Method for scaling production of bio-inspired nanomaterials

Abstract

A process of preparing polydopamine nanoparticles includes exposing a solution of dopamine in a solvent to a continuous flowing gas mixture to produce the polydopamine nanoparticles, wherein the gas mixture comprises oxygen and an inert gas.

Description

METHOD FOR SCALING PRODUCTION OF BIO-INSPIRED NANOMATERIALSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional Application No. 63 / 561,074, filed on March 4, 2024, which is incorporated herein by reference in their entirety.GOVERNMENT RIGHTS

[0002] This invention was made with government support under Grant No. 1017105 from the Air Force Office of Scientific Research - Multidisciplinary Research Program of the University Research Initiative (AFOSR-MURI). The government has certain rights in the invention.FIELD

[0003] The present technology is generally related to the production of colloidal suspensions of poly dopamine particles of less than 1 pm in diameter.SUMMARY

[0004] In one aspect, a process of preparing polydopamine nanoparticles includes exposing a solution of dopamine, or a salt thereof, in a solvent to a continuous flowing gas mixture to produce the polydopamine nanoparticles, wherein the gas mixture includes oxygen and an inert gas. In some embodiments, the inert gas may nitrogen, helium, argon, and the like. In any of the above embodiments, the gas mixture may include oxygen and the inert gas in a ratio of about 20:80 to a ratio of about 95:5. In any of the above embodiments, the gas mixture may include oxygen and the inert gas in a ratio of from about 40:60 to about 95:5. In any of the above embodiments, the gas mixture may include oxygen and nitrogen in a ratio of about 20:80 to a ratio of about 95:5. In any of the above embodiments, the gas mixture may include oxygen and nitrogen in a ratio of from about 40:60 to about 95:5.

[0005] In any of the above embodiments, the polydopamine nanoparticles may have an average size of about 10 nm to about 500 nm. In any of the above embodiments, thepoly dopamine nanoparticles may have an average size of about 100 nm to about 200 nm. In any of the above embodiments, the polydopamine nanoparticles may have an average size of about 150 nm to about 270 nm. In any of the above embodiments, the poly dopamine nanoparticles may have a poly dispersity index from about 0.01 to 0.05.

[0006] In any of the above embodiments, the continuous flowing gas mixture may be introduced at a rate such that the amount of oxygen in the gas mixture remains substantially constant as the dopamine is oxidized to the polydopamine. In any of the above embodiments, the continuous flowing gas mixture may be continuously sparged (i.e. bubbled) into the solution of dopamine in the solvent. The continuous flowing gas mixture, in any embodiments herein, may be an inert gas such as nitrogen, argon, helium, etc. The flowing gas mixture may be used to control the initiation of the reaction.

[0007] In any of the above embodiments, the solution of dopamine may be prepared by dissolving a dopamine salt, such as the hydrochloride salt, in a basic aqueous solution. In any of the above embodiments, the basic aqueous solution may include sodium hydroxide.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIGs. 1 A and IB are graphs of dynamic light scattering (DLS) measurements of aliquots taken during the first 70 minutes of polydopamine (PDA) nanoparticles reaction, according to the examples. Circles designate an open-air system; squares designate a 20% oxygen / 80% nitrogen gas flow system. Multiple circles at the same time points represent multimodal distributions.

[0009] FIGs. 2 A and 2B are graphs of DLS measurements of PDA nanoparticles collected with varied oxygen / nitrogen compositions over the course of 70 minutes (min), according to the examples. In FIG. 2A, the average particle diameter is presented, and in FIG. 2B, the poly dispersity index is presented with varied O2 composition and open to air. Data points correspond to individual DLS measurements collected on reaction aliquots isolated under inert atmosphere. Lines through points are guides for the eyes. Figure legends show O2 percentage of flow gas and average particle diameter (d) after 70 min of reaction time.

[0010] FIGs. 3 A and 3B are transmission electron microscopy (TEM) images of synthesis done using 40% (FIG. 3 A) and 80% (FIG. 3B) oxygen compositions with average particle diameters and standard deviations (all scale bars are 500 nm), according to the examples. See Table 1 and FIG. 9 for triplicate reaction results.

[0011] FIG. 4 A and 4B are graphs related to the monitoring of particle diameter (FIG. 4A) and poly dispersity (FIG. 4B) over time for reactions with 80% O2 composition of gas flow, according to the examples. Data points correspond to individual DLS measurements.

