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. 2023 Apr 3;12(4):510–517. doi: 10.1021/acsmacrolett.3c00044

Molecular Weight-Dependent Diffusion, Biodistribution, and Clearance Behavior of Tetra-Armed Poly(ethylene glycol) Subcutaneously Injected into the Back of Mice

Shohei Ishikawa †,*, Motoi Kato ‡, Jinyan Si †, Lin Chenyu †, Kohei Kimura †, Takuya Katashima †, Mitsuru Naito §, Masakazu Kurita ‡,*, Takamasa Sakai †,*
PMCID: PMC10116643  PMID: 37012585

Abstract

graphic file with name mz3c00044_0007.jpg

Four-armed poly(ethylene glycol) (PEG)s are essential hydrophilic polymers extensively utilized to prepare PEG hydrogels, which are valuable tissue scaffolds. When hydrogels are used in vivo, they eventually dissociate due to cleavage of the backbone structure. When the cleavage occurs at the cross-linking point, the hydrogel elutes as an original polymer unit, i.e., four-armed PEG. Although four-armed PEGs have been utilized as subcutaneously implanted biomaterials, the diffusion, biodistribution, and clearance behavior of four-armed PEG from the skin are not fully understood. This paper investigates time-wise diffusion from the skin, biodistribution to distant organs, and clearance of fluorescence-labeled four-armed PEGs with molecular weight (Mw) ranging from 5–40 kg/mol subcutaneously injected into the back of mice. Changes over time indicated that the fate of subcutaneously injected PEGs is Mw-dependent. Four-armed PEGs with Mw ≤ 10 kg/mol gradually diffused to deep adipose tissue beneath the injection site and distributed dominantly to distant organs, such as the kidney. PEGs with Mw ≥ 20 kg/mol stagnated in the skin and deep adipose tissue and were mainly delivered to the heart, lung, and liver. The fundamental understanding of the Mw-dependent behavior of four-armed PEGs is beneficial for preparing biomaterials using PEGs, providing a reference in the field of tissue engineering.

Poly(ethylene glycol) (PEG)s are representative hydrophilic and biocompatible polymers utilized to synthesize biomaterials such as artificial extracellular matrix (ECM), drug delivery carriers, and hydrogels because of their bioinert nature originating from high volume exclusion, low immune reaction, and protein exclusion.1−4 Owing to their unique characteristics, COVID-19 vaccines include PEGs with a molecular weight (Mw) of approximately 2 kg/mol, which is widely shared and studied by several scientists and clinicians, indicating an increasing focus on PEG application and characteristics.5−7 Drugs comprising or conjugating with PEGs, such as PEGylated materials, administered intravenously or intramuscularly in vivo, are first distributed to organs such as the heart, lungs, liver, and kidneys before being excreted from the body through the clearance system.8−10 The biodistribution and excretion of molecules intravenously injected can be affected by the polymer Mw, molecular structure, charge, and hydrophilic/hydrophobic properties.8,11−14 Therefore, establishing the basis of biodistribution of polymers in vivo has facilitated the development of interferon, vaccine dispersant, and PEGylated drugs.15 Intelligent polymer micelles consisting of PEG copolymers have been developed to accumulate in tumors via enhanced permeability and retention effects. Moreover, methods for establishing controlled drug delivery systems have been proposed, resulting in clinical trials.16 This success is due to the extensive research on the biodistribution and clearance of polymers by researchers worldwide. Therefore, basic information regarding biodistribution and excretion is critical for the development of polymeric biomaterials for clinical implementation.

Although several reports have extensively examined the fate of intravenous-injected polymeric composites, the clearance behavior of PEGs injected subcutaneously remains unclear. Four-armed PEG, in particular, functions as a fundamental polymer to produce biomaterials and is thus suitable for preparing PEG-based hydrogels,17,18 which serve as hemostatic agents, artificial vitreous body, and cell scaffolds.19−22 When PEG hydrogels are implanted subcutaneously and the bond between four-armed PEGs is cleaved by chemical or physical stimuli, the polymeric clusters consisting of four-armed PEG are obtained as eluates. In particular, when a gel is prepared from four-armed PEG, and the formed bonds are completely cleaved, the original four-armed PEG is obtained as an eluate. However, even the biodistribution and clearance behavior of four-armed PEG subcutaneously, especially its Mw-dependence, is still elusive, limiting its clinical application. This information provides a concrete reference for using PEG hydrogels as biomaterials.

