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. 2023 Jul 18;3(8):2117–2122. doi: 10.1021/jacsau.3c00339

Multi-Stimuli Responsive Sequence Defined Multi-Arm Star Diblock Copolymers for Controlled Drug Release

Subrata Dolui 1, Bhanendra Sahu 1, Sk Arif Mohammad 1, Sanjib Banerjee 1,*
PMCID: PMC10466323  PMID: 37654577

Abstract

graphic file with name au3c00339_0006.jpg

Star-shaped polymeric materials provide very high efficiency toward various engineering and biomedical applications. Due to the absence of straightforward and versatile synthetic protocols, the synthesis of sequence-defined star-shaped (co)polymers has remained a major challenge. Here, a facile approach is developed that allows synthesis of a series of unprecedented discrete, multifunctional four-, six-, and eight-arm star-shaped complex macromolecular architectures based on a well-defined triple (thermo/pH/light)-stimuli-responsive poly(N-isopropylacrylamide)-block-poly(methacrylic acid)-umbelliferone (PNIPAM-b-PMAA)n-UMB diblock copolymer, based on temperature responsive PNIPAM segment, pH-responsive PMAA segment, and photoresponsive UMB end groups. Thus, developed star-shaped copolymers self-assemble in water to form spherical nanoaggregates of diameter 90 ± 20 nm, as measured by FESEM. The star-shaped copolymer’s response to external stimuli has been assessed against changes in temperature, pH, and light irradiation. The star-shaped copolymer was employed as a nanocarrier for pH responsive release of an anticancer drug, doxorubicin. This study opens up new avenues for efficient star-shaped macromolecular architecture construction for engineering and biomedical applications.

Keywords: stimuli-responsive polymer, star polymers, photoresponsive, self-assembly, drug release

In recent years, because of their unique properties, stimuli-responsive sequence defined1−3 functional materials have drawn a lot of attention for a variety of biotechnological applications, including but not limited to drug and gene delivery, catalysis, MRI contrast agents, tissue engineering, and targeted cell detection.4−9 Compared to single- or dual-stimuli-responsive materials, multi-responsive10,11 molecular materials exhibit improved diversity, fine-tunable stimuli response and physicochemical properties. Light has recently gained a lot of attention among all the various stimuli because it can provide temporal control and precise ON/OFF switching.12−14 However, to date, the existing multi-stimuli-responsive materials are unable to provide the desired specificity and tunability. This might be due to the difficulty in precise control of the functionality, degradability, hydrophilicity, etc. Additionally, challenging multistep synthesis and exhaustive purification protocols have restricted deeper fundamental understanding of the multi-stimuli-responsive materials. Extensive research and development of various reversible-deactivation radical polymerization (RDRP) techniques have allowed the synthesis of well-defined polymers.15 Atom transfer radical polymerization (ATRP),16,17 single electron transfer-living radical polymerization (SET-LRP),18 reversible addition fragmentation chain transfer (RAFT) polymerization,19 organometallic-mediated radical polymerization (OMRP),20 and nitroxide-mediated radical polymerization (NMP)21 are some of the extensively used RDRP techniques.

Star polymers,22,23 a type of branched macromolecular structures with linear “arms” emanating from a central branching point, also known as the “core”, can be synthesized via three main approaches: (a) core-first, (b) coupling-onto, or (c) arm-first approach.22,23 However, it is widely known that side reactions, such as star-star coupling, can unintentionally broaden the dispersity and lead to poorly defined polymers. Furthermore, the polymerization techniques (mostly RDRP) employed for the synthesis of star polymers have some disadvantages such as (a) extremely difficult catalyst removal leading to coloration and toxicity of the final product (for ATRP)24 and (b) inefficient catalyst recovery resulting in impurity in the final polymer (for SET-LRP).25 Considering the importance and demand of smart functional polymers for industrial applications, there is an unmet need to design facile protocols for the synthesis of functional polymers for newer applications.

