With the development of three-dimensional (3D) printed technology, 3D printed alloy implants, especially titanium alloy, play a critical role in biomedical fields such as orthopedics and dentistry. However, untreated titanium alloy implants always possess a bioinert surface that prevents the interface osseointegration, which is necessary to perform surface modification to enhance its biological functions. In this article, we discuss the principles and processes of chemical, physical, and biological surface modification technologies on 3D printed titanium alloy implants in detail. Furthermore, the challenges on antibacterial, osteogenesis, and mechanical properties of 3D-printed titanium alloy implants by surface modification are summarized. Future research studies, including the combination of multiple modification technologies or the coordination of the structure and composition of the composite coating are also present. This review provides leading-edge functionalization strategies of the 3D printed titanium alloy implants.

Polyetheretherketone (PEEK) has the potential to overcome some of the disadvantages of titanium interbody implants in anterior cervical and discectomy and fusion (ACDF). However, PEEK shows an inferior biological behavior regarding osseointegration and bioactivity. Therefore, the aim of the study was to create a bioactive surface coating on PEEK implants with a unique nanopore structure enabling the generation of a long-lasting interfacial composite layer between coating material and implant. Seventy-two PEEK implants-each thirty-six pure PEEK implants (PI) and thirty-six PEEK implants with a sprayed coating consisting of nanocrystalline hydroxyapatite (ncHA) embedded in a silica matrix and interfacial composite layer (SPI)-were inserted in the femoral condyles of adult rats using a split-side model. After 2, 4 and 8 weeks, the femur bones were harvested. Half of the femur bones were used in histological and histomorphometrical analyses. Additionally, pull-out tests were performed in the second half. Postoperative healing was uneventful for all animals, and no postoperative complications were observed. Considerable crestal and medullary bone remodeling could be found around all implants, with faster bone formation around the SPI and fewer regions with fibrous tissue barriers between implant and bone. Histomorphometrical analyses showed a higher bone to implant contact (BIC) in SPI after 4 and 8 weeks (p < 0.05). Pull-out tests revealed higher pull-out forces in SPI at all time points (p < 0.01). The presented findings demonstrate that a combination of a bioactive coating and the permanent chemical and structural modified interfacial composite layer can improve bone formation at the implant surface by creating a sustainable bone-implant interface. This might be a promising way to overcome the bioinert surface property of PEEK-based implants.

Focal knee resurfacing implants (FKRIs) are intended to treat cartilage defects in middle-aged patients. Most FKRIs are metal-based, which hampers follow-up of the joint using magnetic resonance imaging and potentially leads to damage of the opposing cartilage. The purpose of this study was to develop a nondegradable thermoplastic polyurethane (TPU) FKRI and investigate its osseointegration. Different surface roughness modifications and biphasic calcium phosphate (BCP) coating densities were first tested in vitro on TPU discs. The in vivo osseointegration of BCP-coated TPU implants was subsequently compared to uncoated TPU implants and the titanium bottom layer of metal control implants in a caprine model. Implants were implanted bilaterally in stifle joints and animals were followed for 12 weeks, after which the bone-to-implant contact area (BIC) was assessed. Additionally, 18F-sodium-fluoride (18F-NaF) positron emission tomography PET/CT-scans were obtained at 3 and 12 weeks to visualize the bone metabolism over time. The BIC was significantly higher for the BCP-coated TPU implants compared to the uncoated TPU implants (p = .03), and did not significantly differ from titanium (p = .68). Similar 18F-NaF tracer uptake patterns were observed between 3 and 12 weeks for the BCP-coated TPU and titanium implants, but not for the uncoated implants. TPU FKRIs with surface modifications could provide the answer to the drawbacks of metal FKRIs.