In this study, we characterized the diffusion, biodistribution to distant organs, and clearance behavior of four-armed PEG with a Mw of 5–40 kg/mol subcutaneously injected into the back of mice. Red fluorescence was used to partially functionalize four-armed PEG and visualize PEG localization, which was evaluated by fluorescence imaging analyses. In vitro permeation studies using a porous membrane revealed the Mw-dependent permeation behavior. Time-wise changes in the diffusion behavior from the injection site and in dissected deep adipose tissue beneath the injection site were characterized by observing fluorescence intensity at 0, 1, 4, 24, 48, 72, and 168 h after subcutaneous injection. Furthermore, biodistribution to distant organs, such as the heart, lung, liver, and kidney, was evaluated by dissecting these organs and observing the fluorescence intensity, which suggested a Mw-dependent biodistribution. Our findings indicate that PEG with Mw below 10 kg/mol would be suitable precursors of hydrogels implanted subcutaneously because it readily diffuses once dissociated in subcutaneous tissue.

In this study, amine-terminated four-armed PEGs with Mw values of 5, 10, 20, and 40 kg/mol (hereafter referred to as PEG5, PEG10, PEG20, and PEG40, respectively) were partly modified using Alexa Fluor 594 (Alexa) through a condensation reaction between primary amine of PEG and N-hydroxysuccinimide ester (NHS) of Alexa to track diffusion, biodistribution, and clearance behavior of the four-armed PEGs (Figure 1a). To ensure consistent fluorescence intensity across different Mw PEG aqueous solutions, we maintained a constant mole of Alexa conjugated to the PEG relative to its weight. This means that the modification rate of Alexa to the end of the PEG differs for each PEG. As a result, the relative fluorescence intensity of a 10 g/L PEG solution in neutral phosphate-buffered saline (PBS) was similar to that of Alexa, even though the Mw differed (Table S1), indicating that the fluorescence was successfully tethered to PEGs regardless of the Mw. Furthermore, since the amide cross-linking between PEG and Alexa hardly dissociates under in vivo conditions (pH 7.4 and 37 °C),23 fluorescence showed PEG localization and not that of Alexa molecules cleaved from PEGs.

Figure 1.

Figure 1

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Characterization of Alexa-modified PEGs. (a) Conceptual chemical structure of four-armed PEGs. Four-armed PEGs functionalized with propyl amine were modified using Alexa Fluor 594 (termed Alexa). The molecular weight (Mw) of PEGs was 5, 10, 20, and 40 kg/mol, thereafter denoted as PEG5, PEG10, PEG20, and PEG40, respectively. (b) Viscosity (η) relative to PBS as a function of Mw. Circle and triangle symbols represent the η values of PEGs and Alexa-modified PEGs, respectively. (c) Diagram of permeation behavior after addition of the Alexa-modified PEG solutions. (d) Percent permeated Alexa (black circle) and Alexa-modified PEG5 (red square), PEG10 (green triangle), PEG20 (blue inverted triangle), and PEG40 (purple left-arrowed triangle) from the top to the bottom compartment. Inset image shows percent permeated up to 1 h.

It is well-known that PEG can form nanoparticles when modified with hydrophobic fluorescence molecules.12 We confirmed that Alexa-modified PEGs did not form nanoparticles under experimental conditions on the basis of viscosity and permeation measurements (Figure 1b-d). The viscosity of Alexa-modified PEG solutions was nearly the same as those of original PEG solutions regardless of Mw (Figure 1b), hinting that the modification did not induce polymeric nanoparticles. The slight increase in relative viscosity with Mw is likely due to an increase in the hydrodynamic radius.24,25 Moreover, we investigated the permeation behavior of PEG using a membrane with a pore size of 3.0 μm (Figure 1c and d). The permeation rate decreased with increasing Mw, and Mw-dependent permeation was observed for 24 h. After 24 h, the percent permeated was 99.0%, 94.7%, 93.8%, 88.9%, and 87.4% for Alexa, PEG5, PEG10, PEG20, and PEG40, respectively. This Mw-dependent permeation strongly suggests that the PEGs were successfully modified by Alexa, and PEG nanoparticles were negligible. Notably, theories expect the non-negligible retardation effect caused by porous structure, even when the radii of the diffusive (PEGs; ∼nm) are much smaller than the pore size (∼ μm).26 Therefore, Alexa-modified four-armed PEG most probably exists as a polymer, allowing a detailed discussion of the Mw-dependence, as detailed in the following sections.

