Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5610_Библиотеки_им_академика_М_И_Перельмана
.pdf
https://t.me/med1917
Chapter 9
https://t.me/med1917
Ultrasmall-in-Nano
Ryan D. Mellor
9.1 Introduction
Ultrasmall-in-Nano constructs consist of sub-5 nm particles, typically gold
nanoparticles (AuNPs), assembled into nanostructures, resulting in particles which
have the advantageous properties of both size scale (Li and Lane 2019). The core
particles are synthesized in the sub-5 nm range to ensure that after they have served
their purpose in vivo, they can safely be excreted by the body’s natural systems.
These cores are assembled into the 100–500 nm range to have enhanced optical and
biodistribution properties, however, this assembly must be reversible to allow for
regeneration of the initial sub-5 nm cores (Fig. 9.1).
These constructs have garnered particular interest in the field of cancer
theranostics due to their unique physicochemical properties. These properties
include increased circulation times (Patra et al.
tumour tissue due to the enhanced permeability and retention effect (Duan and Li
2013), and specifically in the case of AuNPs strong absorbance in the
phototherapeutic window (Kim and Lee 2018). Once at the site of the tumour, the
same properties of the particle that allow for detection of the tumour and monitoring
of the tumour environment will permit the particles to be used therapeutically via
heat-induced apoptosis, namely strong absorbance in the phototherapeutic window
(Diwu and William
To display the desired optical properties, specifically, a bathochromic shift in
absorbance upon clustering, the ultrasmall particles must come into close proximity
to one another. The effect of interparticle electromagnetic coupling is propor tional to
the inverse of interparticle distance (Le et al.
1994).
2018), superior accumulation in
2015), suggesting that the most
R. D. Mellor (✉)
UCL School of Pharmacy, University College London, London, UK
e-mail: ryan.mellor.16@ucl.ac.uk
© The Editor(s) (if applicable) and The Author(s), under exclusive license to
Springer Nature Switzerland AG 2024
I. F. Uchegbu et al. (eds.), Fundamentals of Pharmaceutical Nanoscience,
https://doi.org/10.1007/978-3-031-59478-6_9
183
184 R. D. Mellor
https://t.me/med1917
Fig. 9.1 Generalized principle of the ultrasmall-in-nano approach
prominent bathochromic shift is obtained when the ultrasmall particles are as close
as possible without touching to avoid irreversible fusion, as would be observed with
other aggregation methods, for example, upon the addition of glucosamine phosphate to small AuNPs (Martínez et al. 2019).
9.2 The Need for Excretion
The excretability of AuNPs used in medical applications carries profound implications, in terms of clinical outcome but also sociologically and economically.
While gold itself is inert and biocompatible, problems arise when considering
persistence of the gold in the body (Li and Lane 2019). The body’s main mechanism
for excretion of compounds from circulation, specifically, via the renal pathway, is
not efficient at removing particles larger than 5 nm in diameter (Soo Choi et al.
2007). This is mainly due to the functional pore size of the glomerular capillary wall
of 4.5–5 nm (Dai 2015) and larger particles will instead rely on elimination via the
hepatobiliary pathway. Consequently, particles below this threshold are desirable to
avoid the potential retention of gold in the body.
From a societal standpoint, public perception and acceptance are paramount.
Injected nanoparticles, especially those that are not excretable, can trigger scepticism
and apprehension among the public. Even if scientific evidence supports their safety,
concerns may persist, potentially hindering the adoption of valuable medical treatments. These sociological factors could influence regulatory processes, creating
hurdles for approval and integration into healthcare.
On the economic front, safety testing and gaining FDA approval are essential but
resource-intensive processes. Non-excretable nanoparticles would necessitate extensive, long-term safety studies, dramatically increasing development costs and
timeframes. In contrast, smaller, excretable nanoparticles require shorter and more
9 Ultrasmall-in-Nano 185
https://t.me/med1917
streamlined testing processes, which can significantly reduce the economic burden
on developers. Additionally, market viability is closely tied to public acceptance. If
people are reluctant to embrace non-excretable nanoparticles due to perceived risks,
the market for such treatments may remain limited, discouraging investment in
research and development. Therefore, ensuring that AuNPs are small enough to be
excretable not only addresses health concerns but al
approval, lowers research
more practical and economically viable option for medical applications.
costs, and enhances market acceptance, making them a
so facilitates regulatory
9.3 Size-Dependent Properties of Nanoparticles
Almost any material exhibits distinct size-dependent properties across different
scales, including atomic, nano, and bulk scales (Roduner 2006). Consequently, a
wide range of materials can be categorized as ‘nanomaterials’ when their dimensions
fall within the scale of 1– 1000 nm. In the subsequent section, we will employ AuNPs
as a model to explore the intriguing size-dependent phenomena. It is important to
note that the principles discussed here are broadly applicable to various types of
nanoparticles.
