Comparative study of the in vitro apatite-forming ability of poly(epsilon-caprolactone)-silica sol-gels using three osteoconductivity tests (static, dynamic, and alternate soaking process)

A New Class II Poly (ε-Caprolactone)-Silica Hybrid: Synthesis and In Vitro Apatite Forming Ability

The synthesis of a new class II poly(ε-caprolactone)-silica hybrid has been carried out using tin (II) 2-ethylhexanoate as the catalyst. Swelling behaviour, solid state 29 Si NMR and other techniques indicate the formation of interconnected organic-inorganic materials. An in vitro apatite forming ability test performed on this new class of material compared with an equivalent class I poly(ε-caprolactone)-silica sol-gel hybrid (identical silica content) showed the absence of apatite formation on the class II hybrid surface and calcium phosphate precipitation on the class I hybrid surface. This effect may be linked to less silicic acid being released in the simulated body fluid for the class II hybrid compared to the class I hybrid.

Biomimetic strategies for bone repair and regeneration

The osseointegration rate of implants is related to their composition and surface roughness. Implant roughness favors both bone anchoring and biomechanical stability. Osteoconductive calcium phosphate (Ca-P) coatings promote bone healing and apposition, leading to the rapid biological fixation of implants. It has been clearly shown in many publications that Ca-P coating accelerates bone formation around the implant. This review discusses two main routes for the manufacturing of polymer-based osteoconductive scaffolds for tissue engineering, namely the incorporation of bioceramic particles in the scaffold and the coating of a scaffold with a thin layer of apatite through a biomimetic process.

Multi-layer porous fiber-reinforced composites for implants: in vitro calcium phosphate formation in the presence of bioactive glass

OBJECTIVES

Glass-fiber-reinforced composites (FRCs), based on bifunctional methacrylate resin, have recently shown their potential for use as durable cranioplasty, orthopedic and oral implants. In this study we suggest a multi-component sandwich implant structure with (i) outer layers out of porous FRC, which interface the cortical bone, and (ii) inner layers encompassing bioactive glass granules, which interface with the cancellous bone.

METHODS

The capability of Bioglass(®) 45S5 granules (100-250μm) to induce calcium phosphate formation on the surface of the FRC was explored by immersing the porous FRC-Bioglass laminates in simulated body fluid (SBF) for up to 28d.

RESULTS

In both static (agitated) and dynamic conditions, bioactive glass granules induced precipitation of calcium phosphate at the laminate surfaces as confirmed by scanning electron microscopy.

SIGNIFICANCE

The proposed dynamic flow system is useful for the in vitro simulation of bone-like apatite formation on various new porous implant designs containing bioactive glass and implant material degradation.

Biological Responses to New Advanced Surface Modifications of Endosseous Medical Implants

Implantable medical devices are increasingly important in the practice of modern medicine. However, patients with severely poor bone quality and quantity require highest implant osseointegration for the long-term success. A number of newly-developed advanced surface modifications of medical implants have recently been introduced to the medical implant system. Understanding the mechanisms by which osteogenic cells respond to such materials is therefore of major importance in developing the most effective materials to promote functional osseointegration. Diverse studies using materials with a wide range of new surface modification techniques have demonstrated the pivotal role of surface treatments in cell adhesion, proliferation and lineage specific differentiation. These events underlie the tissue responses required for bone healing following implant placement, with the interaction between adsorbed proteins on the implant surface and surrounding cells eliciting body responses to the treated implant surface. This review illustrates tissue responses to the implant material following implant placement and highlights cellular responses to new advanced implant surface modifications. Such information is of utmost importance to further develop several new advanced surface modifications to be used in the new era medical implantable devices.

Nucleation and growth of biomimetic apatite layers on 3D plotted biodegradable polymeric scaffolds: effect of static and dynamic coating conditions

Apatite layers were grown on the surface of newly developed starch/polycaprolactone (SPCL)-based scaffolds by a 3D plotting technology. To produce the biomimetic coatings, a sodium silicate gel was used as nucleating agent, followed by immersion in a simulated body fluid (SBF) solution. After growing a stable apatite layer for 7 days, the scaffolds were placed in SBF under static, agitated (80 strokes min(-1)) and circulating flow perfusion (Q=4 ml min(-1); t(R)=15s) for up to 14 days. The materials were characterized by scanning electron microscopy/energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and thin-film X-ray diffraction. Cross-sections were obtained and the coating thickness was measured. The elemental composition of solution and coatings was monitored by inductively coupled plasma spectroscopy. After only 6 h of immersion in SBF it was possible to observe the formation of small nuclei of an amorphous calcium phosphate (ACP) layer. After subsequent SBF immersion from 7 to 14 days under static, agitated and circulating flow perfusion conditions, these layers grew into bone-like nanocrystalline carbonated apatites covering each scaffold fiber without compromising its initial morphology. No differences in the apatite composition/chemical structure were detectable between the coating conditions. In case of flow perfusion, the coating thickness was significantly higher. This condition, besides mimicking better the biological milieu, allowed for the coating of complex architectures at higher rates, which can greatly reduce the coating step.

