System and method for controlling bioadhesion at an interface

Abstract

This invention provides a method for controlling adhesive properties at an interface between a polymer patch and a tissue. In one embodiment, said method comprises the steps of: a) Applying superparamagnetic nanostickers coated with a first polymer onto said tissue, wherein said first polymer has an affinity to said polymer patch; b) Applying a magnetic field to affect anchorage of said superparamagnetic nanostickers on said tissue; and c) Attaching said polymer patch onto said tissue.

Description

Dkt. 008-24-A-PCT SYSTEM AND METHOD FOR CONTROLLING BIOADHESION AT AN INTERFACE FIELD OF THE INVENTION

[0001] The present invention relates to systems and methods for controlling bioadhesion.BACKGROUND OF THE INVENTION

[0002] Natural biological tissues exhibit different mechanical and surface properties. These disparate features make their connections with engineering materials quite difficult due to the lack of universal methods for tuning the interfacial bonding over a wide range. However, the precise control of interfacial properties, including modulus and adhesion on diverse biological tissues, requires overcoming multiple inherent and external barriers. An interface-enhanced strategy by spatiotemporal anchoring of magnetic nanostickers for controlled bioadhesive properties is proposed. Fully exploiting the interactions from nanostickers by remote control enables the attached patch to achieve extremely high adhesion energy (-1250 J m'2) and interfacial fatigue resistance with a threshold of -50 J m'2, at a very low area density of nanostickers (4 pg / mm2). The controlled interfacial properties as well as adhesion-related space and time, lead to comprehensively tunable bioadhesion on diverse tissues such as skin, intestine, liver, and kidney, which are strongly desired in biomedical applications. Long-term integration with fragile tissues further demonstrates that the anchored biointerface can adapt to the in vivo (female Sprague-Dawley rats) environment and promote postoperative recovery. The biointerface bridged by intelligent nanostickers prompts the methodology for bioadhesion towards controllable orientation.

[0003] Setting up robust biointerfaces between dynamic wet biological tissues and hydrogels holds a significant promise for medical electronics and tissue regeneration1'5. Different strategies using adhesive bonds and topological connections to form tissue-hydrogel hybrids serve as alternatives or adjuncts for conventional sutures, staples, clips, and commercial bio-glues6'10. Although reliable biointerfaces can secure hydrogels on targetedtissues to generate effective adhesion, they are difficult to form and challenging to control in terms of interfacial properties and adhesion -related space and time. For example, chemical anchoring using carbodiimide chemistry suffers from spatiotemporal uncontrollability and poor interfacial fatigue resistance11 12. Furthermore, the limited availability of functional groups and external barriers such as biofluids and stratum comeum severely impede the anchoring agents from forming an interpenetrating network with tissues13 14. A rational approach to addressing these issues may involve control systems to steer the anchoring agents with sufficient driving force. The emergent high-power ultrasound has innovated the application of hydrogels with high adhesion energy and interfacial fatigue threshold on pig skin by pressure-gradient propulsion of the anchoring primers15. However, contact ultrasound probes may discomfort the body and are unsuitable for activating adhesion on fragile parts (e.g., diseased regions) and deep tissues (Table I)16'18. Current interfacial bonding technologies have not yet demonstrated that bioadhesion can be controlled comprehensively according to desired demands.

[0004] Micro / nanomaterials powered by different exogenous energy sources such as light19, chemicals20, and magnetism21, have shown high controllability in their mechanical motion within narrow and confined lumens22, which distinguishes them from the behaviors of passive micro / nanomaterials. Compared with other types of actuation, magnetic field have remarkable advantages including harmlessness, programmability, transparency, and deep penetration, allowing remote and precise steering of micro / nanomaterials by applying appropriate force and torque23,24. Although an individual micro / nanomaterial provides minimal bonding energy with tissues, the collective interactions particularly for the magnetic dipole-dipole interactions between the programmed micro / nanomaterials could synergistically augment their cohesive force and thus improve the interfacial adhesion energy25. The repertoire of micro / nanomaterials lies in bridging tissues and applied hydrogels through a remote magnetic field. Guiding the magnetic micro / nanomaterials to anchor on tissues requires strong propulsion to pass through the external barriers26, and once settled, these micro / nanomaterials can immobilize thehydrogels. For secure immobilization and high controllability on tissues, the prepared micro / nanomaterials exhibit stable superparamagnetic properties with high magnetic saturation. In the meantime, surface functionalization of the micro / nanomaterials can introduce abundant intermolecular interactions such as hydrogen bonding and coulomb force with the hydrogels for interfacial gelation.

[0005] The magnetic control bioadhesion is implemented by a robust hydrogel patch and cationic biopolymer-coated superparamagnetic nanostickers (Figure 1). This invention reports a strategy to enhance tissue-hydrogel interfaces that not only relies on conventional energy dissipation by a soft hydrogel layer, but also incorporates hard nanostickers around the tissuehydrogel interface to enhance resistance to interfacial failure. The robust mechanical properties of the hydrogel patch can prevent the scission of the interfacial hydrogel layer and unfavorable swelling in biofluids. The anchorage of high-strength nanostickers at the tissue-hydrogel interface provides stress transmission and resists crack formation in the hydrogel layer. Taking advantages of the integrated energy dissipation and interfacial enhancement, a minimal area density of nanostickers (4 pg / mm2) can realize an ultrahigh adhesion energy around 1250 J m"2and interfacial fatigue threshold of ~50 J m'2. Adhesive properties can be further precisely controlled by magnetic parameters, showing tunable ability for different applications. The remote magnetic field also enables the untethered nanostickers to be anchored on various biological tissues, even in lumens and fragile body parts.Table 1: Overview of different methods and strategies for adhesion on biological tissues. Advantages and disadvantages are detailed for different methods and strategies to show the advancement of magnetic control bioadhesion.Adhesion Adhesion Pro (s) in adhesion Con (s) in adhesion strategies mechanismsConventional Adhesive Chemical High adhesion energy; Permanent and irreversible methods bonds anchor Available under complex bonding; Uncontrollable interfacial environment spatiotemporally; Moderate (e.g., biofluids) fatigue resistanceNon- Temporary and reversible Low adhesion energy; Easycovalent bonding; Abundant bonding failure under complex bond designs for interfacial interfacial environment (e.g., interactions (e.g., biofluids); Poor fatigue hydrogen bonding, charge resistance; Uncontrollable interaction) spatiotemporally Topological Topological Adhesive properties (e.g., Require complex and timeconnection interlocking adhesion energy, consuming processing on Physical reversibility) are tunable biological surfaces; entanglement by customized designs; Uncontrollable Mechanical Stimuli-responsive spatiotemporally in high level; interlock adhesion (e.g., UV, pH, Moderate fatigue resistance temperature) isachievable; Availableunder complexphysiological environment(e.g., biofluids)Emerging Ultrasound US-induced High adhesion energy; Unsuitable for fragile body Methods mediation cavitation Strong fatigue resistance; parts (e.g., diseased region) and Precise control in space deep tissues due to the thick and time; Applicable to ultrasound probe and high diverse hydrogels and pressure exerted by the probe; anchoring agents Acute thermal effects and potential damages under high power of treatment Magnetic Magnetic High adhesion energy with Non-uniform distribution of control field gradient minimum anchoring nanostickers due to magnetic and vortex agents; Strong fatigue field gradientresistance; Remote controlin adhesive properties(e.g., adhesion energy,adhesion-related space andtime); Applicable todiverse patches andanchoring agents;Harmless and applicable toa wide range of body partsSUMMARY OF THE INVENTION

[0006] This invention provides a method for controlling adhesive properties at an interface between a polymer patch and a tissue. In one embodiment, said method comprises the steps of: a) Applying superparamagnetic nanostickers coated with a first polymer onto said tissue, wherein said first polymer has an affinity to said polymer patch; b) Applying a magnetic field to affect anchorage of said superparamagnetic nanostickers on said tissue; and c) Attaching said polymer patch onto said tissue.