AuNPs offer an excellent platform for investigating size-dependent properties
due to our ability to precisely control their size (ranging from 1 to 330 nm), shape
(including spheres, rods, stars, plates, cubes, cages, and shells), and surface chemistry. This versatility within the AuNP design space allows researchers to isolate and
scrutinize a singl e variable while keeping all other parameters constant, making them
an invaluable tool in the study of nanomaterial properties. Furthermore, understanding how different shapes impact properties can shed light on various applications of
these nanoparticles in diverse fields.
9.3.1 Effect on Opsonization
When nanoparticles are introduced into the bloodstream, a dynamic interplay occurs
between these nanoparticles and proteins. These proteins readily bind to the
nanoparticles, forming what is termed a ‘protein corona’—a biological identity
enveloping the nanoparticle (Monopoli et al. 2011). Within this protein corona, a
fraction of proteins, including opsonins like complement proteins (Merle et al. 2015)
and antibodies (Chiu et al. 2019), act as molecular tags. These tags serve to designate
the nanoparticles for uptake by phagocytes, facilitating their elimination from the
body. While this process is crucial for the immune system’s function in removing
pathogens, diseased cells, and protein aggregates (Cockram et al. 2021), it leads to
the unwanted consequence of shortened nanoparticle circulation in the bloodstream.
One effective strategy to mitiga te this issue involves altering the surface chemistry of
the nanoparticles, a technique exemplified by PEGylation (Petros and DeSimone
186 R. D. Mellor
https://t.me/med1917
2010; Yoo et al. 2010). However, the nanoparticle size stands as an equally influ-
ential factor.
Research indicates that nanoparticles and proteins of simil ar sizes interact due to
van der Waals forces, and this interaction strength scales with the radii of the
particles (Lane et al.
ened opsonization, as evidenced by experiments involving particles with diameters
ranging from 7 to 22 nm (Deng et al.
attributed, in part, to the larger surface area of these particles. Nevertheless, surface
area alone does not provide a comprehensive explanation, as studies have
highlighted an elevation in the density of adsorb ed proteins on larger nanoparticles
(Kaur and Forrest 2012). This trend, however, is not indefinitely sustainable. At a
critical point, the diminishing curvature of the nanoparticle surface renders it practically flat from the perspective of a protein. Research establishes this size threshold
to be approximately 50 nm, beyond which the binding of proteins diminishes with
further size increase (Lacerda et al.
the intricate relationship between nanoparticle dimensions and the dynamics of
opsonization.
2015). Consequently, larger nanoparticles experience height-
2012). The increased opsonization can be
2010). This intriguing phenomenon underscores
9.3.2 Effect on Cellular Internalization
In the realm of theranostic applications, the influence of nanoparticle size on cellular
internalization holds significant importance. Depending on the specific purpose, the
internalization process can either be encouraged or suppressed. When the objective
is not reliant on intracellular activity, such as imaging or photothermal therapy
(PTT), suppression of internalization is advantageous. This facilitates the efficient
removal of nanoparticles post-application (Yu and Zheng
applications involving intracellular actions, promoting internalization is beneficial.
However, such promotion must be balanced to minimize systemic toxicity, often
achieved through nanoparticle surface coatings with targeting components
(Ruoslahti et al. 2010).
The internalization of nanoparticles is heavily reliant on receptor-mediated endocytosis (Jiang et al.
between nanoparticle size and the rate of internalization. Larger nanoparticles
possess the ability to bind with multiple cell-surface receptors simultaneously,
prompting the cell membrane to envelop the particle due to reduced Gibbs free
energy. On the other hand, smaller nanoparticles can only interact with a limited
number of receptors at once. This eliminates the risk of localized receptor scarcity,
which could otherwise hinder the overall particle uptake rate. However, both size
categories face challenges. Larger particles require significant cell membrane surface
area for envelopment, while smaller particles demand higher cell membrane
curvature—both posing kinetic and energetic disadvantages. Research,
encompassing both theoretical (Gao et al.