The current work presents a facile synthesis protocol for the preparation of a series of unprecedented multifunctional complex macromolecular architectures based on well-defined multi-arm star triple (thermo/pH/light)-stimuli-responsive poly(N-isopropylacrylamide)-block-poly(methacrylic acid)-umbelliferone {(PNIPAM-b-PMAA)n-UMB} diblock copolymers, based on temperature-responsive PNIPAM segment, pH-responsive PMAA segment and photoresponsive UMB end groups (Scheme 1) toward the development of pH responsive “anti-cancer” drug release nanocarriers. This is also the first report of the use of a multi-arm star (PNIPAM-b-PMAA)n-UMB diblock copolymer-derived nanocontainer for construction of a pH responsive “anti-cancer” drug release vehicle. The synthetic route of triple (thermo/pH/light)-stimuli-responsive four-, six-, and eight-arm star (PNIPAM-b-PMAA)n-UMB diblock copolymers is presented in Scheme 1. Photoresponsive UMB functionalities were introduced into the periphery of the multi-arm star (PNIPAM-b-PMAA)n diblock copolymers to ensure their easy accessibility during intermolecular reactions leading to a reversibly cross-linked network.

Scheme 1. Schematic Pathway for Synthesis of Multi-Arm Star (PNIPAM-b-PMAA)n-UMB Diblock Copolymers.

Scheme 1

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The molecular structure of the star-shaped (PNIPAM-b-PMAA)4-UMB diblock copolymer was ascertained by 1H NMR (Figure 1) and IR (Figure S3) spectroscopic analysis. A 1H NMR spectrum stack plot of the P1–P6 species leading to the synthesis of the four-arm star (PNIPAM-b-PMAA)4-UMB diblock copolymer revealed the respective characteristic peak(s) of the NIPAM segment26 at 1.21 (−CH(CH3)2 of NIPAM repeat unit, signal g, g′), 1.3–2.1 (−CH–CH2 of the NIPAM repeat unit, signal e), 3.3 (−OCH2 of pentaerythritol repeat unit, signal a), 3.6 (−CH(CH3)2 of NIPAM repeat unit adjacent to CONH, signal f), 5.5 (−CONH of NIPAM repeat unit, signal b), 7–8 (−CH of CPAD aromatic unit, signal h), 2.1 (C–CH3 of TBMA repeat unit, signal i), 1.5–1.7 (O–C(CH3)3 of TBMA repeat unit, signal j), 6.8 (−CH of UMB aromatic repeat unit, signal k);27,28 and 6.5 (COOH of PMAA, signal j′). Disappearance of the 1H NMR signal corresponding to the tert-butyl ester functionalities of the (PNIPAM-b-PTBMA)4-UMB diblock copolymers upon hydrolysis further confirmed the synthesis of the (PNIPAM-b-PMAA)4-UMB diblock copolymer.29

Figure 1.

Figure 1

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1H NMR spectra of linear PNIPAM-CTA (P1), four-arm star (PNIPAM)4-CTA (P2), four-arm star (PNIPAM-b-PTBMA)4-CTA (P3), four-arm star (PNIPAM-b-PTBMA)4-Br (P4), four-arm star (PNIPAM-b-PTBMA)4-UMB (P5), and four-arm star (PNIPAM-b-PMAA)4-UMB (P6) in CDCl3. *Solvent (CDCl3) peak.

