Frei modellierbare Hydroxylapatit-Kollagen-Komposite zur Sanierung oss�rer Defekte

An update on hydroxyapatite/collagen composites: What is there left to say about these bioinspired materials?

Hydroxyapatite (HAp)/collagen-based composite materials have been a constant in the development of bioinspired materials for bone tissue engineering. The most fundamental research works focus on combining HAp, due to its chemical similarity with the mineral component of bones, and collagen, which is the most abundant protein in the body. Modern studies have explored different two-dimensional (2D) and 3D structures, in order to obtain biomaterials with specific physicochemical, mechanical, and biological characteristics that can be applied in distinct biomedical applications. However, as there is already so much work developed with these materials, it is crucial to question: what can still be done? What is the importance of current know-how for the future of bioinspired materials? In this paper we intend to review and update the available methodologies to synthesize HAp/collagen composites, along with their characteristics. In addition, the future of these materials in terms of applications and their potential as a cutting-edge technology is discussed.

Buccal fat pad versus sandwich graft for treatment of oroantral defects: A comparison

AIM

To compare the efficacy of buccal fat pad (BFP) graft with sandwich graft (hydroxyapatite crystals embedded within collagen sheath) in closure of oroantral defects.

MATERIALS AND METHODS

A 2-year prospective study was conducted; 20 patients were included in the study were divided into two groups having 10 patients in each. Group I patients underwent surgical closure of oroantral fistula with sandwich graft and Group II patients with buccal pad of fat.

RESULTS

In Group I, the mean pain scores were 7.60 ± 0.84, 3.90 ± 1.10, 2.30 ± 1.16, 1.10 ± 0.99 and 0.40 ± 0.70 at immediate post-op., 1, 3, 6 and 12 week time intervals, respectively, whereas in Group II these were 7.30 ± 0.67, 3.50 ± 0.53, 1.70 ± 0.48, 1.00 ± 0.47 and 0.30 ± 0.48, respectively, at the corresponding time intervals. In Group I, swelling was seen to be present in 10 (100%), 7 (70%), 2 (20%) and nil (0%) patients at 1, 3, 6 and 12 weeks, respectively, whereas in Group II, it was seen to be present in 10 (100%), 10 (100%), 2 (20%) and nil (0%) patients at the corresponding time intervals. At 1 week, infection was seen to be present in 1 (10%) patient of Group I and 2 (20%) patients of Group II. At 3 and 6 weeks, infection was seen to be present in 1 (10%) patient of Group I and none of the patients of group II. No radiologic evidence of bone formation was seen in either group up to 1 week. At 3 week interval, there were 6 (60%) patients in Group I and nil (0%) in Group II showing bone formation, thus showing a statistically significant difference between the two groups. By 6 week time interval, radiologic evidence of bone formation was seen in 9 (90%) patients of Group I but in no patients of Group II, thereby showing a statistically very highly significant (P < 0.001) difference between the two groups. In Group I, in 1 (10%) patient, graft was rejected by first week; however, no further graft rejection took place. In Group II, no case of graft rejection was reported.

CONCLUSIONS

The sandwich graft technique yielded a more promising closure of oroantral communication by provision of a more biologically apt base in terms of regeneration of lost bone structure at the floor of the maxillary sinus.

Influence of different modifications of a calcium phosphate bone cement on adhesion, proliferation, and osteogenic differentiation of human bone marrow stromal cells

Collagen and noncollagenous proteins of the extracellular bone matrix are able to stimulate bone cell activities and bone healing. The modification of calcium phosphate bone cements used as temporary bone replacement materials with these proteins seems to be a promising approach to accelerate new bone formation. In this study, we investigated adhesion, proliferation, and osteogenic differentiation of human bone marrow stromal cells (hBMSC) on Biocement D/collagen composites which have been modified with osteocalcin and O-phospho-L-serine. Modification with osteocalcin was carried out by its addition to the cement precursor before setting as well as by functionalization of the cement samples after setting and sterilization. hBMSC were cultured on these samples for 28 days with and without osteogenic supplements. We found a positive impact especially of the phosphoserine-modifications but also of both osteocalcin-modifications on differentiation of hBMSC indicated by higher expression of the osteoblastic markers matrix metalloproteinase-13 and bone sialo protein II. For hBMSC cultured on phosphoserine-containing composites, an increased proliferation has been observed. However, in case of the osteocalcin-modified samples, only osteocalcin adsorbed after setting and sterilization of the cement samples was able to promote initial adhesion and proliferation of hBMSC. The addition of osteocalcin before setting results in a finer microstructure but the biological activity of osteocalcin might be impaired due to the sterilization process. Thus, our data indicate that the initial adhesion and proliferation of hBMSC is enhanced rather by the biological activity of osteocalcin than by the finer microstructure.

Heparin modification of calcium phosphate bone cements for VEGF functionalization

A promising strategy to promote angiogenesis within an engineered tissue is the local and sustained delivery of an angiogenic factor by the substitute itself. Recently, we reported on functionalization of Biocement D (BioD) and several modifications of this calcium phosphate bone cement with vascular endothelial growth factor (VEGF). Maintenance of biological activity of VEGF after release from the cement was improved by modification of BioD with mineralized collagen type I (BioD/coll). However, BioD/coll composites showed a higher initial burst of VEGF release than do the unmodified BioD. In the present study, VEGF release from BioD/coll composites modified with different amounts of heparin was investigated. We found a distinct reduction of the initial burst of release by adding heparin in a concentration-dependent manner. Moreover, the heparin modification had a positive impact on the biological activity of released VEGF. An advancement of biological properties of BioD/coll by addition of heparin was further shown by improved adhesion of endothelial cells on the cement surface. Characterization of material properties of the heparin-modified BioD/coll composites revealed a finer microstructure with smaller HA-particles and a higher specific surface area than heparin-free BioD/coll. However, higher amounts of heparin resulted in a reduced compressive strength. The rheological properties of these cement pastes have been found to be favorable for good handling particularly with regard to their clinical application.

Calcium phosphate bone cements, functionalized with VEGF: release kinetics and biological activity

Calcium phosphate bone cements are of great interest for bone replacement since the nanocrystalline structure allows their remodelling into native bone tissue. A strategy to accelerate vascularization of the implant region is the functionalization with vascular endothelial growth factor (VEGF), which is known to mediate angiogenesis in vivo. In this study, the release of recombinant human VEGF (rhVEGF(165)) following physical adsorption to Biocement D (BioD) and several modifications were investigated. Our data demonstrate a high VEGF binding capacity of BioD and a sustained release with a moderate initial burst. A proliferation assay using endothelial cells revealed maintenance of biological activity of VEGF after release from BioD. Release behavior of BioD was not improved by modification with mineralized collagen type I, as well as with a combination of mineralized collagen with O-phospho-L-serine and sodium citrate, respectively. In contrast, a positive impact of these modifications on the activity of released VEGF was observed; in case of the phosphoserine- and sodium citrate-modified cements, the biological efficacy of released VEGF was even higher than that of nonreleased control VEGF. We conclude that the bone implant material BioD and, especially, the phosphoserine modification may support activation of angiogenesis by delivery of VEGF in a local and sustained manner.