Conductive biopolymer implant for enhancing tissue repair and regeneration using electromagnetic fields

Abstract

Embodiments of the present invention relate generally to the field of tissue repair and regeneration. More specifically, embodiments of the present invention relate to medical devices, materials or constructs, such as conductive biocompatible polymers having one or more networks of metal nanowires that enhance tissue repair and regeneration using electromagnetic fields.

Claims

1. A medical device, comprising: at least one connected network of metal nanowires; and at least one biocompatible fibrillar biopolymer, wherein the device exhibits electric conductivity in at least one direction across the device, and at least some of the network of metal nanowires are encapsulated in at least part of the biocompatible fibrillar biopolymer having at least partially aligned fibrils in at least one direction which coincides with an alignment of the encapsulated metal nanowires and the network of nanowires span a majority of the length of the biocompatible fibrillar biopolymer, forming a layer with sheet resistance less than 100 k/sq, said metal nanowires consist essentially of metal, said metal nanowires have a cross-section dimension of less than 100 nm, and the concentration of said metal in the biocompatible fibrillar biopolymer is less than 1 wt %.

2. The medical device of claim 1 wherein the device is biocompatible with body tissue.

3. The medical device of claim 1 wherein the concentration of metal nanowires is in the range from 50 g to 50 mg per liter.

4. The medical device of claim 1 wherein said biocompatible fibrillar biopolymer is collagen.

5. The medical device of claim 1 wherein the concentration of metal nanowires is high enough to enable antimicrobial properties of the device.

6. The medical device according to claim 1, further comprising: the at least one connected network of metal nanowires located between two biocompatible fibrillar biopolymer layers, and made by a method comprising the steps of: depositing a water-based solution or gel containing metal nanowires on a first biocompatible fibrillar biopolymer layer; removing water from the water-based solution or gel to form the at least one connected network of metal nanowires on the first biocompatible fibrillar biopolymer layer; laminating the first biocompatible fibrillar biopolymer layer with the at least one connected network of metal nanowires thereon to a second biocompatible fibrillar biopolymer layer to form a laminated construct; and treating the laminated construct to enhance the connection between metal nanowires and to cross-link at least one of the biocompatible fibrillar biopolymer layers included in the construct.

7. The medical device according to the claim 6 wherein the water-based solution or gel is a water solution of metal nanowires.

8. The medical device according to the claim 7 wherein the water-based solution or gel further comprises at least one of: cross-linking molecules, glycoproteins, proteoglycans, bioactive or chemically active materials.

9. The medical device according to the claim 6 wherein the water-based solution or gel is a mixture of biopolymer and metal nanowires.

10. The medical device according to the claim 9 wherein the water-based solution or gel is an acidic water-based solution or acidic water-based gel of collagen.

11. The medical device according to the claim 6 wherein the second biocompatible fibrillar biopolymer layer is comprised of one or more biocompatible fibrillar biopolymers and metal nanowires.

12. The medical device according to the claim 6 wherein the at least one connected network of metal nanowires is augmented by fibrils of the biopolymer of at least one of the first and second biocompatible fibrillar biopolymer layers.

13. The medical device according to the claim 6 wherein the at least one connected network of metal nanowires is encapsulated by one or more of the first or second biocompatible fibrillar biopolymer layers.

14. The medical device according to the claim 6 wherein the laminated construct comprises a multilayer stack wherein at least one interface between layers has formed thereon a deposited suspension of metal nanowires.