[0007] This invention also provides a system for controlling adhesive properties at an interface between a polymer patch and a tissue using the method of this invention. In one embodiment, said system comprises: a) A gradient-based rotating magnetic field source for generating said magnetic field; b) said polymer patch; and c) said superparamagnetic nanostickers.BRIEF DESCRIPTION OF THE FIGURES

[0008] Figures 1A and IB show the comparison of conventional energy dissipation strategy and interface-enhanced strategy. Figure 1A shows that conventional strategy relies on large energy dissipation by the bridged interfacial polymer layer. Figure IB shows that interface-enhanced strategy can integrate energy dissipation with great interfacial enhancement through the layer of anchored nanostickers and robust patch. For conventional strategy, the toughness of interfacial polymer layer is increased as the patch is tough. The strategy focuses on improving the dissipated mechanical energy TD; however, the scarce functional groups and external barriers on tissue surfaces will tremendously decrease the intrinsic work of adhesion TO, which weakens the anchoring effect of bridged polymer layer. The decreased TO will also impedes the effective deformation and mechanical dissipation that are generated from the interface and the patch, resulting in a low TD. For interface-enhanced strategy, the anchored nanostickers between the tissues and robust patch will significantly improve the interfacial strength for high TO. The highly cohesive nanostickers ascribed to abundant interparticle interactions such as strong magnetic force further provide stress transmission for peeling andresist the crack formation at the interfacial patch layer for high TD. As adhesion energy relates to both TO and TD1, and TD can be influenced by TO, the efficient strategy to achieve robust bioadhesion should take both into account.

[0009] Figures 2A to 2F show the precise control of magnetic nanostickers for enhanced interfacial bioadhesion. Figure 2A shows the schematic illustrating the magnetic control of nanostickers to bridge tissues with hydrogel patches. Figure 2B shows that the adhesion force mapping compares the adhesion force distribution between the nanostickers-anchored surface and the pig skin surface. Inset shows real images of nanostickers’ anchorage. Figure 2C shows the adhesion force distribution of the anchored skin with different quantities of nanostickers.Figure 2D shows the average adhesion force generated by different quantities of nanostickers.Figure 2E shows the work of retraction produced by different quantities of nanostickers.Figure 2F shows the average work of retraction measured on diverse tissues (50 pg of nanostickers).

[0010] Figure 3 shows that adhesion energy is measured from pig skin-patch hybrids anchored with different nanostickers. Different cationic polymer-coated nanostickers between the skin and patch can all improve the adhesion energy.

[0011] Figures 4A and 4B show that adhesion energy is measured from hydrogel patches with various mechanical properties. Figure 4A shows that adhesion energy can be improved by magnetic control of nanostickers for anchoring with various hydrogel patches on pig skin. Stress-displacement curves in Figure 4B compare the mechanical properties of various hydrogel patches.

[0012] Figure 5 shows the TEM imaging of prepared Fe3O4@chitosan nanostickers. Fe3O4@chitosan nanostickers are well dispersed with minor aggregation in water.

[0013] Figures 6A and 6B show the zeta potential distributions of superparamagnetic particles and Fe3O4@chitosan. Superparamagnetic particles in Figure 6A show a negative surface potential averaged at -20.6 mV. Fe3O4@chitosan nanostickers in Figure 6B show apositive surface potential at +19.6 mV.

[0014] Figure 7 shows the FTIR spectra of the main components in Fe3O4@chitosan. Characteristic peaks generated in Fe3O4@chitosan indicate that the surface functionalization of superparamagnetic particles do not change their chemical properties.

[0015] Figure 8 shows the magnetic hysteresis curves of superparamagnetic particles and Fe3O4@chitosan. Magnetic saturation of Fe3O4@chitosan shows a stable superparamagnetic property, which is close to that of superparamagnetic particles.

[0016] Figures 9A to 9C show the TEM imaging of Fe3O4@chitosan nanostickers after magnetic attraction. Fe3O4@chitosan nanostickers in Figure 9A show a dense aggregation under a magnet, suggesting the promotion of high cohesive force. Figure 9B shows the EDS analysis of the element content in Fe3O4@chitosan nanostickers. Element mapping in Figure 9C suggests that chitosan is well functionalized on FesCU nanoparticles.

[0017] Figure 10 shows the spatial control of nanostickers for high-resolution anchoring.

[0018] Figure 11 shows the SEM images of the lyophilized pig skin. Nanostickers are densely aggregated and tightly anchored on the skin surface.

[0019] Figure 12 shows the water blasting test. Nanostickers are spatially controlled for anchoring on pig skin within a circle. The anchored nanostickers can withstand the water blasting (2 bar) for 1 min without obvious damage.

[0020] Figures 13A to 13F show the magnetic control of nanostickers for tunable adhesive properties. Figure 13A shows the representative curves of different skin-patch hybrids by lapshear tests. Figure 13B shows the shear strength of the skin-patch hybrid anchored by different quantities of nanostickers. Figure 13C shows the representative curves of the skin-patch hybrids with and without nanostickers by 180° peel tests. Figure 13D shows that the adhesion energy varies with different quantities of nanostickers. Figure 13E shows the comparison of the adhesive performance of nanostickers with other representative nanoparticle-based adhesives. Figure 13F shows the interfacial crack propagation rate (dc / dti) versus differentenergy release rates G at an average area density of 4 pg / mm2.

[0021] Figure 14 shows the tensile test of the nanostickers-anchored skin-patch hybrid. The interfacial strength between the pig skin and patch is stronger than the mechanical strength of the robust patch (anchored area: 2 cm of width / 2.5 cm of length).

[0022] Figure 15 shows a tensile test demonstrating the robust interface between nanostickers-anchored skin and patch. (Video is available upon request)

[0023] Figure 16 shows the process of peeling the patch from the anchored skin-patch hybrid. The anchored skin-patch interface is so robust that makes the patch to extend with a large deformation. Furthermore, most nanostickers remain anchored on skin upon peeling.

[0024] Figure 17 shows that the skin-patch interface is greatly enhanced as shown by the large deformation of the patch during peeling. (Video is available upon request)

[0025] Figures 18A to 18C show the representative cyclic peel curves for investigating fatigue resistant ability. Crack extension for each cycle dc / dx at different energy release rates G: 10 J m'2(Figure 18A), 50 J m'2(Figure 18B), and 80 J m'2(Figure 18C).

[0026] Figure 19 shows the magnetic scalar potential distribution at the center XY plane. Magnetic field lines demonstrate that the gradient exists at different distance to the center.