OBJECTIVE: This study presents a surface modification method to treat the zirconia implant abutment materials using a helium cold atmospheric plasma (CAP) jet in order to evaluate its efficacy on oral bacteria adhesion and growth.
METHODS: Yttrium-Stabilized Zirconia disks were subjected to helium CAP treatment; after the treatment, zirconia surface was evaluated using scanning electron microscopy, a contact angle measuring device, X-ray photoelectron spectroscopy for surface characteristics. The response of Streptococcus mutans and Porphyromonas gingivalis on treated surface was evaluated by a scanning electron microscopy, MTT assay, and LIVE/DEAD staining. The biofilm formation was analyzed using a crystal violet assay.
RESULTS: After the helium CAP jet treatment, the zirconia surface chemistry has been changed while the surface topography remains unchanged, the bacterial growth was inhibited, and the biofilm forming decreased. As the treatment time increases, the zirconia abutment showed a better bacterial inhibition efficacy.
CONCLUSIONS: The helium CAP jet surface modification approach can eliminate bacterial growth on zirconia surface with surface chemistry change, while surface topography remained.
CONCLUSIONS: Soft tissue seal around dental implant abutment plays a crucial role in maintaining long-term success. However, it is weaker than periodontal barriers and vulnerable to bacterial invasion. CAP has a potential prospect for improving soft tissue seal around the zirconia abutment, therefore providing better esthetics and most of all, prevent peri-implant lesions from happening.

As total joint replacements increase annually, new strategies to attain solid bone-implant fixation are needed to increase implant survivorship. This study evaluated two morphologies of titania nanotubes (TiNT) in in vitro experiments and an in vivo rodent model of intramedullary fixation, to simulate joint arthroplasty conditions. TiNT surfaces were prepared via an electrochemical etching process, resulting in two different TiNT morphologies, an aligned structure with nanotubes in parallel and a trabecular bone-like structure. in vitro data showed bone marrow cell differentiation into osteoblasts as well as osteoblastic phenotypic behavior through 21 days. In vivo, both TiNT morphologies generated greater bone formation and bone-implant contact than control at 12 weeks, as indicated by μCT analyses and histology, respectively. TiNT groups also exhibited greater strength of fixation compared to controls, when subjected to wire pull-out testing. TiNT may be a promising surface modification for promoting osseointegration.

Titanium implant surfaces may serve as attachment substrates for various cell types. Since carbon adsorption on titanium is inevitable, this study examined the negative/positive biological reaction of osteoblasts and fibroblasts on carbon-deposited titanium surfaces. Osteogenic MC3T3-E1 and fibrogenic NIH/3T3 cells were separately cultured on titanium disks on which carbon deposition was experimentally regulated to achieve titanium/carbon ratios of 6.5, 0.02, 0.005, and 0. The initial attachment of cells demonstrated that the quantity of attached osteoblasts on Ti/C (0.005) surfaces was 20% lower than that on Ti/C (6.5) surfaces at 4 h of culture. A 40% reduction in cell attachment at 24 h transferring from Ti/C (6.5) to Ti/C (0.005) surfaces highlighted the negative effect of carbon deposition on osteoblast attachment. However, the initial attachment of fibroblasts, which depended on carbon deposition, increased, and the quantity of cells on Ti/C (0.005) surfaces was almost twice that on Ti/C (6.5) surfaces at 4 h of culture. The levels of common differentiation markers of collagen synthesis were also differentially carbon-dependent as total collagen deposition on Ti/C (0.005) decreased by > 30% compared to that on Ti/C (6.5) in osteoblasts after 7 days of culture. In contrast, collagen synthesis in fibroblasts markedly increased as was evident by the increase in carbon deposition. These inverse effects indicate that carbon deposition on a titanium surface would likely be a disadvantage for bone formation, but might represent an effective option for achieving better wound healing and soft tissue sealing around the surface of an implant-neck region. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1869-1877, 2018.

Avulsion, epidermal marsupialization, and infection cause failure at the skin-material interface. A robust interface would permit implantable robotics, prosthetics, and other medical devices; reconstruction of surgical defects, and long-term access to blood vessels and body cavities. Torus-shaped cap-scaffold structures were designed to work in conjunction with negative pressure to address the three causes of failure. Six wounds were made on the backs of each of four 3-month old pigs. Four unmodified (no caps) scaffolds were implanted along with 20 cap-scaffolds. Collagen type 4 was attached to 21 implants. Negative pressure then was applied. Structures were explanted and assessed histologically at day 7 and day 28. At day 28, there was close tissue apposition to scaffolds, without detectable reactions from defensive or interfering cells. Three cap-scaffolds explanted at day 28 showed likely attachment of epidermis to the cap or cap-scaffold junction, without deeper marsupialization. The combination of toric-shaped cap-scaffolds with negative pressure appears to be an intrinsically biocompatible system, enabling a robust skin-material interface. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1307-1318, 2017.

