Biomedical subjects

David Dean

Publications and source records attributed to David Dean.

23 records · Page 2Linked to original sources

PubMed2002

Orthognathic surgery outcome analysis: 3-dimensional landmark geometric morphometrics.

Traditional cephalometric analysis of 2-dimensional (2D) landmarks has been limited to distances, indices, and angles. Quantitative results vary depending on what baseline is chosen. Geometric morphometric techniques, such as Procrustes superimposition, assume all landmarks carry equivalent information. Using these methods, landmark coordinates (x, y, z) facilitate comparison of patients and "normative"shapes and assessment of pre- to postoperative outcomes. Pre- and postoperative lateral and frontal cephalograms and stereophotograms were taken of a 48-year-old Caucasian man and a 38-year-old Caucasian woman. Coordinates of 3D hard tissue landmarks were collected directly from scanned cephalograms, and 3D soft tissue landmarks were collected onscreen. Procrustes superimpositions of pre- and postoperative 3D craniodental landmark coordinates and 3D soft tissue coordinates were made, and scatter plots were created to show the surgical shape change separately for each patient. Procrustes superimposition of the preoperative and "normative craniodental data (18-year-old male and female Bolton standards) provided both qualitative and quantitative evaluations of the patients, allowing a better determination of the required treatment. Unlike traditional baseline-dependent methods, Procrustes shape analysis produces a single useful measure of surgical shape change or comparison to normative shape.

Adult↗

PubMed2000

The brush inquiry: An opportunity to investigate health outcomes in a well-characterized cohort.

The Brush Inquiry was conducted in Cleveland, Ohio, from 1926-1942 to longitudinally document the growth and development of healthy children and adults. The Brush population was a heterogenous group with a broad representation of racial and socioeconomic groups. Data collection included radiographs of several parts of the body; motor, mental, and psychological tests; health, nutrition, and prenatal history; body measurements and family history. The early results of the inquiry were used to establish standards for normal childhood growth and development. Today, many of these subjects (88%) are in the age range of 60-80, facilitating the continuity of the inquiry to study early indicators for later health outcomes. This article reviews the origins of the inquiry, characteristics of the population, and the prospects for future research using this cohort. Am. J. Hum. Biol. 12:1-9, 2000. Copyright 2000 Wiley-Liss, Inc.

Journal Article↗

PubMedDate not supplied

Photoinitiated cross-linking of the biodegradable polyester poly(propylene fumarate). Part I. Determination of network structure.

In this work, we investigated the mechanism involved in the photoinitiated cross-linking of the polyester poly(propylene fumarate) (PPF) using the initiator bis(2,4,6-trimethylbenzoyl) phenylphosphine oxide (BAPO). It was hypothesized that BAPO has the ability to cross-link PPF into solid polymer networks, without the use of a cross-linking monomer, because two pairs of radicals, both involving a fast adding phosphinoyl radical, were formed upon UV irradiation of BAPO. Spectroscopic investigation first confirmed the addition of BAPO derived radicals to the PPF olefin. Investigations of fumarate conversion and bulk network properties were then undertaken, using the BAPO initiator and a monoacylphosphine oxide (MAPO) initiator which contains a single photolabile bond. Results show that a single BAPO phosphinoyl radical was primarily responsible for the formation of a highly cross-linked PPF network and the additional radical pair which may be formed does not dramatically alter fumarate conversion or bulk network properties. From these results, the network structure of BAPO initiated, photo-cross-linked PPF may be deduced. Finally, this study demonstrates a method for inferring cross-linked network structures by contrasting properties of bulk materials formed from similar cross-linking initiators.

Biocompatible Materials↗

PubMedDate not supplied

Photoinitiated cross-linking of the biodegradable polyester poly(propylene fumarate). Part II. In vitro degradation.

This study investigated the in vitro degradation of both solid PPF networks and porous PPF scaffolds formed by photoinitiated cross-linking of PPF polymer chains. Three formulations of scaffolds of differing porosity and pore size were constructed by varying porogen size and content. The effects of pore size and pore volume on scaffold mass, geometry, porosity, mechanical properties, and water absorption were then examined. Throughout the study, the solid networks and porous scaffolds exhibited continual mass loss and slight change in length. Porogen content appeared to have the greatest effect upon physical degradation. For example, scaffolds initially fabricated with 80 wt % porogen content lost approximately 30% of their initial PPF content after 32 weeks of degradation, whereas scaffolds fabricated with 70 wt % porogen content lost approximately 18% after 32 weeks of degradation. For all scaffold formulations, water absorption capacity, porosity, and compressive modulus were maintained at constant values following porogen leaching. These results indicate the potential of photo-cross-linked PPF scaffolds in tissue engineering applications which require maintenance of scaffold structure, strength, and porosity during the initial stages of degradation.

Biocompatible Materials↗

PubMedDate not supplied

Effect of transforming growth factor beta 2 on marrow-infused foam poly(propylene fumarate) tissue-engineered constructs for the repair of critical-size cranial defects in rabbits.

This study investigates the osseointegration of poly(propylene fumarate) (PPF) with beta-tricalcium phosphate (beta-TCP) scaffolds in a critical-size (diameter, 1.6 cm), cranial defect in 4-month-old rabbits (n = 51), killed at 6 or 12 weeks. Two molecular weights of PPF were used to produce bilayer scaffolds with 0.5-mm solid external and 2.0-mm porous internal layers. The porous layer was infused with bone marrow aspirate, with half the animals receiving 0.8 microg of transforming growth factor beta2 (TGF-beta2). No foreign body or inflammatory response was observed externally or on histological examination of explants. Statistical analysis of histological areal and linear measures of new bone formation found significantly more bone at the later sacrifice time, followed by implants receiving TGF-beta2, followed by low molecular weight PPF implants. Approximately 40% of the explants were tested for incorporation strength with a one-point "push-in" test. Because no permanent fixation was used, implant strength (28.37-129.03 N; range, 6.4 to 29.0 lb of resistance) was due entirely to new bone formation. The strongest bone was seen in implants receiving TGF-beta2-infused marrow in animals killed at 12 weeks. These results support the use of PPF as an osteogenic substrate and future research into preoperative fabrication of critical size and supercritical-size cranial prosthetic implants.

Animals↗