Phase transformations during processing and in vitro degradation of porous calcium polyphosphates.

A 2-Step sinter/anneal treatment has been reported previously for forming porous CPP as biodegradable bone substitutes [9]. During the 2-Step annealing treatment, the heat treatment used strongly affected the rate of CPP degradation in vitro. In the present study, x-ray diffraction and (31)P solid state nuclear magnetic resonance were used to determine the phases that formed using different heat treating processes. The effect of in vitro degradation (in PBS at 37 °C, pH 7.1 or 4.5) was also studied. During CPP preparation, ß-CPP and γ-CPP were identified in powders formed from a calcium monobasic monohydrate precursor after an initial calcining treatment (10 h at 500 °C). Melting of this CPP powder (at 1100 °C), quenching and grinding formed amorphous CPP powders. Annealing powders at 585 °C (Step-1) resulted in rapid sintering to form amorphous porous CPP. Continued annealing to 650 °C resulted in crystallization to form a multi-phase structure of ß-CPP primarily plus lesser amounts of α-CPP, calcium ultra-phosphates and retained amorphous CPP. Annealing above 720 °C and up to 950 °C transformed this to ß-CPP phase. In vitro degradation of the 585 °C (Step-1 only) and 650 °C Step-2 annealed multi-phase samples occurred significantly faster than the ß-CPP samples formed by Step-2 annealing at or above 720 °C. This faster degradation was attributable to preferential degradation of thermodynamically less stable phases that formed in samples annealed at 650 °C (i.e. α-phase, ultra-phosphate and amorphous CPP). Degradation in lower pH solutions significantly increased degradation rates of the 585 and 650 °C annealed samples but had no significant effect on the ß-CPP samples.

Integration of tissue-engineered cartilage with host cartilage: an in vitro model.

BACKGROUND: We developed a tissue-engineered biphasic cartilage bone substitute construct which has been shown to integrate with host cartilage and differs from autologous osteochondral transfer in which integration with host cartilage does not occur. QUESTIONS/PURPOSES: (1) Develop a reproducible in vitro model to study the mechanisms regulating tissue-engineered cartilage integration with host cartilage, (2) compare the integrative properties of tissue-engineered cartilage with autologous cartilage and (3) determine if chondrocytes from the in-vitro formed cartilage migrate across the integration site. METHODS: A biphasic construct was placed into host bovine osteochondral explant and cultured for up to 8 weeks (n = 6 at each time point). Autologous osteochondral implants served as controls (n = 6 at each time point). Integration was evaluated histologically, ultrastructurally, biochemically and biomechanically. Chondrocytes used to form cartilage in vitro were labeled with carboxyfluorescein diacetate which allowed evaluation of cell migration into host cartilage. RESULTS: Histologic assessment demonstrated that tissue-engineered cartilage integrated over time, unlike autologous osteochondral implant controls. Biochemically there was an increase in collagen content of the tissue-engineered implant over time but was well below that for native cartilage. Integration strength increased between 4 and 8 weeks as determined by a pushout test. Fluorescent cells were detected in the host cartilage up to 1.5 mm from the interface demonstrating chondrocyte migration. CONCLUSIONS: Tissue-engineered cartilage demonstrated improved integration over time in contrast to autologous osteochondral implants. Integration extent and strength increased with culture duration. There was chondrocyte migration from tissue-engineered cartilage to host cartilage. CLINICAL RELEVANCE: This in vitro integration model will allow study of the mechanism(s) regulating cartilage integration. Understanding this process will facilitate enhancement of cartilage repair strategies for the treatment of chondral injuries.

Improving fretting corrosion resistance of CoCrMo alloy with TiSiN and ZrN coatings for orthopedic applications.

