Guided bone regeneration (GBR) is commonly used in combination with the installment of titanium implants. The application of a membrane to exclude non-osteogenic tissues from interfering with bone regeneration is a key principle of GBR. Membrane materials possess a number of properties which are amenable to modification. A large number of membranes have been introduced for experimental and clinical verification. This prompts the need for an update on membrane properties and the biological outcomes, as well as a critical assessment of the biological mechanisms governing bone regeneration in defects covered by membranes. The relevant literature for this narrative review was assessed after a MEDLINE/PubMed database search. Experimental data suggest that different modifications of the physicochemical and mechanical properties of membranes may promote bone regeneration. Nevertheless, the precise role of membrane porosities for the barrier function of GBR membranes still awaits elucidation. Novel experimental findings also suggest an active role of the membrane compartment per se in promoting the regenerative processes in the underlying defect during GBR, instead of being purely a passive barrier. The optimization of membrane materials by systematically addressing both the barrier and the bioactive properties is an important strategy in this field of research.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/eos.12364

Guided bone regeneration: materials and biological mechanisms revisited.

Platelet-rich plasma (PRP) is currently used in different medical fields. The interest in the application of PRP in dermatology has recently increased. It is being used in several different applications as in tissue regeneration, wound healing, scar revision, skin rejuvenating effects, and alopecia. PRP is a biological product defined as a portion of the plasma fraction of autologous blood with a platelet concentration above the baseline. It is obtained from the blood of patients collected before centrifugation. The knowledge of the biology, mechanism of action, and classification of the PRP should help clinicians better understand this new therapy and to easily sort and interpret the data available in the literature regarding PRP. In this review, we try to provide useful information for a better understanding of what should and should not be treated with PRP.

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A Review of Platelet-Rich Plasma: History, Biology, Mechanism of Action, and Classification.

Although platelets are widely recognized as having a critical role in primary hemostasis and thrombosis, increasing experimental and clinical evidence identifies these enucleated cells as relevant modulators of other physiopathological processes including inflammation and tissue regeneration. These phenomena are mediated through the release of growth factors, cytokines, and extracellular matrix modulators that sequentially promote (i) revascularization of damaged tissue through the induction of migration, proliferation, differentiation, and stabilization of endothelial cells in new blood vessels; (ii) restoration of damaged connective tissue through migration, proliferation, and activation of fibroblasts; and (iii) proliferation and differentiation of mesenchymal stem cells into tissue-specific cell types. For these reasons, platelet-rich plasma (PRP) derivatives are used in regenerative medicine for the treatment of several clinical conditions including ulcers, burns, muscle repair, bone diseases, and tissue recovery following surgery. The benefits of PRP administration are associated with an economical advantage, taking into consideration that PRP administration does not require complex equipment or training for its execution. Moreover, due to their primary autologous origin, concerns of disease transmission or immunogenic reactions can be disregarded. Thus, platelet-enriched materials have become highly relevant in the last decade and constitute a growing focus of experimental and clinical study in the context of wound healing and tissue regeneration. However, despite the diverse applications, the efficacy of regenerative treatments using PRP is being called into question due to the lack of large controlled clinical trials and the lack of consensus regarding the PRP preparation techniques. This review describes the biological mechanisms underlying PRP's regenerative effects, the different methods of preparation and application of these biomaterials, and the controversies and future prospects related to the use of PRP in regenerative medicine.

Platelets in wound healing and regenerative medicine.

The use of stem cells has been reported to improve hair regrowth in several therapeutic strategies, including reversing the pathological mechanisms, that contribute to hair loss, regeneration of hair follicles, or creating hair using the tissue-engineering approach. Although various promising stem cell approaches are progressing via pre-clinical models to clinical trials, intraoperative stem cell treatments with a one-step procedure offer a quicker result by incorporating an autologous cell source without manipulation, which may be injected by surgeons through a well-established clinical practice. Many authors have concentrated on adipose-derived stromal vascular cells due to their ability to separate into numerous cell genealogies, platelet-rich plasma for its ability to enhance cell multiplication and neo-angiogenesis, as well as human follicle mesenchymal stem cells. In this paper, the significant improvements in intraoperative stem cell approaches, from in vivo models to clinical investigations, are reviewed. The potential regenerative instruments and functions of various cell populaces in the hair regrowth process are discussed. The addition of Wnt signaling in dermal papilla cells is considered a key factor in stimulating hair growth. Mesenchymal stem cell-derived signaling and growth factors obtained by platelets influence hair growth through cellular proliferation to prolong the anagen phase (FGF-7), induce cell growth (ERK activation), stimulate hair follicle development (β-catenin), and suppress apoptotic cues (Bcl-2 release and Akt activation).

Advances in Regenerative Stem Cell Therapy in Androgenic Alopecia and Hair Loss: Wnt pathway, Growth-Factor, and Mesenchymal Stem Cell Signaling Impact Analysis on Cell Growth and Hair Follicle Development.

Background:Platelet-rich plasma (PRP) has proven to be a very safe therapeutic option in the treatment of tendon, muscle, bone, and cartilage injuries. Currently, several commercial separation syst...

Concentrations of Blood Components in Commercial Platelet-Rich Plasma Separation Systems: A Review of the Literature.

The utility of platelet-rich plasma (PRP) has spanned various fields of dermatology from chronic ulcer management to trichology and aesthetics, due to its role in wound healing. Though PRP is being used over a long time, there is still confusion over proper terminology to define, classify and describe the different variations of platelet concentrates. There is also a wide variation in the reported protocols for standardization and preparation of PRP, in addition to lack of accurate characterization of the tested products in most articles on the topic. Additionally, the high cost of commercially available PRP kits, precludes its use over a larger population. In this article, we review the principles and preparation methods of PRP based on available literature and place our perspective in standardizing a safe, simple protocol that can be followed to obtain an optimal consistent platelet yield.

Dhurat R

Papers

Principles and Methods of Preparation of Platelet-Rich Plasma: A Review and Author's Perspective.