Gradient cross-linked biodegradable polyelectrolyte nanocapsules for
intracellular protein drug delivery
Shujun Shu
a
, Xinge Zhang
a
,
*
, Zhongming Wu
b
, Zhen Wang
a
, Chaoxing Li
a
,
*
a
Key Laboratory of Functional Polymer Materials Ministry of Education, Institute of Polymer Chemistry, Nankai University, 94# Weijin Road, Tianjin 300071, PR China
b
Metabolic Diseases Hospital, Tianjin Medical University, Tianjin 300070, PR China
article info
Article history:
Received 3 February 2010
Accepted 11 April 2010
Available online 14 May 2010
Keywords:
Gradient cross-linked
Polyelectrolyte
Layer by layer technique
Reduction sensitive
Intracellular drug delivery
abstract
Gradient shell cross-linked hollow polyelectrolyte nanocapsules composed of cysteamine conjugated
chitosan and dextran sulfate were prepared by layer-by-layer adsorption on
b
-cyclodextrin (
b
-CD)
functionalized silica spheres followed by cross-linking thiols and removal of silica core. This disulfide
bond gradient cross-linked nanocapsules combined reduction and pH sensitive. Gradually increased
from the inside to the outside of the cross-linking degree, one purpose is to ensure that cross-linking
disulfide bond after reduction cleavage still has pH sensitive, on the other hand is to avoid cross-linked
contraction of internal damage the crystal and bioactivity of protein drugs. Disulfide cross-linked
nanocapsules were used to enhance the physical stability against acidic pH conditions compared to the
un-cross-linked ones. Bovine serum albumin, as a model protein drug, was loaded inside nanocapsules.
The disulfide bond cross-linked nanocapsules are intended to remain more stable in physiological pH and
decrease the loss of protein drugs caused by the gastric cavity, and can release the drugs in the intra-
cellular environment after glutathione reduction.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
Protein and peptide drugs are normally restricted to intravenous
administration because they are easily hydrolyzed in the acidic
stomach, degraded by proteolytic enzymes in the gastrointestinal
(GI) tract and metabolized via enterophepatic circulation. There-
fore, the development of oral administration system of protein
drugs is a challenging opportunity for researchers [1e3]. One
possibility to overcome this problem is to encapsulate them in
colloidal nanocapsules that can protect the protein from being
degraded in the GI tract and facilitate their release in cell envi-
ronment [4e6].
Hollow nanocapsules prepared by layer-by-layer (LBL) tech-
nique of colloidal particles hold promise for diverse applications,
including drug delivery, microreactors. A key challenge for the
application of LBL capsules is to stabilize them at physiological
conditions while also being able to trigger capsule disassembly
with an external stimulus or in an intracellular environment, such
as glutathione reduction, releasing encapsulated substances [7e9].
Reduction sensitive biodegradable capsules have emerged as
a fascinating class of biomedical materials that can be elegantly
applied for intracellular triggered gene and drug delivery. The
design rationale of reduction sensitive capsules usually involves
incorporation of disulfide linkage in the main chain, at the side
chain, or in the cross-linker [10]. Reduction sensitive capsules are
characterized by an excellent stability in the circulation and in
extracellular fluids, whereas they are prone to rapid degradation
under a reductive environment present in intracellular compart-
ments such as the cytoplasm and the cell nucleus. This remarkable
feature renders them distinct from their hydrolytically degradable
counterparts and extremely intriguing for the controlled delivery of
a variety of bioactive molecules including DNA, antisense oligo-
nucleotide, proteins drugs, etc. It is evident that reduction sensitive
biodegradable capsules are highly promising functional biomate-
rials that have enormous potential in formulating sophisticated
drug and gene delivery systems.
Glutathione (GSH) is a tripeptide found within cells at milli-
molar concentrations [11,12]. Glutathione tripeptide is the most
abundant low-molecular-weight biological thiol and GSH/gluta-
thione disulfide is the major redox couple in animal cells. In blood
and in extracellular matrices and on the cell surface, the proteins
are rich in stabilizing disulfides as a result of a relatively high redox
potential due to a low concentration of GSH (approximately 2e20
m
M
). In contrast, inside cells the concentration of GSH is 0.5e10 m
M
that is kept reducing by NADPH and glutathione reductase, main-
taining a highly reducing environment inside cells [13].
*
Corresponding authors. Tel.: þ86 22 2350 1645; fax: þ86 22 2350 5598.
E-mail addresses: zhangxinge@nankai.edu.cn (X. Zhang), lcx@nankai.edu.cn
(C. Li).
Contents lists available at ScienceDirect
Biomaterials
journal homepage: www.elsevier.com/locate/biomaterials
0142-9612/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biomaterials.2010.04.016
Biomaterials 31 (2010) 6039e6049