Enhancing the Mechanical Properties and Biocompatibility of Polysiloxane-Based Biomaterials

Polysiloxane (PST) is widely used in the medical field because of its good stability and compatibility. However, affected by its composition, the material itself has poor mechanical properties, which greatly limits the application of polysiloxane. Improving the comprehensive performance of polysiloxane is an important research at present. The curing reactivity of polysiloxane-modified CE resins with different epoxy group contents was studied, and the mechanical properties of the materials were improved. The test results show that the modified material has a glass transition temperature of 284.0 ℃, tensile strength and flexural strength of 84.7 MPa and 118.3 MPa respectively [1]. Polydimethylsiloxane was introduced into polyvinyl alcohol (PVA) through anionic polymerization to prepare a new type of polyvinyl alcohol grafted polysiloxane, and the properties of the material were studied [2]. A new type of skin barrier material was obtained by compounding polysiloxane and polyvinyl alcohol, and its performance was studied. The results show that the material can meet multiple performance requirements of skin barrier materials, and can play an important role in the field of damaged skin repair [3]. Based on this, this experiment prepared a new type of polysiloxane material with reference to the method of literature [4], and studied its biological safety and medical applicability.

1 Experimental part

1.1 Materials and equipment

Main materials: Polydimethylsiloxane (H2N—PDMS—NH2) (AR), Xinhongyue Chemical; Ethylene Carbonate (EC) (AR), Qilu New Materials; Isophorone Diisocyanate (IPDI) ( AR), Chengtai Chemical; Dibutyltin Dilaurate (DBTL) (AR), Qilu New Materials; 1,2-Butanediol (BDO) (AR), Chengyang New Materials.

Main equipment: 101A electric heating oven, Erfang Precision Machinery; FTIR-650G infrared spectrometer, Hengmei Electronics; DSC-500A differential scanning calorimeter, Donglai Instruments; UItima IV wide-angle X-ray diffractometer, Sanopu Instruments: HLC-8320 Gel Permeation Chromatography, Huishi Instruments; WL-A Tensile Testing Machine, Wolin Equipment.

1.2 Test method

1.2.1 Preparation of soft segment HO—PDMS—OH

A certain amount of H2N-PDMS-NH2 was put into a three-neck flask with a volume of 100 mL, then a metered amount of EC was added, and the reaction was stirred at constant temperature. The stirring speed, reaction temperature and time were 250 r/min, 80 °C and 2 h, respectively. Raise the reaction temperature to 80 °C and continue the reaction for 1 h; then raise the reaction temperature to 90 °C and react for 1 h to obtain the soft segment HO—PDMS—OH. The soft segment formula is shown in Table 1.

1.2.2 Preparation of Si-TPU

(1) Put a certain amount of soft segment HO—PDMS—OH into the three-necked flask, and then carry out water removal treatment through a vacuum distillation device. The decompression conditions are: decompression pressure -0.095 MPa, decompression temperature is 115 ℃ , the stirring speed is 100 r/min, and the water removal time is 1.5 h;

(2) After cooling down to 75°C, reduce the pressure to normal pressure. Put a quantitative amount of IPDI into a three-necked flask, then put the catalyst DBTL with a mass fraction of 0.03%, and react at 85 °C for 2 h;

(3) Put in the metered BDO chain extension reaction for 0.5 h to obtain the polymer. Then pour it into the mold prepared in advance and perform electrothermal curing treatment. The curing temperature and time are 100 ℃ and 12 h, respectively, to obtain Si-TPU;

(5) Preparation of microscopic gastric tubes by 3D printing. The test configuration is shown in Table 2.

1.3 Performance test

1.3.1 Infrared spectrum test

The material functional groups were tested by infrared spectrometer.

1.3.2 Molecular weight analysis

The molecular weight of the material was analyzed by gel permeation chromatography.

1.3.3 Thermal Stability Analysis (DSC)

Thermal stability analysis was performed by differential scanning calorimetry.

1.3.4 Mechanical property test

The mechanical properties of the material were tested by a tensile testing machine.

