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D Christiansen

Publications and source records attributed to D Christiansen.

9 recordsLinked to original sources
PubMed1991

Use of collagen film as a dural substitute: preliminary animal studies.

Cadaver grafts, laminated metallic materials, and synthetic fabrics have been evaluated as dural substitutes. Use of cadaver tissues is limited by fear of transmission of infectious disease while use of synthetic materials is associated with implant encapsulation and foreign body reactions. The purpose of this study is to evaluate the use of collagen film as a dural substitute. Collagen films prepared from bovine skin were used to replace the dura of rabbits and histological observations were made at 16, 28, 42, and 56 days postimplantation. Controls consisted of dura that was removed and then reattached. Control dura showed no signs of inflammation or adhesion to underlying tissue at 16 and 28 days postimplantation. By 56 days postimplantation, extensive connective tissue deposition was observed in close proximity to adjacent bone as well as pia arachnoid adhesions. Implanted collagen film behaved in a similar manner to control dura showing minimal inflammatory response at all time periods. At 56 days postimplantation collagen film appeared strongly infiltrated by connective tissue cells that deposited new collagen. The results of this study suggest that a reconstituted type I collagen film crosslinked with cyanamide acts as a temporary barrier preventing loss of fluid and adhesion formation. It is replaced after approximately 2 months with host collagen with limited inflammatory and fibrotic complications. Further studies are needed to completely characterize the new connective tissue formed as well as long-term biocompatibility and functioning of a reconstituted collagen dural substitute.

Animals↗
PubMed1989

Development of a reconstituted collagen tendon prosthesis. A preliminary implantation study.

A reconstituted collagen tendon prosthesis was developed and implanted in rabbit Achilles tendons. The prosthesis was prepared by extruding type-I collagen into fibers and crosslinking it either with glutaraldehyde or with dehydrothermal treatment followed by exposure to carbodiimide. A tendon prosthesis was assembled by coating a longitudinal array of the fibers with uncrosslinked collagen. In one leg of the rabbit, the Achilles tendon was replaced with the synthetic tendon; in the contralateral leg of the animal, the tendon was excised, devascularized, and anastomosed as an autogenous graft. The autogenous tendon grafts were seen to be infiltrated centrally by fibroblasts and capillaries ten weeks postoperatively and to have been partially replaced by repair tissue twenty weeks postoperatively. Three weeks after implantation, all collagen implants were noted to have been infiltrated with fibrous tissue. At ten weeks, reorganization of collagenous tissue was observed in and around the prostheses, and the carbodiimide-crosslinked implants had been resorbed and replaced by normal-appearing neotendon. The implants that had been treated with glutaraldehyde were resorbed more slowly and were surrounded by more inflammatory cells, compared with the prostheses that had been treated with carbodiimide. Neotendon in the glutaraldehyde-treated prostheses matured more slowly. When the implants were examined at intervals after the operation, their mechanical properties approached those of fresh tendon. The initial strength of the carbodiimide-treated implants was lower than that of the fresh autogenous grafts. Twenty weeks after implantation, the strength and modulus of the carbodiimide-treated implants approached those of fresh tendon.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Achilles tendon replacement by a collagen fiber prosthesis: morphological evaluation of neotendon formation.

Reconstituted type I collagen was processed into fibers which were subsequently severely dehydrated and cyanamide cross-linked. Fibers prepared by this method were stronger and more resistant to degradation than uncrosslinked fibers. When used as a tendon replacement prosthesis, morphological events occurred which were observed by light, scanning, transmission electron microscopy and electron histochemistry. Resorption was the initial host response to the prosthesis and involved gradual biodegradation. Formation of a host-replacement tendon was the second response. Increased collagen fibril diameters and a transition in the proteoglycan/collagen fibril interactions occurred in the newly developing connective tissue between 3 and 10 weeks postimplantation. These extracellular matrix transitions were major events occurring during wound healing and led to the assembly of a mature connective tissue. When used as a tendon prosthesis, these collagen fibers rapidly resorb while allowing simultaneous formation of aligned connective tissue. The fibers may have other applications in the fields of Orthopaedic Surgery, Neurosurgery and Biomaterials Research.