[0027] Figures 20A to 20F show the motion of nanostickers and anchoring mechanism.Figure 20A shows the schematic illustration of actuating the nanostickers with gradient-based rotating magnetic field. Figure 20B shows the field strength distribution along the Y-axis at different distance (Z). Figure 20C shows a horizontal slice of field strength distribution at Z = 55 mm. Figure 20D shows that adhesion energy varies with the distance dmt. Figure 20E shows the shear stress distribution of an individual nanosticker without magnetic control. Representative snapshots in Figure 20F show the increasing trend in shear stress as nanostickers assemble together.

[0028] Figures 21A to 21C show that the adhesion energy is controlled with different magnetic parameters. Figure 21A shows that the adhesion energy varies with the time ofmagnetic steering. Figure 21B shows that the adhesion energy is increased after magnetic treatment. Experimental data indicate that adhesion energy after 3 h of magnetic treatment can reach the peak and is close to that after 5 h of magnetic treatment. Fitted data with a polynomial implies the variation trend: T = -17.2t2+ 172.9 It + 61.25 = -17.2(t-5.03)2+495.83; t is the time after magnetic treatment and T represents the adhesion energy at t. Fitted data show that the adhesion energy at 3 h is approaching to the adhesion energy at 5 h. Figure 21C shows that the adhesion energy can be controlled by frequency of rotating magnetic field.

[0029] Figure 22 shows the magnetic force and torque analysis. The main driving power of a single nanosticker for motion and anchoring is divided into four parts (left): gradient magnetic force Fgradient, magnetic torque Tm-nanosticker, nanosticker interactions Fnanostickers(include magnetic force between nanostickers Fm-nanostickers and intermolecular interactions Fintermoiecuie), and gravity Gnanosticker. The magnetic gradient is extracted from the plot of magnetic field strength versus distance dmt (right). The force and torque are estimated for a nanosticker standing vertically above the center of magnet2. According to the magnetic field strength at dmt = 3 cm (Figures 3B and 3C) and magnetization curve in Figure 12, Fgradientand Tm-nanostickercan be formulated asFgradient ~ Ivnanosticker ' V) B dvnanosticker— M ■ VBlFgradientl ~ 35000 X 3.94mnanosticker ~ 1-38 X 10 ITT-nano sticker (^0 Tm-nanosticker I ^nanosticker M X B d-vnanosticker— M X B\Tm-nanosticker\ ~ 0.045 X 'i^,000i^T-nanos ticker 1.58 X 10 1 lnanosticker ' Tfl), Fnanostickers can be formulated as Fnanostickers— Fm-nanostickers+ Fintermoiecuie, and Gnanosticker is formulated aS I Gnan0Sf ickerI nanosticker 9 - nanosticker )' •

[0030] Figures 23A to 23C show that nanostickers are assembled into different aggregation morphology upon different rotating frequency of magnetic field. In Figure 23A, optical microscope shows that nanostickers are randomly dispersed without magnetic field, while themorphology varies with the increased rotating frequency upon magnetic steering. Figure 23B shows the schematic illustration for the aggregation morphology by the assembly of nanostickers. Process diagram in Figure 23C describes the variation tendency of aggregation morphology as the rotating frequency is increased.

[0031] Figure 24 shows the comparison of adhesion energy induced by nanostickers with different viscosity. High-viscosity nanostickers generate larger hindrance than low-viscosity nanostickers upon magnetic control.

[0032] Figures 25A and 25B are the simulation for the motion of nanostickers without and with magnetic field. Figure 25A shows an individual nanosticker without magnetic control can produce negligible velocity. Figure 25B shows that the flow rate is largely improved with the increased chain length of assembled nanostickers.

[0033] Figures 26A and 26B show the propelling nanostickers to anchor on biofluid-contaminated pig skins. Images in Figure 26A show that nanostickers can pass through the biofluids such as PBS, blood, and lard to anchor on the skin. In Figure 26B, peeling of the patch displays that the skin-patch interfaces can be bridged by nanostickers even the skins are contaminated.

[0034] Figure 27 shows the measured adhesion energy on different biofluid-contaminated pig skins. Nanostickers can still be well anchored on biofluid-contaminated skins for patch attachment.

[0035] Figures 28A to 281 show the application of nanostickers on various tissues for magnetic control bioadhesion. Figure 28A shows that the bioadhesive properties can be controlled over a wide range. Figure 28B shows that stable and conformal adhesion enables the nanostickers-anchored patch to tolerate various mechanical deformation. Figure 28C shows an intestinal lumen inserted with an inflatable ball is used to explore the extensibility and compliance of the anchored patch. Figure 28D shows the resistance responses of the patch during the contraction-relaxation movements. Figure 28E shows the resistance variationsduring repeated contraction-relaxation cycles. Figure 28F shows the endoluminal delivery of the nanostickers for patch attachment. Figure 28G shows the optimized adhesion energy by magnetic control bioadhesion on diverse tissues. Figure 28H shows the live / dead staining assay after 24 h of culture in NIH 3T3 fibroblasts shows that cells cultured with nanostickers have similar morphology and viability to cells cultured without nanostickers. Figure 281 shows the in vitro biocompatibility of the nanostickers assessed by cell proliferation assay using mesenchymal stem cells, NIH 3T3 fibroblasts, and intestinal epithelial cells after 72 h of culture.

[0036] Figure 29 shows real-time resistance responses to reflect the small movement of intestine. (Video is available upon request)

[0037] Figures 30A and 30B are images showing the procedures of magnetic control bioadhesion in intestinal lumen. Figure 30A shows that nanostickers are delivered into the target region for anchoring and then the thin patch can be attached. In Figure 30B, the attached patch shows a conformal and stable adhesive interface with the intestinal lumen to bear with the mechanical movement.

[0038] Figures 31A to 31H show that the magnetic control bioadhesion assists disease treatment. Figure 31A shows the schematic illustration of the magnetic control of nanostickers in anchoring the anastomotic stoma for patching. Figure 31B shows the entire treatment procedures for the diseased intestine (1: Excision of the diseased part; 2: Anastomose of the stoma by sutures; 3: Anchoring the stoma with magnetic nanostickers). Figure 31C shows the sectional view of the nanostickers-anchored intestine and circular patch. Figure 31D shows the images of each treatment procedure. Figure 31E shows that the adhesion energy varies over time after magnetic treatment. The fitted curve denotes the variation tendency.Figure 31F shows the representative hemotoxylin and eosin staining images of the normal and patched groups. Figure 31G shows the thickness of the intestinal wall in the normal and patched groups (mean ± SD, n = 3; ns represents not significant). Figure 31H shows the histopathologic analysis of the number of inflammatory cells in the normal and patched groups(mean ± SD, t-test, n = 3, *P < 0.05, **P < 0.01).

[0039] Figures 32A to 32C show the long-term bioadhesion in vivo. Despite the adhesion energy is decayed after 10 days, it is still applicable as the patch should have been infiltrated by the tissues and integrated together. In Figure 32A, the patch is attached on the anchored stomach surface and implanted in abdomen, which remains good adhesion after 10 days.Figure 32B shows the adhesion energy measurement on different days after implantation in vivo. Histological analysis in Figure 32C indicates that the nanostickers-anchored patch generates few stimuli to the underlying tissues (Left: normal group; Right: patched group).

