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Medical Patent Abstract
A medical barrier includes a sheet of unsintered substantially unexpanded
hydrophilic polytetraflouroethylene (PTFE) polymer material having
a density in a range of about 1.2 gm/cc to about 2.3 gm/cc, and
preferably in the range of about 1.45 gm/cc to about 1.55 gm/cc,
and having at least one textured surface. In accordance with one
embodiment, the sheet has one textured surface and one substantially
smooth surface, and has substantially uniform strength in all directions.
Medical Patent Claims
What is claimed is:
1. A guided tissue regeneration membrane comprising a high density
polytetrafluoroethylene sheet having at least a portion of at least
one surface thereof that is hydrophilic, which renders the membrane
surface substantially compatible with water, body fluids, blood
and aqueous solutions, wherein said at least a portion of at least
one surface comprises a hydrophilic polymer grafted to said surface.
2. The guided tissue regeneration membrane according to claim 1,
in which said membrane is constructed of high density, unexpanded,
unsintered PTFE.
3. The guided tissue regeneration membrane according to claim 1,
wherein said membrane has a density in the range of a density in
a range of about 1.2 gm/cc to about 2.3 gm/cc.
4. The guided tissue regeneration membrane according to claim 1,
wherein said membrane has one textured surface and one substantially
smooth surface.
5. The guided tissue regeneration membrane according to claim 1,
in which the hydrophilic portion of said membrane is limited to
the peripheral borders of the membrane.
6. The guided tissue regeneration membrane according to claim 1,
in which the hydrophilic portion of said membrane is limited to
the central portion of the membrane.
7. The guided tissue regeneration membrane according to claim 1,
in which the hydrophilic portion of said membrane is linked via
covalent bonds to bioactive molecules.
8. The guided tissue regeneration membrane according to claim 7,
wherein said bioactive molecules include growth factors, cytokines,
morphogenetic proteins, cell attractants, and adhesion molecules.
9. The guided tissue regeneration membrane according to claim 8,
wherein the source of said bioactive molecules is selected from
the group consisting of autologous, allogenic, xenogenic and synthetic.
10. A guided tissue regeneration membrane comprising a high density
polytetrafluoroethylene sheet having at least a portion of at least
one surface thereof that is hydrophilic, which renders the membrane
surface substantially compatible with water, body fluids, blood
and aqueous solutions, wherein said at least a portion of at least
one surface comprises a reactive chemical compound grafted to said
surface.
11. A guided tissue regeneration membrane comprising a high density
polytetrafluoroethylene sheet having at least a portion of at least
one surface thereof that is hydrophilic, which renders the membrane
surface substantially compatible with water, body fluids, blood
and aqueous solutions, wherein said at least a portion of at least
one surface comprises a surface treated by a chemical reaction to
make said surface hydrophilic.
12. A guided tissue regeneration membrane comprising a high density
polytetrafluoroethylene sheet having at least a portion of at least
one surface thereof that is hydrophilic, which renders the membrane
surface substantially compatible with water, body fluids, blood
and aqueous solutions, wherein said at least a portion of at least
one surface comprises a surface treated by a process to make said
surface hydrophilic.
13. The guided tissue regeneration membrane as claimed in claim
12, wherein said process comprises etching.
14. A method of repairing a defect in alveolar bone underlying
gingival tissue, which comprises the steps of: placing a sheet of
hydrophilic polytetraflouroethylene polymer material over said defect
between the bone and the gingival tissue; securing the gingival
tissue over the sheet; allowing the defect to heal under the sheet;
and, removing the sheet after the defect has healed, wherein said
sheet of hydrophilic polytetraflouroethylene polymer material comprises
polytetrafluoroethylene sheet having least a portion of at least
one surface thereof that is hydrophilic, which renders the membrane
surface substantially compatible with water, body fluids, blood
and aqueous solutions, and wherein said at least a portion of at
least one surface comprises a hydrophilic polymer grafted to said
surface.
15. The method as claimed in claim 14, wherein said hydrophilic
polytetraflouro ethylene polymer material comprises: unsintered
substantially unexpanded polytetraflouroethylene polymer material.
16. The method as claimed in claim 15, wherein said polytetraflouroethylene
polymer material has a density in a range of about 1.2 gm/cc to
about 2.3 gm/cc.
17. The method as claimed in claim 14, wherein said sheet has one
textured surface and one substantially smooth surface.
18. The method as claimed in claim 17, including placing said substantially
smooth surface in contact with said bone.
19. The method as claimed in claim 14, including the step of: placing
a metallic dental implant into said alveolar bone defect prior to
placing the sheet.
