Construction and Characterization of a Novel Sustained-Release

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Agricultural and Environmental Chemistry

Construction and characterization of a novel sustainedrelease delivery system for hydrophobic pesticides using biodegradable PDA-based microcapsules aihua Zou, Ying Yang, Jiagao Cheng, Vasil M Garamus, and Na Li J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.8b00877 • Publication Date (Web): 30 May 2018 Downloaded from http://pubs.acs.org on May 30, 2018

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Journal of Agricultural and Food Chemistry

Construction and characterization of a novel sustained-release delivery system for hydrophobic pesticides using biodegradable PDA-based microcapsules Aihua Zoua∗#, Ying Yanga#, Jiagao Chengb, Vasil M. Garamusc, Na Lid

a

State Key Laboratory of Bioreactor Engineering and Institute of Applied Chemistry,

Shanghai Key Laboratory of Functional Materials Chemistry, School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai 200237, P.R. China b

School of Pharmacy, East China University of Science and Technology, Shanghai

200237, P.R. China c

Helmholtz-Zentrum Geesthacht, Centre for Materials and Coastal Research,

D-21502 Geesthacht, Germany d

National Center for Protein Science Shanghai and Shanghai Institute of

Biochemistry and Cell Biology, Shanghai 201210, P.R. China

∗

Corresponding author

Aihua Zou School of Chemistry and Molecular Engineering East China University of Science and Technology Meilong Road 130 200237 Shanghai, P.R. China E-mail: [email protected] Tel: +86 64252231 #

These authors contributed equally to this work. 1

ACS Paragon Plus Environment


1

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Abstract

2

Microcapsule formulations have been highly desirable and widely developed for

3

pesticide’s effective utilization and environmental pollution reduction. However,

4

commercial and traditional microcapsule formulations of lambda-cyhalothrin (LC)

5

were prepared by complicated synthesis and thereby specific organic solvents were

6

needed. In this work, LC was encapsulated into a versatile, robust and biodegradable

7

polydopamine (PDA) microcapsule by self-polymerization of dopamine. LC-loaded

8

PDA microcapsules were characterized by transmission electron microscopy (TEM),

9

small-angle X-ray scattering (SAXS) and thermogravimetric analysis measurements

10

(TGA). LC-loaded PDA microcapsules have uniform morphology with nanoscale,

11

decent LC loading content (>50.0%, w/w), good physicochemical stability and

12

sustained release properties. The bioassay against sanitary insect pest (Musca

13

domestica) showed that the bioactivity and long-term efficiency of LC-loaded PDA

14

microcapsules was superior to that of the commercial formulation. All of these

15

results demonstrated that LC-loaded PDA microcapsule could be applied as a

16

commercial LC microcapsule formulation with better environmental impact and

17

higher effective delivery.

18

Keywords:

19

self-polymerization; sustained release

lambda-cyhalothrin;

pyrethroids;

microcapsule;

20 21 22 2


polydopamine;

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23 24

1. Introduction

25

Pyrethroids（PRYs）, such as lambda-cyhalothrin (LC), are the synthetic analogs

26

of natural insecticide pyrethrum discovered in chrysanthemum flowers,1 and have

27

been widely used as insecticides in hygiene as well as for crop protection.2 Because

28

of PRYs’ high effectiveness at low dosages in agricultural situations, they account

29

for around 30% of insecticides applied globally3 and are still expected to be

30

increased compared with organophosphorus and organochlorine insecticides.

31

However, PRYs have been listed by an EU working group as suspected

32

endocrine-disrupting chemicals,4 and many studies have illustrated excessive

33

exposure to PYRs could cause liver damage.5 Besides, its poor solubility in aqueous

34

media limits the application of pesticide formulations with high efficacy and safety.6

35

Therefore, it is extremely necessary to mitigate the above impacts and reduce the

36

associated risk.