The IR spectrum (Figure S3) stack plot of the P1–P6 species leading to the synthesis of the four-arm star (PNIPAM-b-PMAA)4-UMB diblock copolymer exhibited the characteristic peaks at 1453, 1536, and 1635 cm–1, which are attributed to −CH3 (bending), C–N (bending), and C=O (stretching). The peak at 845 cm–1 is attributed to the C–Br stretching frequency of the four-arm star (PNIPAM-b-PTBMA)4-Br diblock copolymer. The presence of the tert-butyl ester functionality in the (PNIPAM-b-PTBMA)4-UMB copolymer was confirmed by the peaks for ester C=O stretching at 1635 cm–1 and −C(CH3)3 bending at 1367 cm–1 and the presence of UMB in the (PNIPAM-b-PTBMA)4-UMB copolymer was confirmed by the peak for C–O stretching frequency of the aromatic ester functionality 1325 cm–1. After hydrolysis of the tert-butyl ester groups of the (PNIPAM-b-PTBMA)4-UMB copolymer, the intensity of the peak for −C(CH3)3 bending at 1367 cm–1 decreases, and a new peak appears at 3387 cm–1 attributed to the stretching vibrations of the −OH groups of the −COOH functionalities. Disappearance of the peaks corresponding to the tert-butyl ester functionalities of four-arm star (PNIPAM-b-PTBMA)4-UMB diblock copolymers upon hydrolysis further confirms the successful synthesis of the (PNIPAM-b-PMAA)4-UMB diblock copolymers.

The four-arm star (PNIPAM-b-PMAA)4-UMB diblock copolymer self-assembled in water at pH 7.4, forming nanospherical aggregates, as shown by field emission scanning electron microscopy (FESEM; Figure 2a, DFESEM = 90 ± 20 nm) and dynamic light scattering (DLS; Figure 2c, Dh = 190 nm). A little bit higher diameter value (190 nm) of the nanoaggregates measured by DLS than that by FESEM is probably the result of hydrodynamic nature of the nanoaggregates during DLS measurement.

Figure 2.

Figure 2

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(a) FESEM image of the (PNIPAM-b-PMAA)4-UMB aggregates, (b) histogram of (PNIPAM-b-PMAA)4-UMB aggregates obtained from FESEM analysis, and (c) size distributions of the (PNIPAM-b-PMAA)4-UMB nanoaggregates by DLS.

To study the encapsulation capacity of the (PNIPAM-b-PMAA)4-UMB diblock copolymer nanocarrier, coumarin 102 (C102), a hydrophobic dye encapsulation, was studied using UV–vis spectroscopy. Results of this study revealed that the characteristic C102 absorbance (at 395 nm)30,31 gradually decreased with time as shown in Figure 3a, leading to 42% encapsulation after 24 h incubation as shown in Figure 3c. The intensity of the fluorescence emission spectrum of C102 (Figure 3b) decreases after encapsulation compared with that of neat C102 solution, suggesting successful encapsulation of C102. The absorption and fluorescence intensity of C102 decreased after encapsulation inside the core of the nanocarrier due to a decrease in the solution concentration of C102 after encapsulation in the core of the self-aggregated nanospheres of the (PNIPAM-b-PMAA)4-UMB copolymer. Furthermore, the fluorescence light microscopic image shown in Figure 3d depicted green light-emitting beads of C102 encapsulated (PNIPAM-b-PMAA)4-UMB nanocarriers, confirming successful C102 encapsulation inside the hydrophobic core of the nanocarriers. This experiment proved that (PNIPAM-b-PMAA)4-UMB diblock copolymer self-aggregates may enable encapsulation of guest molecule and act as a nanocarrier.

Figure 3.

Figure 3

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(a) UV–vis spectra of C102 at different time intervals after incubating with self-aggregated (PNIPAM-b-PMAA)4-UMB diblock copolymer; (b) fluorescence emission spectra of C102 solution before and encapsulation with (PNIPAM-b-PMAA)4-UMB nanocarriers (excitation wavelength: 390 nm); (c) % encapsulation of C102 with time; and (d) fluorescent microscopy images of C102 encapsulated (PNIPAM-b-PMAMA)4-UMB nanocarriers.

The synthesized four-arm star (PNIPAM-b-PMAA)4-UMB diblock copolymer was observed to have pH response due to the presence of pH-responsive PMAA segment bearing −COOH functionalities. From the pH metric titration of an aqueous solution of the four-arm star (PNIPAM-b-PMAA)4-UMB diblock copolymer, pKa was found to be 2.0 (Figure S6). Thus, it is expected that the −COOH functionalities of the four-arm star (PNIPAM-b-PMAA)4-UMB diblock copolymer remain deprotonated above the pKa value and protonated below the pKa value.

