The present study was designed to investigate the local microenvironment of octacalcium phosphate in a granule form upon biomolecules adsorption utilizing an indicator-immobilized-gel-sheet for measuring pH. We previously showed that octacalcium phosphate enhances bone regeneration during its progressive hydrolysis into hydroxyapatite if implanted in bone defects. The gel-sheet was made from a photocrosslinkable prepolymer solution, which can easily immobilize a pH indicator (bromothymol blue; BTB) in the hydrogel. The indicator-immobilized-gel-sheet was mounted on a biochip which was made of polydimethylsiloxane (PDMS) with a flow channel. The pH value was calculated by detecting the color changes in the gel-sheet and displayed as the pH distribution. After pre-adsorption of bovine albumin, β-lactoglobuline or cytochrome C onto octacalcium phosphate granules, the granules with the gel-sheet were further incubated in Tris-HCl buffer solution in the absence or presence of fluoride, known as an accelerator of octacalcium phosphate hydrolysis. pH values of the gel-sheet surrounding octacalcium phosphate granules showed a decrease from pH 7.4 to 6.6 in relation to the proteins adsorbed. Overall, the proposed pH-sensitive gel can be used to detect the pH around octacalcium phosphate granules with a high spatial resolution.
MonfouletLEBecquartPMarchatD. The pH in the microenvironment of human mesenchymal stem cells is a critical factor for optimal osteogenesis in tissue-engineered constructs. Tissue Eng Part A2014; 20: 1827–1840.
2.
RazaqSWilkinsRJUrbanJP. The effect of extracellular pH on matrix turnover by cells of the bovine nucleus pulposus. Eur Spine J2003; 12: 341–349.
3.
WaldmanSDCoutoDCOmelonSJ. Effect of sodium bicarbonate on extracellular pH, matrix accumulation, and morphology of cultured articular chondrocytes. Tissue Eng2004; 10: 1633–1640.
4.
ShikinamiYOkunoM. Bioresorbable devices made of forged composites of hydroxyapatite (HA) particles and poly-L-lactide (PLLA): Part I. Basic characteristics. Biomaterials1999; 20: 859–877.
5.
ChowLC. Next generation calcium phosphate-based biomaterials. Dent Mater J2009; 28: 1–10.
6.
ToyaHItoAFujimoriH. In vitro estimation of calcium phosphate with pH-controlled simulated body fluid. Transact-Mater Res Soc Japan2001; 26: 1247–1250.
7.
MiyatakeNKishimotoKNAnadaT. Effect of partial hydrolysis of octacalcium phosphate on its osteoconductive characteristics. Biomaterials2009; 30: 1005–1014.
8.
OgoseAKondoNUmezuH. Histological assessment in grafts of highly purified beta-tricalcium phosphate (OSferion (R)) in human bones. Biomaterials2006; 27: 1542–1549.
9.
BrownWESmithJPLehrJR. Octacalcium phosphate and hydroxyapatite: crystallographic and chemical relations between octacalcium phosphate and hydroxyapatite. Nature1962; 196: 1050–1055.
10.
CraneNJPopescuVMorrisMD. Raman spectroscopic evidence for octacalcium phosphate and other transient mineral species deposited during intramembranous mineralization. Bone2006; 39: 434–442.
11.
ImaizumiHSakuraiMKashimotoO. Comparative study on osteoconductivity by synthetic octacalcium phosphate and sintered hydroxyapatite in rabbit bone marrow. Calcified Tissue Int2006; 78: 45–54.
SuzukiO. Octacalcium phosphate (OCP)-based bone substitute materials. Japan Dental Sci Rev2013; 49: 58–71.
14.
SuzukiOKamakuraSKatagiriT. Bone formation enhanced by implanted octacalcium phosphate involving conversion into Ca-deficient hydroxyapatite. Biomaterials2006; 27: 2671–2681.
15.
SuzukiONakamuraMMiyasakaY. Bone formation on synthetic precursors of hydroxyapatite. Tohoku J Exp Med1991; 164: 37–50.
16.
SuzukiOYagishitaHYamazakiM. Adsorption of bovine serum-albumin onto octacalcium phosphate and its hydrolyzates. Cell Mater1995; 5: 45–54.
17.
SuzukiOKamakuraSKatagiriT. Surface chemistry and biological responses to synthetic octacalcium phosphate. J Biomed Mater Res B Appl Biomater2006; 77: 201–212.
18.
NishikawaRAnadaTIshiko-UzukaR. Osteoblastic differentiation of stromal ST-2 cells from octacalcium phosphate exposure via p38 signaling pathway. Dent Mater J2014; 33: 242–251.
19.
HirayamaBAnadaTShiwakuY. Immune cell response and subsequent bone formation induced by implantation of octacalcium phosphate in a rat tibia defect. RSC Adv2016; 6: 57475–57484.
20.
TakamiMMochizukiAYamadaA. Osteoclast differentiation induced by synthetic octacalcium phosphate through receptor activator of NF-kappa B ligand expression in osteoblasts. Tissue Eng Part A2009; 15: 3991–4000.
21.
WangXGSuzawaTMiyauchiT. Synthetic octacalcium phosphate-enhanced reparative dentine formation via induction of odontoblast differentiation. J Tissue Eng Regen Med2015; 9: 1310–1320.
22.
