The response of mineralizing culture systems to microtextured and polished titanium surfaces

A Multidisciplinary Journey towards Bone Tissue Engineering

Millions of patients suffer yearly from bone fractures and disorders such as osteoporosis or cancer, which constitute the most common causes of severe long-term pain and physical disabilities. The intrinsic capacity of bone to repair the damaged bone allows normal healing of most small bone injuries. However, larger bone defects or more complex diseases require additional stimulation to fully heal. In this context, the traditional routes to address bone disorders present several associated drawbacks concerning their efficacy and cost-effectiveness. Thus, alternative therapies become necessary to overcome these limitations. In recent decades, bone tissue engineering has emerged as a promising interdisciplinary strategy to mimic environments specifically designed to facilitate bone tissue regeneration. Approaches developed to date aim at three essential factors: osteoconductive scaffolds, osteoinduction through growth factors, and cells with osteogenic capability. This review addresses the biological basis of bone and its remodeling process, providing an overview of the bone tissue engineering strategies developed to date and describing the mechanisms that underlie cell-biomaterial interactions.

Wettability and pre-osteoblastic behavior evaluations of a dense bovine hydroxyapatite ceramics

In this study, the wettability, cell viability, and roughness of an experimental dense bovine hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂] ceramic block were evaluated so that, in the future, it could be used as a base material for dental implants. The results to commercial zirconia and a commercially pure titanium (Ti) alloy were compared. The surface roughness and contact angles were measured. An in vitro evaluation was conducted by means of tests in which pre-osteoblastic MC3T3-E1 cells were placed in indirect and direct contact with these materials. For cell viability, a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and crystal violet test were conducted. A qualitative analysis was conducted using variable pressure scanning electron microscopy (SEM). No statistically significant differences were observed in wettability and roughness tests among the groups. In both the MTT assay and crystal violet test, all groups demonstrated satisfactory results without cytotoxicity. SEM showed cell adhesion and cell proliferation results on the material surfaces after 24 h and 48 h. In conclusion, this dense Ca₁₀ (PO₄)₆(OH)₂ ceramic can be considered as a potential biocompatible material.

Titanium Coating of the Boston Keratoprosthesis

Purpose

We tested the feasibility of using titanium to enhance adhesion of the Boston Keratoprosthesis (B-KPro), ultimately to decrease the risk of implant-associated complications.

Methods

Cylindrical rods were made of poly(methyl methacrylate) (PMMA), PMMA coated with titanium dioxide (TiO₂) over a layer of polydopamine (PMMA_TiO2), smooth (Ti) and sandblasted (Ti_SB) titanium, and titanium treated with oxygen plasma (Ti_ox and Ti_SBox). Topography and surface chemistry were analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Adhesion force between rods and porcine corneas was measured ex vivo. Titanium sleeves, smooth and sandblasted, were inserted around the stem of the B-KPro and implanted in rabbits. Tissue adhesion to the stem was assessed and compared to an unmodified B-Kpro after 1 month.

Results

X-ray photoelectron spectroscopy demonstrated successful deposition of TiO₂ on polydopamine-coated PMMA. Oxygen plasma treatment did not change the XPS spectra of titanium rods (Ti and Ti_SB), although it increased their hydrophilicity. The materials did not show cell toxicity. After 14 days of incubation, PMMA_TiO2, smooth titanium treated with oxygen plasma (Ti_ox), and sandblasted titanium rods (Ti_SB, Ti_SBox) showed significantly higher adhesion forces than PMMA ex vivo. In vivo, the use of a Ti_SB sleeve around the stem of the B-KPro induced a significant increase in tissue adhesion compared to a Ti sleeve or bare PMMA.

Conclusions

Sandblasted titanium sleeves greatly enhanced adherence of the B-KPro to the rabbit cornea. This approach may improve adhesion with the donor cornea in humans as well.

Translational Relevance

This approach may improve adhesion with donor corneas in humans.