Total hip replacement is the most effective treatment for late stage osteoarthritis. However, adverse local tissue reactions (ALTRs) have been observed in patients with modular total hip implants. Although the detailed mechanisms of ALTRs are still unknown, fretting corrosion and the associated metal ion release from the CoCrMo femoral head at the modular junction has been reported to be a major factor. The purpose of this study is to increase the fretting corrosion resistance of the CoCrMo alloy and the associated metal ion release by applying hard coatings to the surface. Cathodic arc evaporation technique (arc-PVD) was used to deposit TiSiN and ZrN hard coatings on CoCrMo substrates. The morphology, chemical composition, crystal structures and residual stress of the coatings were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffractometry. Hardness, elastic modulus, and adhesion of the coatings were measured by nano-indentation, nano-scratch test, and the Rockwell C test. Fretting corrosion resistance tests of coated and uncoated CoCrMo discs against Ti6Al4V spheres were conducted on a four-station fretting testing machine in simulated body fluid at 1Hz for 1 million cycles. Post-fretting samples were analyzed for morphological changes, volume loss and metal ion release. Our analyses showed better surface finish and lower residual stress for ZrN coating, but higher hardness and better scratch resistance for TiSiN coating. Fretting results demonstrated substantial improvement in fretting corrosion resistance of CoCrMo with both coatings. ZrN and TiSiN decreased fretting volume loss by more than 10 times and 1000 times, respectively. Both coatings showed close to 90% decrease of Co ion release during fretting corrosion tests. Our results suggest that hard coating deposition on CoCrMo alloy can significantly improve its fretting corrosion resistance and could thus potentially alleviate ALTRs in metal hip implants.

Transforming Growth Factor ß Enhances Tissue Formation by Passaged Nucleus Pulposus Cells In Vitro.

The nucleus pulposus (NP) is composed of NP and notochord cell. It is a paucicellular tissue and if it is to be used as a source of cells for tissue engineering the cell number will have to be expanded by cell passaging. The hypothesis of this study is that passaged NP and notochordal cells grown in three-dimensional (3D) culture in the presence of transforming growth factor ß (TGFß) will show enhanced NP tissue formation compared with cells grown in the absence of this growth factor. Bovine NP cells isolated by sequential enzymatic digestion from caudal intervertebral discs were either placed directly in 3D culture (P0) or serially passaged up to passage 3 (P3) prior to placement in 3D culture. Serial cell passage in monolayer culture led to de-differentiation, increased senescence and oxidative stress and decreases in the gene expression of NP and notochordal associated markers and increases in de-differentiation markers. The NP tissue regeneration capacity of cells in 3D culture decreases with passaging as indicated by diminished tissue thickness and total collagen content when compared with tissues formed by P0 cells. Immunohistochemical studies showed that type II collagen accumulation appeared to decrease. TGFß1 or TGFß3 treatment enhanced the ability of cells at each passage to form tissue, in part by decreasing cell death. However, neither TGFß1 nor TGFß3 were able to restore the notochordal phenotype. Although TGFß1/3 recovered NP tissue formation by passaged cells, to generate NP in vitro that resembles the native tissue will require identification of conditions facilitating retention of notochordal cell differentiation. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:438-449, 2020.

Differential response of human blood leukocytes to brushite, monetite, and calcium polyphosphate biomaterials.

Calcium phosphate-based biomaterials are extensively used for bone replacement and regeneration in orthopedic, dental, and maxillofacial surgical applications. The injury induced by surgical implantation of bone replacement graft materials initiates a cascade of host responses, starting with blood-biomaterial contact, protein adsorption on the material surface, blood coagulation, and leukocyte responses. During the initial acute inflammatory response, polymorphonuclear neutrophils (PMNs) and monocytes, abundant circulating leukocytes of the myeloid lineage, are recruited to the site of inflammation. In addition to responding to pathogenic challenges, these cells respond to particulate substances within the body including crystals of monosodium urate (MSU). Host responses toward grafts impact short- and long-term success in tissue engineering and regenerative applications. Although multinucleated osteoclasts, formed by monocyte/macrophage fusion, are generally thought to be responsible for resorption of implant biomaterials, the ability of different biomaterials to trigger PMNs, which are invariably present at the early stages after implant surgery, and are abundant in the oral cavity, has never been tested. In this article, we present analysis of the response of human blood-derived PMNs and monocytes toward brushite, monetite, and calcium polyphosphate (CPP) biomaterial substrates and compare this to the response to MSU crystals, the latter serving as a positive control. Employing multicolor flow cytometry to look at PMN and monocyte cell surface markers of activation to gauge the response to different biomaterials, we found that both types of myeloid cells are highly activated after exposure to brushite, monetite, and MSU but not CPP. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 108B:253-262, 2020.