1.3.5 Cytotoxicity test

By co-culturing with mouse fibroblasts (L929 cells), observe the growth of L929 cells.

2 Results and discussion

2.1 Functional group analysis

2.1.1 Analysis of soft segment HO—PDMS—OH functional group

The synthesized soft segment HO-PDMS-OH was analyzed by infrared spectroscopy, and the results are shown in Figure 1.

It can be seen from Figure 1 that when EC and H2N-PDMS-NH2 are polyaddition, the terminal amino group reacts with the carboxyl group, so in the soft segment HO-PDMS-OH, the characteristic peaks of the terminal amino group belonging to H2N-PDMS-NH2 and the carboxyl group belonging to EC disappear [5-6]. The product of polyaddition reaction is imino group, carbonyl group and terminal hydroxyl group on the carbamate group, so the peak intensity and peak shape of these structural characteristics can be observed in the soft segment HO-PDMS-OH [7]. In conclusion, EC and H2N-PDMS-NH2 successfully undergo polyaddition reaction to prepare soft segment HO-PDMS-OH.

2.1.2 Si-TPU functional group analysis

Figure 2 is the results of infrared spectroscopy analysis.

It can be seen from Figure 2 that after the reaction, the characteristic peak of the isocyanate group at 2 264 cm-1 disappears, which indicates that the isocyanate group is completely reacted during the reaction, and at the same time, it can be seen in the infrared curve of Si-TPU The carbonyl on the carbamate group was observed (

CO) and imino (-NH) stretching vibration peaks, but no allophanate or biuret structures appear, which proves the successful preparation of Si-TPU materials [8-9]. It can be seen from Figure 2(a) that the molecular weight of the soft segment is fixed, and the carbonyl group of Si-TPU (CO) and imino (—NH) characteristic peaks gradually increase with the increase of hard segment content. This is because the increase in the hard segment content in the system increases the number of carbamate groups, which enhances the characteristic peak on the carbamate group [10]. It can be seen from Figure 2(b) that the intensity of characteristic peaks decreases with the increase of soft segment molecules when the hard segment content is fixed. This is because the more the molecular weight of the soft segment in the system, the farther the distance of the carbamate group is, which reduces the density of the carbamate group and affects the intensity of the carbamate characteristic peak .

2.2 Si-TPU crystalline state analysis

Due to the large thermodynamic difference between the soft segment and the hard segment of polyurethane, there is a certain spontaneous microphase separation. Both the amorphous and ordered structures of the soft and hard segments have a great impact on the performance of polyurethane. Therefore, the crystalline state of Si-TPU was analyzed by WAXD, and the results are shown in Figure 3.

It can be seen from Figure 3 that 12° and 21° in the WAXD curve are respectively the amorphous dispersion peaks of the soft segment PDMS and the non-PDMS segment in the polymer chain, which shows that the Si-TPU soft and hard segment states are both amorphous, No obvious crystalline state appeared.

2.2 Molecular weight and distribution analysis

Table 3 is the molecular weight result of the material.

It can be seen from Table 3 that the molecular weight distribution of all Si-TPU polymers is about 2.1, and the Mn is relatively close, controlled at 45,000-75,000 u, which can meet the needs of industrial processing.

2.3 DSC analysis

The thermal effect of polyurethane with temperature changes was analyzed by DSC. The results are shown in Figure 3, where Tg is the glass transition temperature value, which is used to characterize the influence of hard segments and soft segments on the polyurethane network structure.