37

LC, as the model pesticide of PRYs, its conventional formulations mainly involve

38

emulsifiable concentrate (EC), wettable powders (WP), microemulsion (ME), and

39

emulsion in water (EW). These formulations have some problems including dust

40

drift, rain fastness, and poor dispersion, which will further cause low pest control

41

efficacy and severe environmental pollution.7,8 More importantly, conventional

42

formulations usually experience a rapid decrease in effect after the early burst

43

release of active ingredient which has induced serious concerns on ecological 3



44

environment.9 Currently, microcapsule has been developed and commercialized as

45

controlled delivery system. The loading of pesticide into microcapsule could

46

improve pesticide utilization by the continuous and stable release of pesticide for a

47

specified period of time, which also would result in the long-term pesticide validity,

48

the decrease of pesticide application frequency and environmental pollution. 10-13

49

Moreover, the encapsulation of LC in microcapsule can kept LC unaffected by the

50

external environment, which consequently enhance the physicochemical stability of

51

the active ingredients.14,

52

For the microencapsulation of active ingredient, the paramount problem is

53

selecting environmentally friendly and biodegradable wall materials, and the

54

polymer carriers have aroused evolving interests. Polymers, including octyl-grafted

55

amphiphilic alginate-amide derivative (OAAD),15 polyacrylamide,16 chitosan,17 and

56

polylactide (PLA),18 have been widely applied in pesticide delivery systems.

57

Polydopamine (PDA), inspired by the composition of adhesive proteins in mussels,

58

is a fascinating and natural material with outstanding properties.19,20 Many different

59

methods have been utilized for the assembly of DA (dopamine) on various templates

60

by the spontaneous oxidative polymerization. Hard templates, such as silica (SiO2)

61

particles,21 polystyrene (PS) microspheres,22 calcium carbonate (CaCO3) particles,23

62

and magnetic nanoparticles particles24,25 have been used as sacrificial templets. On

63

the contrary, emulsion droplets, such as dimethyldiethoxysilane (DMDES) emulsion

64

system, can be used as soft templates as well.26,27 However, as DA can 4


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self-polymerize in a weekly alkaline solution (pH = 8.5), soft templates have

66

restricted its application for the pesticides that tend to hydrolyze in alkaline

67

medium.27 More importantly, conventionally emulsions are generated by surfactants

68

which may cause foam problems in further applications.

69

Herein, LC-loaded PDA microcapsules are prepared by the spontaneous oxidative

70

polymerization of a dopamine solution on silica particles, followed by removal of

71

the template to form microcapsules. Compared with traditional commercial LC

72

microcapsule formulations, the LC-loaded PDA microcapsule is free of organic

73

solvents and surfactants and is based on biodegradable material. The structure, LC

74

loading content, sustained release, and insecticidal biological assays of LC-loaded

75

PDA microcapsule are investigated (Figure 1) in this study, to our best knowledge

76

the first time. Results show that the versatile and robust microcapsules display

77

decent loading content, excellent stability and controlled-release behavior as well as

78

good biological activeness on sanitary insect pest. Therefore, it is assumed that this

79

LC-loaded PDA microcapsule is more environmental friendly for further exploration

80

as a commercial LC microcapsule formulation.

81

2. Materials and Methods

82

2.1 Materials

83

Lambda-Cyhalothrin (LC, >95%) were kindly provided by Yangnong Chemical

84

Co., Ltd. (Yangzhou, China). Dopamine hydrochloride (DA, ≥99%) was from

85

Sigma-Aldrich Company. Tris- (hydroxymethyl) aminomethane (TRIS), tetraethyl5



86

orthosilicate (TEOS), N, N-Dimethylformamide (DMF), hydrofluoric acid (HF),

87

ammonium fluoride (NH4F), and ammonium hydroxide (NH3H2O) were from

88

Shanghai Titan Scientific Co., Ltd. All other chemicals were of analytical grade

89

without further purification.

90

2.2 Preparation of the LC-loaded PDA microcapsule

91

Blank PDA microcapsules were formed using layer-by-layer (LBL) assembly

92

method that was firstly described by Frank Caruso et al.21 50 mg silica particles

93

were dispersed in 20 mL 10 mM Tris-HCl buffer solution (pH= 8.5); subsequently,

94

40 mg dopamine(DA) was added under constant agitation for 24 hours at room

95

temperature. The preparation of silica particles was also investigated (Supporting

96

Information). PDA film was deposited on silica particles by the oxidative

97

self-polymerization of dopamine.19,21,22 PDA capsules were then obtained by etching

98

the SiO2 from the PDA-coated silica particles with 2 M HF/8 M NH4F solution (pH

99

= 5). The precipitate was centrifuged (6000 rpm) and washed at least thrice with

100

deionized water, and then dried under vacuum at 40 °C for 12 h.