Substrate architecture and fluid-induced shear stress during chondrocyte seeding: role of alpha5beta1 integrin.

Chondrocyte behaviour has been shown previously to be influenced by the architecture of the substrate on which the cells are grown. Chondrocytes cultured on fully porous titanium alloy substrates showed greater spreading and more matrix accumulation when compared to cells grown on porous-coated substrates with solid bases. We hypothesized that these features developed because of differences in fluid-induced shear stresses due to substrate architecture and that integrins mediate these responses. Computational fluid dynamics analyses predicted that cells on fully porous substrates experience time-dependent shear stresses that differ from those experienced by cells on porous-coated substrates with solid bases where media flow-through is restricted. To validate this model, the seeding protocol was modulated to affect fluid flow and this affected cell spreading and matrix accumulation as predicted. Integrin blocking experiments revealed that alpha5beta1 integrins regulated cell shape under these two conditions and when cell spreading was prevented the increased accumulation of collagen and proteoglycans by chondrocytes seeded on fully porous substrates did not occur. Identifying the substrate-induced mechanical and molecular mechanisms that influence chondrocyte behaviour and tissue formation may ultimately lead to the formation of a tissue that more closely resembles natural articular cartilage.

"Biologic width"and crestal bone remodeling with sintered porous-surfaced dental implants: a study in dogs.

PURPOSE: The aim of this study was to obtain histometric measurements of bone and peri-implant mucosal tissue contact with implants of 2 sintered porous-surfaced designs. The "short-collar" design had a collar height (smooth coronal region) of 0.75 mm, while the "long-collar" model had a smooth coronal region of 1.8 mm. MATERIALS AND METHODS: Implants (2 per side) were placed in healed mandibular extraction sites of 4 beagle dogs using a submerged technique. After 4 weeks of healing, they were uncovered and used to support fixed partial dentures for a 9-month period. After sacrifice, specimens were retrieved and nondemineralized sections were examined histometrically to determine the most coronal bone-to-implant contact (first BIC) using the microgap as a reference and standard mucosal parameters of "biologic width." RESULTS: Significant (P = .001) differences in first BIC were found between designs (1.97 mm for long-collar versus 1.16 mm for short-collar implants) for posteriorly located implants but not for anteriorly located ones (1.21 mm versus 1.38 mm; P = .40). If crestal bone loss involved sintered surface, fibrous connective tissue ingrowth was observed to replace lost bone. No significant differences in peri-implant mucosal measurements (total peri-implant mucosal thickness; length of the epithelial component of this mucosa, and thickness of the connective tissue component) were detected between implant designs. CONCLUSIONS: Results suggest that "biologic width" accommodation drives initial crestal bone loss with sintered porous-surfaced implants. Histometric data obtained for bone contact showed no significant differences between the long- and short-collar implant designs.

Multi-axial mechanical stimulation of tissue engineered cartilage: review.

The development of tissue engineered cartilage is a promising new approach for the repair of damaged or diseased tissue. Since it has proven difficult to generate cartilaginous tissue with properties similar to that of native articular cartilage, several studies have used mechanical stimuli as a means to improve the quantity and quality of the developed tissue. In this study, we have investigated the effect of multi-axial loading applied during in vitro tissue formation to better reflect the physiological forces that chondrocytes are subjected to in vivo. Dynamic combined compression-shear stimulation (5% compression and 5% shear strain amplitudes) increased both collagen and proteoglycan synthesis (76 +/- 8% and 73 +/- 5%, respectively) over the static (unstimulated) controls. When this multi-axial loading condition was applied to the chondrocyte cultures over a four week period, there were significant improvements in both extracellular matrix (ECM) accumulation and the mechanical properties of the in vitro-formed tissue (3-fold increase in compressive modulus and 1.75-fold increase in shear modulus). Stimulated tissues were also significantly thinner than the static controls (19% reduction) suggesting that there was a degree of ECM consolidation as a result of long-term multi-axial loading. This study demonstrated that stimulation by multi-axial forces can improve the quality of the in vitro-formed tissue, but additional studies are required to further optimize the conditions to favour improved biochemical and mechanical properties of the developed tissue.

