Quantification of Adhesiveness of Osteoblasts to Titanium Surfacesin Vitroby the Micropipette Aspiration Technique

Host inflammatory response and clinical parameters around implants in a rat model using systemic alendronate and zoledronate acid drug administrations

Implant outcomes in comparison to a natural tooth in a rat model using systemic alendronate and zoledronate acid drug administrations were assessed. Fifty-four Sprague–Dawley rats were randomly allocated into two experimental groups (drug application of zoledronic acid; 0.04 mg/kg intravenously once a week and alendronic acid; 0.2 mg/kg subcutaneously five times a week) and one control group with 18 animals in each group. Drug delivery was conducted for a period of 4 months. After 4 weeks either a zirconia or a titanium implant was immediately inserted in the socket of the first molar of the upper jaw. In vivo investigations included host inflammatory parameters and the implant survival and success rates for up to 3 months. Material incompatibilities against titanium and zirconia nanoparticles were evaluated in vitro after stimulation of rat spleen cells. In vivo, IL-6 release around titanium implants demonstrated significantly higher values in the control group (p = 0.02) when compared to the zoledronic acid group. Around the natural tooth without drug administration, the control group showed higher IL-6 values compared with the alendronic acid group (p = 0.01). In vitro, only lipopolysaccharide and not the implant’s nanoparticles stimulated significant IL-6 and TNFα production. In terms of the primary aim of in vivo and in vitro IL-6 and TNFα measurements, no implant material was superior to the other. No significant in vitro stimulation of rat spleen cells was detected with respect to titanium oxide and zirconium oxide nanoparticles.

Magnetic nanoparticles for the measurement of cell mechanics using force-induced remnant magnetization spectroscopy

Cell mechanics is a crucial indicator of cell function and health, controlling important biological activities such as cell adhesion, migration, and differentiation, wound healing, and tissue integrity. Particularly, the adhesion of cancer cells to the extracellular matrix significantly contributes to cancer progression and metastasis. Here we develop magnetic nanoparticle-based force-induced remnant magnetization spectroscopy (FIRMS) as a novel method to measure cell adhesion force. Before FIRMS experiments, interactions of magnetic nanoparticles (MNPs) with cells were investigated from a cell mechanics perspective. Subsequently adhesion force for three commonly used cancer cell lines was quantified by FIRMS. Our results indicated that the application of MNPs produced indistinguishable effects on cell viability and cell mechanical properties under experimental conditions for the FIRMS method. Then cell adhesion force was obtained, which provides force information on different cancer cell types. Our work demonstrates that MNP-based FIRMS can be applied to probe cell adhesion force and offer an alternate means for understanding cell mechanics.

Bioactivity of a sol–gel-derived hydroxyapatite coating on titanium implants in vitro and in vivo

Background

Hydroxyapatite is widely used as a coating on metallic implants to promote bioactivity. The coating is typically produced using a high temperature, resulting in phase heterogeneity and coating delamination, which may lead to failure of the coating clinically. Development of a simple and low-temperature hydroxyapatite coating technique may improve the bone bonding ability of implants.

Objectives

To investigate responses to hydroxyapatite-coated titanium produced by a newly developed sol–gel by osteoblasts in vitro and bone in vivo.

Methods

Osteoblast proliferation was characterized using a methyl thiazolyl tetrazolium assay and cell calcification with an Alizarin red S assay, and the results were compared with those of uncoated titanium. Uncoated and coated screws were inserted into the trabecular bone of New Zealand white rabbit legs. These implants were evaluated mechanically and histologically after 7, 12, and 24 weeks.

Results

Hydroxyapatite-coated titanium showed a significantly greater cell proliferation and mineralization than uncoated titanium. Extraction torques for the coated screws increased with time of implantation and were significantly greater than those of uncoated screws. We observed bone fragments attached to the surface of all coated screws after removal, but none on uncoated screws. Hematoxylin and eosin-stained bone showed no active inflammatory responses to implantation at any time examined. Bone surrounding either uncoated or coated screws followed typical remodeling stages, but maturation of bone healing was faster with coated screws.

Conclusions

The sol–gel-derived hydroxyapatite coating showed bioactivity, indicating its potential application as an alternative coating technique to improve the bone bonding ability of implants.