[0012] FIG. 5 is a schematic drawing of an experimental setup for the preparation of polydopamine nanoparticles, according to various embodiments.

[0013] FIGs. 6 A and 6B are graphs of reaction flow volume (FIG. 6 A) and average particle diameter (FIG. 6B), according to the examples.

[0014] FIGs. 7 A and 7B are TEM images of poly dopamine nanoparticles prepared with an oxygen: nitrogen ratio of 80:20 based on volume, according to the examples. In FIG. 7A, the volume is 150 ml and the flow of the oxygen / nitrogen gas is 215 mL / min and showing an average particle size of 211 nm. In FIG. 7B, the volume is 200 ml and the flow of the oxygen / nitrogen gas is 255 mL / min and showing an average particle size of 216 nm.

[0015] FIG. 8 is a graph of particle size distribution for produced poly dopamine, according to the examples.

[0016] FIG. 9 is overlay ed histograms from TEM images (FIG. 3) of the population of the PDA nanoparticles synthesized three times using 40% and 80% O2 compositions with average, standard deviation, and % relative standard deviation for the three trials at each composition. Color is used to help distinguish between the histograms, according to the examples.DETAILED DESCRIPTION

[0017] Various embodiments are described hereinafter. It should be noted that the specific embodiments are not intended as an exhaustive description or as a limitation to the broader aspects discussed herein. One aspect described in conjunction with a particularembodiment is not necessarily limited to that embodiment and can be practiced with any other embodiment s).

[0018] As utilized herein with respect to numerical ranges, the terms “approximately,” “about,” “substantially,” and similar terms will be understood by persons of ordinary skill in the art and will vary to some extent depending upon the context in which it is used. If there are uses of the terms that are not clear to persons of ordinary skill in the art, given the context in which it is used, the terms will be plus or minus 10% of the disclosed values. When “approximately,” “about,” “substantially,” and similar terms are applied to a structural feature (e.g., to describe its shape, size, orientation, direction, etc.), these terms are meant to cover minor variations in structure that may result from, for example, the manufacturing or assembly process and are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the disclosure as recited in the appended claims.

[0019] The use of the terms “a” and “an” and “the” and similar referents in the context of describing the elements (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the embodiments and does not pose a limitation on the scope of the claims unless otherwise stated. No language in the specification should be construed as indicating any non-claimed element as essential.

[0020] The present technology results from an investigation of the controlled synthesis of amorphous, organic, bio-inspired polydopamine (PDA) nanoparticles under varying atmospheric conditions. Specifically, the role of oxygen (O2) partial pressure on the distribution of PDA particles during synthesis is analyzed. It has been determined thatcontrol of O2 content impacts the quality, speed, and reliability of PDA nanoparticle production. The results indicate that 40% or higher O2 compositions lead to superior outcomes, including reduced poly dispersity index (PDI) values and enhanced reproducibility. As an illustration, introducing an 80% O2 to the composition results in reduced synthesis time. This breakthrough suggests the potential for large-scale or continuous reaction schemes, offering substantial time and resource savings for applications involving PDA nanoparticles and similar materials.

[0021] Poly dopamine (PDA) is a complex, bioinspired, amorphous material synthesized by the autoxidation of a dopamine precursor.2’3The simplicity of its implied polymeric form belies an underlying diversity of structure and function that is both a challenge and boon to materials discovery. The multitude of physical forms and variants of PDA have attracted attention across diverse fields such as environmental studies, sensing, and biological and biomedical fields.4'6PDA has been referred to as a universal adhesive2that is able to coat a wide variety of surfaces, whether inorganic or organic, such as noble metals, oxides, polymers, semiconductors, and ceramics.2PDA is also isolable as a freestanding material in various form factors including colloidally stable spherical nanoparticles. The synthesis and study of PDA and related bio-inspired amorphous organic nanomaterials are being investigated for ultraviolet (UV) and other electromagnetic radiation blocking,7'12thermal regulation,13bioinspired structural color,14'21imaging agents,22'34and drug delivery35,36.