A pilot study to assess the performance of a partially threaded sintered porous-surfaced dental implant in the dog mandible.

PURPOSE: The purpose of this study was to compare patterns of crestal bone remodeling with 2 sintered porous-surfaced dental implant designs during a 14-month functional period. MATERIALS AND METHODS: Two root-form press-fit dental implants were evaluated in healed extraction sites in dog mandibles. The standard (control) design was a press-fit implant with a 2-mm machined collar; the remainder of the implant had a sintered porous surface. The test or "hybrid" design had 3 coronal machined threads instead of a machined collar; the remainder of the implant had a sintered porous surface. RESULTS: Standardized radiographs indicated significantly less crestal bone loss (0.82 to 0.93 mm versus 1.45 to 1.5 mm) with the hybrid design and a slower approach toward an apparent steady state (12 to 14 months for the hybrid versus 7 months for the standard design). Morphometric assessment of back-scattered scanning electron micrographs confirmed that crestal bone loss was significantly less for the hybrid design on all but the lingual implant aspect. CONCLUSION: The addition of coronal threads to an implant relying on a sintered porous surface geometry for its long-term osseointegration reduced the extent of crestal bone loss compared to a machined collar region.

Inorganic polyphosphates enhances nucleus pulposus tissue formation in vitro.

Disc degeneration is associated with low back pain for which currently there is no optimal therapy so there is a great need to identify new treatment approaches. Inorganic polyphosphates (polyP) are linear polymers of orthophosphate units varying in chain length and present in many cell types. As polyP has anabolic effects on chondrocytes, we hypothesized that polyP treatment would enhance matrix accumulation by nucleus pulposus (NP) cells. NP cells isolated from bovine caudal discs were grown in 3D culture under normoxic or in select experiments under hypoxic conditions, in the presence or absence of various concentrations and sizes of polyP. Gene expression was determined using RT-PCR. Matrix accumulation was quantified by measuring proteoglycan and collagen contents. DAPI fluorescence shift was used to stain for polyP in tissue. DAPI staining showed polyP present predominantly in the pericellular region of in vitro formed tissue. PolyP treatment enhanced matrix accumulation in a concentration and chain length dependant manner. NP cells exposed to polyP-22 (22 phosphate units length) showed an increase in gene expression of aggrecan, Collagen II, Sox 9, and MMP-13 which was maintained for the 14 days of culture. This suggests that polyP may enhance NP tissue formation in vitro by upregulating the expression of matrix genes. As polyP enhances proteoglycan accumulation even under hypoxic conditions, this raises the possibility that polyP may be a novel treatment to induce NP regeneration. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:41-50, 2017.

Effect of glycerol concentrations on the mechanical properties of additive manufactured porous calcium polyphosphate structures for bone substitute applications.

This article addresses the effects of glycerol (GLY) concentrations on the mechanical properties of calcium polyphosphate (CPP) bone substitute structures manufactured using binder jetting additive manufacturing. To achieve this goal, nine types of water-based binder solutions were prepared with 10, 12.5, and 15 wt % GLY liquid-binding agent, mixed, respectively, with 0, 0.75, and 1.5 wt % ethylene glycol diacetate (EGD) flow enhancer. The print quality of each of the solutions was established quantitatively using an image processing algorithm. The print quality analysis narrowed down the solutions to three batches containing 1.5 wt % EGD and variable amount of GLY. These solutions were used to manufacture porous CPP bone substitute samples, which were characterized physically to determine shrinkage, porosity, microstructure, and compression strength. The 12.5 wt % GLY, 1.5 wt % EGD solution resulted in the highest mechanical strength after sintering (34.6 ± 5.8 MPa), illustrating similar mechanical properties when compared to previous studies (33.9 ± 6.3 MPa) of additively manufactured CPP bone substitutes using a commercially available binder. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 828-835, 2017.