[0040] Figure 33 shows the drug release investigations after 24 h of attachment. FITC-labeled nanostickers are anchored on the tissue, showing bright green fluorescence. Meanwhile, rhodamine-loaded patch shows that most rhodamine (red fluorescence) is released into the tissue, as suggested by the colocalization of nanostickers and rhodamine. (FITC: excitation at 495 nm; rhodamine 6G: excitation at 550 nm)

[0041] Figure 34 shows the survival rate comparison in different sutured groups. The 100% survival rate in patched groups indicates that the anchored patch can protect the injured intestines from serious complications to improve the survival rate.

[0042] Figure 35 shows the histological analysis of enlarged images of the normal and patched groups. The patched group shows the structure of repaired intestines is similar to that of normal group, and the patch has been well infiltrated by tissues for long-term integration.DETAILED DESCRIPTION OF THE INVENTION

[0043] This invention provides a method for controlling adhesive properties at an interface between a polymer patch and a tissue. In one embodiment, said method comprises the steps of: a) Applying superparamagnetic nanostickers coated with a first polymer onto said tissue, wherein said first polymer has an affinity to said polymer patch; b) Applying a magnetic field to affect anchorage of said superparamagnetic nanostickers on said tissue; and c) Attaching said polymer patch onto said tissue.

[0044] In one embodiment, said polymer patch is made of a hydrogel.

[0045] In one embodiment, said hydrogel comprises one or more selected from the group consisting of single-network PAAm, Alginate (Alg), Agar, PNIPAM, and their copolymers, that is double-network PAAm-Alg, PAAm-Agar, PAAm-PNIPAM, and PNIPAM-Alg.

[0046] In one embodiment, said hydrogel comprises an anionic polymer.

[0047] In one embodiment, said anionic polymer comprises one or more selected from the group consisting of alginate, agar, and N-isopropyl acrylamide (NIPAM).

[0048] In one embodiment, said first polymer is a cationic polymer.

[0049] In one embodiment, said first polymer comprises one or more polymers selected from the group consisting of chitosan, PEI, PAA, collagen, and gelatin.

[0050] In one embodiment, said superparamagnetic nanostickers comprise one or more selected from the group consisting of Fe, Co, Ni, Mn, and their oxides.

[0051] In one embodiment, said adhesive properties comprise one or more selected from the group consisting of adhesion force, work of adhesion, shear strength, interfacial fatigue resistance and adhesion energy.

[0052] In one embodiment, said magnetic field is a gradient-based rotating magnetic field.

[0053] In one embodiment, said gradient-based rotating magnetic field is applied for a period of time ranging from 0 to 60 min.

[0054] In one embodiment, said gradient-based rotating magnetic field is applied at a frequency of 0 to 20 Hz.

[0055] In one embodiment, said gradient-based rotating magnetic field is applied at a strength of 0 to 200 mT.

[0056] In one embodiment, said gradient-based rotating magnetic field is generated by permanent magnets (including any shapes) and electromagnetic coils (including any configurations).

[0057] This invention also provides a system for controlling adhesive properties at an interface between a polymer patch and a tissue using the method of this invention. In one embodiment, said system comprises: a) A gradient-based rotating magnetic field source for generating said magnetic field; b) said polymer patch; and c) said superparamagnetic nanostickers.

[0058] Precise control of bioadhesion

[0059] The process for interfacial enhancement of bioadhesion includes the dispersion and wireless actuation of nanostickers, followed by simply attaching a hydrogel patch (Figure 2A).The well-dispersed nanostickers facilitate manipulation and subsequent anchorage, which can be used by spraying, dropping, and brushing. A gradient-based rotating magnetic field beneath the tissues can rotate and propel the nanostickers, providing controlled adhesive properties through active repulsion of surrounding barriers and penetration into the tissue surface. Multiple interactions from the nanostickers, including strong magnetic attraction and crosslinks with the robust patch, ensure together a stable tissue-patch interface. To verify the universality and feasibility of magnetic control method in bioadhesion, nanostickers are prepared with various cationic polymers (chitosan, polyethyleneimine, and gelatin) for standard 180° peel tests (Figure 3). Despite differences in charge density and structure of the coated polymer, all prepared nanostickers can distinctly increase their adhesion energy on robust pig skin. The adhesion effects of different dual-crosslinked hydrogel patches (PAAM-Alg, PAAM-Agar, and PNIPAM-Alg) (Figure 4A) were also investigated, because the hybrid network usually can provide exceptional mechanical properties compared to single networks27,28. The adhesion energy increases with improved mechanical robustness of hydrogel patches, suggesting that the interfacial bridging by nanostickers is robust enough to contend against the mechanical deformation of patches (Figure 4B)29. These results indicate that a variety of nanostickers and hydrogel patches can be applied with magnetic control method. To study the interfacial regulation by nanostickers upon peeling, Fe₃O₄@chitosan and polyacrylamide-alginate(PAAm-Alg) were chosen for following demonstration. The robust PAAm-Alg patch (fracture stress ~368 KPa) promotes failure occurs at the tissue-hydrogel interface instead of the bulk. The prepared Fe₃O₄@chitosan nanostickers are optimal for interfacial bridging, exhibiting a small diameter averaging around 10 nm, positive surface potential at +19.6 mV, and stable superparamagnetic saturation at 58 emu g⁻1(Figures 5 to 8). Magnetic dipole-dipole interactions are verified when the scattered Fe₃O₄@chitosan nanostickers present strong magnetic attraction (Figures 9A to 9C).

[0060] Spatial control of anchoring is first demonstrated by masking the skin and wirelessly steering the nanostickers at different area densities. The clover-shaped patterns with small sizes of 10 mm, 15 mm, and 20 mm indicate the precise and high-resolution spatial control (Figure 10). With the quantity of nanostickers applied at 10 pg, 50 pg, and 100 pg, the area density increases accordingly to 0.37 μg / mm2, 0.82 μg / mm2, and 0.92 μg / mm2, respectively. The bonding state of nanostickers is examined by scanning electron microscope, revealing that the compact nanostickers are highly cohesive and firmly anchored on the pig skin (Figure 11).Water blasting test further substantiates that the nanostickers are tightly anchored on the skin surface, which can withstand high impact without visible damage (Figure 12). Atomic force microscope (AFM) is then used to measure the adhesion force generated at different area densities. Compared to the pig skin surface, adhesion force mapping shows a remarkable elevation of the adhesion force on the nanostickers-anchored surface (Figure 2B). The average adhesion force of the pig skin surface is 25.35 nN, which increases to 32.33 nN, 35.61 nN, and 38.37 nN by raising the area density of anchored nanostickers from 0.37 μg / mm2(10 μg) to 0.92 μg / mm2(100 μg) (Figures 2C and 2D). Moreover, the retraction force and distance are accurately recorded by the AFM tip, revealing the work of retraction (F / ΔL) from the anchored nanostickers (Figure 2E). The work of retraction is elevated from 2.08 N / m to 2.32 N / m when the area density of nanostickers increases from 0.37 μg / mm2to 0.82 μg / mm2. However, further increasing the area density to 0.92 μg / mm2decreases the work of retraction to 2.04 N / m. Thisreduction should be caused by the excessive nanostickers that cannot be adequately anchored, as evidenced by the presentation of two peaks in the retraction curve. The anchored nanostickers also improve the work of retraction measured on diverse tissues, indicating the magnetic control method has broad applicability (Figure 2F).