[0022] As interest in materials’ design with PDA nanomaterials continues to grow, understanding and controlling its synthesis becomes paramount, with a need for consistency and quality in terms of a variety of physical factors such as particle size, shape, and polydispersity. Without high quality, reproducible synthetic methods, optimization of complex structure-property relationships such as those involved in structure color37will face considerable barriers. Given the interest in PDA and related bio-inspired polymer materials, it is not surprising that many synthetic procedures have been developed, with focus on the impact of reaction temperature,38additive oxidants,1and relative precursor concentrations.38,39Encouragingly, previous studies have found particle size is affected by the reaction temperature such that the PDA particles of diameter d = 94 - 291 nm (RSD ~ 20%) can be synthesized by changing the temperature within the range of 25 - 70 °C.38Increased temperature results in an enhancement of the reaction rate, leading to a desirable reductionof the synthesis time. The reaction may be modulated by increasing the dopamine (DA) concentration or decreasing the base concentration to increase average particle diameter.39To achieve the reported results, reaction times vary from 5 h to a day or more.38, 40, 41

[0023] It has now been found that the introduction and mass transport of O2 within the reaction vessel has a significant impact on reaction times and reproducibility. O2 has been used as an oxidant for PDA formation, and amongst the many descriptions of this reactivity, diffusion from the ambient environment is the general method of introduction after the initial dissolved O2 is depleted. Despite the known importance of O2 to the rate, morphology, and quality of the reaction, only a single experimental study looking at PDA thin-film formation has gathered data at non-atmospheric O2 concentrations.42In this work, higher O2 concentration was found to reduce aggregate formation and thereby produce more homogeneous films with shorter deposition time than PDA synthesized under atmospheric O2 conditions. In recent years, there has been a proliferation of syntheses for PDA and other amorphous synthetic biomaterials with melanin-like characteristics in free-standing colloidal nanoparticle form. Although synthesis of such materials can be far less tolerant to random fluctuations in conditions, O2 introduction remains unstandardized.

[0024] Improved standardization for this reaction is particularly important given the multifunctional nature of the end product. The synthesis of PDA is a complex reaction, posing challenges for conventional investigation methods.1An oxidant such as O2 plays a pivotal role, driving the initial steps from DA to 5,6-indolequinone.

[0025] In Scheme 1, steps 1, 2, 4, 5, 7, and 8 depend solely on the presence of O2 which makes the O2 solubilization rate a critical factor on the progression of the PDA nanoparticle reaction.1Notably, these crucial steps traditionally rely on O2 already present in the reaction mixture and then on O2 that is able to diffuse into the stirring solution. By loosely capping, or by using a long-necked flask for the reaction, the rate can be slowed such that rapid stirring allows for a homogeneous distribution of the reactive species. It also must be noted that steps 1-8 do not necessarily proceed linearly in the formation of the amorphous polymeric material known as polydopamine and different monomeric forms can be incorporated as well as reacted further with the reactive oxygen radicals produced in solution.Scheme 1. Initial steps of PDA reaction including the two-step oxidations of the monomers.1

[0026] To develop a more robust approach to this reaction while simultaneously introducing a quantitative control parameter, a gas flow of a tunable oxygen / nitrogen composition was used. This method addresses uncontrolled pre-reaction of starting materials by maintaining a constant O2 composition through steady gas flow, and maintaining a homogeneous reactivity at a faster reaction rate by injection of O2 directly into the mixing solution. These factors do not mitigate the complexity of O2 reactivity in the formation of PDA entirely, but they represent a streamlined synthetic method to enhance reproducibility, control, precise characterization, and production speed. Herein, we evaluate the advantages of strict control over the reaction environment by first establishing oxygen- free conditions to prepare the reaction without uncontrolled product formation and then using a controlled-flow atmosphere with tunable O2 partial pressure to study and regulate the formation of spherical particle properties such as size, distribution, and reaction time with high reproducibility.

[0027] In an initial test of the effect of gas flow, a PDA reaction with a controlled flow atmosphere of approximately atmospheric O2 conditions (20:80 O2:N2) was prepared and rigorously characterized. These results were then contrasted with PDA prepared using atmospheric O2.

[0028] While there are a multitude of PDA nanoparticle syntheses describing properties of particles made via atmospheric O2 as a reagent, we describe controlled versions of the open-air reaction here to facilitate direct comparison under otherwise identical conditions. This also allowed for work-up, characterization, and statistical analysis in an identical manner. Reaction progress was monitored by dynamic light scattering (DLS) through aliquots drawn during the first 70 min to determine the average particle diameter, particle distribution, and percent relative populations.