To observe the clearance of PEGs from the subcutaneous tissue, we first subcutaneously injected a PBS solution of Alexa-modified PEGs in the back of mice (Figure 2a), and changes in local fluorescence intensity were evaluated by bidirectional imaging at 0, 1, 4, 24, 72, and 168 h postinjection (Figure 2b). From the top view, circular red fluorescence was observed on the initial injection site. With the decrease of fluorescence at the initial injection site, the fluorescence spread to nearby tissue, demonstrating the diffusion of PEG molecules over time (Figure 2b). Quantitative analyses of local fluorescence images illustrated decreased injected PEG over time (Figure 2c) and the differences between PEGs of different Mw. While PEG5 almost disappeared at 72 h, those with Mw > 5 kg/mol gradually attenuated over 168 h but did not completely disappear. The Mw-dependent diffusion behavior in vivo was comparable to that of in vitro permeation despite its diffusion speed being different. The diffusion behavior from the side view was consistent with the findings from the top view, showing a Mw-dependent diffusion to deeper tissues that is composed of a two-phase profile: (i) initial rapid diffusion and (ii) gradual diffusion (Figure 2d-f). The initial rapid diffusion is due to the resilience of the subcutaneous tissue expanded by the injection of PEG solution. When the solution is injected into subcutaneous tissue, the internal pressure under the skin temporarily increases, and the injected PEG solution is forced to diffuse until subcutaneous tissue returns to its pre-expansion state. After the initial rapid and forced diffusion, the slower diffusion is consistent with the known lymphatic system,27 which removes fluid and solutes from the interstitial space. Therefore, subcutaneously injected PEG molecules may diffuse toward deep tissues such as deep adipose tissue beneath the injection site. Indeed, fluid in the skin and subcutaneous tissues was absorbed from collective lymph vessels or diffused to deep tissue, such as adipose tissues; transported into blood vessels via lymph nodes;27,28 and distributed to distant organs. It is reasonable to consider that macromolecules such as PEGs follow the same route.

Figure 2.

Figure 2

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Diffusion behavior of Alexa-modified PEGs subcutaneously injected into the back of mice. (a, d) Diagram of injection site from the top (a) and side (d) of mice. (b, e) Fluorescence images from the top (b) and side (e) of mice at 0, 1, 4, 24, 72, and 168 h postinjection with Alexa-modified PEGs solutions. Scale bar: 5 mm. (c, f) Changes in fluorescence intensity over time from the top (c) and side (f) of mice after injection of Alexa (black circle), Alexa-modified PEG5 (red square), PEG10 (green triangle), PEG20 (blue inverted triangle), and PEG40 (purple left-arrowed triangle). Dashed lines between plots are shown as a guide.

Deep adipose tissue, including beneath the injection site (extending back to the axillar), was dissected as subcutaneous tissues toward regional lymph nodes (Figure 3a). Fluorescence intensity changes over time were evaluated with samples obtained at 0, 1, 4, 24, 72, and 168 h after injection (n = 3 each; Figure 3b,c). Alexa-labeled PEG was detected within deep adipose tissues collected just after injection (0 h), indicating that subcutaneously injected PEG was reached into the deep tissues away from the injection site due to initial forced diffusion via solution injection. Time-wise analyses illustrated differential findings between PEG with different Mw. Fluorescent signals with PEG5 disappeared promptly, similar to that in the Alexa-only solution. Signals with PEG10 extended evenly to the whole tissues and consistently decreased over 168 h of observation, while the reduction of the spread of fluorescence signals of PEG20 and PEG40 stagnated within 168 h of observation. Thus, diffusion of PEG from adipose tissue could be differentially classified into the following three categories: (i) fast solution-like diffusion (PEG5), (ii) gradual diffusion (PEG10), and (iii) resistant diffusion (PEG20 and PEG40).

Figure 3.

Figure 3

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Distribution of Alexa-modified PEGs in the deep adipose tissues of mice. (a) Diagram of dissected subcutaneous deep adipose tissues toward regional lymph nodes. Photographs show representative deep adipose tissues. Scale bar: 5 mm. (b) Fluorescence images of deep adipose tissues at 0, 1, 4, 24, 72, and 168 h postinjection with Alexa and Alexa-modified PEGs. Scale bar: 5 mm. (c) Time-wise fluorescence intensity changes in the adipose tissues after injecting Alexa (black circle), Alexa-modified PEG5 (red square), PEG10 (green triangle), PEG20 (blue inverted triangle), and PEG40 (purple left-arrowed triangle). Dashed lines between plots are shown as a guide.

