The potential utility of high-intensity ultrasound to treat osteoarthritis.

Osteoarthritis (OA) is a widespread musculoskeletal disease that reduces quality of life and for which there is no cure. The treatment of OA is challenging since cartilage impedes the local and systemic delivery of therapeutic compounds (TCs). This review identifies high-intensity ultrasound (HIU) as a non-contact technique to modify articular cartilage and subchondral bone. HIU enables new approaches to overcome challenges associated with drug delivery to cartilage and new non-invasive approaches for the treatment of joint disease. Specifically, HIU has the potential to facilitate targeted drug delivery and release deep within cartilage, to repair soft tissue damage, and to physically alter tissue structures including cartilage and bone. The localized, non-invasive ultrasonic delivery of TCs to articular cartilage and subchondral bone appears to be a promising technique in the immediate future.

Surface roughness enhances the osseointegration of titanium headposts in non-human primates.

It is well recognized that micrometer and nanometer sized surface features enhance the skeletal attachment of implants within bone. However, little is known regarding the integration of implants placed outside the bone but in contact with the surface. Loosening of chronic skull anchored headposts in non-human primate based experiments can be a factor. The purpose of this study was to evaluate the effect of a simple and easily applied surface texture on bone apposition to titanium implants fixed to the periosteal surface of the skull. Implants possessed either a polished surface or a textured surface created by grit-basting followed by acid etching. The percent of bone in contact with the implant surface (bone apposition) to three polished and three textured implants was evaluated in one adult female monkey after 14 weeks. Upon harvest, implants were processed for undecalcified histology and regions of bone apposition were quantified using backscatter electron microscopy and digital image analysis. The bone apposition to textured implants was 62±20% and to polished implants was 42±21%. The application of a peak-and-pit like texture to the surface of titanium implants significantly increased bone apposition to titanium implants placed on the periosteal surface of the skull. This study demonstrates that titanium headposts can easily be modified to improve osseointegration using equipment and supplies available to most neurophysiological laboratories. In addition, implant texturing may have utility in areas including skeletal trauma and reconstruction where devices are placed in contact with the bone surface.

Direct visualization and quantification of bone growth into porous titanium implants using micro computed tomography.

The utility of porous metals for the integration of orthopaedic implants with host bone has been well established. Quantification of the tissue response to cementless implants is laborious and time consuming process requiring tissue processing, embedding, sectioning, polishing, imaging and image analysis. Micro-computed tomography (µCT) is a promising three dimensional (3D) imaging technique to quantify the tissue response to porous metals. However, the suitability and effectiveness of µCT for the quantification of bone ingrowth remains unknown. The purpose of this study was to evaluate and compare bone growth within porous titanium implants using both µCT and traditional hard-tissue histology techniques. Cylindrical implants were implanted in the distal femora and proximal tibiae of a rabbit. After 6 weeks, bone ingrowth was quantified and compared by µCT, light microscopy and backscattered electron microscopy. Quantification of bone volume and implant porosity as determined by µCT compared well with data obtained by traditional histology techniques. Analysis of the 3D dataset showed that bone was present in the pores connected with openings larger 9.4 µm. For pore openings greater than 28.2 µm, the size of the interconnection had little impact on the bone density within the porosity for the titanium foams.

A droplet-based building block approach for bladder smooth muscle cell (SMC) proliferation.

Tissue engineering based on building blocks is an emerging method to fabricate 3D tissue constructs. This method requires depositing and assembling building blocks (cell-laden microgels) at high throughput. The current technologies (e.g., molding and photolithography) to fabricate microgels have throughput challenges and provide limited control over building block properties (e.g., cell density). The cell-encapsulating droplet generation technique has potential to address these challenges. In this study, we monitored individual building blocks for viability, proliferation and cell density. The results showed that (i) SMCs can be encapsulated in collagen droplets with high viability (>94.2 +/- 3.2%) for four cases of initial number of cells per building block (i.e. 7 +/- 2, 16 +/- 2, 26 +/- 3 and 37 +/- 3 cells/building block). (ii) Encapsulated SMCs can proliferate in building blocks at rates that are consistent (1.49 +/- 0.29) across all four cases, compared to that of the controls. (iii) By assembling these building blocks, we created an SMC patch (5 mm x 5 mm x 20 microm), which was cultured for 51 days forming a 3D tissue-like construct. The histology of the cultured patch was compared to that of a native rat bladder. These results indicate the potential of creating 3D tissue models at high throughput in vitro using building blocks.