15. The medical device according to the claim 6 wherein the treating step is a dehydrothermal treatment.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The foregoing and other aspects of embodiments of the present invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:

(2) FIG. 1 is a schematic drawing illustrating a connected network of metal nanowires according to some embodiments of the present disclosure;

(3) FIG. 2 is a cross-sectional view of multilayered device or construct showing two conductive layers formed by metal nanowire networks according to some embodiments of the present disclosure;

(4) FIG. 3 depicts a 2-D wire grid model of a connected nanowire network according to another embodiment of the present disclosure;

(5) FIGS. 4A and 4B are atomic force microscope (AFM) measurements of a collagen material with silver nanowires formed therein according to some embodiments of the present disclosure;

(6) FIG. 5A is an AFM of a conductive network of silver nanowires formed in a material according to some embodiments of the present disclosure;

(7) FIG. 5B illustrates a histogram of angles of the silver nanowires in the material of FIG. 4A;

(8) FIGS. 6A and 6B are photographs showing human fibroblast cells aligned on a fibilar collagen material with silver nanowires according to embodiments of the present disclosure at day 5 and day 11 of growth, respectively; and

(9) FIGS. 7A and 7B illustrate electrical properties of a collagen material scaffold with silver nanowires formed therein according to some embodiments of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

(10) It is to be understood that both the foregoing general description and the following description are exemplary and explanatory only and are not restrictive of the methods and devices described herein. In this application, the use of the singular includes the plural unless specifically state otherwise. Also, the use of or means and/or unless stated otherwise. Similarly, comprise, comprises, comprising, include, includes, including, has, have, and having are not intended to be limiting.

(11) Example embodiments are described herein in the context of medical devices and biocompatible materials, and methods of making. Those of ordinary skill in the art will realize that the following description is illustrative only and is not intended to be in any way limiting. Other embodiments will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will now be made in detail to various implementations of the example embodiments as illustrated in the accompanying drawings. The same reference indicators will be used to the extent possible throughout the drawings and the following description to refer to the same or like items.

(12) Embodiments of the present invention describe methods to produce medical devices, constructs or implants comprised of compatible polymers with metal nanowires useful for implantation or applied to various tissues to enhance repair and regeneration when used with electrotherapy, among other uses. In some embodiments the biopolymer material or implants are comprised of collagen with silver nanowires. Of particular advantage the conductivity of such devices, materials or implants may be selectively controlled by inducing magnetic fields and thus inducing cellular activities to enhance or promote tissue healing as well as provide antibacterial properties and active electric stimulation.

(13) For purposes of the following description, Nanowire means an elongated nanoparticle with an aspect ratio at least 2. In some embodiments, and without limitation, a typical aspect ratio is at least 100.

(14) Nanoparticle means a particle which has at least one dimension less than 100 nm.

(15) Partially align(ed) nanowires means that at least about 20% of the nanowires are oriented within about 15 degree from a chosen direction.

(16) Various embodiments of the medical devices and materials of the present invention are also referred to as constructs, scaffolds, collagen scaffolds, implants and/or bio-devices. The terms biocompatible polymer and biopolymer are sometimes used interchangeably.

(17) In some embodiments the one or more metal nanowires have a concentration in the range from about 50 g to 50 mg per liter. In some embodiments, the metal nanowires are at least partially aligned in at least one direction.

(18) FIG. 1 is a simplified schematic drawing illustrating one example of a connected network of metal nanowires 100. As used herein the term connected sometimes refers to electrical connection or electrical coupling between one or more of the individual metal nanowires as shown in FIG. 1. In this example a plurality of connected networks 102, 104, 106, 108 are shown and the networks are substantially oriented in a similar direction. An electric potential of alternating polarity is applied to each of the networks. Those of skill in the art will recognize that other arrangements and configurations are possible given the teaching herein, and that all such modifications are within the scope of the present disclosure and appended claims.

(19) The at least one biocompatible polymer may be comprised of a fibrillar biopolymer. In this instance, the fibrillar biopolymer may have at least partially aligned fibrils in at least one direction. In some embodiments, this partial alignment of the fibrils substantially coincides with the partial alignment of the nanowires.

(20) The at least one biopolymer may be comprised of collagen, such as but not limited to collagen 1. The one or more metal nanowires may be selected from any one or more of: Ag, Au, Pt, Ti, Fe, Ni, Si, V, Co, Cu or Zn, and combinations thereof. In one example the metal nanowires are comprised of silver. In some embodiments, a plurality of metal nanowires are provided and the nanowires form a conductive net or network.