Detailed PEG diffusion in subcutaneous tissues was further analyzed in a lump of adipose tissues and axillary lymph nodes collected 4 h after PEG10 injection (gradual diffusion pattern; Figure 4a). Of these PEGs, PEG10 diffuses relatively gradually compared with the other PEG samples, which can be reliably pinpointed experimentally for the distribution of PEG. With dispersed distribution throughout the tissues, localized PEGs were confirmed in lymph nodes (Figure 4b). A portion of the subcutaneously injected PEGs migrates into regional lymph nodes. Similar to reports for macromolecules,27,29 the lymphatic vascular plays a significant role in the migration of subcutaneously injected PEGs into the blood circulatory system.

Figure 4.

Figure 4

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Representative images of adipose 4 h after PEG10 injection. (a) Representative bright vision (left) and fluorescence image (right) of deep adipose tissues. A solid green line indicates the position of the section. Scale bar: 2 mm. (b) Slice image of deep adipose samples stained with hematoxylin and eosin (H&E; top) and visualized by PEG and DAPI (bottom). In H&E staining, yellow and orange dotted lines show the lymph nodes and deep adipose tissue, respectively. In the fluorescence image, red and blue show PEG-modified with Alexa and DAPI-stained nuclei, respectively. White arrows show PEGs accumulated in lymph nodes. Scale bar: 1 mm.

It is well-known that circulating macromolecules such as PEG show a differential organ distribution depending on their Mw.8,12,13 Especially in the kidney, macromolecules smaller than the glomerular diameter migrate into the glomerulus, accumulate, and are excreted into the urine, while larger ones are hardly secreted.30 In the study presented here, the hydrodynamic diameter of PEG10 corresponded to the size of the known glomerular filtration limit (3–5 nm).

To observe the systemic distribution profiles of PEG after subcutaneous injection, over time fluorescence intensity changes in the heart, lung, liver, and kidney were evaluated at 0, 1, 4, 24, 72, and 168 h postinjection (n = 3 each; Figure 5a,b, and Figure S1). Consistent with a previous report, there was an apparent difference between the kidney and the other organs.8 In the kidney, the signal intensities of PEG5 and PEG10 (peaked at 1–4 h) were higher than those of PEG20 and PEG40, while signals of PEG20 and PEG40 (peaked at 24 h) were higher in the heart, lung, and livers (Figure 5b).

Figure 5.

Figure 5

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Biodistribution of Alexa-modified PEGs injected subcutaneously into the back of mice. (a) Representative photos of the heart, lung, liver, and kidney. Scale bar: 5 mm. (b) Fluorescence intensity changes over time of Alexa (black circle), Alexa-modified PEG5 (red square), PEG10 (green triangle), PEG20 (blue inverted triangle), and PEG40 (purple left-arrowed triangle) distributed in the heart, lung, liver, and kidney. Dashed lines between plots are shown as a guide.

To evaluate the biodistribution and clearance behavior of PEGs in the kidney, urine collected from the bladder underwent fluorescence analysis (Figure 6a). Although a reliable quantitative evaluation was difficult, fluorescence signals could be detected in Alexa, PEG5, and PEG10 samples at earlier time points (1 to 4 h). Further histological analyses of the kidney samples obtained 4 h after PEG10 injection revealed highly accumulated fluorescence in glomeruli (Figure 6b).

Figure 6.

Figure 6

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Clearance behavior of PEGs in the kidney. (a) Photos and fluorescence images of urine collected from the bladder at 0, 1, 4, 24, 72, and 168 h after injection with Alexa and Alexa-modified PEGs solution. Scale bar: 5 mm. (b) Histological images of the kidney 4 h after injection with PEG10. The location of H&E staining and sliced fluorescence images are indicated by green, blue, and black lines. Scale bar: 5 mm in the photographs and fluorescence images and 0.5 mm in histological images. The renal cortex glomerulus is indicated using black and white arrows.

