GEL-FORMING BLOCK COPOLYMERS

Abstract

Provided is a block copolymer comprising a polymer block (A) formed from repeating units of formula (I):

##STR00001## wherein R.sup.1 is methyl or ethyl, and a polymer block (B) formed from repeating units of formula (II):

##STR00002## as well as a hydrogel comprising the block copolymer.

Claims

1. A block copolymer comprising a polymer block (A) formed from repeating units of formula (I): ##STR00017## wherein R.sup.1 is methyl or ethyl, and a polymer block (B) formed from repeating units of formula (II): ##STR00018##

2. The block copolymer in accordance with claim 1, wherein R.sup.1 is methyl.

3. The block copolymer in accordance with claim 1, wherein the number of repeating units of formula (I) forming each polymer block (A) is, independently for each polymer block (A) if more than one polymer block (A) is present, 5 or more and 100 or less.

4. The block copolymer in accordance with claim 3, wherein the number of repeating units of formula (I) forming each polymer block (A) is, independently for each polymer block (A) if more than one polymer block (A) is present, 10 or more and 70 or less.

5. The block copolymer in accordance with claim 1, wherein the structure of the polymer block (A) is represented by formula (Ia): ##STR00019## wherein R.sup.1 is methyl or ethyl, and n is 5 or more and 100 or less.

6. The block copolymer in accordance with claim 1, wherein the number of repeating units of formula (II) forming each polymer block (B) is, independently for each polymer block (B) if more than one polymer block (B) is present, 5 or more and 100 or less.

7. The block copolymer in accordance with claim 6, wherein the number of repeating units of formula (II) forming each polymer block (B) is, independently for each polymer block (B) if more than one polymer block (B) is present, 5 or more and 70 or less.

8. The block copolymer in accordance with claim 7, wherein the number of repeating units of formula (II) forming each polymer block (B) is, independently for each polymer block (B) if more than one polymer block (B) is present, 10 or more and 33 or less.

9. The block copolymer in accordance with claim 1, wherein the structure of the polymer block (B) is represented by formula (IIa): ##STR00020## wherein m is 5 or more and 100 or less.

10. The block copolymer in accordance with claim 1, which is a triblock copolymer having the structure (A)-(B)-(A).

11. The block copolymer in accordance with claim 1, wherein the total number of repeating units in the block copolymer is in the range of 40 to 180.

12. The block copolymer in accordance with claim 1, wherein the ratio of the total number of repeating units of formula (I) forming the polymer block(s) (A) to the total number of repeating units of formula (II) forming the polymer block(s) (B) in terms of the numbers of repeating units, is in the range of 20:1 to 1:1.

13. A hydrogel comprising the block copolymer in accordance with claim 1.

14. A process for the formation of a hydrogel, comprising the step of keeping an aqueous solution of the block copolymer in accordance claim 1 at a temperature of 20° C. or less.

15. The process in accordance with claim 14, wherein the aqueous solution of the block copolymer is kept at a temperature of 15° C. or less.

16. The process in accordance with claim 14, wherein the aqueous solution comprises the block copolymer at a concentration of 3 wt % to 40 wt %, based on the total weight of the solution as 100 wt %.

17. The process in accordance with claim 16, wherein the aqueous solution comprises the block copolymer at a concentration of 5 wt % to 30 wt %, based on the total weight of the solution as 100 wt %.

18. A method for 3D printing, wherein the hydrogel in accordance with claim 13 is printed as a support material.

19. A method for transporting a sensitive material, wherein the hydrogel in accordance with claim 13 is used as a matrix for the sensitive material.

Description

EXAMPLES

General Synthesis of a Block-Copolymer:

[0073] Under dry and inert conditions, initiator and 2-methyl-2-oxazoline (MeOx) were added to dry benzonitrile (PhCN) and stirred for several hours at 110° C. The full monomer conversion was verified by .sup.1H-NMR-spectroscopy before adding the monomer for the second block. The mixture was cooled to room temperature and 2-phenyl-2-oxazine (PheOzi) was added. After stirring at 120° C. overnight the monomer (MeOx) for the third block was added. After completion of the third block, termination was carried out using the respective terminating agent and stirring for several hours at 45° C. After cooling to room temperature, potassium carbonate was added and the mixture was stirred for 5 hours. The solvent was removed at reduced pressure and the flask was placed in a vacuum drying oven at 40° C. and 20 mbar for 2 days. The product was dissolved in deionized water, dialyzed overnight using a membrane with a MWCO of 1 kDa and freeze-dried. FIG. 1 illustrates the structure of the resulting block copolymer, wherein m and n have the meanings defined above.

[0074] The polymers are characterized via NMR, size exclusion chromatography and rheology.

