Multifunctional Amine Mesoporous Silica Spheres Modified with Multiple Amine as Carriers for Drug Release

Mesoporous silica spheres were synthesized by using Stöber theory (MSN-40). Calcination of the mesostructured phase resulted in the starting solid. Organic modification with aminopropyl groups resulted in two MSN-40 materials: named MSNNH 2 and MSN-DQ-40, respectively. These two kinds of samples with different pore sizes (obtained from 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethox-ysilane (NQ-62) and modified NQ-62) showed control of the delivery rate of ibuprofen (IBU) from the siliceous matrix.The obtained sample frommodified NQ-62 has an increased loading rate and shows better control of the delivery rate of IBU than the obtained sample from NQ-62. These three solids were characterized using standard solid state procedures. During tests of in vitro drug release, an interesting phenomenon was observed: at high pH (pH 7.45), IBU in all carriers was released slowly; at low pH (pH 4.5), only a part of the IBU was slowly released from this carrier within 25 hours; most IBU was effectively confined in mesoporous material, but the remaining IBU was released rapidly and completely after 25 hours.


Introduction
Mobil Oil [1] reported M41S mesoporous silica materials in 1992.In 2001, Vallet-Regi et al. used MCM-41 as a drug carrier of ibuprofen [2] creating the field of mesoporous silica biomedical research.Although there are many kinds of inorganic nanomaterials that have been widely reported for biomedical applications [3], mesoporous silica nanoparticles (MSNs) show their unique features in this field.MSNs can withstand thermal and mechanical stress as well as pH and oxidative degradation.They have low toxicity and good biocompatibility [4][5][6][7].The drug loading capacity can be changed by adjusting the pore diameter.Surface modification can control the drug release rate [8].These nanoparticles have the following remarkable characteristics [8][9][10][11][12]: (1) there exist ordered pore networks, uniform pore size, and precise control of drug loading and release; (2) the large pore volume can store more drugs; (3) high surface area means that the adsorption ability of drug is strong; (4) the surface contains a large amount of Si-OH-functional group functionalization offers better control of drug loading and releasing.These unique features have made mesoporous materials an excellent material for drug delivery and many other potential applications [13,14].
Instrumentation.The powder X-ray diffraction (XRD) patterns were recorded on a Bruker D8 X-ray diffractometer with Ni-filtered CuK radiation (40 kv, 40 mA).Fouriertransform infrared (FI-IR) spectra were collected on Nicolet iS50 spectrophotometer using KBr pellets, and nitrogen sorption isotherms were measured at with a Micromeritcs ASAP 2020.Before measurements, the samples were degassed in a vacuum at 100 ∘ C for at least 12 hours.The Brunauer-Emmett-Teller (BET) method was utilized to calculate the specific surface areas (S BET ) using adsorption data.By using the Barrett-Joyner-Halenda (BJH) model, the pore volumes and pore size distributions were derived from the adsorption branches of isotherms.Transmission electron microscopy (TEM) of samples was observed on JEM-2100 electron microscopy at 160 KV.Scanning electron microscopy (SEM) images were taken with a JEOL-JSM-7500F electron microscope operating at 20 KV.Thermogravimetric analysis (TG-DTA/DSC) was conducted in air on a STA 449C Jupiter5 thermal analyzer.The samples were heated from 30 to 1000 ∘ C with a heating rate of 10 ∘ C/min in air.

Synthesis of Mesoporous Silica.
To 220 ml of deionized water mixed with 80 ml of methanol, there was added ammonia water to a pH of 11.24.Next, 0.58 g of CTAB was added with uniform mixing with a rotating speed of 1200 rpm.The temperature rose to 40 ∘ C. Then 5 ml of TEOS was added dropwise.After 1 min, a white precipitate appeared.The reaction proceeded for 3 hours and was then aged for 3 hours.It was filtered to obtain a white solid.The solid was dried at 70 ∘ C in air for 24 hours.This was then calcined at 420 ∘ C. The material was named MSN-40.