In the current study, time-wise distribution of subcutaneously injected PEGs in the skin, subcutaneous deep adipose tissue, lymph nodes, and distant organs such as the heart, lung, liver, and kidney was comprehensively characterized. Our findings are consistent with the hypothesis that a portion of subcutaneously injected PEGs is collected into the circulation system via lymphatic nodes and distributed to distant organs. PEG in distant organs is considered to be in equilibrium with the circulatory system, and PEGs in the circulatory system are defined by influx from subcutaneous tissues and excretion from the kidney and liver. Based on our analyses, PEGs with lower Mw, such as PEG5 and PEG10, disappear from the skin and subcutaneous tissues and are delivered to and possibly excreted dominantly in the kidney. The entire process was rapid. On the other hand, PEGs with higher Mw, such as PEG 20 and PEG40, resided for longer periods in the skin, subcutaneous tissues, and distant organs other than the kidney.

On the basis of these experimental results, the following two essential points were made. First, the Mw value of PEG should be carefully selected according to the biomedical application. PEG with Mw ≥ 40 kg/mol accumulates in the liver and is consequently advantageous for drug delivery carrier applications, which require long-term localized action, such as Pegasys (also called Peginterferon α-2a).31 On the other hand, ethylene glycol units are cleaved by in vivo oxidative biodegradation on a long time scale, resulting in the generation of toxic radicals.32 Thus, although PEG has unique biocompatibility, it is advisible to utilize PEGs with suitable Mw. In particular, for the development and use as hydrogel scaffolds that require complete disappearance after functionalization as biomaterials, it may be reasonable to select PEGs with a Mw below 10 kg/mol as precursors of hydrogels because such PEGs show gradual diffusion and clearance, primarily in the kidney.

Second, fluorescent labeling and detection are more advantageous than the previously described methods. The present detection method is superior to existing methods for real-time imaging. To observe the clearance behavior of intravenously injected polymers, radiolabeled isotopes such as 14C and 125I have been introduced into PEG molecules instead of fluorescence-labeled PEG molecules.8,13 However, the real-time clearance behavior could not be observed owing to technical difficulties, thereby limiting the real-time evaluation of subcutaneous distribution. Furthermore, introducing such isotopes is not ideal because this requires a multistep synthetic process,13 and isotopes show toxicity.33,34 The fluorescence labeling in this study is reasonable, in terms of the simple preparation method and low toxicity of the fluorescence dye. On the other hand, multiple fluorescence imaging is also one of the important properties of our study, allowing us to clearly detect PEG localization in distant organs by detecting various fluorescence, such as cells and polymers (as shown in Figure 4b and 6b).

Nevertheless, despite these advantages, this red fluorescence imaging is unsuitable for real-time observation in deep tissues, because it is difficult to detect fluorescence due to high tissue absorption and autofluorescence.35 For this reason, the Mw-dependent clearance pathway was not fully investigated, as the fluorescence intensity could not be observed in the excrement. Such a clearance pathway is essential for the biocompatible evaluation of polymers where scaffolds are implanted to regenerate defective tissues. In this case, employing near-infrared (NIR) fluorescence may allow the real-time detection of PEGs because of the relatively minimum tissue absorption and autofluorescence. Therefore, although special equipment is required, multiple methods, such as isotope and NIR observation, should be applied in the future to comprehensively detect PEG localization.

In summary, Alexa-modified PEGs subcutaneously injected into the backs of mice showed Mw-dependent diffusion in the skin, biodistribution to distant organs, and clearance behavior. PEGs with Mw ≤ 10 kg/mol gradually diffused in the subcutaneous tissue, migrated to deep adipose tissue, and distributed to distant organs, mainly the kidney. On the other hand, PEGs with a Mw ≥ 20 kg/mol stagnated in the skin and were mainly delivered to the heart, lungs, and liver. The findings of this study clarify the basis of the in vivo diffusion, biodistribution, and clearance behavior of four-armed PEGs, which are currently extensively used as basic materials for producing clinically relevant biomaterials. It is noteworthy that even tetra-armed polymers, ideal eluates of PEG hydrogels, cannot easily diffuse and accumulate in specific organs. Conventional eluates of PEG hydrogels exist as polymeric clusters with higher Mw,36 further retarding their clearance. These clusters possibly remain in subcutaneous tissue and deep adipose until their molecular weight falls below 10 kg/mol. Taken together, the observed diffusion, biodistribution, and clearance behavior clarified the fate of four-armed PEGs, thus providing an essential reference for synthesizing and implementing PEG-based biomaterials.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsmacrolett.3c00044.

