1. Introduction
Nanoencapsulation for in vivo administration provides numerous benefits, such as enhancing effectiveness and safety by protecting the substances from degradation or elimination [
1,
2]. This technique contributes to increased absorption and improved bioavailability, optimizing distribution, and extending circulation time while simultaneously reducing toxicity [
2,
3]. Some nanomaterials offer advantages such as enhanced solubility and loading capacity, improved delivery efficiency, and protection from degradation due to the stability provided by the nanocarriers [
1,
2,
3]. However, nanoparticle delivery has many limitations. Nanocarriers are very prone to interact with biomolecules in the bloodstream, creating the so-called “biocorona” [
4], which results in recognition by the immune system [
5]. Upon arrival to the target cells, many nanocarriers are trapped in endocytic vesicles and end up being degraded by lysosomes, diminishing the drug delivery efficiency [
6].
Recent studies suggest that nanocarriers show an average efficiency of delivering to the desired target of less than 1% [
7,
8], leaving space for a significant improvement in targeted delivery. As a result, nanoparticles coated with cell membranes have been proposed as a way to address these problems, as they show a combination of the advantages present in natural nanomaterials such as cell membrane-derived nanomaterials, and artificial nanocarriers, such as the aforementioned polymeric or inorganic nanocarriers [
9,
10,
11,
12].
Cell membrane-coated nanoparticles are biomimetic nanoparticles that are constituted by a cell membrane cover and synthetic nanoparticles [
5]. They offer several advantages over bare nanomaterials, such as increased biocompatibility, due to the similarity of biological membranes to cellular materials, reducing the risk of immune system rejection [
13]. The presence of biological membranes enhances biodistribution by guiding nano-vectored materials to target cells, utilizing membrane receptors recognizable by the target cells. This aspect represents a significant area of study, applicable to immune system cells [
13], central nervous system [
14], as well as a large number of cancer cells (
Table 1). Additionally, coated nanocarriers demonstrate improved drug release control and efficiency, as the biological membranes can degrade or fuse with target cells, releasing the drug at the desired location [
9,
15]. Specifically, the biological camouflage provided by these membranes protects nanoparticles from the body’s defense systems, extending their lifespan and reducing the risk of premature elimination [
13,
15,
16,
17,
18,
19,
20]. The ability to target particles to specific cells, facilitated by the presence of receptors on biological membranes, is a key advantage that positions nanomaterials coated with biological membranes as a promising option for targeted delivery.
As this pioneering methodology is still in its nascent stages, our study aims to comprehensively review the recent advancements in this technology. Specifically, we delve into various studies conducted to date, focusing on elucidating the techniques employed for obtaining cell membrane fragments. We provide detailed insights into the processes involved in isolating these membranes and coating nanoparticles with them. The ultimate goal of this review is to review the technology to generate cell membrane-coated nanoparticles, showcasing their potential for achieving tissue-specific targeting. This review aims to clearly outline the significance of the study within the broader context of this emerging field.
3. Membrane Donor Cells
The selection of a specific cell type is contingent upon the target tissue or application. Typically, cancer cells are employed to specifically target the corresponding cancerous tissue, while white or red blood cells may be used for applications with less specific targets. Most of these cell types were employed to facilitate the precise targeting of nanoparticles to specific tissues. However, some of these cells served a dual purpose by inducing immune stimulation against cancer.
Many different cell types have been used for nanoparticle membrane coating (
Table 1). Notably, a range of cancer lines has been used, including cervical and ovarian cancers [
22,
23,
24,
25], multiple myeloma [
26], melanoma [
12,
27,
28,
29,
30,
31,
32,
33], leukemia [
24,
34,
35,
36,
37,
38,
39,
40,
41,
42,
43,
44,
45], breast cancer [
6,
38,
41,
46,
47,
48,
49,
50,
51,
52,
53,
54,
55,
56,
57], neuroblastoma [
58], colon carcinoma [
24,
59], head and neck squamous cell carcinoma [
60,
61,
62,
63], lung cancer [
55,
64], glioma [
65,
66], glioblastoma [
67,
68], prostate cancer [
69], and liver cancer [
70]. Furthermore, beyond cancer cells, a multitude of non-cancer cells has also been utilized, such as leukocytes [
71,
72], [
71] macrophages [
71,
73,
74,
75,
76,
77,
78], erythrocytes [
19,
30,
47,
49,
79,
80,
81,
82,
83,
84,
85,
86,
87,
88,
89,
90], dendritic cells [
91], neutrophils [
88,
92,
93,
94,
95], mesenchymal stem cells [
96,
97,
98,
99,
100], platelets [
49,
72,
85,
86,
101,
102,
103], fibroblasts [
50,
104], embryonic kidney cells [
105], vaginal endothelial cells [
106], neural stem cells [
107], microglial cells [
68], and keratinocytes [
108].
