Bone-tissue engineering: complex tunable structural and biological responses to injury,drug delivery,and cell-based therapies

Bone loss and failure of proper bone healing continues to be a significant medical condition in need of solutions that can be implemented successfully both in human and veterinary medicine. This is particularly true when large segmental defects are present, the bone has failed to return to normal form or function, or the healing process is extremely prolonged. Given the inherent complexity of bone tissue – its unique structural, mechanical, and compositional properties, as well as its ability to support various cells – it is difficult to find ideal candidate materials that could be used as the foundation for tissue regeneration from technological platforms. Recently, important developments have been made in the implementation of complex structures built both at the macro- and the nano-level that have been shown to positively impact bone formation and to have the ability to deliver active biological molecules (drugs, growth factors, proteins, cells) for controlled tissue regeneration and the prevention of infection. These materials are diverse, ranging from polymers to ceramics and various composites. This review presents developments in this area with a focus on the role of scaffold structure and chemistry on the biologic processes that influence bone physiology and regeneration.     

Cetuximab conjugated vitamin E TPGS micelles for targeted delivery of docetaxel for treatment of triple negative breast cancers

We developed a system of Cetuximab-conjugated micelles of vitamin E TPGS for targeted delivery of docetaxel as a model anticancer drug for treatment of the triple negative breast cancer (TNBC), which shows no expression of either one of the hormone progesterone receptor (PR), estrogen receptor (ER) and epidermal growth factor receptor 2 (HER2) and is thus more difficult to be treated than the positive breast cancer. Such micelles are of desired particle size, drug loading, drug encapsulation efficiency and drug release profile. Their surface morphology, surface charge and surface chemistry were also characterized. The fibroblast cells (NIH3T3), HER2 overexpressed breast cancer cells (SK-BR-3), ER and PR overexpressed breast cancer cells (MCF7), and TNBC cells of high, moderate and low EGFR expression (MDA MB 468, MDA MB 231 and HCC38) were employed to access in vitro cellular uptake of the coumarin 6 loaded TPGS micelles and cytotoxicity of docetaxel formulated in the micelles. The high IC50 value, which is the drug concentration needed to kill 50% of the cells in a designated period such as 24 h, obtained from Taxotere^® showed that the TNBC cells are indeed more resistant to the free drug than the positive breast cancer cells. However, the therapeutic effects of docetaxel could be greatly enhanced by the formulation of Cetuximab conjugated TPGS micelles, which demonstrated 205.6 and 223.8 fold higher efficiency than Taxotere^® for the MDA MB 468 and MDA MB 231 cell lines respectively.     

Optical control of cell differentiation on synthetic collagen-like scaffolds

Abstract

We have developed biocompatible scaffolds that enable cell fate control with visible light. The scaffolds are based on synthetic collagen-like polypeptide, poly(prolyl-hydroxyprolyl-glycyl) {poly(Pro-Hyp-Gly)} which has been used for cosmetics and other healthcare applications. Bioactive peptides were conjugated to the scaffolds via photoactivation reaction utilizing 488?nm visible light. In addition, the use of a photocleavable crosslinker enables dissociation of chemical moieties by 405?nm laser irradiation. The synthesis scheme enables optical control to attach and detach functional peptides in pre-patterned shapes. Using bone forming peptide (BFP), we demonstrate that calcium deposition by rat bone stromal cells can be directed on the scaffold. Using other signaling molecules and three-dimensional scaffolds, controlled differentiation of stem cells can be achieved by spatio-temporally specific irradiation of confocal microscope laser.     