  • Additional experimental details, materials, and methods; results of tests conducted to evaluate fluorescence intensity; photos of collected tissues (PDF)

Author Contributions

⊥ S.I. and M.K. contributed equally. S.I. and M.K. designed the study. S.I., M.K., J.S., L.C.Y., and K.K. performed all the experiments. S.I., M.K., T.K., and M.N. performed data acquisition and/or analysis. All authors drafted and reviewed the manuscript. Administrative, technical, and supervisory tasks were handled by S.I., M.K., and T.S.

This work was supported by Grant-in-Aid for the Japan Society for the Promotion of Science (JSPS) Fellows (Grant No. 20J01344), Early-Career Scientists (Grant No. 21K18063) to S.I., JSPS Fellows (Grant No. 21J10828) to M.K., Transformative Research Areas (Grant No. 20H05733) to T.S., Challenging Research (Pioneering) (Grant No. 20K20609) to M.K., the Japan Science and Technology Agency (JST) CREST (Grant No. JPMJCR1992) to T.S., the Japan Agency for Medical Research and Development (AMED) Moon-shot R&D (Grant No. 21zf0127002h0001) to T.S. and M.K. This study was also supported by Data Creation and Utilization-Type Material Research and Development Project grant number JPMXP1122714694 to T.S.

The authors declare no competing financial interest.

Supplementary Material

mz3c00044_si_001.pdf (359.2KB, pdf)