Ferrari 2007) and experimental (Chithrani et al. 2006; Liu et al. 2013a) approaches,
2008; Gao et al. 2005
). This gives rise to a nuanced interplay
2005; Yuan et al. 2010; Decuzzi and
2015). Conversely, for
9 Ultrasmall-in-Nano 187
https://t.me/med1917
indicates an optimal internalization range of approximately 25–50 nm. Nonetheless,
this range’s effectiveness is subject to the particle’s surfa ce chemistry (Li and Lane
2019) and the specific cell line under examination (Albanese et al. 2012). Broadly,
the range of 10–100 nm is acknowledged as optimal for fostering internalization,
with particles outside this range encountering the aforementioned challenges.
9.3.3 Effect on Renal Clearance
Efficient renal clearance of injected agents is crucial to prevent potential hazards
arising from agent accumulation or decomposition within the body. Renal clearance
relies on the hydrodynamic diameter of particles relative to the kidney filtration
threshold (KFT), approximately 5.5 nm (Longmire et al. 2008; Liu et al. 2013b).
This threshold is determined by the size of glomerular pores responsible for filtering
blood plasma.
Particles with a hydrodynamic diameter of up to 8 nm can be filtered by the
kidneys, but this is conditional upon the particles having a positive surface charge.
This positive charge facilitates interactions with the filtration barrier, which are not
operational for neutral or negatively charged particles (Adhipandito et al. 2021).
Particles that are not able to be filtered by the kidneys will rely on the slower
hepatobiliary pathway for clearance if they are to be excreted at all.
There exists a critical size range for renally clearable particles, typically falling
within 1–5 nm. The existence of a lower limit is assumed to be due to the fact that
particles below 1 nm can enter the approximately 1 nm pores of the glomerular
glycocalyx. This is evidenced by the exponential decrease in the rate of glomerular
filtration with decreasing particle size for atomically precise AuNPs below 1 nm,
where the size is inferred from the particles’ mass as determined by electrospray
ionization mass spectroscopy (Du et al. 2017).
Multiple studies (Semmler-Behnke et al. 2008; Balogh et al. 2007) have consistently demonstrated that particles larger than 5 nm exhibit low to undetectable levels
in the urine due to their inability to pass through glomerular pores. Inst ead, they tend
to accumulate in the liver and are eventually excreted via the hepatobiliary pathway.
In contrast, particles smaller than 5 nm show significantly higher rates of excretion
through both renal and hepatobiliary pathways. More than 50% of the injected dose
(%ID) can be cleared within hours (Hainfeld et al. 2006), in contrast to larger
particles that may take weeks (Renaud et al. 1989) to months (Sadauskas et al.
2009) for clearance.
It is important to emphasize that the fate of nanoparticles is determined by their
hydrodynamic diameter, not their solid core size. This distinction is evident when
varying the molecular weight and therefore the thickness of a PEG coating while
maintaining a gold core size of 2.5 nm. Particles with a hydrodynamic diameter of
less than 5 nm exhibit preferential renal clearance, while those with a diameter
exceeding 5 nm show reduced clearance rates, consistent with larger particles (Zhao
2014). This correlation between size and excretion rate follows an exponential
et al.
188 R. D. Mellor
https://t.me/med1917
trend (Zhou et al. 2011). For instance, particles measuring 2, 6, and 13 nm demonstrate renal clearance efficiencies of 50%, 4%, and 0.5%, respectively, 24 h postinjection.
9.3.4 Effect on Biodistribution
Biodistribution of nanoparticles is influenced by several factors, including particle
size, shape, and surface chemistry. It is crucial to recognize that altering one of these
parameters can either enhance or counter the effects of another. Nevertheless, when
other factors remain constant, particle size exhibits a significant correlation with
biodistribution. Figure
biodistribution.
In general, smaller nanoparticles tend to exhibit a broader distribution throughout
the body compared to larger ones. A study, which involved intravenous injection of
particles with sizes of 10, 50, 100, and 250 nm, 24 h post-injection (De Jong et al.