101

The blank and dry PDA microcapsules were then dispersed in DMF with LC

102

dissolved in and stirred for 24 hours to obtain LC-loaded PDA microcapsules. The

103

precipitate was centrifuged and washed with deionized water thrice to remove

104

unentrapped and resuspended pesticide, and then dried under vacuum at 40 °C for 12

105

h to get LC-loaded PDA microcapsules.

106

2.3 Characterization of PDA microcapsule 6


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The morphology and structure of PDA microcapsule were determined by

108

Transmission electron microscopy (TEM) using JEM-1400 electron microscope

109

(JEOL, Japan).

110

Small angle X-ray scattering (SAXS) provides statistically relevant information

111

on internal structure of mesoporous materials in solution during the different steps

112

from formation of carrier to the loading with active compound.28-31

113

The mean or global features of blank PDA microcapsule and LC-loaded PDA

114

microcapsule were evaluated SAXS data collected at beamline BL19U2 of the

115

National Center for Protein Science Shanghai at Shanghai Synchrotron Radiation

116

Facility. Both samples were dispersed in water at low concentration. The detecting

117

range of momentum transfer q (q = 4π sin θ/λ, where θ is half of the scattering angle)

118

was 0.002-0.5 Å−1 by setting the sample-to-detector distance. Scattered X-ray

119

intensities were detected by a Pilatus 1M detector (DECTRIS Ltd).

120

The thermal stability of LC-loaded PDA microcapsule was measured by

121

thermogravimetric analysis (PerkinElmer Pyris Diamond TG/DTA). It was

122

performed by heating the specimens from 40 to 800 ℃ at 10 ℃/min in air flow (100

123

mL/min).

124

2.4 Lambda-Cyhalothrin loading content

125

To determine the amount of LC loaded in the microcapsules, the content of the LC

126

loading was tested as follows: a certain amount of LC-loaded PDA microcapsules

127

was suspended in ethanol solution and sonicated for 30 min to destroy the 7



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128

microcapsules structure, making all the loaded LC dissolved in ethanol solution. The

129

concentration of LC was determined by UV-vis spectroscopy. The calibration curve

130

of absorbance versus LC concentration was plotted in Supporting information. LC

131

loading content was calculated as the following equation:

132

LC loading content =

133

2.5 In vitro release of lambda-cyhalothrin from LC-loaded PDA microcapsule

× 100%

(1)

134

The in vitro release behavior of LC from LC-loaded PDA microcapsule in

135

different release medium was investigated. A certain amount of LC-loaded PDA

136

microcapsules was added separately to ethanol solution, 50% ethanol/water (50:50,

137

v/v) mixture, and 45% ethanol/water (45:55, v/v) mixture under magnetic agitation

138

at ambient temperature. 4.0 mL samples were removed at predetermined intervals,

139

and the same volume fresh medium was added. The collected samples were

140

centrifugated (6000 rpm) to obtain the supernatant of the mixture, and the amount of

141

released LC was quantified by UV-vis spectrophotometer analysis. The calibration

142

curve of absorbance versus LC concentration was plotted in Supporting information.

143

All experiments were conducted at room temperature (25 ℃).

144

2.6 Insecticidal biological assays

145

2.6.1Insecticidal activity against sanitary insect pest (Musca domestica)

146

A bioassay of LC-loaded PDA microcapsules against sanitary insect pest, musca

147

domestica, was evaluated according to the method described in the previous report32

148

using a commercial formulation as control. The LC- loaded PDA microcapsules 8


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were dispersed in water with Tween 80 as wetting agent and the concentration of

150

800 mg/L was considered for the present study. Two glass plates (200 mm × 200 mm)

151

with nonabsorbent surface were treated with 0.5 mL insecticide formulations

152

separately and dried by airing. For each glass forced-exposure device, 20 individuals

153

were introduced after a mild anesthesia with ethyl ether; the devices were then put

154

on the glass plates when the individuals resumed normal activities. The number of

155

dead individuals was recorded every minute until the completion of 20 minutes. For

156

evaluation, three replicates were carried out. Evaluation were made on a dead/alive

157

basis, toxicity regression equations, half knock-down time (KT50), and confidence

158

limits were calculated by Origin software. 18 The toxicity regression equation was

159

given as below:

160 161

Y = bX + a

(2)

Where Y is the mortality rate of treated group. X is the logarithm of time. KT50

162

means the time when the mortality rate of the treated group was 50%.