20. The method as claimed in claim 14, wherein the hydrophilic
portion of said membrane is linked via covalent bonds to bioactive
molecules.
21. The method as claimed in claim 20, wherein said bioactive molecules
include growth factors, cytokines, morphogenetic proteins, cell
attractants, and adhesion molecules.
22. The method as claimed in claim 21, wherein the source of said
bioactive molecules is selected from the group consisting of autologous,
allogenic, xenogenic and synthetic.
23. A method of repairing a defect in alveolar bone underlying
gingival tissue, which comprises the steps of: placing a sheet of
hydrophilic polytetraflouroethylene polymer material over said defect
between the bone and the gingival tissue; securing the gingival
tissue over the sheet; allowing the defect to heal under the sheet;
and, removing the sheet after the defect has healed., wherein said
sheet of hydrophilic polytetraflouroethylene polymer material comprises
polytetrafluoroethylene sheet having least a portion of at least
one surface thereof that is hydrophilic, which renders the membrane
surface substantially compatible with water, body fluids, blood
and aqueous solutions, wherein said at least a portion of at least
one surface comprises a reactive chemical compound grafted to said
surface.
24. A method of repairing a defect in alveolar bone underlying
gingival tissue, which comprises the steps of: placing a sheet of
hydrophilic polytetraflouroethylene polymer material over said defect
between the bone and the gingival tissue; securing the gingival
tissue over the sheet; allowing the defect to heal under the sheet;
and, removing the sheet after the defect has healed, wherein said
sheet of hydrophilic polytetraflouro ethylene polymer material comprises
polytetrafluoroethylene sheet having least a portion of at least
one surface thereof that is hydrophilic, which renders the membrane
surface substantially compatible with water, body fluids, blood
and aqueous solutions, wherein said at least a portion of at least
one surface comprises a surface treated by a chemical reaction to
make said surface hydrophilic.
25. A method of repairing a defect in alveolar bone underlying
gingival tissue, which comprises the steps of: placing a sheet of
hydrophilic polytetraflouroethylene polymer material over said defect
between the bone and the gingival tissue; securing the gingival
tissue over the sheet; allowing the defect to heal under the sheet;
and, removing the sheet after the defect has healed, wherein said
sheet of hydrophilic polytetraflouroethylene polymer material comprises
polytetrafluoroethylene sheet having least a portion of at least
one surface thereof that is hydrophilic, which renders the membrane
surface substantially compatible with water, body fluids, blood
and aqueous solutions, wherein said at least a portion of at least
one surface comprises a surface treated by a process to make said
surface hydrophilic.
26. The method as claimed in claim 25, wherein said process comprises
etching.
27. A method of preserving alveolar ridge profile following extraction
of a tooth, which comprises the steps of: placing a sheet of hydrophilic
polytetraflouroethylene polymer material over the tooth extraction
site between the bone and the gingival tissue surrounding the extraction
site; and, at least partially closing the gingival tissue over the
sheet, wherein said sheet of hydrophilic polytetraflouroethylene
polymer material comprises a polytetrafluoroethylene sheet having
at least a portion of at least one surface thereof that is hydrophilic,
which renders the membrane surface substantially compatible with
water, body fluids, blood and aqueous solutions, and wherein said
at least a portion of at least one surface comprises a hydrophilic
polymer grafted to said surface.
28. The method as claimed in claim 27, including the step of: filling
the extraction site with particulate grafting material prior to
placing the sheet.
29. The method as claimed in claim 27, wherein said hydrophilic
polytetraflouroethylene polymer material comprises: unsintered substantially
unexpanded polytetraflouroethylene polymer material.
30. The method as claimed in claim 29, wherein said polytetraflouroethylene
polymer material has a density in a range of about 1.2 gm/cc to
about 2.3 gm/cc.
31. The method as claimed in claim 27, wherein said sheet has one
textured surface and one substantially smooth surface.
32. The method as claimed in claim 31, including placing said substantially
smooth surface in contact with said bone.
33. The method as claimed in claim 27, wherein the hydrophilic
portion of said membrane is linked via covalent bonds to bioactive
molecules.
34. The method as claimed in claim 33, wherein said bioactive molecules
include growth factors, cytokines, morphogenetic proteins, cell
attractants, and adhesion molecules.
35. The method as claimed in claim 33, wherein the source of said
bioactive molecules is selected from the group consisting of autologous,
allogenic, xenogenic and synthetic.
