conjugated cross-linked acrylic polymer (FA-CLAP) hydrogel showed higher cellular uptake than the non folate conjugated form. So this can be suggested as a better delivery system for site specific release of hydrophobic cancer drugs.

Synthesis of Dextran/Methoxy Poly(ethylene glycol) Block Copolymer

We synthesized a block copolymer composed of dextran and methoxy poly(ethylene glycol) (mPEG). To accomplish this, the end group of dextran was modified by reductive amination. The aminated dextran (Dextran-NH2) showed the intrinsic peaks of both dextran at 3~5.5 ppm and hexamethylene diamine at 1~2.6 ppm at1H nuclear magnetic resonance (NMR) spectrum. The amino end group of dextran was conjugated with mPEG to make the block copolymer consisting of dextran/mPEG (abbreviated as DexPEG). The synthesized aminated dextran and DexPEG were characterized using1H NMR and gel permeation chromatography (GPC). The molecular weight and conjugation yield were estimated by comparing the intensity ratio of the proton peaks of the glucose molecule (4.9 ppm and 3.3~4.0 ppm) to that of the ethylene group of mPEG (3.7 ppm). Abundant hydroxyl group in the dextran chain can be used as a source of bioactive agent conjugation.

Cross-linked acrylic hydrogel for the controlled delivery of hydrophobic drugs in cancer therapy

Objective:

To investigate cross-linked hydrogels prepared via inverse emulsion polymerization to entrap poorly aqueous soluble drugs. Polyethylene glycol cross-linked acrylic polymers were synthesized and the loading and release of curcumin, a model hydrophobic drug, was investigated.

Methods:

Physicochemical characteristics of hydrogels were studied with ¹³C nuclear magnetic resonance, Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, differential scanning calorimetry, and swelling. Polymerization of the acrylic acid with cross-linked polyethylene glycol diacrylate was characterized with ¹³C nuclear magnetic resonance imaging and Fourier transform infrared spectroscopy.

Results:

The in vitro release rate of curcumin showed that there was a sustained release from the hydrogel with increased cross-linking; the release rate depended on the pH of the releasing medium. Intracellular and cytotoxicity studies were carried out in human cervical cancer cell lines.

Conclusion:

The results suggest cross-linked acrylic polymers can be used as efficient vectors for pH-sensitive, controlled delivery of hydrophobic drugs.

Impregnation of tubular self-assemblies into dextran hydrogels

Amine groups are the building units of proteins. The incorporation of amine groups into polyethylene glycol diacrylate (PEGDA) hydrogel through dextran-allyl isocyanate-ethylamine (Dex-AE) enhances sustained protein release by introducing effective interactions. To investigate such an interaction effect and to improve protein release, we impregnated self-assembled tubular structures from dextran-bromoethylamine (Dex-BH) and dextran-chloroacetic acid (Dex-CA) into Dex-AE/PEGDA hydrogel. The morphology data obtained from scanning electron microscopy (SEM) reveal that pure PEGDA hydrogel had no effect on the distribution of the self-assembled tubules; the introduction of Dex-AE brought about the dispersion of these tubules, and an increase in Dex-AE content led to more evenly distributed structures. Moreover, the implantation of the self-assembled tubules had no distinct effect on the swelling capacity of the hybrid self-assembly embedded hydrogels. The in vitro albumin release study was carried out in a pH 7.4 buffer solution; the results show that the implantation of the self-assembly into the hydrogels reduced the burst release and prolonged the protein release time. These findings demonstrate that the impregnation of tubular self-assembly into hydrogel makes the hybrid hydrogel an excellent protein delivery system.

Effects of precursor and cross-linking parameters on the properties of dextran-allyl isocyanate-ethylamine/poly(ethylene glycol diacrylate) biodegradable hydrogels and their release of ovalbumin

In this paper, we studied the effects of molecular weight of poly(ethylene glycol diacrylate) (PEGDA) precursor, the degree of substitution (DS) of both allyl isocyanate (AI) and amine groups in dextran-based precursor (Dex-AE), and photoinitiator concentration on Dex-AE/PEGDA hydrogel formation and its ovalbumin (OVA) release. FT-IR spectra showed chemical bond interaction between amine and urethane groups of the hydrogel carriers with OVA. The increase in PEGDA molecular weight led to a faster OVA release because of a more open gel network structure. The study on the DS of AI in Dex-AE precursor showed that an increase in AI did not result in a prominent gel network structure difference. However, the urethane groups in Dex-AE precursor showed some interactions with OVA and, thus, resulted in a slower release rate. The incorporation of amine group into Dex-AE precursor did not affect the gel network structure, but reduced the OVA release rate, and the level of reduction increased with an increasing amine group substitution into the Dex-AE precursor. This reduction could be attributed to the interaction between the amine groups in the gel carrier and OVA. An increase in the photoinitiator concentration showed no effect on the gel network structure or OVA release.