Multi-arm star (PNIPAM-b-PMAA)n-UMB diblock copolymers were expected to exhibit responsivity against changes in temperature due to the presence of temperature-responsive PNIPAM segments. Compared to the cloud point (TCP) of the neat PNIPAM homopolymer at 31.9 °C, the TCP values of the four-, six-, and eight-arm star (PNIPAM-b-PMAA)n-UMB diblock copolymers were determined to be 57.9, 60.1, and 46.4 °C at pH 6.5, as measured by turbidimetry32,33 (Figure S7). The effect of pH of the solution on the TCP of the four-arm star (PNIPAM-b-PMAA)4-UMB diblock copolymer was also investigated. The TCP changes from 42.4 °C at pH 1.5 to 57.1 °C at pH 6.5 (Figure S7a). This result suggests that solution pH has an influence on the TCP of the copolymer. This is probably because at a pH below 2.0, the four-arm star (PNIPAM-b-PMAA)4-UMB diblock copolymer exists in its neutral form with all of the −COOH functionalities as protonated (pKa of the four-arm star (PNIPAM-b-PMAA)4-UMB diblock copolymer was estimated to 2.0, please refer to Figure S6). Deprotonation of the −COOH groups of the PMAA segments at a pH ≥ 2.0 leads to more hydrophilicity and an increase in the TCP value.

Due to the presence of photoresponsive UMB end groups (which undergo reversible dimerization under 365/254 nm light irradiation) in the multi-arm star (PNIPAM-b-PMAA)n-UMB diblock copolymers, the copolymer is expected to exhibit light responsivity. Light responsiveness of the thin film of the (PNIPAM-b-PMAA)4-UMB diblock copolymer was investigated by irradiating the film with UVA (λmax = 365 nm) and UVC (λmax = 254 nm) light. The progress of the photoinduced cross-linking/de-cross-linking was studied by UV–vis spectroscopy, by monitoring the changes in UMB absorbance at 320 nm (Figure S8a,b).

Model experiments with a hydrophobic dye, C102, suggested that the (PNIPAM-b-PMAA)4-UMB diblock copolymer nanocarrier is capable of encapsulating hydrophobic drug molecules. A model anticancer drug, doxorubicin (DOX), was selected to study the pH-responsive drug release behavior. Notably, when compared to a healthy cell with a pH of 7.4, the cancer cell extracellular matrix pH is acidic in nature (pH ∼ 6.4–6.8).34 DOX was first loaded into the (PNIPAM-b-PMAA)4-UMB nanocarrier and then pH-responsive release of DOX from the (PNIPAM-b-PMAA)4-UMB nanocarrier was investigated using UV–vis spectroscopy (Figure 4). Results revealed that this nanocarrier exhibits successful pH-responsive release of DOX at 37 °C, at pH 5, indicating that the excellent pH-controlled release characteristics result from the unique pH-responsivity nanocarrier.

Figure 4.

Figure 4

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Graphical representation of the doxorubicin (DOX) release profile of the DOX-loaded four-arm star (PNIPAM-b-PMAA)4-UMB (P6) diblock copolymer nanocarrier.

In summary, herein we report, for the first time, synthesis of four-, six-, and eight-arm star triple (thermo/pH/light)-stimuli-responsive (PNIPAM-b-PMAA)n-UMB diblock copolymers, based on temperature-responsive PNIPAM segment, pH-responsive PMAA segment, and photoresponsive UMB end groups. This copolymer was employed to achieve pH-responsive anticancer drug release. The synthesized multi-arm star multi-stimuli-responsive polymer could be useful for application in engineering and biomedical fields as sensors and actuators. There are collective advantages of this facile synthetic approach for the production of multifunctional architectures for emerging applications.

