細胞を含んだハイドロゲルの刺激細胞挙動のひずみ勾配チップ

要約

組織工学用セルの配置を調整する同心円状細胞を含んだハイドロゲルの非連続的なグラデーション静的系統を提供する単純なアプローチを紹介します。

要約

人工細胞の配置については、組織工学の分野でのホットな話題です。過去の研究のほとんどは、複雑な実験的プロセスおよび汚染の問題に通常関連付けられている質量システム制御、使用して細胞を含んだハイドロゲルのひずみ誘起細胞の単一の位置合わせを調査しました。したがって、この記事では PDMS のプラスチック カバー、UV 透明なガラス基板 3 D ゲルの細胞挙動の刺激のため流体チップを用いた勾配静的ひずみを構築するシンプルなアプローチを提案する.流体の商工会議所でのオーバー ロードの写真パターン形成可能なセル プレポリマーは、カバーの凸曲面 PDMS 膜を生成できます。UV 架橋後湾曲した PDMS 膜とバッファー洗浄、調査細胞の微小環境下で同心円形パターンをさまざまなグラデーションの株の下で動作は外部機器なしの単一の流体チップで自己確立です。NIH3T3 細胞をゲル上 15-65% から様々 なひずみの刺激との連携で、ジオメトリの指導の下で細胞の配置の傾向の変化を観察した後示した。3 日間培養後ハイドロゲル ジオメトリは、細胞が高圧縮ひずみハイドロゲル伸長方向に沿って整列低圧縮ひずみ, セルの配置を支配しました。これらの間は、細胞は、ハイドロゲルの伸長とパターン化ハイドロゲルの幾何学指導の根本的な指導の逸散によるランダムな配置を示した。

概要

ネイティブの微小環境を模したブロック素材として、ゲルの細胞外マトリックス (ECM) を含む再細胞の成長をサポートする生体模倣組織足場を構築できます。組織の機能を所有するには、組織のセルの配置は必須要件です。さまざまな 2 D (すなわち表面上で培養した細胞) と 3 D (すなわちハイドロゲルにカプセル化細胞) セルの配置は、培養または細胞またはマイクロ フレキシブル基板上にカプセル化することによって達成されている- またはナノ パターン¹。マイクロ アーキテクチャの 3 D セルの配置はより魅力的な微小環境は、ネイティブの組織構築^2,3,4に近いです。3 D のセルの配置のための一般的なアプローチは、ハイドロゲル形^2,3の幾何学的なキューです。短軸方向に細胞増殖の制限された空間のため細胞はマイクロ パターン化ハイドロゲルの長軸方向に沿って配置を目指しています。別のアプローチは、ストレッチ方向^4,5並列セルの配置を達成するためにゲルに引張のストレッチを適用することです。

圧縮ひずみなどの ECM ゲル上生物物理刺激または電気のフィールドは、適切な組織統合、増殖および分化^1,2,3の細胞機能を調整できます。多くの研究は、複数機械制御ユニット^4,6,7,8,9を使用して、一度に 1 つのひずみ条件を適用することによって細胞の挙動を調査するために行われています。たとえば、機械式ステップ モーターの使用は圧迫や共通のアプローチ^7,10されている 3 D セルでカプセル化されたコラーゲンのゲルの上に伸ばし。しかし、そのような制御装置は余分なスペースを必要とする、インキュベーター^7,9,11,12の汚染の問題に直面しています。さらに、大型の楽器は、再現性の高い¹³を提供する正確に制御環境を与えることはできません。

細胞を含んだヒドロゲルは、医用マイクロ スケールで通常用いられることを考えると、同時に 3 D 模倣構造体外^{2,14,15,16,17,18}細胞の挙動を調査するためのひずみ/ストレッチ刺激の範囲を生成する MEMS 技術を組み合わせることが有利です。たとえば、マイクロ流体チップの PDMS 膜を変形するガス圧を使用して、異なる系統^9,16に細胞の分化を運転系統に上昇を与えることができます。ただし、クリーン ルームやモーター、ポンプ、バルブ、圧縮ガスのソフトウェア管理の統合で複雑なチップ製造プロセスなど、多くの技術的課題があります。

この作品は、同心の円形ハイドロゲル パターンと柔軟な PDMS 膜を用いた自律的勾配の静的ひずみマイクロ流体チップを取得する単純なアプローチを紹介します。異なり、既存のアプローチのほとんどは、当社のプラットフォームは黄色い部屋の外を作製できるし、孵化の間に外部機器なしの携帯カプセルのヒドロゲルを同心円のグラデーションの系統を自己生成所有しているポータブルと使い捨ての小型デバイスです。ハイドロゲル形状の組み合わせによって影響を受けた 3T3 繊維芽細胞の挙動と 3 日間のグラデーションひずみチップで 3 D の ECM 模倣環境内セルの配置の観察の間に様々 な引張ストレッチ指導の手がかりを示した。