[0029] As presented in FIGs. 1 A and IB, there is a clear difference in the behavior between the two sets of particles when observed during the reaction. Use of atmospheric O2 results in multiple, distinct populations. The large size difference in the populations, and the lack of DLS signal from the largest populations at longer times indicates that these likely result from aggregate formation and eventual irreversible precipitation. In the gas flow system, this affect was not observed, likely due to a far more homogeneous distribution of O2 and its reactive products as a function of time as well as within the reaction volume. Several factors pertaining to the size distributions are worth mentioning here: 1) the multimodal distribution observed here may be improvable through iterative optimization of reaction conditions; and 2) the existence of a poor or multiple distributions may never be detected if the only characterization method is TEM analysis of the final particles after extraction and washing steps. Neither of these offers a viable solution to produce a commercial-scale product: condition-optimization is not generalizable nor scalable when the major issue to overcome is mass transport and separation of the aggregate species results in an unacceptably low yield.

[0030] Also of interest in FIGs. 1 A and IB, a slight increase in the average particle diameter is seen in the gas flow compared to the open-air system. This aligns with our initial hypothesis that gas diffusion in the open system exposed to atmospheric O2 is inefficient for replenishing depleted soluble O2 compared to the gas flow system.

[0031] This observation prompted an exploration of different oxygen / nitrogen composition atmospheres to determine if there was an optimal composition for PDA synthesis. The O2:N2 ratio was varied from 20:80 to 80:20 while maintaining a constant overall gas flow rate and again used DLS to track the reaction by monitoring the nanoparticle size and distribution. FIGs. 2A and 2B shows that final particle diameter increases with increasing O2 availability, with the effect leveling off once 50% of the totalatmosphere is O2. In the initial stages of the reaction, particle growth is accelerated in reactions with higher O2 concentration, demonstrating a link between O2 availability and reaction rate. These observations indicate the importance of a readily available, uniform concentration of O2 on the reaction outcome. The introduction of a gas flow directly into the reaction mixture not only provides O2 but provides an agitating force that facilitates mass transport and O2 dissolution in the reaction mixture.

[0032] The poly dispersity index (PDI) of the reaction is used to quantify the correlation between the average particle diameter (X) and the standard deviation (G) with a lower PDI indicating a narrower particle size distribution following Equation 1 :PDI = G2 / A (1)Higher O2 partial pressure was found to correlate with a significant reduction in the PDI over the course of the reaction (FIG. 2B). In particular, reactions performed under an O2 partial pressure similar to atmospheric conditions (20% O2) were found to have the highest PDIs. Interestingly, compared to the control reaction under ambient atmospheric O2 conditions, the gas flow system consistently yielded a narrower distribution, regardless of the percent O2 used, see FIG. 2B.

[0033] Reactions with gas flow O2 compositions of 40% and 80%, representing oxygen-rich and oxygen-poor ends of the low-PDI range, were chosen for further investigation into the reproducibility of high-quality particles. To corroborate the DLS information about particle size and distribution, transmission electron microscopy (TEM) images were collected and analyzed (FIGs. 3 A and 3B). While DLS measures the hydrodynamic diameter of particles in solution, TEM can be used to determine of the size and shape of the electron-dense area that corresponds to the shape and size of the core particle. To maintain consistency between the methods, TEM was performed on the completed reaction mixture without selective washing, extraction, or preparation techniques used to bias the observed population compared to the reaction population. All size statistics are the result of datasets containing 500 or more particles. TEM and DLS measurements of individual syntheses demonstrate consistent maintenance of low PDI from batch to batch, further supported by their percent relative standard deviation (% RSD) (Table 1, below). These results can be quantified by comparing the statistics across all batches for a given set of conditions: avg,TEM = 160±9 nm (% RSD = 6) and tZavg,TEM = 204±15 nm (% RSD = 7) for40 and 80% O2 flow reactions respectively, and avg,DLs = 207±l 1 nm (% RSD = 5) and avg,DLs = 244±18 nm (% RSD = 8) for 40 and 80% O2 flow reactions, respectively. While ambient O2 reactivity has traditionally relied on slow reactivity to yield quality nanomaterials, the DLS data for three reactions with a flow of 80% O2 (FIGs. 4A and 4B) shows consistent completion with low PDI after only 36 min, with aliquots taken at 36, 50, and 70 min yielding tZavg,PDi = 242±11, 249±15, and 244±18 nm, indicating reaction completion. These data illustrate the reproducibility through different trials and the potential for the use of controlled gas flow as the transformative technology to enable high- throughput materials discovery for the complex and exciting class of synthetic melanin-like materials, such as PDA.Table 1. Average particle diameter with standard deviation, PDI, and % RSD from DLS and TEM measurements for both 40% and 80% oxygen composition reactions.