Tissue response to the components of a hydroxyapatite-coated composite femoral implant.

Bone loss around femoral implants used for THA is a persistent clinical concern. It may be caused by stress shielding, generally attributed to a mismatch in stiffness between the implants and host bone. In this regard, a fatigue resistant, carbon fiber (CF) composite femoral implant with bone-matching stiffness has been developed. This study evaluated the tissue response to the three material components of this implant in normal and textured (blasted with 24 grit alumina) surfaces: the hydroxyapatite (HA) coating, the CF composite and the intermediate crystalline HA particulate composite layer to bond to the HA coating (blended). Sprague-Dawley rats underwent bilateral femoral implantation each receiving two rod-like implants. Bone apposition to the HA (37%) and textured Ti (41%) implants was not significantly different. Bone apposition to the untextured CF (14%) and blended (19%) implants and polished Ti (8%) implants was significantly lower. Bone apposition to the textured CF (9%) and blended (11%) implants was lower (but not statistically from the as received or untextured counterparts). Nearly all sections from femurs containing CF implants presented CF debris. There was no evidence of localized bone loss or any strong immune response associated with any of the implant materials. All materials were well tolerated with minimal inflammation despite the presence of particulate debris. The high degree of bone apposition to the HA-coated composite implants and the lack of short-term inflammation and adverse tissue response to the three material implant component support continued evaluation of this composite technology for use in THA.

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.

Novel carbon fiber composite for hip replacement with improved in vitro and in vivo osseointegration.

A novel composite femoral stem has been developed to match cortical stiffness and achieve fixation by osseointegration with the primary goal to reduce cortical bone loss associated with stress shielding. The femoral stem consists of three distinct material layers: the first is a long carbon fiber (CF) in a polyamide 12 (PA12) polymer matrix (PA12/CF); the second is a PA12/HA (hydroxyapatite) interface; and the third is a plasma-sprayed coating of HA. In vitro studies with MG63 cells indicated that the HA surface supported improved proliferation and differentiation of osteoblast-like cells as determined by alkaline phosphatase activity and osteocalcin production when compared with Ti-6Al-4V (Ti64). In vivo studies comparing the composite and Ti64 rods in the rabbit femur demonstrated significantly higher bone apposition to the composite than Ti64 rods. The results of this study indicate that the invasion of surrounding bone cells and thus osteointegration together with its bone-matching mechanical properties make the PA12/CF/HA stem a promising hip replacement candidate.

A physical vapor deposition method for controlled evaluation of biological response to biomaterial chemistry and topography.

The purpose of this study was to characterize a technique to effectively mask surface chemistry without modifying surface topography. A thin layer of titanium was deposited by physical vapor deposition (PVD) onto different biomaterial surfaces. Commercially pure titanium disks were equally divided into three groups. Disks were either polished to a mirror finish, grit blasted with alumina particles, or grit blasted and subsequently plasma sprayed with a commercial grade of hydroxyapatite (HA). A subgroup of each of these treatment types was further treated by masking the entire disk surface with a thin layer of commercially pure titanium deposited by PVD. A comparison of surface topography and chemical composition was carried out between disks within each treatment group. Canine marrow cells were seeded on all disk surfaces to determine the stability of the PVD Ti mask under culture conditions. The PVD process did not significantly alter the surface topography of any samples. The thin titanium layer completely masked the underlying chemistry of the plasma sprayed HA surface and the chemistry of the plasma vapor deposited titanium layer did not differ from that of the commercially pure titanium disks. Aliquots obtained from the media during culture did not indicate any significant differences in Ti concentration amongst the Ti and Ti-masked surfaces. The PVD application of a Ti layer on HA coatings formed a stable, durable, and homogenous layer that effectively masked the underlying surface chemistry without altering the surface topography.

Spontaneous bilateral Achilles tendon rupture in a patient treated with oral levofloxacin.

