Lignin-based fluorescence hollow nanoparticles: Their preparation, characterization, and encapsulation properties for doxorubicin

Highlights

A fluorescent modified lignin-based hollow nanoparticle with stable structure and controllable size was prepared.

The fluorescent modified nanoparticles can be treated as a drug delivery platform for hydrophilic drug.

The lignin-based nanoparticles exhibited excellent bio-compatibility and along acting fluorescence performance.

Abstract

Lignin shows strong adsorption, biodegradability and non-toxicity, and has opened a research hotspot in the design and manufacture of controllable [nanomaterials](https://www.sciencedirect.com/topics/engineering/nanomaterial “Learn more about nanomaterials from ScienceDire…

Highlights

A fluorescent modified lignin-based hollow nanoparticle with stable structure and controllable size was prepared.

The fluorescent modified nanoparticles can be treated as a drug delivery platform for hydrophilic drug.

The lignin-based nanoparticles exhibited excellent bio-compatibility and along acting fluorescence performance.

Abstract

Lignin shows strong adsorption, biodegradability and non-toxicity, and has opened a research hotspot in the design and manufacture of controllable nanomaterials for drug delivery. However, lignin-based materials, with both diagnostic and therapeutic functions, have yet to be developed. In this work, enzymatically hydrolysable lignin (EHL) was used to prepare blue fluorescent lignin copolymer by grafting 1-Pyrenebutyric acid onto lignin via amidation reaction and then formed self-assembled nanoparticles. The results show that such lignin-based hollow nanoparticles exhibit characteristics of fluorescent functions, size controlled and stable structure within 15 days. For anticancer drug Doxorubicin, the encapsulation efficiency and drug loading reached, respectively, 50% and 10%. This encapsulation had no cytotoxicity, and sustained-release effect on the drug. The aim of this study was to develop the multifunctional bio-nanomaterials for medical applications, through simple, environmentally friendly, low-cost methods.

Introduction

As a by-product of bio-refining, the output of enzymatic hydrolysable lignin (biomass butanol lignin, EHL) has increased year by year with the progress of the bio-refining industry [[1], [2], [3], [4], [5]]. Compared with lignin from paper mill waste liquor, EHL has higher reactivity and lower molecular weight [6]. It is a renewable raw material with good biodegradability and biocompatibility, as well as low toxicity [7,8]. As one kind of amphiphilic polymer, lignin can self-assemble into micro-nanomaterials or nanomaterials in solution for medical applications [9]. Anticancer drugs have good therapeutic effects on pathological tissues in the process of disease treatment, but they also show considerable toxicity and side effects [10]. Accordingly, transport and action mechanisms have always been important research emphases for such drugs.

The ideal drug delivery system should be made of easily available material sources, have a low cost of synthesis, modifiable surfaces, and, critically, low or no toxicity [11,12]. Chen et al. [13] synthesized a series of amino acid grafted EHL by nucleophilic substitution. The research showed that the modified lignin exhibited good biocompatibility and excellent inhibitory effect on Gram-positive bacteria. In another study, lignin nanospheres with broad-spectrum UV adsorption and excellent antioxidant properties were produced by Wu et al. [14] via reverse self-assembly, which was achieved by taking alkali lignin and grafting benzophenone moiety. And cytotoxicity experiments indicated the novel lignin-based sunblock showed good biocompatibility and safety. Using self-assembly method, Sipponen et al. [15] prepared lignin nanoparticles from wheat straw soda lignin, and entrapped 3.5% budesonide the particles. Although, the EE was only 35%, <300 mg of the nanoformulation would fulfil the daily dosage of this anti-inflammatory corticosteroid drug. Figueiredo et al. [16] entrapped the poorly water-soluble drugs SFN and BZL as a cytotoxic agent in lignin nanoparticles prepared from softwood kraft lignin. Loading capacities of 7–8% were obtained at 68–77% EE. Nanoparticles could improve drugs release profiles and consequently enhanced their anticancer activity, and their surface chemistry can allow the modification with targeting moieties in order to increase the cellular uptake into specific cells for cancer therapies. Therefore, developing fluorescent hollow nanomaterials with both diagnostic and therapeutic functions, will not only equip them for such diverse functions as fluorescence microscopy imaging and drug delivery, but will also show unique application prospects in the field of cancer diagnosis and treatment [[17], [18], [19]].