Modification of NQ-62.
We used polyamine silane coupling agents [25,30,31].To a 50 ml round-bottom flask, 15 ml absolute ethanol was added with 0.1 g of sodium.This was stirred to dissolve the sodium.Then, 10.3 g of NQ-62 (0.1 equivalent) was added and mixed with 5 g (0.1 equivalent) of triethanolamine.This was stirred to reflux for 10 hours, cooled, and rotary evaporated to remove the absolute ethanol.The solution obtained at 175 ∘ C was heated at high temperature with stirring for 36 hours to yield a red brown, sticky substance.We added a small amount of ether to wash the triethanolamine and then added acetone to remove the NQ-62.Anhydrous ethanol solution was added to the precipitate.This was filtered and vacuum distilled to yield a brown viscous material named MDNQ.The experimental process is as mentioned in Scheme 1.

Functionalization of Mesoporous Silica.
For functionalization, a 2010 report on the multiamine functionalization of mesoporous silica was used [26].Here, 400 mg MSN-40 was dispersed in 50 ml dry toluene followed by 1.6 ml NQ-62 and 18 hours of stirring at 40 ∘ C.This was filtered while hot and washed three times with dry toluene to remove unreacted NQ-62.The solid obtained at 70 ∘ C was dried in an oven for 24 hours.The substance was named the MSN-NH 2 -40 (Scheme 2): an aminofunctional mesoporous silica. . ( 1 is showing the initial mass of IBU;  2 is showing mesoporous adsorbent added to hexane solution;  is showing IBU concentration of the solution prepared by diluting 2 ml of filtrates to 50 ml in volumetric flask;  is showing the volume of hexane solution for drug loading.

Releasing of IBU.
In our release experiment, each sample is loaded in phosphate buffered saline (PBS) at pH 4.5 and pH 7.45.The nanoparticles (60 mg) were placed in 8000-14000 MWCO dialysis bags with 8 ml PBS.The dialysis solution was 250 ml of PBS at pH 4.5 or pH 7.45 at 37 ∘ C. The stirring speed was 500 rpm.Three mL aliquots were taken periodically and measured with absorbance as described above [32,33].At the same time, equal volume of fresh release fluid was added.Calculation of the accumulated concentration of released IBU is based on the following equation: is the real concentration of IBU released at time ;   is the apparent concentration measured by UV-vis spectrometry of the release fluid sample at time ; V is the volume of sample taken at the predetermined time intervals;  is the total volume of release fluid.is very good.At 0.8 < p/p0 < 1 area, the material has a hysteresis loop due to the clearance hole, that is, the mesoporous structure of the cavity or the accumulation of clearance particles or mesoporous structure of the cavity.The corresponding pore size distribution plots were calculated with the BJH method [34] (Figure 3 .76nm, and 1.74 nm.This confirms amine functionalization and loading of IBU.The average pore volume and surface area were estimated via the BET method (see Table 1).Table 1 shows that, after modification, the MSN-40's pore size, specific surface area, and pore volume decrease.The decreases of specific surface areas are due to the reason that the presence of pendant organic chains covalently bonded to the inorganic network have the ability to partially block the entrance of nitrogen molecules [35], and indicated that organic groups were fastened inside mesopores.After IBU loading, their texture parameters also decrease indicating multiamine chains into mesoporous channels.
Figures 5(c) and 5(d) are the infrared spectra of MSN-40 loaded with IBU and sample MSN-NH 2 -40 and MSN-DQ-40 loading IBU, respectively.Figure 5(c) contains secondary amine and primary amine N-H stretching vibration peak (3500-3000 cm −1 ).The stretching vibration peaks of Si-O-Si appear at 1078 cm −1 and 1230 cm −1 , and the asymmetry vibration peaks appear at 807 cm −1 ; Si-OH has a symmetrical stretching vibration peak at 954 cm −1 , but Figure 5(d) does not show this peak.This is because the head group on the NQ-62 interacted with the Si-OH of the hydrogen bond.The stretching vibration peaks of the Si-O bond appear at 459 cm −1 .Figure 5(c) has peaks at 2810 cm −1 and 2930 cm −1 from the -CH 2 of stretching vibration peak.There are almost no peaks at 2810 cm −1 and 2930 cm −1 in Figures 5(c) and 5(d) indicating that the templating agent is almost removed.The bands at 2843 cm −1 and 2937 cm −1 appear in Figures 5(a 1430-1600 cm −1 of IBU are obvious.The -COOH peak of the MSN/IBU system decreased significantly, and a new peak at 1569 cm −1 is obvious because of the coexistence of interaction between -COOH and -NH 2 forming a -CO-NH.We conclude that the IBU has been successfully loaded on the surface of the mesoporous silica, that NQ-62 is successfully grafted on the surface of the mesoporous silica, that the MDNQ is successfully grafted on the surface of MSN, and that the template agent is almost completely removed.Figure 6 shows the TG curves of the materials.All samples show an obvious weight loss up to 100 ∘ C due to the desorption of physically adsorbed water [38].In addition, there is no obvious weight loss attributed to the disintegration of MSN-40 suggesting that the MSN-40 is thermally stable.The MSN-40/CTAB has significant weight loss due to surfactant CTAB loss of MSN-40/CTAB at 100-500 ∘ C. For amine functionalized samples, the TG curves have a rapid weight loss at 200-800 ∘ C, which is due to the removal of multiamine groups [21].This is significant evidence of the existence of amine groups on the surface and inner pore of MSN-40 [21,38,39].The MSN-DQ-40 can be further confirmed due to fairly obvious weight loss compared to MSN-NH 2 -40.This indicates that the grafting amount of multiamine groups on MSN-DQ-40 is much higher than MSN-NH 2 -40., respectively, at pH 4.5.Within 25 hours, the release is slow after a burst release.This might be because -COOH and -NH 2 form a peptide bond.The amide has slow hydrolysis in the acidic environment with heating (37 ∘ C).This is the opposite of the literature [4] reporting a "switch effect" [17][18][19][20][21] in amino-modified mesoporous silica.We achieved an open channel amino-modified mesoporous silica.For Figure 7(d), our experimental condition was that we got the nanoparticles (12 mg) process release of experiment.

