CN112206347B

CN112206347B - Composite bone cement with molecular weight matching and performance enhancing functions as well as preparation method and application thereof

Info

Publication number: CN112206347B
Application number: CN202011097483.3A
Authority: CN
Inventors: 全昌云; 冯小瑜
Original assignee: Sun Yat Sen University
Current assignee: Sun Yat Sen University
Priority date: 2020-10-14
Filing date: 2020-10-14
Publication date: 2022-06-03
Anticipated expiration: 2040-10-14
Also published as: CN112206347A

Abstract

The invention discloses a composite bone cement with a molecular weight matching and performance enhancing function, a preparation method and application thereof. The composite bone cement with the matched molecular weight and enhanced performance consists of a solid component and a liquid component, wherein the solid component comprises polymethyl methacrylate, a methyl methacrylate-styrene block copolymer and an initiator; the liquid component comprises methyl methacrylate and a promoter; the molecular weight of the methyl methacrylate-styrene block copolymer is less than or equal to that of the polymethyl methacrylate

The invention can coordinate the balance between the mechanical property of PMMA bone cement viscosity and the too fast viscosity change through the molecular weight matching of PMMA and P (MMA-co-St), thereby not only meeting the operation requirements of clinicians, but also meeting the mechanical property of bone cement with PMMA with lower molecular weight, and having larger application prospect without adding other additives for enhancing the mechanical property.

Description

Composite bone cement with molecular weight matching and performance enhancing functions as well as preparation method and application thereof

Technical Field

The invention relates to the technical field of medical materials, in particular to composite bone cement with size matching and performance enhancement, and a preparation method and application thereof.

Background

Polymethyl methacrylate (PMMA) bone cement is a vertebroplasty material widely applied at present due to the advantages of good mechanical properties and capability of being made into any shape for rapid forming. At present, more than 70 PMMA bone cements are available in the market, and the PMMA bone cements are widely applied to orthopedic filling materials and fixing materials, particularly to vertebral body compression fracture treatment in vertebroplasty, can quickly stabilize the damaged vertebral body, and relieve the symptoms of patients. The bone cement is mainly formed by polymerizing polymethyl methacrylate (powder) and monomer methyl acrylate (liquid). PMMA has no odor and stable performance. MMA is a colorless liquid, with a pungent odor, being volatile, flammable, lipophilic, and cytotoxic. Under certain conditions, the PMMA can be polymerized and cured by itself to form the polymer PMMA. Due to the fiber characteristics of polymer molecules and the extension and winding capacity of the polymer molecules, the molecular weight becomes an important factor of the performance of the polymer molecules, and the larger the molecular weight is, the stronger the intermolecular action is, and the better the tackifying effect is. The PMMA with high molecular weight can meet the mechanical property of the bone cement, but the blending and injection time of the bone cement is too short (viscosity changes too fast) to be beneficial to clinical operation, and the mechanical property of the bone cement cannot reach the standard due to the low molecular weight of the PMMA. Therefore, a bone cement material which can coordinate the balance between the mechanical property of the PMMA bone cement viscosity and the too fast viscosity change, can meet the operation requirements of clinicians, and can meet the mechanical property of the bone cement by using PMMA with lower molecular weight is needed to be found. Patent CN 108096629A discloses a polymethylmethacrylate bone cement, consisting of a solid component and a liquid component, comprising solid components a and B, wherein the solid component a comprises polymethylmethacrylate, a methyl methacrylate-styrene block copolymer, and the solid component B comprises mineralized collagen; the polymerization reaction time, the viscosity of the polymer and the heat released are influenced by regulating the molecular weight and the addition proportion of the components such as polymethyl methacrylate, methyl methacrylate-styrene block copolymer and the like, and the mechanical property and the biocompatibility of the bone cement are improved by additionally adding a mineralized collagen component with good osteogenic activity. Because the molecular weight and the addition proportion of the polymethyl methacrylate and the methyl methacrylate-styrene block copolymer in the solid component A can not meet a certain matching relationship, the effect of improving the mechanical property of the bone cement is poor.