Development of photocrosslinked sialic acid containing polymers for use in Abeta toxicity attenuation

beta-Amyloid peptide (Abeta), the primary protein component in senile plaques associated with Alzheimer's disease (AD), has been implicated in neurotoxicity associated with AD. Previous studies have shown that the Abeta-neuronal membrane interaction plays a crucial role in Abeta toxicity. More specifically, it is thought that Abeta interacts with ganglioside rich and sialic acid rich regions of cell surfaces. In light of such evidence, we have hypothesized that the Abeta-membrane sialic acid interaction could be inhibited through use of a biomimic multivalent sialic acid compound that would compete with the cell surface for Abeta binding. To explore this hypothesis, we synthesized a series of photocrosslinked sialic acid containing oligosaccharides and tested their ability to bind Abeta and attenuate Abeta toxicity in cell culture assays. We show that a polymer prepared via the photocrosslinking of disialyllacto-N-tetraose (DSLNT) was able to attenuate Abeta toxicity at low micromolar concentrations without adversely affecting the cell viability. Polymers prepared from mono-sialyl-oligosaccharides were less effective at Abeta toxicity attenuation. These results demonstrate the feasibility of using photocrosslinked sialyl-oligosaccharides for prevention of Abeta toxicity in vitro and may provide insight into the design of new materials for use in attenuation of Abeta toxicity associated with AD.

Modeling the release of proteins from degrading crosslinked dextran microspheres using kinetic Monte Carlo simulations

To optimize and predict the release of proteins from biodegradable microspheres based on crosslinked dextran, a fundamental understanding of the mechanisms controlling their release is necessary. For that purpose, a mathematical model has been developed to describe the release of proteins from these hydrogel-based microspheres. A kinetic Monte Carlo scheme for the degradation of a small domain inside the microsphere was developed. The results from this were used in a second kinetic Monte Carlo scheme to model the diffusion and the subsequent release of proteins. The only processes included in this model are diffusion and degradation. The general effects of diffusion, crosslink density, protein loading, and clustering of proteins on the release were investigated. The model crosslink density (Xmodel) and the model diffusivity (Dmodel) were fitted to experimental release data of BSA monomer from hydroxyethyl methacrylated dextran (dex-HEMA) microspheres. By using the experimental release curves of liposomes and BSA monomer, it was found that (1) the model crosslink density (Xmodel) scales with the hydrodynamic diameter (dh) as dh(1.64) and (2) the diffusivity of the protein (Dmodel) scales approximately with 1/dh (Stokes-Einstein). Using these scaling relations, quantitative predictions of the release curves of BSA dimer, immunoglobulin G and human growth hormone were possible. In conclusion, this model may play an important role in the optimization, understanding and prediction of the release of various proteins from degradable hydrogels.

Preparation of recombinant human bone morphogenetic protein-2 loaded dextran-based microspheres and their characteristics

AIM

To prepare new pharmaceutical forms with sustained delivery properties of recombinant human bone morphogenetic protein-2 (rhBMP2) for tissue engineering and guided tissue regeneration (GTR) use.

METHODS

rhBMP2-loaded dextran-based hydrogel microspheres (rhBMP2-MPs), which aimed to keep rhBMP2 bioactivity and to achieve long-term sustained release of rhBMP2, were prepared by double-phase emulsified condensation polymerization. The physical, chemical performances and biological characteristics of those microspheres were studied both in vitro and in vivo.

RESULTS

The microspheres' average diameter was 30.33+/-4.32 microm with 75.4% ranging from 20 microm to 40 microm and the drug loading and encapsulation efficiency were 7.82% and 82.25%, respectively. The rhBMP2-releasing profiles in vitro showed that rhBMP2 release could be maintained more than 10 d. The rhBMP2-MPs, with good swelling and biodegradation behavior, could be kept for 6 months at below 4 degree without significant characteristic change or bioactivity loss. Cytology studies showed that rhBMP2-MPs could promote the proliferation of periodontal ligament cells (PDLCs) approximately 10 d, while the bioactivity of concentrated rhBMP2 solution could keep no more than 3 d. Scanning electron microscope showed that rhBMP2-MPs could be enchased into the porous structure of calcium phosphate ceremic (CPC) and the eugonic growth of PDLCs in CPC/rhBMP2-MPs scaffolds. Animal experiments indicated that using CPC/rhBMP2-MPs scaffolds could gain more periodontal tissue regeneration than using rhBMP2 compound firsthand with CPC (CPC/rhBMP2).

CONCLUSION

By encapsulating rhBMP2 into dextran-based microspheres, a small quantity of rhBMP2 could achieve equivalent effects to the concentrated rhBMP2 solution and at the same time, could prolong rhBMP2 retention both in vitro and in vivo.

Polyesters based on diacid monomers

Polymers with ester linkages in their main chain comprise a family of polymers with immense diversity and versatility. This review deals with the preparation of such polymers from dicarboxylic acid monomers, and the result in terms of properties and applicability. Polyesters alone, and their copolymers with amides, anhydrides, urethanes, imides, ethers or other functional groups, offer countless opportunities to tune the properties of the resulting material within a broad range. Of particular interest is the inherent biodegradability of the ester linkage. Biodegradability is sought after in a wide range of applications, above all in the preparation of environmentally friendly polymers and biomedical materials for temporary surgical use and in drug delivery.