Elastic protein-based polymers in soft tissue augmentation and generation

Molecular self association in water through hydrogen bonding is a powerful organizational force leading to a three-dimensional hydrogen-bonded network (water structure) that profoundly influences solvent properties. Localized perturbations in the chemical potential of water as by, for example, contacting with a solid surface, induces compensating changes in water structure that can be sensed tens of nanometers from the point of origin using the surface force apparatus (SFA) and ancillary techniques. These instruments reveal attractive or repulsive forces between opposing surfaces immersed in water, over-and-above that anticipated by continuum theory (DLVO), that are attributed to a variable density (partial molar volume) of a more-or-less ordered water structure, depending on the water wettability (surface energy) of the water-contacting surfaces. Water structure at surfaces is thus found to be a manifestation of hydrophobicity and, while mechanistic/theoretical interpretation of experimental results remains the subject of some debate in the literature, convergence of experimental observations permit a quantitative definition of the heretofore relative terms `hydrophobic' and `hydrophilic'. In particular, long-range attractive forces (< 100 nm) are detected only between surfaces exhibiting a water contact angle > 65 deg (defined as hydrophobic surfaces with pure water adhesion tension τ⁰ = γ⁰ cos < 30 dyn cm^-1 where γ⁰ is water interfacial tension = 72.8 dyn cm^-1). Short range repulsive forces (< 5 nm) arc detected between surfaces exhibiting < 65 deg (hydrophilic surfaces, τ⁰ > 30 dyn cm^-1). These findings together with other lines of chemical evidence suggest at least two distinct kinds of water structure and reactivity: a relatively less-dense water region against hydrophobic surfaces with an open hydrogen-bonded network and a relatively more-dense water region against hydrophilic surfaces with a collapsed hydrogen-bonded network. Solvent properties of interfacial water profoundly influence the biological response to materials in a surprisingly straightforward manner when key measures of biological activity sensitive to interfacial phenomenon are scaled against water adhesion tension τ⁰ of contacting surfaces. Protein adsorption, activation of blood coagulation, and bioadhesion are offered as examples in point, illustrating that the hydrophobic/hydrophilic contrast in the biological response to materials, often disputed in biomaterials science, is very clear when viewed from the perspective of water structure and reactivity at surfaces.     

Polysaccharide‐Based Polyanion–Polycation–Polyanion Ternary Systems in the Concentrated Regime and Hydrogel Form

In the field of bioactive biomaterials, multi‐biopolymer systems are of particular interest as they represent potential extra cellular matrix (ECM) mimics. Ternary mixtures composed of alginate, hyaluronan, and a lactose‐modified chitosan undergo a rheological investigation that reveal the presence of polyanion‐polycation supramolecular structures, which dissolve once the third (polyanion) component is added. Two selected ternary mixtures are used for the preparation of calcium–alginate hydrogels and their mechanical performance and stability are found to be strongly influenced by the relative composition in terms of the two non‐gelling components. The presence in the mixture of bioactive polysaccharides leads to a notable improvement in the proliferation of primary culture of chondrocytes.

     

Clickable Poly(ethylene glycol)‐Microsphere‐Based Cell Scaffolds

Clickable poly(ethylene glycol) (PEG) derivatives are used with two sequential aqueous two‐phase systems to produce microsphere‐based scaffolds for cell encapsulation. In the first step, sodium sulfate causes phase separation of the clickable PEG precursors and is followed by rapid geleation to form microspheres in the absence of organic solvent or surfactant. The microspheres are washed and then deswollen in dextran solutions in the presence of cells, producing tightly packed scaffolds that can be easily handled while also maintaining porosity. Endothelial cells included during microsphere scaffold formation show high viability. The clickable PEG‐microsphere‐based cell scaffolds open up new avenues for manipulating scaffold architecture as compared with simple bulk hydrogels.

     

Polymeric scaffolds as stem cell carriers in bone repair

Although bone has a high potential to regenerate itself after damage and injury, the efficacious repair of large bone defects resulting from resection, trauma or non‐union fractures still requires the implantation of bone grafts. Materials science, in conjunction with biotechnology, can satisfy these needs by developing artificial bones, synthetic substitutes and organ implants. In particular, recent advances in polymer science have provided several innovations, underlying the increasing importance of macromolecules in this field. To address the increasing need for improved bone substitutes, tissue engineering seeks to create synthetic, three‐dimensional scaffolds made from polymeric materials, incorporating stem cells and growth factors, to induce new bone tissue formation. Polymeric materials have shown a great affinity for cell transplantation and differentiation and, moreover, their structure can be tuned in order to maintain an adequate mechanical resistance and contemporarily be fully bioresorbable. This review emphasizes recent progress in polymer science that allows relaible polymeric scaffolds to be synthesized for stem cell growth in bone regeneration. Copyright © 2013 John Wiley & Sons, Ltd.