163

2.6.2 Skin irritation test

164

In order to investigate the opportunities for safe application,33 the skin irritation

165

experiment of LC-loaded PDA microcapsules was conducted. Considering people

166

usually wash up after the pesticide application procedure, so the time of applying

167

pesticide is less than 4 hours, and the skin irritation within 4 hours is pivotal. 0.03 g

168

LC-loaded PDA microcapsules and the commercial formulation were diluted by 40

169

times and then were applied to the back of the hand (2 cm ×3 cm) to observe the 9



170

skin irritation within 4 hours, respectively.

171

3. Results and discussion

172

3.1 Optimization of LC-loaded PDA microcapsule

173

As described by Feng Zhou et al., DMF is a good dispersing solvent for PDA MC.

174

And DMF has an appropriate dielectric constant, which resulting in the occurrence

175

of a chemical potential gradient for LC loading into PDA MC.22 Therefore, DMF

176

was chosen as the solvent for the preparation of LC loading into PDA MC, as

177

illustrated in Figure 1.

178

In order to optimize the formulation of LC-loaded PDA microcapsule, the effect

179

of LC concentration, the volume of LC solution, and the amount of added blank

180

PDA microcapsules on the LC loading were studied. The details were evaluated in

181

Table 1. As shown in Table 1, the LC concentration was changed from 10.0 to 50.0

182

mg/mL with a distinct increase in LC loading content from 26% to 48%. Under the

183

same LC concentration (50 mg/mL) and blank PDA microcapsule amount (30 mg), a

184

decrease in LC loading content from 48% to 30% was observed with the volume

185

change of LC solution from 45.0 to 10.0 mL. With the increase of the amount of

186

blank PDA microcapsules from 20 to 50 mg, the loading content of LC existed a

187

reduction from 53% to 43%. From Table 1, it can be concluded that the desired LC

188

loading content (>50%) can be achieved with relative high LC concentration (30-50

189

mg/mL), moderate LC solution volume (35-45 mL) and blank PDA microcapsules

190

amount (20-40 mg). And the LC loading content of these LC-loaded PDA MC 10


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almost kept the same after 30 days, which revealed a good stability over time.

192

Therefore, No.9 formulation was chosen for further study.

193

3.2 Morphology and structure characterization of PDA microcapsule

194

TEM images of PDA microcapsule were determined by using JEM-1400 electron

195

microscope. As shown in Figure 2a and 2b, the dark part (core) was the silica

196

particle and the light part (shell) was deposited PDA with a thickness of 20-30 nm.

197

After removing the silica core by HF/ NH4F solution, the blank PDA capsules were

198

obtained (Figure 2c, 2d). As shown in Figure 2c and 2d, the PDA microcapsules

199

with a diameter of 300-400 nm were uniform with intact shells, confirming the

200

successful preparation of blank PDA microcapsules. Then LC were loaded in the

201

blank microcapsules, and the morphology and structure of LC-loaded PDA MC were

202

same as the blank MC.

203

The rearrangement of PDA microcapsules after LC loading was determined by

204

SAXS. Figure. 3 showed the relative scattering intensity (I) of blank PDA

205

microcapsule and LC-loaded PDA microcapsule as a function of the scattering

206

vector q (Supporting information) The internal of scattering vectors corresponds to

207

studied objects of length scale from 4-310 nm (2π/qmax- 2π/qmin).34 There are no

208

Bragg diffraction peaks at scattering patterns that points on absence the long-range

209

order in the system. Instead of Bragg peaks the maximum in the low q range has

210

been observed, indicating that there is repulsive interaction between the

211

microcapsules in both of the blank and LC-loaded PDA microcapsule system. The 11



212

peak position is connected with distance between the microcapsules in first

213

approximation as 2π/q (q is position of maximum),35,36 and they were 150 nm (blank

214

MC) with qmax = 0.00414 nm-1 and 130 nm (LC MC) with qmax= 0.00468 nm-1

215

separately. Loading with LC resulted in decreasing distance between PDA MC due

216

to decreasing repulsion between microcapsules. It could be explained that part of LC

217

was located at the surface of PDA MC.