(21) Of particular advantage, the one or more metal nanowires can be aligned within the material in a desired orientation. In some embodiments the nanowires are aligned in the material to provide the material with conductivity in at least one direction. The metal nanowires are augmented or coated by fibrils of the biopolymer.

(22) The concentration of metal nanowires present in the biopolymer may be selected as desired. In some embodiments the concentration of the metal nanowires is below, or does not exceed, the level at which the metal would be considered toxic to a human or animal. In some embodiments, the concentration of the metal nanowires is sufficient to enable antimicrobial properties of the material.

(23) Additional components may be added, for example the mixture of nanowires in the biocompatible polymer may further include one more of: crosslinking molecules, glycoproteins, proteoglycans, bioactive or chemically active materials, or mixtures thereof.

(24) FIG. 2 shows a cross-sectional view of multilayered device or construct 200 showing two conductive layers formed by metal nanowire networks according to some embodiments of the present disclosure. In one example, the multilayered device is broadly comprised of two conductive layers 202, 204 separated by an insulator 206. Top conductive layer 202 has formed therein a network of metal nanowires 1 formed primarily near the top surface of the layer 202. Bottom conductive layer 204 is a biopolymer and has a network of metal nanowires 208 formed therein that are substantially encapsulated within the layer 204. Preferably, layer 204 exhibits a low metal ion diffusion speed.

(25) In one example illustration we have incorporated silver nanowires into reconstituted collagen constructs. The ratio of collagen to silver nanowires can be varied depending on the usage of the material. Silver nanowires can be dispersed throughout the collagen or instead deposited in a layer on the surface of the collagen or between collagen sheets. Application of an external instrument to generate an electric current can be achieved throughout the collagen as in an application for wound healing. Alternatively, the collagen/silver nanowire construct can be assembled into a suture-like construct and inserted, for example, in the heart to act as a pacemaker or into ischemic tissue to induce vascularization. Also, silver nanowire constructs can be assembled into tubes to act to accelerate nerve regeneration, other constructs are made for specific uses in tissues to enhance repair and restore function.

(26) There are two important limitations for the concentration of silver nanowires in the biopolymer. They are: (1) silver (Ag) toxicity level measured in mg/g (ratio of the nanowire amount to the weight of the biopolymer or scaffold material), which is reported to be 10 mg/g; and (2) the silver antimicrobial level measured in mg/g (ratio of the nanowire amount to the weight of the biopolymer or scaffold material), which is reported to be 0.01 mg/g.

(27) One model of a connected nanowire network is a 2D wire-grid, as shown in FIG. 3, where L is the length of the nanowires and a is the diameter of nanowires.

(28) The corresponding concentration of the silver nanowires in the collagen scaffold of the thickness h is:

(29) $3.7**\frac{a^2}{L*h}$
where the dry collagen density is 1.42 g/cm3 and silver density is 10.5 g/cm3. Thus, the electrically conductive collagen scaffold that includes this 2D wire-grid has antimicrobial effect and has no toxicity if:

(30) ${10}^{-5}3.7**\frac{a^2}{L*h}{10}^{-2}.$

(31) In the case of collagen scaffold with thickness h=5 micron, L=10 micron, and a=50 nm we have:

(32) $3.7**\frac{a^2}{L*h}=0.00058.$

(33) Therefore this collagen scaffold has electrical conductivity and antimicrobial properties. The concentration of silver is significantly below the toxic level. This design is possible because the silver nanowires have a high aspect ratio (200).

(34) The sheet resistance of the 2D silver wire-grid model is equal to:

(35) $R=\frac{4{}_{e}L}{a^2}$
where .sub.e=1.6*10.sup.8 -m. In the considered model we have L=10 micron, a=50 nm, and therefore R=81.6 /sq. The ideal contact between nanowires is assumed in this model. In an operating system one would assume at least one order of magnitude higher resistance for the same concentration of nanowires as in the model.

