While the growth of cells in two-dimensions is frequently used for the preparation and examination of cultured cells in vitro, it lacks the characteristics of intact,
in vivo tissue which, for example, includes cell-cell and cell-matrix interactions.
For example, three-dimensional collagen substrates have been utilized to culture a variety of cells including breast
epithelium (Yang,
Cancer Res. 41:1021 (1981)), vascular
epithelium (Folkman et al., Nature 288:551(1980)), and hepatocytes (Sirica et al.,
Cancer Res. 76:3259 (1980)), however long-term culture and proliferation of cells in such systems has not yet been achieved.
However, numerous complications and the generally unsatisfactory nature of long-term aesthetic results caused the procedure to be rapidly abandoned.
More recently, the use of injectable
silicone became prevalent in the 1960's for the correction of minor defects, although various inherent complications also limited the use of this substance.
Due to these potential complications,
silicone is not currently approved for general clinical use.
It has also been suggested to compound extremely small particulate species in a lubricious material and inject such combination micro-
particulate media subcutaneously for both soft and
hard tissue augmentation and repair, however success has been heretofore limited.
Subsequent undesirable micro-
particulate media migration and serious granulomatous reactions frequently occur with the injection of this material.
However. while these aforementioned materials create immediate augmentation and / or repair of defects, they also have a tendency to migrate and be reabsorbed from the original
injection site.
The poor results initially obtained with the use of non-biological injectable materials prompted the use of various non-immunogenic, proteinaceous materials (e.g.,
bovine collagen and
fibrin matrices).
Clinical protocols calling for repeated injections of atelocollagen are, in practice, primarily limited by the development of immunogenic reactions to the
bovine collagen.
The increased
viscosity, and in particular irregular increased
viscosity resulting in “lumpiness,” not only rendered the material more difficult to utilize, but also made it unsuitable for use in certain circumstances.
However, like
glutaraldehyde, GAG may be released into the tissue causing unforeseen long-term effects on human subjects.
Additionally, a reduction of collagen
blood clotting capacity may also be deleterious in the application in
bleeding wounds, as
fibrin clot contributes to an adhesion of the graft to the surrounding tissue.
It should be noted, however, that there is no quantitative evidence which demonstrates that human collagen injection results in lower levels of
implant degradation than that which is found with
bovine collagen preparations.
Furthermore, the utilization of autologous collagen preparation and injection is limited to those individuals who have previously undergone
surgery, due to the fact that the initial culture from which the collagen is produced is derived is from the tissue removed during the surgical procedure.
Therefore, it is evident that, although human collagen circumvents the potential for
immunogenicity exhibited by bovine collagen, it fails to provide long-term therapeutic benefits and is limited to those patient who have undergone prior
surgical procedures.
Clinical utilization of FIBREL® has been reported to often result in an overall lack of
implant uniformity (i.e., “lumpiness”) and
longevity, as well as complaints of patient discomfort associated with its injection.
Therefore, in conclusion, none of the currently utilized
protein-based injectable materials appears to be totally satisfactory for the augmentation and / or repair of the subjacent
dermis and
soft tissue.
In addition, other frequently encountered difficulties with the aforementioned methodologies include non-uniformity of the injectate, unpredictable
longevity of the aesthetic effects, and a 4-6 week period of post-injection
inflammation and swelling.
However, unfortunately, these forms of treatment have all exhibited numerous disadvantages.
For example, split thickness autographs generally show limited
tissue expansion, require repeated surgical operations, and give rise to unfavorable aesthetic results.
Epidermal autographs require long periods of time to be cultured, have a low success (“take”) rate of approximately 30-48%, frequently form spontaneous
blisters, exhibit contraction to 60-70% of their original size, are vulnerable during the first 15 days of engraftment, and are of no use in situations where there is both epidermal and dermal tissue involvement.
Similarly, epidermal allografts (cultured allogenic keratinocytes) exhibit many of the limitations which are inherent in the use of epidermal autographs.
However, this too has met with limited success due to, for example,
graft rejection and unfavorable aesthetic results.
However, subsequent attempts to reproduce the living
skin equivalent using human fibroblasts and keratinocytes has met with only limited success.
However, when one (or both) of the vocal cords becomes totally or partially immobile, there is a
diminution in the voice quality due to an inability to regulate and maintain the requisite tension and proximity of the damaged cord in relation to that of the operable cord.
Vocal cord
paralysis may be caused by
cancer, surgical or mechanical trauma, or similar afflictions which render the vocal cord incapable of being properly tensioned by the constrictor muscles.
However, this procedure is now considered unacceptable due to the inability of the injected TEFLON® to close large glottic gaps, as well as its tendency to induce inflammatory reactions resulting in the formation of fibrous infiltration into the injected cord.
Moreover, removal of the injected TEFLON® may be quite difficult should it subsequently be desired or become necessary.
Although
SILASTIC® implants have proved to be superior over TEFLON® injections, there are several areas of dissatisfaction with the procedure including difficulty in the
carving and
insertion of the block, the large amount of time required for the procedure, and a lack of an efficient methodology for locking the block in place within the
thyroid cartilage.
In addition, vocal cord
edema, due to the prolonged nature of the procedure and repeated voice testing during the operation, may also prove problematic in obtaining optimal voice quality.
However, these materials have also proved to be less than ideal due to difficulties in the
sizing and shaping of the
solid implants as well as the potential for subsequent immunogenic reactions.