Cell-scaffold adhesion dynamics measured in first seconds predicts cell growth on days scale – optical tweezers study

Understanding the cell-biomaterial interface from the very first contact is of crucial importance for their successful implementation and function in damaged tissues. However, the lack of bio- and mechano-analytical methods to investigate and probe the initial processes on the interface, especially in 3D, raises the need for applying new experimental techniques. In our study, optical tweezers combined with confocal fluorescence microscopy were optimized to investigate the initial cell-scaffold contact and to investigate its correlation with the material-dependent cell growth. By the optical tweezers-induced cell manipulation accompanied by force detection up to 100 pN and position detection by fluorescence microscopy, accurate adhesion dynamics and strength analysis was implemented, where several attachment sites were formed on the interface in the first few seconds. More importantly, we have shown that dynamics of cell adhesion on scaffold surfaces correlates with cell growth on the days scale, which indicates that the first seconds of the contact could markedly direct further cell response. Such a contact dynamics analysis on 3D scaffold surfaces, applied for the first time, can thus serve to predict scaffold biocompatibility.

Effects of functionalization of PLGA-[Asp-PEG]n copolymer surfaces with Arg-Gly-Asp peptides, hydroxyapatite nanoparticles, and BMP-2-derived peptides on cell behavior in vitro

Functionalization of polymer surfaces has been recognized as a valuable tool to improve their properties that significantly influence cellular behaviors, such as adhesion, proliferation, migration, and differentiation. In stem cell-mediated bone tissue engineering, surface multifunctionalization of polymeric scaffolds with cell-adhesive, osteoconductive, and osteoinductive biomolecules is a critical strategy to improve such properties. However, the traditional surface modification techniques such as physical deposition/adsorption, chemical modification, grafting, and plasma techniques have great limitations for immobilization of multiple bioactive molecules due to multistep procedures. Recently, a universal technique based on mussel-inspired self-polymerization of dopamine is developed for multifunctional coatings in a simple way. In our study, we used this newly developed technique to incorporate three biomolecules, cell adhesion-promoting (K)16 GRGDSPC peptides, osteoconductive hydroxyapatite (HAp) nanoparticles, and osteoinductive bone morphogenetic protein-2-derived P24 peptides, to functionalize poly(lactide-co-glycolide) (PLGA)-[Asp-PEG]n scaffolds, and the effects on biological behaviors of co-cultured rabbit-derived bone marrow stromal cells in vitro were investigated. The results showed (K)16 GRGDSPC, HAp, and P24 could be immobilized onto the scaffolds through predeposition of polydopamine (pDA) ad-layer, and the surface-modified scaffolds were noncytotoxic as well as the virgin scaffold. The pDA-assisted codeposition of (K)16 GRGDSPC, HAp, and P24 on the scaffold surfaces significantly promoted cell adhesion, proliferation, osteodifferentiation, and mineralization in vitro with synergistic effects. Taken together, the functionalized PLGA-[Asp-PEG]n polymeric scaffolds achieved significantly elevated affinity, osteoconductive and osteoinductive ability, and may be a potentially promising bone graft substitute for bone repair.

Effects of titanium particle size on osteoblast functions in vitro and in vivo

The formation of titanium (Ti)-wear particles during the lifetime of an implant is believed to be a major component of loosening due to debris-induced changes in bone cell function. Radiographic evidence indicates a loss of fixation at the implant-bone interface, and we believe that the accumulation of Ti particles may act on the bone-remodeling process and impact both long- and short-term implant-fixation strengths. To determine the effects of various sizes of the Ti particles on osteoblast function in vivo, we measured the loss of integration strength around Ti-pin implants inserted into a rat tibia in conjunction with Ti particles from one of four size-groups. Implant integration is mediated primarily by osteoblast adhesion/focal contact pattern, viability, proliferation and differentiation, and osteoclast recruitment at the implant site in vivo. This study demonstrates the significant attenuation of osteoblast function concurrent with increased expression of receptor activator of nuclear factor kappaB ligand (RANKL), a dominant signal for osteoclast recruitment, which is regulated differentially, depending on the size of the Ti particle. Zymography studies have also demonstrated increased activities of matrix metalloproteinases (MMP) 2 and 9 in cells exposed to larger Ti particles. In summary, all particles have adverse effects on osteoblast function, resulting in decreased bone formation and integration, but different mechanisms are elicited by particles of different sizes.