Description of NMR and GPC:

Nuclear Magnetic Resonance Spectroscopy (NMR)

[0075] NMR spectra were recorded on a Fourier 300 (300.12 MHz), Bruker Biospin (Rheinstetten, Germany) at 298 K. The spectra were calibrated to the signal of residual protonated solvent (CDCl.sub.3 at 7.26 ppm).

Gel Permeation Chromatography (GPC)

[0076] Gel permeation chromatography (GPC) was performed on an Agilent 1260 Infinity System, Polymer Standard Service (Mainz, Germany) with HFIP containing 3 g/L potassium trifluoroacetate as eluent; precolumn: 50×8 mm PSS PFG linear M; 2 columns: 300×8 mm PSS PFG linear M (particle size 7 μm; pore size 0.1-1,000 kg/mol). The columns were kept at 40° C. and flow rate was 0.7 mL/min. Prior to each measurement, samples were filtered through 0.2 μm PTFE filters, Roth (Karlsruhe, Germany). Conventional calibration was performed with PEG standards (0.1-1,000 kg/mol) and data was processed with WinGPC software.

[0077] Results from NMR and GPC analysis of different block copolymers (A: MeOx 35 blocks containing 35 repeating units derived from MeOx) are shown in the following Table 1. The ratio of blocks A and B can be determined in an appropriate non-selective solvent by comparing the signals of appropriate side chain signals of block A and block B. Endgroup analysis for the determination of the average degree of polymerization can be conducted after appropriate base line correction using the signal of initiator or termination fragment in relation to the signal of the polymer backbone or an appropriate polymer side chain signal. Alternatively, or in addition, this can be conducted in a solvent selective from one block, for example block A. The average degree of polymerization of block A can then be obtained by endgroup analysis, whereby the overall average degree of polymerization can be obtained by considering the molar ratio of block A and block B.

TABLE-US-00001 TABLE 1 Number average molar mass, ratio of oxazine/ oxazoline (Ozi/Ox) units, dispersity     and yield of the synthesized triblock copolymers used in this study. M.sub.n.sup.a Ozi/Ox M.sub.n.sup.c yield Polymer [kg/mol] ratio .sup.b [kg/mol] [%] A-PPheOzi.sub.15-A (B1) 8.7  1:3.9 3.7 1.22 89 A-PPheOzi.sub.15-A (B2) 8.6  1:4.1 3.8 1.28 83 A-PPheOzi.sub.15-A (B3) 8.7  1:3.9 2.8 1.23 81 A-PPheOzi.sub.15-A (B4) 8.7 /1:3.9 2.3 1.30 89 A-PPheOzi.sub.5-A 7.0  1:14 4.0 1.29 70 A-PPheOzi.sub.30-A 10.9  1:2.2 4.0 1.26 79 .sup.aValues obtained theoretical by [M].sub.0/[I].sub.0. .sup.b Values calculated from .sup.1H-NMR side chain analysis (PPheOzi/PMeOx). .sup.cObtained from GPC (T = 40° C., 0.7 mL/min (HFIP), poly(ethylene glycol) standards). .sup.dObtained from GPC by using M.sub.w/M.sub.n).

Rheology Method Description

[0078] Rheology experiments were performed using an Anton Paar (Ostfildern, Germany) Physica MCR 301 system utilizing a plate-plate geometry (25 mm diameter) equipped with a solvent trap and Peltier element. All aqueous samples were stored after dissolving for 48 h at 5° C. The temperature-sweep was performed in oscillation mode from 5-50° C. (Heat-rate: 0.05° C./s), using a fixed amplitude of 0.1% and angular frequency of 10 rad/s. The long-time gelation experiment was performed at an amplitude of 0.1% and an angular frequency of 1 rad/s for several hours. To investigate the viscoelastic properties the linear viscoelastic region (LVR) was obtained by performing amplitude sweeps at different concentrations (5-40 wt. %) from 0.01% to 500% strain deformation and a fixed angular frequency of 10 rad/s at 5° C. For steady shear experiments, the control shear rate mode was used from 0.01 to 10 1/s at 5° C./s.

[0079] FIG. 2 shows amplitude-sweeps of block copolymer B1 (cf. Table 1) of different concentrations (5 wt. %: storage modulus G′: filled squares, loss modulus G″: filled circles; 10 wt. %: G′: empty squares, G″: empty circles; 15 wt. %: G′: filled triangle up, G″: filled triangle down and 20 wt. %: G′: empty triangle up, G″: empty triangle down) at 5° C. and an angular frequency of 10 rad/s.