36. A method of preserving alveolar ridge profile following extraction
of a tooth, which comprises the steps of: placing a sheet of hydrophilic
polytetraflouroethylene polymer material over the tooth extraction
site between the bone and the gingival tissue surrounding the extraction
site; and, at least partially closing the gingival tissue over the
sheet, wherein said sheet of hydrophilic polytetraflouroethylene
polymer material comprises a polytetrafluoroethylene sheet having
at least a portion of at least one surface thereof that is hydrophilic,
which renders the membrane surface substantially compatible with
water, body fluids, blood and aqueous solutions, wherein said at
least a portion of at least one surface comprises a reactive chemical
compound grafted to said surface.
37. A method of preserving alveolar ridge profile following extraction
of a tooth, which comprises the steps of: placing a sheet of hydrophilic
polytetraflouroethylene polymer material over the tooth extraction
site between the bone and the gingival tissue surrounding the extraction
site; and, at least partially closing the gingival tissue over the
sheet, wherein said sheet of hydrophilic polytetraflouroethylene
polymer material comprises a polytetrafluoroethylene sheet having
at least a portion of at least one surface thereof that is hydrophilic,
which renders the membrane surface substantially compatible with
water, body fluids, blood and aqueous solutions, wherein said at
least a portion of at least one surface comprises a surface treated
by a chemical reaction to make said surface hydrophilic.
38. A method of preserving alveolar ridge profile following extraction
of a tooth, which comprises the steps of: placing a sheet of hydrophilic
polytetraflouroethylene polymer material over the tooth extraction
site between the bone and the gingival tissue surrounding the extraction
site; and, at least partially closing the gingival tissue over the
sheet, wherein said sheet of hydrophilic polytetraflouroethylene
polymer material comprises a polytetrafluoroethylene sheet having
at least a portion of at least one surface thereof that is hydrophilic,
which renders the membrane surface substantially compatible with
water, body fluids, blood and aqueous solutions, wherein said at
least a portion of at least one surface comprises a surface treated
by a process to make said surface hydrophilic.
39. The method as claimed in claim 38, wherein said process comprises
etching.
Medical Patent Description
FIELD OF THE INVENTION
Aspects of the present invention relate generally to implantable
medical products and more particularly to a hydrophilic high density
polytetrafluoroethylene (PTFE) medical barrier for use in guided
tissue regeneration in the repair of bone defects, and particularly
in the repair of alveolar and maxillofacial bone defects.
BACKGROUND
The basic concepts which led to the clinical procedure of guided
tissue regeneration were reported by Melcher in 1976 in the Journal
of Periodontics. This work identified four distinct connective tissue
cell phenotypes in the periodontium; the gingival corium, periodontal
ligament, cementum and bone. Melcher proposed that the healing response
that occurs after wounding is dependent on the phenotype of cells
that repopulate the area. With the knowledge that epithelial cells
from the gingival soft tissues would proliferate at a faster rate
than bone or periodontal ligament cells, the early efforts at guided
tissue regeneration focused on epithelial exclusion by various mechanical
means, including the placement of a thin sheet of biocompatible
material between the bone defect and overlying soft tissue. Histological
evaluation of animal tissues confirmed the hypothesis that if the
more aggressive and faster growing gingival epithelial cells were
prevented from entering a periodontal bone defect during the healing
phase, then new cementum, bone, and periodontal ligament would be
formed from undifferentiated mesenchymal cells originating from
the adjacent bone, cementum and bone marrow would selectively repopulate
the defect.
At present, there is significant interest in the repair and regeneration
of bony defects that may result from surgery such as the removal
of cysts, the removal of tooth roots, bone loss from infection or
inflammatory process around teeth or dental implants, bone atrophy,
trauma, tumors or congenital defects. Bone loss may result in pain,
loss of function, mobility and subsequent loss of teeth, mobility
and subsequent loss of dental implants, and recurrent infections.
Additionally, deficient bone volume precludes adequate prosthetic
reconstruction. Wound healing studies indicate that the most complete
healing of oral and maxillofacial bone defects occurs when gingival
epithelial and connective tissue cells are prevented from entering
the bony defect.
There are several commercially available products that have been
used successfully as guided tissue regeneration membranes, including
those made from expanded polytetrafluoroethylene (PTFE), high density
PTFE, bovine type I collagen, polylactide/polyglycolide co-polymers,
calcium sulfate and even human skin. A review of the scientific
literature indicates that no single ideal membrane material exists,
but that each type of product has its own advantages and disadvantages.