Methods

Materials

The materials used are 4-cyano-4-(phenylcarbonothioylthio) pentanoic acid (CPAD, 97%, Sigma-Aldrich), 2,2′-azobis(2-methylpropionitrile) (AIBN, ≥98%, Sigma-Aldrich), N-isopropylacrylamide (NIPAM, ≥99%, TCI chemicals), tert-butyl methacrylate (TBMA, ≥99%, Sigma-Aldrich), N,N′-dicyclohexylcarbodiimide (DCC, ≥99%, Sigma-Aldrich), doxorubicin hydrochloride (DOX, ≥98%, Sigma-Aldrich), 4-(dimethylamino)pyridine (DMAP, ≥99%, Sigma-Aldrich), pentaerythritol (≥99%, Sigma-Aldrich), dipentaerythritol (Sigma-Aldrich), tripentaerythritol (Sigma-Aldrich), bromine (Br2, ≥99.5%, Sigma-Aldrich), triethylamine (Et3N, ≥99.5%, Sigma-Aldrich), umbelliferone (UMB, ≥99%, Sigma-Aldrich), trifluoroacetic acid (CF3COOH, ≥99.0%), toluene (≥99.5%, Sigma-Aldrich), dichloromethane (DCM, ≥99.8%, Sigma-Aldrich), hexane (≥95%, Sigma-Aldrich), and 1,4-dioxane (≥99%, Sigma-Aldrich). Milli-Q water with a specific resistivity of 18.2 ΜΩ cm at 25 °C was used in all of the experiments. Diethyl ether (Merck, India) was purified by distillation just before use in the polymerization. Chloroform-d (CDCl3) used for NMR spectroscopy was purchased from Sigma-Aldrich.

Synthesis of Multi-arm Star (PNIPAM-b-PMAA)n-UMB Diblock Copolymer

Synthesis of multi-arm star (PNIPAM-b-PMAA)n-UMB diblock copolymer involves the following steps, as explained typically for the synthesis of the (PNIPAM-b-PMAA)4-UMB diblock copolymer. Similar methods were followed for the synthesis of six- and eight-arm star (PNIPAM-b-PMAA)n-UMB diblock copolymers, except dipentaerythritol and tripentaerythritol were used as the multifunctional cores, respectively, instead of pentaerythritol.

Synthesis of Linear PNIPAM-CTA (P1)

Linear (PNIPAM-CTA) was synthesized under an inert atmosphere using a monowave 200 automated synthesizer using [NIPAM]0/[CPAD]0/[AIBN]0 in a molar ratio of 100:1:0.1. First, the required amounts of NIPAM, AIBN, and CPAD were dissolved in toluene in a microwave vessel, equipped with a stirring bar, and heated at 90 °C for 1 h with continuous stirring in a microwave reactor. After the polymerization, the crude mixture was precipitated in prechilled hexane, and the polymer (P1) was isolated by centrifugation.

1H NMR (400 MHz, CDCl3, δ ppm of P1, Figure 1): 1.21 (−CH(CH3)2 of NIPAM repeat unit, signal g-g′), 1.3–2.1 (−CH–CH2 of the NIPAM repeat unit, signal e), 3.6 (−CH(CH3)2) of NIPAM repeat unit adjacent to CONH, signal f), 5.5 (−CONH of NIPAM repeat unit, signal b), 7.0–8.0 (−CH of CPAD unit, signal h).

Synthesis of Four-Arm Star (PNIPAM)4-CTA (P2)

Typically, pentaerythritol (1 equiv), PNIPAM-CTA (P1) (6 equiv), and DMAP (0.6 equiv) were dissolved in dry DCM . The solution was cooled to 0 °C, and DCC (7.2 equiv.) in DCM was added dropwise into the mixture. The reaction mixture was stirred at room temperature for 60 h. After this, unreacted dicyclohexylurea was filtered out, and (PNIPAM)4-CTA was isolated.