プロトコル

1. GelMA Synthesis

1. Weigh 10 g of gelatin powder and add it to a glass flask with 100 mL ofDulbecco's phosphate-buffered saline (DPBS). Put a magnetic stir bar into the flask and place the flask on a stirring hot plate.
2. Cover the flask with aluminum foil to avoid water evaporation. Set the hot plate temperature to 50-60 °C and the stirrer at 100 rpm for 1 h to dissolve the gelatin powder well.
3. After the gelatin has dissolved, add 8 mL of methacrylic anhydride very slowly (one drop per second) using a pipette. Let it react at 60 °C for 3 h.
4. Add pre-warmed DPBS (40 °C) to the flask to a final volume of 500 mL and allow this mix well for 15 min to stop the reaction.
5. Meanwhile, cut a dialysis membrane (14 kDa cut-off molecular weight) into several 25 cm-long tubes. Immerse them in deionized (DI) water for 15 min and make a knot to close one end of the dialysis tubes.
6. Load the appropriate amount (30 - 60 mL) of the polymer solution into the dialysis tubes and close the other end. Place them in a 5-L plastic beaker with DI water for a week. Renew the DI water twice a day and maintain the solution at 40 - 50 °C during the dialysis process.
7. Collect the solution from the tube in a 500-mL glass bottle. Pour ~450 - 500 mL of solution in a 500-mL filter cup (pore size of 0.22 µm) and apply a vacuum to the filter cup to force the solution to pass through the filter membrane for sterilization.
8. Transfer the sterilized polymer into several 50-mL sterilized tubes and store them in a -80 °C freezer for 3 - 5 days.
9. Freeze-dry the -80 °C polymer for 1 week using a freeze dryer to form GelMA. Store the GelMA in a -80 °C freezer.

2. 3-(Trimethoxysilyl)propyl Methacrylate (TMSPMA) Modification

1.  Cut commercial glass slides into two small pieces (25 mm x 37.5 mm) and immerse them in 0.5 M NaOH solution for 4 h. Wash the slides with a large amount of DI water.
2. Place the slide on a rack inside a glass container with 95% ethanol and clean using an ultrasonicator at 43 kHz for 15 min. Air dry the glass slide.
3. Immerse the glass slides in 5% TMSPMA in 99.5% ethanol for 1 h.
4. Wash the slides in 95% ethanol, air dry the slides, and anneal the TMSPMA coating in an oven at 80 °C for 2 h.

3. Chip Fabrication

1. Take one 2 mm- and one 0.3 mm-thick polymethylmethacrylate (PMMA) plate, apply double-sided tape to one side of the PMMA surface, and release the liner on one side. Leave two 2 mm-thick PMMA plates and one 1 mm-thick plate without double-sided tape.
2. Laser-cut a 2 mm-thick PMMA plate without double-sided tape to 42 mm x 30 mm to make the bottom plate. Cut a 2 mm-thick PMMA plate with double-sided tape to make the boundary frame, with outer dimensions of 42 mm x 30 mm and inner dimensions of 37.5 mm x 25 mm.
3. Laser-cut the 0.3 mm-thick PMMA plate with double-sided tape into a 12-mm center circle with two 2 mm-wide and 8 mm-long flow channels on opposite sides of the circle (Figure 1a).
4. To prepare the PMMA mold for casting the PDMS cover, assemble the three pieces of PMMA components from steps 3.2-3.3 (Figure 1b) using double-sided tape.
5. Laser-cut a 2 mm-thick PMMA plate with double-sided tape into a 5 cm x 5 cm piece with a 3 x 3 array of 8.5 mm x 8.5 mm hollow rectangles. Cut another 5 cm x 5 cm piece with a 3 x 3 array of 4-mm hollow circles. Laser-cut a 1 mm-thick PMMA plate without double-sided tape into a 5 cm x 5 cm PMMA bottom plate.
6. Prepare the PMMA mold for casting the PDMS plug by assembling the three pieces of PMMA components from step 3.5 (Figure 1c) using double-sided tape.
7. Prepare the PDMS cover and PDMS plug by properly mixing 30 g of PDMS elastomer and 3 g of PDMS curing agent; degas the mixture under a vacuum chamber for 1 h.
8. Cast 1.8-2.0 g of the mixture into the PMMA mold for the PDMS cover and use the appropriate amount to fill each cavity of the PMMA mold for the PDMS plug. Cast 10 g of uncured PDMS mixture in a blank 10-cm plastic plate. Put these molds in a vacuum chamber to degas for 30 min.
9. Cure the PDMS for 2 h at 80 °C. After cooling down the cured PDMS on the mold, detach the PDMS covers and the PDMS plugs from the PMMA molds.
10. Punch two holes with diameters of about 3 mm at the ends of flow channels of the PDMS covers.
11. Cut the PDMS sheet molded from the 10-cm plastic plate into many 1 cm x 1 cm cubes and punch a 3-mm hole in each PDMS cube. Glue two uncured 1 cm x 1 cm PDMS cubes onto the openings of the PDMS cover (to serve as medium reservoirs and to aid in the curing process of the gradient circular hydrogel patterns) and cure for 1 h at 80 °C.
12. Bond the PDMS covers with the two PDMS reservoirs onto a TMSPMA-coated slide by pre-treating the bonding side of the PDMS cover and the TMSPMA-coated slide under an oxygen plasma machine (30 W RF power (high mode) and 600 mTorr compressed air) or a high-frequency electronic corona generator (115 V, 50/60 Hz, 0.35 A) for 90 s of O₂ plasma treatment.
13. Contact the plasma-treated surface of the PDMS covers and the TMSPMA slide and press them closely for permanent bonding through the formation of an Si-O-Si bond.
    NOTE: Placing the chip in an oven at 80 °C for 1 h can further enhance the bonding strength.
14. After cooling, immerse the chips in 95% ethanol for 15 min and air dry. Then, sterilize the chips under UV irradiation for 1 h and store them in a box wrapped in aluminum foil in the laminar hood.