An example of a current commercially available product employs
a low-density expanded version of polytetrafluoroethylene (ePTFE)
which presents a open-structure matrix to the gingival epithelial
and connective tissue cells. This expanded version of PTFE is characterized
by a low density of about 1.0 gm/cc or less and a porous, hydrophobic
surface. In spite of the hydrophobic surface, soft tissue cells
readily incorporate into the expanded matrix due to the open, porous
structure of the material. While this connective tissue ingrowth
is said to effectively prevent the migration of epilthelial cells,
it presents a difficult problem to the patient and surgeon in the
later stages of the regenerative procedure. After several weeks
to several months, the non-absorbable low-density hydrophobic ePTFE
barrier membrane must be removed. The incorporated cells and fibrous
connective tissue make removal painful and traumatic to the patient
and very time-consuming for the surgeon. The low-density open-matrix
design of ePTFE devices also provides a location for the ingress
of food particles, bacteria, and other foreign bodies which, in
turn, create post-operative problems with the device such as inflammation,
infection, wide exposure of the barrier material with wound dehiscence,
and gingival recession. Any of these complications may require early
removal of the barrier material, therefore compromising the treatment
outcome. Low-density open-matrix or open-structure materials are
generally soft and flimsy such that they will not mechanically support
tissue above the defect during normal functional activities within
the mouth causing a breakdown of the barrier's effectiveness. The
articles described by Scantlebury, et. al. in U.S. Pat. Nos. 5,032,445
and 4,531,916 are such ePTFE devices.
Other products incorporate bio-absorbable polymer technology into
their design. Such products are made from dense collagen matrices
of human or bovine origin, which are broken down via hydrolysis
and absorbed into the body fluids following several weeks to several
months of implantation. While such devices eliminate the need for
a second surgical procedure to remove them, some patients may exhibit
a vigorous antigenic response to the devices which delays and often
prevents the desired healing process within the defect, and may
cause dehiscence of sutured wounds. Even in the absence of a specific
antigenic response to implanted collagen, breakdown and resorption
of these devices often results in generalized inflammatory cascade
including neutrophil and macrophage activation. This foreign-body
response also produces undesirable effects with regard to healing
kinetics and pain. Bio-resorption time also varies significantly
from patient to patient, presenting both patient and surgeon with
an uncertainty regarding overall healing rate and pain management.
Examples of collagen membranes in the literature are BioMend.RTM.
and BioGide.RTM.. The articles described by Li in U.S. Pat. No.
5,206,028 and Geistlich in U.S. Pat. No. 5,837,278 are examples
of such devices.
Synthetic polymers of lactide, glycolide and their various copolymers
are also used as guided tissue regeneration barriers. These materials
are biodegradeable and offer the benefits of avoiding a surgical
procedure for their removal. However, use of these materials results
in inflammatory responses similar to those seen with naturally derived
polymers such as collagen. In addition, the resorption profile may
be unpredictable from patient to patient. These materials are also
highly porous which renders them susceptible to bacterial colonization
and contamination with foreign materials in the oral cavity in the
event of exposure. A synthetic membrane barrier exhibiting similar
characteristics is Vicryl.RTM. (polyglactin) periodontal mesh, Resolute.RTM.
periodontal membrane described by Hayes et al, in U.S. Pat. No.
6,031,138 and Cytoplast.RTM. Resorb regenerative membrane.
Other products used as surgical membranes for the treatment of
jaw and alveolar bone defects are human freeze-dried laminar bone
and human freeze-dried dura mater obtained from human cadavers.
These materials are bio-absorbable and osteoconductive, but carry
a small but unknown risk of human disease transmission from donor
to host. The risk of disease transmission precludes the use of this
material by many surgeons and patients.
In an effort to provide a material with the biocompatibility and
chemical inertness of PTFE but without the disadvantages of the
porous open surface structure of expanded PTFE, a high density PTFE
membrane material has been used and has achieved widespread clinical
acceptance.
In U.S. Pat. No. 5,957,690 and U.S. Pat. No. 6,019,764 the use
of a flexible high-density polytetrafluoroethylene (PTFE) sheet
material was disclosed as a material suitable for guided tissue
regeneration procedures. High density PTFE is substantially nonporous
or microporous so as not to incorporate cells or attach to fibrous
adhesions. By presenting a smooth surface to the biological materials,
a high density PTFE barrier is easily inserted and removed following
extended implantation periods. A similar high density PTFE barrier
material is disclosed in U.S. Pat. No. 5,480,711. Examples of such
products used for guided tissue regeneration include smooth and
textured surface, hydrophobic high density PTFE such as Cytoplast.RTM.Regentex
and TefGenFD.RTM..