Calcium polyphosphate particulates for bone void filler applications.

This study investigates the characteristics of porous calcium polyphosphate particulates (CPPp) formed using two different processing treatments as bone void fillers in non- or minimally load-bearing sites. The two calcium polyphosphate particulate variants (grades) were formed using different annealing conditions during particulate preparation to yield either more slowly degrading calcium polyphosphate particulates (SD-CPPp) or faster degrading particulates (FD-CPPp) as suggested by a previous degradation study conducted in vitro (Hu et al., Submitted for publication 2016). The two CPPp grades were compared as bone void fillers in vivo by implanting particulates in defects created in rabbit femoral condyle sites (critical size defects). The SD-CPPp and FD-CPPp were implanted for 4- and 16-week periods. The in vivo study indicated a significant difference in amount of new bone formed in the prepared sites with SD-CPPp resulting in more new bone formation compared with FD-CPPp. The lower bone formation characteristic of the FD-CPPp was attributed to its faster degradation rate and resulting higher local concentration of released polyphosphate degradation products. The study results indicate the importance of processing conditions on preparing calcium polyphosphate particulates for potential use as bone void fillers in nonload-bearing sites. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 874-884, 2017.

Sol gel-derived hydroxyapatite films over porous calcium polyphosphate substrates for improved tissue engineering of osteochondral-like constructs.

Integration of in vitro-formed cartilage on a suitable substrate to form tissue-engineered implants for osteochondral defect repair is a considerable challenge. In healthy cartilage, a zone of calcified cartilage (ZCC) acts as an intermediary for mechanical force transfer from soft to hard tissue, as well as an effective interlocking structure to better resist interfacial shear forces. We have developed biphasic constructs that consist of scaffold-free cartilage tissue grown in vitro on, and interdigitated with, porous calcium polyphosphate (CPP) substrates. However, as CPP degrades, it releases inorganic polyphosphates (polyP) that can inhibit local mineralization, thereby preventing the formation of a ZCC at the interface. Thus, we hypothesize that coating CPP substrate with a layer of hydroxyapatite (HA) might prevent or limit this polyP release. To investigate this we tested both inorganic or organic sol-gel processing methods, asa barrier coating on CPP substrate to inhibit polyP release. Both types of coating supported the formation of ZCC in direct contact with the substrate, however the ZCC appeared more continuous in the tissue formed on the organic HA sol gel coated CPP. Tissues formed on coated substrates accumulated comparable quantities of extracellular matrix and mineral, but tissues formed on organic sol-gel (OSG)-coated substrates accumulated less polyP than tissues formed on inorganic sol-gel (ISG)-coated substrates. Constructs formed with OSG-coated CPP substrates had greater interfacial shear strength than those formed with ISG-coated and non-coated substrates. These results suggest that the OSG coating method can modify the location and distribution of ZCC and can be used to improve the mechanical integrity of tissue-engineered constructs formed on porous CPP substrates. STATEMENT OF SIGNIFICANCE: Articular cartilage interfaces with bone through a zone of calcified cartilage. This study describes a method to generate an "osteochondral-like" implant that mimics this organization using isolated deep zone cartilage cells and a sol-gel hydroxyapatite coated bone substitute material composed of calcium polyphosphate (CPP). Developing a layer of calcified cartilage at the interface should contribute to enhancing the success of this "osteochondral-like" construct following implantation to repair cartilage defects.

Differential regulation of matrix degrading enzymes in a TNFalpha-induced model of nucleus pulposus tissue degeneration.