Cervical and ovarian cancer cells were used to favor the cytosolic delivery of cargo inside living cells [
22] or for homologous targeting [
23]. Multiple myeloma cells were chosen to target their equivalent counterparts, ensuring specificity in cargo delivery [
26]. In the case of melanoma cells, their use was geared towards promoting the delivery and internalization of therapeutic or antigenic materials [
12], or for photoimmunotherapy [
27]. Leukemia cells were employed to deliver cargo into leukemia cells [
35] or were genetically modified to express a protein that can specifically target a tissue [
37]. Neuroblastoma cells were employed for their capacity to capture neurotoxins effectively [
58]. Breast cancer cells were used to target homologous cells and deliver cargo [
6]. Similarly, colon carcinoma [
59] head and neck squamous cell carcinoma [
60], lung cancer [
55], glioma [
65,
66], [
65] glioblastoma [
67,
68], [
67] prostate cancer [
69], and liver cancer [
70] cells were selected for homologous targeting, ensuring precision in cargo delivery to specific tissues.
In the case of non-cancer cells, leukocytes were harnessed for their capacity to target specific tissues effectively [
71]. Erythrocytes were used to target cancer tissues, due to their elasticity and capacity to diffuse into the tumor extracellular matrix [
80]. Dendritic cells were employed to promote tumor immune effects [
91]. Vaginal endothelial cells were used to protect the cells from a toxin [
106]. Neural stem cells were used to cross the blood-brain barrier and specific targeting [
107]. Neutrophils [
92], mesenchymal stem cells [
96], fibroblasts [
50,
104], embryonic kidney cells [
105], microglial cells [
68], and keratinocytes [
108] were also used for specific targeting.
Some investigations opted to combine membranes from different cells so that the coated nanoparticles benefited from the characteristics of both types of source cells. When hybrid membrane-coated nanoparticles were developed by combining two cell types, leukocytes were chosen to mitigate immune recognition [
72], platelets were selected for their notable ability to bind to cancer cells [
72], and erythrocytes due to their long circulation times [
49] and immune-evasion capability [
30]. Additionally, breast cancer cells [
47,
49], were incorporated in hybrid membrane coating to ensure precise targeting of homologous cells.
Table 1.
Donor cell types for nanoparticle coating applications.
Table 1.
Donor cell types for nanoparticle coating applications.
Donor cell |
Cell lines |
Application |
References |
|
Cervical and ovarian cancer |
HeLa |
Homologous targeting |
[22,23,24,25] |
|
Multiple myeloma |
ARD, KMS11, 5TGM1 |
[26] |
|
Melanoma |
B16-F10, MDA-MB-435 |
[12,27,28,29,30,31,32,33] |
|
Leukemia |
CHRF-288-11, C1498, RAW264.7, THP-1, Jurkat, HL-60 |
[24,34,35,36,37,38,39,40,41,42,43,44,45] |
|
Breast cancer |
4T1, MCF-7, MDA-MB-231, MDA-MB-468 |
[6,38,41,46,47,48,49,50,51,52,53,54,55,56,57] |
|
Colon carcinoma |
CT-26 |
[24,59] |
|
Head and neck squamous cell carcinoma |
CAL 27, SCC7 |
[60,61,62,63] |
|
Lung cancer |
NCI-H460, A549 |
[55,64] |
|
Glioma |
GL261, C6, U87MG |
[65,66] |
|
Glioblastoma |
U251 |
[67,68] |
|
Prostate cancer |
RM-1 |
[69] |
|
Liver cancer |
HepG2 |
[70] |
|
Fibroblasts |
NIH 3T3 |
[50,104] |
|
Embryonic kidney cells |
HEK293 |
[105] |
|
Vaginal endothelial cells |
VK2/E6E7 |
[106] |
|
Neural stem cells |
Primary cells |
[107] |
|
Microglia |
HMC3 |
[68] |
|
Keratinocytes |
Hacat |
[108] |
|
Mesenchymal stem cells |
Primary cells |
[96,97,98,99,100] |
|
Neuroblastoma |
Neuro-2a |
Neurotoxin capture |
[58] |
|
Erythrocytes |
Primary cells |
Cancer tissue targeting |
[19,30,47,49,79,80,81,82,83,84,85,86,87,88,89,90] |
|
Avoidance of immune recognition |
|
Leukocytes |
Primary cells |
[71,72,73,74,75,76,77,78,88,91,92,93,94,95] |
|
Platelets |
Primary cells |
Cancer cell binding ability |
[49,72,85,86,101,102,103] |
|
8. Discussion
An interesting factor to analyze after reviewing the methods is the membrane isolation efficiency, but almost none of the researchers gave information about it. Zou et al. mentioned how easy the erythrocytes were to isolate [
99], while Fang et al. stated that their membrane isolation was successful [
12]. Only Ferreira et al. gave specific results of the membrane isolation efficiency, reporting that 80% of the membrane was retained after isolation [
67].