A case of bilateral rupture of the Achilles tendon in a patient treated with levofloxacin for cystitis is reported. A 76-year-old woman suddenly developed painful ankles one day after levofloxacin treatment. Drug therapy was switched to amoxicillin/clavulanate on the fourth day. Sonography revealed a serious condition of tendinosis with complete bilateral full-thickness rupture on day 6. Tendons were both repaired in the same surgical session. Pathological anatomy of the specimens reported fatty tissue lobules with panniculitis and histiocytosis. Ankles were immobilized postoperatively with a plaster cast. Achilles tendon rupture may occur as an adverse side effect of short-term use of levofloxacin, a fluoroquinolone antibiotic. This adverse effect is a rare and poorly understood complication of this antibiotic therapy. A review of the literature is provided.

Zoledronic acid causes enhancement of bone growth into porous implants.

The effect of zoledronic acid on bone ingrowth was examined in an animal model in which porous tantalum implants were placed bilaterally within the ulnae of seven dogs. Zoledronic acid in saline was administered via a single post-operative intravenous injection at a dose of 0.1 mg/kg. The ulnae were harvested six weeks after surgery. Undecalcified transverse histological sections of the implant-bone interfaces were imaged with backscattered scanning electron microscopy and the percentage of available pore space that was filled with new bone was calculated. The mean extent of bone ingrowth was 6.6% for the control implants and 12.2% for the zoledronic acid-treated implants, an absolute difference of 5.6% (95% confidence interval, 1.2 to 10.1) and a relative difference of 85% which was statistically significant. Individual islands of new bone formation within the implant pores were similar in number in both groups but were 69% larger in the zoledronic acid-treated group. The bisphosphonate zoledronic acid should be further investigated for use in accelerating or enhancing the biological fixation of implants to bone.

Acid-etched microtexture for enhancement of bone growth into porous-coated implants.

We designed an in vivo study to determine if the superimposition of a microtexture on the surface of sintered titanium beads affected the extent of bone ingrowth. Cylindrical titanium intramedullary implants were coated with titanium beads to form a porous finish using commercial sintering techniques. A control group of implants was left in the as-sintered condition. The test group was etched in a boiling acidic solution to create an irregular surface over the entire porous coating. Six experimental dogs underwent simultaneous bilateral femoral intramedullary implantation of a control implant and an acid etched implant. At 12 weeks, the implants were harvested in situ and the femora processed for undecalcified, histological examination. Eight transverse serial sections for each implant were analysed by backscattered electron microscopy and the extent of bone ingrowth was quantified by computer-aided image analysis. The extent of bone ingrowth into the control implants was 15.8% while the extent of bone ingrowth into the etched implants was 25.3%, a difference of 60% that was statistically significant. These results are consistent with other research that documents the positive effect of microtextured surfaces on bone formation at an implant surface. The acid etching process developed for this study represents a simple method for enhancing the potential of commonly available porous coatings for biological fixation.

Correction of the abnormal mineral ion homeostasis with a high-calcium, high-phosphorus, high-lactose diet rescues the PDDR phenotype of mice deficient for the 25-hydroxyvitamin D-1alpha-hydroxylase (CYP27B1).

Mutations in the 25-hydroxyvitamin D-1alpha-hydroxylase gene (CYP27B1; 1alpha-OHase) cause pseudo vitamin D deficiency rickets (PDDR), while mutations in the vitamin D receptor (VDR) cause hereditary vitamin D resistance rickets. Animal models of both diseases have been engineered. The bone phenotype of VDR-ablated mice can be completely rescued by feeding the animals with a high-calcium, high-phosphorus, high-lactose diet. We have attempted to rescue the PDDR phenotype of mice deficient for the 1alpha-OHase gene by feeding them with the high-calcium diet. The rescue regimen consisted of feeding a diet containing 2% calcium, 1.25% phosphorus, 20% lactose (rescue diet) from 3 weeks of age until sacrifice at 8.5 weeks of age. Blood biochemistry analysis revealed that the rescue diet corrected the hypocalcemia and secondary hyperparathyroidism. Despite the restoration of normocalcemia, 1alpha-OHase(-/-) (and 1alpha-OHase(+/-)) animals fed the rescue diet initially gained weight less rapidly than control mice fed normal mouse chow. Although 1alpha-OHase(-/-) mice fed the rescue diet eventually reached the same weight as control animals, the treatment did not entirely correct bone growth, as femur size remained significantly smaller than that of control. Bone histology and histomorphometry confirmed that the rickets and osteomalacia were cured. The rescue diet also restored the biomechanical properties of the bone tissue within normal parameters. These results demonstrate that correction of the abnormal mineral ion homeostasis by feeding with a high-calcium rescue diet is effective to rescue the PDDR phenotype of 1alpha-OHase mutant mice. This treatment, however, does not appear as effective as 1,25(OH)(2)D(3) replacement therapy since bone growth remained impaired.

