A CpG-rich RNA and an RNA helicase tightly associated with the DNA demethylation complex are present mainly in dividing chick embryo cells.

In the developing chicken embryo, active DNA demethylation requires both RNA and proteins (Nucleic Acids Res. 25, 2375-2380, 1997; ibid. 25, 4545-4550, 1997, FEBS Lett. 449, 251-254, 1999a). In vitro assays indicate that in the 5- and 12-day-old embryos the highest specific activity of 5-methylcytosine DNA glycosylase is found in the brain, the eyes and the skin. In situ hybridization with antisense CpG-rich RNA tightly associated to the DNA demethylation complex shows a restricted expression pattern only in proliferating tissues such as the neuroepithelia of the brain in 5-day-old embryos. The RNA is absent in differentiated tissues like the skeletal and heart muscle, liver and the crystallin-producing cells in the lens. The CpG-rich RNA is transcribed in a developmental stage-specific rather than in a cell-specific manner. In contrast transcripts of DNA methyltransferase are found in dividing and quiescent cells. In situ hybridization with a probe of a RNA helicase which is also associated with the DNA demethylation complex shows a very similar localization in mitotically active tissues as the CpG-rich RNA. The content of 5-methylcytosine in individual cells was determined with a specific monoclonal antibody and cytometric analysis on tissue sections. The results indicate that proliferating cells have on the average 15% more methylated cytosines than non-dividing cells. This represents roughly 3x10(6) more methylation sites per haploid genome.

Soft porous PTFE-composite alloplasts: tissue-bonding characteristics.

Experimental and clinical investigations over the past three decades have validated numerous hypotheses about tissue bonding of prostheses. Highly porous PTFE composite has been demonstrated to be an effective, inert, scaffold-like matrix onto which other materials can become physically bonded to achieve a tissue-specific result. Hydrophilic agents such as carbon and aluminum oxide stimulate ingrowth of fibroblasts that secrete collagen. These additives promote a robust and durable alloplast-soft tissue union composed mostly of collagen that is watertight. Bone-growth stimulants-such as hydroxyapatite-when added to highly porous PTFE stimulate tissue ingrowth and maturation that is more bone like.

Experimental development of a fixed volume, gravity draining, prosthetic urinary bladder.

A fixed volume, semi-rigid, gravity draining prosthetic urinary bladder has been developed in experimental animals. The conceptual model demands: 1) an encrustation resistant lumenal surface; 2) successful urothelial-prosthesis and bowel-prosthesis anastomoses; 3) a transcutaneous abdominal wall prosthesis that bonds with skin, muscle, bladder, and peritoneum which resists external and intraluminal bacterial challenge; and 4) an air permeable, fluid impermeable filter which allows passive filling and gravity evacuation of urine. The principles involved have been successfully tested in rodents, rabbits, swine, and dogs. To date two total alloplastic prosthetic bladders fabricated from Biolor II and Proplast have been inserted in mini-swine for 4 weeks.

Buried quasi-integrated enucleation implant of Proplast II. A preliminary report.

A preliminary report of a new design for a buried quasi-integrated implant made of Proplast II (Vitek, Inc., Houston, Texas, U.S.A.) is presented. The design is intended to combine the benefits of an integrated and buried implant.

Experience with a polymer glenoid fossa prosthesis for partial or total temporomandibular joint reconstruction.

Glenoid fossa prostheses, alone or in combination with metallic condyles, were placed in 192 joints (127 patients) for temporomandibular joint reconstruction. Anatomic requirements, material characteristics, indications, and surgical technique are presented.

Proplast stabilized stemless trapezium implant.

Forty-five stemless Proplast-covered silicone rubber trapezium implants were used in 40 patients after trapeziectomy for either osteoarthritis, rheumatoid arthritis, or trauma. Three implants were later removed from two patients because of traumatic dislocations. One implant was removed from a patient after trauma because of persistent pain. Five patients were followed from 40 to 44 months; nine patients were followed from 31 to 39 months; 15 patients were followed from 20 to 29 months; six patients were followed from 14 to 19 months; five patients were followed from 6 to 9 months. The average follow-up time was 24 7/10 months. Before surgery 5% of the patients had continuous spontaneous pain, 35% of the patients had pain with all motion, and 60% of the patients had pain with limited normal daily use. At this time of our report, 65% of the patients are without symptoms, 21% of the patients have slight intermittent pain, and 14% of the patients have pain with strenuous use only. Tripod pinch improved 243% in male patients and 113% in female patients. All patients have good circumduction and metacarpophalangeal (MP) and interphalangeal (IP) joint motion. The stemless feature permits relatively free metacarpal joint motion without great stress being applied to the capsule that is covering the implant.

A comparison of porous composite PTFE/graphite and PTFE/aluminum oxide facial implants in primates.

Comparison of tissue ingrowth density values for Proplast I and its aluminum oxide analog, Proplast II, when implanted on the primate infraorbital rim and inferior border of the mandible, showed no difference between the two test materials. A similar comparison of local cellular response ratings showed slightly less response to Proplast II. Microscopic and clinical examination did not otherwise reveal any significant differences in biologic reaction to these materials.

Growth of tissue into a porous, low modulus coating on intramedullary nails: an experimental study.

The ingrowth of tissue into a coating of inert, highly porous, low-modulus composite of polytetrafluorethylene polymer and pyrolytic graphite on four-fluted intramedullary nails was used for stabilization of middiaphyseal femoral osteotomies and examined by microangiography. The observations were correlated with information obtained by histologic, microradiographic and tetracycline fluorescence technology. There was rapid healing of the osteotomy. The coating was invaded throughout by blood vessels and fibrous tissue. Invasion by bone was negligible. The composite thus appeared to retain its initial flexibility when implanted into the femoral intramedullary cavity. The force to distract both coated and uncoated nails was measured on intact femora. The unit retention strength increased to an average of 6.3 kg/cm2 up to 24 weeks, which is consistent with reported values. The composite would thus appear to have potential use as a coating for endoprostheses to produce enduring physiologic fixation.

Obliteration of traumatically induced articular surface defects using a porous implant.

Trauma to articular surfaces penetrating through the subchondral bone can result in areas of incomplete healing. Intraarticular adhesions can originate from these loci of disorganized fibrous bone and cartilage and, along with the incongruous surface, limit motion. In a group of 28 white New Zealand rabbits, 44 standard size defects were created in the prepatellar intercondylar femoral grooves. Twenty-seven were filled with Proplast, a porous implant material. Seventeen were left as controls. The animals were killed at intervals from 3 to 51 weeks. The implant areas were studied grossly and histologically. Granulation outgrowth and adhesions were not seen. From 12 weeks on, normal-appearing hyaline cartilage covered the surface, and bone ingrowth was found within the implant.