The coating efficiency is also an important factor to analyze because it shows how successful the coating was. In this regard, most of the researchers report a successful coating, showing the complete coating of the particles with TEM imaging or the analysis of zeta potential comparing the potential of the coated nanoparticles with those of the nude nanoparticle and the isolated membrane. Only 3 of the reviewed articles gave an exact value of coating efficiency. Liu et al. reported a 90,21% efficiency [
95], which is in line with the reports of complete or almost complete coating given by all the investigations that analyzed it with TEM and zeta potential. Conversely, Li et al. report a 21% coating efficiency with a sonication method [
51], and Liu et al. measured the coating with a fluorescence quenching essay where they used a quencher that cannot cross membranes and therefore only affects their uncoated parts, state that up to 90% of the nanoparticles are only partially coated and 60% of them are only 20% coated [
24]. These results open the door for future improvements to the coating techniques.
Most of the coatings caused an increment of around 10 to 30 nm to the diameter of the nanoparticles. But there were many cases where the increase was notably higher, such as Liu et al. (66 nm) [
78], Ren et al. (59 nm) [
53], Li et al. (56 nm) [
94], Bu et al. (80 nm) [
108] or Li et al. (140 nm) [
54]. These results can be attributed to an imperfect membrane coating of the nanocarriers, either by having more than one layer of membrane fragments or by the creation of aggregates of those fragments on the surface of the particle. Conversely, Huang et al. report a more exceptional result where they observed a reduction of the size of the nanoparticles, diminishing from 150.1 to 137.3 nm [
68]. The researches attribute this decrease in size to the pressures to which the particles are subjected to during the extrusion process [
68].
The particle-membrane interactions were covered by only a handful of the reviewed articles, because most of them were focused on the effects of the cargo loaded on the nanoparticles on the cells. Despite that, some articles give interesting information about these interactions. Ferreira et al. and Scully et al. explain that the coating is achieved by electrostatic interactions that favor the right-side orientation of the membrane [
46,
67]. Chen et al. and Liu et al. also state that negatively charged nanoparticles give better results than positively charged nanocarriers due to their electrostatic interactions [
5,
24]. Luk et al. stated that the negatively charged cores created a more subtle interaction, allowing the membranes to retain their structure and fluidity, whereas the positively charged cores created strong electrostatic interactions that can cause the collapse of the membrane and thus create aggregates of nanoparticles and membrane fragments [
110]. Mornet et al. went further and analyzed the effect of differently charged membranes on the coating. They observed that highly negative membranes didn’t achieve a successful coating, but moderately negatively charged membranes were able to completely coat the nanoparticles [
111]. Xia et al. attribute these interactions to the presence of dense negatively charged sialic acid moiety present in the outer membrane side, that allows the right side of the membrane to coat the nanoparticles when a negatively charged core is used but causes the formation of aggregates when positively charged nanoparticles are used because of these negative charges located in the outer side of the membrane [
112]. Zhao et al. and Zhang et al. state that a higher concentration of H+ in the tumoral microenvironment favors the dissociation of the membrane and the nanoparticle, allowing for a faster release of the cargo [
25,
73].
The biological and micro/nano interactions responsible for tissue-specific therapeutics using these nanoparticles are very diverse. The most common approach was to take profit from the homotypic targeting allowed by the “self-recognition” molecules present on the target tissue [
46], especially among those who wanted to target cancers with patient-derived tumor cells, because cancer cells have surface antigens that allow multicellular aggregation through homophilic adhesion domains [
91]. Some of them rely on the presence of proteins in the membrane coat of the nanocarriers that attach to receptors of the target cells, allowing thus their internalization via endocytosis, such as Tiwari et al. [
56], who relied on the presence of heparanase, syndecan-1 and glypican-1, that target HSPG receptors, unchaining the endocytosis. The particles that were designed to avoid immune recognition profited from immune and other blood cells components, especially from macrophages and erythrocytes, respectively, such as macrophages’ SIRPα receptor, to which the CD47 proteins of the membranes of the donor cell bind to be recognized by the macrophages and avoid phagocytosis [
113]. Some opted for the decoration of membranes with targeting molecules, such as aptamers, that target the tumors [
100]. Another alternative was to genetically modify the donor cells to overexpress a protein that targets a specific protein from the target tissue, such as the rabies viral glycoprotein used by et al. to target acetylcholine receptors on cerebrovascular endothelial cells and nerve cells [
107]. Another example of this is the use of antibodies linked to the membrane, designed to target the aimed cells [
40].