Relative contributions of chemistry and topography to the osseointegration of hydroxyapatite coatings.

The purpose of the current study was to ascertain the relative contributions of surface chemistry and topography to the osseointegration of hydroxyapatite-coated implants. A canine femoral intramedullary implant model was used to compare the osseous response to commercially pure titanium implants that were either polished, grit-blasted, plasma-sprayed with hydroxyapatite, or plasma-sprayed with hydroxyapatite and masked with a very thin layer of titanium using physical vapor deposition (titanium mask). The titanium mask isolated the chemistry of the underlying hydroxyapatite layer without functionally changing its surface topography and morphologic features. At 12 weeks, the bone-implant specimens were prepared for undecalcified thin section histologic evaluation and serial transverse sections were quantified with backscattered scanning electron microscopy for the percentage of bone apposition to the implant surface. Bone apposition averaged 3% for the polished implants and 23% for the grit-blasted implants. Bone apposition to the hydroxyapatite-coated implants averaged 74% whereas bone apposition to the titanium mask implants averaged 59%. Although there was significantly greater osseointegration with the hydroxyapatite-coated implants, 80% of the maximum bone forming response to the implant surfaces developed with the titanium mask implants. This simple, controlled experiment revealed that topography is the dominant factor governing bone apposition to hydroxyapatite-coated implants.

Fibrous tissue ingrowth and attachment to porous tantalum.

This study determined the soft tissue attachment strength and extent of ingrowth to a porous tantalum biomaterial. Eight dorsal subcutaneous implants (in two dogs) were evaluated at 4, 8, and 16 weeks. Upon retrieval, all implants were surrounded completely by adherent soft tissue. Implants were harvested with a tissue flap on the cutaneous aspect and peel tested in a servo-hydraulic tensile test machine at a rate of 5 mm/min. Following testing, implants were dehydrated in a solution of basic fuschin, defatted, embedded in methylmethacrylate, and processed for thin-section histology. At 4, 8, and 16 weeks, the attachment strength to porous tantalum was 61, 71, and 89 g/mm respectively. Histologic analysis showed complete tissue ingrowth throughout the porous tantalum implant. Blood vessels were visible at the interface of and within the porous tantalum material. Tissue maturity and vascularity increased with time. The tissue attachment strength to porous tantalum was three- to six-fold greater than was reported in a similar study with porous beads. This study demonstrated that porous tantalum permits rapid ingrowth of vascularized soft tissue, and attains soft tissue attachment strengths greater than with porous beads.

Characteristics of bone ingrowth and interface mechanics of a new porous tantalum biomaterial.

We have studied the characteristics of bone ingrowth of a new porous tantalum biomaterial in a simple transcortical canine model using cylindrical implants 5 x 10 mm in size. The material was 75% to 80% porous by volume and had a repeating arrangement of slender interconnecting struts which formed a regular array of dodecahedron-shaped pores. We performed histological studies on two types of material, one with a smaller pore size averaging 430 microm at 4, 16 and 52 weeks and the other with a larger pore size averaging 650 microm at 2, 3, 4, 16 and 52 weeks. Mechanical push-out tests at 4 and 16 weeks were used to assess the shear strength of the bone-implant interface on implants of the smaller pore size. The extent of filling of the pores of the tantalum material with new bone increased from 13% at two weeks to between 42% and 53% at four weeks. By 16 and 52 weeks the average extent of bone ingrowth ranged from 63% to 80%. The tissue response to the small and large pore sizes was similar, with regions of contact between bone and implant increasing with time and with evidence of Haversian remodelling within the pores at later periods. Mechanical tests at four weeks indicated a minimum shear fixation strength of 18.5 MPa, substantially higher than has been obtained with other porous materials with less volumetric porosity. This porous tantalum biomaterial has desirable characteristics for bone ingrowth; further studies are warranted to ascertain its potential for clinical reconstructive orthopaedics.