[0061] Controlled bioadhesive properties

[0062] To elucidate the controllable bioadhesion between the skin and patch, a series of mechanical tests are performed. Lap-shear tests reveal that the shear strength of the anchored skin-patch hybrid can reach 187 KPa, which is more than 5 times of the shear strength tested without nanostickers (Figure 13A). The anchored skin-patch interface unexpectedly shows that the interfacial strength is even stronger than the mechanical strength of the robust patch, providing direct evidence for interfacial enhancement between the skin and patch (Figure 14 and Figure 15). The shear strength of the anchored skin-patch hybrid improves when the quantity of nanostickers increases from 0 mg to 2 mg (area density ranges from 0 μg / mm2to 4 μg / mm2). When the quantity of nanostickers exceeds this point to 3 mg (area density: 6 μg / mm2), the shear strength reduces to 74 KPa (Figure 13B). This result suggests that the area density of nanostickers approaches saturation, for which the excessive nanostickers can impair the interfacial bridging with the skin and patch. Afterwards, peel tests demonstrate that the anchored skin-patch hybrid can achieve a high adhesion energy at 1250 J m-2with an average area density of nanostickers at 4 μg / mm2, which is elevated for 90 times when compared to the adhesion energy measured without nanostickers (Figure 13C, Figure 16, and Figure 17). The area densities of nanostickers for optimized adhesion energy investigated by the AFM and peel tests show some variation since they are different testing methods. The quantity of nanostickers also significantly influence the adhesion energy (Figure 13D), for which the highest adhesion energy is obtained when 2 mg of nanostickers is immobilized within an area of 2 cm x 2.5 cm (W x L). This trend correlates well with the previous lap-shear tests. Taking advantage of the gradient-based rotating magnetic control for immobilization, minimal nanostickers are able toobtain a high adhesion energy. The adhesion energy generated from per milligram of nanostickers is -625 J m'2when the area density reaches 4 pg / mm2(Table 2). The ultralow dosage of magnetic nanostickers, coupled with their adhesive performance, far outperforms previous nanoparticle-based adhesives (Figure 13E)15,30'32.Table 2: Comparison of the adhesive performance between different nanoparticle-based adhesives. Compared to other representative nanoparticle-based adhesives, magnetic control method enables nanostickers to have a high adhesion energy at an ultralow dosage.Nanoparticle Mass of nanoparticles in Adhesion energy Referenceadhesive dispersion for bioadhesion generated from permilligram2 wt%, ChsNCS 4-6 mg / 200-300 μL 83.3-125 J m-2Science 377, 751-755(2022)2 wt%, CNC-CHO 4-6 mg / 200-300 μL 30-45 J m-2Science 377, 751-755(2022)40 wt%, TSN 6 mg / 15 μL ~1.7 J m-2Nat. Commun. 8, 15807(2017)30 wt%, AL-30 4.5 mg / 15 μL 1.3-2.2 J m-2Nature 505, 382-385(2014)20 wt%, ANP ~20 mg / ~100 μL ~60 J m-2Nat. Commun. 14, 5378(2023)1 wt%, Nanostickers 1 mg / 100 μL ~625 J m-2 /

[0063] Cyclic peel tests are then performed to explore the fatigue-resistant adhesive properties (Figures 18A to 18C). The cyclic energy release rate G, defined as Fc / W (F is the given peel force that less than the steady-state peel force; W is the width of patch), is applied on the attached patch for TV cycles; and the interfacial crack propagation rate dc / dN is measured from the interfacial crack extension c and cycle number N. Different energy release rates are investigated to generate the plot of dc / dN along with G, in which the interfacial fatigue threshold τ₀ can be calculated by straightly extending the plot to the intercept of the G axis33,34. The nanostickers elevate τ₀ from ~2 J m-2to ~50 J m-2, suggesting that the fatigue resistance of magnetic control bioadhesion is significantly better than the typical covalent bonding around25 J m-2(Figure 13F)12. Different from weak interactions of usual physical linkages such as the topological connection (Table 1), the enhanced interface evidenced by these results is even stronger than the interfacial interactions of chemical linkages.

[0064] Anchoring mechanism of nanostickers

[0065] To illuminate the motion of nanostickers and anchoring mechanism steered by the magnetic control method, the magnetic field used in the mechanical tests is simulated (Figure 19). A sphere permanent magnet with a 50 mm diameter is placed under the tissues, which can steer the nanostickers to rotate and propel into the tissue surface for anchoring (Figure 20A).The magnetic field is parallel to the XY plane and generated on the top of the magnet, and its strength can be easily controlled by adjusting the distance between the top surface of the magnet and tissue surface dmt. The magnetic field distribution shows that the field strength decreases with the increased distance of Z (Z = dmt +where rm is the radius of the magnet) and the in-plane distance to the centerline (original point) (Figure 20B). The practical distance in all tests is set as Z = 55 mm based on the magnetic field strength, and the simulation displays that the magnetic field distribution is uniform on the XY plane that is 30 mm above the top surface of the magnet (Figure 20C). Peel tests substantiate that the distance between the magnet and the skin surface can cause a remarkable variation of adhesion energy, and the skinpatch hybrid shows a very low adhesion energy at 26.8 J m-2without magnetic steering (Figure 20D). In addition, the highest adhesion energy is achieved with 10 min of steering and 3 Hz of rotational frequency, also displaying that the adhesive properties can be controlled by the duration of magnetic treatment and the frequency of rotating magnetic field (Figures 21A to 21C). Rotating nanostickers in a system with a low Reynolds number such as the case of this invention can generate a strong vortex due to the convection35 36, wherein the magnetic and hydrodynamic drag forces and their torques synergistically control the motion of nanostickers (Figure 22). It is observed that the nanostickers are dispersed randomly on the skin when there is no magnetic field, while the increased rotating frequency of the magnetic field leads todifferent assembled morphologies (Figures 23A to 23C). This phenomenon is similar to the formation of micro / nanorobotic swarms in many dynamic fluids37. Therefore, it is hypothesized that the gradient force pulls the nanostickers toward the magnet and the torque-induced vortex assists in assembling the nanostickers on the skin. To prove the hypothesis, nanostickers with high-viscosity chitosan (200-600 mpa.s) are prepared to create strong hindrance for their motion and assembly. The high-viscosity nanostickers provide much lower adhesion energy than low-viscosity nanostickers, suggesting that the gradient force and torque take important roles in anchoring of tissues (Figure 24). The motion and shear stress around the nanostickers are next simulated to help illustrate the anchoring mechanism. The nanostickers present negligible velocity and shear stress in water without magnetic control (Figures 20E and 25A).However, velocity and shear stress increase dramatically around the nanostickers when a rotating magnetic field is applied. Meanwhile, the induced flow rate and shear stress are both improved by the increased length of assembled nanostickers (Figures 20F and 25B).According to these results, it is confirmed that magnetic field precisely controls the nanostickers for tunable bonding on tissue surfaces.