Disclosure of Invention

The invention aims to overcome the defects and shortcomings in the prior art and provide the composite bone cement with the molecular weight matching and the performance enhancement.

The second purpose of the invention is to provide a preparation method of the composite bone cement with the molecular weight matching and enhancing performance.

The third purpose of the invention is to provide the application of the composite bone cement with the enhanced performance of molecular weight matching.

The above object of the present invention is achieved by the following technical solutions:

a composite bone cement with matching and enhancing performance of molecular weight is composed of a solid component and a liquid component, and is characterized in that: the solid component comprises a polymethineMethyl methacrylate, methyl methacrylate-styrene block copolymer and initiator; the liquid component comprises methyl methacrylate and a promoter; the molecular weight of the methyl methacrylate-styrene block copolymer (P (MMA-co-St)) is less than or equal to that of polymethyl methacrylate (PMMA)

The invention determines the relationship between the molecular weight of small molecule P (MMA-co-St) copolymer and high molecular weight PMMA, fills the intermolecular gap left when the high molecular weight PMMA is piled up by the small molecule P (MMA-co-St) copolymer, when the molecular weight of P (MMA-co-St) is slightly smaller, the P (MMA-co-St) can be uniformly distributed in PMMA with larger molecular weight to fill the intermolecular gap, so that the compression strength of the bone cement is obviously improved, when the range is in the invention, the compression strength of the composite bone cement is in an increasing relationship along with the molecular weight and the dosage of the P (MMA-co-St) polymer, but the small molecule P (MMA-co-St) can not be filled in the range of the gap of the high molecular weight PMMA to cause the incapability of filling, thereby effectively improving the mechanical property of the bone cement, the balance between the mechanical property of the PMMA bone cement viscosity and the too fast viscosity change can be coordinated, the operation requirements of clinicians can be met, and the mechanical property of the bone cement can be met by PMMA with lower molecular weight.

Preferably, the mass ratio of the polymethyl methacrylate to the methyl methacrylate-styrene block copolymer is 1: 1-2.

Preferably, the mass volume ratio of the solid component to the liquid component is 1: 3-4 mL.

Preferably, the initiator is Benzoyl Peroxide (BPO).

Preferably, the accelerator is N, N-dimethyl-p-toluidine (DMT).

More preferably, the molecular weight of the polymethyl methacrylate is 750000, the molecular weight of the methyl methacrylate-styrene block copolymer is 60000-116000, and the compressive strength of the bone cement can reach more than 75 MPa.

The invention also provides a preparation method of the composite bone cement with the molecular weight matching and enhancing performance, which is characterized in that the composite bone cement is prepared by mixing the solid component and the liquid component in a corresponding proportion, uniformly stirring, pouring into a mould and curing.

Preferably, the solid component and the liquid component are mixed in a mass-to-volume ratio of 1: and (3-4 mL) uniformly mixing.

Further preferably, the solid component and the liquid component are mixed in a mass-to-volume ratio of 1: 3mL of the mixture was mixed.

In addition, the invention also provides application of any one of the molecular weight matching enhanced composite bone cement in preparation of an orthopedic implant material. The relationship that the compression strength of the composite bone cement increases along with the molecular weight and the dosage of the P (MMA-co-St) polymer in a certain range is found by researching the molecular weight and the dosage of the P (MMA-co-St) polymer, and the mechanical property of the bone cement can be adjusted by matching the certain molecular weight P (MMA-co-St) and the PMMA. The method provides a powerful theoretical basis for the research of adding active ingredients and antibacterial bone cement in the future.