[0034] We have shown herein that the synthesis of an amorphous, organic, bioinspired materials, namely poly-dopamine (PDA) in its colloidal nanoparticle form, can be synthesized with higher quality, more quickly, and more reliably by carefully controlling the atmosphere during the reaction. In particular, since O2 and its reactive products are important to the formation of the monomeric species that constitute PDA, the concentration and distribution of O2 are key to the reactivity. Specifically, percent O2 compositions of 40% or greater exhibit the favorable results regarding lower PDI values and enhanced reproducibility. The improvement in reaction time observed with the gas flow system. In some embodiments, an 80% O2 partial pressure results in an about 30 min reaction time compared to a typical 24 h reaction time under ambient conditions. From a functional materials standpoint, access to this fast, reliable reaction scheme provides an improved platform for accessing more complex utility from PDA: better control of metal chelation forcatalysis, bioactivity, or contrast, multi-polymeric core-shell structures and continuous growth schemes for structure-color functionality and custom radiation-absorption characteristics.

[0035] The present invention, thus generally described, will be understood more readily by reference to the following examples, which are provided by way of illustration and are not intended to be limiting of the present invention.EXAMPLES

[0036] Methods or Experimental Section. Materials. Dopamine hydrochloride (99%, Lot# M25H010 & X311025) was purchased from Alfa Aesar and Thermo Scientific, respectively. Sodium hydroxide (IN; Certified 0.995-1.005 N, Lot# 193250 & 215879) was purchased from Fisher Scientific. Purchased chemicals were used without further purification. Milli-Q water was used in all experiments.

[0037] Synthesis of Poly dopamine. Dopamine hydrochloride (0.1 g) was dissolved in water (50 mL) and sparged with N2 gas to remove dissolved O2 while stirring vigorously. A base, 1 N NaOH (0.53 mL), was then injected into the reaction. After five minutes of mixing, the oxygen / nitrogen gas mixture with the desired percent composition was bubbled through the solution. Aliquots were periodically removed and diluted (0.25mL H2O, 0 °C) under N2 atmosphere to halt growth throughout the reaction to monitor the nanoparticles’ growth. FIG. 5 shows the experimental setup with flow meters on the left, making the desired gas mixture composition flown through the oxygen sensor #1 to determine the percent O2. Then, the gas mixture is bubbled through the solution via a stainless-steel injection needle (gauge 20.) The oxygen sensor #2 is monitoring the outgoing percent O2.

[0038] Particle Characterization. Transmission electron microscopy (TEM) images were acquired using a Jeol 1400 plus at 80 kV. Dynamic Light Scattering (DLS) was determined using Malvern Zetasizer Nano - ZS90.

[0039] Data availability. All in-house code and setup details have been deposited in a structured and version-controlled repository on Zenodo. The codebase is openly available under the MIT License to foster transparency and reproducibility. These data can be accessed via the following DOI: 10.5281 / zenodo.7927253.

[0040] Method of Scaling. Materials. Dopamine hydrochloride (99%, Lot# X311025) was purchased from Thermo Scientific. Sodium hydroxide (IN; Certified 0.995- 1.005 N, Lot# 215879) was purchased from Fisher Scientific. Purchased chemicals were used without further purification. Milli-Q water was used in all experiments.

[0041] Synthesis of Poly dopamine. A solution of dopamine hydrochloride was prepared using 2 mg / mL of Milli-Q water for 150, 200, and 250 mL reaction volumes in a 500 mL Morton three-neck flask. Rubber septas were employed to seal the external necks of the flask. A vacuum flow control joint, equipped with tubing leading to an oxygen sensor II on the apparatus, was greased and secured with a keck clamp onto the middle neck of the Morton flask. The solution was sparged using nitrogen gas for 4 hours to remove all dissolved oxygen while stirring at 1200 RPM. Nitrogen gas was introduced to the reaction using a 20 gauge needle, and the same gauge needle was used to flow the nitrogen out of the system. The nitrogen flow rate was adjusted based on the reaction volume. During this step, the control joint remained closed.

[0042] After sparging, NaOH was introduced (10.6 pL of 1 N NaOH was added per 1 mL of the solution). The solution was stirred for 5 minutes under a nitrogen atmosphere to ensure thorough base mixing. The exhaust needle was then removed, and the vacuum flow control joint was opened.