While high density PTFE medical barriers provide advantages over
macroporous barriers, the smooth surface of the high density PTFE
barriers sometimes leads to dehiscence of the soft tissue overlying
the barrier. The dehiscence problem is caused in part by the fact
that the smooth surface of high density PTFE will not incorporate
cells and will not attach to fibrous adhesions as compared to expanded
PTFE.
An additional clinical problem exhibited by high density PTFE is
related to its hydrophobicity, or tendency to repel water. The chemical
composition and resulting surface chemistry of a material determine
its interaction with water. Hydrophobic materials have little or
no tendency to adsorb water and water tends to "bead"
on their surfaces in discrete droplets. Hydrophobic materials possess
low surface tension values and lack active groups in their surface
chemistry for formation of "hydrogen-bonds" with water.
In the natural state, PTFE exhibits hydrophobic characteristics,
which requires surface modification to render it hydrophilic. All
previously disclosed products, whether constructed from expanded
PTFE or high density PTFE have such hydrophobic characteristics.
It is well known in the art that biomaterial surfaces exhibiting
hydrophobic characteristics are less attractive in terms of cell
attachment. This is an advantage in some respects, as it prevents
the ready attachment and migration of certain bacteria into the
interstices of the material. However, in terms of interaction with
host tissue, this characteristic may be less desirable and may contribute
to dehiscence, or loss of soft tissue covering over the membrane
during the course of healing. Dehiscence is a common clinical complication
of guided tissue regeneration therapy, with an incidence of up to
60% according to the published literature. The clinical sequelae
may indeed be serious, resulting in infection and failure of the
procedure. The dehiscence phenomenon has been observed with both
high density and expanded PTFE membrane devices, both of which to
date have only been available with hydrophobic surfaces.
Although there are no reports of hydrophilic PTFE used in the construction
of guided tissue regeneration membranes or similar implantable devices,
hydrophilic, surface modified PTFE has a history of use as a filter
in applications such as basic chemical and laboratory filtration,
water purification, filtration of intravenous lines, blood oxygenators
and extracorporeal hemofiltration devices.
U.S. Pat. No. 5,282,965 relates to a hydrophilic porous fluorocarbon
membrane filter for liquids, which is used in microfiltration or
ultrafiltration of liquids such as chemicals and water, and to a
filtering device using said membrane filter. The filter is treated
with low temperature plasma (glow discharge) to create a hydrophilic
surface. Specifically this invention relates to a membrane filter
for liquids, which is suitably used to filtrate chemicals for washing
silicon wafers in semiconductor industries, and to a filtering device.
A hydrophilic semi-permeable PTFE membrane is disclosed in U.S.
Pat. No. 5,041,225. This invention describes hydrophilic, semi-permeable
membranes of PTFE and their manufacture, and further describes membranes
suitable for use in body fluid diagnostic test strips and cell support
members. In this instance, the intent of the hydrophilic membrane
is to cover the target area of a diagnostic test strip with a semi-permeable
membrane of a controlled pore size so that a fluid sample applied
to such a membrane be applied in a controlled manner through the
membrane to the underlying reagents. It should be noted that this
invention discloses an in-vitro device and does not mention or anticipate
use as a surgical implant.
Hydrophilic polymer membranes have been developed for use in the
pharmaceutical industry as disclosed in U.S. Pat. No. 5,573,668
which describes a hydrophilic microporous membrane for drug delivery
and a method for its preparation. Hydrophilicity is achieved by
the application of a thin hydrophilic polymer shell, where the shell
does not substantially alter the complex geometry of the membrane.
Typically, drug delivery devices of non-resorbable polymers such
as described in this patent are placed on the skin with adhesive,
and are not surgically implanted.
Hydrophilic polymer membranes, which are biocompatible, antithrombogenic,
and incorporate functional groups for immobilization of bioactive
molecules are disclosed in U.S. Pat. No. 5,840,190. Specifically,
this patent deals with membrane separators used in machines involved
in the extracorporeal circulation of blood such as heart-lung machine
oxygenators, hemofiltration units of dialysis machines, invasive
blood gas sensors and artificial organs such as artificial pancreas
and skin.
There are two methods described in this patent for fabrication
of these surface modified membranes. "Method A" describes
preparation of a casting solution containing the membrane forming
polymer and then precipitating the casting solution in a bath containing
the surface modifying polymer. "Method B" describes preparation
of the casting solution containing the membrane forming polymer
as well as the surface modifying polymer, and then precipitating
the membrane from the casting solution in a coagulation bath. While
this method may work with many polymers, including cellulose, cellulose
acetate, polysulfone, polylamide, polyacrylonitrile, and polymethylmethacrylate,
neither method is feasible with PTFE. Further, there is no mention
of PTFE within the text or claims of this patent.