2008), revealed distinct patterns. The largest particles (100 and 250 nm) were
detectable in the blood, liver, and spleen, with negligible quantities (0.1%ID) in
the kidneys. In contrast, the smaller 50 nm particles were additionally found in the
lungs and heart. Only the smallest 10 nm particles were detected in the testis,
9.2 provides an overview of how particle properties impact
Fig. 9.2 Biodistribution of nanoparticles. Arrows indicate routes of administration (green), distribution (grey), and clearance (yellow). Approaches for modulating biodistribution are shown on the
right, where desirable (green) and undesirable (red) characteristics are given for select organs
9 Ultrasmall-in-Nano 189
https://t.me/med1917
thymus, and brain, with a larger quantity (1%ID) present in the kidneys. Across all
sizes tested, the highest organ accumulation was consistently observed in the liver.
Another study, comparing particles of sizes 15, 50, 100, and 200 nm, reported
nearly identical results, with the exception of 50 nm particles, which were also
detected in the brain (Sonavane et al.
investigation. It is important to note that variations in animal models and nanoparticle preparations between the two studies may account for this diff erence
(Khlebtsov and Dykman
2011).
2008), a surprising finding worthy of further
9.3.5 Effect on Tumour Accumulation
Tumour accumulation is a critical factor in the efficacy of cancer theranostics. In
diagnostic applications, the ability of a construct to accumulate at the tumour site is
essential for distinguishing it from healthy tissue and identifying the tumour itself. In
therapeutic applications, tumour accumulation enables the focused delivery of
treatment to diseased tissue, maximizing its effectiveness while minimizing adverse
side effects.
One popular approach is to functionalize the surface of constructs with tumourtargeting antibodies, aptamers, peptides, or small molecules; however, this is outside
of the scope of this section; the reader is referred to the review ‘Active targeting of
AuNPs as cancer therapeutics’ (Goddard et al.
Passive targeting, based on the size of nanoparticles (NPs), offers a promising
approach to achieve tumour accumulation. Nanoparticles within the size range of
40–400 nm (Subhan et al.
retention (EPR) effect. This effect results from the unique characteristics of tumour
vasculature, characterized by leaky blood vessels compared to the tight endothelial
junctions found in healthy tissue, as well as reduced lymphatic drainage. These
factors collectively lead to the passive and preferential accumulation of NPs in
tumour tissue by preventing the clearance of cytotoxic compounds (Greish 2010).
To ensure the effectiveness of passive targeting, it is imperative that the therapeutic nanoparticles remain in circulation for as long as possible. Achieving an
extended half-life requires careful functionalization of the NPs to adjust their size,
surface charge, hydrophobicity, and surface chemistry. These modifications serve to
reduce renal and phagocytic clearance mechanisms (Blanco et al. 2015).
However, it is worth noting that the existence and effectiveness of the EPR effect
in humans have been the subject of substantial debate in the scientific community,
despite clear evidence of its presence in animal models (Nichols and Bae 2014;
Danhier 2016).
The size of nanoparticles is a pivotal factor in their ability to accumulate at
tumour sites. Particles smaller than 10 nm tend to distribute widely across various
tissues (De Jong et al. 2008), including both healthy and diseased areas. While they
can penetrate tumour vasculature (Perrault et al. 2009) more easily, their rapid
diffusion into and out of the tumour can limit their accumulation. In contrast, larger
2021) c an leverage the enhanced permeability and
2020) for an overview of the subject.
190 R. D. Mellor
https://t.me/med1917
particles, approaching or exceeding 1 μ m, are unable to pass through the tumour’s
smaller fenestrae, with pores in the order of a few hundred nanometres (Jain and
Stylianopoulos 2010), or diffuse effectively into solid tumours. However, this
limitation may not be problematic in diagnostic applications where localization at
the tumour boundary suffices.
As discussed in the previous section, smal ler particles generally exhibit longer
circulation times, leading to increased tumour accumulation compared to their larger
counterparts. Notably, ultrasmall AuNPs have demonstrated particularly high
tumour accumulation when compared to AuNPs larger than 10 nm (Huang et al.
2012).