It can be seen from Figure 3 that Si-TPU polymers have two glass transition temperatures, of which the Tg at -123 °C is caused by the soft segment HO-PDMS-OH; the other Tg that occurs near room temperature is generated by the hard segment . The hard segment aggregates with each other under the action of hydrogen bonds to form a hard segment micro-domain, which is the physical cross-linking point of the long polymer chain during the polymerization process [14-15]. It can be seen from Figure 3(a) that when the molecular weight of the soft segment is fixed, the higher the content of the hard segment, the glass transition temperature near room temperature begins to increase gradually, from 9 °C to 50 °C, because the hard segment in the system contains The more wax, the higher the average molecular weight of the hard segment, and the greater the number of hydrogen bonds between the hard segments, so the energy required for the movement of the chain segments is also higher, which significantly increases the Tg of the hard segment . It can be seen from Figure 3(b) that when the hard segment content is fixed, the glass softening point close to room temperature also increases gradually, from 6 °C to 45 °C. This is because with the increase of the molecular weight of the soft segment in the system, the average molecular weight of the hard segment also increases to a certain extent, and more hydrogen bonds are formed between the hard segments, which improves the ability required for the movement of the chain segment and increases the glass transition temperature of the hard segment. .

2.4 Mechanical property test

Table 4 is the mechanical performance test results.

It can be seen from Table 4 that with the increase of the hard segment, the elongation at break decreases, and the strength of other mechanical properties increases to a certain extent. The main reason for this change is that the increase in the hard segment content will lead to the average hard segment length in the polymer system, which increases the number of physical crosslinks in the system and the number of hydrogen bonds in the molecular chain. Under the synergistic effect of the two, the increase The tensile strength of the polymer [19-20]. However, the increase of physical cross-linking points may restrict the movement of molecular chains, resulting in a certain decrease in the elongation at break. When the hard segment content is 39%, the tensile strength of the polymer reaches 20.3 MPa, the toughness also reaches 52.8 J/m3, and the elongation at break is about 378%. At the same time, it can also be observed from Table 4 that when the hard segment content in the system is fixed, with the increase of the molecular weight of the soft segment, the change of the mechanical properties of the polymer is consistent with the increase of the hard segment. This is because with the increase of the molecular weight of the soft segment in the system, the average length of the hard segment of the material also increases to a certain extent, which limits the deformation of the material to a certain extent.

2.5 Cytotoxicity test

In the mechanical performance test results, it has been determined that the A6 material has good mechanical properties. Therefore, taking this group of materials as an example, a cytotoxicity test was performed on it; Figure 4 shows the results of the cytotoxicity test.

It can be seen from Figure 4 that the L929 cells maintained a relatively healthy growth rate after being cultured in the A6 extract for 72 h. And with the increase of time, the cell growth rate is relatively similar, both exceeding 80%. The growth state of the cells was evaluated by referring to the toxicity classification method of the United States Pharmacopoeia; according to this classification, it can be determined that the polymer prepared in this test has low toxicity to mouse fibroblasts and can be used as a biomedical material.

3 Conclusion

(1) In the infrared curve of Si-TPU, it can be observed that the carbonyl group on the carbamate group (CO) and imino (—NH) stretching vibration peaks, but no allophanate or biuret structure appears, which proves that Si-TPU material was successfully prepared;

(2) The soft and hard segments of all Si-TPU materials are in an amorphous state, and there is no crystallization;

(2) The molecular weight distribution of all Si-TPU polymers is about 2.1, and the Mn is relatively close, controlled at 4.5×104～7.5×104, which can meet the needs of industrial processing;

(3) DSC analysis results show that with the increase of hard segment content or soft segment molecular weight in the system, the glass transition temperature caused by the soft segment does not change, only the glass transition temperature of the hard segment changes. When the molecular weight of the soft segment is fixed, the glass transition temperature of the hard segment increases from 9 ℃ to 50 ℃ with the increase of the content of the hard segment; when the content of the hard segment in the system is fixed, the glass transition temperature of the hard segment increases from 6 ℃ to 45 ℃ with the increase of the molecular weight of the soft segment ;

(4) With the increase of hard segment content and soft segment molecular weight, the tensile strength, hardness and toughness of the material all increase to a certain extent, but the elongation at break decreases to a certain extent. When the hard segment content is 39%, the tensile strength of the polymer reaches 20.3 MPa, and the toughness also reaches 52.8 MJ/m3.

(5) Cytotoxicity test results: L929 cells were cultured in the A6 extract, and the relative growth rate of the cells exceeded 80%, meeting the requirements of the United States Pharmacopoeia, showing good biological safety and medical applicability.