A method for coating a hydrophobic polymer so as to render said
membrane hydrophilic is disclosed in U.S. Pat. No. 4,525,374. This
method is said to be particularly for treating polypropylene or
polytetrafluoroethylene in which the filter membrane is contemplated
to have a pore size not larger than two (2) microns. The treating
solution has Triethanolamine Dodecylbenzene Sulfonate (LAS) as the
active ingredient. Treatment of expanded PTFE filters such as Poreflon.RTM.
and GoreTex.RTM. are described in the context of filters for various
chemical fluids such as intravenous fluids. There is no disclosure
of use of said devices as a medical implant or guided tissue regeneration
membrane.
A number of challenges are encountered in the design of the ideal
GTR barrier. For example, the membrane must be dense enough to resist
passage of unwanted cells such as epithelial cells and bacteria,
yet be able to allow the passage of biological fluids, oxygen and
nutrients required to sustain the viability of the regenerated tissue
as well as the overlying tissue. The porosity of currently available
products varies widely, from fully dense to over 30 microns in average
pore size. According to the literature, those with larger pore size
typically have a higher infection rate in clinical use. In contrast,
the fully dense materials, while exhibiting superior characteristics
in terms of infection resistance, are criticized due to the concern
that they are unable to conduct the passage of nutrients in an efficient
manner. Thus, there is a need for an improved membrane material
of sufficient density to prevent the ingress of unwanted cells and
bacteria, and yet be able to readily allow passage of biological
fluids, molecules and oxygen.
A second major design issue involves the surface macrogeometry.
The barrier membrane must be smooth enough to achieve a high degree
of biocompatibility, yet must integrate well with the surrounding
tissue to achieve clinical stability. Current products, with the
exception of smooth surface dense PTFE membranes, rely on a complex
three-dimensional surface structure to facilitate such tissue integration.
A highly porous surface, while it is ideal for tissue ingrowth,
presents problems with regard to bacterial contamination. An improved
surface is needed which would encourage attachment of cells and
tissues to achieve clinical stability without sacrificing the advantages
of a smooth surface.
It is thus advantageous to provide a barrier device of dense, hydrophilic
PTFE which will provide for selective cell repopulation of bone
defects that does not allow the incorporation of cells or fibrous
materials, has an improved hydrophilic surface for enhancement of
cell attraction and attachment and for improved wetting by body
fluids, is easy to remove after extended implantation periods, will
not provide a location for contamination by foreign particles or
bacteria, will not elicit a foreign-body inflammatory response,
does not have the potential to transmit human infectious disease,
is soft and supple such that compliance is similar to soft tissues,
will facilitate retention of particulate grafting materials, and
is convenient to use.
SUMMARY
In accordance with some exemplary embodiments, the present invention
provides a medical barrier that includes a sheet of hydrophilic,
unsintered substantially unexpanded polytetrafluoroethylene (PTFE)
polymer material having a density in a range of about 1.2 gm/cc
to about 2.3 gm/cc, and preferably in the range of about 1.45 gm/cc
to about 1.55 gm/cc, and having at least one textured surface. In
one embodiment, the sheet has one textured surface and one substantially
smooth surface, and has substantially uniform strength in all directions.
The sheet of medical barrier of the present invention has a thickness
in a range of about 0.125 mm to about 0.25 mm. Preferably, the textured
surface is formed by a plurality of indentations formed in the surface
of the sheet. The indentations have a depth less than the thickness
of the sheet and each indentation has a nomimal width of about 0.5
mm. The indentations are distributed substantially uniformly over
the surface of the sheet. In some embodiments, the indentations
are distributed over the surface of the sheet at about 196 indentations
per square centimeter.
The medical barrier of the present invention is particularly well
adapted for use in guided tissue regeneration in the repair of bone
defects, and particularly in the repair of alveolar bone defects.
The barrier prevents the entry of rapidly migrating gingival tissue
cells into the defect and allows the alveolar bone to regenerate.
During healing, the gingival tissue adheres somewhat to the textured
surface of the barrier to anchor the gingival tissue over the barrier,
thereby preventing dehiscence or splitting open of the tissue covering
the material. However, the high density unexpanded substantially
non-porous nature of the medical barrier of the present invention
prevents gingival tissue from growing into or through the barrier.
Thus, after the bone defect has healed, the barrier may be removed
with a minimum of trauma to the gingival tissue.
