Abstract

Bone induction by different calcium phosphate biomaterials has been reported previously. With regard to (1) whether the induced bone would disappear with time due to the absence of mechanical stresses and (2) whether this heterotopically formed bone would give rise to uncontrolled growth, a long-time investigation of porous hydroxyapatite ceramic (HA), porous biphasic calcium phosphate ceramic (TCP/HA, BCP), porous α-tricalcium phosphate ceramic (α-TCP) and porous β-tricalcium phosphate ceramic (β-TCP) was performed in dorsal muscles of dog, for 2.5 years. Histological observation, backscattered scanning electron microscopy observation and histomorphometric analysis were made on thin un-decalcified sections of retrieved samples. Normal compact bone with bone marrow was found in all HA implants (n=4) and in all BCP implants (n=4), 48±4% pore area was filled with bone in HA implants and 41±2% in BCP implants. Bone-like tissue, which was a mineralised bone matrix with osteocytes but lacked osteoblasts and bone marrow, was found in all β-TCP implants (n=4) and in one of the four α-TCP implants. Both normal bone and bone-like tissues were confined inside the pores of the implants. The results show that calcium phosphate ceramics are osteoinductive in muscles of dogs. Although the quality and quantity varied among different ceramics, the induced bone in both HA and BCP ceramics did neither disappear nor grow uncontrollably during the period as long as 2.5 years.

Abstract

The biological performance of biomaterials is strongly influenced by their protein adsorption characteristics, which are related to the structures and properties of both the biomaterial and the protein. In the present study two groups of hydroxyapatite (HA) and biphasic calcium phosphate (BCP) ceramic powders were fabricated by different drying processes. The roles of the phase composition and microstructure of the powders in the adsorption of various model proteins were evaluated. The experimental results showed that BCP always had a higher ability to adsorb fibrinogen, insulin or type I collagen (Col-I) than HA. The microporosity and micropore size of the CaP particles also had a strong impact on their protein adsorption characteristics. HA and BCP particles with higher microporosities and/or more micropores >20 nm in diameter could adsorb more fibrinogen or insulin. However, amounts of adsorbed Col-I were largely unaffected by the microstructure of HA and BCP particles.

Abstract

The protein/biomaterial interactions of three biomaterials used in hard tissue surgery were studied in vitro. A dynamic flow system and two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) were used to investigate the adsorption of proteins from diluted human plasma on hydroxyapatite, alumina and zirconia, with regard to total protein binding capacity, relative binding capacity for specific proteins and flow-through and desorption patterns. The ceramics were characterized regarding physico-chemical properties; namely, chemical composition by elementary analyses and specific surface, pore volume and pore size distribution using the BET-method and Hg-porosimetry.

The materials were found to adsorb a surprisingly low amount of plasma proteins, leaving more than 70% of the surface free. The cellular response will therefore be highly affected by the physico-chemical properties of the material, in contrast to a surface fully covered with proteins. Regarding the adsorption of proteins, most proteins exhibited similar flow-through patterns on the three adsorbents. The exceptions with different flow-through patterns were apolipoprotein D (Apo D), apolipoprotein J (Apo J), complement factor C1s (C1s), complement factor C3 (C3), ceruloplasmin, fibrinogen, α₁ B glycoprotein and α₂ HS glycoprotein and serum retinal-binding protein (SRBP). The role of these proteins on acceptance or rejection of implants has to be investigated.

Abstract

Bone tissue engineering is a promising alternative to bone grafting. Scaffolds play a critical role in tissue engineering. Composite scaffolds made of biodegradable polymers and bone mineral-like inorganic compounds have been reported to be advantageous over plain polymer scaffolds by our group and others. In this study, we compared cellular and molecular events during the early periods of osteoblastic cell culture on poly(l-lactic acid)/hydroxyapatite (PLLA/HAP) composite scaffolds with those on plain PLLA scaffolds, and showed that PLLA/HAP scaffolds improved cell survival over plain PLLA scaffolds. Most cells (MC3T3-E1) on PLLA/HAP scaffolds survived the early culture. In contrast, about 50% of the cells initially adhered to the plain PLLA scaffolds were detached within the first 12 h and showed characteristics of apoptotic cell death, which was confirmed by TUNEL staining and caspase-3 activation. To investigate the mechanisms, we examined the adsorption of serum protein and adhesion molecules to the scaffolds. The PLLA/HAP scaffold adsorbed more than 1.4 times of total serum protein and much greater amounts of serum fibronectin and vitronectin than pure PLLA scaffolds. Similarly, significantly larger amounts of individual adhesion proteins and peptides (fibronectin, vitronectin, RGD, and KRSR) were adsorbed on the PLLA/HAP scaffolds than on the PLLA scaffolds, which resulted in higher cell density on the PLLA/HAP scaffolds. Furthermore, β1 and β3 integrins and phosphorylation of Fak and Akt proteins in the cells on the PLLA/HAP scaffolds were significantly more abundent than those on PLLA scaffolds, which suggest that enhanced adsorption of serum adhesion proteins to PLLA/HAP scaffolds protect the cells from apoptosis possibly through the integrin–FAK–Akt pathway. These results demonstrate that biomimetic composite scaffolds are advantageous for bone tissue engineering.

Two types of hydroxyapatite (HA) ceramic particles were respectively fabricated by conventional and microwave sintering processes. The conventionally sintered HA was abbreviated as HACS, and the microwave sintered one was HAMS. The phase compositions, surface morphologies and zeta potentials of both particles were respectively analyzed with X-ray diffraction (XRD), scanning electron microscope (SEM) and zetasizer. Bovine serum albumin (BSA) and lysozyme (LSZ) were selected as models to study their adsorption behaviors on HACS and HAMS. Results confirm that both HA particles crystallize completely, but HACS has larger crystal grain size than HAMS. Although both HACS and HAMS show negative surface zeta potentials in phosphate buffered saline (PBS, pH 7.4), the former has higher absolute value than the latter. Besides, both HA particles exhibit different adsorption ability for BSA and LSZ, and HACS adsorbs fewer BSA but more LSZ than HAMS. The microwave sintering can be a good method to produce nano-HA ceramics with excellent bioactivity.

以常规马弗炉和微波烧结两种方式分别制备羟基磷灰石陶瓷颗粒, 对其相组成、微观形貌、表面zeta电位以及蛋白吸附行为进行分析对比. 结果显示, 尽管两种烧结方式制备的羟基磷灰石陶瓷颗粒具有相同的相组成, 但是它们的微观结构、表面zeta电位和蛋白吸附行为存在明显差异. 相对于常规烧结, 微波烧结得到的颗粒具有丰富的微孔隙和接近于纳米尺度的晶粒尺寸, 其表面zeta电位值更小, 能够吸附更多的牛血清白蛋白和更少的溶菌酶. 微波烧结在制备高生物活性纳米羟基磷灰石陶瓷上可能是一种较为理想的方法.