218

The linearity of the log I-log q scattering profile revealed the fractals property of

219

the PDA MC. As shown in Figure 3, the α (the absolute value of slope) of scattering

220

intensities for both samples for q > 0.03 were 4.95±0.35 (blank MC) and 4.67±

221

0.38 (LC MC). Because both of the α values for two samples were larger than 4

222

(diffuse interface), there was penetration of solvent (i.e. water, the dispersion

223

medium) into the surface of microcapsules (i.e. the shell).37 And after loaded with

224

LC, the α value was decreased, meaning that the extent of penetration was

225

decreased;37 it further confirmed once more that part of LC was loaded on the

226

surface of the microcapsules.

227

3.3 Thermal stability of LC-loaded PDA microcapsule

228

The thermal stability of blank PDA microcapsule and LC-loaded PDA

229

microcapsule were systematically evaluated by thermogravimetric analysis (TGA) in

230

air flow. Figure 4a showed that the thermal degradation temperature at 5% weight

231

loss (T5%) of LC-loaded PDA microcapsule was around 200 ℃, which is slightly

232

higher than that of blank PDA microcapsule (170 ℃). The higher T5% of LC-loaded 12


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PDA microcapsule could be ascribed to the effect of LC (decomposition temperature

234

275 ℃, ) which slowing down the degradation of PDA microcapsule to some extent.38

235

To get the differential thermogravimetry analysis (DTG) peak temperature (the

236

temperature at maximum weight loss rate), the DTG curves39 were demonstrated in

237

Figure 4b and 4c. For LC-loaded PDA microcapsule (Figure 4c), there presented a

238

sharp peak (around 250 ℃) of main degradation ahead of a low shoulder peak,

239

while this phenomenon was in opposite to the result of blank PDA microcapsule

240

(Figure 4b). Combined with Figure 4a, the sharp peak (around 250 ℃) of LC-loaded

241

microcapsule was considered as the result of a combination of both PDA and LC

242

degradation.38 The DTG curves were in consistence with the TG curves, which

243

demonstrated together the successful preparation of LC-loaded PDA MC with good

244

thermal stability.

245

3.4 In vitro release behavior of lambda-cyhalothrin from LC-loaded PDA

246

microcapsule

247

The release behaviors of LC from the LC-loaded PDA microcapsules were

248

studied in different solvents (Figure 5), such as ethanol, 50% ethanol aqueous

249

solution, and 45% ethanol aqueous solution. The profiles indicated that the lower the

250

ethanol concentration was, the slower the release rate of microcapsules was. LC

251

release was fastest in ethanol, and reached release equilibrium after 30 min.

252

However, in 50% and 45% ethanol aqueous solution, the equilibriums were achieved

253

after 12 hours and 24 hours, respectively. 13



254

The loading and release behavior are both primarily determined by the properties

255

of the microcapsules, the gradient of chemical potential across the capsules, the

256

nature of the active ingredient, solvent, and temperature, among other things.22,40-43

257

DMF is chosen as the solvent in the preparation of LC-loaded PDA MC, and the

258

loading efficiency is above 50%, which could be because DMF is a good dispersing

259

medium for PDA MC and also has an appropriate dielectric constant, resulting in the

260

presence of a chemical potential gradient, which finally propelled LC loading.22,44,45

261

In addition, there exists hydrogen bonds between LC and the catechol groups of

262

PDA. In ethanol, the LC inside the LC-loaded PDA microcapsules leads to a

263

concentration gradient across the wall, and as a consequence, high osmotic pressure

264

derives within the system; what’s more, compared with DMF, there is strong

265

hydrogen bonding between LC and ethanol. Therefore, the release of LC from

266

microcapsules is supposed to be easy in ethanol solution. Also considering the

267

solubility difference of LC in ethanol, 50% ethanol aqueous solution, and 45%

268

ethanol aqueous solution, the release rate was decreased with the decreased LC

269

solubility in these solvents46 The release profiles of LC in above solvents

270

demonstrated the sustained-release properties of LC-loaded PDA microcapsules;

271

more importantly, it provided theoretical basis for further study of LC-loaded PDA

272

microcapsule suspension.