The release kinetics were given by almost all of the reviewed articles, but most of them only studied the difference of released cargo at different pH values. As expected, more cargo was released and also in a faster way when the coated nanocarriers were in more acidic conditions, such as those present at the tumor microenvironments, than in normal physiological conditions (i.e., pH 7.4) [
56,
100]. But among those who actually compared coated and non-coated particles, there were different results. Some like Qi
et al., Zhang
et al., Li et al. and Lin et al. report similar release kinetics between both types of carriers, with a minimal difference in speed and total release, as coated nanoparticles were a bit slower and released a bit less cargo than their non-coated counterparts [
23,
77,
86,
90]. Conversely, Ma et al. observed that coated nanoparticles released less cargo at pH 7.4 but at pH 5.5 were more effective in the release than the non-coated ones [
91]. Others, such as Li et al. and Chen et al. observed that coated nanoparticles released 10% less of the total cargo than those that were not coated during the first 12-24 hours, but in the long term (5-7 days) both end up releasing the same amount of cargo [
62,
64]. Tian et al. observed a great difference in released cargo between coated and non-coated nanoparticles (16.85% against 40.1%), releasing thus less cargo during circulation and improving drug delivery [
96]. A similar result is reported by Qu
et al., who observed a similar difference but both coated and non-coated nanoparticles release higher amounts of cargo (33% versus 50%) [
26], and by Scully
et al., who reported a 12% release of cargo after 24 h and 16% after 48 hours in coated nanocarriers, whereas the non-coated released 30 and 37%, respectively [
46]. Parodi et al. studied the release kinetics of two different cargos (doxorubicin and BSA) [
71]. There were very significant differences in the release of both cargos between coated and non-coated carriers, being 20% against 45% release of doxorubicin after 3 hours, and 15 versus 25% after 3 hours and 80 versus 90% after 48 hours, respectively [
71]. In Liu
et al.’s study, non-coated cores were able to deliver the whole cargo after 72 h, but their coated counterparts only released 50% of it in those 72 h, requiring 120 h to release 90% of the cargo [
92]. Liu stated that the use of PEG and the membrane coating improved the stabilization of the nanoparticles, allowing the reported better retention of the cargo in the nanocarriers [
92]. Du et al. saw almost no difference in release between coated and non-coated nanocarriers at pH 7.4 (both around 11%) but noticed a significant 16% difference at pH 5.0 [
66]. Despite not releasing less at physiological conditions and being less efficient at tumor conditions, the low release at pH 7.4 allows for an enhanced cargo accumulation at tumor sites and a reduction of toxicity to other tissues [
66]. Xie et al. noted that at pH 7.4 coated carriers released much less cargo than the non-coated ones (24.3% against 37.9%), but at pH 5.5, both released more similar amounts (76.1% versus 84.1%) [
98]. Gong et al. reported a bigger difference at pH 7.4 (40% against 65%), but at pHs 5.5 and 4.7 those differences are reduced significantly, especially at pH 4.7, where the difference is almost negligible [
41]. These results from Xie et al. and Gong et al. show that the coating protects the nanoparticles and avoids the loss of cargo before arriving at the tumor, improving thus the loading capacity and the drug release behavior [
98].
These coating techniques were evaluated through a comparison between cell membrane-coated nanoparticles and their non-coated counterparts and/or free cargoes. In all studies conducting cellular uptake analyses, improvements were consistently observed compared to non-coated nanocarriers and free substances. While some studies reported a twofold increase in uptake, others, like Fang
et al., noted a remarkable 40-fold improvement [
12]. Certain investigations extended their analysis by comparing uptake in the target cell type with other cell types to assess specificity. For instance, Bai et al. observed significantly higher uptake in the target cells compared to other cell types [
59]. Furthermore, certain studies prioritized investigating immune avoidance, noting a reduction in phagocytosis of coated nanoparticles by macrophages compared to non-coated nanocarriers [
39,
71,
81,
92]. In summary, cell membrane-coated nanoparticles consistently demonstrated improvements in uptake, specificity, or immune evasion compared to their non-coated counterparts.