[0066] Selective bioadhesion on various tissues

[0067] Different viscous biofluids are used to contaminate pig skin to examine the propulsion of nanostickers in complex environments (Figures 26A and 26B). The magnetic nanostickers can be effectively propelled through external barriers for robust bioadhesion (Figure 27). It is noteworthy that the nanostickers enable the patch to have on-demand adhesive properties. As a demonstration, the single-sided patch generally shows opposite adhesive properties while the double-sided patch can adhere to two pieces of pig livers simultaneously (Figure 28A). For applications in biological tissues, the mechanical mismatch between the patch and tissues can accelerate adhesive failures and increase the risk of inflammation38. However, the adhesive properties of nanostickers on different tissues and the thickness of the patch for conformal adhesion can be actively controlled. For example, nanostickers with anarea density around 0.5 μg / mm2make a thin patch (thickness -100 pm) highly compliant with the pig intestine, showing excellent tolerance to external forces and torques (Figure 28B).Surround patching also demonstrates that the adhesion can withstand the contraction and expansion of the intestine, as occurs in starvation and fullness (Figure 28C). The conformal contact with the pig intestine suggests that the patch could serve as a good bioelectronic sensor to reflect the intestinal condition. During multiple cycles of contraction and relaxation, the patch shows rapid electrical responses (ΔR / R₀) to monitor the small movement of the intestine (Figure 28D and Figure 29). The real-time resistance variations indicate that the contact between the intestine and patch is highly stable (Figure 28E). As the nanostickers are steered remotely, it also demonstrates that magnetic control bioadhesion can be achieved in the intestinal lumen (Figure 28F). The nanosticker dispersion is delivered into the lumen by a catheter and then actuated by magnetic field for anchoring. Following that, the thin patch is attached on the target region with the help of an endoscope (Figure 30A). The patch tightly adheres to the internal surface even under continuous turning, displaying a very stable adhesive interface (Figure 30B). Quantitative measurement confirms that the nanostickers can promote bioadhesion between the patch and different wet tissues by remote control, while the patch presents very low adhesion when applied without nanostickers (Figure 28G). As the main components of the prepared nanostickers are approved by the Food and Drug Administration (FDA)39,40, the nanostickers show excellent biocompatibility with various mammalian cells (Figures 28H and 28I).

[0068] Magnetic control bioadhesion in surgical operations

[0069] The remotely controlled properties enable the magnetic nanostickers to have significant potential in bridging fragile parts (e.g., diseased regions) or deep tissues with functional patches in vivo. Enterectomy and anastomosis are frequently used to treat many diseases such as tissue necrosis, tumors, ischemia, and trauma41'43. For postoperative management, the tissue patch can prevent the migration of biofluids from the surgical site, asleakage can cause serious bacterial infections. Additionally, intense inflammation in the diseased region can induce complications such as tissue adhesion. The covered patch can therefore provide adhesion prevention between the diseased parts and other tissues. An excised intestinal tract model was developed in Sprague-Dawley rats to implement the magnetic control method and examine its feasibility and therapeutic effect (Figure 31A). The long-term adhesive properties and biocompatibility demonstrate that magnetic control bioadhesion is applicable to postoperative treatment, which requires long-time functionality (Figures 32A to 32C). The nanostickers are spread and steered after the suture-based anastomosis, providing controlled anchoring for the thin patch (Figure 31B). Despite the sutured anastomotic stoma, small gaps between the two ends of the intestines may still exist. Spraying an appropriate concentration of nanosticker dispersion (-500 pg in total) around the stoma helps the patch fully cover these gaps with controlled and suitable adhesive properties, also avoiding harmful intestinal stenosis due to overly strong adhesion (Figure 31C). To further mitigate the risks of infection and inflammation, a levofloxacin-loaded thin patch is applied on the sutured stoma, showing stable and compliant bioadhesion (Figure 31D and Figure 33). After attaching the patch, the adhesion energy increases and reaches a steady state around 3 h, allowing for repositioning the patch if it is misplaced initially (Figure 31E). The patched groups show a survival rate at 100%, in striking contrast to the high mortality rate of the sutured groups without patch treatment (Figure 34). Histomorphological analysis is performed to inspect the healing of the anastomotic stoma after 10 days of treatment. The patched groups display comparable intestinal structures to the normal groups (Figure 31F), with a similar thickness of the intestinal wall (Figure 31G). The inflammatory response in the patched groups is also close to the normal results (Figure 31H). Furthermore, the long-term intact intestine-patch interface facilitates cell migration and tissue integration, evidenced by the strong infiltration of blood vessels and collagen fibers in the patch (Figure 35).

[0070] Concluding statement

[0071] In summary, a strategy to enhance the tissue-hydrogel interface by intelligently steering nanostickers on diverse tissues has been developed. The interfacial adhesive properties can be greatly boosted and precisely controlled by setting related magnetic parameters. The spatiotemporal control of anchoring by remote magnetic field has many advantages over other typical adhesion strategies, particularly for bioadhesion on fragile body parts and deep tissues. The feasibility of magnetic control method is verified using a 50-mm-diameter permanent magnet, and the method is universal to versatile nanostickers and hydrogel patches. However, it is possible that the controllability of nanostickers and their anchoring effects could be improved if the magnetic field was provided by a larger magnet. Compared to passive diffusion of bridging polymers into tissues for anchoring, the active control of nanostickers for rotation and propulsion endows bioadhesion with intelligence and extends its applicable scenarios, serving as a strong alternate or adjunct for medical supplies and contributing to precise medical treatment. Nevertheless, further improvement on the uneven distribution of nanostickers caused by the intrinsic magnetic field gradient deserves further exploration, which could expand the controllability and adhesive properties.

[0072] Methods

[0073] Chemicals and Materials. Ferric trichloride hexahydrate (FeCh • 6H2O; 99%), Ferrous sulfate heptahydrate (FeSO4 7H2O; > 99%), Calcium chloride dehydrate (CaCh 6H2O; > 99%), Hydrochloric acid (HC1; 37%), Ammonium hydroxide solution (NH3 H2O; 25%-28%), Chitosan (low viscosity: < 200 mpa.s), gelatin (-250 g; Bloom), Oxalyl chloride (> 99%), Sodium tripolyphosphate (98%), Sodium alginate (viscosity: 200 ± 20 mpa.s), Agar (low gel strength; 700- 900 g / cm2), N, N'-Methylenebis(acrylamide) (BIS; 99%), N, N, N', N'-tetramethylethylenediamine (TEMED; 99%), Ammonium persulfate (APS; 99.99%) were purchased from Aladdin Chemicals. Acrylamide (AAm, 99%), NIPAM (> 98%) were purchased from J& K Scientific Ltd. Polyethylenimine (PEI; Mn - 10 kDa, branched) was purchased from Sigma-Aldrich. Chitosan (viscosity: 200-600 mpa.s) was purchased from TCI(Shanghai) Development Co. Ltd. Adiposederived mesenchymal stem cell, 3T3 cell, and intestinal cell were provided by the Faculty of Medicine, The Chinese University of Hong Kong. Pig tissues, including skin, intestine, liver, and kidney, were freshly obtained from the slaughterhouse. The bioabsorbable suture is purchased from Shanghai Pudong Jinhuan Medical Supplies Co. Ltd. DI water with a resistivity of 18.2 MQ was used during the experiments. All commercially obtained chemicals and materials are used without further purification.