4. Static Gradient Strain on the Cell-laden Hydrogel

1. Print and cut a piece of photomask, 25 mm x 37.5 mm in size, by printing the layout in Figure 2b on a transparent film. Adjust the printed size of Figure 2b to match the dimension in Figure 2a.
2. Prepare 100 mL of DMEM medium with 10% FBS, 1% Pen-Strep, and 250 mL of DPBS in a 37 °C water bath to use as the cell culture medium.
3. Weigh 25 mg of freeze-dried GelMA into 0.3 mL of prewarmed (37 °C) cell culture medium in a 1.5-mL black microcentrifuge tube. Put the microcentrifuge tube on a laboratory stirrer/hot plate until the GelMA dissolves in the medium.
4. Weigh 50 mg of photoinitiator into 1 ml of DPBS in a microcentrifuge tube and place it in an 80 °C oven for 15 min or until the photoinitiator has dissolved.
5. Take 25 µL of the 10% photoinitiator from step 4.4 and add it to the microcentrifuge tube from step 4.3. Pipette several times to mix well.
6. Count 3 x 10⁶ NIH 3T3 cells using an automated cell counter. Centrifuge the suspension at 200 x g for 5 min, discard the supernatant, and re-suspend the cells in 175 µL of cell culture medium.
7. Add the cell solution from step 4.6 to the microcentrifuge tube from step 4.5 to get a prepolymer cell solution of 5% GelMA, 0.5% photoinitiator, and ~6 x 10⁶ 3T3 cells/mL. After mixing, load 100 µL of cell prepolymer in a 100-µL micro syringe.
8. Manually align (see Figure 3a) a piece of the photomask onto the bottom slide of the sterilized gradient strain chip and simply fix the position using a small drop of DI water in between. Connect the 100-µL micro-syringe loaded with prepolymer cell solution to the inlet of the chip.
9. Place (see Figure 3b) 50 µL of prepolymer cell solution in the flow channel using the micro-syringe and then plug the outlet using a PDMS plug. Inject an extra 40 µL of solution to create a convex bulge in the circular PDMS membrane.
10. Move the chip with the photomask (bottom), micro-syringe (inlet), and PDMS plug (outlet) from step 4.9 under a UV lamp (365 nm, 9 mW/cm²) and expose it for 30 - 45 s to crosslink the concentric circular hydrogel in the fluidic chamber.
11. Remove the PDMS plug and the micro-syringe to release the liquid pressure (see Figure 3c). Use a 1-mL syringe loaded with prewarmed DPBS to wash out uncrosslinked resins 3 times by flushing from the inlet to the outlet.
12. Fill the flow channel with about 100 µL of cell culture medium.
13. Place the chip in a sterilized culture dish and culture in a 5% CO₂ atmosphere at 37 °C for a week. Refresh the medium every day.
14. Take images of three chips on day 0 after 4 h of incubation, as a control group, and three chips on day 3, as the experimental set, using a microscope with a 20X objective. Measure the line width of each hydrogel from line 1 to line 12 using software (e.g., ImageJ) to calculate the compress strains ( Figure 4).
    NOTE: The elongation percentage is calculated by dividing the value of the line width difference between 40 µL and 0 µL by the line width at 40 µL.