1H NMR (400 MHz, CDCl3, δ ppm of P2, Figure 1): 1.21 (−CH(CH3)2 of NIPAM repeat unit, signal g-g′), 1.3–2.1 (−CH–CH2 of the NIPAM repeat unit, signal e), 3.3 (−OCH2 of pentaerythritol repeat unit, signal a), 3.6 (−CH(CH3)2 of NIPAM repeat unit adjacent to CONH, signal f), 5.5 (−CONH of NIPAM repeat unit, signal b), 7.0–8.0 (−CH of CPAD unit, signal h).

Synthesis of Four-Arm Star (PNIPAM-b-PTBMA)4-CTA (P3)

Typically, four-arm star (PNIPAM)4-CTA, AIBN, TBMA, and 1,4-dioxane were taken in a microwave vessel equipped with a stirring bar and heated at 60 °C for 1 h. After the polymerization, the crude mixture was precipitated in prechilled diethyl ether and the polymer was isolated by centrifugation.

1H NMR (400 MHz, CDCl3, δ ppm of P3, Figure 1): 1.21 (−CH(CH3)2 of NIPAM repeat unit, signal g-g′), 1.3–2.1 (−CH–CH2 of the NIPAM repeat unit, signal e), 1.5–1.7 (O–C(CH3)3 of TBMA repeat unit, signal j), 2.1 (-C–CH3 of TBMA repeat unit, signal i), 3.3 (−OCH2 of pentaerythritol repeat unit, signal a), 3.6 (−CH(CH3)2 of NIPAM repeat unit adjacent to CONH, signal f), 5.5 (−CONH of NIPAM repeat unit, signal b), 7.0–8.0 (−CH of CPAD unit, signal h).

Synthesis of Four-Arm Star (PNIPAM-b-PTBMA)4-Br (P4)

Typically, four-arm star (PNIPAM-b-PTBMA)4-CTA (1 equiv) was dissolved in DCM and then purged with N2 for 5 min. Into this vial, a quantitative amount of Br2 (24 equiv) was added and stirred at room temperature for 3 h under dark conditions. After this, the crude mixture was precipitated in prechilled hexane, and the polymer was isolated by centrifugation.

1H NMR (400 MHz, CDCl3, δ ppm of P4, Figure 1): 1.21 (−CH(CH3)2 of NIPAM repeat unit, signal g-g′), 1.3–2.1 (−CH–CH2 of the NIPAM repeat unit, signal e), 1.5–1.7 (O–C(CH3)3 of TBMA repeat unit, signal j), 2.1 (-C–CH3 of TBMA repeat unit, signal i), 3.3 (−OCH2 of pentaerythritol repeat unit, signal a), 5.5 (−CONH of NIPAM repeat unit, signal b), 3.6 (−CH(CH3)2) of NIPAM repeat unit adjacent to CONH, signal f).

Synthesis of Four-Arm Star (PNIPAM-b-PTBMA)4-UMB (P5)

Typically, (PNIPAM-b-PTBMA)4-Br was dissolved in dry tetrahydrofuran (THF) in a two-necked round-bottomed flask equipped with a stir bar. Then, UMB and Et3N were added into the reaction flask at 0 °C, and the reaction mixture was stirred at room temperature for 24 h. After the reaction, the reaction mixture was filtered, and the filtrate was dried to obtain four-arm star (PNIPAM-b-PTBMA)4-UMB.

1H NMR (400 MHz, CDCl3, δ ppm of P5, Figure 1): 1.21 (−CH(CH3)2 of NIPAM repeat unit, signals g-g′), 1.3–2.1 (−CH-CH2 of the NIPAM repeat unit, signal e), 1.5–1.7 (O–C(CH3)3 of TBMA repeat unit, signal j), 2.1 (-C–CH3 of TBMA repeat unit, signal i), 3.3 (−OCH2 of pentaerythritol repeat unit, signal a), 3.6 (−CH(CH3)2 of NIPAM repeat unit adjacent to CONH, signal f), 5.5 (−CONH of NIPAM repeat unit, signal b), 6.8 (−CH of UMB repeat unit, signal k).