Compared with the prior art, the invention has the following beneficial effects:

according to the invention, by regulating the proportion of the methyl methacrylate-styrene block copolymer with lower molecular weight and the polymethyl methacrylate polymer with higher molecular weight of the bone cement and matching the molecular weight of PMMA and P (MMA-co-St), the balance between the mechanical property of PMMA bone cement viscosity and the too fast viscosity change can be coordinated, so that the requirements of clinicians on operation can be met, the mechanical property of the bone cement can be met by using PMMA with lower molecular weight, and other auxiliary agents for enhancing the mechanical property are not required to be added, so that the application prospect is wide.

Drawings

FIG. 1 shows PMMA and P (MMA-co-St) as spheres of two different radii.

FIG. 2 is a schematic representation of the molecules of higher molecular weight PMMA with the spaces between the molecules to fill the approximate molecular weight of the smaller molecular weight P (MMA-co-St).

FIG. 3 shows the ratio MMA/St of the monomers in accordance with 7: 3 Synthesis of P (MMA-co-St)¹H NMR spectrum.

FIG. 4 shows the ratio MMA/St of the monomers in accordance with 8: 2 Synthesis of P (MMA-co-St)¹H NMR spectrum.

FIG. 5 shows the compressive strength of synthetic bone cements of different molecular weights of P (MMA-co-St) polymer and PMMA in different ratios (where MS denotes P (MMA-co-St) polymer).

FIG. 6 is a graph showing high molecular weight PMMA molecules and P (MMA-co-St) filling between the molecules to provide compressive strength of the bone cement.

FIG. 7 shows the survival rate of rBMSCs in PMMA/P (MMA-co-St) composite bone cement.

Detailed Description

The invention is further described with reference to the drawings and the following detailed description, which are not intended to limit the invention in any way. Reagents, methods and apparatus used in the present invention are conventional in the art unless otherwise indicated.

Unless otherwise indicated, reagents and materials used in the following examples are commercially available.

The invention aims to seek a blending method of bone cement with optimal viscosity and mechanical property by regulating the proportion of powder of polymer with lower molecular weight and higher molecular weight of the bone cement. Due to intermolecular gaps left when PMMA molecules having a large molecular weight are stacked, if it can be filled with P (MMA-co-St) copolymer having a small molecular weight, the mechanical properties of bone cement can be greatly enhanced. Because the overall natural tendency of the macromolecular chain is in a curled state, the longer the macromolecular chain is, the more the molecular conformation is, the higher the possibility that the molecular chain is curled into various shapes is, and the better the flexibility of the molecule is. Therefore, we equate PMMA and P (MMA-co-St) into spheres of two different radii as shown in FIG. 1.

According to the relationship r of the square of the distance between the ends of the polymer chains and the molecular weight²The relationship between the mean square end distance and the mean square radius of rotation when the molecular weight is sufficiently large<R_g ²>＝<r²>And 6, obtaining the corresponding relation between the equivalent sphere radius and the average molecular weight. By recalculating the molecular-to-molecular gaps of the higher molecular weight PMMA of known molecular weightApproximate molecular weight of the smaller molecular weight P (MMA-co-St) was filled, as shown in FIG. 2:

the radius of P (MMA-co-St) is PMMA according to the geometrical relationship

Can be just embedded in the gaps between PMMA molecules. Given the molecular weight of PMMA of 750000, the required molecular weight of P (MMA-co-St) should be around 116000.

The PMMA bone cement which is most applied clinically consists of two parts, namely powder and liquid, wherein the main component of the powder is polymethyl methacrylate, and the main component of the liquid is a methyl methacrylate monomer. The invention designs PMMA/P (MMA-co-St) composite bone cement, wherein the powder component is polystyrene methyl methacrylate (P (MMA-co-St)), PMMA and Benzoyl Peroxide (BPO), and the liquid component is Methyl Methacrylate (MMA) and N, N-dimethyl-P-toluidine (DMT). Through the above calculation model, an optimum matching relationship between PMMA of high molecular weight and P of low molecular weight (MMA-co-St) is sought. Polymethyl methacrylate, described below, was purchased from Sigma (CAS number: 9011-14-7), and P (MMA-co-St) of small molecular weight was synthesized by itself.