[0074] Preparation of superparamagnetic particles. 1.35 g of FeCl₃·6H₂O was dissolved with 0.83 mL of HCl in 5 mL of water. 0.69 g of FeSO₄·7H₂O was dissolved with 0.42 mL of HCl in 2.5 mL of water. The clear Fe3+and Fe2+solutions were then mixed under protection by argon. 4 mL of NH₃·H₂O was injected into the mixed solution and stirred for 40 min. The black sediment was finally washed by DI water and ethanol after centrifugation.

[0075] Preparation of Fe3O4@chitosan nanosticker dispersion. 30 mg of superparamagnetic particles was slowly dropped into a 3 mL of chitosan solution, which was dissolved in HC1 solution to get a pH of approximately 5.5. 1.5 mg of sodium tripolyphosphate dissolved in 1 mL of water was added dropwise into the mixture to assist with surface coating. The mixed solution was stirred at 1000 rpm for 30 min at room temperature. Fe3O4@chitosan nanostickers were obtained by washing three times with DI water and ethanol after centrifugation at 10000 rpm for 30 min. The quality of the nanostickers was weighed after drying in a vacuum oven. The Fe3O4@chitosan nanosticker dispersion was sonicated adequately (UC-650; 50% amplitude of power 650 W) and used at a constant concentration (1 wt%, 10 mg / mL) unless otherwise specified.

[0076] Preparation of various cationic polymer-coated nanostickers. For preparing Fe₃O₄@PEI nanostickers, 25 mL of oxalyl chloride (10 mg / mL) was added to 10 mg of Fe₃O₄ dispersion with stirring for 24 h, and the precipitate was obtained by washing with DI water and centrifugation. After that, 5 mg of the precipitate was re-dispersed in 20 mL of water and mixed with 20 mL of PEI solution (10 mg / mL) for 24 h reaction. Fe3O4@PEI nanostickerswere collected by washing with DI water and ethanol after centrifugation. Finally, they were sonicated for dispersion. For preparing Fe3O4@gelatin nanostickers, 500 mg of gelatin was dissolved in 50 mL of DI water by vigorously stirring at 60°C. After cooling down, the Fe3+and Fe2+solutions with molar ratio at 2: 1 were added into the gelatin solution and kept stirring for 2 h. Following that, NH₃·H₂O was added into the solution until the pH reached ~11. The black suspension was further stirred for 6 h and then washed with DI water and ethanol after centrifugation at 10000 rpm for 30 min. A well dispersed Fe3O4@gelatin suspension was obtained by sonication.

[0077] Preparation of different hydrogel patches. For preparing the PAAm-Alg patch, 1 g of AAm was dissolved in 5 mL of water and then stirred with 250 mg of sodium alginate for 12 h. The monomer solution was transparent and sequentially mixed with 70 pL of BIS (2%, wt%), 30 µL of TMEMD, and 760 µL of APS (70 mg / mL) for mixing. The precursor solution was uniformly dropped onto a 10 cm × 10 cm glass mold and rapidly immersed into a CaCl₂ solution (20%, wt%) for 12 h. The thickness of the patch could be controlled by the applied amount of precursors. For preparing the PAAm-Agar patch, 250 mg of agar powder was dissolved in water by stirring at 90°C, followed by blending with 1 g of AAm solution with 30 pL of BIS (2%, wt%), 10 µL of TMEMD, and 300 µL of APS (70 mg / mL). The mixture was rapidly dropped onto a glass mold with solidification for 12 h. For preparing the PNIPAM-Alg patch, 1 g of NIPAM and 250 mg of sodium alginate were dissolved in water and stirred for 12 h. Afterwards, they were added with 50 µL of BIS (2%, wt%), 20 µL of TMEMD, and 500 µL of APS (70 mg / mL). The mixture was dropped onto a glass mold and rapidly immersed into a CaCl₂ solution (20%, wt%) for 12 h at an ice bath.

[0078] Magnetic control bioadhesion. Tissues obtained from freshly slaughtered swine were used to implement the magnetic control strategy. Different quantities of nanosticker dispersions were uniformly spread (sprayed, dropped, or brushed) onto the designated region. Then, a 50-mm-diameter sphere permanent magnet was placed under the tissues at a certain distance. Therotating frequency, and duration of magnetic treatment were set to control the motion and anchoring of nanostickers on tissue surfaces. Unless otherwise specified, the distance between the top surface of the magnet and the tissue surface was 3 cm, the rotating frequency was 3 Hz, and the duration of magnetic treatment was 10 min.

[0079] Adhesion energy tests ex vivo. 180° peel tests were performed using INSTRON-5566 according to the ASTM D2256 standard. A rigid polyethylene terephthalate film was adhered to the backside of the patch with cyanoacrylate glue to prevent large extension during peeling. The patch was attached on different tissues after controlling the nanostickers to complete the anchorage. Peel tests were conducted after 3 h of attachment for most evaluations unless otherwise stated. The patch attached on tissues without nanostickers served as the control group. One mechanical clamp was fixed to the end of tissues and the other mechanical clamp was fixed to the end of patch. The loading speed was constant at 1 mm / s. Real-time forcedisplacement data were recorded by the load cell and the adhesion energy was evaluated by two times of the steady force (F') divided by the width of patch (W). Each evaluation was repeated three times to acquire the average value of adhesion energy.

[0080] Shear strength tests ex vivo. A patch was attached on the tissues with or without the anchorage of nanostickers. The anchored area was 2 cm × 2.5 cm (width × length) to ensure adequate connections between the patch and the tissues. Lap-shear measurements were then performed to evaluate the uniaxial tensile force-displacement data using the INSTRON-5566 machine. Shear strength was evaluated according to the tensile force divided by the adhesive area.

[0081] Interfacial fatigue resistance tests. Cyclic 180° peel tests were performed by setting the cycle number (N) and applied force (Fc) in the INSTRON-5566 machine. The applied peel force was less than the steady-state peel force, and the interfacial crack extension (c) was recorded with cycle number N to calculate the dcd\. Different energy release rates G, definedas Fc / W (W is the width of the patch), were applied to plot the dc / dN along with G. The interfacial fatigue threshold τ₀ was calculated by linearly extending the plot to the intercept of the G axis.

[0082] Simulations of magnetic field and motion of nanostickers. Simulations were conducted with COMSOL Multiphysics 5.5. For the magnetic field simulation, the magnet was modeled as N52- grade NdFeB with a spherical shape and a diameter of 50 mm (dmagnet = 50 mm), with the surrounding environment modeled as air. For the simulation of nanostickers’ motion, which would induce the flow field and pressure by the magnetic steering, the liquid medium was assumed to be water, and laminar flow was applied. The walls were defined as non-slipping boundaries. To illuminate the variation trend of different assembled morphologies, the chain-like magnetic nanostickers were modeled as rigid balls with a diameter of 100 nm. A rotation domain with a dynamic mesh was used to simulate the rotational motion of magnetic nanostickers with different chain lengths. The rotation frequency was set to 3 Hz and the snapshots were extracted at t = 1 s.

[0083] Electrical response investigations. Nanostickers with an area density around 0.5 μg / mm2were steered for anchoring on the pig intestine, and then a thin patch with a thickness -100 pm was attached. Tinfoil was used to help immobilize the wire on both ends of the patch, which was also sealed with polyimide tapes. The wires were gripped by the probes of ohmmeter to record the real-time resistance variations when the intestine was moved.