It is currently difficult to guarantee the stability of fluorescence of lignin for the diversity of sources, complex molecular structure and low fluorescence quantum yield. Therefore, fluorescence labeling lignin is an effective method to prepare lignin-based fluorescent materials at present. In the previous work the team grafted fluorescent molecule pyrene onto lignin and then prepared a lignin-based nanoparticles for nanometer probe by ultrasonic treatment [20]. However, the alkyl silanization reaction of lignin in tetrahydrofuran solution will cause the condensation of lignin molecules and reduce the solubility of modified lignin, thereby limiting the regulation of lignin structure. Herein, we report on a further improved method to prepare fluorescent modified lignin-based hollow nanoparticles with controllable structure via self-assembling. The hollow nanoparticles have potential applications in both nano-probe and drug delivery. As shown in Scheme 1, the lignin with fluorescent groups was synthesized by amidation reaction of EHL and 1-pyrenebutyric acid, which was then used to self-assemble hollow nanoparticles. This kind of materials possesses the hollow spherical morphology and fluorescence properties and can be used to load the antitumor drug doxorubicin (DOX). Fluorescent particle localization and recognition can be used to track the dynamics of drug molecules, and the anticancer activity of drugs can in turn be used to treat and monitor pathological tissues in real time [[21], [22], [23]]. This showed unique application prospects for cancer diagnosis and treatment.

Section snippets

Materials

EHL was acquired from the Hong Kong Laihe Biotechnology Co., Ltd. The hydroxyl content, number-average molecular mass, and polydispersity of EHL are 2.67 mmol/g, 1430 g/mol, and 1.22, respectively. Tetrahydrofuran (THF) and diethyl ether of analytical-grade purity was provided by the Beijing Chemical Reagents Company. 3-aminopropyltriethoxysilane (APTES), 1-Pyrenebutyric acid (PBA), dicyclohexylcarbodiimide (DCC), 4-Dimethlaminopyridine (DMAP) and doxorubicin hydrochloride (DOX, at purity >98%)

Preparation and characterization of P-EHL microspheres

In Fig. 1A and B, the TEM images displayed that EHL raw materials with irregularly shaped block structures were changed into uniform spherical nanoparticles (P-LHNPs; Table S1, B2) via molecular modification and self-assembly. The TEM image of P-LHNPs displayed the spherical hollow structure with a clear contrast between the center and the shell. And the SEM image inset of P-LHNPs showed there was a single hole on the surface of the particle (Fig. 1B). The specific surface area and pore volume

Conclusions

Lignin-based hollow nanoparticles with tracking, encapsulating and sustained-release properties for drug molecules were successfully prepared, by amidation modification and molecular self-assembly. The hollow nanoparticles showed uniform and stable size as well as controllable structure, and their suspensions showed good colloidal properties. Their relatively hydrophobic shell and hydrophilic core structure also facilitated the loading of the hydrophilic molecular drug DOX. The encapsulation

CRediT authorship contribution statement

Y Zhou and Y Han performed the study design, acquisition of data and manuscript writing. G Li and F Xiong participated in the study design and manuscript editing. F Chu is the corresponding author who designed the study, reviewed and revised the manuscript, provided funding support. All authors read and approved the final manuscript.

Acknowledgments

This study was financially support from the National Natural Science Foundation of China (31770610), Jiangsu Province Biomass Energy and Materials Laboratory in the Institute of Chemical Industry of Forest Products, CAF (JSBEM202011), National Natural Science Foundation of China (21801216), and thanks to Tsinghua University for in term of the structure testing of nanoparticles and Shanghai Freedom Biotech CO., Ltd. for the help with the biological cell testing.