273

3.5 Insecticidal biological assays

274

With the purpose of demonstrating the applicability of the LC-loaded PDA 14


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microcapsule as a favorable formulation in public hygiene and agriculture, an

276

insecticidal biological assay of this formulation against Musca domestica was

277

studied with a commercial LC microcapsule formulation as control. Haixin Cui et

278

al.18 have organized the bioassay tests of LC-loaded polylactic microcapsules against

279

plutella xylostella; the microcapsule (0.68 µm) had the lowest half lethal

280

concentration value (LC50, around 25 µg/mL) among the other two microcapsules,

281

suggesting that efficacy of pesticide gradually increased with the decrease of the

282

microcapsule size.

283

Compared with the above formulations, as indicated in Figure 6 and Table 2, both

284

of the commercial LC microcapsule formulation and the LC-loaded PDA

285

microcapsule had a high 24 h mortality around 100%, but the LC-loaded PDA

286

microcapsule had a lower KT50 (half knock-down time）value, suggesting an

287

advantage of high efficiency. Both samples were treated against Musca domestica

288

after 30 days storage. The results showed that the KT50 value of commercial

289

microcapsule experienced a large increase while the one of the LC-loaded PDA

290

microcapsule presented a slight rise, implying that the LC-loaded PDA microcapsule

291

had an improvement in long-term validity when compared with the commercial one.

292

The high efficacy and long-term validity of LC-loaded PDA MC could be explained

293

by the nanoscale formulation and the adhesion of PDA microcapsules on the surface

294

of pests, which can improve the permeability and absorptivity of pesticide.47,48

295

Polydopamine is inspired by the composition of adhesive proteins in mussels. Phillip 15



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296

B.

297

surface-adherent polydopamine films onto a wide range of inorganic and organic

298

materials.19 More importantly, there were rapid release (absorbed on the PDA MC

299

surface) and sustained release (loaded into the PDA MC) of LC in practical

300

application, and this combined release profile also gave the LC-loaded PDA MC

301

formulation fine efficacy and long-time validity.

Messersmith

has

used

dopamine

self-polymerization

to

form

thin,

302

According to the skin irritation test, both of the samples were diluted by 40 times,

303

and had no irritate to hands after 1 hour’s contact, LC-loaded PDA microcapsule

304

formulation had slight irritate to hands after 3 hours contact, while the control group

305

still had no irritation. Compared with the nanoscale of LC-loaded PDA MC, the

306

controlled commercial formulation was micro-sized, resulting in the difficulty of

307

absorption through the skin. Considering that most sold commercial LC

308

microcapsule formulations presented irritation after 1 hour’s contact, the LC-loaded

309

PDA microcapsule was thought to have been improved in irritation, which could be

310

attributed to its biocompatible material and free of hazardous organic solvents.

311

There was a connection between the irritation and pesticide efficacy, and it was

312

supposed that higher pesticide efficacy leaded to higher irritation.49 Therefore, the

313

results of skin irritation test had confirmed that the LC-loaded PDA microcapsule

314

had stroked a good balance between pesticide efficacy and irritation compared with

315

the commercial LC microcapsule formulations.

316

In summary, PDA microcapsules were used as a carrier for LC via the assembly 16


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317

of DA on the template. The PDA microcapsule with proper size and surface property

318

was versatile, robust and biodegradable, also it eliminated the requirement of

319

considerable hazardous organic solvent and surfactants used by common

320

commercial formulations. The results of TEM and SAXS showed the uniform

321

morphology and hollow structure. Furthermore, the microcapsules exhibited

322

superior bioactivity and long-term validity than the commercial formulation, which

323

should be explained by the sustained-release properties and the adhesion of PDA

324

microcapsule on the surface of pests. It is envisioned that such an environmentally

325

friendly microcapsule formulation using biodegradable material for LC shows great

326

potential for wide applications in public health & agriculture. Further research has

327

been conducted to make the LC-loaded PDA microcapsule a well-dispersed

328

microcapsule suspension with decent suspending rate and pourability.