Conclusions
We demonstrated the feasibility of controlling the delivery rate of drugs occluded in MSN-40 matrixes by functionalizing the pore wall with a silane coupling agent and modified silane coupling agent.For IBU, which contains an acid group, the well-ordered MSN-40 matrixes are functionalized with aminopropyl moieties (namely, MSN-NH 2 and MSN-DQ-40) to decrease delivery.They showed pH-responsive control for drug release.At high pH (pH 7.45), IBU drug loaded in MSN-40 matrixes releases slowly within 50 hours; at low pH (pH 4.5), the IBU was slowly released within 25 hours but was released rapidly and completely after 25 hours.for its linguistic assistance during the preparation of this manuscript.
Figure 1 is the MSN-40 of the scanning electron microscope.The materials are spherical with an average particle size of 100 ± 17 nm.Figure 2 shows TEM images of the three samples at different magnifications.These samples show agglomeration, nonuniformity, and spherical morphologies.Spherical MSN-40 porous structure offers uniform distribution of multiamine chains [21] inside and outside the pores.The open-framework structure becomes increasingly vague in Figures 2(d), 2(e), and 2(f) indicating that multiamine chain is grafted inside and outside the pores.Figure 3 shows MSN-40, MSN-NH 2 -40, MSN-DQ-40, MSN-NH 2 -40/IBU, and MSN-DQ-40/IBU adsorption/desorption isotherms as well as the distribution of pore size and pore volume.

Figure 7 (
d) represents the MSN-NH 2 -40 and MSN-DQ-40 in the buffer solution at pH 4.5 release rate of IBU within 26 hours.The MSN-NH 2 -40 slowly releases IBU, and MSN-DQ-40 can release IBU in full.MDNQ offers good enrichment effects for IBU with stable release in a weak acid environment for 24 hours.
Table 2 shows the loading rate of MSN-40, MSN-NH 2 -40, and MSN-DQ-40 at 36 hours and 72 hours.Within 36 hours, the MSN-NH 2 -40 loading rate of IBU was only 10.68%, while MSN-DQ-40 reached 49.47%.Within 72 hours, the MSN-NH 2 -40 reached 46.93% for IBU suggesting that the loading rate of NQ-62 after modification is low.The pore diameter and volume as well as the specific surface area are reduced, which decreases adsorption.The MDNQ-modified MSN has an increased