Background: Reports have concluded that platelet-rich plasma (PRP) is an effective and safe biological approach in the treatment of knee osteoarthritis (OA). However, no consensus has been established regarding the number of injections required to observe a therapeutic effect. Purpose: To compare the clinical effectiveness reported in randomized controlled trials (RCTs) of single versus multiple PRP injections in the treatment of knee OA. Study Design: Systematic review; Level of evidence, 1. Methods: A comprehensive search was conducted for RCTs published between 1970 and 2019 that compared the effect of single versus multiple PRP injections on pain and functionality in patients with knee OA. Searched databases included MEDLINE, Scopus, Embase, Web of Science, and the Cochrane Central Register of Controlled Trials. A data extraction form was designed to obtain bibliographic information of the study as well as patient, intervention, comparison, and outcomes of interest data. A random-effects model was used to pool quantitative data from the primary outcomes. Results: We included 5 clinical trials with a low-moderate risk of bias that reported data for 301 patients. Meta-analysis showed that, at 6 months after the intervention, single and multiple (double or triple) injections had similar pain improvement, with no significant differences (standardized mean difference [SMD], 0.61 [95% CI, −1.09 to 2.31]; I ² = 97%; P = .48). A significant improvement in knee functionality was observed in favor of multiple injections (SMD, 2.29 [95% CI, 0.45-4.12]; I ² = 97%; P = .01). Subanalysis showed that the significant improvement was only evident for the results of single versus triple injections (SMD, 3.12 [95% CI, 0.64-5.60]; I ² = 97%; P = .01). Conclusion: According to our results, a single injection was as effective as multiple PRP injections in pain improvement; however, multiple injections seemed more effective in joint functionality than a single injection at 6 months. We consider that the available evidence is still insufficient, and future research on this specific topic is needed to confirm our results.

Cardiovascular diseases are a leading cause of death worldwide. Current treatments directed at heart repair have several disadvantages, such as a lack of donors for heart transplantation or non-bioactive inert materials for replacing damaged tissue. Because of the natural lack of regeneration of cardiomyocytes, new treatment strategies involve stimulating heart tissue regeneration. The basic three elements of cardiac tissue engineering (cells, growth factors, and scaffolds) are described in this review, with a highlight on the role of artificial scaffolds. Scaffolds for cardiac tissue engineering are tridimensional porous structures that imitate the extracellular heart matrix, with the ability to promote cell adhesion, migration, differentiation, and proliferation. In the heart, there is an important requirement to provide scaffold cellular attachment, but scaffolds also need to permit mechanical contractility and electrical conductivity. For researchers working in cardiac tissue engineering, there is an important need to choose an adequate artificial scaffold biofabrication technique, as well as the ideal biocompatible biodegradable biomaterial for scaffold construction. Finally, there are many suitable options for researchers to obtain scaffolds that promote cell–electrical interactions and tissue repair, reaching the goal of cardiac tissue engineering.