OBJECTIVE: The objective of the current study was to examine whether the nanoindentation parameters can assess the alteration of bone quality resulting from different degrees of bone remodeling between bone tissue ages around the dental implant interface with different treatments and healing periods.
METHODS: Dental implants were placed in mandibles of six male dogs. Treatment groups included: resorbable blast media-treated titanium (Ti) implants, alumina-blasted zirconia implants (ATZ), alumina-blasted zirconia implants applied with demineralized bone matrix (ATZ-D), and alumina-blasted zirconia implants applied with rhBMP-2 (ATZ-B). Nanoindentation modulus (E), hardness (H), viscosity (η), and viscoelastic creep (Creep/P max) were measured for new and old bone tissues adjacent to the implants at 3 and 6 weeks of post-implantation. A total of 945 indentations were conducted for 32 implant systems.
RESULTS: Significantly lower E, H, and η but higher Creep/P max were measured for new bone tissues than old bone tissues, independent of treatments at both healing periods (p < 0.001). All nanoindentation parameters were not significantly different between healing periods (p > 0.568). ATZ-D and ATZ-B implants had the stiffer slope of correlation between E and Creep/P max of the new bone tissue than Ti implant (p < 0.039).
CONCLUSIONS: Current results indicated that, in addition to elastic modulus and plastic hardness, measurement of viscoelastic properties of bone tissue surrounding the implant can provide more detailed information to understand mechanical behavior of an implant system.
CONCLUSIONS: Ability of energy absorption in the interfacial bone tissue can play a significant role in the long-term success of a dental implant system.

The quality of soft-tissue integration plays an important role in the short- and long-term success of dental implants. The aim of the present study was to provide a surface modification approach for zirconia implant abutment materials and to evaluate its influence on fibroblast behavior and oral bacteria adhesion, which are the two main factors influencing the quality of peri-implant soft-tissue seal. In this study, polydopamine (PDA)-coated zirconia was prepared and the surface characteristics were evaluated using scanning electron microscopy, atomic force microscopy, a contact-angle-measuring device, X-ray photoelectron spectroscopy, and Raman spectroscopy. The responses of human gingival fibroblasts (HGFs) to PDA-coated zirconia; i.e., adhesion, proliferation, morphology, protein synthesis, and gene expression, were analyzed. Additionally, the adhesion of Streptococcus gordonii and Streptococcus mutans to zirconia after PDA coating was assessed by scanning electron microscopy and live/dead staining. The material surface analyses suggested the successful coating of PDA onto the zirconia surface. The PDA coating significantly increased cell adhesion and proliferation compared with pristine zirconia. HGFs exhibited a high degree of spreading and secreted a high level of collagen type I on PDA-modified disks. Upregulation of integrin α5, β1, β3 and fibronectin was noted in HGFs cultured on PDA-coated zirconia. The number of adherent bacteria decreased significantly on zirconia after PDA coating. In summary, our result suggest that PDA is able to modify the surface of zirconia, influence HGFs\' behavior and reduce bacterial adhesion. Therefore, this surface modification approach holds great potential for improving soft-tissue integration around zirconia abutments in clinical application.

In this work, we use FEA to test the hypothesis that a low-modulus coating of a cylindrical zirconia dental implant would reduce the stresses in the peri-implant bone and we use design optimization and the rule of mixture to estimate the elastic modulus and the porosity of the coating that provides optimal stress shielding. We show that a low-modulus coating of a dental implant significantly reduces the maximum stresses in the peri-implant bone without affecting the average stresses thus creating a potentially favorable biomechanical environment. Our results suggest that a resilient coating is capable of reducing the maximum compressive and tensile stresses in the peri-implant bone by up to 50% and the average stresses in the peri-implant bone by up to 15%. We further show that a transitional gradient between the high-modulus core and the low-modulus coating is not necessary and for a considered zirconia/HA composite the optimal thickness of the coating is 100 µ with its optimal elastic at the lowest value considered of 45 GPa.