Permanent Percutaneous/Permucosal Portals: Osseointegrated Devices

Permanent Percutaneous/Permucosal Portals: Osseointegrated Devices

Corresponding author: Dr. Robert E. Baier, Oral Diagnostic Sciences, the State University of New York at Buffalo; Email: baier@buffalo.edu

Abstract

Unmet needs for safe, hygienic permanent “through-the-skin” ports for catheters, power and fluid conduits and cranial elec- trodes—as well as other applications—can now be confidently fulfilled by the use of osseointegrated devices using materials and principles underlying the half-century success of dental implants. Choice of unique commercially pure titanium screw- like fixtures that avoid fibrous encapsulation to allow biomechanically secure and infection-resistant bone bonding now favors placement of implants in diverse body zones, based on this record of craniomaxillofacial success internationally. Significant clinical experience with FDA-approved implants retaining facial prostheses encourages an expansion of such portals to brain electrodes and to shunts employed to regulate adult normal pressure hydrocephalus (NPH), prior to exploration of neonatal use.

Keywords: Titanium; Osseointegration; Percutaneous; Permucosal; Catheters; Shunts; Electrodes

Abbreviations

cpTi : Commercially Pure Titanium;

Ti6Al4V = titanium, 6-aluminum, 4-vanadium alloy; CST = Critical Surface Tension;

NPH = Normal Pressure Hydrocephalus; UV-A = ultraviolet A light

Introduction

In Texas in 1981, founding president of the Society For Bioma- terials [1], C. William Hall, MD of the Southwest Research Insti- tute in San Antonio described for the world many significant unmet challenges of safely penetrating the body’s integuments [2]. A simultaneous review of the numerous applications wait- ing, and the disabling failure modes of all then-known artificial percutaneous devices was provided by a leading investigator of these devices [3]. Entering the Year 2000, these special con- cerns were still being reported [4], but with the indication that the emerging international success of permanent dental im- plants—especially those comprising commercially pure titani- um (cpTi) implants introduced by P-I Branemark of Sweden in 1970 [5]– held promise for numerous extra-oral applications, as well.

This had been preceded by a London –based Workshop of inter- national experts, calling for the employment of osseointegra- tion in orthopedics and other diverse specialties to little avail [6]. Important gains were made, however, in Branemark-influ- enced specialty rehabilitation clinics [7] and the dental com- munity began to recognize the potentially universal value of the osseointegration principle, once properly understood [8].

Reported here is that “the correct algorithm (has been) at- tained that will make [a] permanent percutaneous implant[s] possible”[2].

Materials and Methods (Research)

The material exclusively utilized for these true trans-muco- sal and skin-crossing implants, into bone, was required to be cpTi. The mechanism for the Osseointegration process has been speculatively described as involving cpTi’s scavenging of wound-healing-released free radicals into the cpTi’s super- ficial oxide layer, in a process called “catalytic reduction”[9]. This is basically the dark reaction that is the reverse of pho- tocatalytic oxidation by cpTi’s release of free radicals in UV-A light. It was important that the cpTi’s surfaces be scrupulously free from contamination, as indicated by having an appropri- ately high Critical Surface Tension [10].

Figure 1. A typical clinically placed implant of commercially pure titanium, which permanently Osseointegrates with skeletal bone and maintains an infection-free seal via epithelial normal hygiene. Courtesy of R. Duthie, BUD Industries, manufacturer

Demonstrating the percutaneous long-term security of the cpTi interfaces to the bone and overlying tissue was a series of clinical cases [11] utilizing the illustrated BUD Implant (Figure

1) fabricated and inserted as described in an Implant System Patent of 1990 [12]. A series of FDA approvals for these medi- cal devices was obtained [13].

Success criteria for the Osseointegrated skin-penetrating cpTi fixtures were as described in concurrent publications by inter- national teams [14]. The most important observation has been that, unlike the surrounding tissue of natural teeth, clearly infected peri-implant, like periodontal, sulcus regions do not cause breakdown of the secure bone-to-implant attachments. Simple hygienic measures are sufficient to achieve long-term function and security of these portals.