The osseous response to corundum blasted implant surfaces in a canine hip model.

The purpose of this study was to examine the radiographic and histologic response to corundum blasted implant surfaces of varying roughness in a canine total hip arthroplasty model. Three types of tapered femoral implants were made from titanium alloy and were identical in every respect except surface finish. The entire surface of the femoral implant had a 2.9-, 4.2-, or 6.7-micron average surface roughness (Ra) from blasting with 60-, 24-, or 16-grit corundum particles, respectively. Twenty-two stems in 11 dogs were evaluated at 6 months. Twenty-one of the stems showed osseointegration, whereas in one stem a fibrous interface developed. Abundant new periimplant bone formation occurred, particularly within the intramedullary canal where trabeculae spanned implant to endosteal cortex gaps as large as 5 mm. Bone apposition with the 60-, 24-, and 16-grit stems averaged 31.7%, 32%, and 27.9%, respectively; the differences were not statistically significant. However, the pattern of new bone formation was different in that the average length of each region of bone apposition for the 60- and 24-grit surfaces was 50% greater than that for the coarser 16-grit surface. The observations of this study indicate that because of their highly osteoconductive nature, corundum blasted surfaces represent an important and valuable technology for the design of noncemented implants.

Tissue response to porous tantalum acetabular cups: a canine model.

This study evaluated the osseous tissue response to a noncemented metal-backed acetabular component made of a new porous tantalum biomaterial. Eleven dogs with bilateral total hip arthroplasties (22 acetabular implants) were studied for a period of 6 months. Thin section histology, high-resolution radiography, and backscattered scanning electron microscopy revealed that all 22 implants had stable bone-implant interfaces. Regions of bone ingrowth were present in all histologic sections. The depth of bone ingrowth varied from 0.2 mm to the maximal limit of 2 mm. Analyzing contiguous regions of interest across the full bone-implant interface, the mean bone ingrowth for all sections was 16.8% +/- 5.7%. In the peripheral regions of the cup where bone-implant contact was most consistent, bone ingrowth averaged 25.1% +/- 10.1%. The data indicate that the porous tantalum material is effective for biologic fixation in the dog and may provide a suitable alternative to other porous materials used in acetabular cup design.

Effect of flexibility of the femoral stem on bone-remodeling and fixation of the stem in a canine total hip arthroplasty model without cement.

The purpose of this study was to compare, with regard to fixation of the implant and femoral bone resorption, two fully porous-coated stems of different stiffnesses in a canine total hip arthroplasty model. A bilateral arthroplasty was carried out with insertion of a titanium-alloy stem (which had stiffness properties comparable with those of the canine femur) on one side and with insertion of a composite stem (which was three to fivefold more flexible than the canine femur) on the contralateral side. Eight femora were evaluated at six months and eight, at eighteen months after the operation, to determine the extent of bone ingrowth, periprosthetic cortical area, intracortical porosity, and bone-remodeling. Despite the markedly greater flexibility of the composite stems, no significant difference could be detected (with the numbers available), with regard to the overall degree of femoral stress-shielding, cortical area, or cortical porosity, between these stems and the stiffer, titanium-alloy stems at either time-period. However, the composite stems had less bone ingrowth and more formation of radiopaque lines than did the titanium-alloy stems. At eighteen months, the values for bone ingrowth were 9.7 +/- 5.38 percent (mean and standard deviation) for the composite stems compared with 28.1 +/- 5.31 percent for the titanium-alloy stems (p = 0.003). Furthermore, the histological sections from the femora containing a composite stem showed radiopaque lines indicative of fibrous ingrowth approximately threefold more often than did those from the femora containing a titanium-alloy stem (p = 0.02).