Intervertebral disc degeneration occurs commonly and is linked to persistent back pain and the development of disc herniation. The mechanisms responsible for tissue catabolism have not yet been fully elucidated. Previously we characterized an in vitro model of TNFalpha-induced nucleus pulposus degeneration, which demonstrates decreased expression of matrix macromolecules, increased expression of matrix degrading enzymes, and the activation of aggrecanase-mediated proteoglycan degradation [Seguin, C.A., Pilliar, R.M., Roughley, P.J., and Kandel, R.A. 2005. Tumor necrosis factor-alpha modulates matrix production and catabolism in nucleus pulposus tissue. Spine 30: 1940-1948]. This study explores the intracellular pathways activated during TNFalpha-induced matrix degradation. We demonstrate that in nucleus pulposus cells, the p38 and JNK pathways regulate induction of MMP-1 and -3; p38, JNK, and NF-kappaB regulate the induction of MMP-13; and ERK regulates the up-regulation of MT1-MMP mRNA in response to TNFalpha. Induction of ADAMTS-4 and -5 mRNA occurred downstream of NF-kappaB activation. Depletion of tissue proteoglycans was mediated by ERK and NF-kappaB-dependent "aggrecanase" activity, suggesting MT1-MMP and ADAMTS-4 and -5 as effectors of TNFalpha-induced tissue catabolism.

Formation of a nucleus pulposus-cartilage endplate construct in vitro.

Intervertebral disc (IVD) degeneration is a common problem and treatment options for persistent symptomatic disease are limited. Tissue engineering is being explored for its ability to reconstitute the functional components of the IVD. The purpose of this study was to determine whether it was possible to form in vitro a triphasic construct consisting of nucleus pulposus (NP), cartilage endplate (CEP), and a porous calcium polyphosphate (CPP) bone substitute. Bovine articular chondrocytes were placed on the top surface of a porous CPP construct and allowed to form cartilage in vitro. Nucleus pulposus cells were then placed onto the in vitro-formed hyaline cartilage. At 24 h scanning electron microscopy demonstrated that the NP cells maintained their rounded morphology, similar to NP cells placed directly on porous CPP. At 8 weeks histological examination of the triphasic constructs by light microscopy showed that a continuous layer of NP tissue had formed and was fused to the underlying cartilage tissue, which itself was integrated with the porous CPP. The incorporation of the cartilage layer was beneficial to the construct by improving tissue attachment to the CPP, as demonstrated by increased peak load and increased energy required for failure during shear loading when compared to a biphasic construct composed of nucleus pulposus-bone substitute only. This study demonstrates that it is possible to generate a multi-component construct with the incorporation of a CEP-like layer resulting in improved bone substitute-to-IVD tissue interface characteristics.

Threaded versus porous-surfaced implants as anchorage units for orthodontic treatment: three-dimensional finite element analysis of peri-implant bone tissue stresses.

PURPOSE: A 3-dimensional finite element model was developed to investigate the cause of different crestal bone loss patterns observed around sintered porous-surfaced and machined (turned) threaded dental implants used for orthodontic anchorage in a previously reported animal study. MATERIALS AND METHODS: Twenty-noded structural solid elements with parabolic interpolation between nodes were used for modeling the bone-implant interface zone. A 3-N traction force acting between either 2 porous-surfaced or 2 machined threaded implants placed in canine premolar mandibular sites and bone profiles observed at initiation and 22 weeks of orthodontic loading were modeled. RESULTS: Higher maximum stresses in peri-implant bone next to the coronal region of the implants were predicted with the machined threaded implants at both the initial and final time points, with the values 20% greater than those predicted after the 22-week loading period. These values were approximately 200% greater than those predicted for the porous-surfaced implants, for which a more uniform stress distribution was predicted. DISCUSSION: The finite element model results indicated that the observed greater retention of crestal bone next to the porous-surfaced implants was attributable to lower peak stresses developing in crestal peri-implant bone with this design, which decreased the probability of bone loss related to local overstressing and bone microfracture. CONCLUSION: The predicted lower stresses were a result of the more uniform transfer of force from implant to bone with the porous-surfaced implants, which was a consequence of the interlocking of bone and implant possible with this design.

Evaluating interface strength of calcium phosphate sol-gel-derived thin films to Ti6Al4V substrate.