[0043] The procedure required the establishment of an 80 / 20 (vol% / vol%) Oxygen / Nitrogen gas composition measured via an oxygen sensor within the apparatus, alongside the determination of the desired flow rate. The flow rates were set for 150 mL and 200 mL solutions at 215 mL / min and 255 mL / min, respectively. The oxygen / nitrogen composition gas was then introduced to the reaction using the 18-gauge long needle. Relevant data are illustrated in FIGs. 6A, 6B, 7A, 7B, 8, and 9.References:1. Salomaki, M.; Marttila, L.; Kivela, H.; Ouvinen, T.; Lukkari, J., Effects of pH and Oxidants on the First Steps of Poly dopamine Formation: A Thermodynamic Approach. J Phys Chem B 2018, 122 (24), 6314-6327.2. Lee, H.; Dellatore, S. M.; Miller, W. M.; Messersmith, P. B., Mussel-inspired surface chemistry for multifunctional coatings. Science 2007, 318 (5849), 426-30.3. Liebscher, J.; Mrowczynski, R.; Scheldt, H. A.; Filip, C.; Hadade, N. 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[0044] While certain embodiments have been illustrated and described, it should be understood that changes and modifications can be made therein in accordance with ordinary skill in the art without departing from the technology in its broader aspects as defined in the following claims.

[0045] The embodiments, illustratively described herein may suitably be practiced in the absence of any element or elements, limitation or limitations, not specifically disclosed herein. Thus, for example, the terms “comprising,” “including,” “containing,” etc. shall be read expansively and without limitation. Additionally, the terms and expressions employedherein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the claimed technology. Additionally, the phrase “consisting essentially of’ will be understood to include those elements specifically recited and those additional elements that do not materially affect the basic and novel characteristics of the claimed technology. The phrase “consisting of’ excludes any element not specified.

[0046] The present disclosure is not to be limited in terms of the particular embodiments described in this application. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and compositions within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds, compositions, or biological systems, which can of course vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0047] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

[0048] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a nonlimiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like, include the number recited and refer to ranges which can be subsequently broken down into subrangesas discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member.

[0049] All publications, patent applications, issued patents, and other documents referred to in this specification are herein incorporated by reference as if each individual publication, patent application, issued patent, or other document was specifically and individually indicated to be incorporated by reference in its entirety. Definitions that are contained in text incorporated by reference are excluded to the extent that they contradict definitions in this disclosure.

[0050] Other embodiments are set forth in the following claims.

Claims

WHAT IS CLAIMED IS:

1. A process of preparing polydopamine nanoparticles, the process comprising exposing a solution of dopamine, or a salt thereof, in a solvent to a continuous flowing gas mixture to produce the polydopamine nanoparticles, wherein the gas mixture comprises oxygen and an inert gas.

2. The process of claim 1, wherein the inert gas comprises nitrogen.

3. The process of claim 1 or 2, wherein the gas mixture comprises oxygen and the inert gas in a ratio of from about 20:80 to about 95:5.

4. The process of any one of claims 1 to 3, wherein the gas mixture comprises oxygen and the inert gas in a ratio of from about 40:60 to about 95:5.

5. The process of any one of claims 1 to 4, wherein the gas mixture comprises oxygen and the inert gas in a ratio of from about 80:20.

6. The process of any one of claims 1 to 5, wherein the polydopamine nanoparticles have an average size of about 10 nm to about 500 nm.

7. The process of any one of claims 1 to 6, wherein the polydopamine nanoparticles have an average size of about 100 nm to about 200 nm.

8. The process of any one of claims 1 to 7, wherein the poly dopamine nanoparticles have an average size of about 150 nm to about 270 nm.

9. The process of any one of claims 1 to 8, wherein the continuous flowing gas mixture is introduced at a rate such that the amount of oxygen in the gas mixture remains substantially constant as the dopamine is oxidized to the polydopamine.

10. The process of any one of claims 1 to 9, wherein the solution of dopamine is prepared by dissolving dopamine hydrochloride in a basic aqueous solution.

11. The process of any one of claims 1 to 10, wherein the basic aqueous solution comprises sodium hydroxide.

12. The process of any one of claims 1 to 11, wherein the continuous flowing gas mixture is continuously sparged into the solution of dopamine in the solvent.

13. The process of any one of claims 1 to 12, wherein the poly dopamine nanoparticles have a poly dispersity index from about 0.01 to 0.05.

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