[0084] Endoluminal delivery of nanostickers for bioadhesion. The nanosticker dispersion was delivered into the lumen of the pig intestine by a catheter under the guidance of an endoscope. Then, the sphere permanent magnet was placed 3 cm under the intestine and actuated at a rotating frequency of 3 Hz for 10 min. Afterwards, a thin patch was delivered and applied through the endoscope. The attached patch on the intestine was rotated by continuous movement to examine the stability of adhesive interface. Snapshots was captured by the camera of endoscope.

[0085] Live / dead staining assay. Calcein-AM and Propidium Iodide kits were used to determine the cellular state. 104of cells in a confocal dish were incubated with nanostickers to get a concentration at 500 pg / mL for 24 h. After that, the cell medium was discarded and the cells were washed by fresh medium to remove the extra nanostickers. Calcein-AM and Propidium Iodide (2 pL) were added into the cells and incubated at 37°C for 30 min. Live / dead staining was then observed by fluorescence microscope (model).

[0086] Biocompatibility evaluations. Mesenchymal stem cells, NIH 3T3 cells, and intestinal epithelial cells were used to evaluate the cell viability. 104of cells with 100 pL of medium in each well were cultured in different 96-well microplates. Nanostickers were added into the culture medium and subsequently transferred into the cell medium to get different concentrations from 0 pg / mL to 500 pg / mL for 72 h of incubation. The above medium was then discarded, and each well was added with 100 pL of MTS solution (1 mg / mL in fresh medium). After 2 h, the supernatant was removed and replaced with 100 pL of DMSO. After shaking the microplates for 1 min, cell viabilities could be evaluated by comparing the absorbance at 490 nm. In addition, cell viabilities without nanostickers were set as control groups.

[0087] Drug release investigations. To demonstrate the localization of the drug and nanostickers, rhodamine 6G was modeled as the drug loaded in the patch, and nanostickers were labeled with FITC. The FITC-labeled nanostickers were prepared by reacting 1 mg of nanostickers with 2 mmol of FITC for 24 h, followed by washing with DI water after centrifugation. The rhodamine-loaded patch was prepared by mixing the precursor solution of the patch with 2 mmol of rhodamine 6G and then solidifying. After the FITC-labeled nanostickers were actuated to anchor on the tissues, the rhodamine-loaded patch was attached. The release tests were observed using a confocal fluorescence microscope (model).

[0088] Magnetic control bioadhesion for treating fragile tissues. All animal surgery operations were reviewed and approved by the Institutional Animal Care and Use Committeein Shenzhen (approval number: TOP-IACUC-2024-0101), which were performed in compliance with the law on experimental animals by China Committee for Research and Animal Ethics. Intestinal tract injury models were implemented in female Sprague-Dawley rats (-300 g) to investigate the applicability of the magnetic control strategy. All surgical equipment was sterilized by iodophor solution. The rats were anesthetized by isoflurane, followed by shaving the hair on the abdomen under the help of 7% sodium sulfide solution. Afterwards, the abdomen was disinfected with iodophor and opened to expose the intestines. The intestines were excised with a length of 1 cm and a width of 0.5 cm by enterectomy to create the injury until approaching the mesentery. Following that, the two ends of the cut intestines were carefully aligned and anastomosed using bioabsorbable sutures to prevent stenosis or leak. 500 uL of nanosticker dispersion (1 wt%) was uniformly sprayed onto the anastomotic stomas and then actuated by a 50-mm-diameter sphere permanent magnet below the stomas. After successful anchorage, a levofloxacin-loaded (-200 mg) thin patch with a thickness of -100 pm was attached to surround the stomas. Finally, the patched intestines were replaced into the abdomen, followed by suturing the separated tissues. The sutured groups without patch treatment were used for comparison.

[0089] Histological assessment. All rats were sacrificed, and intestinal histology specimens were obtained on day 10. Healthy intestines were set as the normal groups. The vertically sectioned intestines under the patch were set as treated groups, ensuring the acquisition of the anastomotic region. The samples were preserved in 4% paraformaldehyde solution for fixation. To perform the histomorphological analysis, the samples were embedded in paraffin and cut within 5 pm in thickness and then they were stained by hematoxylin-eosin. The stained structures were observed by an optical microscope. The thickness of the intestinal wall includes the serosa, muscularis, and mucosa, and the number of infiltrated inflammatory cells in the normal and patched groups were compared to determine the healing efficacy.

[0090] Statistical analysis. All results were shown as mean ± standard derivation via at least three samples unless otherwise noted. Statistical significance tests were performed using t-test function in Origin software. P values less than 0.05 were regarded as statistically significant among the compared samples.

[0091] Adhesion energy tests in vivo. Rats were performed with the same surgery operations and treatment. The sutured intestines without anchoring of nanostickers and attached by the patch were set as normal groups. The rats were sacrificed at different time to take out the intestine-patch hybrids from the abdomen, including the nanostickers-anchored patches and the normal patches. 180° peel tests were then performed to investigate the adhesion energy variations.

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Claims

What is claimed is:

1. A method for controlling adhesive properties at an interface between a polymer patch and a tissue, comprising the steps of:a. Applying superparamagnetic nanostickers coated with a first polymer onto said tissue, wherein said first polymer has an affinity to said polymer patch; b. Applying a magnetic field to affect anchorage of said superparamagnetic nanostickers on said tissue; andc. Attaching said polymer patch onto said tissue.

2. The method of claim 1, wherein said polymer patch is made of a hydrogel.

3. The method of claim 2, wherein said hydrogel comprises one or more selected from the group consisting of single-network PAAm, Alginate, Agar, PNIPAM, and their copolymers, that is double-network PAAm-Alg, PAAm-Agar, PAAm-PNIPAM, and PNIPAM-Alg.

4. The method of claim 2, wherein said hydrogel comprises an anionic polymer.

5. The method of claim 2, wherein said anionic polymer comprises one or more selected from the group consisting of alginate, agar, and N-isopropyl acrylamide.

6. The method of claim 4, wherein said first polymer is a cationic polymer.

7. The method of claim 1, wherein said first polymer comprises one or more polymers selected from the group consisting of chitosan, PEI, PAA, collagen, and gelatin.

8. The method of claim 1, wherein said superparamagnetic nanostickers comprise one or more selected from the group consisting of Fe, Co, Ni, Mn, and their oxides.

9. The method of claim 1, wherein said adhesive properties comprise one or more selected from the group consisting of adhesion force, work of adhesion, shear strength, interfacial fatigue resistance and adhesion energy.

10. The method of claim 1, wherein said magnetic field is a gradient-based rotating magnetic field.

11. The method of claim 10, wherein said gradient-based rotating magnetic field is applied for a period of time ranging from 0 to 60 min.

12. The method of claim 10, wherein said gradient-based rotating magnetic field is applied at a frequency of 0 to 20 Hz.

13. The method of claim 10, wherein said gradient-based rotating magnetic field is applied at a strength of 0 to 200 mT.

14. The method of claim 10, wherein said gradient-based rotating magnetic field is generated by permanent magnets and electromagnetic coils.

15. A system for controlling adhesive properties at an interface between a polymer patch and a tissue using the method of claim 1, comprising:a. A gradient-based rotating magnetic field source for generating said magnetic field;b. said polymer patch; andc. said superparamagnetic nanostickers.

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