References

  1. Lin C. C.; Anseth K. S. PEG Hydrogels for the Controlled Release of Biomolecules in Regenerative Medicine. Pharm. Res. 2009, 26 (3), 631–643. 10.1007/s11095-008-9801-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Knop K.; Hoogenboom R.; Fischer D.; Schubert U. S. Poly(Ethylene Glycol) in Drug Delivery: Pros and Cons as Well as Potential Alternatives. Angew. Chemie - Int. Ed. 2010, 49 (36), 6288–6308. 10.1002/anie.200902672. [DOI] [PubMed] [Google Scholar]
  3. Slaughter B. V.; Khurshid S. S.; Fisher O. Z.; Khademhosseini A.; Peppas N. A. Hydrogels in Regenerative Medicine. Adv. Mater. 2009, 21 (32–33), 3307–3329. 10.1002/adma.200802106. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Suk J. S.; Xu Q.; Kim N.; Hanes J.; Ensign L. M. PEGylation as a Strategy for Improving Nanoparticle-Based Drug and Gene Delivery. Adv. Drug Delivery Rev. 2016, 99, 28–51. 10.1016/j.addr.2015.09.012. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Bruusgaard-Mouritsen M. A.; Johansen J. D.; Garvey L. H. Clinical Manifestations and Impact on Daily Life of Allergy to Polyethylene Glycol (PEG) in Ten Patients. Clin. Exp. Allergy 2021, 51 (3), 463–470. 10.1111/cea.13822. [DOI] [PubMed] [Google Scholar]
  6. Sellaturay P.; Nasser S.; Islam S.; Gurugama P.; Ewan P. W. Polyethylene Glycol (PEG) Is a Cause of Anaphylaxis to the Pfizer/BioNTech MRNA COVID-19 Vaccine. Clin. Exp. Allergy 2021, 51 (6), 861–863. 10.1111/cea.13874. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Garvey L. H.; Nasser S. Anaphylaxis to the First COVID-19 Vaccine: Is Polyethylene Glycol (PEG) the Culprit?. Br. J. Anaesth. 2021, 126 (3), e106–e108. 10.1016/j.bja.2020.12.020. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Longley C. B.; Zhao H.; Lozanguiez Y. L.; Conover C. D. Biodistribution and Excretion of Radiolabeled 40 KDa Polyethylene Glycol Following Intravenous Administration in Mice. J. Pharm. Sci. 2013, 102 (7), 2362–2370. 10.1002/jps.23506. [DOI] [PubMed] [Google Scholar]
  9. Yu M.; Zheng J. Clearance Pathways and Tumor Targeting of Imaging Nanoparticles. ACS Nano 2015, 9 (7), 6655–6674. 10.1021/acsnano.5b01320. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Webster R.; Didier E.; Harris P.; Siegel N.; Stadler J.; Tilbury L.; Smith D. PEGylated Proteins: Evaluation of Their Safety in the Absence of Definitive Metabolism Studies. Drug Metab. Dispos. 2007, 35 (1), 9–16. 10.1124/dmd.106.012419. [DOI] [PubMed] [Google Scholar]
  11. Doan T. N.; Bernard F. C.; McKinney J. M.; Dixon J. B.; Willett N. J. Endothelin-1 Inhibits Size Dependent Lymphatic Clearance of PEG-Based Conjugates after Intra-Articular Injection into the Rat Knee. Acta Biomater. 2019, 93, 270–281. 10.1016/j.actbio.2019.04.025. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Kang H.; Rho S.; Stiles W. R.; Hu S.; Baek Y.; Hwang D. W.; Kashiwagi S.; Kim M. S.; Choi H. S. Size-Dependent EPR Effect of Polymeric Nanoparticles on Tumor Targeting. Adv. Healthc. Mater. 2020, 9 (1), 1901223. 10.1002/adhm.201901223. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Yamaoka T.; Tabata Y.; Ikada Y. Distribution and Tissue Uptake of Poly(Ethylene Glycol) with Different Molecular Weights after Intravenous Administration to Mice. J. Pharm. Sci. 1994, 83 (4), 601. 10.1002/jps.2600830432. [DOI] [PubMed] [Google Scholar]
  14. Huang X.; Li L.; Liu T.; Hao N.; Liu H.; Chen D.; Tang F. The Shape Effect of Mesoporous Silica Nanoparticles on Biodistribution, Clearance, and Biocompatibility in Vivo. ACS Nano 2011, 5 (7), 5390–5399. 10.1021/nn200365a. [DOI] [PubMed] [Google Scholar]
  15. Naito M.; Watanuki Y.; Toh K.; Yum J.; Kim B. S.; Taniwaki K.; Ogura S.; Ishida H.; Cho M.; Chaya H.; Miyajima K.; Yamasaki Y.; Osada K.; Minegishi K.; Aoki Y.; Miyata K. Size-Tunable PEG-Grafted Copolymers as a Polymeric Nanoruler for Passive Targeting Muscle Tissues. J. Controlled Release 2022, 347 (April), 607–614. 10.1016/j.jconrel.2022.05.030. [DOI] [PubMed] [Google Scholar]
  16. Bae Y.; Kataoka K. Intelligent Polymeric Micelles from Functional Poly(Ethylene Glycol)-Poly(Amino Acid) Block Copolymers. Adv. Drug Delivery Rev. 2009, 61 (10), 768–784. 10.1016/j.addr.2009.04.016. [DOI] [PubMed] [Google Scholar]
  17. Sakai T.; Matsunaga T.; Yamamoto Y.; Ito C.; Yoshida R.; Suzuki S.; Sasaki N.; Shibayama M.; Chung U. Il. Design and Fabrication of a High-Strength Hydrogel with Ideally Homogeneous Network Structure from Tetrahedron-like Macromonomers. Macromolecules 2008, 41 (14), 5379–5384. 10.1021/ma800476x. [DOI] [Google Scholar]