Differential expression of osteo-modulatory molecules in periodontal ligament stem cells in response to modified titanium surfaces

This study assessed differential gene expression of signaling molecules involved in osteogenic differentiation of periodontal ligament stem cells (PDLSCs) subjected to different titanium (Ti) surface types. PDLSCs were cultured on tissue culture polystyrene (TCPS), and four types of Ti discs (PT, SLA, hydrophilic PT (pmodPT), and hydrophilic SLA (modSLA)) with no osteoinductive factor and then osteogenic activity, including alkaline phosphatase (ALP) activity, mRNA expression of runt-related gene 2, osterix, FOSB, FRA1, and protein levels of osteopontin and collagen type IA, were examined. The highest osteogenic activity appeared in PDLSCs cultured on SLA, compared with the TCPS and other Ti surfaces. The role of surface properties in affecting signaling molecules to modulate PDLSC behavior was determined by examining the regulation of Wnt pathways. mRNA expression of the canonical Wnt signaling molecules, Wnt3a and β-catenin, was higher on SLA and modSLA than on smooth surfaces, but gene expression of the calcium-dependent Wnt signaling molecules Wnt5a, calmodulin, and NFATc1 was increased significantly on PT and pmodPT. Moreover, integrin α2/β1, sonic hedgehog, and Notch signaling molecules were affected differently by each surface modification. In conclusion, surface roughness and hydrophilicity can affect differential Wnt pathways and signaling molecules, targeting the osteogenic differentiation of PDLSCs.

Bone Physiology, Biomaterial and the Effect of Mechanical/Physical Microenvironment on MSC Osteogenesis: A Tribute to Shu Chien's 80th Birthday

Professor Shu Chien is a world-renowned leader and founder of Bioengineering. In particular, he has made seminal contributions to advancing our systematic and insightful understanding of how cells perceive their physical/mechanical environment and coordinate cellular functions. In this review, as part of a tribute to Prof. Shu Chien's scientific achievement, we summarize the research progress in understanding the physiology of bone cells interacting with different mechanical/physical environments during bone tissue regeneration/repair. We first introduce the cellular composition of the bone tissue and the mechanism of the physiological bone regeneration/repair process. We then describe the properties and development of biomaterials for bone tissue engineering, followed by the highlighting of research progresses on the cellular response to mechanical environmental cues. Finally, several latest advancements in bone tissue regeneration and remaining challenges in the field are discussed for future research directions.

Altered cell motility and attachment with titanium surface modifications

BACKGROUND

Titanium implants are widely used in dentistry to replace lost teeth. Various surface modifications have been used to improve implant retention and osseointegration. This study is designed to compare the ability of three titanium surfaces to promote cell attachment and cell motility of cells relevant to periodontal tissues.

METHODS

Three clinically relevant surfaces were tested: 1) machined titanium; 2) a titanium surface roughened through acid etching (dual thermal-etched titanium [DTET]); and 3) a titanium surface roughened with nanometer-scale calcium phosphate deposition (nanoscale calcium phosphate-impregnated titanium [NCPIT]). Cell attachment and migration were examined for four cell types: rat osteosarcoma cells, human osteoblasts, and gingival and periodontal ligament (PDL) fibroblasts.

RESULTS

All four cell types attached to each of the three titanium surfaces equally by 2 hours, and the PDL and gingival fibroblasts generally displayed less attachment than the osteosarcoma cells and osteoblasts. The cells displayed differential motility and long-term attachment to each of the titanium surfaces. Osteosarcoma cells displayed preferential motility on NCPIT, whereas PDL fibroblasts were more motile on machined titanium, and gingival fibroblasts moved more rapidly on both DTET and NCPIT. Osteoblasts displayed little motility on any of the titanium surfaces and lost viability on NCPIT after 24 hours. Gingival fibroblasts lost attachment to machined titanium.

CONCLUSIONS

Periodontal cells displayed differential motility and long-term attachment to titanium surfaces. Selective modification of titanium surface properties in various regions of an implant may be useful in guiding specific cell populations to specific locations where they might best aid in osseointegration and soft tissue remodeling.

Applications of microscale technologies for regenerative dentistry

While widespread advances in tissue engineering have occurred over the past decade, many challenges remain in the context of tissue engineering and regeneration of the tooth. For example, although tooth development is the result of repeated temporal and spatial interactions between cells of ectoderm and mesoderm origin, most current tooth engineering systems cannot recreate such developmental processes. In this regard, microscale approaches that spatially pattern and support the development of different cell types in close proximity can be used to regulate the cellular microenvironment and, as such, are promising approaches for tooth development. Microscale technologies also present alternatives to conventional tissue engineering approaches in terms of scaffolds and the ability to direct stem cells. Furthermore, microscale techniques can be used to miniaturize many in vitro techniques and to facilitate high-throughput experimentation. In this review, we discuss the emerging microscale technologies for the in vitro evaluation of dental cells, dental tissue engineering, and tooth regeneration.