Synthesis of Four-Arm Star (PNIPAM-b-PMAA)4-UMB (P6)

Typically, CF3COOH (5 times excess, 20 equiv) was added dropwise to a solution of four-arm star (PNIPAM-b-PTBMA)4-UMB DCM, and the reaction mixture was stirred for 72 h at room temperature. After this, the final product, the four-arm star (PNIPAM-b-PMAA)4-UMB diblock copolymer, was isolated after purification by washing with hexane.

1H NMR (400 MHz, CDCl3, δ ppm of P6, Figure 1): 1.21 (−CH(CH3)2 of NIPAM repeat unit, signal g-g′), 1.3–2.1 (−CH–CH2 of the NIPAM repeat unit, signal e), 2.1 (-C–CH3 of MAA repeat unit, signal i), 3.3 (−OCH2 of pentaerythritol repeat unit, signal a), 3.6 (−CH(CH3) of NIPAM repeat unit adjacent to CONH, signal f), 5.5 (−CONH of NIPAM repeat unit, signal b), 6.8 (−CH of UMB repeat unit, signal k), 6.5 (-COOH of PMAA, signal j′).

Aggregation Procedure

Typically, the four-arm star (PNIPAM-b-PMAA)4-UMB diblock copolymer (3 mg) was dissolved in water (3 mL) and was kept in a closed vial for 24 h.

Dye Uptake Procedure

Typically, the four-arm star (PNIPAM-b-PMAA)4-UMB diblock copolymer was added to a solution of C102, and it was kept undisturbed for 24 h. The percent dye encapsulation with time was monitored by UV–vis spectroscopy. After 24 h, dye encapsulated polymer spheres were collected by centrifugation and washed thoroughly to remove any physisorbed dye.

pH Titration

pH of an aqueous solution of the four-arm star (PNIPAM-b-PMAA)4-UMB diblock copolymer was adjusted to pH 1.5, and then the solution was titrated against 0.25 N NaOH solution until the pH reached 12.5. During this titration study, the solution pH was detected using a pH meter.

Preparation of DOX-Loaded Four-Arm Star (PNIPAM-b-PMAA)4-UMB

Typically, 10 mg of four-arm star (PNIPAM-b-PMAA)4-UMB was added to a solution of 3 mg of DOX in 10 mL of water, and the mixture was stirred for 24 h under dark conditions in a shaker. Finally, the DOX-loaded star polymer (DOX-polymer) was isolated by centrifugation.

Drug Release Study

The pH-responsive release of DOX from the DOX-polymer (as obtained via protocol mentioned above) was studied at pH 5 and 37 °C as follows: 5 mL of phosphate buffer (pH 7.4) or phosphate-citrate buffer (pH 5.5) and 10 mg of DOX polymer were combined and incubated at the aforementioned temperature. At regular intervals, the percent drug release was monitored by UV–vis spectroscopy (at the wavelength 481 nm).

Acknowledgments

This research was supported by the grants from SERB, Government of India through Early Career Research Award (ECR/2018/001990) and Core Research Grant (CRG/2022/002359), DSIR, Government of India through CRTDH grant (CRTDH-11011/1/2022-IRD) and in part by the Research Initiation Grant from IIT Bhilai. The authors also thank Central Instrument Facility, IIT Bhilai for the equipment facilities. B.S. thanks UGC, Government of India for a fellowship. Dr. Sudip Sau (NISER-Bhubaneswar) is acknowledged for helping with NMR measurements.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacsau.3c00339.

  • Tables of results, additional analyses including UV-Vis, NMR and IR spectra (PDF)

Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. CRediT: Subrata Dolui conceptualization, investigation, methodology, writing-original draft, writing-review & editing; Bhanendra Sahu investigation, methodology, writing-review & editing; Sk Arif Mohammad investigation, methodology, writing-review & editing; Sanjib Banerjee conceptualization, funding acquisition, methodology, project administration, resources, supervision, writing-review & editing.

The authors declare the following competing financial interest(s): One or more of the authors have filed a patent application related to the subject matter discussed in this article.

Supplementary Material

au3c00339_si_001.pdf (487.9KB, pdf)

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