EXAMPLE 1 preparation of starting Material

1. Synthesis of P (MMA-co-St):

(1) purification of raw materials:

purifying styrene: 150mL of styrene was placed in a 250mL separatory funnel, washed repeatedly with 1mol/L aqueous NaOH until the color changed from pink to colorless, and then washed with deionized water until neutral as determined by pH paper. After drying over night with anhydrous sodium sulfate, a little p-tert-butylcatechol was added and distilled under reduced pressure.

MMA purification: washing with NaOH water solution until colorless, and washing with deionized water until neutral. Drying with anhydrous sodium sulfate, adding a little hydroquinone, and distilling under reduced pressure.

BPO purification: adding 5g of BPO and 20mL of chloroform into a 100mL beaker, continuously stirring to dissolve the BPO and the chloroform, and filtering to obtain a filtrate; adding 50mL of methanol into a 100mL beaker, sealing and placing in a refrigerator at 4 ℃ for cooling; slowly dripping the filtrate into cooled methanol, stirring until the needle crystals are not increased, filtering, and vacuum drying.

(2) Preparation of a dispersant:

1mol/L MgCl₂preparation of an aqueous solution: 10.15g of magnesium chloride hexahydrate is added into a 50mL volumetric flask for constant volume, shaken up and transferred into a blue-mouth flask.

Preparation of 1mol/L NaOH aqueous solution: 10g of NaOH is taken out to be constant volume in a 250mL volumetric flask, shaken up and transferred to a blue-mouth bottle.

Preparation of 1% polyvinyl alcohol (PVA): 0.5g PVA was stirred in a 100mL beaker and heated to 95 ℃ in an oil bath until completely dissolved, cooled, and transferred to a blue-necked flask after shaking up to a volume of 50 mL.

(3) Synthesis of P (MMA-co-St)

P (MMA-co-St) is synthesized by means of suspension polymerization. Into a three-necked flask were placed 40mL of deionized water, 3mL of 1% PVA aqueous solution, 3mL of 1mol/L MgCl₂Heating the aqueous solution and 6mL of 1mol/L NaOH aqueous solution to 50 ℃ in an oil bath, wherein the mechanical stirring speed is 300 rpm; 7mL of MMA and 3mL of styrene were added, and 0.2g of BPO was added after heating to 70 ℃ to continue the reaction at 80 ℃ for 3 to 6 hours. In the same way, when 8mL of MMA and 2mL of styrene are added, the amount of the 1% PVA aqueous solution is 2mL, and other conditions are not changed, finally obtaining polymethyl methacrylate styrene beads with uniform size and hard texture. Washing with 1mol/L hydrochloric acid for 3 times, washing with deionized water to neutrality, and drying under reduced pressure. Grinding with ball mill after completely drying, grinding into powder, drying and storing.

2. Characterization of P (MMA-co-St)

Molecular weight characterization of P (MMA-co-St): molecular weight of P (MMA-co-St) copolymer was determined by Waters Breeze gel permeation chromatograph GPC with tetrahydrofuran as mobile phase and solvent, sample concentration 2mg/mL, sample size 100. mu.L.

Table 1 shows the various batches of monomer MMA/St according to 7: and 3, regulating and controlling the dosage and the rotating speed of PVA to synthesize P (MMA-co-St), wherein the MMA/St of the monomer is 8: 2 (MMA-co-St), the weight average molecular weights Mw of the synthesized P were 60000D, 69000D, 75000D, and 129000D, respectively. The following table 1 is specifically provided:

TABLE 1

This is because rapid agitation of the water-insoluble monomer and initiator in the water-containing vessel results in the formation of small initiator-containing droplets which are stable under the action of the dispersant and undergo bulk polymerization in the droplets. When the amount of PVA used or the rotation speed in the reaction system is increased, the size of the particles is reduced, and the molecular weight is reduced; when the proportion of styrene is high, the polymerization degree is low due to steric hindrance of a benzene ring structure, so that the molecular weight of a product is higher when the proportion of MMA is increased than before. According to the previously preset optimal molecular weight of 116000, the group with the highest mechanical property of four groups synthesized should have Mw of 75000, and since the group with Mw of 129000 exceeds the preset optimal molecular weight, the intermolecular gap left when PMMA molecules are stacked may not be effectively filled, but the exact result needs to be verified by combining a tensile test.