[0080] FIG. 3 illustrates a temperature-sweep of block copolymer B1 from 5 to 50° C. with a 15 wt. % aqueous polymer solution, Amplitude 1%, angular frequency 10 rad/s. Storage modulus is shown by squares, loss modulus by circles. At 27° C. the structure undergoes first changes and at 30° C. the structure dissolves

[0081] In FIG. 4, the gelation kinetics of block copolymer B1 at 5° C. of a 15 wt. % aqueous polymer solution are shown. Amplitude 1%, angular frequency 10 rad/s. Storage modulus is shown by squares, loss modulus by circles. The reorganization of the hydrogel takes place in a time frame of 100 minutes.

[0082] FIG. 5 shows the viscosity of hydrogels of block copolymer B1 in dependency of applied shear rate and different polymer concentrations at 5° C.

3D Printing Experiments

[0083] In order to demonstrate the suitability of the hydrogels in accordance with the invention as materials for 3D printing, scaffolds using 10, 15, and 20 wt % of A-PPheOzi.sub.15-A and 20 wt % of A-PPheOzi.sub.30-A hydrogels in water were printed using a 3D bioprinter equipped with a conical nozzle with 0.25 mm inner diameter for the extrusion of the hydrogel. A four-layer 10×10 line wood-pile structure was first printed. The strength of a 10 wt % A-PPheOzi15-A hydrogel was low and strand fusion was observed, which is in line with the yield point of the system. Nevertheless, a 3D cube could be printed. Also, the 20 wt % A-PPheOzi.sub.30-A hydrogel could be successfully printed in 24 layers, but again some strand fusion was observed and shape fidelity was limited. Using the 20 wt % and 15 wt % hydrogels of A-PPheOzi.sub.15-A at a printing speed of 600 mm/min, 24-layer constructs of 10×10 lines, 1 mm strand distance and 0.25 mm layer height could be conveniently printed. Excellent shape fidelity and layer integrity were obtained.

[0084] FIG. 6 shows the results for the dispense printing of the 20 wt % A-PPheOzi.sub.15-A hydrogels (Block Copolymer B1, cf. Table 1; extrusion-based printing setup, conical nozzle with 0.25 mm inner diameters; speed: 600 mm/min); (A): printed 24-layer scaffold (dimensions: 10×10 mm; 1 mm strand distance; 0.25 mm layer height); (B): Light microscopy image of (A) (Top view).

[0085] To highlight the potential of the hydrogels as, e.g., a sacrificial matrix material or component in a hybrid system, the temperature was increased on the previously printed scaffolds, upon which strand fusion and collapse of the hydrogel network were observed and the gel liquefied rapidly. Accordingly, a mild temperature stimulus compatible with cell culture conditions can be used to remove scaffolds printed with the hydrogels in accordance with the invention. This can be very useful if used as a sacrificial support matrix to assist in printing of materials, which by themselves are not easily 3D printed with good shape fidelity.

BRIEF DESCRIPTION OF DRAWINGS

[0086] FIG. 1 illustrates an exemplary structure of a block-copolymer in accordance with the invention.

[0087] FIG. 2 shows amplitude-sweeps of block copolymer B1 (cf. Table 1) of different concentrations (5 wt. %: storage modulus G′: filled squares, loss modulus G″: filled circles; 10 wt. %: G′: empty squares, G″: empty circles; 15 wt. %: G′: filled triangle up, G″: filled triangle down and 20 wt. %: G′: empty triangle up, G″: empty triangle down) at 5° C. and an angular frequency of 10 rad/s.

[0088] FIG. 3 illustrates a temperature-sweep of block copolymer B1 from 5 to 50° C. with a 15 wt. % aqueous polymer solution, Amplitude 1%, angular frequency 10 rad/s. Storage modulus is shown by squares, loss modulus by circles. At 27° C. the structure undergoes first changes and at 30° C. the structure dissolves.

[0089] In FIG. 4, the gelation kinetics of block copolymer B1 at 5° C. of a 15 wt. % aqueous polymer solution are shown. Amplitude 1%, angular frequency 10 rad/s. Storage modulus is shown by squares, loss modulus by circles. The reorganization of the hydrogel takes place in a time frame of 100 minutes.

[0090] FIG. 5 shows the viscosity of hydrogels of block copolymer B1 in dependency of applied shear rate and different polymer concentrations at 5° C.

[0091] FIG. 6 shows the results for the dispense printing of the 20 wt % A-PPheOzi.sub.15-A hydrogels (Block Copolymer B1, cf. Table 1; extrusion-based printing setup, conical nozzle with 0.25 mm inner diameters; speed: 600 mm/min); (A): printed 24-layer scaffold (dimensions: 10×10 mm; 1 mm strand distance; 0.25 mm layer height); (B): Light microscopy image of (A) (Top view).