The interface shear strength of Ca-P thin films applied to Ti6Al4V substrates have been evaluated in this study using a substrate straining method--a shear lag model. The Ca-P films were synthesized using sol-gel methods from either an inorganic or organic precursor solution. Strong interface bonding was demonstrated for both film types. The films were identified as non-stoichiometric hydroxyapatite but with different Ca/P ratios. The Ca-P films were 1-1.5 microm thick and testing and analysis using the shear lag approach revealed a shear strength of approximately 347 and 280 MPa for Inorganic and Organic Route-formed films, respectively. Overall, the exceptional mechanical properties of Ca-P/Ti6Al4V system along with the inherent advantages of sol-gel processing support continued studies to utilize this technology for bone-interfacing implant surface modification.

Influence of anionic monomer content on the biodegradation and toxicity of polyvinyl-urethane carbonate-ceramic interpenetrating phase composites.

The objective of this study was to characterize a series of anionic biodegradable polymer resins for their compatibility in a biological environment, comparing them with respect to the influence of ionic function on enzyme catalyzed biodegradation when the polymers were incorporated into a porous calcium polyphosphate (CPP) 3-D structure to form an interpenetrating phase composite (IPC). The swelling behavior of the polymers was investigated by immersing the cured polymer resins in growth media at 37 degrees C. In vitro cytotoxicity of the polymer resins was assessed using a HeLa cell line. Cell viability increased when the amount of low molecular weight monomer was minimized. Despite observing that the addition of carboxylic acid groups into the polymer resin chains contributed to an improvement of the chemical bonding between the polymer and the CPP, the addition of high ionic content into the resin led to the greatest loss of bending strength for the samples incubated in phosphate buffer and cholesterol esterase enzyme solutions, when compared to their as made state. The increased degradation for the higher ionic component materials and their loss of physical strength was attributed to enhanced hydrolysis within the materials and by water transport deep within the composites, via the anionic components of the resin. The findings indicated that the introduction of anionic content must be optimized to promote increased mechanical performance for the CPP, balancing the features of polymer CPP bonding versus polymer swelling and cytotoxicity.

Cementless implant fixation--toward improved reliability.

Cementless implants offer the advantage of fixation by direct bone-to-implant osseointegration, thereby avoiding the use of a synthetic intermediary material (such as acrylic bone cement) of limited mechanical strength. Successful osseointegration, however, depends on several conditions being satisfied during the peri-implant bone healing period, including the need for limited early loading resulting in minimal relative movement at the implant-bone interface. Sintered porous- and plasma spray-coated implants represent the most common cementless orthopedic implants in current clinical use, although novel cast structures also are being investigated. All stand to benefit from surface modifications currently being explored to enhance osteoconductive or osteoinductive characteristics of the implants. The faster osseointegration that such modified surface designs potentially might offer would result in more reliable and convenient (from the patient perspective) cementless implants. Encouraging results of early animal-based studies exploring such modifications have been reported.

Calcium phosphate sol-gel-derived thin films on porous-surfaced implants for enhanced osteoconductivity. Part I: Synthesis and characterization.

Thin sol-gel-formed calcium phosphate (Ca-P) films were formed on sintered porous-surfaced implants as an approach to increasing the rate of bone ingrowth. The films were prepared using either an inorganic precursor solution (with calcium nitrate tetrahydrate and ammonium dihydrogen phosphate) or an organic precursor solution (with calcium nitrate tetrahydrate and triethyl phosphite). We report on the formation and characteristics of the films so formed. Film characteristics were assessed by thin film X-ray diffraction, diffuse-reflectance infrared Fourier transform spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. In addition, thin sections were prepared either across or parallel to the Ca-P/Ti6Al4V interface and examined by transmission electron microscopy. Both approaches resulted in the formation of nanocrystalline carbonated hydroxyapatite films but with different Ca/P ratios and structures, the Inorganic Route-formed film having a lower Ca/P ratio (1.46 cf 2.10 for the Organic Route-formed film) and having a more irregular topography. An interfacial reaction product (CaTi(2)O(5)) was identified by selected area electron diffraction with the Inorganic Route-formed film only.