Preparation of P (MMA-co-St)¹H NMR nuclear magnetic resonance: p (MMA-co-St) polymer structure was determined by 400MHz NMR instrument Bruker Avance III, Germany, with a sample concentration of 8mg/mL, deuterated chloroform (CDCl)₃) As solvent, Trimethylsilyl (TMS) as internal standard.

FIG. 3 FIG. 4 shows the monomers MMA/St according to 7: 3 and 8: process for preparing P (MMA-co-St) copolymer synthesized at 2¹The H NMR spectrum was calculated to be 27.6% and 19.7% styrene, respectively.

EXAMPLE 2 Synthesis of bone Cement

At room temperature, mixing a solid component and a liquid component of the bone cement according to a mass-volume ratio (W/V) of 1: 3, uniformly stirring, pouring into a mould, and knocking out and taking out a sample after completely curing.

Wherein the solid phase component is PMMA, P (MMA-co-St) and BPO, the liquid phase component is MMA and DMT, and the curing temperature is measured by a long rod thermometer. The raw material ratio, the injection time, the curing time and the curing temperature thereof are shown in the following table 2.

TABLE 2

Note: the weight average molecular weights in the above table are all expressed as the molecular weight of P (MMA-co-St)

By recording the injectable time and curing temperature it was found that: the bone cement added with the P (MMA-co-St) polymer can obviously delay the injectable time and effectively reduce the curing temperature of the system. Bone cement is not an adhesive, and the attachment of bone cement to bone and the attachment of bone cement to prosthesis is entirely mechanical, without chemical or molecular interaction, and does not provide surface adhesion. The bone cement penetrates into cancellous bone and is a form-matching connection. When the P (MMA-co-St) polymer with lower molecular weight is added into the bone cement as powder, the fluidity of the system is better, the injection time of a doctor in clinic can be prolonged, and the bone cement can be more effectively absorbed by cancellous bone in the injection process.

Example 3 mechanical Property testing

Mechanical characterization of the bone cement in example 2 the compression properties of the finished test product were selected primarily. The test method comprises the following steps: compression experiment bone cement samples were ground into cylinders of 12mm in length and 6mm in diameter. A universal materials tester (WD-5A) was used, and the loading rate was 5 mm/min. And recording a stress-deformation graph of the sample, taking the stress when the K value in the stress-deformation curve is 2%, and dividing the stress by the cross section area of the cylinder to obtain the compressive strength. All mechanical properties were tested according to ISO 5833 international standard.

The mechanical properties of the PMMA/P (MMA-co-St) composite bone cement in the invention are characterized by compression strength. From FIG. 5, the compressive strength of the cement with P (MMA-co-St) polymer added thereto was significantly increased as compared with that of the pure PMMA cement, and the compressive strength of the PMMA/P (MMA-co-St) cement in the same ratio was increased in a certain range as the molecular weight was increased until the compressive strength was decreased after the molecular weight was increased to 116000. This is because the slightly smaller molecular weight can be uniformly distributed in the PMMA with larger molecular weight to fill the intermolecular gap, so that the compressive strength of the bone cement is significantly improved, and all of them reach 75MPa or more, as shown in fig. 6. The method also provides strong theoretical support for the bone cement with active components and antibacterial drugs added later according to the corresponding relation between the molecular weight of the added P (MMA-co-St) polymer and the compression strength of the composite bone cement.