In contrast to hydrophobic PTFE, it has been found that hydrophilic
PTFE membranes exhibit a greater affinity for cellular adhesion,
attachment and spreading. In addition, with respect to bone cell
interaction with biomaterial surfaces, hydrophilic surfaces have
been shown to promote increased mineralization and osteoblastic
differentiation as measured by alkaline phosphatase (ALP) activity
compared to hydrophobic surfaces. Transmission of body fluids, such
as blood and plasma occurs more readily with hydrophilic membranes.
Clinically, this results in faster and more predictable soft tissue
coverage, improved soft tissue attachment without requiring ingrowth,
and fewer wound healing complications when compared to similar devices
manufactured from hydrophobic PTFE. Thus, the present invention
provides a significant clinical and biological advantage over current,
hydrophobic PTFE guided tissue regeneration membranes.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing the textured surface of the
medical barrier of the present invention.
FIG. 2 is a perspective view showing the untextured surface of
the medical barrier of the present invention.
FIG. 3 is an enlarged view of the textured surface of the medical
barrier of the present invention.
FIG. 4 is a lateral cross-sectional view of a maxillary bony defect
resulting from the extraction of a tooth.
FIG. 5 is a lateral cross-sectional view of the maxillary bony
defect of FIG. 4 showing the placement of the medical barrier of
the present invention to cover the bony defect with the mucoperiosteal
flap sutured over the medical barrier.
FIG. 6 is a lateral cross-sectional view showing the healed maxillary
bony defect of FIG. 4 with the gingival tissue healed over the medical
barrier of the present invention.
DETAILED DESCRIPTION
Referring now to the drawings, and first to FIGS. 1 and 2, a medical
barrier according to one embodiment of the present invention is
designated generally by the numeral 11. Barrier 11 comprises a sheet
of unsintered substantially unexpanded hydrophilic polytetrafluoroethylene
(PTFE) polymer. As shown in FIG. 1, barrier 11 includes a textured
surface 13, and as shown in FIG. 2, an untextured surface 14. Barrier
11 has a density in the range of about 1.2 gm/cc to about 2.3 gm/cc,
and preferably in the range of about 1.45 gm/cc to about 1.55 gm/cc.
Barrier 11 has a sheet thickness in the range of about 0.125 mm
to about 0.25 mm. As shown in FIG. 3, the textured surface of the
exemplary embodiment is formed by a plurality of indentations 15
formed in surface 13 of barrier 11. In some embodiments, indentations
15 may be hexagonal in shape, although other shapes are within the
scope of the present invention. The indentations have a depth less
than the thickness of the sheet, and in the illustrated embodiment
indentations 15 are about 0.15 mm deep. In some implementations,
indentations 15 are about 0.5 mm wide.
Indentations 15 are distributed substantially uniformly over surface
13 of barrier 11 at about 150 indentations per square centimeter
to about 250 indentations per square centimeter. In accordance with
some exemplary implementations, indentations 15 are distributed
over surface 13 of sheet 11 at about 196 indentations per square
centimeter.
The barrier of the present invention is made by first forming a
thin sheet of unsintered PTFE and then embossing the sheet with
indentations. PTFE resin is mixed with a lubricant such as mineral
spirits to form a paste. The paste is then calendered in multiple
passes between rollers to form a thin flat sheet of the desired
thickness in the range of about 0.125 mm to 0.25 mm. The calendering
is performed multiple times in multiple directions to reduce the
thickness of the sheet and to impart substantially uniform strength
in all directions to the sheet. The lubricant is removed by drying
the sheet at temperature somewhat above the boiling point of the
mineral spirit lubricant, but well below the sintering temperature
of PTFE, which is about 327 degrees C. The foregoing process steps
result in a flat sheet of unsintered PTFE about 0.125 to 0.25 mm
thick, having a density in the range of about 1.2 gm/cc to about
2.3 gm/cc, and having substantially uniform strength in all directions.
The resulting flat sheet has two substantially smooth surfaces.
After the sheet has been dried, the sheet is embossed to form the
indentations in one of its surfaces. In some embodiments, the embossing
step may be performed by placing a sheet of patterned polymer mesh
on top of the unembossed sheet of unsintered PTFE. The patterned
polymer sheet material, such as polyethylene or polypropylene, may
be harder and have more compressive strength than the unsintered
PTFE material. One such polymer sheet is embodied in a fine pore-size
sheet filter material manufactured by Tetko, Switzerland. The polymer
sheet has a pattern that is embossed into the polymer sheet. The
polymer sheet and the unsintered PTFE sheet are passed together
between a pair of rollers, which emboss the pattern of the polymer
sheet into one surface of the unsintered PTFE sheet. After embossing,
the polymer sheet may be discarded.