5. Cell Staining for Alignment Analysis

1. Use a syringe to inject 4% paraformaldehyde (PFA) in DPBS at RT into the flow chip for 15 min for the fixation of the cell-laden hydrogel.
   NOTE: Caution. PFA is toxic and should be handled with care.
2. Replace the solution with 0.5% cell membrane permeating solution in DPBS for 10 min to permeabilize the cell membrane at RT.
3. PBS wash the samples 3 times with 5- to 10-min interval between washes (using a loaded syringe, as in step 5.1).
4. Load 1% BSA solution into the fluidic channel for 45-60 min at RT (using a loaded syringe through the inlet port).
5. Add 1.5 mL of methanol into the vial with Alexa Fluor 488 phalloidin to yield a final concentration of 6.6 µM stock solution.
6. Take 5 µL of Alexa Fluor 488 phalloidin from step 5.5 and dilute it in 200 µL of DPBS with 0.1% BSA to form a final concentration of 0.165 µM Alexa Fluor 488 phalloidin.
7. Add 200 µL of the mixture solution to the fluidic channel using a micropipette and incubate the chip at 37 °C for 45 - 60 min for actin staining. PBS wash (as above) the samples 3 times.
8. Prepare 1 µg/mL DAPI in PBS, flow it through the chip, and stain cell nuclei at 37 °C for 5 min.
9. Pipette DPBS into the fluidic channel to wash out the staining solution and refill the fluidic chamber with PBS solution to take images with a fluorescence microscope.
10. Capture the fluorescent images of the 3T3 cells in the hydrogels using an inverted fluorescence microscope under 40X magnification with a CCD detector and filter sets of ex/em at 488/520 nm and 358/461 nm for Alexa Fluor 488 phalloidin (actin) and DAPI (nucleus), respectively.

結果

完成したグラデーションひずみ刺激チップの各円形のハイドロゲルの機械的変化を比較するためは 0 μ L (図 4 a) の注入量と 40 μ L (図 4 b) では、同じチップの 2 つの各円形のハイドロゲルの線幅をそれぞれ測定しました。各サークルでパーセントの伸びを 0 μ L 注入チップ (図 4 c) に対応するハイドロ?...

ディスカッション

本稿でハイドロゲル図形指導及び引張ストレッチ後細胞の配向挙動を比較する単純なアプローチについて報告する.柔軟な PDMS 膜は、同心の円形ヒドロゲルの高さ別の生成のためのドームの曲率を作成します。圧力を解放した後 PDMS 膜は自動的にセンターで最大と外側の境界で最小勾配ひずみ/伸長を形成するマイクロ パターンのヒドロゲルに力を適用します。グラデーションの歪みの形成は?...

資料

Name	Company	Catalog Number	Comments
1.5 mL black microcentrifuge tube	Argos Technologies	03-391-161	This one can be replaced with a neutral color of 1.5 mL tube covered with aluminun foil
10x DPBS	Sigma-Aldrich	56064C
Alexa Fluor 488 phalloidin	Invitrogen	A12379
BSA	Sigma	A1595
Calcein	Molecular Probe	C1430	For labeling viable cells
CCD	PCO. Imaging	Pixelfly qe
Cell membrane permeating solution	Sigma-Aldrich	X100	0.5% Triton X-100 for permeating cell membrane
DAPI	Sigma-Aldrich	D8417	Cell nucleus staining
Dialysis membrane	Sigma-Aldrich	D9527	Molecular weight cut-off = 14,000
DMEM	Gibco	11995-065
Double-side tape	3M	8003
FBS	Hyclone	SH30071.03
Gelatin	Sigma-Aldrich	G2500	gel strength 300, type A, from porcine skin
High frequency electronic corona generator	Electro-technic products	MODEL BD-20
Methacrylic Anhydride	Sigma-Aldrich	276685
Micro syringe	Hamilton	80501	50 μL
Microscope	Olympus	IX71	Include two filter sets: LF405/LP-B-000 and LF488/LP-C-000 from Semrock
Oxygen plasma machine	Harrick plasma	PDC-001
Paraformaldehyde	Sigma-Aldrich	P6148	For fixing cell
PDMS	DOW CORNING	Sylgard 184	Mixture for PDMS chip cast-molding fabrication
Pen-Strep	Gibco	10378-016	penicillin/streptomycin
Photoinitiator	CIBA	Irgacure 2959
Propidium iodide	Sigma-Aldrich	P4170	For labeling dead cells
Sterile Filtration cup	Millipore	SCGPT05RE
TMSPMA	Sigma-Aldrich	440159	For hydrogel immobilization
Ultrasonicator	Delta	D150H	150W, 43kHz
UV light	DAIHAN	WUV-L10
Freeze Dryer	FIRSTEK	150311025
NIH3T3(fibroblast)	Food Industry Research and Development Institute(FIRDI)	08C0011
MOXI Z Mini Automated Cell Counter	ORFLO	MXZ001