329 330

Abbreviations Used

331

PDA, polydopamine; LC, lambda-cyhalothrin; LC-PDA MC, LC-loaded PDA

332

microcapsule; TEM, transmission electron microscopy; SAXS, small-angle X-ray

333

scattering; PRYs, pyrethroids; EC, emulsifiable concentrate; WP, wettable powders;

334

ME, microemulsion; EW, emulsion in water; OAAD, octyl-grafted amphiphilic

335

alginate-amide derivative; PLA, polylactide; DA, dopamine; PS, polystyrene;

336

DMDES,

337

N-dimethylformamide; KT50 , half knock-down time; TGA, thermogravimetric

dimethyldiethoxysilane;

LBL,

layer-by-layer;

17


DMF,

N,


338

analysis; T5%, the thermal degradation temperature at 5% weight loss; DTG, the

339

differential thermogravimetry analysis; LC50, half lethal concentration value.

340

Acknowledgement

341

Funding

342

The present study was supported by grants from the National Key Research and

343

Development Plan (No. 2017YFD0200306), the National Natural Science

344

Foundation of China (No. 31200617), and Knowledge Innovation Program of CAS

345

(Grant No. 2013KIP103).

346

Supporting Information Description

347

Additional information on preparation of silica particles, SAXS results and

348

standard curves of LC in different solvents.

349

References

350

(1) Hata, Y.； Zimmermann, S.； Quitschau, M.； Kaiser, M.； Hamburger, M.；

351

Adams, M. Antiplasmodial and antitrypanosomal activity of pyrethrins and

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25



Page 26 of 30

Table1 Optimization of LC-loaded PDA microcapsule formulation No.

LC conc.

vol. of LC solution

MC amt.

LC loading content

(mg/mL)

(mL)

(mg)

(%)

1

10.0

45.0

30.0

26

2

20.0

45.0

30.0

28

3

30.0

45.0

30.0

47

4

40.0

45.0

30.0

48

5

50.0

45.0

30.0

48

6

50.0

35.0

30.0

45

7

50.0

15.0

30.0

37

8

50.0

10.0

30.0

30

9

50.0

45.0

20.0

53

10

50.0

45.0

40.0

49

11

50.0

45.0

50.0

43

Table 2 Toxicity regression equations of the formulations and the 95% confidence interval of the KT50 values formulation

regression equation

95% confidence interval

cml/1d

Y = 1.915X - 1.117

6.18 - 7.90

cml/30d

Y = 2.791X - 2.166

8.73 - 9.30

LC-PDA MC/1d

Y = 1.645X - 0.817

4.84 - 8.26

LC-PDA MC/30d

Y = 2.976X - 1.994

6.12 - 7.74

26


Page 27 of 30


Figure 1. Schematic representation of the preparation of LC-loaded PDA microcapsule and their application in sanitary insect pest.

Figure 2 TEM images of PDA coated silica particles (a,b) and blank PDA microcapsules (c,d) ( b, d:

zoom of up to 2× was performed to visualized the

details for the PDA coated silica particle and blank PDA MC, respectively . )

a

c

b

d

27



Figure 3 SAXS curves of blank PDA microcapsule and LC-loaded PDA microcapsule

Figure 4 (a) TG curves of blank PDA microcapsule and LC-loaded PDA microcapsule in air flow; (b) DTG curves of blank PDA microcapsule (c) DTG curves of LC-loaded PDA microcapsule in air flow

28


Page 28 of 30

Page 29 of 30


Figure 5 Release profiles of LC from LC-loaded PDA microcapsules in different solvents. Data are presented as the mean ± standard deviation (n = 3)

29



Figure 6 The KT50 values and 24h mortality of LC-loaded PDA microcapsule formulation and the commercial LC microcapsule formulation

TOC Graphic

30


Page 30 of 30

Construction and Characterization of a Novel Sustained-Release

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