9.3.6 Effect on Toxicity
The relationship between the size of AuNPs and their toxicity is a subject of
considerable interest in the literature. However, drawing definitive conclusions has
proven challenging due to variations in synthesis methods, capping ligands, cell/
animal models, dosages, and routes of administration (Sani et al.
toxicity has been observed in the case of ultrasmall AuNPs (diameter less than 2 nm),
especially when the bare gold surface is exposed (Schmid et al. 2017). This heightened toxicity in ultrasmall AuNPs may be attributed to their wider biodistribution
and extended circulation times, in contrast to larger particles that tend to accumulate
rapidly in the liver.
The majority of studies tend to characterize AuNPs as non-toxic. In cases where
toxicity is observed, it is often attributed to the capping ligands rather than the gold
core itself.
In contrast, a specific investigation took a closer look at citrate-capped AuNPs
ranging from 3 to 100 nm. This study conducted an in vitro MTT
(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay using Hela
cells to evaluate the particles. Interestingly, the results showed virtually no cytotoxicity, with over 80% cell viability across the entire size range (3–100 nm) at all tested
concentrations, which went up to 0.4 mM. Additionally, the study assessed the
average lifespan (L50) of BALB/c mice following intraperitoneal dosing with
8 mg/kg/week for each particle size. Surprisingly, no toxicity or lethality was
observed for the small particles (3 and 5 nm) or the large particles (50 and
100 nm). However, intermediate-siz ed particles (8, 12, 17, and 37 nm) all exhibited
an L50 of less than 21 days. The authors of this study suggest that this zone of
toxicity is attributed to particles being small enough to enter cells but large enough to
evade triggering a specific immune response (Chen et al.
2009).
2021). Notably,
9 Ultrasmall-in-Nano 191
https://t.me/med1917
9.3.7 Effect on Optical Properties
Nanoparticle size exerts a profound influence on the nanoparticle’s optical properties, making the manipulation of AuNPs an efficient avenue for achieving desired
effects (Lee and El-Sayed
plasmon resonance (SPR), a unique phenomenon that materializes at specific wavelengths depending on particle size and shape. This characteristic is exclusive to the
nanoscale, setting it apart from the atomic and bulk scales of gold (Mohapatra et al.
2018).
The implications of SPR in AuNPs are far-reaching, finding utility in various
applications. It underpins diagnostic methods such as surface-enhanced Raman
spectroscopy (SERS) (Langer et al.
(SORS) (Mosca et al.
techniques like photothermal therapy (PTT) (Wei et al. 2019) and photodynamic
therapy (PDT) (Chen et al. 2020).
For diagnostic and therapeutic purposes, it is imperative that the SPR band falls
within the phototherapeutic window, typically ranging from 650 to 850 nm. This
spectral range is characterized by minimal absorption by biomolecules in human
tissue, enabling deeper penetration of incident laser light (Diwu and William 1994).
However, a noteworthy challenge arises as particles exhibiting this SPR band tend to
reside in the size range of 100–200 nm (Niu et al.
for renal excretion.
Generally, larger nanoparticles exhibit a redshifted SPR peak compared to their
smaller counterparts (Njoki et al. 2007). For example, ultrasmall particles (~5 nm)
demonstrate SPR peaks around 515–520 nm, while larger particles, exceeding
100 nm, display a bathochromic shift beyond 570 nm (Haiss et al. 2007). This
shift is accompanied by a broadening of the resonance (Lee and El-Sayed
Njoki et al. 2007).
Furthermore, it is worth noting that SERS intensity rises with increasing particle
size (Njoki et al. 2007). This observation holds immense significance in the realm of
theranostic applications of AuNPs. Greater SERS intensity equates to the ability to
detect particles at lower concentrations and at greater depths. Nonetheless, additional
research is warranted to unravel the intricate interplay between particle size, laser
wavelength, and SERS intensity (Njoki et al. 2007).
2005). A fundamental property of AuNPs is their surface
2020) and spatially offset Raman spectroscopy
2021). Furthermore, it plays a pivotal role in therapeutic
2007), making them problematic
2005;
9.4 Methods to Synthesize Ultrasmall AuNPs
The precise control of size, shape, and surface chemistry of ultrasmall AuNPs is of
paramount importance in various fields. This control can be achieved through a
variety of methods, ranging from eco-friendly approaches like green synthesis
involving microorganisms or plant extracts (Bharadwaj et al. 2021; Xin Lee et al.
2016; Esther and Sridevi 2017) to physical techniques such as laser ablation
Соседние файлы в папке Библиотека им академика М.И. Перельмана