KanekoHKamiieJKawakamiH. Proteome analysis of rat serum proteins adsorbed onto synthetic octacalcium phosphate crystals. Anal Biochem2011; 418: 276–285.
23.
SuzukiONakamuraMMiyasakaY. Maclura pomifera agglutinin-binding glycoconjugates on converted apatite from synthetic octacalcium phosphate implanted into subperiosteal region of mouse calvaria. Bone Miner1993; 20: 151–166.
24.
KimHMHimenoTKokuboT. Process and kinetics of bonelike apatite formation on sintered hydroxyapatite in a simulated body fluid. Biomaterials2005; 26: 4366–4373.
25.
SakaiSAnadaTTsuchiyaK. Comparative study on the resorbability and dissolution behavior of octacalcium phosphate, beta-tricalcium phosphate, and hydroxyapatite under physiological conditions. Dent Mater J2016; 35: 216–224.
26.
HwangEYPappasDJeevarajanAS. Evaluation of the paratrend multi-analyte sensor for potential utilization in long-duration automated cell culture monitoring. Biomed Microdevice2004; 6: 241–249.
27.
LiCYZhangXBHanZX. A wide pH range optical sensing system based on a sol-gel encapsulated amino-functionalized corrole. Analyst2006; 131: 388–393.
28.
PoolerPMWahlMLRabinowitzAB. pH measurement: a comparison of results using glass membrane electrodes vs solid-state electrodes as a function of solution composition. Anal Biochem1998; 256: 238–240.
29.
SilverIA. Measurement of pH and ionic composition of pericellular sites. Philos Trans R Soc Lond B Biol Sci1975; 271: 261–272.
30.
KirchhofKAndarAYinHB. Polyelectrolyte multilayers generated in a microfluidic device with pH gradients direct adhesion and movement of cells. Lab Chip2011; 11: 3326–3335.
31.
WuMHLinJLWangJ. Development of high throughput optical sensor array for on-line pH monitoring in micro-scale cell culture environment. Biomed Microdevice2009; 11: 265–273.
32.
KlaukeNMonaghanPSinclairG. Characterisation of spatial and temporal changes in pH gradients in microfluidic channels using optically trapped fluorescent sensors. Lab Chip2006; 6: 788–793.
33.
MaruyamaHAraiFFukudaT. On-chip pH measurement using functionalized gel-microbeads positioned by optical tweezers. Lab Chip2008; 8: 346–351.
34.
NomuraSNakaoMNakanishiT. Real-time imaging of microscopic pH distribution with a two-dimensional pH-imaging apparatus. Anal Chem1997; 69: 977–981.
35.
MaruyamaHFukudaTAraiF. Functional gel-microbead manipulated by optical tweezers for local environment measurement in microchip. Microfluid Nanofluid2009; 6: 383–390.
36.
SternHEfrosB. Adaptive color space switching for tracking under varying illumination. Image and Vision Comput2005; 23: 353–364.
37.
HondaYKamakuraSSasakiK. Formation of bone-like apatite enhanced by hydrolysis of octacalcium phosphate crystals deposited in collagen matrix. J Biomed Mater Res B2007; 80 b: 281–289.
38.
MorenoECKresakMZahradniR. Fluoridated hydroxyapatite solubility and caries formation. Nature1974; 247: 64–65.
39.
FowlerBOMorenoECBrownWE. Infra-red spectra of hydroxyapatite, octacalcium phosphate and pyrolysed octacalcium phosphate. Archive Oral Biol1966; 11: 477–492.
40.
ShiwakuYAnadaTYamazakiH. Structural, morphological and surface characteristics of two types of octacalcium phosphate-derived fluoride-containing apatitic calcium phosphates. Acta Biomater2012; 8: 4417–4425.
41.
SugeTIshikawaKMatsuoT. Changes in the crystallinity of hydroxyapatite powder and structure of enamel treated with several concentrations of ammonium hexafluorosilicate. Am J Dent2012; 25: 299–302.
42.
IijimaMNelsonDGPanY. Fluoride analysis of apatite crystals with a central planar OCP inclusion: concerning the role of F− ions on apatite/OCP/apatite structure formation. Calcif Tissue Int1996; 59: 377–384.
43.
TungMSTomazicBBrownWE. The effects of magnesium and fluoride on the hydrolysis of octacalcium phosphate. Arch Oral Biol1992; 37: 585–591.
44.
LeeWKKoJSKimHM. Effect of electrostatic interaction on the adsorption of globular proteins on octacalcium phosphate crystal film. J Colloid Interf Sci2002; 246: 70–77.
45.
WenHBde WijnJRvan BlitterswijkCA. Incorporation of bovine serum albumin in calcium phosphate coating on titanium. J Biomed Mater Res1999; 46: 245–252.
46.
PetersTJr. Serum albumin. Adv Protein Chem1985; 37: 161–245.
47.
McKenzieHASawyerWH. Effect of pH on beta-lactoglobulins. Nature1967; 214: 1101–1104.
48.
SegalMSBeemE. Effect of pH, ionic charge, and osmolality on cytochromec-mediated caspase-3 activity. Am J Physiol Cell Physiol2001; 281: C1196–C1204.
49.
ShiwakuYHondaYAnadaT. Analysis of physicochemical properties of octacalcium phosphate prepared by hydrolysis and co-precipitation with fluoride ions. J Ceram Soc Japan2010; 118: 402–405.