Porous bioactive nanostructured scaffolds for bone regeneration: a sol-gel solution

Considerable advances have been seen in materials with tailored nanostructures in recent years, owing, in part, to increased demands placed on material properties in fields, such as tissue regeneration and wound healing. This review focuses on the developments made in nanoporous bioactive glasses, their novel nanocomposites and their application to bone regeneration. Bioactive glasses have the ability to stimulate new bone growth as they dissolve in the body. Sol-gel bioactive glasses have a nanoporosity that provides sites for cell attachment and tailorable degradation rates. Importantly, the glasses can be made into interconnected porous structures that can be used as 3D templates for bone growth, although, because they are glasses, they cannot be implanted directly into sites that are under cyclic loading. Composites provide a partial solution to this problem, although their bioactive and degradation properties are not ideal, therefore novel nanocomposites are needed. The route to these potentially ideal materials is described.

Modern biomaterials: a review - bulk properties and implications of surface modifications

This review concerns the importance of length and time on physicochemical interactions between living tissue and biomaterials that occur on implantation. The review provides information on material host interactions, materials for medical applications and cell surface interactions, and then details the extent of knowledge concerning the role(s) that surface chemistry and topography play during the first stage of implant integration, namely protein adsorption. The key points are illustrated by data from model in vitro studies. Host implant interactions begin nanoseconds after first contact and from then on are in a state of flux due to protein adsorption, cell adhesion and physical and chemical alteration of the implanted material. The many questions concerning the conformational form and control of bound proteins and how this may impact on cell adhesion in the first instance and later on cell signalling and implant integration can be answered by systematic investigations using model materials. Only then we will be in a more informed position to design new materials for use in the body.

Micro-computed tomography (micro-CT) as a potential tool to assess the effect of dynamic coating routes on the formation of biomimetic apatite layers on 3D-plotted biodegradable polymeric scaffolds

This work studies the influence of dynamic biomimetic coating procedures on the growth of bone-like apatite layers at the surface of starch/polycaprolactone (SPCL) scaffolds produced by a 3D-plotting technology. These systems are newly proposed for bone Tissue Engineering applications. After generating stable apatite layers through a sodium silicate-based biomimetic methodology the scaffolds were immersed in Simulated Body Fluid solutions (SBF) under static, agitation and circulating flow perfusion conditions, for different time periods. Besides the typical characterization techniques, Micro-Computed Tomography analysis (micro-CT) was used to assess scaffold porosity and as a new tool for mapping apatite content. 2D histomorphometric analysis was performed and 3D virtual models were created using specific softwares for CT reconstruction. By the proposed biomimetic routes apatite layers were produced covering the interior of the scaffolds, without compromising their overall morphology and interconnectivity. Dynamic conditions allowed for the production of thicker apatite layers as consequence of higher mineralizing rates, when comparing with static conditions. micro-CT analysis clearly demonstrated that flow perfusion was the most effective condition in order to obtain well-defined apatite layers in the inner parts of the scaffolds. Together with SEM, this technique was a useful complementary tool for assessing the apatite content in a non-destructive way.

Bioactive composite materials for tissue engineering scaffolds

Synthetic bioactive and bioresorbable composite materials are becoming increasingly important as scaffolds for tissue engineering. Next-generation biomaterials should combine bioactive and bioresorbable properties to activate in vivo mechanisms of tissue regeneration, stimulating the body to heal itself and leading to replacement of the scaffold by the regenerating tissue. Certain bioactive ceramics such as tricalcium phosphate and hydroxyapatite as well as bioactive glasses, such as 45S5 Bioglass, react with physiologic fluids to form tenacious bonds with hard (and in some cases soft) tissue. However, these bioactive materials are relatively stiff, brittle and difficult to form into complex shapes. Conversely, synthetic bioresorbable polymers are easily fabricated into complex structures, yet they are too weak to meet the demands of surgery and the in vivo physiologic environment. Composites of tailored physical, biologic and mechanical properties as well as predictable degradation behavior can be produced combining bioresorbable polymers and bioactive inorganic phases. This review covers recent international research presenting the state-of-the-art development of these composite systems in terms of material constituents, fabrication technologies, structural and bioactive properties, as well as in vitro and in vivo characteristics for applications in tissue engineering and tissue regeneration. These materials may represent the effective optimal solution for tailored tissue engineering scaffolds, making tissue engineering a realistic clinical alternative in the near future.