(36) It should be noted that a variety of other metal nanowires can be introduced into similar constructs according to the present teaching.

(37) Embodiments of the present invention are useful in a number of applications. In one example, the material may be used as a sheet of material, such that the invention can be applied to cover a dermal wound or the surface of a fracture. The material may be used as a tube, wherein the inventive material can be used as a nerve guide for the repair of damaged nerves. The material my be used as a suture, and can be inserted into failing and/or ischemic tissues such as the kidney, heart, or muscle to enhance blood flow and repair as well as enhance function, for example, to induce insulin secretion by the pancreas or contraction of the heart muscles.

(38) Flowing blood contains electrolytes with positive and negative charges. The flow of electrolytes through the silver wire impregnated conduit will induce a small electromagnetic field. Such fields are known to enhance healing. Accordingly the silvered conduit will promote endothelial regeneration, thereby accelerating the resurfacing of the lumen of the conduit by a monolayer of endothelial cells. Restoration of a normal and complete endothelial lining will promote vascular homeostasis, as the endothelium produces panoply of paracrine factors that induce vasorelaxation; that inhibit abnormal vascular smooth muscle growth and re-narrowing of the lumen; that inhibit immune cell infiltration and inflammation; and that prevent thrombus from forming on the vessel wall and obstructing blood flow.

(39) Alternatively, an external magnetic field can be imposed on the conduit, causing a weak electrical current to be generated in the silver wires of the conduit. Weak electrical currents are known to enhance healing. It is expected that in this situation, the endothelial monolayer would be regenerated at an accelerated rate. The rapid endothelialization of the conduit would preserve its patency, due to the mechanisms described above (i.e. inhibition of aberrant vascular smooth muscle cell growth, platelet adherence and immune cell infiltration).

(40) The weak magnetic field generated by the blood flowing through the conduit, is proportional to the amount of electrolyte solution flowing through the conduit. Since the concentration of electrolytes in the blood are tightly regulated in a narrow range, the strength of the magnetic field is directly proportional to blood flow. It is possible to measure the strength of the magnetic field by external devices. Because the strength of the magnetic field is dependent upon blood flow, its detection and quantification permits an assessment of blood flow through the conduit. Since the flow of blood through the conduit is dependent upon its patency, the magnetic field is an indication of the patency of the conduit. Furthermore, since the flow of blood through the conduit is directly related to the fourth power of the internal radius of the conduit, one can determine if the internal radius of the conduit has become smaller (as would occur with the adherence of thrombus, or with abnormal thickening of the vessel wall, ie. restenosis).

EXPERIMENTAL

(41) A number of experiments were conducted as described below. These examples are shown for illustration purposes only and are not intended to limit the invention in any way.

(42) Examples of multilayer collagen scaffolds with silver nanowires are shown in the figures. FIGS. 4A and 4B are AFM measurements of impregnated nanowires in the tendon-like collagen layer. FIGS. 5A and 5B are AFM measurements of connected network of silver nanowires on the interface of one layer. Photos of human fibroblast cells plated on aligned fibrilar collagen matrix with impregnated silver nanowires are presented in FIGS. 6A and 6B, and show a high degree of cell alignment indicating that the impregnated nanowires have not altered the aligned fibrillar structure of the collagen.

(43) Electrical properties of the collagen scaffold with impregnated silver nanowires are shown in FIGS. 7A and 7B. The nanowires are augmented by collagen fibrils therefore only the traces of nanowires are seen at the map of the electrical current distribution.

(44) Typical sheet resistance of the scaffold with silver nanowires varies from 100 /sq (interface depositionFIGS. 5A and 5B) to 100 k/sq (impregnated coatingFIGS. 4A and 4B).

(45) The foregoing methods, materials, constructs and description are intended to be illustrative. In view of the teachings provided herein, other approaches will be evident to those of skill in the relevant art, and such approaches are intended to fall within the scope of the present invention.