Achilles Tendon↗
PubMed1988

Mechanical properties of septal cartilage homografts.

The compressive mechanical properties of untreated and chemically and physically treated nasal septum homografts were determined. Mechanical properties of control, saline-, thimerosal (Merthiolate)- and Alcide-treated specimens were similar. At high strains, the stiffness of treated cartilage ranged from 12.8 to 22.5 MPa and was unaffected by storage time. In comparison, irradiated and freeze-dried nasal septum exhibited stiffnesses of 35 and 37.5 MPa, respectively, after approximately 1 month of storage. These values of stiffness were significantly different from controls at a 0.95 confidence level. On the basis of these results, it was concluded that Alcide and Merthiolate treatment did not alter the compressive mechanical properties of cartilage and that a combination of these treatments may adequately sterilize and preserve nasal septum homografts.

Adolescent↗
PubMed1988

Clinical applications of electron microscopy in the analysis of collagenous biomaterials.

Scanning and transmission electron microscopy are of clinical value in assessing the interaction between biomaterials and ingrowing tissues. Ultrastructural information allows the clinician and biomaterials specialist to determine events occurring during wound healing and the biocompatibility of prosthetic devices. This paper reviews some of the experimental and clinical studies done in our laboratory on the use of natural and reconstituted collagen as replacements for connective tissues. Consideration is given to collagen flakes used for the treatment of dermal ulcers, a collagen fiber prosthesis used for tendon and ligament replacement, the effects of chemical preservatives on cartilage used for replacement of tissues during plastic surgery and the growth and orientation of nerve cells on reconstituted collagen fibers. Our results show that reconstituted collagen can be prepared into prosthetic devices which encourage cell attachment and orientation thereby facilitating healing of injured tissues. Furthermore chemical preservation of cartilagenous tissues kills chondrocytes resulting in eventual resorption by inflammatory cells.

Biocompatible Materials↗
PubMed1986

Customary diet, anthropometry, and dyslipoproteinemia in selected North American populations. The Lipid Research Clinics Program Prevalence Study.

The intake of nutrients, determined by 24 hr diet recall, and body measurements were obtained in 8250 free-living white study participants divided into 20 to 49 and 50 + age groups for males and female nonusers and users of gonadal hormones. They were classified into dyslipoproteinemia (DLP) phenotypes: hyperHDL, hypoHDL, IIA, hpypoLDL, IV, and normal. The dyslipoproteinemia DLP phenotypes, compared with the normal, had biologically meaningful differences in nutrient intake and indexes of obesity that were most marked for males aged 20 to 49 years as shown in the table (below). Those with the hyperHDL phenotype were thinner and ingested more energy and more alcohol and less carbohydrate as percent kilocalories (%kcal). Individuals classified as hypoHDL were fatter and tended to ingest less energy and less alcohol as %kcal. Persons with the type II phenotype were fatter and ingested less energy. Those with hypoLDL tended to be thinner and ingested more energy. Individuals with the type IV phenotype were fatter, ingested less energy and carbohydrate and more alcohol as %kcal. Similar trends were observed in female nonusers of hormones aged 20 to 49 and to a lesser extent in the 50 + age groups and in female users of hormones. Dietary protein, cholesterol, total fat, and polyunsaturated and saturated fatty acids had no consistent associations with DLP phenotype, and sucrose and starch had no association independent of total carbohydrate. This is the first evidence of an association of customary diet and DLP phenotypes in the free-living population. Equating energy intake with energy expenditure, persons with the high-risk phenotypes, IIA, IV, and hypoHDL, compared with the normal, had decreased energy expenditure and were fatter, whereas those with the low-risk phenotypes, hyperHDL and hypoLDL, had increased energy expenditure and were thinner.

Adult↗
PubMed1974

Dignity in aging.

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Adaptation, Psychological↗