After embossing, the sheet may be treated by various methods known
in the art to impart hydrophilic characteristics to the membrane
surface. These methods include the addition of a second polymer
or hydrophilic chemical compound, chemical treatment of the membrane
surface, laser etching or glow discharge plasma etching. The surface
modified embossed unsintered PTFE sheet may be cut into smaller
sheets of various shape and size for packaging and distribution.
The surface modification to make the surface hydrophilic may be
applied selectively to the surface. For example, the hydrophilic
portion of the surface may be limited only to the central part of
the surface. Alternatively, the hydrophilic portion of the surface
may be limited to the marginal parts of the surface.
After surface modification, the membrane may be modified further
by linking the hydrophilic portion or portions to bioactive molecules,
preferably by covalent bonds. Examples of such bioactive molecules
include, growth factors, cytokines, morphogenetic proteins, cell
attractants, adhesion molecules, and the like. The source of such
bioactive molecules may be autologous, allogenic, xenogenic or synthetic.
Referring now to FIGS. 4-6, there is illustrated the manner of
use of the barrier of the present invention. FIG. 4 is a lateral
cross-sectional view of an adult human maxilla after a tooth extraction.
The bone of the alveolar process is designated by the numeral 17.
Soft tissue gingiva 19 covers bone 17. A tooth socket is designate
by the numeral 21.
Socket 21 is an example of a bone defect. Other examples of bone
defects are those caused by periodontal disease, cyst formation,
surgery, or trauma. Normal healing of a defect includes migration
of foreign cells such as fibroblasts and gingival epithelial cells.
As the cells proliferate into the defect, they inhibit bone cell
regeneration, which results in overall loss of bone mass. In the
case of extractions, the loss of bone mass results in a loss of
alveolar ridge profile.
Referring now to FIG. 5, there is shown one method of using the
barrier of the present invention. Socket 21 is shown packed with
granular particles of hydroxyapatite as a precursor to bone. Those
skilled in the art will recognize that other materials or articles,
such as encloseouss-type dental implants, may be placed into socket
21. The packed socket 21 is covered with a layer 23 of the barrier
of the present invention. The smooth side of the barrier is placed
over socket 21 and bone 17. Thus, the textured of the barrier is
positioned adjacent the gingival tissue 19. The substantially uniform
strength in all directions of the material of the present invention
allows the surgeon to shape layer 23 over socket 21 and bone 17.
After layer 23 is placed over socket 21 and bone 17, the gingival
flaps 19 are sutured over layer 23. Layer 23 holds the hydroxy apatite
particles in place in socket 21 during healing and prevents migration
of cells and connective tissue into socket 21. However, connective
tissue forms a weak attachment with the textured surface of layer
23, without growing through the material. The attachment is weak
enough that the layer may be removed after healing without significant
trauma but is strong enough to prevent the dehiscence.
Referring to FIG. 6, there is shown the extraction site after healing,
but prior to removal of layer 23. As shown in FIG. 6, the alveolar
ridge profile 25 is preserved and the gingival tissue 19 is completely
healed over ridge 25. Layer 23 may be removed by making a small
incision (not shown) in gingival tissue 19 to expose a portion of
layer 23. The layer 23 may then be pulled out with forceps or the
like. Since the connective tissue attaches only weakly to the hydrophilic
textured surface of the material of the present invention, the material
may be pulled out easily and without trauma to the patient.
From the foregoing, it may be seen that the medical barrier of
the present invention overcomes the shortcomings of the prior art,
and is particularly well adapted for use in guided tissue regeneration
in the repair of bone defects, as for example in the repair of alveolar
bone defects. The barrier prevents the entry of rapidly migrating
gingival tissue cells into the defect and allows the alveolar bone
to regenerate. During healing, the gingival tissue adheres somewhat
to the hydrophilic textured surface of the barrier to anchor the
gingival tissue over the barrier, thereby preventing dehiscence
or splitting open of the tissue covering the material. However,
the high density unexpanded substantially non-porous nature of the
medical barrier of the present invention prevents gingival tissue
from growing into or through the barrier. Thus, after the bone defect
has healed, the barrier may be removed with a minimum of trauma
to the gingival tissue.
Aspects of the present invention have been illustrated and described
in detail with reference to particular embodiments by way of example
only, and not by way of limitation. It will be appreciated that
various modifications and alterations may be made to the exemplary
embodiments without departing from the scope and contemplation of
the present disclosure. It is intended, therefore, that the invention
be considered as limited only by the scope of the appended claims.
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