Example 4 in vitro cytotoxicity testing of bone cements

1. Preparation and pretreatment of samples

A group of PMMA/P (MMA-co-St) composite bone cement compounded according to the charge of example 2 was prepared in the best compression strength in example 3, and cylindrical bone cement samples having a length of 5mm and a diameter of 6mm were ground, 5 parallel specimens were set for each group, and the mass of each specimen was weighed as y g. In 48-well plates, the plates were soaked in 75% ethanol and Phosphate Buffered Saline (PBS), respectively, for 1 day.

2. Preparation of leach liquors

The PBS solution was aspirated from the above prepared sample, and the sample was soaked with a volume of DMEM containing serum and double antibody for one day. DMEM dosage calculation formula: y (g) x 5(ml/g) ═ z ml, where z is the number of volumes of DMEM.

3. MTT test

P4 mouse bone marrow mesenchymal stem cells (rBMSCs) were inoculated into 48-well plates, 5000 cells per well were added with 200. mu.l of the culture medium and incubated for 24 hours, 100. mu.l of the culture medium was aspirated, 100. mu.l of the bone cement extract prepared in step 2 was added per well, 100. mu.l of the fresh culture medium was added to the control group, after 24 hours and 48 hours of incubation, respectively, the culture medium was aspirated, 20. mu.l of MTT and 180. mu.l of the fresh culture medium were added, after 4 hours of incubation at 37 ℃, 200. mu.l of DMSO was added and incubated for 10 minutes, 150. mu.l was taken out into 96-well plates, and the absorbance (OD) at a wavelength of 570nm was measured.

As can be seen from FIG. 7, the survival rate of rBMSCs in PMMA/P (MMA-co-St) composite bone cement is above 80%. The result shows that the PMMA/P (MMA-co-St) composite bone cement has no toxic and side effect.

The above results show that the present invention is feasible to improve the compressive strength of bone cement by determining the relationship between the molecular weight of a small molecule of P (MMA-co-St) copolymer and that of a large molecular weight PMMA, filling the intermolecular gaps left when the large molecular weight PMMA molecules are stacked by the small molecule of P (MMA-co-St) copolymer, and that the compressive strength of the composite bone cement increases with both the molecular weight and the amount of the P (MMA-co-St) polymer when in a certain range, thereby improving the mechanical properties of the bone cement without the need of additional additives.

Claims

1. A composite bone cement with matching and enhancing performance of molecular weight is composed of a solid component and a liquid component, and is characterized in that: the solid component comprises polymethyl methacrylate, methyl methacrylate-styrene block copolymer and an initiator; the liquid component comprises methyl methacrylate and a promoter; the molecular weight of the methyl methacrylate-styrene block copolymer is less than or equal to that of the polymethyl methacrylate

The mass ratio of the polymethyl methacrylate to the methyl methacrylate-styrene segmented copolymer is 1: 1-2.

2. The composite bone cement of claim 1, wherein the mass-to-volume ratio of the solid component to the liquid component is 1 g: 3-4 mL.

3. The composite bone cement of claim 1, wherein the initiator is benzoyl peroxide.

4. The composite bone cement of claim 1, wherein the accelerator is N, N-dimethyl-p-toluidine.

5. The composite bone cement of claim 1, wherein the weight average molecular weight of the polymethylmethacrylate is 750000, and the weight average molecular weight of the methylmethacrylate-styrene block copolymer is 60000-116000.

6. The preparation method of the molecular weight matching enhanced composite bone cement as claimed in any one of claims 1 to 5, characterized in that the solid component and the liquid component in corresponding proportion are mixed and stirred uniformly, poured into a mold and cured to obtain the final product.

7. The method according to claim 6, wherein the solid component and the liquid component are mixed in a mass-to-volume ratio of 1 g: and (3-4 mL) uniformly mixing.

8. The method according to claim 7, wherein the solid component and the liquid component are mixed in a mass-to-volume ratio of 1 g: 3mL of the mixture was mixed.

9. Use of the molecular weight matching enhanced composite bone cement of any one of claims 1 to 5 in the preparation of an orthopedic implant material.