  18. Sakai T.Physics of Polymer Gels; Wiley-VCH Verlag, 2020. 10.1002/9783527346547. [DOI] [Google Scholar]
  19. Okata S.; Hoshina K.; Hanada K.; Kamata H.; Fujisawa A.; Yoshikawa Y.; Sakai T. Hemostatic Capability of a Novel Tetra-Polyethylene Glycol Hydrogel. Ann. Vasc. Surg. 2022, 84, 398–404. 10.1016/j.avsg.2022.01.016. [DOI] [PubMed] [Google Scholar]
  20. Hayashi K.; Okamoto F.; Hoshi S.; Katashima T.; Zujur D. C.; Li X.; Shibayama M.; Gilbert E. P.; Chung U. Il; Ohba S.; Oshika T.; Sakai T. Fast-Forming Hydrogel with Ultralow Polymeric Content as an Artificial Vitreous Body. Nat. Biomed. Eng. 2017, 1 (3), 1–7. 10.1038/s41551-017-0044. [DOI] [Google Scholar]
  21. Ishikawa S.; Kamata H.; Chung U. Il; Sakai T. On-Demand Retrieval of Cells Three-Dimensionally Seeded in Injectable Thioester-Based Hydrogels. RSC Adv. 2021, 11 (38), 23637–23643. 10.1039/D1RA01934A. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Ishikawa S.; Yoshikawa Y.; Kamata H.; Chung U. Il; Sakai T. Simple Preparation of Injectable Hydrogels with Phase-Separated Structures That Can Encapsulate Live Cells. ACS Appl. Mater. Interfaces 2022, 14 (31), 35444–35453. 10.1021/acsami.2c09906. [DOI] [PubMed] [Google Scholar]
  23. East A. L. L. On the Hydrolysis Mechanisms of Amides and Peptides. Int. J. Chem. Kinet. 2018, 50 (10), 705–709. 10.1002/kin.21194. [DOI] [Google Scholar]
  24. Tsenoglou C. Molecular Weight Polydispersity Effects on the Viscoelasticity of Entangled Linear Polymers. Macromolecules 1991, 24 (8), 1762–1767. 10.1021/ma00008a012. [DOI] [Google Scholar]
  25. Ambrosio L.; Borzacchiello A.; Netti P. A.; Nicolais L. Properties of New Materials: Rheological Study on Hyaluronic Acid and Its Derivative Solutions. J. Macromol. Sci. - Pure Appl. Chem. 1999, 36 (7–8), 991–1000. 10.1080/10601329908951195. [DOI] [Google Scholar]
  26. Ogston A. G. The Spaces in a Uniform Random Suspension of Fibres. Trans. Faraday Soc. 1958, 54, 1754–1757. 10.1039/tf9585401754. [DOI] [Google Scholar]
  27. Kagan L.; Gershkovich P.; Mendelman A.; Amsili S.; Ezov N.; Hoffman A. The Role of the Lymphatic System in Subcutaneous Absorption of Macromolecules in the Rat Model. Eur. J. Pharm. Biopharm. 2007, 67 (3), 759–765. 10.1016/j.ejpb.2007.04.002. [DOI] [PubMed] [Google Scholar]
  28. Porter C. J. H.; Charman S. A. Lymphatic Transport of Proteins after Subcutaneous Administration. J. Pharm. Sci. 2000, 89 (3), 297–310. . [DOI] [PubMed] [Google Scholar]
  29. Suami H.; Scaglioni M. F. Lymphatic Territories (Lymphosomes) in the Rat: An Anatomical Study for Future Lymphatic Research. Plast. Reconstr. Surg. 2017, 140 (5), 945–951. 10.1097/PRS.0000000000003776. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Nakaoka R.; Tabata Y.; Yamaoka T.; Ikada Y. Prolongation of the Serum Half-Life Period of Superoxide Dismutase by Poly(Ethylene Glycol) Modification. J. Controlled Release 1997, 46 (3), 253–261. 10.1016/S0168-3659(96)01605-7. [DOI] [Google Scholar]
  31. Zeuzem S.; Welsch C.; Herrmann E. Pharmacokinetics of Peginterferons. Semin. Liver Dis. 2003, 23, 023–028. 10.1055/s-2003-41631. [DOI] [PubMed] [Google Scholar]
  32. Lynn A. D.; Kyriakides T. R.; Bryant S. J. Characterization of the in Vitro Macrophage Response and in Vivo Host Response to Poly(Ethylene Glycol)-Based Hydrogels. J. Biomed. Mater. Res. - Part A 2009, 93 (3), 941–953. 10.1002/jbm.a.32595. [DOI] [PubMed] [Google Scholar]
  33. Gill M. R.; Falzone N.; Du Y.; Vallis K. A. Targeted Radionuclide Therapy in Combined-Modality Regimens. Lancet Oncol. 2017, 18 (7), e414–e423. 10.1016/S1470-2045(17)30379-0. [DOI] [PubMed] [Google Scholar]
  34. Finlay I.; Mason M.; Shelley M. Radioisotopes for the Palliation of Metastatic Bone Cancer: A Systematic Review. Lancet Oncol. 2005, 6 (June), 392–400. 10.1016/S1470-2045(05)70206-0. [DOI] [PubMed] [Google Scholar]
  35. Ma Y.; Tong S.; Bao G.; Gao C.; Dai Z. Indocyanine Green Loaded SPIO Nanoparticles with Phospholipid-PEG Coating for Dual-Modal Imaging and Photothermal Therapy. Biomaterials 2013, 34 (31), 7706–7714. 10.1016/j.biomaterials.2013.07.007. [DOI] [PubMed] [Google Scholar]
  36. Katashima T.; Sakurai H.; Chung U.-I.; Sakai T. Dilution Effect on the Cluster Growth near the Gelation Threshold. Nihon Reoroji Gakkaishi 2019, 47 (2), 61–66. 10.1678/rheology.47.61. [DOI] [Google Scholar]

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