Results

The proper definition of the term “Osseointegration” is that no capsular fibrous tissue intervenes between the implanted ma- terial and living host bone, excepting a universal 100-200 Ang- strom thick “conditioning film” of glycoprotein separating all

non-physiologic materials from all biological adjacent phases. This means, of course, that the universally encountered “for- eign body reaction” to deliberately or accidentally implanted materials is not—in fact—universal, and that a new principle of material accommodation into biological tissues has been discovered!

After 40 years of dental experience, in the biologically and chemically hostile (to biomaterials) environment of the mouth, about 8,000,000 dental implants will be placed this year worldwide. The reliable expectation is that their interphases with bone and overlying tissue will sustain their infection-re- sistant and mechanical integrity despite constant variation of temperature, mechanical load, and chemical constituents in a permanently moist environment for the life of each patient.

Given the excellent results obtained in the mouth, and the con- current results reported for maxillofacial implants of the same qualities, the prospects for realizing diverse true long-term percutaneous and permucosal implants have been reached. Nonetheless, confirmations of these findings are still arriving from both in vitro and in vivo models to evaluate these inter- faces [15, 16].

The challenge has now shifted from the once-judged-impossi- ble permanent tissue-to-port interface to the interiors of those ports where synthetic material-to-material passage must be obtained, often in a tissue-growth-agile manner [17]. One such immediate trial site for these permanent portals is recom- mended to be in the adult skull where catheter-based shunting is applied to overcome normal pressure hydrocephalus effects that simulate Alzheimer’s syndrome [18]. It is not yet known if similar applications in neonatal or growing skull bones will be geometrically sustainable [19]. Chronically implanted neural electrodes, which fail due to tissue reaction and loosening at the skull, should immediately benefit [20], however.

It is obvious, of course, that this dependence on osseointegra- tion presumes the presence of nearby “Osseo” tissue, limiting potential soft tissue applications because of the usual fibrous scar capsule response [21]. Good news is that proper modula- tion of the surface properties of a variety of biomaterials, in- ducing different degrees of tissue response by control of their Critical Surface Tensions, may lead to interfaces of similarly high integrity away from bony sites [22].

Implementation

Consultation with experts in craniomaxillofacial intervention has encouraged further exploration of this concept and en- gaged bioengineering/biomaterials students have noted the specific need for safer, less expensive intervention in children and older adults with revised hydrocephalus shunts (estimat- ed 40,000/year in the US). Current surgical costs for revising these, unfortunately, frequent shunt failures (by infection and occlusion) are estimated at $35,000 per case, reducible to approximately $10,000 per case with titanium portals osse- ointegrated into skulls, with expected lower pain and suffer- ing for patients. Prior work of Schaaf [11] and Duthie [12, 13] has demonstrated that both the anticipated surgical and reg- ulatory difficulties for these implant procedures have already been overcome, and discussions with Oral and Maxillofacial Surgeons suggest their readiness to cooperate with neurosur- gical specialists in placing such implants, as they are already placing about 8,000,000 osseointegrating dental implants in patients around the world in 2016. The neurosurgeons could then, more swiftly, safely, and effectively perform shunt re- placements through the fixed portals when the need arises. A current commercialization plan is being developed around University at Buffalo’s New Technology Disclosure of specific portal designs and fabrication steps [23].

Conclusion

The intimate bonding of cpTi to living bone, with only an in- tervening molecular “conditioning layer” of glycoprotein, pro- vides a long-term sustainable interface between the interior and exterior of the living body. Thereby, long-sought perma- nent portals for power and fluidic transfer across percutane- ous and permucosal regions can emulate the excellent results of dental implants, and provide for a host of new therapeutic and diagnostic implements with higher-than-previously real- ized security and integrity.

Future research should continue to seek this same security for the bonds of soft tissues to biomaterials.

Attention to proper implant surface preparation will be critical to these forecast discoveries [24].

Acknowledgement

The basic findings of these studies were developed with the support and enthusiasm of Dr. J. R. Natiella, under his Grant No. DE-04226, from the National Institute of Dental Research, in 1981.

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