Biomedical subjects

David Knaack

Publications and source records attributed to David Knaack.

3 recordsLinked to original sources

PubMed2004

Donor age and gender effects on osteoinductivity of demineralized bone matrix.

Allogeneic demineralized bone matrix (DBM) has been used extensively as a clinical graft material because of its inherent osteoinductive and osteoconductive properties. There is continued debate over the acceptable age range of donors for bone and whether the effectiveness of the tissue as a graft is influenced by gender. Contradictory evidence has been obtained with DBM prepared from both animals and humans. The goal of the present investigation was to evaluate the effect of donor age and gender on the osteoinductivity of DBM prepared from human donors [male (133) and female (115) donors grouped in 10-year age brackets up to 85 years] with a statistically relevant sample size using the athymic rat ectopic bone formation model. Among males, there was a statistically significant linear association between age and osteoinductivity value (p <.001), but not among females (p =.20). The rate of change among males was 0.009 units per year. The biological relevance of such a small change in osteoinductivity is likely to be negligible, as the total variation explained by the regressions was only 8.2%. A two-way ANOVA as related to donor age (only donors < 76 years of age) and gender yielded no significant statistical association of osteoinductivity with age group, gender, and their interaction. The results confirm that properly processed demineralized bone from donors through at least 85 years of age is a viable grafting material.

Adolescent↗

PubMed2004

Osteochondral defect repair by demineralized cortical bone matrix.

It has been reported that demineralized bone matrix (cortical or trabecular bone) contains intrinsic cytokines. In the present study, we tested allogeneic demineralized bone matrix for its capacity to resurface osteochondral defects in a rabbit model with the assumption that the intrinsic cytokines in demineralized bone matrix will facilitate the recruitment of progenitor cells from bone marrow into the defect. It was further assumed that these intrinsic bioactive factors would modulate these cells to differentiate into osteochondrogenic lineage and, thus, functionally repair the osteochondral defect. The biocompatibility of demineralized bone matrix was first tested by loading rabbit bone-marrow-derived mesenchymal stem cells into porous demineralized trabecular bone matrix that was then cultured for 3 days. The cell growth in demineralized trabecular bone matrix was examined by scanning electron microscopy. Loaded rabbit bone-marrow-derived mesenchymal stem cells attached to the trabeculae of demineralized trabecular bone matrix; some cells appeared to be round and others were spread and contacted other cells. Allogeneic rabbit demineralized cortical bone matrix or demineralized trabecular bone matrix was implanted into a full-thickness osteochondral defect in the load-bearing area of the medial femoral condyle of young adult rabbits. At 6 and 12 weeks after surgery, gross and histological examination showed that the defects were repaired up to 95% of their depth. The repair tissue using demineralized cortical bone matrix was composed of subchondral bone and a top layer of cartilage that was smooth and integrated with the adjacent cartilage in most of the specimens. Most of the repair tissue in the defect filled with demineralized trabecular bone matrix had a fibrillated surface without integration with the adjacent cartilage. These results indicate that demineralized cortical bone matrix may be potentially useful to repair osteochondral defects by managing the host's intrinsic reparative cells.

Animals↗

PubMed2002

Polymer--calcium phosphate cement composites for bone substitutes.

The use of self-setting calcium phosphate cements (CPCs) as bioresorbable bone-replacement implant materials presently is limited to non-load-bearing applications because of their low compressive strength relative to natural bone. The present study investigated the possibility of strengthening a commercially available CPC, alpha-BSM, by incorporating various water-soluble polymers into the cement paste during setting. Several polyelectrolytes, poly(ethylene oxide), and the protein bovine serum albumin (BSA) were added in solution to the cement paste to create calcium phosphate-polymer composites. Composites formulated with the polycations poly(ethylenimine) and poly(allylamine hydrochloride) exhibited compressive strengths up to six times greater than that of pure alpha-BSM material, with a maximum value reached at intermediate polymer content and for the highest molecular weight studied. Composites containing BSA developed compressive strengths twice that of the original cement at protein concentrations of 13-25% by weight. In each case, XRD studies correlate the improvement in compressive strength with reduced crystallite dimensions, as evidenced by a broadening of the (0,0,2) reflection. This suggests that polycation or BSA adsorption inhibits crystal growth and possibly leads to a larger crystal aspect ratio. SEM results indicate a denser, more interdigitated microstructure. The increased strength was attributed to the polymer's capacity to bridge between multiple crystallites (thus forming a more cohesive composite) and to absorb energy through plastic flow.

Animals↗