New insight into the mechanism of hip prosthesis loosening: effect of titanium debris size on osteoblast function

The incidence of rheumatoid arthritis and osteoarthritis is on the rise due to our expanding elderly population. Total joint arthroplasty is the most successful, prevalent treatment modality for these and other degenerative hip conditions. Despite the wide array of prosthetic devices commercially available, hip prostheses share a common problem with a gradual and then accelerating loss of bone tissue and bone-implant interface integrity, followed by implant instability and loosening. Implant failure is largely the result of inevitable wear of the device and generation of wear debris. To provide information for the development of improved prosthetic wear characteristics, we examined the effects of size-separated titanium particles on bone forming cell populations. We demonstrate unequivocally that particle size is a critical factor in the function, proliferation, and viability of bone-forming osteoblasts in vitro. In addition, we have elucidated the time-dependent distribution of the phagocytosed particles within the osteoblast, indicating an accumulation of particles in the perinuclear area of the affected cells. The report finds that particle size is a critical factor in changes in the bone formation-related functions of osteoblasts exposed to simulate wear debris, and that 1.5-4 microm titanium particles have the greatest effect on osteoblast proliferation and viability in vitro. The size of titanium particles generated through wear of a prosthetic device may be an important consideration in the development of superior implant technology.

A centrifugation cell adhesion assay for high-throughput screening of biomaterial surfaces

A quantitative analysis of cell adhesion is essential in understanding physiological phenomena and designing biomaterials, implant surfaces, and tissue-engineering scaffolds. The most common cell adhesion assays used to evaluate biomaterial surfaces lack sensitivity and reproducibility and/or require specialized equipment and skill-intensive operation. We describe a modified centrifugation cell adhesion assay that uses simple and convenient techniques with standard laboratory equipment and provides reliable, quantitative measurements of cell adhesion. This centrifugation assay applies controlled and uniform detachment forces to a large population of adherent cells, providing robust statistics for quantifying cell adhesion. The applicability of this system to the design and characterization of biomaterial surfaces is shown by evaluating cell adhesion on substrates using different coating proteins, cell types, seeding times, and relative centrifugal forces (RCF). Results verify that this centrifugation cell adhesion assay represents a simple, convenient, and standard method for high-throughput characterization of a variety of biomaterial surfaces and conditions.

Cell interactions with polyelectrolyte multilayer films

The short-term interactions of chondrosarcoma cells with polyelectrolyte multilayer films built up by the alternate adsorption of poly(L-lysine) (PLL) and poly(L-glutamic acid) (PGA) was studied in the presence and in the absence of serum. The films and their interaction with serum proteins were first characterized by means of optical waveguide lightmode spectroscopy, quartz crystal microbalance, and zeta potential measurements. In a serum-containing medium, the detachment forces measured by the micropipet technique were about eight times smaller on PGA-ending than on PLL-ending films. For these latter ones, the adhesion force decreased when the film thickness increased. In a serum-free medium, the differences between the negative- and positive-ending films were enhanced: adhesion forces on PLL-ending films were 40-100% higher, whereas no cellular adherence was found on PGA-terminating films. PGA-ending films were found to prevent the adsorption of serum proteins, whereas important protein adsorption was always observed on PLL-ending films. These results show how cell interactions with polyelectrolyte films can be tuned by the type of the outermost layer, the presence of proteins, and the number of layers in the film.

Extracellular matrix cell adhesion peptides: functional applications in orthopedic materials

This review describes research on selected peptide sequences that affect cell adhesion as it applies in orthopedic applications. Of particular interest are the integrin-binding RGD peptides and heparin-binding peptides. The influence of these peptides on cell adhesion is described. Cell adhesion is defined as a sequence of four steps: cell attachment, cell spreading, organization of an actin cytoskeleton, and formation of focal adhesions. RGD sequences clearly influence cell attachment and spreading, whereas heparin-binding sequences appear to be less efficient. Collectively, these sequences appear to promote all steps of cell adhesion in certain cell types. This review also addresses issues related to peptide immobilization, as well as potential complexities that may develop as a result of using these versatile cell-binding sequences. Also described are future directions in the field concerning use of existing and more sophisticated peptide substrata.