Microfluidic collagen patterning for tendon regeneration

We present a microfluidic approach to align collagen fibers for tendon regeneration. Collagen fibers with a specific orientation were patterned in a microfluidic channel by introducing collagen solution through integrated microstructures. The fluid flow in the pillar array was evaluated by computational modeling, and the aligned collagen fibers were analyzed quantitatively. Then, primary rat tenocytes were cultured on oriented and not-oriented collagen micropatterns, and their phenotypical commitment was evaluated. We believe that such a platform would be useful to replicate in vivo microenvironment for the study of regenerative processes

Bioinorganics: synthetic growth factors for bone regeneration

Bone tissue is naturally able to regenerate when damaged. However, in many large defects caused by fractures due to aging or osteoporosis, trauma, tumor removal, etc., the natural regenerative ability of bone is not sufficient to fully heal the defect. In such cases, a graft is required to support the process of regeneration. While natural bone grafts, especially autografts, are widely applied in such conditions, their use is associated with important disadvantages. To overcome these limitations, a wide range of natural and synthetic alternatives has been developed, which are available off-the-shelf in large quantities. However, their clinical performance has always been considered inferior to that of autografts. Therefore, in the past decades, extensive research efforts have been invested in developing bone graft substitutes with improved properties and clinical performance. One of these strategies includes chemical modification of the existing bone graft substitutes with bioinorganics such as strontium (Sr2+), magnesium (Mg2+), zinc (Zn2+), etc. In this thesis, the effects of Sr2+, cobalt (Co2+) and fluoride (F-) were evaluated on the osteogenic differentiation of hMSCs. The results of these studies showed that cells might be influenced directly by the presence of the bioinorganics in their microenvironment, or indirectly through changes in the physicochemical properties of the CaPs, caused by the incorporation of bioinorganics into their structure. It was also shown that using cocktails of different bioinorganics might be an interesting strategy to affect different biological processes simultaneously. The effects of Co2+ ions incorporated into CaP coatings on vascularization were evaluated in an intramuscular goat model. The results showed that the presence of Co2+ in CaP coatings enhanced the new blood vessel formation and maturation, which in itself is considered beneficial in the process of bone regeneration. Finally, a model biomaterial based on polymer microspheres, to act as a carrier for bioinorganics was developed in this thesis. This simplified platform was successfully tested in vitro for screening direct effects of bioinorganics on hMSCs, independent of the properties of the carrier material

Biomaterial-induced pathway modulation for bone regeneration

Embryogenic developmental processes involve a tightly controlled regulation between mechanical forces and biochemical cues such as growth factors, matrix proteins, and cytokines. This interplay remains essential in the mature body, with aberrant pathway signaling leading to abnormalities such as atherosclerosis in the cardiovascular system, inflammation in tendon tissue, or osteoporosis in the bone. The aim of bone regenerative strategies is to develop tools and procedures that will harness the body's own self-repair ability in order to successfully regenerate even very large and complex bone defects and restore normal function. To achieve this, understanding pathways that govern processes of progenitor differentiation towards the osteogenic lineages, their phenotypical maintenance, and the construction of functional bone tissue is imperative to subsequently develop regenerative therapies that mimic these processes. While a body of literature exists that describes how biochemical stimuli guide cell behavior in the culture dish, due to the lack of an appropriate mechanical environment, these signals are often insufficient or inappropriate for achieving a desirable response in the body. Moreover, bone regenerative therapies rarely rely on a biochemical stimulus, such as a growth factor alone, and instead often comprise a carrier biomaterial that introduces a very different microenvironment from that of a cell culture dish. Therefore, in this review, we discuss which biomaterials elicit or influence pathways relevant for bone regeneration and describe mechanisms behind these effects, with the aim to inspire the development of novel, more effective bone regenerative therapies

Monolithic calcium phosphate/poly(lactic acid) composite versus calcium phosphate-coated poly(lactic acid) for support of osteogenic differentiation of human mesenchymal stromal cells

Calcium phosphates (CaPs), extensively used synthetic bone graft substitutes, are often combined with other materials with the aim to overcome issues related to poor mechanical properties of most CaP ceramics. Thin ceramic coatings on metallic implants and polymer-ceramic composites are examples of such hybrid materials. Both the properties of the CaP used and the method of incorporation into a hybrid structure are determinant for the bioactivity of the final construct. In the present study, a monolithic composite comprising nano-sized CaP and poly(lactic acid) (PLA) and a CaP-coated PLA were comparatively investigated for their ability to support proliferation and osteogenic differentiation of bone marrow-derived human mesenchymal stromal cells (hMSCs). Both, the PLA/CaP composite, produced using physical mixing and extrusion and CaP-coated PLA, resulting from a biomimetic coating process at near-physiological conditions, supported proliferation of hMSCs with highest rates at PLA/CaP composite. Enzymatic alkaline phosphatase activity as well as the mRNA expression of bone morphogenetic protein-2, osteopontin and osteocalcin were higher on the composite and coated polymer as compared to the PLA control, while no significant differences were observed between the two methods of combining CaP and PLA. The results of this study confirmed the importance of CaP in osteogenic differentiation while the exact properties and the method of incorporation into the hybrid material played a less prominent role